Distribution of Genes Encoding Aminoglycoside Modifying Enzymes and Type Staphylococcal Chromosomal Cassette mec in Methicillin-resistant Staphylococcus aureus from Non-tertiary Hospitals

The prevalence of aminoglycoside-modifying enzymes among coagulase negative staphylococci in Iranian pediatric patients

In spite of widespread emergence of aminoglycoside resistance, these drugs are still used in the treatment of staphylococcal infections. This study aimed to investigate the distribution of aminoglycoside resistance and genes encoding aminoglycoside - modifying enzymes (AMEs) as well as Staphylococcal Cassette Chromosome mec (SCCmec) type in coagulase negative staphylococci (CoNS) in pediatric patients. Totally, 93 CoNS isolates were examined for susceptibility to aminoglycosides using disk diffusion and/or E-test methods. AMEs genes and SCCmec types were detected using multiplex PCR. Strain typing was performed using repetitive extragenic palindromic (REP) - PCR assay. The non-susceptibility rates to kanamycin, tobramycin, gentamicin, amikacin and netilmicin were 73%, 59%, 49.5%, 16% and 7.5%, respectively. aac(6')-Ie-aph(2″)-Ia, ant(4')-Ia and aph(3')-IIIa were encountered in 56 (60.2%), 38 (40.8%) and 18 (19.3%) isolates, respectively. In aac(6')-Ie-aph(2″)-Ia- positive isolates, the non- susceptibility rates to kanamycin, gentamicin, tobramycin, amikacin and netilmicin were 83%, 74%, 73%, 49% and 43%, respectively. SCCmec types included type IV (n = 31), I (n = 17), II (n = 5), III (n = 4), and V (n = 2). Three isolates had two types; I + III (n = 2) and III + IV (n = 1) whereas 11 isolates were non-typeable. AMEs genes carriers were distributed frequently into type IV. We found diverse fingerprint patterns among our isolates. In conclusion, there was a strong correlation between alarming rate of aminoglycoside resistance and methicillin resistance. Discordances between phenotypic and genotypic detection of aminoglycoside resistance were discernible. AMEs genes might be related to SCCmec types.