Abstract:
The current study was undertaken to characterize
Escherichia coli and other Enterobacteriaceae in raw and
pasteurized producer-distributor bulk milk (PDBM).
A total of 258 samples were collected from purchase
points in 8 provinces in South Africa. The samples
were tested for antibiotic residues, phosphatase, total
aerobic bacteria, coliforms, and E. coli counts. Matrixassisted
laser desorption/ionization time-of-flight mass
spectrometry was used for identification of isolates.
Escherichia coli isolates were characterized for virulence
factors, antimicrobial resistance, serotypes, and
presumptive E. coli O157:H7. Antibiotic residues and
alkaline phosphatase were detected in 2% of both raw
and pasteurized PDBM (n = 258) and 21% pasteurized
PDBM (n = 104) samples, respectively. A total
of 729 isolates belonging to 21 genera and 59 species
were identified. Escherichia coli, Enterobacter cloacae,
Klebsiella oxytoca, and Raoultella ornithinolytica were
the most abundant species. Spoilage Enterobacteriaceae
species exceeded 50% of the total isolates. Escherichia
coli was detected and isolated from 36% of the milk
samples. Thirty-one E. coli isolates harbored virulence
genes stx1/stx2 and 38% (n = 121) were presumptive
O157:H7. The prevalence of samples with presumptive
shigatoxin producing E. coli was 10%. Antimicrobialresistant
E. coli isolates were detected in 70% of the
milk samples with 36% of stx1/stx2 positive E. coli
showing multi-drug resistance. Information obtained
from the study will be used for modeling the public
health risk posed by milkborne pathogens in PDBM,
which in many cases is consumed by poor and vulnerable
members of the population.
