Dr f.Rashedmarandi

2. Antibiogram panel Designing Dr f.Rashedmarandi

4. Penicillins These penicillins are penicillinase-labile;hydrolyzed by staphylococcal penicillinase

5. Penicillinase-stable penicillin

6. ß- lactam /ß- lactamase inhibitor combinations

7. Cephems III and IV are also referred to as “extended-spectrum cephalosporins.” This does not imply activity against ESBL-producing gram-negative bacteria.

8. Selecting Antimicrobial Agents for Testing and Reporting,criteria • Considerations in the assignment of agents to specific test/report groups include clinical efficacy, prevalence of resistance, minimizing emergence of resistance, cost, FDA clinical indications for usage, in addition to the specific issues described.

9. Reporting Results 1.Susceptible (S) The “susceptible” category implies that isolates are inhibited by the usually achievable concentrations of antimicrobial agent when the recommended dosage is used for the site of infection. 2.Intermediate (I) The “intermediate” category includes isolates with antimicrobial agent MICs that approach usually attainable blood and tissue levels and for which response rates may be lower than for susceptible isolates. The intermediate category implies clinical efficacy in body sites where the drugs are physiologically concentrated (e.g., quinolones and β-lactams in urine) or when a higher than normal dosage of a drug can be used (e.g., β-lactams). This category also includes a buffer zone, which should prevent small, uncontrolled, technical factors from causing major discrepancies in interpretations, especially for drugs with narrow pharmacotoxicity margins. 3.Resistant (R) The “resistant” category implies that isolates are not inhibited by the usually achievable concentrations of the agent with normal dosage schedules, and/or that demonstrate zone diameters that fall in the range where specific microbial resistance mechanisms (e.g., beta- lactamases) are likely, and clinical efficacy of the agent against the isolate has not been reliably shown in treatment studies.

10. Antibacterial Effect&Mechanism of action

11. Antibacterial Effect&Mechanism of action

12. Antibacterial Effect&Mechanism of action

13. “Warning”:

14. Notice!

15. Suggested panelfor routine testing & reporting

16. Salmonella and Shigella When fecal isolates of Salmonella and Shigella spp. are tested, only ampicillin, a quinolone, and trimethoprim-sulfamethoxazole should be reported routinely. In addition, chloramphenicol and a third- generation cephalosporin should be tested and reported for extraintestinal isolates of Salmonella spp.

17. Suggested panelfor routine testing & reporting

18. Suggested panelfor routine testing & reporting

19. staphylococcus Penicillin-susceptible staphylococci are also susceptible to other penicillins, cephems, and carbapenems approved for use by the FDA for staphylococcal infections. Penicillin-resistant, oxacillin- susceptible strains are resistant to penicillinase-labile penicillins, but susceptible to other penicillinase-stable penicillins, β-lactam/β-lactamase inhibitor combinations, relevant cephems, and carbapenems. Oxacillin-resistant staphylococci are resistant to all currently available β-lactam antibiotics. Thus, susceptibility or resistance to a wide array of β-lactam antibiotics may be deduced from testing only penicillin and oxacillin. Routine testing of other penicillins, β-lactamase inhibitor combinations, cephems, and carbapenems is not advised.

20. cefoxitin disk test The cefoxitin disk test is the preferred method for testing S. aureus, S. lugdunensis, and coagulase-negative staphylococci for resistance to the penicillinase-stable penicillins. Cefoxitin is used as a surrogate for detecting oxacillin resistance; report oxacillin as susceptible or resistant based on the cefoxitin result.

21. Suggested panelfor routine testing & reporting

22. . Warning: For Enterococcusspp., cephalosporins,aminoglycosides (except for high-level resistance screening), clindamycin, and trimethoprim-sulfamethoxazolemay appear active in vitro, but are not effective clinically, and isolates should not be reported as susceptible.

23. Enterococcus ß lactamase - enterococcus :susceptible to penicillin,ampicillin,amoxicillin,ampicillin sulbactam,amoxicillin-clavulanic acid,piperacillin,piperacillin tazobactam Prediction with: penicillin disk test ß lactamase + enterococcus : Resistant to penicillin,ampicillin,amoxicillin,ampicillin sulbactam,amoxicillin-clavulanic acid,piperacillin,piperacillin tazobactam a β-lactamase test is the only reliable test for detecting β-lactamase-producing Enterococcus spp.

24. Enterococcus For blood and cerebrospinal fluid isolates(Enterococci), a β-lactamase test is also recommended. Notice: combined therapy with high- dose penicillin or high-dose ampicillin or vancomycin or teicoplanin plusgentamicin or streptomycin for bactericidal action is usually indicated for serious enterococcal infections, such as endocarditis.

25. Alternative drugs for VRE Because of limited alternatives, chloramphenicol, erythromycin, tetracycline (or doxycycline or minocycline), and rifampin may be tested for vancomycin-resistant enterococci (VRE), And consultation with an infectious disease practitioner is recommended.

26. Suggested panelfor routine testing & reporting

27. Suggested panelfor routine testing & reporting

28. Suggested panelfor routine testing & reporting

29. Suggested panelfor routine testing & reporting

30. Pneumococcus from CSF =MIC penicillin and cefotaxime or ceftriaxone or meropenem Vancomycin (MIC or Disk)

31. Pneumococcus from other sites: Oxacillin Disk Screening Test zone ≤ 19 mm =» MIC of penicillin,cefotaxime,ceftriaxone

32. . Susceptibility testing of penicillins and other β-lactams approved by FDA for treatment of Streptococcus pyogenes or Streptococcus agalactiae is not necessary for clinical purposes and need not be done routinely, since as with vancomycin, resistant strains have not been recognized. Interpretive criteria are provided for pharmaceutical development, epidemiology, or monitoring for emerging resistance. Any strain found to be nonsusceptible should be referred to a reference laboratory for confirmation.

33. Suggested panelfor routine testing & reporting

34. Group B streptococci Recommendations for intrapartum prophylaxis for Group B streptococci are penicillin or ampicillin. While cefazolin is recommended for penicillin-allergic women at low risk for anaphylaxis, those at high risk for anaphylaxis may receive clindamycin or erythromycin. Group B streptococci are susceptible to ampicillin, penicillin, and cefazolin, but may be resistant to clindamycin and/or erythromycin. When a Group B streptococcus is isolated from a pregnant woman with severe penicillin allergy (high risk for anaphylaxis), clindamycin and erythromycin should be tested and reported.

35. ESBLs Strains of Klebsiella spp. E. coli, and P. mirabilis that produce ESBLs may be clinically resistant to therapy with penicillins, cephalosporins, or aztreonam, despite apparent in vitro susceptibility to some of these agents.

36. Some of these strains will show zones of inhibition below the normal susceptible population, but above the standard breakpoints for certain extended-spectrum cephalosporins or aztreonam; such strains may be screened for potential ESBL production by using the screening breakpoints .Other strains may test intermediate or resistant by standard breakpoints to one or more of these agents.

37. In all strains with ESBLs, the zone diameters for one or more of the extended-spectrum cephalosporins should increase in the presence of clavulanic acid.

39. Results of initial screen test Result of phenotypic confirmatory Test

40. Screening of Proteus mirabilis for ESBL • Screening of Proteus mirabilis for ESBL production is recommended only when it is deemed clinically relevant (e.g., a bacteremic isolate).

41. For all confirmed ESBL-producing strains, the test interpretation should be reported as resistant for all penicillins, cephalosporins, and aztreonam.

42. staphylococcus Penicillin-susceptible staphylococci are also susceptible to other penicillins, cephems, and carbapenems approved for use by the FDA for staphylococcal infections. (slide4)

43. MRSA • Penicillin-resistant, oxacillin- susceptible strains are resistant to penicillinase-labile penicillins, but susceptible to other penicillinase-stable penicillins, β-lactam/β-lactamase inhibitor combinations, relevant cephems, and carbapenems. slides 5,6

44. MRSA • Oxacillin-resistant staphylococci are resistant to all currently available β-lactam antibiotics.

45. Thus, susceptibility or resistance to a wide array of β-lactam antibiotics may be deduced from testing only penicillin and oxacillin. Routine testing of other penicillins, β-lactamase inhibitor combinations, cephems, and carbapenems is not advised.

46. Historically, resistance to the penicillinase-stable penicillins has been referred to as “methicillin resistance,” thus the acronyms MRSA (for “methicillin-resistant S. aureus”) or MRS (for “methicillin-resistant staphylococci”) are still commonly used, even though methicillin is no longer the agent of choice for testing or treatment.

47. Of the penicillinase-stable penicillins, oxacillin is preferred for in vitro testing. Oxacillin susceptibility test results can be applied to the other penicillinase-stable penicillins, i.e., cloxacillin,dicloxacillin,flucloxacillin,methicillin, and nafcillin.

48. Most resistance to oxacillin in staphylococci is mediated by the mecA gene, which directs the production of a supplemental penicillin-binding protein, PBP 2a, and is expressed either homogeneously or heterogeneously. Homogeneous resistance is easily detected with standard testing methods, whereas heterogeneous expression may be more difficult to detect with some methods because only a fraction of the population (e.g., 1 in 100 000 cells) expresses the resistance phenotype

49. Detection of oxacillin resistance • Detection of oxacillin resistance: Tests for mecA or for the protein expressed by mecA, the penicillin-binding protein 2a (PBP 2a, also called PBP2') are the most accurate methods for prediction of resistance to oxacillin and can be used to confirm disk test results for isolates of staphylococci from serious infections. Isolates of staphylococci that carry the mecA gene, or that produce PBP 2a (the mecA gene product), should be reported as oxacillin resistant. Isolates that do not carry mecA or do not produce PBP 2a should be reported as oxacillin susceptible. Because of the rare occurrence of resistance mechanisms other than mecA, if MIC tests are performed in addition to disk diffusion, isolates for which oxacillin MICs are ≥4 µg/mL and are mecA negative or PBP 2a negative should be reported as oxacillin resistant.

50. Report isolates of staphylococci that carry mecA, or that produce PBP 2a, the mecA gen product, as oxacillin resistant.