Antimicrobial resistance in Acinetobacter baumannii is a growing public health concern and an important pathogen in nosocomial infections. We investigated the genes involved in resistance to carbapenems and cephalosporins in clinical A. baumannii isolates from a tertiary medical centre in Malaysia. A. baumannii was isolated from 167 clinical specimens and identified by sequencing of the 16S rRNA and rpoB genes. The MIC for imipenem, meropenem, ceftazidime and cefepime were determined by the E-test method. The presence of carbapenemase and cephalosporinase genes was investigated by PCR. The isolates were predominantly nonsusceptible to carbapenems and cephalosporins (.70 %) with high MIC values. ISAba1 was detected in all carbapenem-nonsusceptible A. baumannii harbouring the bla OXA-23-like gene. The presence of bla OXA-51-like and ISAba1 upstream of bla OXA-51 was not associated with nonsusceptibility to carbapenems. A. baumannii isolates harbouring ISAba1-bla ADC (85.8 %) were significantly associated with nonsusceptibility to cephalosporins (P,0.0001). However, ISAba1-bla ADC was not detected in a minority (,10 %) of the isolates which were nonsusceptible to cephalosporins. The acquired OXA-23 enzymes were responsible for nonsusceptibility to carbapenems in our clinical A. baumannii isolates and warrant continuous surveillance to prevent further dissemination of this antibiotic resistance gene. The presence of ISAba1 upstream of the bla ADC was a determinant for cephalosporin resistance. However, the absence of this ISAba1-bla ADC in some of the isolates may suggest other resistance mechanisms and need further investigation.
Multidrug-resistant (MDR) Acinetobacter baumannii has increasingly emerged as an important nosocomial pathogen. The aim of this study was to determine the resistance profiles and genetic diversity in A. baumannii clinical isolates in a tertiary medical center in Malaysia. The minimum inhibitory concentrations of carbapenems (imipenem and meropenem), cephalosporins (ceftazidime and cefepime), and ciprofloxacin were determined by E-test. PCR and sequencing were carried out for the detection of antibiotic resistance genes and mutations. Clonal relatedness among A. baumannii isolates was determined by REP-PCR. Sequence-based typing of OXA-51 and multilocus sequence typing were performed. One hundred twenty-five of 162 (77.2%) A. baumannii isolates had MDR phenotype. From the 162 A. baumannii isolates, 20 strain types were identified and majority of A. baumannii isolates (66%, n = 107) were classified as strain type 1 and were positive for ISAba1-bla and ISAba1-bla and had mutations in both gyrA and parC genes at positions, 83 and 80, resulting in serine-to-leucine conversion. REP-PCR analysis showed 129 REP types that generated 31 clones with a 90% similarity cutoff value. OXA-66 variant of the bla genes was predominantly detected among our A. baumannii clinical isolates belonging to ST195 (found in six clones: 1, 8, 9, 19, 27, and 30) and ST208 (found in clone 21). The study helps us in understanding the genetic diversity of A. baumannii isolates in our setting and confirms that international clone II is the most widely distributed clone in Universiti Kebangsaan Malaysia Medical Centre, Malaysia.
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