article · Bulletin of the National Research Centre/Bulletin of the National Research Center
A study of 134 gram-negative bacterial clinical isolates from Muhimbili National Hospital in Dar es Salaam, Tanzania, examined the prevalence and co-occurrence of beta-lactamase resistance enzymes. Overall, 68.6 percent of isolates were resistant to third-generation cephalosporins, 41.8 percent were resistant to carbapenems, 44.8 percent exhibited constitutive AmpC production, and 22.4 percent produced extended-spectrum beta-lactamases. Nearly ten percent of the isolates co-produced both enzymes. Resistance rates were elevated in samples from the adult intensive care unit, with the highest proportions of AmpC producers found in pus specimens. Standard extended-spectrum beta-lactamase testing proved inadequate for identifying AmpC production, displaying poor predictive values and sensitivity. These patterns underscore a high resistance burden and indicate that current routine testing leaves significant gaps in detecting dual resistance mechanisms in clinical environments.
Bacterial infections resistant to crucial antibiotics like cephalosporins and carbapenems pose severe threats to hospitalised patients. When bacteria produce multiple resistance enzymes simultaneously, identifying them through standard laboratory tests becomes difficult. Confirming the high local prevalence of co-occurring resistance mechanisms highlights the need for dedicated detection methods to ensure patients receive effective antibiotics promptly.
The findings point to a direct clinical need for rapid phenotypic diagnostic tests capable of reliably detecting AmpC and extended-spectrum beta-lactamases simultaneously. Diagnostic manufacturers and hospital laboratories could use these insights to guide the development and deployment of rapid resistance testing kits. The research itself represents early-stage surveillance and diagnostic assessment based on standard laboratory methods, without presenting a newly commercialised testing product.
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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.
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DOI: 10.1186/s42269-025-01323-5
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