Browsing by Author "Ervasti, Elisa"

Small colony variants are exceptional form from the wild type bacteria. Most specific feature for small colony variants is significantly smaller colony that can be 1/10 of the size of the original colony. Other features are slow growth and weakened pigmentation. Small colony variants are usually more resistant to antibiotics. Small colony variants have been discovered for many different species, from which S. aureus is the most investigated one. For Bacillus species small colony variants have been discovered for B. weihenstephanensis, B. licheniformis, B. cereus and B. subtilis -bacteria. B. weihenstephanensis is a spore forming and psychotropic bacteria that has been shown to grow in milk and dominate milks microbiota during long cold storage. B. weihenstephanensis bacteria have also been shown to resist nitrogen flushing that has been investigates to longen milks shelf-life. Purpose of this study was to compare the original strain of B. weihenstephanensis to its small colony variants that were discovered during flushing with nitrogen gas. In this study the original strains growth in different temperatures, utilization of carbohydrates and antibiotic resistance was compared to its small colony variants. In this study multiple strains of B. weihenstephanensis were analyzed, other were the original strains and others their small colony variant. Original strains were flushed in nitrogen gas in 15 °C temperature in milk, to see if small colonies would appear, but no stable small colonies appeared during the treatment. Nitrogen gas flushing inhibited the bacterial growth. Bacterial strains in this thesis grew well in 12, 30 and 37 °C temperature and some strains even grew in 43 °C temperature, but no great difference in bacterial growth between two growth media, UHT -milk and BHI -broth were detected. Differences in carbohydrate metabolism were identified with API 50 CH and microplate PM1 methods. According to ATB VET method there was a difference in antibiotic resistance between original strains and their small colony variants, but no difference was identified with microplate PM15. According to this master thesis there were differences between parental strain and its small colony variant in growth, carbohydrate metabolism and antibiotic resistance. As there phenotypic methods results were not compatible with each other, to confirm the discoveries repeats of these analyses are recommended in addition to genotypic methods.