Antimicrobial agents/therapy resistance mechanisms

The ability to detect ESBLs has clinical relevance because it will have an impact on antibiotic therapy. Producers of ESBLs are suspected when susceptibility testing indicates resistance to ceftazidime (but may be paradoxically susceptible to ceftriaxone and cefotaxime by the minimal inhibitory concentration [MIC] or disc diffusion) and susceptible to the cephamycins (11). More recently, a breakpoint of 2 ig/mL to cefpodoxime has been suggested as a standard. Another method of detection is the use of the E-test strip with a gradient of ceftazidime on one side and ceftazidime in combination with clavu-lanate on the other. The ESBLs are thought to be present when enhancement of inhibition is demonstrated. Table 2 highlights some of the more common resistance mechanisms for antimicrobial agents used commonly in the treatment of nosocomial pneumonia. 

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