Research Summary - 4
Biocide tolerance of Salmonella isolates recovered from clinically ill cattle
| Date/Time: |
9/14/2024
14:30
|
| Author: |
Samantha Locke |
| Clinic: |
The Ohio State University |
| City, State, ZIP: |
Columbus, OH 43210 |
S. R. Locke, PhD
1
;
P. Vinayamohan, DVM, PhD
1
;
D. Diaz-Campos, DVM, PhD
2
;
G. Habing, DVM, MS, PhD, DACVPM
;
1Veterinary Preventive Medicine, The Ohio State University, Columbus, OH, 43210
2Veterinary Clinical Sciences, The Ohio State University, Columbus, OH, 43210
Introduction:
Cleaning and disinfection is a common control method to reduce Salmonella transmission in cattle herds However, cleaning and disinfection protocols have had varied effectiveness against Salmonella in farm environments, and residual contamination is often reported. Biocide choice is critical when designing effective cleaning and disinfection protocols, yet little is known regarding Salmonella susceptibility to commercial products. Our objective was to determine the minimum bactericidal concentration (MBC), defined as ≥ 3 log reduction, of six biocides used in livestock production or veterinary medicine. We hypothesized that some label guidelines would not substantially reduce Salmonella.
Materials and methods:
To assess this, a 48-well microtiter assay was developed that included two-fold serial dilutions of Clorox® Germicidal Bleach, chlorine dioxide, chlorhexidine gluconate, KennelSol™, Rescue™, and VirkonS®. The lowest concentration tested was chosen based on the label directions for use and increased to 12 to 14 times the initial concentration, depending on the biocide. A neutralizer was used to inactivate biocides and simulate 10-minutes of contact time between bacteria and biocide, in accordance with some biocide label instructions. A second assay was run concurrently, using sterile water as a sham for neutralizer. Six isolates each from Salmonella serovars Dublin, Newport, and Typhimurium recovered from ill cattle were tested in duplicate. Bacteria were enumerated to determine the log reductions after biocide exposure.
Results:
Dilutions listed on KennelSol™ and VirkonS® labels resulted in eradication of all isolates with or without neutralization. For all isolates, Clorox® MBCs were either 625 or 1250 parts per million (ppm) within the label guideline for hard, nonporous surfaces (2400 ppm). However, the 200 ppm guidance for food contact surfaces failed to significantly reduce any isolates tested, which is a public health concern for cattle-derived Salmonella strains that are transmitted through the food supply. Rescue™ required a 2- to 4-fold concentration above label suggestion to achieve biocidal effects within 10 minutes when neutralized, but MBCs fell within suggested guidelines after 24-hours in the sterile water assay.
Significance:
This assay identified biocides that were rapidly effective against Salmonella. Since isolates were recovered from clinically ill cattle, results may be particularly pertinent for guiding biocide choice on cattle farms experiencing salmonellosis outbreaks. Future work should define MBCs required to significantly reduce Salmonella biofilms and account for potential variation in biocide effectiveness based on surface material.
