Phenotypical examination of the macrolide-lincosamide-streptogramin B resistance in Staphylococcus isolates

Abstract

The aim of the present study was to evaluate the phenotypic characteristics of the macrolidelincosamide-streptogramin B (MLS B) resistance in Staphylococcus aureus and coagulase-negative staphylococci (CNS) strains isolated from various clinical samples in our hospital. The study was conducted on 516 Staphylococcus isolates isolated from various clinical samples in Microbiology Laboratory of Diyarbakir State Hospital between January, 2009 and December, 2009. After the identification of microorganisms via conventional methods and the evaluation of their methicillin resistance profile, disk approximation test was performed using erythromycin (15 µg) and clindamycin (2 µg) disks in order to determine MLS B resistance phenotypes. Of 516 Staphylococcus isolates, 208 were determined to be S. aureus and 308 were CNS. The MLS B resistance of isolates was 56.2%, whereas the resistance due to the efflux pump was determined to be 3.5%. The MLS B resistance phenotype was determined in 38% of S. aureus strains and 68.5% of CNS strains. The presence of MLS B resistance was determined to be higher in methicillin-resistant group (74.7%) compared to the methicillin-susceptible group (23.9%). While constitutive MLS B resistance (cMLS B) and inducible MLS B resistance (iMLS B) were determined in 48.9 and 19.1% of methicillin-resistant S. aureus strains, respectively, these rates were 2.6 and 10.5% for methicillin-susceptible strains, respectively. The rate of constitutive resistance was determined to be 41.5% in methicillin resistant CNS, whereas the rate of inducible resistance was determined to be 35.9%. In methicillin-susceptible CNS group, cMLS B and iMLS B resistances were determined to be 17.6 and 23%, respectively. The cMLS B phenotype was more common among methicillin-resistant S. aureus and CNS group, whereas iMLS B phenotype was more common among methicillin-susceptible S. aureus strains. In conclusion, we suggest that the determination and reporting of the presence of inducible resistance is of great importance regarding the success of therapy; therefore, it would be beneficial to use D test in routine antibiogram studies.