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Identification and characterization of elevated microbial counts in bulk tank raw milk
M C Hayes1, R D Ralyea, S C Murphy
1Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
Journal of Dairy Science
|February 24, 2001
Summary
Sudden bacterial count elevations, or "spikes," in bulk tank milk are often linked to Streptococcus uberis and Escherichia coli. These spikes, ranging up to 600,000 cfu/ml, can be monitored using standard plate counts and Petrifilm aerobic counts.
Area of Science:
- Dairy microbiology
- Food safety and quality control
Background:
- Bulk tank milk bacterial counts can experience sudden elevations, termed "spikes."
- Understanding the microbial causes of these spikes is crucial for maintaining milk quality.
Purpose of the Study:
- To characterize the bacterial composition during sudden elevations in total bacterial counts (spikes) in bulk tank milk.
- To identify the predominant bacterial species associated with these spikes.
Main Methods:
- Analysis of bulk tank milk samples from 13 farms over a 2-week period.
- Microbial analysis included standard plate count (SPC), Petrifilm aerobic count (PAC), somatic cell count, gram-negative, and streptococci enumeration.
- Isolation and identification of predominant bacterial organisms.
Main Results:
- Twenty SPC spikes were observed, with 12 linked to streptococci and 4 to gram-negative organisms.
- Streptococcus uberis was the predominant isolate in 11 spikes, and Escherichia coli in 4 spikes.
- A strong correlation (r = 0.94) was found between SPC and PAC, though not a one-to-one relationship.
Conclusions:
- Streptococci and gram-negative bacteria, particularly Streptococcus uberis and Escherichia coli, are key contributors to bacterial spikes in bulk tank milk.
- Standard plate count and Petrifilm aerobic count are reliable, correlated methods for monitoring bacterial levels.
- A single bulk tank milk sample can represent the overall microbial status of the tank.