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Improved medium for lactic streptococci and their bacteriophages
1New Zealand Dairy Research Institute, Palmerston North, New Zealand.
Abstract:
Incorporation of 1.9% beta-disodium glycerophosphate (GP) into a complex medium resulted in improved growth by lactic streptococci at 30 C. The medium, called M17, contained: Phytone peptone, 5.0 g; polypeptone, 5.0 g; yeast extract, 2.5 g; beef extract, 5.0 g; lactose, 5.0 g; ascorbic acid, 0.5 g; GP, 19.0 g; 1.0 M MgSO(4).7H(2)O, 1.0 ml; and glass-distilled water, 1,000 ml. Based on absorbance readings and total counts, all strains of Streptococcus cremoris, S. diacetilactis, and S. lactis grew better in M17 medium than in a similar medium lacking GP or in lactic broth. Enhanced growth was probably due to the increased buffering capacity of the medium, since pH values below 5.70 were not reached after 24 h of growth at 30 C by S. lactis or S. cremoris strains. The medium also proved useful for isolation of bacterial mutants lacking the ability to ferment lactose; such mutants formed minute colonies on M17 agar plates, whereas wild-type cells formed colonies 3 to 4 mm in diameter. Incorporation of sterile GP into skim milk at 1.9% final concentration resulted in enhanced acid-producing activity by lactic streptococci when cells were inoculated from GP milk into skim milk not containing GP. M17 medium also proved superior to other media in demonstrating and distinguishing between lactic streptococcal bacteriophages. Plaques larger than 6 mm in diameter developed with some phage-host combinations, and turbid plaques, indicative of lysogeny, were also easily demonstrated for some systems.
Insights
Beta-disodium glycerophosphate (GP) supplementation in M17 medium enhances lactic streptococci growth and acid production. This improved medium aids in isolating lactose-negative mutants and distinguishing bacteriophages in lactic streptococci research.
Area of Science:
- Microbiology
- Food Science
- Bacteriology
Background:
- Lactic streptococci are crucial in dairy fermentation.
- Optimizing growth media is essential for studying these bacteria and their associated phages.
- Beta-disodium glycerophosphate (GP) is a potential growth-enhancing supplement.
Purpose of the Study:
- To evaluate the efficacy of beta-disodium glycerophosphate (GP) in a complex medium (M17) for lactic streptococci.
- To assess the utility of M17 medium for isolating bacterial mutants and studying bacteriophages.
- To investigate the impact of GP on acid production in lactic streptococci.
Main Methods:
- Formulation of M17 medium incorporating 1.9% beta-disodium glycerophosphate (GP).
- Comparative growth studies of Streptococcus cremoris, S. diacetilactis, and S. lactis in M17 versus control media.
- Assessment of M17 medium for isolating lactose-fermenting mutants and demonstrating bacteriophage plaques.
- Evaluation of GP-supplemented skim milk for enhanced acid production.
Main Results:
- M17 medium with GP significantly improved the growth of all tested lactic streptococci strains compared to media without GP.
- Enhanced buffering capacity of M17 medium prevented pH drops below 5.70, promoting sustained growth.
- M17 medium facilitated the isolation of lactose-negative mutants and improved visualization of bacteriophage plaques.
- GP incorporation into skim milk enhanced acid-producing activity of lactic streptococci.
Conclusions:
- Beta-disodium glycerophosphate (GP) supplementation in M17 medium is highly effective for lactic streptococci cultivation.
- M17 medium offers advantages for bacterial mutant isolation and bacteriophage characterization.
- GP enhances acid production in lactic streptococci, with implications for dairy fermentation processes.
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