Growth and enterotoxin production of Bacillus cereus in cow, goat, and sheep milk

Lenka Necidová,Žaneta Ševčíková,Bohumíra Janštová,Šárka Bursová,Alena Skočková,Pavla Prachařová,Bohdana Janštová

doi:10.2754/avb201483s10s3

Abstract

The aim of this study was to compare Bacillus cereus growth rates and diarrhoeal enterotoxin production in raw and pasteurized goat, sheep, and cow milk in terms of storage conditions. Milk samples were inoculated with B. cereus (CCM 2010), which produces diarrhoeal enterotoxins. Enterotoxin production was tested by ELISA (Enzyme-Linked Immunosorbent Assay), and the count of B. cereus was determined by the plate method. With raw cow milk, B. cereus growth and enterotoxin production can be completely suppressed; in raw goat and sheep milk, enterotoxin was produced at 22 °C. In pasteurized cow, goat, and sheep milk, the B. cereus count increased under all storage conditions, with more rapid growth being observed at 15 °C (sheep milk) and 22 °C (cow and goat milk). Enterotoxin presence was detected at 15 °C and 22 °C, and with pasteurized cow milk also at 8 °C. Our model experiments have determined that B. cereus multiplication and subsequent enterotoxin production depend on storage temperature and milk type.

Highlights

The aim of this study was to compare Bacillus cereus growth rates and diarrhoeal enterotoxin production in raw and pasteurized goat, sheep, and cow milk in terms of storage conditions
Our experiments revealed variation in B. cereus counts during the culture period and in the time to enterotoxin production, depending on the storage conditions and type of milk
B. cereus was not detected in raw cow milk at a pH of 6.59, where pasteurized milk was positive for B. cereus and enterotoxin, we conclude that B. cereus growth is influenced not by pH count but by competitive microbiota not present in pasteurized milk

Summary

Introduction

The aim of this study was to compare Bacillus cereus growth rates and diarrhoeal enterotoxin production in raw and pasteurized goat, sheep, and cow milk in terms of storage conditions. B. cereus growth and enterotoxin production can be completely suppressed; in raw goat and sheep milk, enterotoxin was produced at 22 °C. The high level of nutrients in milk makes it an especially suitable growth medium for bacteria. These microorganisms can achieve high population densities following contamination during milk processing. Svensson et al (2007) in their study have assumed that the mesophilic isolates of B. cereus from the farm, silo tanks, and pasteurized milk are often high producers of enterotoxin. Major sources of B. cereus in pasteurized milk are spores in raw milk (Lin et al 1998)

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