• Detection of presumptive Bacillus cereus in the Irish dairy farm environment

      O'Connell, Aine; Lawton, Elaine M.; Leong, Dara; Cotter, Paul D.; Gleeson, David E; Guinane, Caitriona M.; Teagasc Walsh Fellowship Programme (Teagasc (Agriculture and Food Development Authority), Ireland, 30/01/2016)
      The objective of the study was to isolate potential Bacillus cereus sensu lato (B. cereus s.l.) from a range of farm environments. Samples of tap water, milking equipment rinse water, milk sediment filter, grass, soil and bulk tank milk were collected from 63 farms. In addition, milk liners were swabbed at the start and the end of milking, and swabs were taken from cows’ teats prior to milking. The samples were plated on mannitol egg yolk polymyxin agar (MYP) and presumptive B. cereus s.l. colonies were isolated and stored in nutrient broth with 20% glycerol and frozen at -80 °C. These isolates were then plated on chromogenic medium (BACARA) and colonies identified as presumptive B. cereus s.l. on this medium were subjected to 16S ribosomal RNA (rRNA) sequencing. Of the 507 isolates presumed to be B. cereus s.l. on the basis of growth on MYP, only 177 showed growth typical of B. cereus s.l. on BACARA agar. The use of 16S rRNA sequencing to identify isolates that grew on BACARA confirmed that the majority of isolates belonged to B. cereus s.l. A total of 81 of the 98 isolates sequenced were tentatively identified as presumptive B. cereus s.l. Pulsed-field gel electrophoresis was carried out on milk and soil isolates from seven farms that were identified as having presumptive B. cereus s.l. No pulsotype was shared by isolates from soil and milk on the same farm. Presumptive B. cereus s.l. was widely distributed within the dairy farm environment.
    • Farm management factors associated with the Bacillus cereus count in bulk tank milk

      O'Connell, Aine; Ruegg, P.L.; Gleeson, David E; Teagasc Walsh Fellowship Programme (Teagasc (Agriculture and Food Development Authority), Ireland, 2013)
      The objective of this study was to determine the on-farm management factors that are associated with the Bacillus cereus count in raw bulk tank milk using a cross sectional study design. Bulk tank milk quality was monitored for B. cereus on 63 dairy farms between July and August 2012. Bulk tank milk samples corresponding with processor milk collection dates were taken over a two week period prior to the farm visit and tested for B. cereus. The four most recent samples taken prior to the on-farm visit were averaged and log transformed to give the outcome variable; mean log10 B. cereus cfu/mL. On-farm data collection included recording observations and providing a questionnaire on basic hygiene, management factors and cow hygiene scoring. All independent variables were analysed individually with the outcome variable using simple linear regression and one-way ANOVA; a multivariable regression model was subsequently developed. Only significant variables were retained in the final model (P < 0.05). The geometric mean B. cereus count for all milk samples was 40 cfu/mL. The start temperature of the cleaning solution wash, dry wiping teats prior to unit application, the feeding of silage and reusing the cleaning solution more than once were all unconditionally associated (P < 0.10) with the B. cereus count in bulk tank milk but did not enter the final multivariable model. B. cereus count was four times greater (201 cfu/mL) when cows had been housed compared to when they were on pasture (50 cfu/mL). The allocation of fresh grass every 12 h (62 cfu/mL) resulted in a decrease in B. cereus count (166cfu/mL every 24 h or greater). The testing of water for bacteriology was associated with an increase in B. cereus count. In conclusion, this study highlights specific management factors associated with the B. cereus count in bulk tank milk.
    • Review of potential sources and control of thermoduric bacteria in bulk-tank milk

      Gleeson, David E; O'Connell, Aine; Jordan, Kieran; Irish Dairy Levy Research Trust (Teagasc (Agriculture and Food Development Authority), Ireland, 2013)
      Bacteria that contaminate milk include thermoduric bacteria that can survive pasteurisation and subsequently grow in the pasteurised milk or contaminate product. Elimination of thermodurics at milking is not feasible. Therefore, knowledge of their source and strategies for their reduction are important. The major sources of thermodurics in milk are contamination of the teat skin from soil and bedding, and subsequent contamination from deposits that can build up on milking equipment surfaces. Hygiene at milking can reduce the number of bacteria contaminating milk. Teat preparation at milking and a recommended plant cleaning procedure are critical to the prevention of the contamination of milk with thermoduric bacteria.