Co-occurrence and importance of AmpC and extended-spectrum beta-lactamases-producing gram-negative bacilli in clinical specimens at a Tertiary Hospital in Dar es Salaam, Tanzania

Abstract

Abstract Background Third-generation cephalosporin-resistant and carbapenem-resistant Enterobacterales are threatening global public health. We investigated the presence of class C beta-lactamase (AmpC) and extended-spectrum beta-lactamase (ESBL) producers and the co-occurrence of AmpC and ESBL in gram-negative bacteria isolated from 134 clinical specimens at Muhimbili National Hospital in Dar es Salaam, Tanzania. Methods We conducted a laboratory-based cross-sectional study involving routinely processed clinical isolates. The Analytical Profile Index-20 test (API20E) was used to identify isolates to species level. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disk diffusion method. The double-disk synergy test was utilized to determine ESBL production. AmpC production was assessed using the disk approximation test, and the disk antagonistic test detected inducible AmpC production. Descriptive data analysis was carried out using SPSS. Results Of the 134 isolates, 22.4% produced ESBL, 41.8% were resistant to carbapenems, and 44.8% exhibited constitutive production of AmpC. Additionally, 68.6% of the isolates were resistant to third-generation cephalosporins, and 9.7% co-produced ESBL and AmpC. Isolates from the adult intensive care unit showed a higher percentage of ESBL and AmpC producers. The highest rate of AmpC producers was found in pus samples (18/25, 72.0%). Sputum samples had significantly fewer AmpC producers (19, 11.1%, p = 0.011). The proportion of ESBL producers was more in pus samples (28.0%) and blood samples (27.0%). Antimicrobial resistance was significantly higher in AmpC and ESBL producers than the counterparts (p < 0.001). AmpC production was not accurately predicted by the ESBL results: It exhibited a sensitivity of 18.3%, a specificity of 72%, a positive predictive value of 43.3%, and a negative predictive value of 42.3%. Principal component analysis revealed potential similarities between Enterobacter spp. and Klebsiella spp. on ESBL and AmpC production. Constitutive AmpC and ESBL producers displayed a positive correlation, while inducible AmpC was orthogonal. Conclusions The findings highlight a significant percentage of isolates producing ESBL and AmpC, with 9.7% exhibiting co-production of ESBL and AmpC and 68.6% resistant to third-generation cephalosporins. Routine testing for AmpC production is essential, as it was poorly predicted by ESBL test results. This complex situation necessitates an urgent need for rapid phenotypic tests to support appropriate prescribing decisions.