60 Chapter 3
dues are present. Potable treated water, if
taken directly from the mains supply, is
microbiologically assured. However, if
untreated water is abstracted from boreholes,
wells, lakes, springs, or rivers it can become
contaminated by microorganisms of fecal
origin (e.g., coliforms), saprophytic microor-
ganisms from the soil and vegetation (e.g.,
Pseudomonas spp., Bacillus spores, and
coryneform), and lactic acid bacteria.Raw Milk Safety
In the United States, one - third of all dairy -
related illnesses still involve raw milk (Ryser,
2001 ). The dangers of drinking raw milk are
considered to be of such a magnitude that
physicians, veterinarians, and dairy farmers
who promote, or even condone such a prac-
tice, may be at risk of legal action (Weisbecker,
2007 ). A study involving sampling bulk raw
milk from eastern South Dakota and western
Minnesota from 131 dairy herds detected
Campylobacter jejuni , pathogenic Esche-
richia coli , L. monocytogenes, Salmonella
spp., and Yersinia enterocolitica in 0.2%,
3.8%, 4.6%, 6.1%, and 6.1% of raw milk
samples, respectively (Jayarao and Henning,
2001 ).
Raw milk can potentially be contaminated
with a wide range of pathogenic microorgan-
isms, not only originating from the animal
itself but also from fecal material which inev-
itably gains access and from environmental
sources such as water (Lafarge et al., 2004 ).
The composition, development, or survival
of this pathogenic microfl ora can be infl u-
enced by factors such as geographical loca-
tion, ambient temperature, underlying disease
status of the herd, and local human popula-
tion. This inevitably determines how the milk
is treated and consumed as well as regula-
tions and interventions imposed by local and
national authorities. The microorganisms
pathogenic to humans that potentially could
be present in raw milk are shown in Table
3.1. This table has been designed as a quickMicrobial contamination of raw milk
mainly arises from the following sources:
udder interior and exterior, including the
teats, milk contact surfaces, and water used
for cleaning and rinsing the milking equip-
ment. Contamination from other sources
such as the milker themself and aerial con-
tamination are considered insignifi cant in
comparison and are not dealt with here.
Udder Interior
Milk drawn aseptically from the quarters of
healthy animals is generally considered
almost sterile. However, animals suffering
from clinical or sub - clinical mastitis may
excrete pathogens such as coagulase - negative
staphylococci, Staphylococcus aureus, envi-
ronmental streptococci such as Streptococcus
agalactiae , coliform bacteria, and Myco-
plasma spp. Other pathogens not associated
with mastitis may also be excreted such
as Mycobacterium bovis, Brucella abortus,
Coxiella burnetii , and Salmonella spp.
Udder Exterior
Much lower contamination of teat and udder
surfaces is apparent during the summer
months in temperate climates when the cows
are out at pasture, compared to the winter,
when they are housed indoors. This is due to
the heavy contamination of bedding material
which can be as high as 10^8 to 10^10 cfu/g. The
microfl ora of the teat and udder exterior is
comprised mainly of Micrococcus spp. and
coagulase - negative staphylococci but also
includes members of the genera Enterococcus,
Bacillus, Clostridium, Yersinia, Aerobacter ,
and Listeria. Among the Bacillus spp. found,
B. licheniformis and B. subtilis are the most
common species.
Milk Contact Surfaces and
Rinse Water
Bacteria may grow in rinse water still remain-
ing after cleaning, particularly if milk resi-