Bug Juice 101

Deanna Moore, MSN, ACNP-BC, CCRN, NREMT-P

Objectives

• Review taxonomy of microorganisms• Describe lab tests used for speciation• Review antibiotic classes, mechanism

of action, spectrum of activity, and dosing considerations

• Review common infections encountered in the hospital setting and appropriate treatment

Taxonomy - Bacterial

• Gram Stain• Acid-Fast Stain• Morphology• Oxygen use• Facultative• Toxins

Gram Stain

• Four step process –

Acid-Fast Stain

• Difficult to ID with normal gram staining

• Red stain does not wash off with acid alcohol– Mycobacterium

• Gram Positive– Two protective layers

• Phospholipid bilayer– Protects bacteria

• Peptidoglycan cell wall– Allows passage of

antimicrobials

• Gram Negative– Three layers

• LPS – protein, Lipid A– Endotoxin

• More difficult to tx

Lab Biomedical Tests

• Catalase – defense against h2o2 and superoxide• Citrate – utilize citrate as only carbon source• Coagulase – determine if pathogenic• Indole – ability to break down tryptophan• Optichin – Id Streptococcus pneumo• Oxidase – Presence of cytochrome oxidase• Urease – enzyme that breaks C-N bond (proteus)

Coagulase Test

– Differientiating between pathogenic strains of Staphylococcus

Catalase

Oxygen Use

• Obligate aerobes

• Facultative anaerobes

• Microaerophilic

• Obligate anaerobes

Gram Positive Cocci

• Streptococci – catalase negative, microaerophilic– Group A beta hemolytic

• “strep” throat, Skin infections – necrotizing fascitis

– Group D alpha hemolytic• Enterococcus faecalis, faecium – UTI, bacteremia

– Pneumoniae – pneumococcus• Pneumonia, meningitis, endocarditis

• Staphylocci – catalase positive, facultative anaerobes– Coagulase Positive

• S. aureus – skin flora – pna, sepsis, uti

– Coagulase Negative• S. epidermidis –skin flora - prosthetics

Gram Positive Rods

• Endospore Forming– Bacillus – anthracis, cereus (food poisoning)

• Regular, Non-endospore forming– Lactobacillus

• Irregular, Non-Endospore forming– Cornyebacterium (diptheria in children) – fac anaerobes, cat +– Listeria – only gp to produce endotoxin – fac an, cat +

• Pna immunosuppressed

• Mycobacteria– Weakly gram positive – Tuberculosis – obligate aerobes

Gram Negative• Aerobic Cocci

– Neisseria – facultative anaerobes, encapsulated (resistant to host organism)

• Meningitidis – meningococcus• Gonorrhea

• Bacilli (rods) - enterics– Facultative anaerobes

• Ecoli• Klebsiella• Serratia• Proteus• Helicobacter pylori• Enterobacter

– Obligate aerobe• Pseudomonas

Gram Negative

• Nonenterics– Obligate aerobes

• Bordetella pertussis

• Legionella

– Facultative anaerobes• Haemophilus influenzae

• Coccobacilli– Acinetobacter - aerobic

Anaerobic Features

• Foul smelling discharge

• Proximity to mucosal membrane

• Necrotic tissue

• Gas formation in tissue or discharge

Anaerobes

• Gram positive bacilli– Clostridium

– Botulinum

– Tetani

– Perfringens

– Difficile

• Gram negative Bacilli– Spore forming rods

-Bacteroides fragilis

• peritonitis

Fungi

• Cell Membrane– Major steroid is ergosterol – object of

antifungals

• Cell Wall– Potent antigens for immune system

• Capsule– Polysaccharide coating in some fungi – very

antiphagocytic for human immune cells

Fungal Infections

• Candida albicans– Thrush, vaginitis, esophagitis

• Histoplasma capsulatum– Lung

• Cryptococcus neoformans– Lung, skin ulcers, HIV

• Aspergillus flavus– Lung

Brief Review - Match

• Enterococcus?

• Coag positive staph?

• Gram positive rod?

• Gram negative enteric?

• Gram negative nonenteric

• Gram negative coccibacillus

• Gram positive rod - anaerobe

• Acinetobacter

• H. flu

• Klebsiella

• Streptococcus

• MRSA

• Lactobacillus

• C diff

As said by J.B.S. Haldane…..

• The danger with germ-killing drugs is that they may kill the patient as well as the germ.

Antimicrobials by MOA

• BACTERIOSTATIC– Control– Inhibit protein synthesis– Intact immune system– Tetracyclines– Doxycycline– Macrolides– Sulfonamides

• BACTERIOCIDAL– Kill– Cell wall inhibitors– PCN– Vanc– Cephalosporins– Carbapenems– Aminoglycosides– Monobactams– Fluoroquinolones– Metronidazole– Isoniazid, Rifampin

Some drugs can be either based on bacteria and drug concentration

Beta-Lactams/Cell Wall Inhibitors

• PCN– Specific step in cell wall synthesis– Only bactericidal if cells are actively synthesizing cell

wall– Resistance

• Inactivation by Beta lactamase – most common– More than 300

• S.aureus, H. flu, Ecoli – still sensative to cephalosporins• Pseudomonas – both PCN and CPN

• Modification of target PCN binding proteins• Impaired penetration of drug• Presence of efflux pump

• PCN G – 1929 – Alexander Fleming– Streptococci, meningococci, enterococci, PCN

susceptible pneumococci, non Betalactamase producing staphylococci

– Lots of resistance – limited use now

• PCN resistant to staphlococcal beta lactamase– Methicillin, Nafcillin

• Systemic staphylococcal – – oxacillin, nafcillin 8-12 g/d (1-2 q 6h)

• Methicillin - nephrotoxicity

Extended Spectrum PCNs• Spectrum of PCN G + Gram Negative

– Penetrate outer membrane– Inactivated by beta lactamases

• Aminopenicillins – ampicillin and amoxicillin– PO/IV, UTIS, Respiratory, OM, sinusitis

• Not effective against klebsiella, pseudomonas, enterobacter, citrobacter, serratia

• Carboxypenicillins – carbenicillin and ticarcillin– Amp spectrum + pseudomonas, enterobacter (ticarcillin)

• Ureidopenicillins – azlocillin, mezlocillin and pipericillin– Above + klebsiella

• Combo drugs: + betalactamase inhibitors – clavulanic acid, sulbactam, tazobactom – increases spectrum Betalactamase prod S. aureus, Gram neg

– Most common – pipercillin-tazobactam –– synergistic activity (8:1)– 3.375 g q 6h– 2.25 g q 8h (renal insufficiency)– Empiric for UTI and intraabdominal sepsis, empiric tx of neutropenic patients with fever

Cephalosporins• First generation:

– Aerobic GPC• Not MRSA, Staph Epi• i.e. cefazolin (Ancef)

• Second generation:– Increased act against aerobic and anaerobic GNR - enteric

• cefoxitin

• Third generation:– Greater activity against GNR, including P. aeruginosa and H. Flu,

less active against aerobic GPC than 1st generation• Ceftriaxone (Rocephin) – severe CAP• Ceftazidime (Fortez) – antipseudomonal – no serious adverse effects

• Fourth generation:– Broad spectrum

• Cefepime – (Pseudomonas, streptococci, MRSA)

Cephalosporin Dosing Considerations

• Adjust dose in renal failure – extend interval rather than deceasing amount– Preserve concentration-dependent bacterial killing– Ceftriaxone requires no dose adjustment in renal failure

• Toxicity – adverse reactions uncommon and nonspecific (rash, N/D)

• Risk for superinfection with 2/3 generation– MRSA, enterococcus + fungi

• 5-15% cross reaction with PCN – avoid with previous anaphylactic reaction to PCN

Carbepenems

• Imipenem – effective against all but MRSA, C. diff, Enterococcus– Inactivated by enzymes on luminal surface of

proximal renal tubules• Impossible to achieve high levels in urine• Cilastatin – enzyme inhibitor

• Meropenem – broadest spectrum– Slightly superior to imipenem secondary to side

effect profile but clinical experience is limited

Dosing Considerations• Imipenem dosing

– 500 mg q 6h– 1000 mg q 6h – pseudomonas– Renal failure – reduced by 50-75%– Generalized seizures in 1-3%

• Most often in those with seizure disorder, mass, renal failure• Max daily dose 2g or 25 mg/kg

• Meropenem dosing– 1 g q 8h– Dose reduction of 50% in renal failure

• Ertapenem– 1 g q 24– Standard dosing inadequate in obesity

• ? Allergy if PCN allergy

Other Beta Lactams

• Monobactams– Resistant to beta lactamases– Active GNR inc pseudomonas, serratia– No activity against GP or anerobes– Aztreonam

• Resembles aminoglycosides, q8h dosing

• Tolerated by PCN allergic

Vancomycin

• Gram positive cocci – all strains of S. aureus (coagulase +, -, MSSA, MRSA), aerobic and anaerobic streptococci

• Active against C. diff

• Enterococcal resistance 1-15%

Dosing Considerations

• 1 g q 12 h

• Infused slowly – 10mg/min

• Continous infusions can achieve bactericidal drug levels in blood

• Dose reduction in renal insufficiency – increase dose interval

• Trough 5-15, need 20 for CNS, lung

Toxicity

• Red Man Syndrome– Rapid administration – vasodilation, flushing,

hypotension – secondary to histamine release• Ototoxicity

– Reversible hearing loss for high freq at high levels (>40)

– Permanent deafness at 80• Nephrotoxicity

– 5% - no apparent relationship with dose– Higher when used with aminoglycosides– Usually returns to normal after cessation of tx

Protein Synthesis Inhibitors

• Bind to or interfere with ribosomes of bacteria

• Tetracyclines

• Macrolides

• Clindamycin

Tetracyclines• Broad spectrum bacteriostatic

– Inhibit protein synthesis• Gram positive + gram negative + anaerobes• Resistance:

– decreased IC accumulation, ribosone protection, enzymatic inactivations• Short acting (tetra), intermediate acting, Long acting (doxy, mino)• Mycoplasma pneumoniae, chlamydiae, rickettsiae, H pylori• Adverse effects

– Superinfection – pseudomonas, proteus, staphylococci, clostridia, candida– Hepatotoxicity, nephrotoxicity, venous thrombosis, photosensitivity,

vestibular sx, calcium chelation• Doxycycline

– No renal adjustment required– Antiseizure meds, barbituates, etoh – decrease half life

Macrolides• May be used for strep/staph in patients allergic to

PCN, Cephalosporins• PO/IV• Erythromycin, clarithromycin, azithromycin• Few side effects – majority with e-mycin

– Gut motility, hepatotoxicity – acute cholestatic hepatitis

• Inhibit P450 (except azithromycin) – theophylline, warfarin, cyclosporine, methylprednisone, digoxin

Clindamycin

• Inhibits protein synthesis • Anaerobes from penetrating wounds of

abdomen• Dental prophylaxis• Female genital tract• PO/IV• Adverse effects: GI upset, impaired liver

function, neutropenia, C DIFF

Antifolate, DNA Gyrase Inhibitors

• Antifolate– Inhibit growth by reversibly blocking folic acid

synthesis

– Sulfonamides

– Trimethoprim

• DNA Gyrase Inhibitors– Block bacterial DNA synthesis

– Fluorinated allow for better systemic levels

– Fluoroquinolones

Sulfonamides/Trimethoprim

• Sulfamethoxazole/Trimethoprim (TMP-SMX)

• Synergy for wide gram +/gram – coverage• S. pneumo, H. Flu, Enteric UTIs• PO/IV• Side effects: n/v/d, hemolytic or aplastic

anemia, thrombocytopenia, skin rash – can be SJS

Fluoroquinolones

• -1987/1996• Two generations – differ in pharmacokinetics and

spectrum– Early – Ciprofloxaxin – staphylocci (MRSA), most

aerobic gram negative bacilli (pseudomonas)• Less active against streptococci

– Newer – Levofloxacin, gatifloxacin, moxifloxacin• Same spectrum as early except against pseudomonas• Increased coverage streptococci, pneumococci, Myco, Hflu• Lung and UTI• Limited value in ICU secondary to limited action on

pseudomonas and MRSA – used as part of multiple drug tx

Dosing Guidelines• Cipro q 8h secondary to shorter half life• Newer q 24• Dose adjustments required for all except moxifloxacin

(liver metabolism)• Considerations:

– Cipro interferes with theophylline and warfarin• Relatively safe

– QT prolongation– Torsades

• Cipro less effective in ICU secondary to resistance of GN• Newer agents not a choice for VAP except in early onset

Protein Synthesis InhibitorsGram Negative Spectrum

• Aminoglycosides

Aminoglycosides

• Derived from cultures of Streptomyces– First - streptomycin– Eight drugs– Three clinically relevant: gentamicin (66), tobramycin

(75) and amikacin (81)– Most active against gram negative bacilli including

pseudomonas– Bactericidal – concentration dependent + postantibiotic

effect– Usually reserved for immunocompromised or unstable

gram negative sepsis

Dosing Considerations

• Based on body weight and renal function– Compare the ideal vs actual body weight and use the

lower of the two for dosing• Small fraction in adipose tissue when considering body

distribution

– Once daily dosing except in endocarditis• Gentamycin: 4-7 mg/kg/d, P 5-10, T<2 (serratia)• Tobramycin: 3-5 mg/kg/d, P 5-10, T <2 (pseudomonas)• Amikacin: 15 mg/kg/d, P 20-30, T<5

– Cleared by kidneys – dosing is adjusted secondary to creatinine clearance

Nephrotoxicity

• Obligate nephrotoxins– Renal impairment will eventually develop if treatment continues– Oxidative injury in cells lining the proximal tubules– Early signs – cylindrical casts in the urine, proteinuria, inability to

concentrate– Urine changes occur during the first week– Cr rises 5-7 days after initiation of therapy– Renal impairment enhanced by hypovolemia, age, preexisting

renal impairment, hypokalemia, hypomagnesemia, concurrent tx with other “kidney” offenders (loops, cyclosporin, cisplatin, vanc)

– Can progress to ARF but usually reversible

Other adverse effects

• Ototoxicity– Irreversible hearing loss and vestibular damage

• Usually not apparent to patient

• Can block Ach release from presynaptic nerve terminals – usually not apparent with therapeutic dosing– Small risk with MG and NDMA

Metronidazole

• Anaerobes• C. diff, Bacteroides• Side effects: No alcohol – disulfiram reaction, GI upset,

neutropenia, paresthesias, caution in CNS disease• Drug interactions

– Coumadin – increased INR– Antiseizure meds – increase elimination of metronidazole– Do not use in pregnancy

Linezolid -

• Newest abx – 2000 – synthetic• Bacteriostatic except bactericidal to streptococci• Inhibits protein synthesis by prevent ribosome

complex formation• Resistant gram positive organisms• Initially only recommended when vancomycin not

effective or tolerated • May be replacement for vancomycin

– MRSA pneumonia due to penetration into respiratory secretions

Dosing Considerations

• 600 mg BID• IV = PO• Safe in short courses• Longer courses (>1 month)

– Thrombocytopenia– Peripheral and optic neuropathy– Peripheral is irreversible, optic partially

resolves

Antifungals• Amphotericin B

– Naturally occuring – fungicidal for most pathogenic fungi in humans

– Most effective yet most toxic• Triazoles

– Synthetic antifungals– Less toxic– Fluconazole, itraconazole, voriconazole

• Echinocandins– New class for invasive candidiasis– Improved spectrum, less drug interactions, no dose modifications– Capsofungin

Amphotericin B - AmB

• IV use only – vehicle to enhance solubility in plasma

• Once daily dosing – 0.5-1mg/kg• Delivered over 4 hours (may be reduced to

1 if tolerated)• Daily infusions until cumulative dose is

achieved – total dose is determined by type and severity of infection – 500 mg – 4 g

Dosing Considerations• Infusion related inflammatory response

– Fever, chills, nausea, vomiting, rigors – 70%– Cytokine release from activated monocytes– Most severe on initial infusion

• Pretreatment with acetaminophen 10-15mg/kg po and diphenhydramine 25 mg po/iv 30 min before. Give meperidine 25 mg iv for rigors

• If symptoms not relieved with pretreatment – add hydrocortisone 0.1 mg/ml to infusion

– Liposomal Amphotericin B• Lipid preparations – enhance binding to fungal cells over mammalian cells –

phospholipid vesicles• Less infusion related side effects, Less nephrotoxicity• Dose 5x higher• Very Costly (10x per mg + increased dose - $16 vs. $828)• Only approved for tx of documented fungal infections in pt intolerant of

standard AmB or empiric coverage in neutropenic with persistent fever

Adverse Effects• Phlebitis – need central access• Nephrotoxicity

– Binds to cholesterol on the surface of renal epithelial cells and produces an injury in the renal tubules – resembles RTA (distal) with increased urinary excretion of K, Mg

– Azotemia 30-40% with possible progression to ARF requiring dialysis– Stablilizes with continued infusions and improves with discontinuation of

therapy– Cr >3 – stop infusions – Aggravated with hypovolemia, concurrent drugs

• Hypokalemia, Hypomagnesemia – – Oral mg supplementation 300-600 daily– Stop with azotemia

Triazoles

• Candida septicemia in ICU - Fluconazole– Hemodynamically stable, Immunocompentent

• Voriconazole– Aspergillosis

– Emperic treatment of neutropenic with persistent fever

• Itraconazole– Invasive aspergillosis

– Doesn’t play well with others

Dosing• Fluconazole

– PO = IV– 400-800 daily dose, double 1st dose to decrease time to steady state (4-5d)– Adjust for renal impairment, Decrease by 50% for CrCl <50 ml/min– Interactions: inhibit cytochrome P450

• Phenytoin, statins, warfarin– No serious toxicity –

• Elevated liver enzymes in 10%• Voriconazole

– Loading 6 mg/kg q 12 for 24 h, then 4 mg/kg q 12h IV– 200 mg po BID – mx dosing– Long infusion – 1-2 h– Well tolerated with minor GI side effects– Elevated liver enzymes with combo with cyclosporin

Echinocandins

• New class – invasive candidiasis– Improved coverage for all Candida species– Less risk of drug interactions– No dose modifications

• Caspofungin– Comparable to AmB

• IV 70 mg initially, then 50 mg daily• Increased dose needed with some antivirals,

rifampin, dexamethasone, antiseizure meds

Duration of Therapy• Bacteremia

– Removable device 10-14 d• Cellulitis

– After acute inflammation 3 d• Kidney

– Cystitis 3d (single dose cipro ER)

– Pyelo 14 d (7 with cipro)

• Bone– Osteomyelitis 42 d

• GI– Cdiff 10-14 d– H pylori 10-14 d

• Lung– Pneumococcal 5 day (afebrile 3-5)– Enterobacter/pseudomonal 21 – 42 d– Staphylcoccal 21-28 d

What about pregnancy?

• Aminoglycosides• Erythomycin• Metronidazole• Nitrofuratoin• Sulfonamides/Trimethoprim• Tetracycle• Fluoroquinolines• Vancomycin• Azoles

Treatments - Match

• Cellulitis • UTI – uncomplicated• UTI - complicated• CAP – hospitalized• CAP – ICU• VAP• C. diff• Candida

• Metronidazole PO• Ancef, PCN• Ceftriazone + azithro• Bactrim• Diflucan• Carbepenem + Vanc• FQ• Amp + gent/zosyn

Questions?????????

References• www.cartoonstock.com• Gilbert, D.N., Moellering, R.C., Eliopoulos, G.M., and

Sande, M.A. The Sanford Guide to Antimicrobial Therapy 2007.

• Hull, M. Clostridium difficile - associated colitis, 2004• Marino, P.L. The ICU Book. 2007• Katzung, B. Basic and Clinical Pharmacology. 2004• Malvinder, P. Pneumocephalus associated with

Bacteroides fragilis meningitis. Journal of Post-graduate medicine, 2004.

• Talaro, A. and Talaro, K. Foundations in Microbiology.1996