Identification and characterisation of aerobic spore-forming bacteria isolated from Maltese cows' milk

Aerobic spore-forming bacteria, mainly Bacillus spp., are of real concern to dairy industries due to their ability to produce hydrolytic extracellular enzymes causing off-flavours and structural defects in pasteurised milk. In this study, bacteria were isolated and characterised from Maltese raw and pasteurised cows' milk samples, with sample collection carried out in both summer and winter seasons. Winter and summer raw milk samples had similar bacterial count, while winter pasteurised milk samples showed a higher level of surviving bacteria than summer pasteurised milk samples. The 16S r RNA sequencing performed on isolates from pasteurised milk showed aerobic spore-forming bacteria (e.g., Bacillus cereus) and a wide range of non-spore forming bacteria were identified including; coryneforms, Enterococcus spp., Streptococcus sp. Growth kinetic studies using B. cereus indicated that the minimum temperature for growth (Tmin), and the maximum cardinal temperatures (Tmax) of the isolated B. cereus were 6.38 °C and 44.23 °C, respectively.