Growth inhibition of enteric pathogens by zinc sulfate: an in vitro study

To determine the inhibition effect of zinc sulfate on isolates of enteric bacteria.

Mueller-Hinton agar containing different concentrations of zinc sulfate was prepared. Isolates used in this study were obtained from local clinics. They were Salmonella typhi, Salmonella groups A, B, C, D and E, Escherichia coli, Enterobacter, Shigella and Vibrio cholerae. Overnight cultures of test organisms in brain-heart infusion broth were adjusted to 0.5 McFarland standard turbidity by adding normal saline with 1 microl of each adjusted broth culture inoculated onto zinc sulfate agar plates. The plates were incubated for 18-20 h at 37 degrees C. The inhibition concentration was recorded as the lowest concentration of zinc sulfate that completely inhibited growth.

All enteric pathogens tested were inhibited by zinc sulfate. Of the isolates, S. typhi was most sensitive since 20% of the strains were inhibited by zinc sulfate of 0.8 mg/ml. Salmonella paratyphi A was inhibited at 1.2 mg/ml. Other Salmonella spp. were inhibited at concentrations between 1.4 and 2.0 mg/ml. V. cholerae O1 and Shigella flexneri demonstrated a similar pattern of inhibition as S. paratyphi A. A higher concentration of zinc sulfate (1.6 mg/ml) was required to completely inhibit Shigella sonnei.

The findings indicate that zinc sulfate has an antimicrobial effect on enteric pathogens and may contribute to the treatment of diarrhea.