Physiological characteristic of psychrotrophic bacilli isolated from raw milk

Abstract

The strains of genus Bacillus are often present as containments in raw milk. Their ubiquitous nature, potentiality to produce thermorcsistent spores, ability to grow and bio­chemical activity at low temperatures, so as pathogenicity of some strains have actualized their significance in food industry. The isolation of psychrotrophic bacilli was conducted after incubation of 10 days at 7±1°C (isolation is achieved only from milk samples which demonstrate the changes of Bacillus number at the start and after 10 days of incubation at 7±1°C). It was examined 56 psychrotrophic strains of bacilli isolated from raw milk. During incu­bation of 10 days at 7±1°C, in 50 samples of raw milk the number of bacilli increased from log 0.8±0.78 to 1.73±0.86, whereas in 6 samples the Bacillus number ranged from log 0.10±0.01 to 2.07±0.47. The differences between mean values of Bacillus number on the first and tenth days of incubation at low temperatures (psychrotrophic condition) were subjected to the t-test. It was noticed a highly significant difference. It was also found that 30.35% of isolated strains were heamolytic, 64.28% degraded lechitin, 5.35% broke down gelatin, 78.57%; de­graded casein. A high percentage of isolated bacilli (97.07%) grew at pH 5.7 and 78.57% multiplied in the presence of 7% NaCl.

Predstavnici roda Bacillus često su prisutni kao kontaminenti u sirovom mleku. Njihova ubikvitarnost, stvaranje tennorezistentnih spora, sposobnost rasta i biohemijska aktivnost pri niskim temperaturama kao i patogenost pojedinih sojeva aktueliziraju njihov značaj u industriji hrane. Izolacija psihrotrofnih bacila je izvedena posle inkubacije sirovog mleka ud 10 dana na 7±1°C. Psihrotrofni bacili su izolovani samo iz uzoraka koji su pokazivali promenu broja bacila na početku inkubacije I posle 10 dana inkubacije na 7±1°C. Testirana su 56 psihrolrofna soja bacila izolovana iz sirovog mleka. Broj bacila se tokom inkubacije od 10 dana na 7±1°C u 50 uzoraka sirovog mleka povećao sa log0.81±0.78na 1.73±0.86, au6uzorakasa log 0.10±0.10na 2.07±0.47. Statistički je utvrđeno da je promenu broja bacila u uslovima niskih temperatura za period od 10 dana visoko značajna. Izolovani psihrotrofni bacili su u 30,35% hemolitični, 64,28% ledtinaza pozitivni, 5,35% sojeva razlaže želatin, a 78,57% sojeva razlazu kazein. Sposobnost rasta u medijumu sa pH 5,7 pokazuje 97.07% sojeva, a 78,57% raste u prisustvu 7% NaCl.