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Growth characteristics of Staphylococcus aureus and Escherichia coli in whey from sequentially infected milk
T Mattila-Sandholm1, T Alivehmas, L Kaartinen
1Food Research Laboratory, Technical Research Centre, Espoo, Finland.
Abstract:
The growth of Staphylococcus aureus and Escherichia coli was followed in bovine whey samples which had been prepared from milk previously incubated with cultures of S. aureus or E. coli. Staphylococcal strains were divided into 2 groups according to their ability to form compact or diffuse colonies on serum soft agar, which is related to the absence or presence of capsule respectively. The growth of compact staphylococci was dependent on the bulk tank milk used whereas diffuse colony forming staphylococci grew equally well in all bulk milk, also in all inoculated milk. The growth of E. coli was markedly enhanced in whey samples prepared from milk preincubated with staphylococci. However, clear growth inhibition was seen with E. coli and S. aureus strains when grown in whey prepared from milk preincubated with E. coli. Results indicate that the growth promotion of pathogens due to compositional changes in milk are of importance during the course of infection because the growth pattern on staphylococci is dependent on these compositional changes. The growth-inhibitory effects caused by E. coli may explain difficulties in isolating this organism.
Insights
Bovine whey composition affects pathogen growth. Staphylococcus aureus growth varied, while Escherichia coli growth was enhanced by S. aureus but inhibited by E. coli, impacting infection dynamics.
Area of Science:
- Microbiology
- Food Science
- Animal Science
Background:
- Bovine milk composition influences microbial growth.
- Pathogenic bacteria like Staphylococcus aureus and Escherichia coli can contaminate milk.
- Understanding their growth dynamics is crucial for food safety and animal health.
Purpose of the Study:
- To investigate the impact of milk pre-incubation with S. aureus and E. coli on subsequent pathogen growth in bovine whey.
- To determine how staphylococcal colony morphology (capsule presence) affects its growth in different milk matrices.
- To elucidate the interactions between S. aureus and E. coli in whey.
Main Methods:
- Preparation of bovine whey from milk pre-incubated with S. aureus or E. coli.
- Culturing of S. aureus (compact and diffuse colony types) and E. coli in prepared whey samples.
- Monitoring and comparison of bacterial growth rates.
Main Results:
- Compact colony-forming S. aureus growth was dependent on the bulk tank milk source.
- Diffuse colony-forming S. aureus and E. coli showed less dependency on milk source.
- E. coli growth was enhanced in whey pre-incubated with S. aureus.
- Both S. aureus and E. coli exhibited growth inhibition in whey pre-incubated with E. coli.
Conclusions:
- Milk compositional changes induced by initial microbial contamination significantly affect subsequent pathogen growth.
- Staphylococcal growth patterns are influenced by milk matrix properties.
- E. coli exhibits both growth-promoting (with S. aureus) and growth-inhibitory (with E. coli) interactions, potentially affecting isolation and infection outcomes.