Longitudinal Study of Shiga Toxin-Producing Escherichia coli and Campylobacter jejuni on Finnish Dairy Farms and in Raw Milk

• Published in: Applied and environmental microbiology Vol. 85; no. 7
• Main Authors: Jaakkonen, Anniina, Castro, Hanna, Hallanvuo, Saija, Ranta, Jukka, Rossi, Mirko, Isidro, Joana, Lindström, Miia, Hakkinen, Marjaana
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01-04-2019
• Subjects: Agricultural pollution; Agricultural practices; Animals; Bacteria; Bovidae; Campylobacter; Campylobacter jejuni; Campylobacter jejuni - classification; Campylobacter jejuni - genetics; Campylobacter jejuni - isolation & purification; Cattle; Consumption; Contamination; Correlation analysis; Culling; Dairy cattle; Dairy farming; Dairy farms; Dairying - instrumentation; Dairying - methods; E coli; Epidemiology; Escherichia coli; Escherichia coli O157 - genetics; Escherichia coli O157 - isolation & purification; Farm management; Farms; Fecal coliforms; Feces; Feces - microbiology; Female; Filters; Finland; Food contamination; Food contamination & poisoning; Food Microbiology; Genomics; Genotype; Genotypes; Health hazards; Health risks; Heat treatment; Hygiene; Intestine; Legislation; Longitudinal Studies; Milk; Milk - microbiology; Milking; Milking machines; Multilocus Sequence Typing; Pathogens; Phylogeny; Risk Factors; Risk management; Sampling; Shedding; Shiga toxin; Shiga Toxin - genetics; Shiga-Toxigenic Escherichia coli - classification; Shiga-Toxigenic Escherichia coli - genetics; Shiga-Toxigenic Escherichia coli - isolation & purification; Stx gene; Whole Genome Sequencing; Finland; milk; STEC; genomics; cattle; Escherichia coli; Campylobacter jejuni
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.02910-18

Shiga toxin-producing
(STEC) and
are notable health hazards associated with the consumption of raw milk. These bacteria may colonize the intestines of asymptomatic cattle and enter bulk tank milk via fecal contamination during milking. We studied the frequency of STEC O157:H7 and
contamination in tank milk (
 = 785) and the in-line milk filters of milking machines (
 = 631) versus the frequency of isolation from cattle feces (
 = 257) on three Finnish dairy farms for 1 year. Despite simultaneous isolation of STEC O157:H7 (17%) or
(53%) from cattle, these bacteria were rarely isolated from milk filters (2% or <1%, respectively) and milk (0%). As revealed by phylogenomics, one STEC O157:H7 strain at a time was detected on each farm and persisted for ≤12 months despite rigorous hygienic measures.
strains of a generalist sequence type (ST-883 and ST-1080) persisted in the herds for ≥11 months, and several other
types were detected sporadically. The
gene carried by STEC was detected more frequently from milk filters (37%) than from milk (7%), suggesting that milk filters are more suitable sampling targets for monitoring than milk. A questionnaire of on-farm practices suggested lower
contamination of milk when major cleansing in the barn, culling, or pasturing of dairy cows was applied, while a higher average outdoor temperature was associated with higher
contamination. Because pathogen contamination occurred despite good hygiene and because pathogen detection from milk and milk filters proved challenging, we recommend heat treatment for raw milk before consumption.
The increased popularity of raw milk consumption has created demand for relaxing legislation, despite the risk of contamination by pathogenic bacteria, notably STEC and
However, the epidemiology of these milk-borne pathogens on the herd level is still poorly understood, and data are lacking on the frequency of milk contamination on farms with cattle shedding these bacteria in their feces. This study suggests (i) that STEC contamination in milk can be reduced, but not prevented, by on-farm hygienic measures while fecal shedding is observable, (ii) that milk filters are more suitable sampling targets for monitoring than milk although pathogen detection from both sample matrices may be challenging, and (iii) that STEC and
genotypes may persist in cattle herds for several months. The results can be utilized in developing and targeting pathogen monitoring and risk management on the farm level and contributed to the revision of Finnish legislation in 2017.