Abstract
Macrolide-lincosamide-streptogramin B antibiotics are considered as alternative drugs to treat infections caused by Staphylococcus aureus. However, the management of the staphylococcal infections may be complicated due to the possibility of clindamycin inducible resistance isolates. This study aimed at assessing the prevalence of inducible clindamycin resistance, and the susceptibility patterns of strains to various antibiotics. Also, it was tried to identify resistance genes and analyze their frequency among clinical S. aureus isolates. The study was conducted over the period of two years. A total of 490 S. aureus strains isolated from various clinical specimens from both inpatients and outpatients were included in the study. Inducible clindamycin resistance was detected by erythromycin-clindamycin disc approximation test (D-test) and broth microdilution method. In vitro antibiotic susceptibility testing of isolates was assessed using the Kirby-Bauer disk diffusion and broth microdilution methods. Antimicrobial resistance genes were analyzed by polymerase chain reaction assay. Of the 490 S. aureus clinical isolates, 16.9% (n = 83) were confirmed as inducible resistance comprising 62 (74.7%) inpatient and 21 (25.3%) outpatient isolates. Out of the 83 isolates, 23 (27.7%) were mupirocin resistant out of which 10 (12%) and 13 (15.7%) were classified as high- and low-level mupirocin-resistant, respectively. Resistance to fusidic acid was observed in 3.6% (n = 3) of the isolates. Of all S. aureus isolates with inducible resistance, five (6%) were confirmed as VISA. The most frequent resistance gene was erm (A) (81.9%), followed by erm (C) (57.8%), ant (4′)-Ia (55.4%), aac(6′)-Ie/aph(2″) (45.8%), tet(M) (41%), aph(3′)-IIIa(34.9%), erm(B) (12%), mupA(12%), and fusB (3.6%). Given to detection rate of inducible phenotype and also in order to avoid therapeutic failures, it seems that susceptibility testing of inducible resistance staphylococci should be routinely performed. The current study also demonstrated that detection of resistance genes and their coincidence is required to combat the multidrug resistant S. aureus strains.
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