Identification and characterization of elevated microbial counts in bulk tank raw milk.
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.
Hayes
M C
MC
Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
Ralyea
R D
RD
Murphy
S C
SC
Carey
N R
NR
Scarlett
J M
JM
Boor
K J
KJ
D000818:Animals; D002452:Cell Count; D015169:Colony Count, Microbial; D006090:Gram-Negative Bacteria / Q000145:classification / Q000302:isolation & purification*; D008892:Milk / Q000382:microbiology*; D011786:Quality Control; D012044:Regression Analysis; D013291:Streptococcus / Q000145:classification / Q000302:isolation & purification*