Determination of antibiotic resistance in clinical isolates of coagulase negative Staphylococci from hospitalized patients in selected hospitals of Tehran

To investigate the prevalence of methicillin and aminoglycoside resistance and gene encoding staphylococcal cassette chromosome mec (SCCmec) and aminoglycoside modifying enzymes in clinical isolates of coagulase negative staphylococci(CoNS) from hospitalized patients. One hundred and three isolates of coagulase negative staphylococci(CoNS) were recovered from various clinical samples from August 2013 to November 2014. All the specimens were identified by conventional microbiological methods. These tests were contained colony morphology, gram stain, catalase, slide and tube coagulase. To determine the sensibility of CoNS to antimicrobial components including Cefoxitin(30µg), Tobramycin(10µg), Kanamycin(30µg), Amikacin(30µg) and Gentamicin(10µg), disk diffusion method was performed by Kirby Bauer antibiotic testing. In order to show the presence of methicillin and aminoglycoside resistant CoNS genes, PCR were demonstrated. In our study the rate of resistance to Cefoxitin, Kanamycin, Gentamicin, Tobramycin and Amikacin were 74(71.8%), 54(52,4%), 51(49.5%), 45(43.7%) and 16(15.5%), respectively. Some strains of CoNS have been detected with intermediate resistance to Kanamycin 4(3.9%), Tobramycin and Amikacin 2(1.9%). In our study, the distribution of mecA gene among clinical isolates of CoNS was 89(86.4%). The prevalence of aminoglycoside resistance genes like ant(4 ')-Ia, aac(6 ')/aph(2 ") and aph(3 ')-IIIa were 89(86.4%), 87(84.5%) and 68(66%), respectively. The rate of coexistence of aac(6’)-Ie-aph(2’’) with aph(3’)-IIIa and aac(6’)-Ie-aph(2’’) with ant(4’)-Ia was 65(63%) and 77(74%), respectively. Resistance to aminoglycosides, develops quickly in coagulase-negative staphylococci from clinical areas where these antimicrobial agents are widely used. Therefore, higher investments should be directed towards identifying coagulase-negative staphylococcus species in healthcare institutions and in the community. Overall, Knowing the epidemiology and antibiotic resistance of CoNS is essential to implement the prevention strategies and reducing antibiotic consumptions