THE COUNTS OF BACTERIA AND OCCURRENCE OF PATHOGENS
CHAPTER ONE
1. O INTRODUCTION
Milk is a complex biological food and by its nature, a good growth medium for many microorganisms, of which bacteria is prominent. Because of the specific production, it is impossible to avoid contamination of milk with microorganisms (bacteria). Therefore, the bacteriological quality of milk is a major factor in determining its safety for consumption (Rojeli, 2003). Bacterial contamination of raw milk can originate from different sources – air, milking equipment, feed, soil, faeces, and grasses ( Coorevits et al., 2008). The number and type of
microorganisms in milk immediately after by factors such as animals and equipment cleanliness, season, and animal health (Rojeli, 2003). It is hypothesized that difference in feeding and housing strategies of cows may affect the bacteriological quality of milk (Coorevit et al., 2008). Rinsing water for milking machine and milking equipment washing also involve some of the reasons for for the presence of higher number of microorganisms including pathogen in raw milk (Bramley, 1990). The condition during storage and transport in refrigerated tanks cause the raw milk micro-biota from predominantly gram’s negative organisms as they grow. Gram’s negative bacteria usually account for more than 90% of the bacterial population in cold raw milk that has been stored. The gram’s negative flora is composed mainly of psychotropic species of Pseudomonas, Achromobacter, Aeromonas, Serratia, Alcaligenes, Chromobacterium, Flavobacterium and Enterobacter (Martins et al., 2006). Organisms unable to grow at refrigeration temperature remains at low number, implying that temperature is an important factor contributing
to the prevalence and proliferation of specific organisms in milk. Pasteurization in raw milk is effective in eliminating all, but not thermodeuric organisms of the genera Mycobacterium, Micrococcus, Streptococcus, Lactobacillus, Bacillus, Clostridium, the Coryneforms and occasionally, some gram’s negative rods (Jay,1996).Psychotrophs can grow at refrigeration temperature below 7 degrees Celsius, produces enzymes, toxins and other metabolites. most of these bacteria produces extra-cellular ,proteolytic and lipolytic enzymes that are secreted into the milk –many of these enzymes are not inactivated by pasteurizing at 72 degree Celsius
for 15 seconds or by ultra- high temperature treatment (Griffith et al., 1981).
