Comparative study of phenotypic-based detection assays for carbapenemase-producing Acinetobacter baumannii with a proposed algorithm in resource-limited settings

Investigating the validity of mCIM and sCIM phenotypic methods in screening Pseudomonas aeruginosa isolates producing IMP, VIM, and NDM metallo-beta-lactamases isolated from burn wounds

Metallo-beta-lactamase-producing Pseudomonas aeruginosa (P. aeruginosa) is a major pathogen in burn wounds, often exhibiting high levels of antibiotic resistance, which complicates treatment strategies. This study deals with the validity of the modified Carbapenem Inactivation Method (mCIM) and the simplified Carbapenem Inactivation Method (sCIM) phenotypic tests for screening metallo-beta-lactamase (MBL) production by P. aeruginosa isolates from a referral burn center in Iran. Forty isolates were obtained between January and June 2021 and identified using conventional biochemical methods. Antimicrobial susceptibility testing was conducted following Clinical and Laboratory Standards Institute (CLSI) 2021 guidelines. mCIM based on CLSI 2023 guidelines was used to detect carbapenemase production. sCIM was also used based on previously developed protocols. PCR was performed to detect blaIMP, blaVIM, and blaNDM genes. The results were analyzed using SPSS and MedCalc. We observed a 90% resistance rate to imipenem and high resistance to other antibiotics, with multidrug-resistant (MDR) strains constituting 95% of the isolates. The mCIM test demonstrated high sensitivity (87.50%) and high negative predictive value (89.47%) and moderate specificity (70.83%) and moderate positive predictive value (66.67%) for detecting MBLs. In contrast, the sCIM test was unreliable, indicating a need for more standardized testing protocols. This study underscores the importance of accurate and timely detection of carbapenemase production to guide effective treatment.

Geographical mapping and temporal trends of Acinetobacter baumannii carbapenem resistance: A comprehensive meta-analysis

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) is of critical concern in healthcare settings, leading to limited treatment options. In this study, we conducted a comprehensive meta-analysis to assess the prevalence of CRAB by examining temporal, geographic, and bias-related variations.

METHODS

We systematically searched prominent databases, including Scopus, PubMed, Web of Science, and EMBASE. Quality assessment was performed using the JBI checklist. Subgroup analyses were performed based on the COVID-19 timeframes, years, countries, continents, and bias levels, antimicrobial susceptivity test method and guidelines.

RESULTS

Our comprehensive meta-analysis, which included 795 studies across 80 countries from 1995 to 2023, revealed a surge in carbapenem resistance among A. baumannii, imipenem (76.1%), meropenem (73.5%), doripenem (73.0%), ertapenem (83.7%), and carbapenems (74.3%). Temporally, 2020-2023 witnessed significant peaks, particularly in carbapenems (81.0%) and meropenem (80.7%), as confirmed by meta-regression, indicating a steady upward trend.

CONCLUSION

This meta-analysis revealed an alarmingly high resistance rate to CRAB as a global challenge, emphasizing the urgent need for tailored interventions. Transparency, standardized methodologies, and collaboration are crucial for the accurate assessment and maintenance of carbapenem efficacy.

Molecular genotyping reveals multiple carbapenemase genes and unique blaOXA-51-like (oxaAb) alleles among clinically isolated Acinetobacter baumannii from a Philippine tertiary hospital

BACKGROUND

Acinetobacter baumannii continued to be an important Gram-negative pathogen of concern in the clinical context. The resistance of this pathogen to carbapenems due to the production of carbapenemases is considered a global threat. Despite the efforts to track carbapenemase synthesis among A. baumannii in the Philippines, local data on its molecular features are very scarce. This study aims to characterize A. baumannii clinical isolates from a Philippine tertiary hospital through genotyping of the pathogen's carbapenemase genes.

METHODS

Antibiotic susceptibility profiling, phenotypic testing of carbapenemase production, and polymerase chain reaction assays to detect the different classes of carbapenemase genes (class A blaKPC, class B blaNDM, blaIMP, blaVIM, and class D blaOXA-23-like, blaOXA-24/40-like, blaOXA-48-like, blaOXA-51-like, ISAba1-blaOXA-51-like, blaOXA-58-like) were performed in all collected A. baumannii, both carbapenem resistant and susceptible (n = 52).

RESULTS

Results showed that the majority of the carbapenem-resistant strains phenotypically produced carbapenemases (up to 84% in carbapenem inactivation methods) and possessed the ISAba1-blaOXA-51-like gene complex (80%). Meanwhile, both carbapenem-resistant and carbapenem-susceptible isolates possessed multi-class carbapenemase genes including blaNDM (1.9%), blaVIM (3.9%), blaOXA-24/40-like (5.8%), blaOXA-58-like (5.8%), blaKPC (11.5%), and blaOXA-23-like (94.2%), which coexist with each other in some strains (17.3%). In terms of the intrinsic blaOXA-51-like (oxaAb) genes, 23 unique alleles were reported (blaOXA-1058 to blaOXA-1080), the majority of which are closely related to blaOXA-66. Isolates possessing these alleles showed varying carbapenem resistance profiles.

CONCLUSIONS

In summary, this study highlighted the importance of molecular genotyping in the characterization of A. baumannii by revealing the carbapenemase profiles of the pathogen (which may not be captured accurately in phenotypic tests), in identifying potent carriers of transferrable carbapenemase genes (which may not be expressed straightforwardly in antimicrobial susceptibility testing), and in monitoring unique pathogen epidemiology in the local clinical setting.

Comparative study of phenotypic-based detection assays for carbapenemases in Acinetobacter baumannii

BACKGROUND

Acinetobacter baumannii is a serious health concern worldwide, causing high mortality rates and limited medical therapy options. Carbapenem resistance is a significant problem in Acinetobacter baumannii isolates. The synthesis of acquired carbapenemases, such as oxacillinases, IMP, NDM, VIM, and KPC enzymes, causes carbapenem resistance.

METHODS

A total of 106 non-repetitive, Acinetobacter baumannii isolates were collected from four major hospitals in Bahrain including 78 carbapenem-resistant Acinetobacter baumannii (CRAB), and 28 carbapenem-susceptible Acinetobacter baumannii (CSAB) isolates. Three phenotypic tests were investigated in this study: including CARBA NP, modified carbapenem inactivation method (mCIM)/EDTA-CIM (eCIM), and modified Hodge test (MHT).

RESULTS

CARBA NP was positive in 50 tested CRAB isolates (100%), and the sensitivity was 100%. The MHT was positive in 73/106 isolates (68.8%), while the sensitivity and specificity of the MHT were 77.6% and 100%. Moreover, only 38/106 (35.8%) isolates were positive for mCIM/eCIM. The sensitivity and specificity of mCIM were 40.4% and 100%.

CONCLUSION

CARBA NP was ideal for phenotypic detection of carbapenemase production, followed by MHT. The m/eCIM demonstrated a lower detection rate in CRAB. Consequently, combining tests would be more accurate. The mCIM/eCIM can easily distinguish between MBLs and serine-carbapenemases due to the frequent co-production of these enzymes in A. baumannii. In hospital setups where molecular characterization tests are not available, CARBA NP seems to be an alternative test in combination with MHT or mCIM/eCIM.

Co-production of metallo-β-lactamase and OXA-type β-lactamases in carbapenem-resistant Acinetobacter baumannii clinical isolates in North East India

Carbapenem-resistant Acinetobacter baumannii poses a significant threat to public health globally, especially due to its ability to produce multiple carbapenemases, leading to treatment challenges. This study aimed to investigate the antibiotic resistance pattern of carbapenem-resistant A. baumannii isolates collected from different clinical settings in North East India, focusing on their genotypic and phenotypic resistance profiles. A total of 172 multidrug-resistant A. baumannii isolates were collected and subjected to antibiotic susceptibility test using the Kirby-Bauer disk diffusion method. Various phenotypic tests were performed to detect extended-spectrum β-lactamase (ESBL), metallo-β-lactamase (MBL), class C AmpC β-lactamase (AmpC), and carbapenem hydrolyzing class D β-lactamase (CHDL) production among the isolates. Overexpression of carbapenemase and cephalosporinase genes was detected among the isolates through both phenotypic and genotypic investigation. The antibiotic resistance profile of the isolates revealed that all were multidrug-resistant; 25% were extensively drug-resistant, 9.30% were pan-drug-resistant, whereas 91.27% were resistant to carbapenems. In the genotypic investigation, 80.81% of isolates were reported harbouring at least one metallo-β-lactamase encoding gene, with blaNDM being the most prevalent at 70.34%, followed by blaIMP at 51.16% of isolates. Regarding class D carbapenemases, blaOXA-51 and blaOXA-23 genes were detected in all the tested isolates, while blaOXA-24, blaOXA-48, and blaOXA-58 were found in 15.11%, 6.97%, and 1.74% isolates respectively. Further analysis showed that 31.97% of isolates co-harboured ESBL, MBL, AmpC, and CHDL genes, while 31.39% of isolates co-harboured ESBL, MBL, and CHDL genes with or without ISAba1 leading to extensively drug-resistant or pan drug-resistant phenotypes. This study highlights the complex genetic profile and antimicrobial-resistant pattern of the isolates circulating in North East India, emphasizing the urgent need for effective infection control measures and the development of alternative treatment strategies to combat these challenging pathogens.

The optimized carbapenem inactivation method for objective and accurate detection of carbapenemase-producing Acinetobacter baumannii

The modified carbapenem inactivation method (mCIM) recommended by the Clinical and Laboratory Standards Institute is not applicable for detecting carbapenemases in Acinetobacter baumannii. Four currently reported phenotypic detection methods, namely, the modified Hodge test, the mCIM, the adjusted mCIM, and the simplified carbapenem inactivation method (sCIM), did not perform well in our 90 clinical A. baumannii isolates. Thus, the minimal inhibitory concentrations (MICs) of carbapenems and the existence and expression of carbapenemase-encoding genes were detected to explain the results. According to the E-test, which was more accurate than the VITEK 2 system, 80.0 and 41.1% were resistant to imipenem (IPM) and meropenem (MEM), respectively, and 14.4 and 53.3% exhibited intermediate resistance, respectively. Five β-lactamase genes were found, of which bla_OXA-51-like, bla_TEM, and bla_OXA-23-like were detected more frequently in 85 non-susceptible strains. The expression of bla_OXA-23-like was positively correlated with the MIC values of IPM and MEM. Therefore, an improved approach based on the mCIM, designated the optimized CIM (oCIM), was developed in this study to detect carbapenemases more accurately and reproducibly. The condition was improved by evaluating the factors of A. baumannii inoculum, incubation broth volume, and MEM disk incubation time. Obvious high sensitivity (92.94%) and specificity (100.00%) were obtained using the oCIM, which was cost-effective and reproducible in routine laboratory work.