Clostridium tyrobutyricum strains exhibit high genetic diversity and differ in their ability to cause late blowing defect in washed-curd cheese.

Clostridium tyrobutyricum is a spore-forming bacterium and is considered to be one of the main causative agents of late blowing defect (LBD) of hard and semi-hard cheeses. However, the spoilage potential of C. tyrobutyricum appears to be strain dependent. Because previous studies have been mostly limited to laboratory liquid media or experimental food models imitating cheese matrix, we (1) characterized 6 strains of C. tyrobutyricum for their ability to cause LBD in washed-curd cheese aged at 8°C and 15°C, and (2) probed the whole-genome data for the genetic markers linked to LBD. Washed-curd cheeses were made with pasteurized cow milk individually inoculated with different C. tyrobutyricum strains. During cheese aging at 8°C, none of the 6 evaluated strains caused changes in cheese consistent with LBD (i.e., accumulation of gas, formation of cracks, and production of butyric acid). Three of the 6 tested strains were, however, able to cause LBD at 15°C; the remaining 3 C. tyrobutyricum strains showed little or no gas and butyric acid production during 160 d aging at 15°C. All 6 strains were additionally evaluated in 3 separate experiments performed in 2 different liquid media (reinforced clostridial medium and enriched milk medium) to determine germination, growth, and gas formation at temperatures between 8°C and 37°C, and pH values between 6.9 and 4.1. All 6 evaluated strains were able to grow and form gas in a liquid medium in at least one replicate at temperatures and pH values as low as 12.5°C and 5.1, respectively. Comparative genomics showed that the 6 strains exhibit high genetic diversity, without specific genetic features that would explain the observed differences in the ability to cause LBD in washed-curd cheese. Future studies would need to compare a larger set of C. tyrobutyricum strains with demonstrated ability or inability to cause LBD in cheese. This ability to cause LBD will most likely have to be determined in actual cheese experiments, as our results show that growth and gas formation in liquid medium models are not always representative of growth and gas formation in cheese.