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. 2015 Aug 20:14:38.
doi: 10.1186/s12941-015-0098-9.

Molecular characterization of extended-spectrum beta-lactamases (ESBLs) produced by clinical isolates of Acinetobacter baumannii in Saudi Arabia

Essam J Alyamani  1 , Mohamed A Khiyami  2 , Rayan Y Booq  3 , Basel M Alnafjan  4 , Musaad A Altammami  5 , Fayez S Bahwerth  6
Affiliations

Molecular characterization of extended-spectrum beta-lactamases (ESBLs) produced by clinical isolates of Acinetobacter baumannii in Saudi Arabia

Essam J Alyamani et al. Ann Clin Microbiol Antimicrob. .

Abstract

Background: Acinetobacter baumannii is a common opportunistic pathogen that causes major nosocomial infections in hospitals. In this study, we hypothesized a high prevalence of A. baumanni ESBL (extended-spectrum beta-lactamase) among all collected isolates.

Methods: A. baumannii isolates (n = 107) from ICU (Intensive care unit) of local hospitals in Makkah were phenotypically and genotypically characterized. The identity and antibiotic susceptibility of A. baumannii strains were determined using the Vitek-2 system. The identified ESBL producers were further analyzed by PCR and sequencing followed by MLST typing. bla TEM , bla SHV , and the bla CTX-M-group genes 1, 2, 8, 9, and 25 were investigated. Furthermore, bla OXA51-like and bla OXA23-like genes were also examined in the carbapenem-resistant A. baumannii isolates.

Results: Our data indicated a high prevalence of A. baumannii ESBL producers among the collected strains. Of the 107 A. baumannii isolates, 94 % were found to be resistant to cefepime and ceftazidime, and aztreonam using the Vitek 2 system. The genes detected encoded TEM, OXA-51-like and OXA-23-like enzymes, and CTX-M-group proteins 1, 2, 8, 9, and 25. MLST typing identified eight sequence type (ST) groups. The most dominant STs were ST195 and ST557 and all of them belong to worldwide clonal complex (CC) 2.

Conclusions: This study has shown that there is a high prevalence of antimicrobial resistance in A. baumannii. The diversity of STs may suggest that new ESBL strains are constantly emerging. The molecular diversity of the ESBL genes in A. baumannii may have contributed to the increased antimicrobial resistance among all isolates.

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Figures

Fig. 1
Fig. 1
Cephalosporin susceptibility pattern by A. baumannii isolates. Among the 107 isolates of A. baumannii tested, 100 isolates (94 %) were confirmed as ESBL producers by phenotypic assay
Fig. 2
Fig. 2
The overall distribution of ESBL and carbapenemase genes detected in A. baumannii isolates
Fig. 3
Fig. 3
UPGMA (unweighted pair group method with arithmetic mean) dendrogram based on the catagorical coefficient applied to the allele IDs. All isolates with at least six loci amplified were included. The dendrogram was generated by BioNumerics 7 software. The ST numbers assigned for each isolate were generated by the Pasteur MLST scheme (http://pubmlst.org/abaumannii/). The tree is a rooted based on the nucleotide sequence of the six and seven housekeeping genes. The analysis was based on data sets that include all STs in the Pasteur MLST databases. The first clade consists of ST195, 208, 218 and 286; the second clade of ST231; the third clade of ST499; the fourth clade of ST 557; the fifth clade of ST222. The sixth and seventh clades have two nontypeable isolates due to low quality sequencing trace files
Fig. 4
Fig. 4
Minimum spanning tree constructed based on the allele IDs
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