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[Pseudomonas aeruginosa in raw and pasteurized milk]
Abstract:
Eighteen strains of Pseudomonas aeruginosa, i.e. 8.87%, were isolated during a year from 203 samples of raw milk. Two Pseudomonas aeruginosa strains, i.e. 4%, were isolated from 50 samples of pasteurized milk. The strains were isolated using propagation techniques in meat-peptone broth with malachite green and on selective media--on centrimide agar (CEM) and on Pseudomonas F agar. All the isolated strains produced protease, whereas lipase was produced by only five strains. The strains were devitalized when exposed to pasteurization temperatures (72 degrees C) for 20 seconds. At cold store temperatures (4 degrees C), Pseudomonas aeruginosa strain cells propagated on average by two orders, inhibitory effects of low temperatures were recorded only with one strain. Inhibitory effects of milk cultures (cream, yogurt) on Pseudomonas aeruginosa were observed; their effects were more clear-cut at the temperature of 4 degrees C. The strains were markedly susceptible to gentamycin.
Insights
Pseudomonas aeruginosa was found in raw and pasteurized milk. While heat killed most strains, cold temperatures and milk cultures inhibited growth, with gentamycin proving effective.
Area of Science:
- Food microbiology
- Dairy science
- Bacterial contamination
Background:
- Pseudomonas aeruginosa is an opportunistic pathogen that can contaminate milk supplies.
- Raw milk poses a higher risk for bacterial contamination compared to pasteurized milk.
Purpose of the Study:
- To isolate and characterize Pseudomonas aeruginosa from raw and pasteurized milk.
- To evaluate the survival and growth of Pseudomonas aeruginosa under different temperature conditions.
- To assess the efficacy of milk cultures and antibiotics against Pseudomonas aeruginosa.
Main Methods:
- Isolation of Pseudomonas aeruginosa using selective media (centrimide agar, Pseudomonas F agar) and broth enrichment.
- Detection of protease and lipase production by isolated strains.
- Exposure of strains to pasteurization temperatures (72°C for 20 seconds) and cold storage (4°C).
- Assessment of inhibitory effects of milk cultures (cream, yogurt) and gentamycin.
Main Results:
- Pseudomonas aeruginosa was isolated from 8.87% of raw milk samples and 4% of pasteurized milk samples.
- All isolates produced protease; five also produced lipase.
- Pasteurization temperatures effectively devitalized the strains.
- Cold storage (4°C) promoted growth of most strains, with limited inhibitory effects observed.
- Milk cultures demonstrated inhibitory effects, particularly at 4°C.
- All strains were highly susceptible to gentamycin.
Conclusions:
- Pseudomonas aeruginosa can be present in both raw and pasteurized milk, though at lower levels in pasteurized products.
- Standard pasteurization effectively eliminates Pseudomonas aeruginosa.
- Cold storage may not be sufficient to inhibit Pseudomonas aeruginosa growth in milk.
- Certain milk-derived products and gentamycin show potential for controlling Pseudomonas aeruginosa contamination.