Strain-Dependent Cheese Spoilage Potential of Clostridium tyrobutyricum.

Lucija Podrzaj,Konrad J Domig,Franziska Küller,Johanna Burtscher

doi:10.3390/microorganisms8111836

Lucija Podrzaj, Konrad J Domig + Show 2 more

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https://doi.org/10.3390/microorganisms8111836

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Abstract

Clostridium tyrobutyricum, a Gram-positive, anaerobic, spore-forming bacterium, is considered as one of the main causative agents for spoilage of hard and semihard cheeses. Growth of C. tyrobutyricum in cheese is critically influenced by ripening temperature and time, pH, salt and lactic acid concentration, moisture and fat content, and the presence of other microorganisms. Previous studies revealed high intraspecies diversity of C. tyrobutyricum strains and variable tolerance toward pH, temperatures, and salt concentrations. These findings indicate that strain-dependent characteristics may be relevant to assess the risk for cheese spoilage if clostridial contamination occurs. In this study, we aimed to compare the phenotypes of 12 C. tyrobutyricum strains which were selected from 157 strains on the basis of genotypic and proteotypic variability. The phenotypic analysis comprised the assessment of gas production and organic acid concentrations in an experimental cheese broth incubated at different temperatures (37, 20, and 14 °C). For all tested strains, delayed gas production at lower incubation temperatures and a strong correlation between gas production and the change in organic acid concentrations were observed. However, considering the time until gas production was visible at different incubation temperatures, a high degree of heterogeneity was found among the tested strains. In addition, variation among replicates of the same strain and differences due to different inoculum levels became evident. This study shows, that, among other factors, strain-specific germination and growth characteristics should be considered to evaluate the risk of cheese spoilage by C. tyrobutyricum.

Highlights

The contamination of cheese milk with endospores of butyric acid-producing clostridia represents a major concern for cheese producers
Silvetti et al demonstrated that pH, salt concentrations, and temperature can affect spore germination, growth, gas production, and reduction potential of vegetative cells and spores of clostridia in an enriched milk medium [10]
The metadata of the remaining strains were checked, and the sample set was narrowed down to a subset of 12 strains, which included the type strain (Cl_20 or DSM 2637) and strains, which were isolated at various sampling times from different food sources and different production locations

Summary

Introduction

The contamination of cheese milk with endospores of butyric acid-producing clostridia represents a major concern for cheese producers. Milk does not provide suitable growth conditions, clostridial endospores may encounter favorable conditions for germination and outgrowth during ripening of hard and semihard cheese This metabolic activity leads to pronounced cheese spoilage [1]. Silvetti et al demonstrated that pH, salt concentrations, and temperature can affect spore germination, growth, gas production, and reduction potential of vegetative cells and spores of clostridia in an enriched milk medium [10]. The aim of this study was to further elucidate the strain-dependent cheese spoilage potential of C. tyrobutyricum For this purpose, we assessed the genetic diversity of 157 clostridial strains. A subset of 11 genetically distinct strains and the type strain were selected for phenotypic analyses by assessing gas and organic acid production at different incubation temperatures in an experimental cheese broth

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