Inducible Clindamycin Resistance in Staphylococcus aureus Isolated from Clinical Samples

Abstract

Introduction:The resistance to antimicrobial agents among Staphylococci is an increasing problem. This has led to renewed interest in the usage of Macrolide-Lincosamide-Streptogramin B (MLSB) antibiotics to treat Staphylococcus aureus (S. aureus) infections. The resistance to macrolide can be mediated by msr A gene coding for efflux mechanism or via erm gene encoding for enzymes that confer inducible or constitutive resistance to MLSBantibiotics. In vitro routine tests for clindamycin susceptibility may fail to detect inducible clindamycin resistance due to erm genes resulting in treatment failure, thus necessitating the need to detect such resistance by a simple D test on a routine basis.Materials and Methods:One hundred and ninety S. aureus isolates were subjected to routine antibiotic susceptibility testing including oxacillin (1 µg) and cefoxitin (30 µg) by modified Kirby Bauer disc diffusion method. Inducible resistance to clindamycin in S. aureus was tested by ‘D test’ as per CLSI guidelines.Results:Twenty (10%) isolates showed inducible clindamycin resistance, 18 (9%) showed constitutive resistance while remaining 16 (8%) showed MS phenotype. Inducible resistance and constitutive resistance were found to be higher in MRSA as compared to MSSA (20%, 16% and 6%, 6%, respectively).Conclusion:Clindamycin is kept as a reserve drug and is usually advocated in severe MRSA infections depending upon the antimicrobial susceptibility results. This study showed that D test should be used as a mandatory method in routine disc diffusion testing to detect inducible clindamycin resistance in Staphylococci for the optimum treatment of patients.

A report on infection dynamics of inducible clindamycin resistance of Staphylococcus aureus isolated from a teaching hospital in India

“…In another laboratory from Karnataka, 10% isolates had inducible clindamycin resistance, 9% had constitutive resistance and 8% had MS phenotype. Inducible resistance and constitutive resistance were found to be higher in MRSA as compared to MSSA (20%, 16% and 6%, 6%, respectively) [18] . The prevalence of MLSB strains both in CA and HA S. aureus isolates, as well as the prevalence of CA-MRSA strains were identified as clinical predictors of both CA-MRSA and MLSB, in Albama, USA [3] .…”

“…6 (4) 33 (14) 9 (3) Wound swabs 32 (18) 4 (2) 24 (7) 5 (3) Skin swabs 21 (13) 4 (2) 17 (8) 4 (2) Nasal swabs 16 (7) 3 (2) 12 (4) 4 (2) Urine 9 (4) 3 (2) 5 (3) 3 (-) Body fluids…”

“…Erythromycin and clindamycin discs (HiMedia, Mumbai) were placed (17依2) mm apart (edge to edge) on a Muller-Hinton agar plate, incubated at 37 °C for 18 h and D-test positivity was identified by the flattening of clindamycin zone between erythromycin and clindamycin discs. Any isolate with "Er-r, Cd-r" was considered as constitutive MLSB resistant strain [14] .…”

Evaluation of constitutive and inducible resistance to clindamycin in clinical samples of Staphylococcus aureus from a tertiary hospital

“…In addition, other authors have found a higher frequency of constitutive resistance in MRSA isolates. Prabhu et al 17 Among the clinical samples of S. aureus, the iMLS B phenotype was identifi ed more frequently in general secretions, peripheral blood, urine andbody fl uids.…”

Staphylococcus Aureus Infections and Their Antibiotic Susceptibility Profile at a Tertiary Care Hospital

“…Trimethoprim-sulfamethoxazole can be used for the treatment of S. aureus infections such as uncomplicated SSTI [15][16][17]. Majority of our S. aureus isolates (77.1%) were sensitive to clindamycin, an important alternative to a beta-lactam antibiotic for S. aureus SSTIs [18,19]. Inducible clindamycin resistance (iMLS B ) was seen in 22.4% of our S. aureus isolates.…”