Abstract
Clindamycin is one of the important alternative antibiotics in the therapy of Staphylococcus aureus infections. Clinical failure of clindamycin therapy has been reported due to multiple mechanisms that confer resistance to macrolides, lincosamides and Streptogramin B (MLSB) antibiotics. In vitro routine tests for clindamycin susceptibility may fail to detect inducible clindamycin resistance due to erm genes, resulting in the treatment failure. Although data from the developed countries have shown to be enormity of the problem, data from the developing countries are lacking. The aim of the study was to distinguish different resistance phenotypes in erythromycin-resistant S. aureus by a simple double-disc diffusion test (D test). A total of 153 S. aureus isolates were subjected to routine antibiotic susceptibility testing, including cefoxitin disc (30 μg) and by oxacillin screen agar. Inducible clindamycin resistance was tested by ‘D test’ as per CLSI guidelines. Odds ratios (OR) and 95 % confidence intervals (95 % CI) were calculated. P values were calculated using SPSS (version 18). Among 153 S. aureus isolates, 42 (27.45 %) were resistant to methicillin, whereas 111 (72.54 %) were methicillin susceptible. Out of the 63 (41.17 %) erythromycin-resistant S. aureus isolates, 14 (9.15 %) showed inducible resistance [P = 0.0002, odds ratio (OR) 18.30; 95 % confidence interval (CI) 8.72–25.77), 20 (13.07 %)] showed constitutive resistance (P = 0.002, OR 14.38, 95 % CI 5.33–21.49), while the remaining 29 (18.95 %) showed inducible phenotype. Inducible and constitutive resistance was found to be higher in MSSA when compared with MRSA. Clinical laboratories should perform D test routinely to guide the clinicians about the inducible clindamycin resistance and to prevent misuse of antibiotics.
Highlights
Inducible and constitutive resistance was found to be higher in methicillin-susceptible S. aureus (MSSA) when compared with methicillin-resistant S. aureus (MRSA)
The increasing prevalence of methicillin resistance among Staphylococci is an increasing problem (Yilmaz et al 2007). This has led to the renewed interest in the usage of macrolide–lincosamide–streptogramin B (MLSB) antibiotics to treat S. aureus infections with clindamycin being the preferred agent due to its excellent pharmacokinetic properties (Deotale et al 2010)
Resistance to MLSB can occur by two different mechanisms: an active efflux mechanism encoded by the msrA gene and ribosomal target modification encoded by the erm gene (MLSB resistance) (Leclercq 2002)
Summary
Inducible and constitutive resistance was found to be higher in MSSA when compared with MRSA. The increasing prevalence of methicillin resistance among Staphylococci is an increasing problem (Yilmaz et al 2007). This has led to the renewed interest in the usage of macrolide–lincosamide–streptogramin B (MLSB) antibiotics to treat S. aureus infections with clindamycin being the preferred agent due to its excellent pharmacokinetic properties (Deotale et al 2010). Erm genes encode enzymes that confer inducible or constitutive resistance to MLS agents via methylation of the 23S ribosomal RNA, thereby reducing binding by MLS agents to the ribosome (Fiebelkorn et al 2003). The present study was undertaken to determine the incidence of MLSB resistance in the clinical isolates of S. aureus and to study the antibiotic sensitivity pattern of S. aureus isolates having the iMLSB phenotype
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