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Beta-lactamase-producing mutants of Streptococcus cremoris

L Khosravi1, W E Sandine

  • 1Department of Microbiology, Oregon State University, Corvallis 97331-3804.

Journal of Dairy Science
|August 1, 1987
PubMed

Insights

Penicillin-resistant Streptococcus cremoris mutants were developed for cheese production. These mutants produce beta-lactamase, conferring resistance to penicillin and related antibiotics, with stable resistance observed over passages.

Area of Science:

  • Food Microbiology
  • Bacteriology
  • Antibiotic Resistance

Background:

  • Streptococcus cremoris is crucial for Cheddar cheese fermentation.
  • Penicillin is used to control spoilage organisms but can affect starter cultures.
  • Developing penicillin-resistant strains could improve cheese production consistency.

Purpose of the Study:

  • To isolate and characterize penicillin-resistant mutants of Streptococcus cremoris.
  • To investigate the mechanism of penicillin resistance in these mutants.
  • To assess the stability and phage sensitivity of the resistant strains.

Main Methods:

  • Induction of mutations using N-methyl-N-nitro-N-nitrosoguanidine.
  • Determination of minimal inhibitory concentrations for penicillin G and beta-lactam antibiotics.
  • Assay for beta-lactamase production.
  • Plasmid DNA analysis and phage sensitivity testing.

Main Results:

  • Six penicillin-resistant mutants of S. cremoris were successfully isolated.
  • Resistant mutants showed a 50-fold increase in minimal inhibitory concentration for penicillin G.
  • Resistance was attributed to beta-lactamase production; plasmid DNA was not detected.
  • Mutants exhibited altered phage sensitivity patterns but retained resistance after 20 passages.

Conclusions:

  • Penicillin-resistant Streptococcus cremoris mutants can be generated and maintain resistance.
  • Beta-lactamase production is the primary mechanism for penicillin resistance in these strains.
  • These resistant mutants have potential applications in cheese manufacturing to mitigate penicillin contamination issues.

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