ISOLATION AND MOLECULAR CHARACTERISATION OF SOME BACTERIA FROM FRESH RAW COW MILK AND HANDLERS IN ZARIA METROPOLIS KADUNA STATE NIGERIA
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Date
2021-01-07
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Ahmadu Bello University Zaria
Abstract
Raw cow milk is one of the most consumed products of animal origin, it is an important
component of human nutrition, especially in the period of growth. Relatively, the composition of
milk makes it an optimum medium for the growth of microorganisms, making it an efficient
vehicle for transmission of disease-causing agents to humans. It is therefore, optimally necessary
to safe guard the quality of raw milk processed all through the dairy chain. The microbiological
quality of fresh raw cow milk from four farms in Zaria metropolis, Kaduna state were evaluated.
The samples were made up of 42 raw cow milks from lactating cows available, 42 swabs from
cow teat; 16 swabs from herd handlers and 5 samples from water used in the cleaning process
making a total of 105. The total aerobic bacteria count (TABC) and total coliform count (TCC) of
raw milk were carried out using plate count method on Nutrient and MacConkey media
respectively. Serial dilutions were carried out using peptone water on all the forty-two (42) raw
milk samples. Isolation of Staphylococcus species and enteric microorganisms were carried out
using plate count method on Mannitol Salt Agar and MacConkey media respectively. The isolates
were identified using standard biochemical procedure and Microgen TM System. Antimicrobial
Susceptibility test was carried out on the identified isolates using the modified Kirby-Bauer
method. Using methods by Blanchard and Nedrud, Helicobacter pylori was cultured on blood
enriched medium supplemented with vancomycin powder. One hundred and two (102) bacteria
consisting of Seventy-six (76) Polymicrobial and twenty-six (26) single cultures were recovered
as positive culture while three (3) had no growth. No significant association was observed between
sampling location and positive bacterial recovery (0.270). The mean TABC and TCC of raw milk
observed in this study were 2.56 ± 0.40 x104cfu/ml and 1.06 ± 0.16 x104cfu/ml respectively.
Acinetobacter iwoffi and other members of Enterobacteriaceae isolates were resistant to
tetracycline (68.75%), erythromycin (71.74%) and metronidazole (100%), while Staphylococcus
species and Micrococcus luteus isolated were methicillin resistant (85%) and resistant to
tetracycline was 75%. High susceptibility was observed to gentamicin (94.34%) and
chloramphenicol (80.85%) by the Enterobacteriaceae isolates, while Chloramphenicol (90%) and
ciprofloxacin (85%) were also active against both the Staphylococcus species and M. luteus
identified in this study. Overall, about 53.8% of the isolates were multiantibiotic resistant. There
was no significant association between sample source and multi-resistance phenotype, however,
isolates from teat swabs were more likely to be non- multiantibiotic resistant (p= 0.555). No
significant association between sampling location and multi-resistance phenotype was observed
(p= 0.145). The percentage of multiple antibiotic resistance index (MARI) of greater than or equal
to 0.3 was observed to be 90% for Staphylococcus species and 92% for Enterobacteriaceae. There
was amplification of nim at 458bp from Proteus mirabilis isolated from the handler and ermB at
639bp from Pseudomonas aeruginosa and Proteus vulgaris from raw milk and S. choleraesus
from the handler. Similarly, tetA (210bp) was obtained from P. aeruginosa and P. vulgaris all from
raw milk. The amplification of cagA virulence marker of H. pylori isolated from raw milk samples
establishes the possibility of the transfer to raw milk consumers via cow milk. This study reveals
high contamination rates coupled with antibiotic resistance of the isolates in Zaria metropolis
which poses a serious therapeutic challenge to the management of food borne acquired diseases.