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MICROBIOLOGY and PARASITOLOGYMedical Board Exam Review
for August 2007
Nenacia Ranali Nirena R. Palma, MD
BACTERIOLOGY
Basic Bacterial Structure
• Appendages– flagella and pili
• cell envelope– capsule, cell wall and plasma
membrane
• cytoplasmic region– genome (DNA), ribosomes
and inclusions
Appendages• Flagella
– filamentous protein structures for motility
• Pili ~ Fimbriae– short, hair-like structures – usually involved in adherence
(attachment) – resist attack by phagocytic
white blood cells – F or sex pilus, mediates the
transfer of DNA
Cell Wall
• Gives rigid support• protects from osmotic lysis• Peptidoglycan– polymer of disaccharides cross-linked by short
chains of amino acids (peptides)– Murein (N-acetylmuramic acid)
Cell Wall
• Gram positive– Thicker
– Teichoic acid – an antigenic determinant
– No endotoxin, except Listeria monocytogenes
• Gram negative– periplasmic space
(contains enzymes, eg beta-lactamases)
– Outer membrane w/ lipopolysaccharide
– Endotoxin = Lipid A
– High lipid content
Plasma/Cytoplasmic Membrane
• site of oxidative phosphorylation and photophosphorylation
• permeability barrier • consist of saturated or monounsaturated fatty
acids (rarely polyunsaturated fatty acids) and do not normally contain sterols
Capsule/Glycocalyx
• Composed of polysaccharide, except Bacillus anthracis (D-glutamate)
• Mediates adherence to surfaces• Protects against phagocytosis
Cytoplasmic Constituents
• Chromosome – typically one large circular molecule of DNA
• Plasmids – extra-chromosomal; genes for antibiotic resistance, enzymes and toxins
• Ribosomes – for protein synthesis
ExotoxinExotoxin EndotoxinEndotoxinSourceSource Gram (+) and gram Gram (+) and gram
(-) bacteria (-) bacteria Cell wall of gram (-) Cell wall of gram (-) bacteria & Listeriabacteria & Listeria
Secreted from Secreted from cellcell
YesYes NoNo
Location of Location of genesgenes
Plasmid or Plasmid or bacteriophagebacteriophage
Bacterial chromosomeBacterial chromosome
toxicitytoxicity highhigh LowLow
vaccinesvaccines toxoidstoxoids No toxoids formed, no No toxoids formed, no vaccines availablevaccines available
Heat stabilityHeat stability Destroyed at 60 CDestroyed at 60 C Stable at 100 C for 1 Stable at 100 C for 1 hourhour
antigenicityantigenicity Induces antitoxinsInduces antitoxins Poorly antigenicPoorly antigenic
Typical Typical diseasesdiseases
Tetanus, botulism, Tetanus, botulism, diphtheriadiphtheria
Meningococcemia, Meningococcemia, sepsis by gram (-) sepsis by gram (-) rodsrods
Gram Stain
• Crystal Violet (the Primary Stain)
• Iodine Solution (the Mordant)
• Decolorizer (ethanol) • Safranin (the
Counterstain) • Water
Gram Positive Cocci
• Staphylococcus– Clusters
• Streptococcus– Chains
• Micrococcus– tetrad
Gram Positive Bacilli
• Bacillus and Clostridium– Produces spores
• Listeria and Corynebacterium
Gram negative Cocci
• Neisseria– diplococci
• Acinetobacter– Coccobacilli– Often gram variable
Gram negative Bacilli
• Enterobacteriaciae– Thin rods
• Hemophilus– Coccobacilli
• Vibrio and Campylobacter– curved
Gram (+) Cocci
Catalase (+)
Staphylococcus
Catalase (-)
Streptococcus
Coagulase (+)
S. aureus
Coagulase (-)
Novobiocin sensitive
S. epidermidis
Novobiocin resistant
S. saprophyticus
α-hemolysis
(green)
S. Pneumo
Optochin sensitive, bile soluble, (+) capsule
Viridans strep.
S. mutans
β-hemolysis
(clear)
Group A
S. pyogenes
Bacitracin sensitive
Group B
S. Agalactiae
Bacitracin resistant
No hemolysis
Enterococcus
E. fecalis
Pepto-
streptococcus
Gram negative
Coccoid
H. influenza
Bordetella pertussis
Pasteurella
Brucella
BacilliCocci
Neisseria
Maltose
fermenter
N. meningitidis
Maltose
Non-fermenter
N. gonorrhea
Lactose fermenter
Fast
Klebsiella
E. Coli
Enterobacter
Slow
Citrobacter
Serratia
Lactose non-fermenter
Oxidase (+)
Pseudomonas
Oxidase (-)
Shigella
Salmonella
Proteus
Genetic Exchange in Bacteria
• Conjugation– cell-to-cell contact as DNA crosses a sex pilus from
donor to recipient
• Transduction– a virus transfers the genes between mating
bacteria
• Transformation– DNA is acquired directly from the environment,
having been released from another cell
Oxygen Requirement• Obligate Aerobes
• Facultative anaerobes– Aerobic but can grow in the absence of oxygen
• Microaerophilic (aerotolerant anaerobes)– Can tolerate low amounts of oxygen
• Obligate anaerobes
Obligate Obligate aerobesaerobes
FacultativFacultative e anaerobeanaerobess
Micro-Micro-aerophilicaerophilic
Obligate Obligate anaerobesanaerobes
Gram (+)Gram (+) NocardiaNocardia
Bacillus cereusBacillus cereusStaph.Staph.
B. B. anthracisanthracis
Corynebac.Corynebac.
ListeriaListeria
ActinomycActinomyceses
StreptococcuStreptococcuss
ClostridiumClostridium
Gram (-)Gram (-) NeisseriaNeisseria
PseudomonasPseudomonas
BordetellaBordetella
LegionellaLegionella
BrucellaBrucella
all other all other gram gram negativesnegatives
SpirochetesSpirochetes
TreponemaTreponema
BorreliaBorrelia
LeptospiraLeptospira
CampylobactCampylobacterer
BacteroidesBacteroides
Acid fastAcid fast MycobacteriumMycobacterium
NocardiaNocardia
No cell No cell wallwall
MycoplasmMycoplasmaa
Koch’s Postulate• The bacteria must be present in every case of the
disease.
• The bacteria must be isolated from the host with the disease and grown in pure culture.
• The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host.
• The bacteria must be recoverable from the experimentally infected host.
Staphylococcus aureus• nonmotile, nonsporeforming facultative anaerobe• fermentation of glucose produces mainly lactic acid• ferments mannitol (distinguishes from S.
epidermidis) • catalase positive • coagulase positive• golden yellow colony on agar
Staphylococcus aureus• Protein A – protect from opsonization and
phagocytosis• Coagulase – clumping factor• Hemolysins• Leukocidins• Hyaluronidase – spreading factor• Staphylokinase• Exfoliatin – scalded skin• Enterotoxins• TSST-1 – superantigen; binds to MHC class II
Staphylococcus aureus• Pneumonia –
cavitations, empyema and effusions
• Endocarditis – acute
• Food poisoning – due to a preformed toxin, onset 1-8 hours
• TSS – tampon use
Staphylococcus aureus
• Treatment– Methicillin– Nafcillin– Dicloxacillin– For MRSA – give Vancomycin
• No vaccine
• Staphylococcus epidermidis–Normal flora of skin– Foley catheters and IV lines–Blood culture contaminant– Infection of prosthetic devices
• Staphylococcus saprophyticus–Urinary tract infections in sexually active
women
Streptococcus pyogenes (GABHS)
• nonmotile, nonsporeforming• capsule composed of hyaluronic acid• exhibit beta (clear) hemolysis on blood agar
Streptococcus pyogenes (GABHS)
• M protein – protection from phagocytosis but susceptible to antibodies
• Streptolysin O - oxygen-labile leukocidin, antigenic
• Streptolysin S – oxygen stable• Pyrogenic/erythrogenic toxin - superantigen• Streptokinase - fibrin lysis
Streptococcus pyogenes (GABHS)• Scarlet fever –
strawberry tongue• Pharyngitis• Rheumatic fever –
sequela of pharyngitis• Glomerulonephritis –
sequela of pharyngitis and skin infections
• Tx: penicillin, erythromycin
• S. agalactiae (Group B)– Beta hemolytic– Neonatal meningitis, pneumonia and sepsis (B for baby)
• Group D Streptococci– Enterococci (E. faecalis, E. faecium)– Non-enterococci (S. bovis, S. equinus)– Urinary and biliary tract infections, SBE– S. bovis associated with colon cancer
Viridans streptococci
• S. salivarius, S. sanguis, S. mitis, S. intermedius, S. mutans
• alpha hemolytic (green)• Optochin resistant• Dental caries (S. mutans)• Subacute bacterial endorcarditis (S. sanguis)
Streptococcus Pneumoniae
• lancet-shaped diplococci
• Alpha-hemolytic, optochin sensitive
• Capsule (Quellung reaction)
Streptococcus Pneumoniae
• Adults: pneumonia and meningitis• Children: otits media
• Pneumonia – lobar with consolidation• Increasing resistance to penicillins, erythromycin, co-
trimoxazole, chloramphenicol
• Pneumococcal vaccine – advised for elderly and asplenic patients
Clostridium perfringens
• Alpha toxin – lecithinase• Spores resistant to cooking
• Gas gangrene/myonecrosis• Food poisoning - abdominal cramps and
diarrhea 8-16 hours after eating contaminated meat or poultry
Clostridium difficile
• Antibiotic associated diarrhea (pseudomembranous colitis)
• Toxin A - causes fluid accumulation in the bowel
• Toxin B - an extremely lethal (cytopathic) toxin • Tx: Metronidazole or vancomycin
Clostridium tetani• Found in soil• terminal spores within a swollen sporangium –
“drumstick appearance”
• Tetanus toxin/tetanospasmin – blocks release of inhibitory glycine neurotransmitter from Renshaw cells in spinal cord
Clostridium tetani
• severe painful spasms and rigidity of the voluntary muscles
• "lockjaw" - spasms of the masseter muscle
• rigidity and violent spasms of the trunk and limb muscles
• Spasms of the pharyngeal muscles - difficulty in swallowing
• Death - interference with the mechanics of respiration
Clostridium tetani
• Vaccines– Immune globulin – preformed Ig– Toxoid – formaldehyde treated toxin
• Penicillin, ventilatory support, muscle relaxant
Clostridium botulinum
• Flaccid paralysis• Floppy babies• Botulinum toxin– Neurotoxin– Toxin ingested in food absorbed in duodenum
and jejunum bloodstream peripheral neuromuscular synapses
– Blocks release of acetylcholine
• Canned foods; ingestion of honey (infants)
Bacillus cereus
• Motile, non-encapsulated• "short-incubation" or emetic form– nausea and vomiting and abdominal cramps– incubation period of 1 to 6 hours– resembles Staphylococcus aureus food poisoning– caused by a preformed heat-stable enterotoxin – Associated with fried rice and eating in Chinese
restaurants
Bacillus cereus
• "long-incubation" or diarrheal form– abdominal cramps and diarrhea with an incubation period
of 8 to 16 hours– Diarrhea may be a small volume or profuse and watery– resembles more food poisoning caused by Clostridium
perfringens– heat-labile enterotoxin - activates intestinal adenylate
cyclase and causes intestinal fluid secretion– meat or vegetable-containing foods after cooking
Bacillus anthracis
• large cells with square ends and centrally-located ellipsoid spores
• Non-motile • Spores on animal products (skin, hide)• Poly-D-glutamate capsule
Bacillus anthracis• Factor I - edema factor (EF); inherent adenylate
cyclase• Factor II - protective antigen (PA), induces protective
antitoxic antibodies; binding (B) domain• Factor III - lethal factor (LF)
• PA+LF combine to produce lethal activity EF+PA produce edema EF+LF is inactive PA+LF+EF produces edema and necrosis and is lethal
Bacillus anthracis• Cutaneous anthrax– via injured skin or mucous membranes – Vesicular papules covered by black eschar
• Inhalation anthrax (woolsorters' disease)– inhalation of spore-containing dust where animal
hair or hides are being handled– begins abruptly with high fever and chest pain– progresses rapidly to a systemic hemorrhagic
pathology and is often fatal
Bacillus anthracis• Gastrointestinal anthrax– Rare– Very high mortality rate
• Tx: Penicillin, tetracyclines and fluoroquinolones effective if administered before the onset of lymphatic spread or septicemia, estimated to be about 24 hours
• Vaccine: protective antigen (three subcutaneous injections given two weeks apart followed by three additional subcutaneous injections given at 6, 12, and 18 months)
Listeria monocytogenes
• Peritrichous flagella are produced at room temperature but not at 37° C
• may be coccoid, so they can be mistaken for streptococci; longer cells may resemble corynebacteria
• Tumbling motility
Listeria monocytogenes
• listeriolysin O • LPS• ability to multiply at low temperatures -
associated with ingestion of milk, meat or vegetable products that have been held at refrigeration temperatures for a long period of time
• Neonatal meningitis and sepsis, abortion, premature delivery
• Tx: ampicillin, no vaccine
Corynebacterium diphtheriae
• Loeffler’s bacillus• aerobic, nonmotile • irregular shaped, club-shaped or V-shaped
arrangements (resembles Chinese letters)• Metachromatic granules
Corynebacterium diphtheriae• Culture: potassium tellurite agar, Loeffler’s
coagulated blood serum• Beta prophage – encodes exotoxin (inhibits
protein synthesis via ADP ribosylation of elongation factor 2 (EF2)
• Pharyngitis with grayish pseudomembrane• Hematogenous spread to affect heart and
neural cells (myocarditis and laryngeal nerve palsy)
Corynebacterium diphtheriae
• Tx: penicillin or erythromycin
• Vaccine: trivalent toxoid (diphtheria, pertussis, tetanus)
Neisseria gonorrhea• Kidney bean shaped• Gram (-) intracellular diplococci• Fimbriae• No capsule• IgA protease, LPS• Culture: Thayer-Martin chocolate agar– V – Vancomycin– C – Colistin (polymixin)– N - Nystatin
Neisseria gonorrhea• Males: urethritis (discharge); painful urination• Females: dyspareunia due to cervicitis; PID,
sterility, ectopic pregnancy, tubo-ovarian abscess, perihepatitis (Fitz-Hugh-Curtis syndrome)
• Neonates: ophthalmia neonatorum• Most common cause of septic arthritis in
sexually active
Neisseria gonorrhea
• Treatment: – Ceftriaxone; Ciprofloxacin or spectinomycin if
allergic to cephalosporins– Plus Doxycycline or azithromycin for Chlamydia– Erythromycin eyedrops – prophylaxis for
ophthalmia neonatorum
• No immunity
Neisseria meningitidis• Meningococcus• Encapsulated, maltose fermenter• Strict human parasite (in nasopharynx)• Respiratory transmission
• IgA protease• Serotypes A, B and C associated with
meningitis (usually type B)
Neisseria meningitidis
• Meningitis – fever, HA, stiff neck, photophobia• Meningococcemia – fever, arthralgias, myalgias,
petechial rash• Waterhouse-Friedrichsen – fulminant; fever, purpura,
DIC, adrenal insufficiency (bilateral adrenal hemorrhage), shock, death
Neisseria meningitidis
• Treatment:– Penicillin or ceftriaxone– Rifampicin for prophylaxis of close contacts
• Vaccine– Against capsular antigens
Enterobacteriaciae• E. coli, Salmonella, Shigella, Klebsiella,
Enterobacter, Serratia, Proteus• Ferments glucose• Oxidase negative• Antigens:– O – somatic (polysaccharide of endotoxin)– H – flagellar– K – capsular
• Lactose fermenters: Klebsiella, E. coli, Enterobactor and Citrobacter
E. coli• 2nd most common cause of neonatal
meningitis• UTI, diarrhea, gram (-) sepsis
• LT (heat labile toxin) – cAMP; similar to cholera toxin
• ST (heat stable) – cGMP
E. coli• Enterotoxigenic (ETEC)– Do not invade– diarrhea in infants and travelers – diarrhea without fever
• Enterohemorrhagic (EHEC)– Serotype O157:H7– moderately invasive – pediatric diarrhea, copious bloody discharge (hemorrhagic
colitis)– hemolytic uremic syndrome (HUS)– inadequately cooked hamburger meat
E. coli• Enteroinvasive (EIEC)– invasive (penetrate and multiply within epithelial
cells)– does not produce shiga toxin– dysentery-like diarrhea (mucous, blood), severe
inflammation, fever – similar to Shigella
• Enteropathogenic (EPEC)– non fimbrial adhesin (intimin)
moderately invasive– usually infantile diarrhea; some inflammation, no
fever;
E. coli
• Index organism for fecal contamination of water (coliforms)
• Treatment– Cephalosporins– Aminoglycosides– Trimethoprim-Sulfamethoxazole– Fluoroquinolones
Salmonella• Non-lactose fermenter, motile, produces H2S
• Vi antigen• Contamination of food and water with animal
feces, except S. typhi (carried only by humans)• 105 organisms – infective dose
Salmonella• Never part of normal flora, always pathogenic• Typhoid fever – fever, rose spots, RLQ pain• Carrier state – in gallbladder• Sepsis – S.cholerasuis, osteomyelitis (in
asplenic patients and those with sickle cell disease)
• Gastoroenteritis – S. enteritidis; watery diarrhea, may contain mucus and trace blood
Salmonella
• Can survive intracellularly in monocytes
• Treatment:– Ciprofloxacin or ceftriaxone for typhoid fever– Fluid and electrolyte replacement in S. enteritidis
as antibiotics may prolong the course of bacterial shedding
Shigella
• 101 organisms – infective dose• Non-motile, no H2S production• No animal reservoir, transmitted via food,
fingers, feces and flies• Never part of normal flora• Shiga toxin – verotoxin; inactivates 60s
ribosomal unit
Shigella
• S.boydii• S.dysenteriae type I - deadly epidemics; HUS• S.flexneri - "group B“; Reiter's syndrome
(urethritis, conjunctivitis, arthritis) • S.sonnei - "Group D" Shigella, accounts for
over two-thirds of the shigellosis
Shigella• Bloody diarrhea, fever, and stomach cramps
starting a day or two after exposure• Usually resolves in 5 to 7 days
• Treament– ampicillin, trimethoprim/sulfamethoxazole,
nalidixic acid, ciprofloxacin– Avoid loperamide or diphenoxylate which
prolong excretion of the organism
Klebsiella pneumoniae
• Usually nosocomial, UTI in px with foley catheters, pneumonia in debilitated px
• 2nd most common cause of sepsis in hospitals (next to E. coli)
• Cavitary pneumonia with red “currant jelly” sputum
• Serratia – bright red pigment
Proteus mirabilis
• Very motile, “swarming” colony on blood agar• Urea-splitting• Cross-reacts with rickettsia• Common cause of UTI and nosocomial
infections
Vibrio cholera• Comma-shaped, single flagella
• Toxin – via ADP ribosylation that permananently activates adenylyl cyclase
• rapidly fatal illnesses - healthy person may become hypotensive within an hour of the onset of symptoms and may die within 2-3 hours if no treatment is provided; first liquid stool to shock in 4-12 hours, with death following in 18 hours to several days
Vibrio cholera
• “rice-water stools”• Treatment:– Immediate fluid and electrolyte replacement– Tetracyclines may shorten the duration of
diarrhea and reduce fluid loss
• V. parahemolyticus– Uncooked seafood– Leading cause of diarrhea in Japan
Campylobacter jejuni
• Comma or S-shaped• Zoonotic (reservoir in wild animals and
poultry)• Fecal-oral transmission or by drinking
unpasteurized milk• Bloody diarrhea
Helicobacter pylori
• Most common cause of duodenal ulcers and chronic gastritis
• Urease (+) – protects from stomach acid• Risk for gastric CA• Treatment:– Combination bismuth, metronidazole, ampicillin
and/or tetracycline– Combination metronidazole, omeprazole and
clarithromycin
Pseudomonas aeruginosa
• Aerobic• single, polar flagellum• Ubiquitous in soil and water• Colony types– rough colony– smooth fried-egg appearance which is large,, with
flat edges and an elevated appearance– mucoid - respiratory and urinary tract secretions,
attributed to the production of alginate slime
Pseudomonas aeruginosa
• Pigments (pyoverdin and pyocyanin)
• Opportunistic pathogen• Wound and burn infections, pneumonia,
sepsis, external otitis (swimmer’s ear), UTI, drug or diabetic osteomyelitis, hot tub folliculitis
Pseudomonas aeruginosa
• Endotoxin (fever, shock)• Exotoxin A (inactivates EF2)
• Treatment– Aminiglycoside plus extended-spectrum penicillin
(piperacillin, ticarcillin)
Bacteroides fragilis• Anaerobic• No lipopolysaccharide• Encapsulated• Predominant flora of colon• Exits colon via break in mucosa in chronic
disease, PID or trauma• Peritoneal abscesses• Tx: metronidazole, clindamycin,
chloramphenicol, drain surgically
Hemophilus influenza
• Coccobacillus• Polysaccharide capsule• Culture:– Chocolate agar with Factor X (hemin) and Factor V
(NAD) present in blood
Hemophilus influenza• Type B
– Leading cause of meningitis in children (6 mos to 1 yr)
– Bacteremia– epiglottitis (obstructive
laryngitis)
• Non-typable– osteomyelitis, and joint
infections– otitis media and sinusitis in
children– pneumonia in infants,
children and adults.
Hemophilus influenza• Treatment – Meningitis: ampicillin for strains of the bacterium
that do not make ß-lactamase, and a third-generation cephalosporin or chloramphenicol for strains that do
– Sinusitis, otitis media and respiratory infections: Amoxicillin with clavulanic acid
– Penicillin-resistant meningitis: Chloramphenicol– Sinusitis or respiratory infection caused by
nontypable H. influenzae: Tetracyclines and sulfa drugs
Hemophilus influenza
• Vaccine– Hib conjugate vaccines - children 15 - 59 months
old should receive a single dose of conjugate vaccine; Children 60 months of age or older and adults normally do not need to be immunized
• Rifampicin prophylaxis in close contacts
Legionella pneumophila
• Identified using silver stain (poor gram stain properties)
• Aerosol transmission from water source habitat
• No person-to-person transmission• Culture: charcoal yeast extract with iron and
cysteine• Atypical pneumonia with high fever and
unproductive cough• Tx: erythromycin
Bordetella pertussis• Gram-negative aerobic coccobacillus that
appears singly or in pairs
• Pertussis toxin – increase in cAMP• Filamentous hemagglutinin – attachment to
ciliated epithelial cells; does not invade• Tracheal cytotoxin – damages ciliated cells• Culture: Bordet-Gengou agar
Bordetella pertussis• Catarrhal stage– Lasts 1-2 weeks, most contagious
• Paroxysmal stage– 2-10 weeks– Lymphocytosis; bursts of non-productive cough
(whoop)– Antibiotics ineffective at this stage
• Convalescent stage
• Tx: erythromycin, if given before the paroxysmal stage
Zoonotic Bacteria• Yersinia pestis– Bipolar staining– flea bite; rodents and prairie dogs– Bubonic plague – swollen regional lymph nodes– “black death”– Tx: Streptomycin, gentamycin, doxycycline
• Brucella– Unpasteurized dairy products– Undulant fever– melitensis (goat/sheep), abortus (cattle), suis
(pigs)
Zoonotic Bacteria• Francisella tularensis– Tick bite; rabbits and squirrels– Tularemia – ulceroglandular lesions (hole in skin,
black base, swollen LN, draining pus)– Tx: gentamycin or streptomycin
• Pasteurella multocida– Animal bite; cats and dogs– Rapid onset cellulitis at bite site– Tx: penicillin
Spirochetes• Borrelia burgdorferi– Bite of Ixodes tick that live on deer and mice
– Lyme disease • Stage I – erythema chronicum migrans (“bull’s
eye” red rash with central clearing
Lyme Disease
• Stage 2 – disseminated stage– Neurologic and cardiac manifestations
• Stage 3 – persistent infection– Autoimmune migratory polyarthritis
• Treatment: Tetracycline
Borrelia recurrentis
• Transmitted via body louse (Pediculus humanus)
• Relapsing fever – antigenic variation– Fever every 8 days– Chills, drenching sweat, headaches, muscle aches
• Culture: during febrile periods only• Treatment: doxycycline or erythromycin
Treponema pallidum• Primary syphilis – painless chancre• Secondary syphilis – disseminated disease,
maculopapular rash on palms and soles, condyloma lata
• Tertiary syphilis – gummas, aortitis, neurosyphilis, Argyll Robertson pupil (accommodates but unreactive to light)
• Congenital syphilis – saber shin, saddle nose, deafness
Treponema pallidum• Non-specific tests: VDRL, RPR• Specific tests: FTA-ABS, MHA-TP• Jarisch Herxheimer reaction – acute
worsening of symptoms after initiation of antibiotics
• Tx: Penicillin G, Erythromycin, Doxycycline
• T. pertenue– Yaws (skin infection, not an STD but VDRL
positive)
Leptospira• Tight coil with hooks on one or both ends (“ice
tongs” appearance)• Direct contact with infected urine or animal
tissue (intact mucous membrane, abraded skin)
• Leptospiremic phase– Spiking temperature, headache, myalgias, red
conjunctiva, photophobia• Immune phase– IgM antibodies; meningismus (neck pain)– urine
Leptospira• Culture: – blood and CSF during the 1st week– Urine during 2nd week to months later
• Weil’s disease (icteric leptospirosis)– Renal failure, hepatitis, mental status changes and
hemorrhage in many organs
• Tx: Penicillin G, Doxycycline
Mycobacterium tuberculosis• Infects only humans• Acid fast (Ziehl-Nielsen stain)• Obligate aerobe• Facultative intracellular parasite• Slow generation time• Culture: Lowenstein-Jensen medium (egg-
based)
Mycobacterium tuberculosis• Virulence factors– Mycolic acid– Cord factor – inhibits neutrophil migration and
damages mitochondria; present only in virulent strains
– Sulfatides – inhibit phagosome from fusing with lysosome
– Wax D – activates protective cellular immune system
Mycobacterium tuberculosis• Primary infection– Middle and lower lung zones– Ghon focus – calcified tubercle in middle or lower
lung zone– Ghon or Ranke complex – focus plus perihilar
lymph node calcified granulomas• Secondary or Reactivation– Pulmonary – apical areas of lungs– Lymph node (scrofula), kidney, spine (Pott’s
disease), joints, CNS– Miliary
Mycobacterium leprae• Hansen’s bacillus• Favors cool areas• not grown in vitro (only in footpads of mice,
armadillos and monkeys)• Transferred through respiratory secretions; less
likely, skin lesions• Lepromatous – most severe form; defective T8 (T
suppressor cells); leonine facies, saddlenose deformity
• Tuberculoid – greater auricular, ulnar, posterior tibial and peroneal nerves usually affected
Mycobacterium lepraeTuberculoidTuberculoid BorderlineBorderline LepromatouLepromatou
ss
Number of Number of skin lesionsskin lesions
singlesingle severalseveral ManyMany
Hair growth Hair growth on skin on skin lesionlesion
absentabsent Slightly Slightly decreaseddecreased
Not Not affectedaffected
Sensation Sensation in lesions of in lesions of the the extremitiesextremities
Completely Completely lostlost
Moderately Moderately lostlost
Not Not affected*affected*
Acid fast Acid fast bacilli in bacilli in scrapingsscrapings
nonenone severalseveral InnumerablInnumerablee
Lepromin Lepromin skin testskin test
Strongly Strongly positivepositive
No reactionNo reaction No reactionNo reaction
Mycobacterium leprae
• Treatment– Long-term oral dapsone (toxicity: hemolysis and
methemoglobinemia)– Alternative: rifampin and combination of
clofazimine and dapsone
Chlamydia• Obligate intracellular parasite• Elementary bodies– Extracellular form– Infectious form, non-replicating, non-
metabolically active
• Reticulate bodies– Intracellular form– Replicating, metabolically active, non-infectious
Chlamydia trachomatis
• Types A, B, C – trachoma• Types D-K – urethritis/PID, ectopic pregnancy,
neonatal pneumonia, inclusion conjunctivitis (ophthalmia neonatorum – inclusion bodies stain with iodine or giemsa)
• Types L1 L2 L3 – lymphogranuloma venereum (positive Frei test)
• Tx: Doxycycline (for adults only), erythromycin (infants and pregnant), azithromycin
Mycoplasma pneumonia• No cell wall• Eaton’s Agent• Cholesterol in cell membrane• Cold agglutinins – agglutination of RBC’s at 4
C, due to cross-reactivity• Dome-shaped colonies with “fried egg”
appearance• Walking pneumonia (fever, with dry non-
productive hacking cough)• Tx: Erythromycin, Tetracycline
MYCOLOGY
Fungi• Eukaryotic with rigid cell wall• chemoheterotrophs (require organic compounds for
both carbon and energy sources)• Obtain nutrients by absorption• obtain nutrients as saprophytes (live off of decaying
matter) or as parasites (live off of living matter)
• Yeast - unicellular fungi which usually appear as oval cells
• Molds - multinucleated, filamentous fungi composed of hyphae
Superficial Mycoses• Malassezia furfur– Tinea/pityriasis versicolor – hypo/hyperpigmented
patches– “spaghetti and meatballs”– Tx: selenium sulfide shampoos; imidazoles
• Exophiala werneckii– Tinea nigra– Black lesions on palms and soles– Tx: topical salicylic acid
Cutaneous Mycoses• Dermatophytes– Microsporum (Wood’s light), Trichophyton,
Epidermophyton floccosum• Branched hyphae• Affects skin, hair and nails– Tinea corporis, cruris, capitis, pedis, unguium,
barbae• Pruritic lesions with central clearing
resembling a ring• Tx: topical imidazoles; oral griseofulvin for
hair and nail involvement
Subcutaneous Mycoses• Sporothrix schenckii– Rose gardener’s disease– Dimorphic fungus that grows on vegetation– Cigar-shaped budding yeast– Local pustule or ulcer with ascending lymphangitis– Tx: Amphotericin B or potassium iodide
• Phialophora and Cladosporium– Chromoblastomycosis – cauliflower warts– Copper-colored sclerotic bodies
Systemic Mycoses
• Dimorphic– Mycelial forms with spores at 25 C on Saboraud’s
agar, yeast at 37 C on blood agar or tissue, except Coccidioides (spherule in tissue)
• Transmitted by spore inhalation• Tx: Amphotericin B, itraconazole
Coccidioides immitis
• San Joaquin valley or desert (“desert bumps,” “valley fever”)
• Mild lung infection• Dissemination: bone
granulomas or meningitis
• Erythema nodosum in 10%
Histoplasma capsulatum
• Bird/bat droppings• Tiny yeasts within
macrophages• Mild pneumonia,
disseminated in immunocompromised
• Mississippi and Ohio river valleys
Blastomyces dermatitidis
• Big, broad-based budding• Almost always symptomatic• From the soil or rotten wood• Rarest systemic mycoses
• Paracoccidioides brasiliensis• “Captain’s wheel” appearance
Opportunistic Mycoses• Candida albicans– oval yeast with
pseudohyphae– Oral thrush in
immunocompromised– Vulvovaginitis– Chronic mucocutaneous
candidiasis– TX: clotrimazole for skin
infections; imidazole supppositories for vaginitis; nystatin for oral thrush; Amphotericin B for sytemic
Cryptococcus neoformans
• Heavily encapsulated yeast• India ink stain• Soil, pigeon droppings• Culture: Saboraud’s agar• Meningitis• Tx: Amphotericin B x 6 months, Flucytosine
Aspergillus fumigatus• Allergic bronchopulmonary aspergillosis –
type I hypersensitivity reaction• Invasive necrotizing pneumonia in AIDS, with
aspergilloma (fungus ball)• not dimorphic• Mold with hyphae that branch at 45 deg.
Angle (V-shaped)
• A. flavus – produces aflatoxin in cereals and nuts (carcinogenic to the liver)
Mucor and Rhizopus
• Mold only – with irregular non-septate hyphae
• Rhinocerebral mucormycosis – assoc. with diabetes
• Proliferate in walls of blood vessels causing infarction of distal tissue
Pneumocystis carinii
• Diffuse interstitial pneumonia
• Yeast• Usually seen in AIDS
patients• Methenamine silver
stain• Tx: co-trimoxazole,
pentamidine, dapsone
Fungi-like bacteria
• Actinomyces israelii– Has sulfur granules– Causes eroding abscesses
• Nocardia asteroides– Acid fast– Lung abscess and cavitations
VIROLOGY
DNA viruses• HHAPPPy (Hepadna, Herpes, Adeno, Pox,
Parvo, Papova)• Double-stranded except Parvo• Linear except Papova (circular, supercoiled)
and Hepadna (circular, incomplete)• Icosahedral except Pox (complex)• Replicate in the nucleus except Pox• Naked: PAP (Parvo, Adeno, Papova)• Enveloped: HPH (Hepadna, Pox, Herpes)
Parvoviridae
• Smallest DNA virus• B19– Fifth disease (erythema infectiosum)– Slapped-cheek appearance– Transient aplastic anemia crisis– Hydrops fetalis– Transmitted via respiratory droplets
Papovaviridae
• Human Papilloma virus– Common warts (types 1 2 4 7)– Genital warts (6 11 16 18)– Cervical cancer (16 18)– Through direct contact
• BK Polyomavirus – nephritis/urethritis• JC Polyomavirus – progressive multifocal
leukoencephalopathy; inhalation of infectious aerosols
Adenoviridae
• Respiratory diseases (3 7 14 21)• Epidemic keratoconjunctivitis “pink eye” (8 11
19 37)• Acute hemorrhagic cystitis (11 21)• Gastroenteritis (40 41)• Hepatitis (1 2 3 5)• Transmitted via respiratory droplets, fecal
matter, hands, fomites
Herpesviridae• HSV 1 – oral lesions; keratoconjunctivitis• HSV 2 – genital lesions– Tzanck smear – multinucleated giant cells with
Cowdry type A inclusion bodies
• Varicella zoster (Human herpesvirus 3)– “dewdrop on a rose petal”– Respiratory droplets or direct contact with
ruptured vesicles– Shingles – single dermatome
Herpesviridae• Epstein Barr virus (HHV 4)– Infectious mononucleosis (kissing disease) – fever,
sore throat, enlarged lymph nodes and spleen– Burkitt’s lymphoma– (+) heterophile antibody– Downey cells – atypical lymphocytes
• Cytomegalovirus (HHV 5)– In milk, saliva, urine and tears– Congenital defects; immunocompromised,
transplant recipients– Owl’s eye inclusion body
Herpesviridae• HHV 6 (Human B-lymphotrophic virus)– Exanthem subitum, roseola infantum, fourth
disease – high fever for 3 to 5 days followed by rash as the fever subsides
– Saliva
• HHV 8 – Sexually transmitted esp. in homosexual men– Kaposi’s sarcoma
Poxviridae
• Largest virus• No animal reservoirs• Variola – smallpox; Guarneri’s inclusion bodies• Vaccinia – cowpox; milkmaid’s blisters• Molluscum contagiosum – small white bumps
with a central dimple, genital region
Hepadnaviridae
• Hepatitis B virus– Acute or chronic hepatitis– Has reverse transcriptase
HBs HBs AgAg
Anti-Anti-HBsAgHBsAg
HBe HBe AgAg
Anti-Anti-HBeAHBeA
gg
Anti-Anti-HBcAgHBcAg
Acute Acute HBVHBV
++ -- ++ -- IgMIgM
Chronic Chronic HBV, high HBV, high infectivityinfectivity
++ -- ++ -- IgGIgG
Chronic Chronic HBV, low HBV, low infectivityinfectivity
++ -- -- ++ IgGIgG
RecoveryRecovery -- ++ -- ++ IgGIgG
ImmunizeImmunizedd
-- ++ -- -- --
RNA viruses• Single stranded except Reoviridae• Replicate in the cytoplasm except
orthomyxoviruses and retroviruses• Enveloped except Calicivirus, Picornavirus,
Reovirus• Helical capsid symmetry except Reo, Picorna,
Toga, Flavi, Calici which have icosahedral symmetry
• Toga, Corona, Retro, Picorna, Calici, Reo, Orthomyxo, Parmyxo, Rhabdo, Bunya, Arena, Filo
Picornaviridae• Smallest RNA virus• Poliovirus – affects anterior horn cells of
spinal cord• Coxsackie A – herpangina; hand foot and
mouth disease• Coxsackie B – aseptic meningitis; pleurodynia,
myocarditis• Echovirus – aseptic meningitis• Rhinovirus – common cold• Hepatitis A virus – acute viral hepatitis
Caliciviridae
• Cup-shaped• Norwalk virus – epidemic viral gastroenteritis
(summer diarrhea)• Hepatitis E virus – endemic hepatitis
Reoviridae
• Rotavirus – leading cause of fatal diarrhea in children
• Colorado tick fever - encephalitis
Togaviridae• Rubella– German measles – 3 day measles– Congenital rubella syndrome – cataracts,
deafness, heart defects, microcephaly
• Alphavirus– Eastern and Western equine encephalitis
• Chikungunya – myositis and arthritis• Onyong-nyong – fever, rash, arthralgia
Flaviviridae
• Dengue – “break bone fever”• Yellow fever• Hepatitis C virus• St. Louis encephalitis• West Nile virus
Arenavirus
• Lymphocytic choriomeningitis virus– Hamsters, animals in rodent breeding facilities
• Lassa fever virus – West Africa
Coronaviridae• 2nd most common cause of common cold• SARS
Retroviridae• Reverse transcriptase• HTLV – adult T-cell leukemia• HIV
– ELISA – screening, highly sensitive, RULE OUT– Western blot – confirmatory, highly specific, RULE
IN
Orthomyxoviridae
• Influenza virus– Hemagglutinin (HA)– Neuraminidase (NA)– Antigenic drift – minor changes; epidemics– Antigenic shift – major reassortment; pandemics– Amantadine and Rimantadine (Influenza A)– Zanamivir, Oseltamivir (Ifluenza A and B)
Paramyxoviridae• Parainfluenza virus – laryngotracheobronchitis
(croup)• Respiratory syncytial virus – most common
cause of pneumonia in infants less than 6 months of age
• Mumps – parotitis• Measles – rubeola– SSPE
Rhabdoviridae
• Zoonotic – all warm-blooded animals; saliva of infected animal
• Bullet-shaped• Negri bodies – collection of virions in the
cytoplasm• Hydrophobia – most characteristic symptom
of the neurologic phase
PARASITOLOGY
Protozoa• Entamoeba hystolytica– Bloody diarrhea, liver abscess; most are
asymptomatic– Trophozoite: single nucleus with ingested RBC– Cyst: 4 small nuclei– Transmission: cyst in water
• Giardia lamblia– “old man’s face,” pear-shaped trophozoite– Bloating, flatulence, foul-smelling diarrhea– Cyst in water
Protozoa• Cryptosporidium– Severe diarrhea in AIDS– Fecal-oral transmission of oocyst
• Trichomonas vaginalis– Foul-smelling green vaginal discharge– Sexually transmitted– Trophozoite: undulating membrane, jerky
movement
Protozoa• Toxoplasma gondii– Brain abscess in HIV– Birth defects– Transmitted via cysts in meat or cat feces– Tx: sulfadiazine + pyrimethamine
• Naegleria– Rapidly fatal meningoencephalitis– Swimming in freshwater lakes (enter via
cribriform plate)
Plasmodia• Vector: Anopheles mosquito• P. falciparum – most severe; cerebral malaria,
almost constant fever• P. malariae – Quartan malaria (every 72
hours)• P. vivax and ovale – Tertian malaria (every 48
hours)
Malaria
• Treatment– Chloroquine– Mefloquine – falciparum resistant to chloroquine– Primaquine – prevent relapse of vivax and ovale– Prophylaxis: mefloquine/chloroquine
Protozoa
• Trypanosoma cruzi– Chaga’s disease – dilated cardiomyopathy,
megacolon, megaesophagus– Reduviid bug “kissing bug”– Tx: Nifurtimox
• T. gambiense/rhodesiense– African sleeping sickness– Tse-tse fly– Tx: suramin for blood-borne disease; melarsoprol
for CNS penetration
Protozoa• Leishmania donovani– Kala-azar – visceral leishmaniasis– Fever, anorexia, weight loss, bone marrow
involvement, splenomegaly– Sandfly– Tx: sodium stibogluconate
• L. tropica (cutaneous, Old World)• L. mexicana (cutaneous, Americas)• L. braziliensis (mucocutaneous, Central/South
America)
Cestodes• Taenia solium (pork tapeworm)– Undercooked pork– Cysticercosis – mass lesions in brain caused by
larva– Tx: Niclosamide, Praziquantel
• Taenia saginata (beef)– No cysticercosis
• Diphyllobothrium latum (fish)– Megaloblastic anemia (B12 deficiency)
Cestodes
• Echinococcus granulosus (dog)– Unilocular hydatid cyst disease – in liver– Anaphylaxis– Humans are dead end hosts
• Hymenolepsis nana (dwarf)– No intermediate host– Eggs directly infectious to humans
Trematodes• Schistosoma– Snails are intermediate hosts– Cercaria – infective stage; skin penetration
(swimmer’s itch)– Fever, chills, diarrhea, lymphadenopathy– S. hematobium (bladder), mansoni (large
intestine), japonicum (small intestine)
• Clonorchis sinensis– Oriental liver fluke– Eating undercooked fish
Trematodes
• Paragonimus westermani– Lung fluke– Chronic cough with bloody sputum– Eating undercooked crab
Intestinal Nematodes• Enterobius vermicularis– Pinworm– Perianal itching– Scotch tape swab
• Trichuris trichiura– Whipworm– Soil-transmitted
• Ascaris lumbricoides– Giant roundworm– Larval migration to lung
Intestinal Nematodes• Ancylostoma/Necator– Hookworm– Microcytic anemia, Skin penetration by larva
• Strongyloides stercoralis– Pneumonitis, eosinophilia– Larvae in stool used for diagnosis– Tx: Ivermectin
• Trichinella spiralis– Eating raw pork with encysted larva– Larva develop in striated muscle– Inflammation of muscle, periorbital edema
Tissue Nematodes• Wuchereria bancrofti– Filariasis – blockage of lymphatics (elephantiasis)– Female Anopheles mosquito– Diethylcarbamazine against microfilariae
• Onchocerca volvulus– River blindness– Female blackflies– Tx Ivermectin
• Loa loa– Deerfly; swelling in skin– TX DEC
Tissue Nematodes
• Dracunculus medinensis– Guinea fire worm disease– Worm protrudes from skin– Ingestion of tiny crustaceans (copepods) in
drinking water
• Toxocara canis– Visceral larva migrans – Blindness due to retinal involvement– Dog: definitive host– Humans: dead end hosts
THANK YOU!