Analysis of Resistance to Macrolide–Lincosamide–Streptogramin B Among mecA-Positive Staphylococcus Aureus Isolates

OBJECTIVES: Genetic determinants conferring resistance to macrolide, lincosamide, and streptogramin B (MLSB) via ribosomal modification such as, erm, msrA/B and ereA/B genes are distributed in bacteria. The main goals of this work were to evaluate the dissemination of MLSB resistance phenotypes and genotypes in methicillin-resistant Staphylococcus aureus (MRSA) isolates collected from clinical samples. METHODS: A total of 106 MRSA isolates were studied. Isolates were recovered from 3 hospitals in Tehran between May 2016 to July 2017. The prevalence of MLSB-resistant strains were determined by D-test, and then M-PCR was performed to identify genes encoding resistance to macrolides, lincosamides, and streptogramins in the tested isolates. RESULTS: The frequency of constitutive resistance MLSB, inducible resistance MLSB and MSB resistance were 56.2%, 22.9%, and 16.6%, respectively. Of 11 isolates with the inducible resistance MLSB phenotype, ermC, ermB, ermA and ereA were positive in 81.8%, 63.6%, 54.5% and 18.2% of these isolates, respectively. In isolates with the constitutive resistance MLSB phenotype, the prevalence of ermA, ermB, ermC, msrA, msrB, ereA and ereB were 25.9%, 18.5%, 44.4%, 0.0%, 0.0%, 11.1% and 0.0%, respectively. CONCLUSION: Clindamycin is commonly administered in severe MRSA infections depending upon the antimicrobial susceptibility findings. This study showed that the D-test should be used as an obligatory method in routine disk diffusion assay to detect inducible clindamycin resistance in MRSA so that effective antibiotic treatment can be provided.

Comparing cerumen bacterial flora in acute otitis externa patients and healthy controls

Cerumen is known as ear wax, produced regularly by cerumen and lipid secretary glands. Regarding the effect of Mazandaran province's humid weather on the prevalence of pathogenic microorganisms, this study was performed to determine the bacterial flora of the ear in patients with acute otitis externa and its comparison with healthy subjects. In this case-control study, cerumen was collected and cultured from 40 patients with clinically diagnosed acute otitis externa and 80 healthy controls. The data were finally analyzed using SPSS. In the study group, Staphylococcus aureus [20.8%], Bacillus [18.9%] and Pseudomonas [11.3%] and in the control group Staphylococcus epidermidis [38.7%] and Diphtheroid [22.4%] were the most common bacteria, respectively. The isolated bacteria from cerumen of healthy subjects were totally different from those of acute otitis externa patients