Identification and Characterization of Elevated Microbial Counts in Bulk Tank Raw Milk

Abstract

The bacterial composition of bulk tank milk from 13 farms was examined over a 2-wk period to characterize sudden elevations in the total bacterial count referred to as "spikes." Bulk tank milk samples collected at each pick-up were analyzed for standard plate count, Petrifilm aerobic count, somatic cell count, gram-negative organisms, and streptococci. Twenty standard plate count spikes were observed: 12 associated with streptococci, 4 associated with gram-negative organisms, 2 associated with streptococci and gram-negative organisms, and 2 that were not definitively characterized. Spikes ranged from 14,000 to 600,000 cfu/ml. Streptococcus uberis was isolated as the predominant organism from 11 spikes, and Escherichia coli was isolated from 4 spikes. Statistical analysis of total bacterial counts indicated a high correlation (r = 0.94) between standard plate counts and Petrifilm aerobic count. Regression analysis of standard plate counts and Petrifilm aerobic counts yielded the equation log10 (standard plate count) = 0.73 + 0.85log10 (Petrifilm aerobic count), indicating that the correlation, although strong, is not one to one. In a related pilot study, triplicate bulk tank milk samples were collected and analyzed for total bacterial count and presumptive streptococcus, gram-negative, and staphylococcus counts. Two-way ANOVA of these triplicate data indicated a lack of significant variation among the triplicate samples, suggesting that one sample can reliably gauge the microbial status of the entire bulk tank.

Relationship between total bacteria counts and somatic cell counts from mammary quarters infected by mastitis pathogens

“…However, linear regression slopes predicted that the same increasing SCC was associated with different numbers of bacteria being shed from the mammary gland according to mastitis pathogen. These results showed that S. agalactiae and other streptococci can cause TBC peaks in bulk tank milk (HAYES et al, 2001;ZADOKS et al, 2004). As mentioned previously, the magnitude of the peak of bulk tank milk TBC will depend on the percentage of infected mammary quarters, the strain of bacteria and stage of infection.…”

“…This correlation was fewer compared to S. aureus, other streptococci, CNS and coliform bacteria. However, S. uberis was identified as a mastitis pathogen causing TBC peaks in bulk tank milk, ranging from 14,000 to 600,000cfu mL -1 (HAYES et al, 2001;ZADOKS et al, 2004). Thus, the impact of mastitis pathogens on bulk tank TBC depends on the percentage of infected mammary quarters and type of bacterial mastitis pathogen involved.…”

Monitoring udder health and milk quality using somatic cell counts

“…Furthermore, farms with high SCC levels more often had high PLC levels. This finding may imply that subclinical mastitis cases cause an increase in bulk milk bacteria count [19]. However, herds with subclinical mastitis may also have problems in the area of general hygiene and milking equipment cleaning and disinfection [1,2].…”

Effect of omitting teat preparation on bacterial levels in bulk tank milk

“…The bacterial levels observed in milk may be influenced by teat preparation practices, sanitation of the milking equipment and the milk storage efficiency (Hayes et al, 2001;Chambers, 2002;Ruegg and Reinemann, 2002;Elmoslemany et al, 2009). Likewise, the presence of thermoduric bacteria in milk is used as an indicator of parlour and equipment hygiene (Jayarao and Wolfgang, 2003).…”