| Popis: |
This chapter talks about aerobic actinomycetes that are now known to be an evolutionarily heterogeneous assemblage of genera. At some stage they all form gram-positive rods, and most of the more commonly isolated species exhibit at least rudimentary branching under certain growth conditions; all grow better under aerobic than anaerobic conditions, a feature distinguishing them from most organisms in the genus Actinomyces. In temperate climates, the respiratory tract is the most frequent portal of entry for the aerobic actinomycetes and therefore the primary site of nocardial infections in the immunocompromised host. PCR paired with restriction endonuclease analysis (REA) has been used for the identification of commonly isolated Nocardia species. With REA of a portion of the HSP gene, Steingrube et al. were able to differentiate among 12 taxonomic groups of Nocardia, in addition to species of Actinomadura, Gordonia, Rhodococcus, Streptomyces, and Tsukamurella. The recommended procedure for Nocardia and the other aerobic actinomycetes is broth microdilution; and panels containing the appropriate dilutions of antimicrobials specifically active against these genera are commercially available. Most isolates of Nocardia species are susceptible to trimethoprim-sulfamethoxazole; one should be careful not to assume too readily that an isolate is resistant to this combination of drugs. The chapter finally points out that sulfonamides or trimethoprim-sulfamethoxazole may not be adequate in certain circumstances, such as patients with central nervous system (CNS) nocardiosis, disseminated disease, or concurrent HIV infection. |
