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Background <p><i>Shigella sonnei</i>, a Gram-negative bacterium, has been identified as a primary causative agent of gastrointestinal disease in humans. Antibiotic resistance has emerged as a critical concern in the context of <i>Shigella</i> species, thereby complicating the effective treatment of shigellosis. The objective of this study was to investigate the expression of the vapBC toxin–antitoxin, virulence factors, antibiotic resistance, and molecular typing of <i>S. sonnei</i> isolates responsible for diarrhea in children admitted to Besaat and Ekbatan educational hospitals in Hamadan province, west of Iran.</p> Materials and methods <p>The research involved the collection of 60 clinical isolates from two hospitals and the subsequent identification of the isolates phenotypically and genotypically using standard biochemical and molecular methods. The antibiotic susceptibility of the isolates was examined using the standard disk diffusion technique. Polymerase chain reaction (PCR) was utilized to detect the <i>vapB</i>,<i> vapC</i>,<i> ipaB</i>,<i> Stx1</i>, and <i>pINV</i> genes. The MIC and sub-MIC of ciprofloxacin were determined by broth microdilution method. The gene expression of the <i>vapC</i> toxin and <i>vapB</i> antitoxin genes under normal and stress conditions (sub-MIC of ciprofloxacin) was evaluated using real-time PCR. The molecular profiles of the isolates were determined using ERIC-PCR.</p> Results <p>It was observed that all isolates (100%) exhibited resistance to azithromycin, ampicillin, and trimethoprim–sulfamethoxazole. The majority of isolates (&gt; 90%) demonstrated resistance to cefotaxime and ceftriaxone, while over 90% exhibited susceptibility to gentamicin and meropenem. Of the isolates, 73.3% demonstrated sensitivity to ciprofloxacin, while 16.6% exhibited sensitivity to imipenem. The isolates exhibited multidrug resistance (MDR). The presence of the <i>pINV</i> and <i>vapBC</i> genes was detected in all isolates, while the <i>ipaB</i> gene was present in 96.6% of isolates and the <i>Stx1</i> gene was absent in all isolates. Expression analysis revealed that <i>vapC</i> was upregulated under conditions of ciprofloxacin sub-MIC stress in comparison with normal conditions. ERIC-PCR banding patterns indicated a high degree of genetic similarity among the isolates. A total of 60 strains were classified into eight genetic clusters, including three prevalent types and five rare types.</p> Conclusion <p>The upregulation of the <i>vapC</i> gene in response to sub-MIC ciprofloxacin stress suggests that the vapBC toxin–antitoxin system is activated in <i>S. sonnei</i> in response to antibiotic stress, potentially contributing to bacterial survival under stressful conditions, including exposure to antibiotics.</p> Clinical trial number <p>Not applicable.</p>

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Central role of vapBC toxin–antitoxin system expression in the pathogenicity and antimicrobial resistance of Shigella sonnei isolates from pediatric diarrheal patients

  • 期刊论文

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  • 发表日期：

    2026年8月3日

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  • Golara Pagheh,
  • Mohammad Yousef Alikhani,
  • Pezhman Karami,
  • Zohreh Shalchi,
  • Younes Mohammadi,
  • Mohammad Taheri

摘要

Background

Shigella sonnei, a Gram-negative bacterium, has been identified as a primary causative agent of gastrointestinal disease in humans. Antibiotic resistance has emerged as a critical concern in the context of Shigella species, thereby complicating the effective treatment of shigellosis. The objective of this study was to investigate the expression of the vapBC toxin–antitoxin, virulence factors, antibiotic resistance, and molecular typing of S. sonnei isolates responsible for diarrhea in children admitted to Besaat and Ekbatan educational hospitals in Hamadan province, west of Iran.

Materials and methods

The research involved the collection of 60 clinical isolates from two hospitals and the subsequent identification of the isolates phenotypically and genotypically using standard biochemical and molecular methods. The antibiotic susceptibility of the isolates was examined using the standard disk diffusion technique. Polymerase chain reaction (PCR) was utilized to detect the vapB, vapC, ipaB, Stx1, and pINV genes. The MIC and sub-MIC of ciprofloxacin were determined by broth microdilution method. The gene expression of the vapC toxin and vapB antitoxin genes under normal and stress conditions (sub-MIC of ciprofloxacin) was evaluated using real-time PCR. The molecular profiles of the isolates were determined using ERIC-PCR.

Results

It was observed that all isolates (100%) exhibited resistance to azithromycin, ampicillin, and trimethoprim–sulfamethoxazole. The majority of isolates (> 90%) demonstrated resistance to cefotaxime and ceftriaxone, while over 90% exhibited susceptibility to gentamicin and meropenem. Of the isolates, 73.3% demonstrated sensitivity to ciprofloxacin, while 16.6% exhibited sensitivity to imipenem. The isolates exhibited multidrug resistance (MDR). The presence of the pINV and vapBC genes was detected in all isolates, while the ipaB gene was present in 96.6% of isolates and the Stx1 gene was absent in all isolates. Expression analysis revealed that vapC was upregulated under conditions of ciprofloxacin sub-MIC stress in comparison with normal conditions. ERIC-PCR banding patterns indicated a high degree of genetic similarity among the isolates. A total of 60 strains were classified into eight genetic clusters, including three prevalent types and five rare types.

Conclusion

The upregulation of the vapC gene in response to sub-MIC ciprofloxacin stress suggests that the vapBC toxin–antitoxin system is activated in S. sonnei in response to antibiotic stress, potentially contributing to bacterial survival under stressful conditions, including exposure to antibiotics.

Clinical trial number

Not applicable.