Antibiotic resistance genes & susceptibility patterns in staphylococci.

BACKGROUND & OBJECTIVES: This study was carried out to evaluate the association between the antibiotic susceptibility patterns and the antibiotic resistance genes in staphylococcal isolates obtained from various clinical samples of patients attending a teaching hospital in Hatay, Turkey.

METHODS

A total of 298 staphylococci clinical isolates were subjected to antimicrobial susceptibility testing. The genes implicated in resistance to oxacillin (mecA), gentamicin (aac(6')/aph(2''), aph(3')-IIIa, ant(4')-Ia), erythromycin (ermA, ermB, ermC, and msrA), tetracyclin (tetK, tetM), and penicillin (blaZ) were amplified using multiplex PCR method.

RESULTS

Methicillin resistance rate among 139 Staphlococcus aureus isolates was 16.5 and 25.9 per cent of S. aureus carried mecA gene. Of the 159 CoNS isolates, methicillin resistance rate was 18.9 and 29.6 per cent carried mecA gene. Ninety four isolates identified as gentamicin resistant phenotypically, contained at least one of the gentamicin resistance genes [aac(6')/aph(2''), aph(3')-IIIa, ant(4')-Ia], 17 gentamicin-susceptible isolates were found as positive in terms of one or more resistance genes [aac(6')/aph(2''), aph(3')-IIIa, ant(4')-Ia] by multiplex PCR. A total of 165 isolates were resistant to erythromycin, and contained at least one of the erythromycin resistance genes (ermA, ermB, ermC and msrA). Phenotypically, 106 staphylococcal isolates were resistant to tetracycline, 121 isolates carried either tetK or tetM or both resistance genes. The majority of staphylococci tested possessed the blaZ gene (89.9%).

INTERPRETATION & CONCLUSIONS: The present results showed that the phenotypic antibiotic susceptibility patterns were not similar to those obtained by genotyping done by multiplex PCR. Rapid and reliable methods for antibiotic susceptibility are important to determine the appropriate therapy decisions. Multiplex PCR can be used for confirmation of the results obtained by conventional phenotypic methods, when needed.