Draft genome sequences of extensively drug resistant and pandrug resistant Acinetobacter baumannii strains isolated from hospital wastewater in South Africa

OBJECTIVES

Acinetobacter baumannii is a significant opportunistic pathogen causing nosocomial infections. Infections caused by A. baumannii are often difficult to treat because this bacterium is often multidrug-resistant and shows high environmental adaptability. Here, we report on the analysis of three A. baumannii strains isolated from hospital effluents in South Africa.

METHODS

Strains were isolated on Leeds Acinetobacter agar and were identified using VITEK®2 platform. Antibiotic susceptibility testing was performed using the Kirby-Bauer Disk diffusion method. Whole-genome sequencing was performed. The assembled contigs were annotated. Multilocus sequence type, antimicrobial resistance, and virulence genes were identified.

RESULTS

The strains showed two multilocus sequence types, ST231 (FA34) and ST1552 (PL448, FG116). Based on their antibiotic susceptibility profiles, PL448 and FG116 were classified as extensively drug-resistant and FA34 as pandrug-resistant. FA34 harbored mutations in LpxA, LpxC, and PmrB, conferring resistance to colistin, but not mcr genes. All three strains encoded virulence genes for immune evasion (capsule, lipopolysaccharide [LPS]), iron uptake, and biofilm formation. FA34 was related to human strains from South Africa; PL448 and FG116 were related to a strain isolated in the United States from a human wound.

CONCLUSIONS

The detection of extensively drug- and pandrug-resistant A. baumannii strains in hospital effluents is of particular concern. It indicates that wastewater might play a role in the spread of these bacteria. Our data provide insight into the molecular epidemiology, resistance, pathogenicity, and distribution of A. baumannii in South Africa.

baumannii; methodological considerations

PURPOSE

Pending approval of new antimicrobials, synergistic combinations are the only treatment option against pandrug-resistant A. baumannii (PDRAB). Considering the lack of a standardized methodology, the aim of this manuscript is to systematically review the methodology and discuss unique considerations for assessing antimicrobial combinations against PDRAB.

METHODS

Post-hoc analysis of a systematic review (conducted in PubMed and Scopus from inception to April 2021) of studies evaluating antimicrobial combination against A. baumannii, based on antimicrobials that are inactive in vitro alone.

RESULTS

Eighty-four publications were reviewed, using a variety of synergy testing methods, including; gradient-based methods (n = 11), disk-based methods (n = 6), agar dilution (n = 2), checkerboard assay (n = 44), time-kill assay (n = 50), dynamic in vitro PK/PD models (n = 6), semi-mechanistic PK/PD models (n = 5), and in vivo animal models (n = 11). Several variations in definitions of synergy and interpretation of each method were observed and are discussed. Challenges related to testing combinations of antimicrobials that are inactive alone (with regards to concentrations at which the combinations are assessed), as well as other considerations (assessment of stasis vs killing, clinical relevance of re-growth in vitro after initial killing, role of in vitro vs in vivo conditions, challenges of clinical testing of antimicrobial combinations against PDRAB infections) are discussed.

CONCLUSION

This review demonstrates the need for consensus on a standardized methodology and clinically relevant definitions for synergy. Modifications in the methodology and definitions of synergy as well as a roadmap for further development of antimicrobial combinations against PDRAB are proposed.

A synergic action of colistin, imipenem, and silver nanoparticles against pandrug-resistant Acinetobacter baumannii isolated from patients

BACKGROUND

The upgrowth and rapid prevalence of pandrug-resistant Acinetobacter baumannii strains that have a pathogenic activity to cause several infections are of considerable influence on the health of communities worldwide. No infections by these bacterial strains were recorded before 1998, and currently, the numbers are on the rise.

METHODS

The A. baumannii strains were isolated from male and female patients in Medical Microbiology Department, King Fahd Medical City (KFMC) in Riyadh, Saudi Arabia between 1/1/2020 to 29/12/2020. The statistical analysis was performed base on sex, age, source of samples, and response to commercially available antibiotics. The A. baumannii strains that resisted all the antibiotics including colistin and imipenem were selected for the synergic test.

RESULTS

The data showed that 62.28%, 77.07% of 342 A. baumannii strains were isolated from males and patients over 35 years of age. A. baumannii strains (pandrug-A. baumannii) that can resist all tested antibiotics were 8.19%. The major source of the A. baumannii isolates was the respiratory system (>50%). Among all isolates (N = 342), azidothymidine-resistant A. baumannii strains were more than 85%. There is a statistically significant difference (P < 0.05) in the number of colistin-resistant A. baumannii strains isolated from males comparing with the female. The combinations of colistin and silver nanoparticles or imipenem and silver nanoparticles resulted in synergistic action led to reduction of MICs of colistin, imipenem, and silver nanoparticles (more than four-fold reduction). Also, the combinations of colistin and imipenem had high synergistic action.

CONCLUSION

The pandrug-resistant A. baumannii strains may represent a current and future threat that must be fought, and the synergy action of antibiotics and nanoparticles may be one of the available, rapid, and easy strategies to confront this global problem.

Extensively drug-resistant and pandrug-resistant Gram-negative bacteria in a tertiary-care hospital in Eastern India: A 4-year retrospective study

OBJECTIVES

Bacteria resistant to different classes of antimicrobial agents are a major threat to humanity and risk leading the world towards the return of the pre-antimicrobial era. This study was undertaken to detect the incidence of extensively drug-resistant (XDR) and pandrug-resistant (PDR) bacteria in a tertiary-care hospital in Bhubaneswar, Odisha, India.

METHODS

Positive bacterial cultures from different clinical samples were identified using a VITEK^®2 compact system and the antimicrobial susceptibility profile of different Gram-negative bacteria was analysed.

RESULTS

A total of 2489 clinical samples were collected and processed for culture during the period January 2013 to April 2017. Of 1103 pure bacterial cultures, 690 (62.6%) were Gram-negative bacteria. The antimicrobial susceptibility profile of Gram-negative bacterial strains revealed that 41.3% (n=285) were XDR and 8.1% (n=56) were PDR. Rates of colistin and tigecycline resistance were 16% and 51.9%, respectively.

CONCLUSION

This situation demands regular surveillance of antimicrobial resistance of Gram-negative bacteria and implementation of an efficient infection control programme.

Activity of TP-6076 against carbapenem-resistant Acinetobacter baumannii isolates collected from inpatients in Greek hospitals

TP-6076 is a synthetic fluorocycline antibiotic that inhibits bacterial protein synthesis. In this study, carbapenem-resistant Acinetobacter baumannii clinical isolates from 13 Greek hospitals were tested for susceptibility to TP-6076 and comparator antibiotics. Broth microdilution plates were used to determine minimum inhibitory concentrations (MICs). A total of 121 non-duplicate A. baumannii isolates were tested. The MIC₅₀ and MIC₉₀ values of TP-6076 were 0.03 mg/L and 0.06 mg/L, respectively. Tigecycline was the second most active antibiotic (MIC₉₀, 2 mg/L), followed by minocycline (MIC₉₀, 8 mg/L). TP-6076 exhibited MIC₉₀ values that were one dilution lower against tigecycline- and minocycline-susceptible isolates than against resistant isolates. There was no difference in the MIC₉₀ value for colistin-susceptible or -resistant isolates. In conclusion, TP-6076 exhibited greater antimicrobial activity in vitro against carbapenem-resistant A. baumannii than comparator antibiotics.

Risk factors of multidrug-resistant, extensively drug-resistant and pandrug-resistant Acinetobacter baumannii ventilator-associated pneumonia in a Medical Intensive Care Unit of University Hospital in Thailand

Ventilator-associated pneumonia (VAP) caused by Acinetobacter baumannii remains a significant cause of morbidity and mortality. Increasing antimicrobial resistance influences the selection of antibiotic treatment especially pandrug-resistant A. baumannii. A retrospective cohort study was conducted in the Medical Intensive Care Unit to identify the risk factors of VAP caused by multidrug-resistant A. baumannii (MDR-AB), extensively drug-resistant A. baumannii (XDR-AB) and pandrug-resistant A. baumannii (PDR-AB). All 337 adult patients with confirmed A. baumannii VAP were included. The incidence of MDR-AB, XDR-AB and PDR-AB were 72 (21.4%), 220 (65.3%) and 12 (3.6%), respectively. The risk factor for MDR-AB was prior use of carbapenems (OR 5.20; 95% CI 1.41-19.17). Risk factors for XDR-AB were the prior use of carbapenems (OR, 6.30; 95% CI, 1.80-21.97) and a high Sequential Organ Failure Assessment (SOFA) score (OR 1.35; 95% CI 1.07-1.71). In PDR-AB, the risk factors were the prior use of colistin (OR, 155.95; 95% CI, 8.00-3041.98), carbapenems (OR, 12.84; 95% CI, 1.60-103.20) and a high Simplified Acute Physiology Score (SAPS II) (OR 1.10; 95% CI 1.01-1.22). In conclusion, previous exposure to antibiotics and severity of VAP were risk factors of drug-resistant A. baumannii. Judicious use of carbapenems and colistin is recommended to prevent the antimicrobial-resistant strains of this organism.