Abstract
Clindamycin has long been an option for treating both methicillin sensitive Staphylococcus aureus (MSSA) and methicillin resistant S. aureus (MRSA) infections. So, it is utmost important to perform the susceptibility test for erythromycin and clindamycin. And, there is concern on use of this antibiotic in the presence of erythromycin resistance because of the possibility of induction of cross-resistance among members of macrolide, lincosamide and streptogramin B (MLSB) group. During August 2011 to May 2012, a total of 207 isolates of S. aureus were isolated and among which 29.47% (61) isolates were confirmed as MRSA by cefoxitin (30 µg) disc. All the isolates were further processed for MLSB resistance test by double disc diffusion test of erythromycin (2 µg) and clindamycin (15 µg) at a distance of 15 and 22 mm between them. This study result show 12.56% (26) and 14.49% (30) of inducible macrolide-lincosamide-streptogramin B phenotype (iMLSB) resistance type at 22 and 15 mm disc distance, respectively, showing 15 mm disc distance is potential than 22 mm and 17.39% (36) of cMLSB resistance type. Similarly, both iMLSB and cMLSB are greater in MRSA than MSSA and constitutes 18.05 (11) and 36.06% (22), respectively. Thus, this study concludes that D-test should be used as a mandatory method and is more potential in 15 mm disc apart. Key words: Staphylococcus aureus, methicillin resistant S. aureus (MRSA), methicillin sensitive S. aureus (MSSA), inducible macrolide-lincosamide-streptogramin B phenotype (iMLSB), cMLSB, D-test.
Highlights
Staphylococcus aureus acquisting mecA gene which encodes PBR-2a with low affinity for -lactams, is methicillin resistant S. aureus (MRSA) (Brumfitt and Hamilton, 1989), which is the major cause of nosocomial and community acquired infection (Frank et al, 1999).Changing pattern in antimicrobial resistance and increasing incidence of MRSA infection have led to treating such infection with MLS antibiotics (Jadhav et al, 2011)
Clindamycin has long been an option for treating both methicillin sensitive Staphylococcus aureus (MSSA) and methicillin resistant S. aureus (MRSA) infections
All MRSA were highly resistant to penicillin (100%), ampicillin (98.36%), ceftazidime (88.53%) and erythromycin (88.53%) while all MRSA were sensitive to vancomycin showing all MRSA isolates were MDR MRSA
Summary
Staphylococcus aureus acquisting mecA gene which encodes PBR-2a with low affinity for -lactams, is methicillin resistant S. aureus (MRSA) (Brumfitt and Hamilton, 1989), which is the major cause of nosocomial and community acquired infection (Frank et al, 1999). Demonstration of iMLSB phenotype in isolates that are susceptible to clindamycin and resistant to erythromycin is possible by using double disk diffusion agar inhibitory assay or D-test (Jadhav et al, 2011; Gadepalli et al, 2006; Steward et al, 2005; Reddy and Reddy, 2012). Antimicrobial susceptibility testing were done by Kirby Bauer's disc diffusion method on Muller-Hinton agar plates using Penicillin (10 U), Ampicillin (10 μg), Cloxacillin (5 μg), Erythromycin (15 μg), Clindamycin (2 μg), Cotrimoxazole (1.25/23.75 μg), Ciprofloxacin (5 μg), Ofloxacin (5 μg), Cefotaxime (30 μg), Chloramphenicol (30 μg) as first line antibiotics and Amikacin (30 μg), Gentamicin (10 μg), Ceftazidime (30 μg), Amoxycillin/Clavulanic acid (20/10 μg) and Vancomycin (30 μg) as second line anitibiotics. S. aureus ATCC 29213 (D-test negative) and S. aureus ATCC 25923 (D-test positive) were used as quality control
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