Addis Ababa University College of Health Sciences

School of Medicine

Dept of Microbiology, Immunology and Parasitology

Afework Kassu, PhDProfessor of Microbiology and Immunology

afeworkkassu@yahoo.com0921221959

Module 6 ScheduleTheme 4 - Microbiology & Parasitology. Week 6 & 7

January 28 - February 10, 2015Date /Time Microbiology Lecture hrs Practical

4. Skin and soft tissue infections 13 hrs total 9 hrs Group Day

28/1/159.00-10:3010:45-12.00

4.1. Streptococcal Infections Staphylococcal infections

2 hrsProf Afework

3 2,53,61,4

WedThurFri

29/1/159.00-10:3010:45-12.00

4.2 - Gas-gangrene4.3 - Leprosy

2 hrsDr Solomon

30/1/159.00-10:3010:45-12.00

4.4 - Viral exantemsViral exantems

2 hrs

Prof Afework

2/2/159.00-10:3010:45-12.00

Test III4.5 - Bone & joint microbial disease Osteomyelistis

1 hrDr Daniel

3/2/159.00-10:3010:45-12.00

Arthritis4.6 - Superficial mycosis

1 hrDr DanielDr Yimtu (1 hr)

4/2/159.00-10:3010:45-12.00

4.7 - Cutaneous mycosis4.8 - Opportunistic fungal infections

2 hrsDr Yimtu

3 1, 42,5 3,6

5/2/159.00-10:3010.45-12:00

4.9 - Scabiasis4.10 – Pediculosis

2 hr Tadesse

6/2/159.00-10:3010:45-12.00

4.11 - Cutaneous Onchocerciasis1 hrs Tadesse

10/2/1510:45-12.00 4.12 - Lesimaniasis

1 hrProf Asrat

3 3,6/1,42,5

Feb 23-27 Final Module exam (Test IV) Feb 23-27

Theme 4. Lectures and seminarsSkin and soft tissue infections

• Staphylococci and streptococci

• Leprosy

• Superficial mycosis

• Cutaneous Mycoses

• Opportunistic fungal infections

• Viral exantem

• Gas-gangrene

-- Scabiasis

-- Pediculosis

• Cutaneous Onchocerciasis and Leishmaniasis

• Bone and Joint microbial diseases - Osteomyelitis

- Arthritis

Theme 4. Microbiology Practical Classes

• Streptococcal & staphylococcal infection (Impetigo, erysipelas)

• Leprosy

• Superficial mycosis

• Cutaneous mycosis

• Subcutaneous mycosis

• Opportunistic fungal infections

• Viral exantem (small pox, herpesviruses, parvoviruses, papiloma virus)

• Gas-gangrene

• Scabiasis

• Pediculosis

• Cutaneous Onchocerciasis and Leishmaniasis

References

• Jawetz Medical Microbiology

• Murray P.R. Rosenthal K.S, Kobayashi G.S, Pfaller M.A. Medical Microbiology

• Robert Boyd. Basic Medical Microbiology

• Others

Staphylococcal and streptococcal infections

Objectives:

Upon completion of this section the student will be able to:

• Discuss the basic characteristics of staphyloccocci and streptococci

• Describe their virulence factors

• Discuss pathogenicity, clinical manifestations, laboratory diagnosis, prevention & control

Staphylococcal and streptococcal infections

Staphylococcus

• Make very large contribution to human commensal flora

• Account for a high proportion of acute and chronic lesions.

• General properties/characteristics of staphylococci

– Gram-positive cocci of uniform size (1m in diameter).

– Arranged in Grape like clusters (but also found single or in

pairs), Staphyle, meaning ‘bunch of grapes’

– Non-motile,

– Non-spore forming

– Aerobic or facultative anaerobes

– Produce catalase

– Resistant to temp as high as 50°C,

drying, high salt concentration

Staphylococci of medical importance

• There are over 30 species of Staphylococcus

• Species of medical importance:

– Staphylococcus aureus

– S. epidermidis

– S. Saprophyticus

Staphylococcus aureus

• S. aureus most important human pathogen than the

other species of staphylococci.

• Is distinguished from the other species by:

- coagulase production

- manitol fermentation and

- hemolysis of RBCs (beta-haemolysis)

More than 90% of S. aureus strains contain plasmids

that encode -lactamases

Cultural characters: • Facultative anaerobe

• Grow on nutrient agar producing golden yellow colonies of 1-2 mm (as a result of the carotenoid pigment that form during growth, hence the species name)

• They produce β-hemolytic colonies on blood agar

Beta hemolysis

Staphylococcus aureus

Biochemical features

• Fermentation of glucose produces mainly lactic acid

• It ferments mannitol (distinguishes from S. epidermidis)

Staphylococcus aureus

Pathogenesis

S. aureus produce disease b/c:

its ability to adhere the cellsspread in tissues & form abscesses,

produce extracellular enzymes and exotoxins.

Staphylococcus aureus

• S. aureus has several important cell wall components & antigens - important virulence factors for S. aureus:

1. Structural componentsa) Capsule or polysaccharide slime layerb) Peptidoglycanc) Teichoic acid d) Protein A

2. Toxins a) Cytotoxinsb) Exfoliative toxins c) Enterotoxins

d) Toxic shock syndrome toxin-1

3. Enzymes: Coagulase, catalase, hyaluronidase, fibrinolysin, lipases, nucleases & penicillinase

Staphylococcus aureus

Fig . Virulence determinants of Staphylococcus aureus

Staphylococcus aureus

• 1. Structural componentsa) Capsule:

- inhibiting the chemotaxis & phagocytosis.- facilitate attachment to catheters & other synthetic materials.

b) Peptidoglycan: - provide osmotic stability,- stimulates production of endogenous pyrogen (endotoxin like activity), - leukocytic chemo-attractant (abscess formation); and - inhibit phagocytosis.

c) Teichoic acid:-regulates cationic concentration at cell membrane and -mediate adherence of the organism to mucosal cells.

d) Protein A: - It binds to the Fc portion of IgG at the complement binding site, there by preventing the activation of complement

Staphylococcus aureus

2. Toxinsa) Cytotoxins: consisting of cytolytic or membrane damaging toxins

(alpha, beta, delta, gamma, leukocidin)

b) Exotoxins: three clinically important exotoxinsi) Enterotoxins: (A-E, G-I) Heat stable (resistant 1000c/30min.), -unaffected by GI enzymes and are a cause of food poisoning, principally associated with vomiting.

ii) Exfoliative toxin: cause desquamation of skin or scalded skin syndrome in young children Serine protease (affect GM4-glycolipids which is more in

children than adults) is produced, which can split the intercellular bridge in the stratum of granular cell layer that leads to epedermolysis.

iii) TSST: common in tampon using manstruating women or individual with wound infection.

Staphylococcus aureus

Staphylococcal enterotoxins, TSSTs and exfoliativetoxin are ‘super antigens’, all bind non-specifically to specific white cells resulting in over production of cytokines giving rise to a toxic shock-like presentation.

• Diseases Associated with Superantigen production: Toxic shock syndrome, psoriasis, rheumatoid arthritis, Diabetes mellitus, Scarlet fever, Eczema

Staphylococcus aureus

c) Enzymes: • Coagulase: causes the clumping of non-capsulated strains

when mixed with a solution containing fibrinogen, e.g. Plasma. Helps encase infection by forming fibrin layer around abscess

• Catalase: Reduces phagocytic killing by converting H2O2 to H2O

• Hyaluronidase: Spreading factors • Fibrinolysin: • Lipases: • Nucleases: • Penicillinase: Disrupts the Beta -lactame rings

Staphylococcus aureus

Factors Biological action

Surface components

Capsule Antiphagocytic

Protein A Inhibits complement fixation, opsonization, and ADCC

Teichoic acid and

lipoteichoic acid

Promote adherence to mucosal surfaces and persistence in tissues by

binding to fibronectin

Enzymes

Catalase Reduces phagocytic killing by converting H2O2 to H2O

Coagulase Helps encase infection by forming fibrin layer around abscess

Degradiative enzymes Promote tissue destruction and bacterial spread

Beta lactamase Confers antibiotic resistance

Toxins

Leukocidins Damage and lyse leukocytes; releases tissue-damaging substances

Enterotoxins Act as superantigens; responsible for gastrointestinal food poisoning

Exfolative toxins Cause splitting of cell junctions in epidermis; responsible for scalded

skin syndrome

Toxic shock syndrome

toxin

Acts as superantigen; promotes massive cytokine release, causes

toxic shock syndrome

DiseasesThe important clinical manifestations caused by S.aureus can

be divided in to two groups: 1. Inflammatory diseases :- Superficial/skin infection (Folliculitis, carbuncles, boils, stye, mastitis,

abscess formation, impetigo, furuncles, cellulites, surgical wound infections and mastitis) and

- Deep-seated/systemic diseases (Osteomyelitis, septic arthritis, endocarditis, meningitis, bronchopneumonia, empyema, etc).

- Bacteraemia with multiple abscesses in tissues: Outbreaks of hospital wound infections commonly occur due to antibiotic resistant staphylococci.

2. Toxin medicated diseases:

These include food poisoning, toxic shock syndrome, and scalded skin syndrome.

Staphylococcus aureus

B. Toxin-mediated staphylococcal diseases1. Food poisoning

– Results from ingestion of preformedenterotoxin in contaminated food that is improperly cooked and kept unrefrigerated for some time.

– Source of contamination of food: the hands or nose of a cook / food handlers /carriers.

– Types of food involved in staphylococcal food poisoning are carbohydrate rich foods, e.g. cakes, pastry, milk, etc.

– IP: short (1-8 hrs) followed by nausea, vomiting, diarrhoea and general malaise with no fever.

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Staphylococcus aureus

2. Toxic shock syndrome (TSS):

– This is associated with TSST-1, first described in menstruating women using tampons. The syndrome also occurs with wound or localized infections.

– TSS has an abrupt onset of fever, vomiting, diarrhoea, muscle pains, rash

– Hypotension, heart and renal failure may occur in severe cases.

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Staphylococcus aureus

Menstruation-associated TSS

F I G U R E 1 6 – 3Pathogenesis of staphylococcal toxic shock syndrome. A. The vagina is colonized with normal floraand a strain of Staphylococcus aureus containing the TSST-1 gene. B. The conditions with tamponusage facilitate growth of the S. aureus and TSST-1 production. C. The toxin is absorbed from thevagina and circulates. The systemic effects may be due to the direct effect of the toxin or via cytokinesreleased by the superantigen mechanism. The toxin is shown binding directly with the Vportion of the T-cell receptor and the class II major histocompatibility complex (MHC) receptor.This V stimulation signals the production of cytokines such as interleukin-1 (IL-1) and tumornecrosis factor (TNF).

3. Staphylococcal scalded skin syndrome (SSSS):

– Occurs due to the exfoliative toxin produced by phage II strains of S. aureus.

– The syndrome occurs in babies and young children.

– It is characterized by large areas of desquamation of the skin and generalized bullae formation.

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Staphylococcus aureus

FIGURE . Evidence of staphylococcal scalded-skin syndrome in a 6-year-old boy.

Nikolsky’s sign, with separation of the superficial layer of the outer epidermal

layer, is visible.

(Richard A. Harvey, Pamella C. Champ, Microbiology, Lippincott’s illustrated reviews, 2nd ed.)

• Epidemiology

• It is normal flora on human skin, nose (25 – 75% carriers) and mucosal surfaces

• The organism can survive on dry surfaces for long periods

• Transmission is from person to person through direct contact or exposure to contaminated fomites(e.g. bed linens, clothing)

• Risk factors include presence of a foreign body such as suture and catheter, previous surgical procedure and use of immuno-suppresser drugs

• Patients at risk for specific disease include:-menstruating women, infants , young children with poor personal hygiene; patients with compromised pulmonary function

Staphylococcus aureus

Laboratory diagnosis:

Specimens– Swabs from lesions: pus, sputum, CSF, blood, urine examined

Gram stain smears: Gram positive cocci in clusters

Culture: – S. aureus colonies show complete haemolysis on blood

agar and golden yellow to cream & occasionally white 1-2 mm in diameter colonies on nutrient agar.

– Colonies are usually large (6-8 mm in diameter), smooth & translucent.

– Mannitol salt agar (MSA) - useful differential and selective medium for recovering S. aureus from fecalspecimens in staphylococcal food-poisoning.

30

Staphylococcus aureus

Isolated colonies are further identified by:1. Catalase test: Staphylococci are catalase positive2. Cougulase test: tested by adding few drops of a broth

culture of the organism to 0.5ml of human or rabbit plasma; coagulation of the plasma occurs within few min.

3. Phage typing: – used for epidemiologic tracing of "out-breaks of

wound infections" in hospitals. S. aureus isolated from wounds, nose, nail bed of attending Drs, nurses and families should be identified by phage typing to reveal the source of infection

– In tracing the source of contamination of food in ‘out-breaks of food poisoning’; the organisms isolated from food, vomitus, stool, nose & nail bed of food handlers are phage typed.

– Most enterotoxin-producing strains of S. aureusbelong to phage group III.

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Staphylococcus aureus

Antimicrobial sensitivity

– Several antibiotics are effective against staphylococci e.g. pen, erythromycin, tetracyclines, ampicillin, cephalosporins.

– S. aureus shows marked ability to develop resistance to antibiotics specially in hospitals.

– Sensitivity testing is therefore essential for the choice of the appropriate antibiotic.

– About 80% of hospital strains of staphylococci are penicillin resistant. This is due to the production of β-lactamase which breaks down the lactam ring in penicillin & cephalosporins

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Staphylococcus aureus

Treatment of S. aureus infections• For penicillin / methicillin sensitive organisms – Penicillin or

cephalosporin• TMP-SMX, rifampicin, Clindamycin, Quinolone• Some recommend combination therapy - Amoxicillin &

clavulanate (Augmentin)

Drug Resistance • Methicillin-resistant S. aureus (MRSA) - (esp in hospital

settings)– Recently, vancomycin resistant S aureus emerging– CA-MRSA (community-acquired–MRSA) cause about half

of the cases– HA-MRSA (Healthcare-Associated-MRSA)

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Staphylococcus aureus

Hemolysis of BAP

alpha hemolysisBeta hemolysis

Staphylococcus aureus

Catalase test

• They are coagulase-negative staphylococci

- Do not produce exotoxins.

- Thus, they do not cause food poisoning or toxic shock

syndrome.

S. epidermidis- Part of the normal flora of the skin and mucous membrane.

- Cause of hospital-acquired infections

- It is involved in indwelling catheters, prosthetic materials,

shunts, surgery

- It is a common cause of prosthetic heart valve endocarditis

- It also causes nosocomial bacteremia; sepsis in neonates

peritonitis in patients with renal failure; cerebrospinal fluid

shunt infections

- Often multiple antibiotic resistance - Methicllin

S. epidermidis & S. saprophyticus

S. saprophyticus• Commonly isolated from animals and their carcasses.

• Coagulase and phosphatase -ve, urease & Lipase +ve

• S. saprophyticus is resistant to the antibiotic Novobiocin, a characteristic used in lab to distinguish it from S. epidermidis

• Infections are almost always community acquired.

• It causes mainly UTI, particularly in sexually active young women.

• It is a 2nd most common cause of UTI, after E. coli in young women accounting for 10-20% .

• It also causes soft tissue infections.

• Quinolones are commonly used in treatment of S. saprophyticusUTI.

Table: Biochemical characteristic of staphylococci

Fig. Flow diagram for the preliminary identification of human Staphylococcus species

Streptococcus

General characteristics:• Non-motile, non-spore forming, catalase-negative

Gram positive cocci arranged in chains or pairs. • Widely distributed in nature, some are commensals in

the throat, intestine.• Others cause human diseases • Others found in water, dust, milk /milk products. • Most are facultative anaerobes and some grow only in

an atmosphere enhanced with carbondioxide.• Elaborate variety of extracellular substances &

enzymes• Their nutritional requirements are complex

necessitating the use of blood or serum-enriched media for isolation

• More than 30 spp are identified.

Streptococcus

Streptococcus

• Scanning electron microscope image of Streptococcus

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StreptococcusClassification:

• Heterogenous group of bacteria I. According to their O2 requirements they are either aerobic or

anaerobic (peptostreptococci).

A. Aerobic streptococci according to their action on RBC in blood agar (3 varieties):

1. Beta haemolytic streptococci: complete haemolysis (clear zone around the colonies on BA) e.g. S. pyogenes, S. agalactiae

2. Alpha haemolytic streptococci: partial haemolysis e.g. Viridans streptococci, S. pneumoniae

3. Non-haemolytic or gamma streptococci: no haemolysis/ change in RBC's, e.g. Enterococci

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Beta haemolysis

alpha-haemolysis)

Gamma haemolysisStreptococcus

StreptococcusII. Classification based on serologic reactivity of cell wall

polysaccharide Ags as originally described by R. Lancefield

• >18 group-specific Ags (Lancefield groups A-U) were

established according to the carbohydrate (C) Ag present in

the cell wall.

• Group A: S. Pyogenes - causes pharyngitis, skin infections • Group B: S agalactiae - causes neonatal septicemia,

meningitis• Group C: S. equisimilis – endocarditis, bactermia, meningitis • Group D: Enterococci – UTI, endocarditis• Group H: S. sanguis – endocarditis, dental caries• Group K: S. salivarius - endocarditis, caries

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III. Classification based on Biochemical (physiologic) properties:- some streptococciare difficult to classify by hemolytic & antigenic xics- biochemical tests are used in their final classification.

Streptococcus

Streptococcus pyogenes

Streptococcus pyogenesGroup A streptococcus (GAS): Streptococcus pyogenes• GAS consists of 1 spp with 40 antigenic types

• S. pyogenes, the most important human pathogen causing diseases including:– Suppurative conditions / Skin infections – Throat infections – Systemic infections – Non-suppurative sequelae

• About 5-15% of normal individuals harbor the bacterium, in their respiratory tract, without signs of disease.

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Streptococcus pyogenesMorphology:

• Gram-positive cocci arranged in chains of varying length & are non motile.

• Some strains are capsulated.

Cultural characters:

• Forms minute colonies

• It grows on blood agar producing β-haemolysis

Antigens

• The cytoplasmic membrane of S. pyogenes has Ags similar to those of human cardiac, skeletal, smooth muscle, heart valve fibroblasts and neuronal tissues, resulting in a molecular mimicry.

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Streptococcus pyogenes

Virulence factors of group A streptococci:

1. M – protein, fibronectin-binding proteins (e.g. F protein) & lipoteichoic acid for attachment

2. Hyaluronic acid capsule: inhibits phagocytosis

3. Exotoxins such as pyrogenic toxin, cause the rash of scarlet fever & systemic toxic shock syndrome

4. Invasins - Streptokinase, streptodornase (DNaseB), hyaluronidase & streptolysins

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Figure: Antigenic structure of S. pyogenes and adhesion to an epithelial cell. The location of peptidoglycanand Lancefield carbohydrate antigen in the cell wall is shown in the diagram. M protein and lipoteichoic

acid are associated with the cell surface and the pili. Lipoteichoic acid and protein F mediatebinding to fibronectin on the host surface.

Streptococcus pyogenes

Protein antigens:

• S. pyogenes: divided into types based on their content of M protein (about 80 types described).

• M protein:

- the most important virulence factor

– is antiphagocytic

- promotes adherence to host epithelial cells

• The protein and other cell wall Ags have important role in the pathogenesis of rheumatic fever.

• Antibodies to these components react with cardiac muscle tissue.

• Other antigens are the T & R proteins - but they are not related to virulence.

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Streptococcus pyogenesToxins and Enzymes:

• More than 20 extracellular products that are antigenic are produced by S. Pyogenes.

Some of the important toxins and enzymes include:

1. Streptokinase (fibrinolysin): It activates plasmin in blood, which can dissolve fibrin in clots, thrombi and emboli, causes fibrinolysis.

2. Streptodornase (deoxyribonuclease): DNAses (types A, B, C, D) that break down DNA and stimulate an antibody response especially against DNAse B.

3. Streptokinase and streptodornase are responsible for the spreading nature of streptococcal infections.

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Streptococcus pyogenes

4. Hyaluronidase: – It destroys hyaluronic acid, the cement substance of

connective tissue. It helps spreading of infection.

5. Streptococcal pyrogenic exotoxins (SPE) (formerly erythrogenic toxin): – An exotoxin produced by some strains of group A

streptococci, lysogenized by a bacteriophage carrying the gene for the toxin,

– Act as superantigens

– It causes vasodilatation of capillaries leading to the rash of scarlet fever.

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Streptococcus pyogenes

6. Streptolysins: There are 2 types:

a. Streptolysin O - (O2 labile):

– Antigenic, stimulates the production of antistreptolysin O (ASO) Ab that can be measured in patients serum.

b. Streptolysin S - (O2 stable):

– Not antigenic, does not stimulate production of Ab

– It hemolyzes red cells and is responsible for the beta -haemolysis produced on blood agar.

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Streptococcus pyogenesPathogenesis:

I. Diseases due to toxins• S. pyogenes: exogenous secondary invader, following

viral dis or disturbances in the normal bacterial flora

1. Streptococcal sore throat and follicular tonsillitis (pharyngitis): It is characterized by enlarged tonsils with purulent exudate, high fever and enlarged cervical lymph nodes; the most common infection caused.

2. Impetigo: A local infection of the skin characterized by formation of blisters which break leaving surface covered with pus or crusts

3. Scarlet fever: disease of children characterized by sore throat and erythematous rash; caused by erythrogenic toxin in susceptible individuals.

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Streptococcus pyogenesII. Diseases due to invasion:

– Diffuse rapidly spreading infections that involve the lymphatics with minimal local suppuration infection can extend to the blood stream.

1. Puerperal sepsis: Infection of the uterus after delivery or abortion leading to endometritis and is associated with bacteremia.

2. Erysipelas: a skin infection characterized by redness, edema and a rapidly advancing margin

3. Soft tissue sepsis: Wound infection, cellulitis, lymphadenitis, necrotizing fascitis - may be complicated by streptococcal septicemia.

4. Acute Bacterial Endocarditis: The organism reaches the heart valve through the blood stream as a complication of any of the primary lesions mentioned before. – The presence of a deformed or rheumatically affected

valve encourages the condition.

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Streptococcus pyogenesIII. NONSUPPURATIVE SEQUELAE:

Post-streptococcal diseases –GN, RF• May occur 1- 4 weeks following a primary inadequately treated

group A streptococcal infection of the skin & RT • The latent period suggests hypersensitivity to streptococcal products

is the most probable cause.• GN- may follow throat or skin infections (pyoderma) while

rheumatic fever follows only throat infections (pharyngitis).

1. Acute glomerulonephritis (AGN):• develops 3 weeks after infection with a nephritogenic strain of

streptococci (types 12, 4, 2 & 49). • Disease is characterized by fever, edema, elevated BUN (azotemia),

hematuria, high BP, low serum complement levels. Blood, albumin, granular casts present in urine.

• The condition is due to Ag-Ab complex deposition on the glomerularbasement membrane (GBM).

• The majority of patients recover completely. However few may die or pass to chronic GN & renal failure.

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Streptococcus pyogenes

2. Rheumatic fever (RF):

• It has a more tendency to recur than GN because RF can result from infection by any of the serotypes of S. pyogeneswhere as GN is associated with only a limited number of these serotypes.

• The onset follows 1-4 weeks after throat infection with group A streptococci.

• The most serious complication of streptococcal throat infection since it may result in damage of the heart valves & muscle.

• RF is characterized by fever, migrating polyarthritis, carditis, Erythema marginatum, Sydenham chorea

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Streptococcus pyogenes

• The pathogenesis of RF is an autoimmune disease.

• Streptococci have Ags immunologically similar to proteins present in the heart valves and muscle, so the Abs produced against streptococci can react with the heart (i.e. cross reactivity) leading to cardiac damage.

• Recurrence of rheumatic activity occurs due to repeated streptococcal infections and every attack adds to the cardiac damage.

• This can be prevented by prophylactic long acting penicillin administration.

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Streptococcus pyogenes

Epidemiology• 5-15% of humans carry S. pyogenes or S. agalactiae in the

nasopharynx.

• Vehicles: foods, like cow’s milk, egg or potato salad

• Infective dose: <1000 cells

• Onset of illness occur within 1-3 days

• Spread by respiratory droplets or by contact with fomites used by the index individual, either patient or carrier

• Skin infections often follow minor skin irritation, such as insect bites.

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Streptococcus pyogenes

Lab diagnosis of streptococcal diseases:

1. Specimens: Swabs from throat or other lesions, pus, or blood in case of bacteraemia

2. Direct smears stained by Gram’s method show Gram-positive cocci in chains.

3. Cultures done on blood agar show colonies producing complete haemolysis

4. Blood cultures: done for bacteremic infections e.g. bacterial endocarditis & puerperal sepsis. In the latter case, it is more valuable in diagnosis than the uterine swab, which is often contaminated with normal flora.

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Streptococcus pyogenes5. Bacitracin test:

• GAS can be differentiated from other other β-hemolytic

streptococci (B, C, G) by their sensitivity to bacitracin.

• The test is done by placing a filter paper disc containing

bacitracin (0.05um) on blood agar inoculated with the

organism. A zone of inhibition around the disc observed

6. Antigen detection tests:

• Rapid detection of group A streptococcal Ags from throat

swab can be done by ELISA or agglutination tests

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Streptococcus pyogenes7. Serologic tests – for anti-streptococcal antibody titers• mainly used for diagnosis of post streptococcal diseases-

Acute GN and acute RF identification

a. Antistreptolysin O (ASO): Abs develop in pt sera with streptococcal infections. Detection of high ASO titre of 1/200 or more is significant.

b. C-reactive protein (CRP):• CRP: abnormal protein that appears in serum in cases of

active RF, other degenerative & inflammatory conditions • It can be tested for by a passive agglutination reaction using

latex particles coated with anti-CRP Abs

• A positive CRP, a high ASO titre and high ESR are helpful in the diagnosis and follow up of cases of RF

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Streptococcus pyogenesTreatment and Chemoprophylaxis:• Penicillin is the drug of choice for treatment of

streptococcal diseases. • Long acting penicillins: given as chemo-

prophylactic measure to children prone to recurrent attacks of streptococcal sore throat or recurrent attacks of RF.

• Erythromycin is also effective, BUT Erythromycin resistance (check MICs by Etest)

• Macrolide resistance in ß-haemolytic streptococci of Lancefield groups A, B, C, G

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Streptococcus agalactiae

Streptococcus agalactiaeGroup B streptococci (GBS): S. agalactiae

• About 10% - 30% of pregnant women are colonized with GBS in the genital tract.

• GBS causes life-threatening infections in newborn infants

• GBS can also cause serious diseases in pregnant women, the elderly, and adults with other illnesses.

• In newborns, GBS is the most common cause of sepsis and meningitis and a common cause of pneumonia.

• GBS disease in newborns usually occurs in the first week of life.

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Streptococcus agalactiae• Babies can also get a slightly less serious "late-onset" form

of GBS disease that develops a week to a few months after birth.

• Adults with illnesses that weaken the immune system, such as diabetes or cancer, are at risk of infection with GBS.

Diagnosis• Lab test of blood or spinal fluid.• Group B streptococci show hippurate hydrolysis

Treatment• Newborns and adults are usually treated with antibiotics

given IV

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Streptococcus agalactiae

Prevention

• Any pregnant woman who has already had a baby with GBS infection or who has a urinary tract infection caused by GBS should be given antibiotics during labor.

• Pregnant women who are colonized with GBS should be offered antibiotics at the time of labor or rupture of the membranes.

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Viridans Streptococci

Group D

Viridans Streptococci

Alpha Haemolytic Streptococci – Group D

Viridans Streptococci Group• Non-pyogenic streptococci • Are biochemically & antigenically diverse group• They form part of the normal flora of the mouth.

• They lack either the polysaccharide-based capsule typical of S. pneumoniae or the Lancefield Ags of the pyogenicmembers of the genus.

• Group D is differentiated from other viridans streptococci by bile solubility and optochin sensitivity.

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Viridans StreptococciViridans and other species

• S. mutans, a contributor to dental caries. It synthesize large sticky polysaccharide such as dextrans or levans from sucrose and participate in dental carries production.

• S. mutans & S. sanguis - odontopathogens responsible for the formation of dental plaque.

• S. mitis, mostly found around cheek region • S. sanguinis, no preference of locations • S. viridans, a cause of endocarditis, dental abscesses• S. salivarius, found on the dorsal side of the tongue• S. salivarius ssp. thermophilus, used in the manufacture of

some cheeses and yogurts • S. constellatus, occasional human pathogen

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Viridans StreptococciDiseases caused by Viridans streptococci:

• Cause sub-acute bacterial endocarditis (SBE) in individuals with congenitally deformed or rheumatically affected heart valves.

• Account for 30 - 40% of cases of endocarditis

• Infection is endogenous: organisms reach the blood stream during tooth extraction or tonsillectomy.

• They settle on the deformed valve and lead to the inflammatory process.

• Mortality: >50%

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Viridans StreptococciLab Diagnosis

Blood culture• Add 5 -10ml of blood to 50 -100ml of broth, incubated at

37oC. • Sub-cultures made on BA every 48 hrs for 10 days.

• The large volume of broth has the following advantages:– Dilutes out antibacterial substance naturally occurring in

serum. – Allows for multiplication of organisms present in few

numbers.– Antagonists to antibiotics taken by the patient can be

added to the broth

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Enterococcus

Group D

Enterococcus

Group D: Non-Haemolytic Streptococci

1. Enterococcus• >12 spp, some of these are - Enterococcus faecalis, E.

fecium

• They are normal inhabitants of the intestine.

• They cause UTI, wound, cholecystitis, blood infections, meningitis, bacteremia (neonates) subacute endocarditis, prostatitis.

• Enterococci are among the most common causes of nosocomial infections, esp in ICU

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Enterococcus• E. faecium causes 5-10% of enteroccal disease• They are more resistant to antibiotics than other

streptococci.

• They show intrinsic resistance to cephalosporins, monobactams, some penicillins.

• They show vancomycin resistance (VRE)

• Combined penicillin and aminoglycosides are used for treatment.

2. Non-enterococcal Group D strains• include Streptococcus bovis and Streptococcus equinus.

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PEPTOSTREPTOCOCCI

ANAEROBIC STREPTOCOCCI

PEPTOSTREPTOCOCCI

• Grow under anaerobic or microaerophilic conditions.

• They are normal inhabitants of the mouth, intestine, URT & female genital tract.

• They are involved in serious mixed anaerobic infections in the abdomen (abscesses), pelvis, lung, brain, the female genital tract and pulmonary tract.

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STREPTOCOCCUS PNEUMONIAE

/Pneumococcus/

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STREPTOCOCCUS PNEUMONIAE/Pneumococcus/

Habitat: • S. pneumoniae is a normal inhabitant of the human upper

respiratory tract (found as commensal)• Virulent pneumococci are often carried in the normal

respiratory tract of healthy people. • The carrier rate of S. pneumoniae in the normal human

nasopharynx is 20-40%.

Morphology: • Gram-positive, catalase-negative, lancet-shaped slightly

elongated and arranged in pairs, non-motile and non-sporulating diplococci.

• Are capsulated in animal tissues. • Capsules may appear as unstained halos around the organism.• They do not display M protein

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Pneumococcus

Biochemical characters:

• Ferment glucose to lactic acid

Cultural characters:

• Doubling time is 20-30 min.

• Contain autolysin (enzyme) – which disrupts and disintegrates the cells

• Most strains of S. pneumoniae are α-hemolytic but can cause β-hemolysis during anaerobic incubation

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Pneumococcus

Pneumococci Viridans Strept

Solubility in bile Soluble Not soluble

Fermentation of inulin

Fermented with acid production

Not fermented

Sensitivity to optochin

Sensitive Not sensitive

Pathogenicity to mice

Pathogenic, cause death of mice on intraperit. injection

Not pathogenic

Quellung test Positive Negative

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- They grow on blood agar producing α-hemolysis similar to that of viridans streptococci from which they are differentiated by the following tests:

PneumococcusAntigenic structure:

• About 90 serotypes of pneumococci based on the chemical specificity of the capsular polysaccharide.

• Serotyping can be done by agglutination or capsule swelling "quellung reaction".When pneumococci of a certain type are mixed with a specific anti-polysaccharide serum of the same type or with a polyvalent antisera on a microscopic slide the capsule swells markedly.

• This is useful for rapid identification and typing the organism either in sputum or in culture.

• No Lancefield group antigen

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PneumococcusPathogenesis:• S. pneumoniae does not produce toxins• It owes its virulence to the capsule, which enables the

organism to invade the tissues and resist phagocytosis.

• Predisposition to disease: if resistance is lowered, e.g. by viral respiratory infections, excessive smoking, alcoholism, malnutrition

Diseases caused by S. pneumoniae• S. pneumoniae is currently the leading cause of invasive

bacterial disease in children and the elderly.

• Causes 80% of lobar pneumonia; conjunctivitis, paranasalsinusitis, OM, meningitis, acute exacerbation of chronic bronchitis, septic arthritis, osteomyelitis, endocarditis, peritonitis, cellulitis, brain abscess.

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Pneumococcus

Laboratory diagnosis of lobar pneumonia:

1. Direct microscopic examination of gram stained sputum smears

2. Sputum cultured on blood agar.

– Pneumococci produce α-haemolytic colonies, which should be differentiated from viridans streptococci.

– S. pneumoniae is a fastidious bacterium, growing best in 5% CO2.

– Nearly 20% of fresh clinical isolates require fully anaerobic conditions.

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Pneumococcus

3. Quellung reaction: Fresh emulsified sputum mixed with polyvalent anti-pneumococcal serum, stained by methyleneblue and examined under the microscope will show a positive ‘quellung reaction’. This is done for rapid identification.

4. Intraperitoneal injection of sputum into mice. The animal dies in 24-48 hrs. The organism can be seen in tissue smears & pure culture can be obtained from heart blood.

Treatment• Pneumococci are sensitive to many antibiotics. • Some isolates have recently been reported to be resistant to

penicillin.

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Pneumococcus

Prophylaxis / Prevention:

• 2 vaccines available to prevent pneumococcal disease

1. Pneumococcal conjugate vaccine (PCV7)

– for infant immunization children,

2. Polyvalent polysaccharide vaccine (PPV23)– for adults - are safe and fairly effective.

– The later is recommended for specially susceptible individuals, e.g. aged (>65 years), debilitated or bed-ridden patients or after splenectomy.

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Addis Ababa University College of Health Sciences

School of MedicineDept of Microbiology, Immunology and Parasitology

Afework Kassu, PhD

Professor of Microbiology and Immunology

afeworkkassu@yahoo.com

0921221959