Emergence of a Potent Multidrug Efflux Pump Variant That Enhances Campylobacter Resistance to Multiple Antibiotics

Abstract

Bacterial antibiotic efflux pumps are key players in antibiotic resistance. Although their role in conferring multidrug resistance is well documented, the emergence of “super” efflux pump variants that enhance bacterial resistance to multiple drugs has not been reported. Here, we describe the emergence of a resistance-enhancing variant (named RE-CmeABC) of the predominant efflux pump CmeABC in Campylobacter, a major zoonotic pathogen whose resistance to antibiotics is considered a serious antibiotic resistance threat in the United States. Compared to the previously characterized CmeABC transporters, RE-CmeABC is much more potent in conferring Campylobacter resistance to antibiotics, which was shown by increased MICs and reduced intracellular accumulation of antibiotics. Structural modeling suggests that sequence variations in the drug-binding pocket of CmeB possibly contribute to the enhanced efflux function. Additionally, RE-CmeABC expands the mutant selection window of ciprofloxacin, enhances the emergence of antibiotic-resistant mutants, and confers exceedingly high-level resistance to fluoroquinolones, an important class of antibiotics for clinical therapy of campylobacteriosis. Furthermore, RE-CmeABC is horizontally transferable, shifts antibiotic MIC distribution among clinical isolates, and is increasingly prevalent in Campylobacter jejuni isolates, suggesting that it confers a fitness advantage under antimicrobial selection. These findings reveal a new mechanism for enhanced multidrug resistance and an effective strategy utilized by bacteria for adaptation to selection from multiple antibiotics.

Point Deletion or Insertion in CmeR-Box, A2075G Substitution in 23S rRNA, and Presence of erm(B) Are Key Factors of Erythromycin Resistance in Campylobacter jejuni and Campylobacter coli Isolated From Central China

“…With regard to that one susceptible isolate carrying point deletion in CmeR-Box, we infer that there might be some unknown mutations, such as the mutations in the cmeABC proteins, which affect its resistant ability. CC-JMJ1 is a specific highly resistant isolate, which does not contain any mutations in CmeR-Box and 23S rRNA, and for erm(B), we infer that it may contain a previously reported resistance-enhancing variant of the efflux pump cmeABC, or due to other unknown mechanisms (Yao et al, 2016).…”

Emerging erm (B)-Mediated Macrolide Resistance Associated with Novel Multidrug Resistance Genomic Islands in Campylobacter

“…S2) (26). The horizontally transferable enhanced multidrug efflux pump gene RE-cmeABC, which was first identified in 2016, mediates resistance to multiple classes of antibiotics, including fluoroquinolones, amphenicols, tetracyclines, and macrolides (19). Thus, C. jejuni isolates 8C and 36C contained a multitude of antimicrobial resistance genes, including RE-cmeABC, erm(B), tet(O), aadE, cat, aphA3, aad9, aph2, aadA, aac, and aph(2Љ)-If, and exhibited high-level resistance to all major antimicrobials, including fluoroquinolone, macrolide, tetracycline, and aminoglycoside drugs that are currently being used in the clinical treatment of Campylobacter infections (Table S1) (27).…”

“…We identified three novel erm(B)-harboring MDRGI types in Campylobacter isolates from chickens, with one of the types, designated type X, being identified in 2 C. jejuni isolates. Sequence analysis revealed that those 2 isolates not only contained the erm(B)-harboring MDRGI but also harbored aminoglycoside resistance genomic islands (ARGIs) and the enhanced multidrug efflux pump-encoding locus RE-cmeABC (19). Thus, the isolates exhibited resistance to all antibiotics commonly used for clinical treatment of Campylobacter infections, including macrolides, fluoroquinolones, aminoglycosides, tetracyclines, lincosamides, and amphenicols.…”

Correlation between gyrA and CmeR Box Polymorphism and Fluoroquinolone Resistance in Campylobacter jejuni Isolates in China

“…Moreover, the extensive use of antibiotics in the poultry industry has led to the increasing prevalence of antibiotic-resistant C. jejuni strains. Some isolates are especially resistant to clinically used antibiotics, such as fluoroquinolones (FQ), which have been commonly used to treat acute bacterial diarrhea (3,5,6). Therefore, surveillance of the FQ susceptibility of C. jejuni is important for not only the purpose of animal breeding but also public health (7,8).…”