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Can beta-lactamase resistance genes in anaerobic Gram-negative gut bacteria transfer to gut aerobes?


The study was conceived with the hypothesis that human aerobic gut flora could act as a reservoir of ß-lactamases and contribute to the emergence of ß-lactam resistance by transferring ß-lactamase genes to resident anaerobes. Thus, we studied the repertoire of ß-lactam resistance determinants (ß-lactamases associated with aerobes and anaerobes) in Gram-negative anaerobes. The phenotypic resistance against ß-lactams and the presence of aerobic and anaerobic ß-lactamases were tested in Gram-negative anaerobic isolates (n = 200) by agar dilution method and targeted PCR, respectively. In addition, whole-genome sequencing (WGS) was used to study the ß-lactam resistance determinants in 4/200 multi-drug resistant (MDR) strains. The resistance to ß-lactams was as follows: imipenem (0.5%), cefoxitin (26.5%), and piperacillin–tazobactam (27.5%). None of the isolates showed the presence of ß-lactamases found in aerobic microorganisms. The presence of anaerobic ß-lactamase genes viz. cfiA, cepA, cfxA, cfiAIS [the intact segment containing cfiA gene (350 bp) and upstream IS elements (1.6–1.7 kb)] was detected in 10%, 9.5%, 21.5%, and 0% isolates, respectively. The WGS data showed the presence of cfiA, cfiA4, cfxA, cfxA2, cfxA3, cfxA4, cfxA5 in MDR strains. The study showed a distinct dichotomy in repertoires of ß-lactamases between aerobes and anaerobes.

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Fig. 1

Data availability

The bacterial genome data are submitted to the Figshare repository (


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We acknowledge the support provided by the Department of Medical Microbiology, PGIMER, Chandigarh.


This work was supported by the Indian Council of Medical Research extramural grant (AMR/ADHOC/181/2019-ECD-II).

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Correspondence to Archana Angrup.

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Sood, A., Sharma, V., Ray, P. et al. Can beta-lactamase resistance genes in anaerobic Gram-negative gut bacteria transfer to gut aerobes?. J Antibiot 76, 355–359 (2023).

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