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138 STERILIZATION 0ISINFErTION Kills All Microorganisms Inactivation or Inhibition of (Including Spores and Microorllanisms (May Not Viruses) A ect Spores) Examples:...

138 STERILIZATION 0ISINFErTION Kills All Microorganisms Inactivation or Inhibition of (Including Spores and Microorllanisms (May Not Viruses) A ect Spores) Examples: [xample: Autoclave (121 'C at 1Spsi Bleach (1:10 Hypochlorite) Autoclave Pressure, for 15 min.) Temperature and Time Incineration Filtration (Physically Removes Microorganisms) Antibiotics and Their Actions ANTIBIOTIC EXAMPLES ACTION NOTES B-lactams Penicillins Inhibits cell wall synthesis Ceftriaxone, Cefotax ime Cephalosporins Carbapenams (lmipenam) Monobactams (Azotreonam) B-lactamase Inhibiting Combin- ations (Augmentin, etc.) Glycopeptides Vancomycin Inhibits cell wall synthesis Drug of choice for Clostridium d ifficile and MRSA Aminoglycosides Gentamicin Inhibits protein synthesis Acts on 30S subunit; not active Tobramycin against anaerobes; used with a Amikacin penicillin for Enterococcus Tetracyclines Tetracycline Inhibits protein synthesis Acts on 30S subunit; affects Doxycycline bone an d teeth in children ; may lead to super infection of yeast Chloramphenicol Chloramphenicol Inhibits protein synthesis Acts on 50S subunit; can cause aplastic anemia MacroIides Erythromycin Inhibits protein synthesis Acts o n 50S subunit; Clindamycin clindamycin for GP and G N anaerobes Quinolines Ciprofloxacin Inhibits nucleic acid Fo r Pseudomonas aeruginosa Norfloxacin synthesis and other aerobes Sulfa Drugs (Sulfonomides) Sulfamethoxazole Analogue of PABA For UTI. enteric infections; used (intermediate in folic acid with trimethoprim (Bactrim, etc.) synthesis) Streptogramins Quinupristin/dalfopristin Inhibits protein sythesis For GP, especially vancomycin resistant Enterococcus faecium Oxazdidinones Linezolid Inhibits protein sythesis For GP, including those resistant to other antibiotics Antibiotics/Susceptibi/i'ty Testing 4. Bactericidal action - kills bacteria without host immune help ANTIMICROBIAL THERAPY 1. Narrow spectrum - only certain 5. Bacteriostatic action - rever sible groups covered inhibition ( ultimate destruction d epends on h ost defen ses) 2. Broad spectrum - Gram pos (GP) and Gram n eg ( GN) coverage 6. Drug combination a. Synergism - combined b etter than 3. Selective toxicity - action against the sum: 1 + 2 = 4 microbe only without injuring cells of b. Antagonism - one d ecreases activity host of other: 1 + 2 = l  139 SUSCEPTIBILITY TESTING c. Inducible strains form a ""D" - 1. Kirby-Bauer Method shaped zone of inhibition a. Disk diffusion b. Mueller-Hinton agar (MH) 7. Detection of MRSA c. Depth = 4mm a. Zone of ::;10 mm with an oxacillin d. pH = 7.2-7.4 (1 µg) disk on Mueller -Hinton e. Physiologic concentration of Ca++ b. Molecular tests for mecA gene and Mg++ f. 35°C, ambient air 8. Vancomycin-Resistant Enter ococci g. 108 organisms (McFarland 0.5) (VRE) h. QC weekly and with each n ew lot of 9. Carbapenem r esistant agar or discs (E. coli, S. aureus, enterobacteriaceae (CRE) P. aeruginosa) a. Enzymes resistant to Ca rhapenem antibiotics 2. Broth methods a. MIC (minimum inhibitory concentration) b. Klebsiella spp. especially K. pneumonia (KPC). E. coli, ❖ Lowest concentration of drug that Enter obac ter prevents in vitro growth ❖ First dilution tube with no visible c. Resistant to penicillin, cephalosporins, growth carbapenem and aztreonam b. MBC ( minimum b acteriostatic d. Modified Hodge test and chromogenic media concentration) ❖ Lowest cor1centration that results 10. Automated AST in >99.9% killing a. BD Phoenix ❖ Subculture l'Ubes near MIC to find b. Microscan Walkaway first plate with no growth c. TREK sensititre 3. E-test d. Vitek l and 2 a. MIC on a stick Sources of Error: Disk Diffusion b. Plastic strips impregnated with ABNORMAi RE'" 'LT PROBARI F rAI 1,~ antimicrobials Tetracycl ine Zone Too Large pH of agar too low and Clinda17.cin Too 4. Modified methods for testing slow- Small with. coli or growing or fastidious bacteria S. aureus Controls a. Haemophilus test medium Tetracycline Zone Too Small pH of agar too high Jnd ClindJmycin Too b. Supplemented MH for S. Large with E. coli or S. aureus Controls pneumoniae c. Supplemented GC agar base for N. Amino~lycoside Zone Too Ca++ and/or Mg++ Sma with P. aeruginosa too high in agar gonorrhoeae Control Aminoglycoside Zone Too Ca++ and/or Mg++ 5. Extended spectrum heta-lactamase large with P. aeruginosa too low in agar Control (ESBL) Zones Universal!)' Too La rgc lnoculum too light a. Enzymes for resistance to extended- on Control Plates Nutritionally poor medium spectrum (third-generation) of Slow.growing organism (not seen with controls) cephalosporins and monobactams Agar depth too thin but do not affect cephamycins Zones Universally Too Small lnoculum too heavy b. Enzyme activity may vary on Control Plates Agar depth too thick c. If an ESBL is detected, all Methicillin Zone Dccreasin~ Methicillin degrading during over Days or Weeks wit refrigerator storage penicillins, cephalosporins, and Control Or~anisms aztreonam should be r eported as Methicillin Zone Methicillin being degraded resistant Indeterminate in Disk Test by strong &--lactamase producing Staphylococci d. E specially consider E scherichia and Colonies within Zone of Mixed culture Klehsi ella as potential ESBL- Inhibition Resistant mutants within producing organisms zone "Zone within a Zone" A swarming Proteus Phenomenon Feather edges of zones 6. D-test around ~enicillin or a. Used for detection of inducible ampicil in disks usually occur with B lactmase clindamycin r esistance. neg. strains of 5. aureus b. Clindamycin 2µg disks and B lactamase pos. H. influenzae with erythromycin 15 µg disks used penicillin or ampicillin