Antimicrobial resistance profiles and genetic elements involved in carbapenem resistance in Acinetobacter baumannii isolates from a referral hospital in Southern Iran

Prevalence and Mechanisms of Carbapenem Resistance in Acinetobacter baumannii: A Comprehensive Systematic Review of Cross-Sectional Studies from Iran

Introduction: Carbapenem-resistant Acinetobacter baumannii (CRAB) is recognized to be among the most difficult antimicrobial-resistant gram-negative bacilli to control and treat. An understanding of the epidemiology of CRAB and the mechanisms of resistance to carbapenems is necessary to develop strategies to curtail their spread. Methods: Electronic databases were searched from January 1995 to December 2017 for all studies, which: (1) provide data on the frequency and antibiotic resistance profile of the isolated A. baumannii and (2) describe the mechanisms of carbapenem resistance in detail. Results: Sixty-eight studies were found referring to mechanisms of carbapenem resistance in clinical isolates of A. baumannii, and 56 studies were found referring to the frequency of CRAB. The pooled frequency of carbapenem resistance was 85.1% (95% confidence interval [CI]: 82.2-88.1) in 8,067 clinical isolates of A. baumannii. Resistances due to bla_OXA23 (55.3%), bla_OXA24 (41.4%), and bla_OXA58 (5.2%) genes were the most prevalent reported mechanisms of resistance to carbapenem, respectively. Conclusions: Our data warn that CRAB will rise if the current situation remains uncontrolled. Better control infection strategies and antibiotic managements, particularly in the health care systems, are needed to limit the spread of this pathogen.

Clonal relationship and the association of the ST218 strain harboring blaOXA-72 gene to mortality in carbapenem-resistant Acinetobacter baumannii bacteremia

BACKGROUND/PURPOSE

In 2017, the World Health Organization categorized carbapenem-resistant Acinetobacter baumannii (CRAB) as a priority 1, critical antibiotic-resistant bacteria. This study analyzed the clinical outcomes and investigated the molecular epidemiology of CRAB bacteremia in a medical center in Northern Taiwan.

METHODS

We collected 62 blood isolates from patients with CRAB bacteremia from January 2014 to December 2015 at MacKay Memorial Hospital and determined the clonal relationship using the PCR-based technique for molecular epidemiology. Medical charts were reviewed for clinical outcomes.

RESULTS

Fifty-six isolates harbored the bla_OXA-51-like and bla_OXA-23-like carbapenemase genes, 4 isolates harbor the bla_OXA-51-like and bla_OXA-24-like carbapenemase genes and 2 isolates harbored only the bla_OXA-51-like gene. After sequencing, all four isolates of bla_OXA-24-like carbapenemase gene were confirmed to be isolates of bla_OXA-72 carbapenemase genes. In multivariate analysis in the 60 patients, the independent mortality risk factors of CRAB bacteremia included ≥65 years (elderly) (Odds ratio, 4.04, 95% CI, 1.10-14.83, p = 0.035), chronic kidney disease (4.36, 1.14-16.72, p = 0.032). Isolates harboring the bla_OXA-72 gene had the same sequence type (ST218) and PFGE pulsotype raising the possibility of intra-hospital transmission, and all infected patients died.

CONCLUSION

This study showed the clonal relationship of isolates harboring the carbapenemase gene in CRAB bacteremia. Patients with the ST218 strain harboring bla_OXA-72 gene had high mortality. This warrants further research to determine the mechanism of virulence and risk factors in order to reduce mortality.

Distribution and Genotyping of Aquatic Acinetobacter baumannii Strains Isolated from the Puzi River and Its Tributaries Near Areas of Livestock Farming

Acinetobacter baumannii is an important health care-associated bacterium and a common multidrug-resistant pathogen. The use of antibiotics in the husbandry industry has raised concerns about drug-resistant A. baumannii strains, which may affect humans. This study aimed to investigate the seasonal distribution of A. baumannii in aquatic environments near areas of livestock farming. The geographic distribution, antibiotic resistance characteristic, and DNA fingerprinting genotype of A. baumannii were also studied. The results showed that environmental A. baumannii was prevalent during the summer and autumn. The hotspots for A. baumannii were found at the sampling sites of livestock wastewater channels (21.4%; 3/14) and the tributaries adjacent to livestock farms (15.4%; 2/13). The prevalence of A. baumannii at these locations was significantly higher than those adjacent to the Puzi River. Multidrug-resistant strain of A. baumannii was not found in this study, with only one strain (5%; 1/20) being resistant to tetracycline. Of the isolates that were obtained, 10% (2/20) and 20% (4/20) were found to be intermediately resistant to tetracycline and sulphamethoxazole/trimethoprim, respectively. The genotyping patterns and clustering analysis indicated that enterobacterial repetitive intergenic consensus sequence polymerase chain reaction (ERIC-PCR) differentiated A. baumannii strains effectively. There were two major clusters that could then be subtyped into 20 A. baumannii strains with 15 profiles. The A. baumannii strains that were isolated from upstream of the Puzi River and livestock wastewater channels were composed of Cluster I. Cluster II only contained isolates from downstream of the Puzi River area. Furthermore, isolates from adjacent sites were shown to have identical profiles (100%). These results suggest that A. baumannii may have spread through free-flowing water in this study. Therefore, we propose that livestock wastewater is one of the sources that contribute to A. baumannii pollution in water bodies. In summary, continuous monitoring of antibiotic pollution in livestock wastewater is required.

Insight into Acinetobacter baumannii: pathogenesis, global resistance, mechanisms of resistance, treatment options, and alternative modalities

Acinetobacter baumannii, once considered a low-category pathogen, has emerged as an obstinate infectious agent. The scientific community is paying more attention to this pathogen due to its stubbornness to last resort antimicrobials, including carbapenems, colistin, and tigecycline, its high prevalence of infections in the hospital setting, and significantly increased rate of community-acquired infections by this organism over the past decade. It has given the fear of pre-antibiotic era to the world. To further enhance our understanding about this pathogen, in this review, we discuss its taxonomy, pathogenesis, current treatment options, global resistance rates, mechanisms of its resistance against various groups of antimicrobials, and future therapeutics.

Detection of Acinetobacter spp. in Blood Cultures by an Improved Fluorescent in Situ Hybridization Assay

Fluorescent in situ hybridization (FISH) allows rapid detection of microorganisms. We aimed (i) to evaluate the sensitivity and specificity of FISH for the detection of Acinetobacter spp. in blood culture specimens and (ii) to test the simultaneous application of two genus-specific probes labeled with the same fluorochrome to increase the fluorescent signal intensity and improve the detection of Acinetobacter spp. Three hundred and twenty blood culture specimens were tested via both the conventional laboratory methods and FISH to detect Acinetobacter spp. The specimens were examined separately with each genus-specific probe Aci and ACA, and also using a mixture of the both probes Aci and ACA. In all examinations, probe EUB338 was used accompanied by Aci and ACA. The specificity of FISH was 100% (97.5% confidence interval [CI] = 98.7% – 100%). The sensitivity of FISH by the use of probe Aci was 96.4% (95% CI = 81.7% – 99.9%), whereas, the sensitivity of this technique by the use of probe ACA as well as by the combination of both probes Aci and ACA was 100% (97.5% CI = 87.7% – 100%). Moreover, simultaneous hybridization by probes Aci and ACA increased the fluorescent signal of Acinetobacter spp. cells to 3+ in 13 specimens. In conclusion, FISH, particularly using a combination of Aci and ACA, is a highly accurate method for the detection of Acinetobacter spp. in blood cultures. Furthermore, simultaneous hybridization by the both probes Aci and ACA can increase the fluorescent signal intensity of Acinetobacter spp. cells in some blood culture specimens and facilitate the detection of these microorganisms.

Epidemiology of multidrug-resistant Acinetobacter baumannii strains in Iran: a systematic review and meta-analysis

Acinetobacter baumannii is an important opportunistic pathogen that causes major public health concern especially in hospitalized patients due to the acquisition of multidrug resistance (MDR). The aim of this study was to systematically review published data about the prevalence rate of MDR-A. baumannii (MDR-AB) from different parts of Iran and provide an overall relative frequency (RF) using meta-analysis. All available national and international databanks were searched to find published studies up to June 2016. Quality of studies was assessed by STROB and PRISMA forms. Because of the significant heterogeneity observed, random effects model was used to combine the results. STATA SE version 11.2 was used for statistical analysis. Out of the 9646 results, 37 suitable articles were extracted according to inclusion and exlusion criteria. The pooled prevalence of MDR-AB was estimated 72% annually. Relative frequency of MDR-AB in different studies varied from 22.8 to 100%. Since the prevalence of MDR-AB is higher than many other countries, measures should be taken to keep the emergence and transmission of these strains to a minimum.