Inducible Clindamycin Resistance in Staphylococcus aureus Isolates in Kermanshah, Iran

 Staphylococcus aureus is the most common agent of nosocomial infections. Macrolide Lincosamide-Streptogramin B (MLSB) antibiotics are the therapeutic choices for treatment of infections due to methicillin resistant S. aureus (MRSA) isolates. The most frequent mechanism for inducible resistance in S. aureus is modification in target site by erm (erythromycin ribosome methylase) genes.

 The aim of this research was to determine inducible MLSB (iMLSB) and detection the erm genes in clinical samples of S. aureus isolated from hospitalized patients in the Imam Reza hospital of Kermanshah, west of Iran.

 This study performed on 126 samples of S. aureus. Identification of isolates were performed using microbiological and biochemical procedures. Inducible resistance to clindamycin was tested by D-test. The prevalence of genes, such as femB, mecA, ermA and ermB was assessed by polymerase chain reaction (PCR).

 Eighty-three cases (65.9%) of isolates were methicillin resistant S. aureus (MRSA). The resistance rate against erythromycin and clindamycin was 67.4% and 52.2%, respectively. Totally, 49 cases (38.9%) of isolates were resistant to both erythromycin and clindamycin indicating constitutive MLSB phenotype (cMLSB); 20 cases (15.9%) isolates showed positive D test indicating inducible MLSB phenotype (iMLSB), while 16 cases (12.7%) were negative for D test indicating MS phenotype. Among 20 cases with iMLSB phenotype, ermC and ermA genes were showed in 7 cases (35%) and 4 cases (20%) isolates, respectively. The ermB gene is not detected in any cases and 9 cases (45%) isolates did not have any erm genes.

 In general, findings of this study showed high frequency of resistance to clindamycin and erythromycin among S. aureus isolates and cMLSB to be the most pattern phenotype and ermC gene is the most common gene in iMLSB phenotype. Because variation of antimicrobial resistance pattern in geographic regions obtaining local results is useful for detecting and more appropriate control of nosocomial infection due to S. aureus isolates.