Emerging Resistance to Antimicrobial Agents in Gram-Positive Bacteria

Summary

The prevalence of penicillin-resistant pneumococci is increasing worldwide. Methods for susceptibility testing, as well as in vitro susceptibility of penicillin-susceptible and -resistant strains to new and existing agents (including oral and parenteral streptogramins), are described.

For all specimens except CSF, oxacillin screening followed by determination of penicillin minimum inhibitory concentrations (MICs) is satisfactory. For CSF, simultaneous testing of penicillin and cefotaxime or ceftriaxone by E-test is necessary. Of all available oral β-lactams, amoxicillin yields the lowest MICs against penicillin-susceptible and -resistant pneumococci, and is the drug of choice for the treatment of otitis media. Cefotaxime and ceftriaxone yield MICs that are low enough to permit therapy of meningitic and nonmeningitic infections (the former in combination with vancomycin). The higher the strain’s benzylpenicillin (penicillin G) MIC, the more likely it is that simultaneous resistance to nonrelated compounds such as tetracyclines, macrolides, and cotrimoxazole (trimethoprim/sulfamethoxazole) will occur. None of the available quinolones should be used for therapy of pneumococcal infections. Of new and experimental drugs, some of the new quinolones, trovafloxacin, and oral and parenteral streptogramins are promising agents. Imipenem is epileptogenic, but meropenem has potential in the therapy of meningitis. Problematical infections caused by penicillin-resistant pneumococci include meningitis and otitis media. The optimal therapy of the latter two diseases has not yet been clearly delineated.