Study on the association between drug‑resistance and gene mutations of the active efflux pump acrAB‑tolC gene and its regulatory genes

The relationship between integrons, antibiotic resistance genes and SXT resistance in Shigella flexneri strains

OBJECTIVE

To investigate the correlation between sulfamethoxazole-trimethoprim (SXT) resistance in Shigella flexneri (S.flexneri) and the presence of integrons and relevant antibiotic resistance genes.

METHODS

We collected 115 strains of Shigella flexneri isolated from feces of children with diarrhea in Jinan from 2012 to 2020 and determined the minimum inhibitory concentration (MIC) of SXT by Etest method. The presence of class 1, class 2, and class 3 integron genes, variable region antibiotic resistance gene cassettes, and sul1, sul2, sul3, and SXT elements were detected using polymerase chain reaction (PCR). Positive results were further analyzed by DNA sequencing and BLAST comparison.

RESULTS

In total, the resistance rate to SXT was 60.9% among the 115 S.flexneri strains. The prevalence of class 1 and class 2 integrons were 88.7% and 87.0%, respectively, with no class 3 integrons detected. Among the strains, 13.0% carried typical class 1 integrons with variable region antibiotic resistance gene cassettes dfrA17-aadA5 and dfrV, while 85.2% carried atypical class 1 integrons with variable region antibiotic resistance gene cassette blaoxa-30-aadA1. The variable region antibiotic resistance gene cassettes of class 2 integrons were all dfrA1+sat1+aadA1. There was a statistical difference between the presence of class 1 integrons and class 2 integrons between the SXT-sensitive and resistant S.flexneri strains (χ2=22.800, χ2=16.365, P<0.01, P<0.01). Integrons carrying dfrV and dfrA1 by integrons also showed a statistical difference in SXT resistance (χ2=9.422, χ2=16.365, P<0.01, P<0.01). PCR revealed the presence of sul1 and sul2 in 13.0% and 47.0% of strains, respectively, with neither sul3 nor SXT elements detected. There was a significant difference between the presence of sul1, sul2 between the SXT-sensitive and resistant S.flexneri strains (χ2=9.588, χ2=65.445, P<0.01, P<0.01).

CONCLUSION

In summary, integrons are involved in SXT resistance of S.flexneri, and dfrV, dfrA1, sul1, sul2 are closely related to SXT resistance of S.flexneri.

SmpB and tmRNA Orchestrate Purine Pathway for the Trimethoprim Resistance in Aeromonas veronii

Small protein B(SmpB) cooperates with transfer-messenger RNA (tmRNA) for trans-translation to ensure the quality control of protein synthesis in prokaryotes. Furthermore, they regulate cell metabolism separately. According to research, SmpB functions as a transcription factor, and tmRNA acts as a small RNA. Purine pathway has been reported to be related to trimethoprim resistance, including hypoxanthine synthesis, adenosine metabolism and guanosine metabolism. Another reason of drug tolerance is the efflux pump of the bacterium. In transcriptomic data, it was shown that the expression of some related enzymes in adenosine metabolism were raised significantly in smpB deletion strain than that of wild type, which led to the differential trimethoprim resistance of Aeromonas veronii (A. veronii). Furthermore, the metabolic products of adenosine AMP, cAMP, and deoxyadenosine were accumulated significantly. However, the expressions of the enzymes related to hypoxanthine synthesis and guanosine metabolism were elevated significantly in ssrA (small stable RNA, tmRNA) deletion strain, which eventually caused an augmented metabolic product xanthine. In addition, the deletion of ssrA also affected the significant downregulations of efflux pump acrA/acrB. The minimal inhibitory concentrations (MIC) were overall decreased after the trimethoprim treatment to the wild type, ΔsmpB and ΔssrA. And the difference in sensitivity between ΔsmpB and ΔssrA was evident. The MIC of ΔsmpB was descended significantly than those of wild type and ΔssrA in M9 medium supplemented with 1 mM adenosine, illustrating that the adenosine metabolism pathway was principally influenced by SmpB. Likewise, the strain ΔssrA conferred more sensitivity than wild type and ΔsmpB in M9 medium supplemented with 1mM guanosine. By overexpressing acrA/acrB, the tolerance to trimethoprim was partially recovered in ΔssrA. These results revealed that SmpB and tmRNA acted on different branches in purine metabolism, conferring the diverse trimethoprim resistance to A. veronii. This study suggests that the trans-translation system might be an effective target in clinical treatment of A. veronii and other multi-antibiotic resistance bacteria with trimethoprim.