Acquisition and transfer of antibiotic resistance genes in association with conjugative plasmid or class 1 integrons of Acinetobacter baumannii.

Udomluk Leungtongkam,Kannipa Tasanapak,Sutthirat Sitthisak,Rapee Thummeepak,Egon Anderson Ozer

doi:10.1371/journal.pone.0208468

Udomluk Leungtongkam, Kannipa Tasanapak + Show 3 more

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https://doi.org/10.1371/journal.pone.0208468

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Journal: PloS one	Publication Date: Dec 6, 2018
Citations: 57	License type: CC BY 4.0

Affiliation: Naresuan University

Abstract

Conjugation is a type of horizontal gene transfer (HGT) that serves as the primary mechanism responsible for accelerating the spread of antibiotic resistance genes in Gram-negative bacteria. The present study aimed to elucidate the mechanisms underlying the conjugation-mediated gene transfer from the extensively drug-resistant Acinetobacter baumannii (XDR-AB) and New Delhi Metallo-beta-lactamase-1-producing Acinetobacter baumannii (NDM-AB) to environmental isolates of Acinetobacter spp. Conjugation experiments demonstrated that resistance to ticarcillin and kanamycin could be transferred from four donors to two sodium azide-resistant A. baumannii strains, namely, NU013R and NU015R. No transconjugants were detected on Mueller-Hinton Agar (MHA) plates containing tetracycline. Plasmids obtained from donors as well as successful transconjugants were characterized by PCR-based replicon typing and S1-nuclease pulsed-field gel electrophoresis (S1-PFGE). Detection of antibiotic resistance genes and integrase genes (int) was performed using PCR. Results revealed that the donor AB364 strain can transfer the blaOXA-23 and blaPER-1 genes to both recipients in association with int1. A 240-kb plasmid was successfully transferred from the donor AB364 to recipients. In addition, the aphA6 and blaPER-1 genes were co-transferred with the int1 gene from the donor strains AB352 and AB405. The transfer of a 220-kb plasmid from the donors to recipient was detected. The GR6 plasmid containing the kanamycin resistance gene (aphA6) was successfully transferred from the donor strain AB140 to both recipient strains. However, the blaNDM-1 and tet(B) genes were not detected in all transconjugants. Our study is the first to demonstrate successful in vitro conjugation, which indicated that XDR-AB contained combination mechanisms of the co-transfer of antimicrobial resistance elements with integron cassettes or with the plasmid group GR6. Thus, conjugation could be responsible for the emergence of new types of antibiotic-resistant strains.

Highlights

The genus Acinetobacter comprises important human pathogens that cause nosocomial infections in immunocompromised hosts
Results of conjugation experiments demonstrated that resistance to ticarcillin and kanamycin could be transferred from four XDR-AB donors to two sodium azide-resistant A. baumannii isolates
The Conjugation frequencies (CF) for ticarcillin resistance ranges between 1.0 × 10−4 and 4.1 × 10−7, which were found to be higher than those reported in a previous study by Zarrilli et al and Krahn et al (2 × 10−5 and 1.0 × 10−6) [32, 33]

Summary

Introduction

The genus Acinetobacter comprises important human pathogens that cause nosocomial infections in immunocompromised hosts. The emergence of extensively drug-resistant A. baumannii (XDR-AB) and New Delhi Metallo-beta-lactamase-1-producing A. baumannii (NDM-AB) is a major and immediate threat to public health worldwide. The production of β-lactamase enzymes, including class A-D enzymes, is the primary mechanism underlying A. baumannii resistance [1,2,3]. The primary mechanism underlying aminoglycoside resistance in A. baumannii is enzymatic inactivation by acetyltransferases (AAC) [4]. The presence of acquired efflux pumps has been reported in Acinetobacter spp. Several Tet efflux pumps, including tet(A) and tet(B), which confer tetracycline resistance, have been acquired by clinical isolates of A. baumannii [5]

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