Characterization of Escherichia coli and other Enterobacteriaceae in producer-distributor bulk milk

Abstract

INTERPRETIVE SUMMARYCharacterization of E. coli and other Enterobacteriaceae in producer-distributor bulk milk, Ntuli, The direct sale of milk from producer-distributor (PD) to consumers is a common practice in many countries. We characterized E. coli and other Enterobacteriaceae in PD bulk milk sold at retail points in South Africa (SA). The study highlighted that there is a potential risk of transferring drug resistant pathogenic E. coli to consumers through the food chain.Information obtained from the study will be used to model the risk of pathogenic E. coli in PD milk and the proposal of most potentially effective mitigation efforts towards enhancing food security. ABSTRACTThe 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 1 antibiotic residues, phosphatase, total aerobic bacteria, coliforms and E. coli counts. Matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used for identification of isolates. E. 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 % (n=258) and 21 % (n=104) of the samples respectively. A total of 729 isolates belonging to 21 genera and 59 species were identified. E. coli, Enterobacter cloacae, Klebsiella oxytoca and Raoultella ornithinolytica were the most abundant species. Spoilage Enterobacteriaceae species exceeded 50 % of the total isolates. E. 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. Prevalence of samples with presumptive shigatoxin producing E. coli (STEC) 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 modelling the public health risk posed by milkborne pathogens in PDBM, which in many cases is consumed by the poor and vulnerable population.

The main spoilage-related psychrotrophic bacteria in refrigerated raw milk

“…This species was also the most frequently identified among lipolytic psychrotrophic microorganisms. Considering the totality of the psychrotrophic microbiota of raw milk, Ntuli et al (2016) identified E. kobei in 0.8% of the 479 isolates. This bacterium belongs to the family Enterobacteriaceae, making it possible that the raw milk in the present study was contaminated directly or indirectly by feces.…”

Enteroaggregative Escherichia coli is the predominant diarrheagenic E. coli pathotype among irrigation water and food sources in South Africa

“…This bacterial collection included 48 isolates from irrigation water (Aijuka et al, 2015;Aijuka, 2014), 29 from irrigated lettuce (Aijuka, 2014), 118 from milk (pasteurized and unpasteurized PDBM) sold by small holder sellers (producerdistributer) (Ntuli et al, 2016) and 10 from street-vendor coleslaw purchased in Pretoria City, South Africa. All isolates collected over these studies were stored at -80°C at the Department of Food Science, University of Pretoria, South Africa in Tryptone Soy Broth (TSB)(Biolab Diagnostics (Pty) Ltd, Midrand, South Africa) containing 30% glycerol (Sigma-Aldrich, St.…”

“…The first study was initiated by The South African Department of Agriculture and Water Research Commission to help characterize the bacterial quality of South African irrigation water (Aijuka et al, 2015). A high prevalence of faecal indicators within milk sold by unregulated retailers alarmed the South African Dairy Development Agency which subsequently initiated the second study to characterize its microbiological quality (Ntuli et al, 2017(Ntuli et al, , 2016.…”

Real‐time loop‐mediated isothermal amplification assays combined with ethidium monoazide bromide and bentonite coated activated carbon for rapid and sensitive detection of viable Escherichia coli O157:H7 from milk without enrichment

“…Ntuli, Njage, and Buys () reported that the prevalence of E. coli O157:H7 in bulk milk samples was in the range of 2%, varied from 13% in Australian, 0.02–2.4% in U.S. and 0.7% in Greek. Zhang et al () investigated 183 chicken samples in 4 provinces (14 cities) of South China by plate count method, and the prevalence of E. coli O157:H7 was 3.28%.…”

“…Another is that VT2-producing E. coli has many serotypes and all are regarded as pathogens, although O157 predominates. The primers designed according to VT2 gene can detect any bacteria carrying VT2 gene(Hara-Kudo et al, 2007) Ntuli, Njage, and Buys (2016). reported that the prevalence of E. coli O157:H7 in bulk milk samples was in the range of 2%, varied from 13% in Australian, 0.02-2.4% in U.S. and 0.7% in Greek Zhang et al (2015).…”