title: Characterization of Escherichia coli and other Enterobacteriaceae in producer-distributor bulk milk.
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. Matrix-assisted 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%. Antimicrobial-resistant 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.
authors.affiliation: Department of Food Science, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa.
authors.forename: V
authors.initials: V
authors.lastname: Ntuli
authors.affiliation: Department of Food Science, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa.
authors.forename: P M K
authors.initials: PMK
authors.lastname: Njage
authors.affiliation: Department of Food Science, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa. Electronic address: Elna.Buys@up.ac.za.
authors.forename: E M
authors.initials: EM
authors.lastname: Buys
mesh_terms: D000818:Animals; D004755:Enterobacteriaceae / Q000302:isolation & purification; D004926:Escherichia coli / Q000302:isolation & purification*; D019453:Escherichia coli O157 / Q000302:isolation & purification; D029968:Escherichia coli Proteins / Q000235:genetics; D008892:Milk / Q000382:microbiology*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins; D037521:Virulence Factors
keywords: Enterobacteriaceae; Escherichia coli; antibiotic resistance; producer-distributor milk; shigatoxin