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Short abstract:

Lactic acid bacteria, once just ferments, are now mainly seen as probiotics, initially defined as growth stimulators, then health enhancers. This proposal focuses on the historical requalification of this scientific object in agronomic and biomedical research in France between the 1970s and 2000s.

Long abstract:

Lactic acid bacteria (LAB) were linked to the probiotic concept in microbiology since the 1970s. This concept, anachronistic during Metchnikoff's era, when he called lactobacillin “ferment”, “microbial medicine”, or “microbe”, similarly applies to most biological work throughout the 20th century that characterized LAB by their fermentative action. These suggest LAB evolved from fermentation agents to entities called probiotics, defined in 1965 as microbial growth stimulators, then in 1974 as microorganisms in interaction with human host health. How to understand this evolution?

STS has employed the probiotic concept to signal a shift in cultural practices, challenging the traditional view of microbes as threats. This paper studies these entities, suggesting that their properties should not be taken for granted, as there are part of a dynamic process. I describe this, following Stéphanie Ruphy, as “layered pluralism”, comprising reasoning styles that ontologically enrich an object with new classes of entities. This proposal calls for greater attention to how scientific activities have led to a reevaluation of LAB, focusing on their microbial properties.

From a study of laboratory practices, using archives, interviews and bibliometrics, I argue that the requalification of LAB coincides with a multidimensional restructuring of laboratory activities with genomics’ emergence and the support from dairy industry, serving as a premise for a new category: the microbiome. This analysis reveals two forms of technical reductionism in the configurations of microbial entities, through genomes and cultured strains, both rooted in a productivist perspective of probiotics as vectors for biotechnological solutions, which frame knowledge construction.