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Does reduced susceptibility to disinfectants compromise colonisation and persistence of Salmonella enterica serovar Typhimurium in chickens?

Abstract number: p1143

Cooles  S.W., Webber  M.A., Randall  L.P., Coldham  N.G., Piddock   L.J.V., Woodward  M.J.

Objectives: 

Reduced susceptibility to some disinfectants has been linked with reduced susceptibility to some antibiotics. The use of disinfectants may select for mutants with reduced susceptibility to both disinfectants and antibiotics, and it would be of concern if such mutants persist and accumulate within the food chain. In this study the ability of mutants derived from Salmonella Typhimurium following exposure to disinfectants to colonise and persist in chickens was compared to that of their isogenic parents in the day-old chick model. Mutants arising from exposure to a common domestic chlorophenol disinfectant (Triclosan) and an aldehyde-based farm disinfectant (Superkill) were studied.

Methods: 

Minimum Inhibitory Concentrations (MIC) of various disinfectants and antibiotics were determined by the agar dilution method. Mutants of Salmonella Typhimurium were selected by plating up to 1010 colony forming units (cfu) on media supplemented with 1 – 2x the MIC of disinfectant. Three mutants exhibiting low (4 mg/L), medium (32 mg/L) and high (>128 mg/L) level resistance to triclosan and two exhibiting increased tolerance to superkill were selected. 1-day-old chicks were infected by oral gavage (c. 104 cfu per bird, c. 1:1 mix of mutant and parent strain) in competitive index experiments. Infection was monitored by twice weekly cloacal swabbing for >= 27 days post-infection. Weighed swabs were vortexed in saline (1 mL), diluted and plated (0.1 mL) onto media with or without antibiotic to differentiate between strains. Colonies were counted after overnight incubation at 37°C. Infection was calculated as cfu/g of faecal matter.

Results: 

All mutants showed reduced susceptibility to some clinical antibiotics. The mutant strains were significantly less able to persist than their parent strains, but persisted in the chicken gut and in some cases, even 23 days post-infection, they amounted to approximately 1% of the total Salmonella population of 10cfu/g faecal matter.

Conclusion: 

Exposure of Salmonella Typhimurium to disinfectants gave rise to mutants with reduced susceptibility to disinfectants and/or antibiotics. Compared to their isogenic parent strains, mutants were still able to persist in the chicken gut to the end of the experiment.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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