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Stimulation of Streptococcus thermophilus growth in mastitic milk
Abstract:
Growth of Streptococcus thermophilus was faster in mastitic milk, aseptically collected following intramammary infusion of Escherichia coli endotoxin, than in normal aseptically collected milk. The contribution of polymorphonuclear leucocytes (PMN), of plasma and plasmin to this stimulation has been investigated. Addition of plasmin to low cell count milk stimulated growth of the streptococcus to the same degree as mastitic milk. However, addition of plasma or PMN from blood or from milk were less stimulatory. The part played by these components in providing casein breakdown products for the weakly proteolytic Str. thermophilus in mastitic milk is discussed.
Insights
Mastitic milk enhances Streptococcus thermophilus growth due to plasmin, an enzyme that breaks down casein. Other milk components like plasma and polymorphonuclear leucocytes (PMN) showed less growth stimulation.
Area of Science:
- Microbiology
- Animal Science
- Biochemistry
Background:
- Mastitis, an inflammation of the mammary gland, alters milk composition.
- Streptococcus thermophilus is a key bacterium in dairy fermentation.
- Understanding factors influencing bacterial growth in milk is crucial for dairy production.
Purpose of the Study:
- To investigate the factors contributing to enhanced Streptococcus thermophilus growth in mastitic milk.
- To determine the specific roles of polymorphonuclear leucocytes (PMN), plasma, and plasmin in stimulating bacterial growth.
Main Methods:
- Aseptic milk collection from cows infused with Escherichia coli endotoxin to induce mastitis.
- Addition of purified plasmin, plasma, and PMN to low cell count milk.
- Monitoring and comparison of Streptococcus thermophilus growth rates in different milk samples.
Main Results:
- Streptococcus thermophilus exhibited significantly faster growth in mastitic milk compared to normal milk.
- Addition of plasmin to milk markedly stimulated bacterial growth, comparable to mastitic milk.
- Plasma and PMN showed a lesser stimulatory effect on Streptococcus thermophilus growth.
Conclusions:
- Plasmin is a key factor in promoting Streptococcus thermophilus growth in mastitic milk.
- Casein breakdown products, facilitated by plasmin, likely support the growth of this weakly proteolytic bacterium.
- Further research can explore targeted interventions to manage bacterial growth in mastitic milk.