The Sub-inhibitory Effect of Azithromycin and Ciprofloxacin on <i>virF</i> Gene Expression in Enteroinvasive <i>Escherichia coli</i> and <i>Shigella flexner</i>i

Bacillary dysentery is an invasive bacterial gastroenteritis that damages the colon epithelium and leads to bloody diarrhea. Enteroinvasive Escherichia coli (EIEC) and Shigella flexner i are two major etiologic agents of the disease. The virF gene is a transcriptional regulator of the virulence genes involved in the invasion of these bacteria. Previous studies have shown that sub-minimum inhibitory concentrations (sub-MICs) of antibiotics have significant effects on bacterial virulence.

This study aimed to evaluate the effects of sub-MICs of ciprofloxacin and azithromycin on S. flexneri and EIEC.

Prototype strains of both bacteria were treated with sub-MICs of 1/2, 1/4, and 1/8 of ciprofloxacin and azithromycin antibiotics. Changes in the expression of the virF gene in antibiotic-treated samples compared to control samples were analyzed using relative real-time polymerase chain reaction (PCR).

The mean expression of the virF gene in all sub-MICs of ciprofloxacin was increased in both S. flexneri and EIEC, while a down-regulation was observed in sub-MICs of azithromycin. These gene expression changes were dose-dependent.

The results demonstrated that the virulence of S. flexneri and EIEC is affected by sub-MICs of azithromycin and ciprofloxacin. Given that azithromycin, unlike ciprofloxacin, reduces the severity of infection at sub-MICs, it is a more appropriate choice with a lower risk for treating acute infections caused by these bacteria.