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. 2021 May 18;9(5):1081.
doi: 10.3390/microorganisms9051081.

Lactic Starter Dose Shapes S. aureus and STEC O26:H11 Growth, and Bacterial Community Patterns in Raw Milk Uncooked Pressed Cheeses

Justine Piqueras  1 , Christophe Chassard  1 , Cécile Callon  1 , Etienne Rifa  2 , Sébastien Theil  1 , Annick Lebecque  1 , Céline Delbès  1
Affiliations

Lactic Starter Dose Shapes S. aureus and STEC O26:H11 Growth, and Bacterial Community Patterns in Raw Milk Uncooked Pressed Cheeses

Justine Piqueras et al. Microorganisms. .

Abstract

Adding massive amounts of lactic starters to raw milk to manage the sanitary risk in the cheese-making process could be detrimental to microbial diversity. Adjusting the amount of the lactic starter used could be a key to manage these adverse impacts. In uncooked pressed cheeses, we investigated the impacts of varying the doses of a lactic starter (the recommended one, 1×, a 0.1× lower and a 2× higher) on acidification, growth of Staphylococcus aureus SA15 and Shiga-toxin-producing Escherichia coli (STEC) O26:H11 F43368, as well as on the bacterial community patterns. We observed a delayed acidification and an increase in the levels of pathogens with the 0.1× dose. This dose was associated with increased richness and evenness of cheese bacterial community and higher relative abundance of potential opportunistic bacteria or desirable species involved in cheese production. No effect of the increased lactic starter dose was observed. Given that sanitary criteria were paramount to our study, the increase in the pathogen levels observed at the 0.1× dose justified proscribing such a reduction in the tested cheese-making process. Despite this, the effects of adjusting the lactic starter dose on the balance of microbial populations of potential interest for cheese production deserve an in-depth evaluation.

Keywords: CoPS; STEC; bacterial diversity; cheese; lactic starter; metagenomics; raw milk.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Level in Log [CFU/g] of S. aureus in milk (D0) and in cheeses at D1 and D28, according to the lactic starter dose (n = 6). The differences according to the dose were estimated by a multiple comparison test, a Dunn’s test. * p < 0.05; ** p < 0.01; n.s. non-significant. For milk samples (n = 6), no statistical tests were performed.
Figure 2
Figure 2
Level in Log [CFU/g] of STEC O26:H11 in milk (D0) and in cheeses at D1 and D28, according to the lactic starter dose (n = 6). The differences according to the dose were estimated by a multiple comparison test, a Dunn’s test. ** p < 0.01; ● tendency; n.s. non-significant. For milk samples (n = 6), no statistical tests were performed.
Figure 3
Figure 3
pH values in milk (D0) and in cheeses at D0.25, D1 and D28, according to the lactic starter dose (n = 6). The differences according to the dose were estimated by a multiple comparison test, a Dunn’s test. ** p < 0.01; ● tendency; n.s. non-significant. For milk samples (n = 6), no statistical tests were performed.
Figure 4
Figure 4
Beta-diversity of (a) Cheese core samples at D8 (n = 18), (b) Cheese core samples at D28 (n = 18), and (c) Cheese rind samples at D28 (n = 18) clustered according to the lactic starter dose; and (d) Cheese core samples at D28 (n = 18) clustered according to the farm. Non-Metric multidimensional scaling (NMDS) based on the Bray Curtis algorithm of bacterial communities. p-value was obtained after permutational MANOVA analysis (Adonis statistical test) and indicates significance between sample groups.
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