Final Examination for the Degree of PhD  - Atinuke Olajide  

Examining Committee
Dr. Michael Rogers, Chair
Dr. Gisele LaPointe, Advisor
Dr. Shu Chen, Advisory Committee Member
Dr. Arthur Hill, Department Member
Dr. Martin Wiedmann, Cornell University, External Examiner

TITLE: AN INVESTIGATION OF THE SPORE FORMING BACTERIA IN A CHEDDAR CHEESE PROCESSING PLANT LOCATED IN ONTARIO, CANADA

ABSTRACT: Spore forming bacteria continue to be a source of concern for dairy processors mostly for their spoilage and less frequently for their pathogenic attributes. This research investigated the bacterial spore forming population in a Cheddar cheese making system from raw milk reception at the plant through the cheese making stages until ripening. Although the raw milk samples met regulatory requirements at the time of processing, at least 100 aerobic spores per ml were present which soon concentrated to 1,000 spores/g along with the milk into the cheese matrix. However, thermoduric bacteria were 1 log higher than aerobic spores in both milk and cheese curds. Bacillus, the most prominent genus, consisted mostly of B. licheniformis species which had a high diversity with only seven of the 23 subtypes present in curds traceable to raw milk. Upon screening the B. licheniformis collection with two new B. paralicheniformis specific markers, a strain of B. paralicheniformis emerged. Bacillus was equally resident in the plant which could have been introduced by the raw milk. Paenibacillus was another important group isolated from the dairy samples which dominated in the aged cheeses up to 20 months of age in the absence of Bacillus. A wide diversity of Paenibacillus species were obtained including some (P. azoreducens, P. barengoltzii, P. woosongensis, P. pabuli and P. phoenicis) which have not been reported in cheese. The most prominent Paenibacillus was P. macerans which produced acid, gas and off-odours. An easy-to-use groEL gene-based detection qPCR assay for P. macerans with a detection limit of 100 CFU/ml was developed. Given the right conditions, there is a possibility for the low level Paenibacillus spores occurring in raw milk to concentrate into cheese, increase in number, germinate, produce unwanted gas and cause undesirable odour. The newly developed markers can be used to improve raw milk characterization prior to milk processing. Spore levels in raw milk need to be monitored in Canada. We propose that it should be used in communicating milk quality similar to somatic cells and total bacterial count, since their levels have been shown to increase significantly in cheese where they can cause problems.