A comprehensive and contemporary "snapshot" of β-lactamases in carbapenem resistant Acinetobacter baumannii

Successful treatment of Acinetobacter baumannii infections require early and appropriate antimicrobial therapy. One of the first steps in this process is understanding which β-lactamase (bla) alleles are present and in what combinations. Thus, we performed WGS on 98 carbapenem-resistant A. baumannii (CR Ab). In most isolates, an acquired bla_OXA carbapenemase was found in addition to the intrinsic bla_OXA allele. The most commonly found allele was bla_OXA-23 (n = 78/98). In some isolates, bla_OXA-23 was found in addition to other carbapenemase alleles: bla_OXA-82 (n = 12/78), bla_OXA-72 (n = 2/78) and bla_OXA-24/40 (n = 1/78). Surprisingly, 20% of isolates carried carbapenemases not routinely assayed for by rapid molecular diagnostic platforms, i.e., bla_OXA-82 and bla_OXA-172; all had ISAba1 elements. In 8 CR Ab, bla_OXA-82 or bla_OXA-172 was the only carbapenemase. Both bla_OXA-24/40 and its variant bla_OXA-72 were each found in 6/98 isolates. The most prevalent ADC variants were bla_ADC-30 (21%), bla_ADC-162 (21%), and bla_ADC-212 (26%). Complete combinations are reported.

Study of genetic diversity, biofilm formation, and detection of Carbapenemase, MBL, ESBL, and tetracycline resistance genes in multidrug-resistant Acinetobacter baumannii isolated from burn wound infections in Iran

Background

Antimicrobial resistance in multidrug-resistant Acinetobacter baumannii (MDR-AB) isolated from burn wound infections is a major concern in intensive care or burns units worldwide, and molecular studies are considered critical strategies for control of MDR-AB outbreaks in this regard. Thus, in this study, antibiotic resistance, biofilm-forming ability, molecular epidemiology of MDR A. baumannii strains recovered from patients with burns were investigated in three major hospital centers of Iran.

Methods

In this cross-sectional research, 163 non-repetitive A. baumannii strains were tested for susceptibility to antimicrobial agents. Polymerase chain reaction (PCR) was performed to characterize ambler classes A, B, and D β-lactamases, ISAba1 and integrons, biofilm formation was also investigated. Clonal relatedness was analyzed using Pulsed-Field Gel Electrophoresis (PFGE).

Results

Among 163 A. baumannii strains collected, 94.5% of them were Carbapenem-Non-Susceptible A. baumannii (CNSAB) and also 90.1 and 52.2% of them were Metallo-β-Lactamases (MBL) and Extended-Spectrum β-Lactamases (ESBL) producing isolates, respectively. Colistin and polymyxin B exhibited excellent activity against CNSAB strains. High prevalence of bla_{OXA − 23-like} (85.1%), bla_VIM (60.5%), bla_{PER − 1} (42.3%), tetB (67.8%), and Class 1 integrons (65.6%) were identified in CNSAB strains. ISAba1 element was associated with 42 (25.8%) and 129 (98.5%) of bla_OXA-51-like and bla_OXA-23-like genes, respectively. 6 clusters with the ability to form strong biofilms were found to be dominant and endemic in our entire areas.

Conclusions

Results of the present study show that antimicrobial resistance in CNSAB isolates from burn wound infections in monitored hospitals in Iran is multifactorial, and also findings of the study suggested that local antibiotic prescription policies should be regularly reviewed, and efficient infection control measures should be observed. Therefore, further strengthening of surveillance of antimicrobial resistance is urgently needed in these regions.

Carbapenem-resistant Acinetobacter baumannii isolates carrying blaOXA genes with upstream ISAba1: First report of a novel OXA subclass from Iran

OBJECTIVES

Carbapenem-resistant Acinetobacter baumannii (CRAB) have emerged as a serious threat to public-health worldwide. This study aimed to determine the antimicrobial susceptibility of A. baumannii isolates in Iran and to investigate oxacillinase-encoding determinants and their association with insertion sequence ISAba1 in CRAB isolates.

METHODS

This study was performed on A. baumannii isolates recovered from patients with burn wound infections during 2013. All isolates were evaluated for antimicrobial susceptibility by the disk diffusion method. Minimum inhibitory concentrations (MICs) of five antibiotics (imipenem, meropenem, polymyxin B, colistin and tigecycline) were determined for all CRAB isolates. PCR was performed to determine the distribution of bla_OXA determinants and ISAba1 insertion upstream of each corresponding gene in the CRAB isolates.

RESULTS

A total of 65 A. baumannii isolates were recovered during the 1-year period, with CRAB accounting for 63 (96.9%) of isolates. Polymyxin B, colistin and tigecycline were the most effective agents against CRAB isolates, with susceptibility rates of 100%, 87.3% and 65.1%, respectively. The proportion of CRAB isolates carrying oxacillinase determinants was as follow: bla_OXA-51-like, 100%; bla_OXA-23-like, 74.6%; bla_{OXA-24/40-like}, 47.6%; and bla_OXA-235-like, 12.7%. ISAba1, ISAba1-bla_OXA-23-like and ISAba1-bla_OXA-51-like were detected in 100%, 41.3% and 1.6% of CRAB isolates, respectively. Co-occurrence of bla_OXA determinants or inserted ISAba1 upstream of the corresponding genes was associated with increased carbapenem MICs (≥128μg/mL).

CONCLUSION

The emergence of high-level CRAB with bla_OXA and ISAba1-bla_OXA family in burn patients is a matter of increasing clinical concern, emphasising the need for infection control efforts to limit such problematic bacteria.

Ceftazidime/avibactam susceptibility by three different susceptibility testing methods in carbapenemase-producing Gram-negative bacteria from Australia

Avibactam (AVI) is a novel β-lactamase inhibitor active against class A, class C and some class D β-lactamases. In combination with ceftazidime, AVI may be useful for the treatment of infections due to Gram-negative bacteria producing carbapenemases from these classes; however, susceptibility data for some of the less common carbapenemases are limited. To assess the in vitro activity of ceftazidime/avibactam (CZA), a panel of 50 diverse carbapenemase-producing Gram-negative bacteria collected from clinical samples in Victoria, Australia, containing KPC, GES, SME, OXA-23 and OXA-48-like carbapenemases were tested for susceptibility to CZA using the broth microdilution (BMD), Etest and disk diffusion methods. All isolates were susceptible to CZA. Etest correlated well with BMD, although Etest minimum inhibitory concentrations (MICs) were generally lower than BMD. Disk diffusion correlated moderately well with BMD, with two interpretive errors. This study confirms phenotypic CZA susceptibility in the carbapenemase groups tested, including the less common OXA-23-producing Escherichia coli, SME-producing Serratia marcescens and GES-5-producing Pseudomonas aeruginosa.

CTX-M-15-Producing Shewanella Species Clinical Isolate Expressing OXA-535, a Chromosome-Encoded OXA-48 Variant, Putative Progenitor of the Plasmid-Encoded OXA-436

Shewanella spp. constitute a reservoir of antibiotic resistance determinants. In a bile sample, we identified three extended-spectrum-β-lactamase (ESBL)-producing bacteria (Escherichia coli, Klebsiella pneumoniae, and Shewanella sp. strain JAB-1) isolated from a child suffering from cholangitis. Our objectives were to characterize the genome and the resistome of the first ESBL-producing isolate of the genus Shewanella and determine whether plasmidic exchange occurred between the three bacterial species. Bacterial isolates were characterized using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), standard biochemical tools, and antimicrobial susceptibility testing. Shewanella sp. JAB-1 and ESBL gene-encoding plasmids were characterized using PacBio and Illumina whole-genome sequencing, respectively. The Shewanella sp. JAB-1 chromosome-encoded OXA-48 variant was cloned and functionally characterized. Whole-genome sequencing (WGS) of the Shewanella sp. clinical isolate JAB-1 revealed the presence of a 193-kb plasmid belonging to the IncA/C incompatibility group and harboring two ESBL genes, bla_CTX-M-15 and bla_SHV-2abla_CTX-M-15 gene-carrying plasmids belonging to the IncY and IncR incompatibility groups were also found in the E. coli and K. pneumoniae isolates from the same patient, respectively. A comparison of the bla_CTX-M-15 genetic environment indicated the independent origin of these plasmids and dismissed in vivo transfers. Furthermore, characterization of the resistome of Shewanella sp. JAB-1 revealed the presence of a chromosome-carried bla_OXA-535 gene, likely the progenitor of the plasmid-carried bla_OXA-436 gene, a novel bla_OXA-48-like gene. The expression of bla_OXA-535 in E. coli showed the carbapenem-hydrolyzing activity of OXA-535. The production of OXA-535 in Shewanella sp. JAB-1 could be evidenced using molecular and immunoenzymatic tests, but not with biochemical tests that monitor carbapenem hydrolysis. In this study, we have identified a CTX-M-15-producing Shewanella species that was responsible for a hepatobiliary infection and that is likely the progenitor of OXA-436, a novel plasmid-encoded OXA-48-like class D carbapenemase.