Sources of Contamination of Bovine Milk and Raw Milk Cheese by Staphylococcus aureus Using Variable Number of Tandem Repeat Analysis

Bernard Poutrel Jaquemine

doi:10.4172/2157-7579.1000246

Abstract

Milk and dairy products are frequently implicated in food-borne infections caused by Staphylococcus aureus and infected animals may contaminate bulk milk. In addition, human handlers, milking equipment, the environment, the udder and the teat skin of dairy animals are possible sources of bulk milk contamination. The main objective of this study was to identify and prioritize the sources of S. aureus contamination of bulk milk and raw milk cheese, and secondly to investigate the diversity of strains involved in bovine mastitis, and test the controversial hypothesis of cross-infection between humans and animals. Four farms manufacturing cheese from raw milk with a total of 135 dairy cows were selected. Bacteriological analyses were performed on quarter milk samples, swabs of udders and teats, the milking machine, bulk milk, cheeses, swabs taken from staff members’ hands and nasal cavities. Typing of S. aureus isolates was carried out using the Multiple Locus Variable Tandem Repeat Analysis [MLVA] including five genes [clfA, clfB coa, fnb and SAV1078] combined with the investigation of the presence of staphylokinase gene [sak]. A total of 537 isolates were genotyped. The genotyping results confirmed that most intramammary infections in each farm were due to a prevalent genotype. The majority of genotypes present on the teat skin were also isolated from quarter milk samples. These isolates are the main sources of the contamination of bulk milk and cheese. The identity of certain genotypes characterized in both humans and animals was sometimes associated with the presence of the sak gene and suggests the existence of cross-contamination and also the occasional involvement of human handlers in the contamination of milk and cheeses.

Highlights

Staphylococcus aureus is an important cause of declared foodborne, and milk and dairy products are among the foods most often implicated [1]
A, B, and C, had a high prevalence of intramammary infection, 37.8%, 33.7% and 39.4% of quarters, respectively and represented approximately 2/3 of the cows (Table 3). This high prevalence could be related to the high contamination of cheeses and suggests, even in the absence of typing results, that intramammary infections were an important source of contamination
This was supported by the low prevalence of mammary infections by S. aureus observed in herd not practicing pre-dipping of teats (herd D) and associated with a relatively low contamination of the cheeses

Summary

Introduction

Staphylococcus aureus is an important cause of declared foodborne, and milk and dairy products are among the foods most often implicated [1]. S. aureus is a major pathogen responsible for severe nosocomial and community-associated infections of humans. Livestock strains may have the capacity to colonize humans and humans represent an important source of new pathogenic strains affecting livestock [2,3,4,5,6]. Controlling milk and cheese contamination is an economic and health stake for all raw milk productions. A decrease in S. aureus contamination of raw milk cheese can only be achieved by reducing S. aureus in the raw milk and by limiting contamination throughout the process of cheese manufacturing. Identifying sources of contamination in dairy herds/cows is key to the development of targeted, appropriate control measures

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Conclusion