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Comparison of results for commercially available microbiological media plates with results for standard bacteriologic testing of bovine milk

Jodi A. Wallace DVM, MSc1, Émile Bouchard DMV, MPVB2, Luc DesCôteaux DMV, MSc3, Serge Messier DMV, PhD4, Denis Du Tremblay DMV5, and Jean-Philippe Roy DMV, MSc6
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  • 1 Ormstown Veterinary Hospital, 1430 Rte 201, Ormstown, QC J0S 1K0, Canada.
  • | 2 Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC J2S 2M2, Canada.
  • | 3 Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC J2S 2M2, Canada.
  • | 4 Département de Pathologie et Microbiologie, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC J2S 2M2, Canada.
  • | 5 Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC J2S 2M2, Canada.
  • | 6 Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC J2S 2M2, Canada.

Abstract

Objective—To compare results for 3 commercially available microbiological media plates with those for standard bacteriologic testing of bovine milk.

Sample—Milk samples from postpartum cows and cows with a high somatic cell count (SCC) or clinical mastitis (CM).

Procedures—Sample-ready Staphylococcus culture medium (SRSC) plates were used to detect Staphylococcus aureus in milk samples obtained from postpartum cows and cows with a high SCC or CM. Rapid coliform count (RCC) plates were used to detect coliforms in milk samples obtained from cows with CM. Aerobic count (AC) plates were used to detect streptococci in CM samples. Fresh mastitic milk samples were frozen and then thawed to evaluate the effects of freezing for the SRSC and RCC plates. The effects of dilution (1:10) of samples were determined. Agreement of results between the commercially available plates and standard bacteriologic testing was evaluated.

Results—The ability of SRSC plates to detect S aureus in milk samples was highest with diluted samples from postpartum cows and cows with a high SCC or CM. Sensitivity of the RCC plate for detection of coliforms was highest with diluted mastitic milk samples. The AC plates had a poor positive predictive value for detection of streptococci in mastitic milk samples. Freezing increased S aureus detection.

Conclusions and Clinical Relevance—Overall, the SRSC and RCC plates were accurate, were easy to use, and yielded results comparable to those of standard bacteriologic testing for the detection of S aureus and coliforms in bovine milk.

Abstract

Objective—To compare results for 3 commercially available microbiological media plates with those for standard bacteriologic testing of bovine milk.

Sample—Milk samples from postpartum cows and cows with a high somatic cell count (SCC) or clinical mastitis (CM).

Procedures—Sample-ready Staphylococcus culture medium (SRSC) plates were used to detect Staphylococcus aureus in milk samples obtained from postpartum cows and cows with a high SCC or CM. Rapid coliform count (RCC) plates were used to detect coliforms in milk samples obtained from cows with CM. Aerobic count (AC) plates were used to detect streptococci in CM samples. Fresh mastitic milk samples were frozen and then thawed to evaluate the effects of freezing for the SRSC and RCC plates. The effects of dilution (1:10) of samples were determined. Agreement of results between the commercially available plates and standard bacteriologic testing was evaluated.

Results—The ability of SRSC plates to detect S aureus in milk samples was highest with diluted samples from postpartum cows and cows with a high SCC or CM. Sensitivity of the RCC plate for detection of coliforms was highest with diluted mastitic milk samples. The AC plates had a poor positive predictive value for detection of streptococci in mastitic milk samples. Freezing increased S aureus detection.

Conclusions and Clinical Relevance—Overall, the SRSC and RCC plates were accurate, were easy to use, and yielded results comparable to those of standard bacteriologic testing for the detection of S aureus and coliforms in bovine milk.

Contributor Notes

Supported by a grant from 3M Canada and Pfizer Animal Health Canada.

Presented in abstract form at the National Mastitis Council Annual Meeting, New Orleans, January 2009; and the American Association of Bovine Practitioners Annual Meeting, Vancouver, BC, Canada, September 2008.

The authors thank Nathalie St-Amour and Dr. Paul Baillargeon for technical assistance.

Address correspondence to Dr. Wallace (jodi.wallace@hvovet.com).