Si-Tuan Nguyen, Minh Thong Nguyen, Duy Nhat Le, Van Chuong Le, Minh Tuan Huynh
In this collection, blaOXA-23 was the genotype most consistently associated with resistance across multiple antimicrobial classes, and blaNDM was associated with resistance mainly when carried together with blaOXA-23. Automated phenotypic classification rarely assigned NDM-producing isolates to Ambler class B, although a carbapenemase result of undetermined class had a high positive predictive value for blaNDM. These single-centre findings are associative; molecular confirmation and clonality analysis are warranted in comparable settings.
BACKGROUND: Carbapenem-resistant Acinetobacter baumannii (CRAB) is a World Health Organization critical-priority pathogen, but the contribution of blaOXA-23 and blaNDM co-carriage to resistance across antimicrobial classes is poorly defined in southern Vietnam.
OBJECTIVES: To describe the carbapenemase gene profile and antimicrobial susceptibility of clinical A. baumannii isolates from a Vietnamese tertiary hospital, to estimate the association between carbapenemase genotypes and class-level resistance, and to assess the concordance between automated phenotypic carbapenemase prediction and multiplex PCR.
METHODS: Single-centre, laboratory-based cross-sectional study of 172 non-duplicate clinical A. baumannii isolates collected consecutively over 28 months. Susceptibility was determined on the BD Phoenix M50 system, except colistin, which was tested by reference broth microdilution, and interpreted according to CLSI M100 (2023). Denominators vary by agent and are reported explicitly. Class-level resistance was resistance to at least one tested agent in the class. Six carbapenemase genes were detected by multiplex PCR. Firth penalized logistic regression (reference genotype: blaOXA-51 only) was used to estimate genotype-resistance associations; concordance was assessed using Cohen's κ, sensitivity, specificity and predictive values.
RESULTS: 158 of 172 isolates (91.9%) met the multidrugresistance definition. blaOXA-51 (98.3%) and blaOXA-23 (83.7%) predominated; blaNDM was detected in 23.3%, and blaOXA-23/blaNDM co-carriage in 16.3% (28/172). Colistin resistance was detected in 3 of 156 evaluable isolates (1.9%). The blaOXA-51/blaOXA-23 genotype was associated with higher odds of resistance in all six classes examined (OR 7.60-18.59, all p ≤0.003). Additional carriage of blaNDM was associated with a further increase for carbapenems (OR 13.10, 95% CI 1.90-90.27), aminoglycosides (16.40, 2.39-112.40), fluoroquinolones (13.10, 1.90-90.27), penicillin/β-lactamase inhibitor combinations (15.31, 2.08-112.97) and trimethoprim/sulfamethoxazole (8.27, 1.36-50.26; all p ≤0.022), but not for extended-spectrum cephalosporins (19.00, 0.90-401.19, p=0.058). The blaOXA-51/blaNDM genotype without blaOXA-23 was not significantly associated with resistance in any class. The BD Phoenix M50 predicted Ambler class D with moderate agreement (κ=0.536) but assigned class B to only 1 of 40 blaNDM-positive isolates (κ = 0.038); all 38 isolates reported as carbapenemase detected, class not determined carried blaNDM.
CONCLUSIONS: In this collection, blaOXA-23 was the genotype most consistently associated with resistance across multiple antimicrobial classes, and blaNDM was associated with resistance mainly when carried together with blaOXA-23. Automated phenotypic classification rarely assigned NDM-producing isolates to Ambler class B, although a carbapenemase result of undetermined class had a high positive predictive value for blaNDM. These single-centre findings are associative; molecular confirmation and clonality analysis are warranted in comparable settings.