The resistance and transmission mechanism of Acinetobacter baumannii isolates in a tertiary care hospital, China

Xenogenetic evolutionary of integrons promotes the environmental pollution of antibiotic resistance genes - Challenges, progress and prospects

Environmental pollution of antibiotic resistance genes (ARGs) has been a great public concern. Integrons, as mobile genetic elements, with versatile gene acquisition systems facilitate the horizontal gene transfer (HGT) and pollution disseminations of ARGs. However, little is understood about the characteristics of ARGs mediated by integrons, which hampers our monitoring and control of the mobile antimicrobial resistance risks. To address these issues, we reviewed 3,322 publications concerning detection methods and pipeline, ARG diversity and evolutionary progress, environmental and geographical distribution, bacterial hosts, gene cassettes arrangements, and based on which to identify ARGs with high risk levels mediated by integrons. Diverse ARGs of 516 subtypes attributed to 12 types were capable of being carried by integrons, with 62 core ARG subtypes prevalent in pollution source, natural and human-related environments. Hosts of ARG-carrying integrons reached 271 bacterial species, most frequently carried by opportunistic pathogens Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. Moreover, the observed emergence of ARGs together with their multiple arrangements indicated the accumulation of ARGs mediated by integrons, and thus pose increasing HGT risks under modern selective agents. With the concerns of public health, we urgently call for a better monitoring and control of these high-risk ARGs. Our identified Risk Rank I ARGs (aacA7, blaOXA10, catB3, catB8, dfrA5) with high mobility, reviewed key trends and noteworthy advancements, and proposed future directions could be reference and guidance for standard formulation.

Molecular Epidemiology and Mechanisms of Carbapenem-Resistant Acinetobacter baumannii Isolates from ICU and Respiratory Department Patients of a Chinese University Hospital

Background

The objective of our study is to estimate the differences in molecular epidemiology and resistance mechanisms in carbapenem-resistant Acinetobacter baumannii (CRAB) isolates from the ICU and respiratory department(RD) in Fourth Affiliated Hospital of Harbin Medical University.

Methods

Carbapenemase genes associated with carbapenem resistance were studied by polymerase chain reaction(PCR). Genotyping was analyzed using multi-locus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE).

Results

Sixty non-duplicate CRAB isolates from the ICU and RD (n=30, respectively) were collected. All of CRAB strains were not resistant to colistin (0%). The CRAB strains from the ICU were significantly more resistant to tigecycline and cefoperazone/sulbactam compared with the RD (23.3% vs 0%, P=0.03; 53.3% % vs 23.3%, P=0.01, respectively). PCR detection of genes associated with CRAB revealed that the ratio in both the ICU and the RD of blaVIM-2, blaIMP-4, blaNDM-1, blaOXA-23, ampC, and mutation of CarO were present in 23.3% vs 0% (P=0.01), 40% vs 10% (P=0.02), 20% vs 0% (P=0.02), 80% vs 56.7%, 16.7% vs 13.3% and 86.7% vs 60% (P=0.04), respectively. Seven genotypes were detected by the PFGE in the RD and the ICU, respectively. Genotype I was significantly more frequent in the ICU compared with the RD (63.3% vs 36.6%, P=0.03). MLST showed that there were 10 ST genotypes in the RD and four in the ICU, but ST92 in both groups was 33.3% vs 63.3% (P=0.03), respectively.

Conclusion

There are differences in molecular epidemiology and resistance mechanisms in the CRAB isolates between the ICU and RD.

Rapid and accurate detection of carbapenem-resistance gene by isothermal amplification in Acinetobacter baumannii

Background

Acinetobacter baumannii (A. baumannii) is one of the pivotal pathogens responsible for nosocomial infections, especially in patients with low immune response, and infection with carbapenem-resistant A. baumannii has been increasing in recent years. Rapid and accurate detection of carbapenem-resistance genes in A. baumannii could be of immense help to clinical staff.

Methods

In this study, a 15-μL reaction system for recombinase polymerase amplification (RPA) was developed and tested. We collected 30 clinical isolates of A. baumannii from the Burn Institute of Southwest Hospital of Third Military Medical University (Army Medical University) for 6 months and tested antibiotic susceptibility using the VITEK 2 system. A. baumannii was detected based on the bla_OXA-51 gene by PCR, qPCR and 15 μL-RPA, respectively. Sensitivity and specificity were evaluated. In addition, PCR and 15 μL-RPA data for detecting the carbapenem-resistance gene bla_OXA-23 were comparatively assessed.

Results

The detection limit of the bla_OXA-51 gene by 15 μL RPA was 2.86 CFU/ml, with sensitivity comparable to PCR and qPCR. No positive amplification signals were detected in non-Acinetobacter isolates, indicating high specificity. However, only 18 minutes were needed for the 15 μL RPA assay. Furthermore, an antibiotic susceptibility test showed that up to 90% of A. baumannii strains were resistant to meropenem and imipenem; 15 μL RPA data for detecting bla_OXA-23 showed that only 10% (n = 3) of A. baumannii isolates did not show positive amplification signals, and the other 90% of (n = 27) isolates were positive, corroborating PCR results.

Conclusion

We demonstrated that the new 15 μL RPA assay for detecting bla_OXA-23 in A. baumannii is faster and simpler than qPCR and PCR. It is a promising alternative molecular diagnostic tool for rapid and effective detection of A. baumannii and drug-resistance genes in the field and point-of-care testing.