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Natural colistin resistance in Edwardsiella tarda
Abstract:
All of 37 recent human isolates of Edwardsiella tarda were resistant to colistin. All strains were resistant to 6.3 mug of sodium colistimethate per ml; 82% of them were resistant to 100 mug/ml. With 34 Salmonella strains, the average minimal inhibitory concentration (MIC) was 1.6 mug of sodium colistimethate per ml. There was virtually no overlapping of MIC values between both groups of bacteria. Using the Kirby-Bauer method and 10-mug colistin disks, inhibition zone diameters were less than 11 mm for all Edwardsiella strains, and larger for all Salmonella strains. An atypical, mannitol-fermenting strain of E. tarda was resistant to colistin. It is concluded that E. tarda is naturally resistant to colistin, that this property may be helpful in differentiation, and that colistin should be tried in enrichment and selective media for the isolation of E. tarda. It was also observed that, under conditions as described, all strains of E. tarda were susceptible to streptomycin and to novobiocin, whereas all strains of Salmonella were resistant.
Insights
Edwardsiella tarda exhibits natural resistance to colistin, a finding useful for differentiating it from Salmonella. This resistance suggests colistin
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Antimicrobial Resistance
Background:
- Edwardsiella tarda is an opportunistic pathogen.
- Colistin is a critical antibiotic for treating multidrug-resistant Gram-negative infections.
- Understanding antimicrobial susceptibility patterns is crucial for effective treatment and diagnostics.
Purpose of the Study:
- To investigate the susceptibility of Edwardsiella tarda isolates to colistin.
- To compare the colistin resistance profile of E. tarda with Salmonella species.
- To evaluate the potential of colistin resistance as a diagnostic marker for E. tarda.
Main Methods:
- Testing 37 human isolates of Edwardsiella tarda and 34 Salmonella strains for colistin susceptibility.
- Determining minimal inhibitory concentrations (MICs) of sodium colistimethate.
- Utilizing the Kirby-Bauer disk diffusion method with colistin disks.
Main Results:
- All 37 Edwardsiella tarda isolates were resistant to colistin, with high MIC values.
- Salmonella strains showed significantly lower MIC values, indicating susceptibility.
- Distinct inhibition zone diameters were observed between E. tarda and Salmonella using the Kirby-Bauer method.
- An atypical, mannitol-fermenting E. tarda strain also demonstrated colistin resistance.
Conclusions:
- Edwardsiella tarda is naturally resistant to colistin.
- Colistin resistance can serve as a valuable characteristic for differentiating E. tarda from Salmonella.
- Colistin may be beneficial in selective and enrichment media for isolating E. tarda.
- All tested E. tarda strains were susceptible to streptomycin and novobiocin, unlike Salmonella.