In vitro activity of azithromycin in Salmonella isolates from Pakistan
1Department of Pathology, Shaukat Khanum Memorial Cancer Hospital and Research Center, Lahore, Pakistan. microreg@msn.com
Introduction:
Enteric fever is caused by Salmonella enterica serovars Typhi and Paratyphi A, B and C. It is a significant public health issue in Pakistan, which is exacerbated by a high level of resistance some isolates display to drugs routinely used in treatment. Azithromycin may be a treatment option for such isolates.
Methodology:
We determined the minimum inhibitory concentrations (MICs) of Salmonella Typhi and Paratyphi isolates against azithromycin in an attempt to gauge its feasibility as a therapeutic option. The MICs were also compared with corresponding disc diffusion zone sizes to see if there was consistency between the two tests. We tested 45 Salmonella enterica isolates using E-tests for MIC detection and azithromycin discs with a concentration of 15µg/ml for disc diffusion testing.
Results:
Salmonella Typhi, Salmonella Paratyphi A, and Salmonella Paratyphi C isolates demonstrated MICs of 2-12mg/L against azithromycin, suggesting that the antibiotic could be used for therapeutic purposes. For Salmonella Paratyphi B, the MICs were 2-48 mg/L. The higher MIC indicates a need for caution when considering use of azithromycin for Salmonella Paratyphi B infections without first testing for the MIC. There was a close correlation between MICs and zone sizes which was statistically significant.
Conclusions:
Our results indicate azithromycin is a potential therapeutic option for enteric fever. Standardized laboratory testing methods and interpretation for azithromycin against Salmonella enterica would allow laboratories to report upon this antibiotic with confidence.
Insights
Azithromycin shows promise for treating drug-resistant enteric fever caused by Salmonella Typhi and Paratyphi. Further standardization of testing is recommended for reliable therapeutic use.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Enteric fever, caused by Salmonella Typhi and Paratyphi, is a major public health concern in Pakistan.
- High antimicrobial resistance rates to standard treatments necessitate alternative therapeutic options.
- Azithromycin emerges as a potential treatment for drug-resistant enteric fever.
Purpose of the Study:
- To evaluate azithromycin's efficacy against Salmonella Typhi and Paratyphi isolates.
- To determine the feasibility of azithromycin as a treatment for enteric fever.
- To assess the correlation between minimum inhibitory concentrations (MICs) and disc diffusion test results.
Main Methods:
- Determined MICs of 45 Salmonella enterica isolates against azithromycin using E-tests.
- Compared MICs with disc diffusion zone sizes for consistency.
- Utilized azithromycin discs (15µg/ml) for diffusion testing.
Main Results:
- Salmonella Typhi, Paratyphi A, and Paratyphi C isolates showed favorable MICs (2-12 mg/L) for azithromycin.
- Salmonella Paratyphi B exhibited a wider MIC range (2-48 mg/L), requiring cautious interpretation.
- A statistically significant correlation was observed between MICs and zone sizes.
Conclusions:
- Azithromycin presents a viable therapeutic option for managing enteric fever.
- Standardized laboratory testing and interpretation are crucial for confident reporting of azithromycin susceptibility.
- Further research into azithromycin's role in treating Salmonella Paratyphi B infections is warranted.
