Detection of Bacillus Species in Milk and Milk Products
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Date
2006
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Publisher
TANUVAS, Chennai
Abstract
The project was aimed at isolating and identifying different Bacillus
species occurring in milk and milk products and to study the incidence,
psychrotrophic nature, proteolytic and lipolytic activities and toxigenicity on
the isolated Bacillus cereus.
Fifty nine raw milk, 60 pasteurized milk, 24 cream, 39 butter,
27 curd, 19 peda, 21 paneer and 20 skim milk powder samples were
collected for the study. A total of 182 Bacillus isolates viz. Bacillus subtilis
(51), Bacillus megaterium (39), Bacillus cereus (28), Bacillus licheniformis
(32), Bacillus coagulans (7), Bacillus sphaericus (8), Bacillus pumilus (9)
and Bacillus circulans (8) were identified.
The mean total viable count (log10 cfu per ml) of raw milk samples
from farm, processing dairies and local vendors was 6.42 ± 0.042,
7.62 ± 0.045 and 7.59 ± 0.067 and the mean aerobic spore count was
4.98 ± 0.029, 5.18 ± 0.033 and 5.03 ± 0.039 respectively.
The mean total viable count (log10 cfu per ml) of pasteurized milk
samples obtained from nine different processing dairies, dairy 7 gave a
lower count of 4.18 ± 0.095 whereas dairy 2 had the highest count of
4.43 ± 0.081. The count in the lab pasteurized samples was the lowest
(3.65 ± 0.078). The mean aerobic spore count was lower in dairy 1
(3.56 ± 0.051) and highest in dairy 2 (3.87 ± 0.112). The lab pasteurized
samples showed the lowest count of 3.09 ± 0.085.
The mean total viable count (log10 cfu per ml) of cream samples from
local vendor and organized dairies was 6.07 ± 0.035 and 5.34 ± 0.040 and
the mean aerobic spore count was 4.57 ± 0.034 and 4.07 ± 0.027
respectively. The mean total viable count (log10 cfu per ml) of butter
samples from organized dairies and local vendors was 5.61 ± 0.027 and
7.06 ± 0.032 and the mean aerobic spore count was 3.54 ± 0.028 and
3.98 ± 0.030 respectively.
The mean total viable count (log10 cfu per ml) of curd samples
obtained from organized dairies and local vendors was 7.74 ± 0.039 and
7.96 ± 0.038 and the mean aerobic spore count was 4.73 ± 0.037 and
5.07 ± 0.062 respectively. The mean total viable count (log10 cfu per ml) of
peda samples collected from organized dairies and local vendors was
4.39 ± 0.053 and 6.16 ± 0.030 and the mean aerobic spore count was
3.71 ± 0.042 and 5.08 ± 0.036 respectively.
The mean total viable count (log10 cfu per ml) of paneer samples
collected from organized dairies and local markets was 5.65 ± 0.061 and
7.62 ± 0.067 and the mean aerobic spore count was 3.67 ± 0.059 and
4.90 ± 0.054 respectively. The mean total viable count (log10 cfu per ml) of
skim milk powder samples from organized government and private dairies
was 4.55 ± 0.028 and 4.68 ± 0.044 and the mean aerobic spore count was
3.54 ± 0.033 and 3.72 ± 0.047 respectively.
The total number of isolates positive for proteolysis were
Bacillus subtilis 27, Bacillus megaterium 23, Bacillus cereus 18,
Bacillus licheniformis 14, Bacillus coagulans 7, Bacillus sphaericus 6,
Bacillus pumilus 7 and Bacillus circulans 6.
The extent of proteolysis, estimated by decrease in casein nitrogen
to true protein (CN/TP) percentage was the highest in Bacillus subtilis
(4.82) followed by Bacillus cereus (4.15), Bacillus licheniformis (4.08),
Bacillus megaterium (3.52), Bacillus circulans (2.89), Bacillus coagulans
(2.79), Bacillus sphaericus (2.71) and Bacillus pumilus (2.56).
The total number of isolates positive for lipolysis was Bacillus subtilis
31, Bacillus cereus 12, Bacillus licheniformis 23 and Bacillus pumilus 6.
Bacillus pumilus produced significantly more lipolysis (0.233 µEq/ml) than
Bacillus cereus (0.222 µEq/ml) followed by Bacillus licheniformis
(0.212 µEq/ml) and Bacillus subtilis (0.205 µEq/ml).
The number of psychrotrophic Bacillus isolates obtained was
Bacillus subtilis 9, Bacillus megaterium 17, Bacillus cereus 12, Bacillus
licheniformis 6, Bacillus coagulans 2, Bacillus sphaericus 1 and Bacillus
pumilus 2.
Twenty eight Bacillus cereus isolates obtained in this study were
analyzed for the presence of 365 bp fragment by PCR and all isolates were
positive confirming their status as Bacillus cereus. Two isolates of Bacillus
cereus were found to be toxigenic and one isolate harboured all the five
genes of B, B’, L1, L2 and ET of the HBL-ET complex whereas the other
one contained four genes in which the B’ component was missing.
Both the toxigenic strains of Bacillus cereus produced similar
discontinuous haemolysis pattern on blood agar and cytotoxic effect on
Vero cell line.
The overall incidence of aerobic spore formers was less when
compared to the total viable count. Because of their proteolytic and lipolytic
activity and resistance to high temperature by forming spores,
contamination of milk and milk products by Bacillus species have to be
controlled by adopting hygiene at the farm level during milk production,
transport, processing, storage and distribution. Storage of milk and milk
products under refrigerated temperature will help to control the proliferation.
Description
Keywords
Veterinary Science, Dairy Science