Cold storage promotes the emergence and proliferation of Janthinobacterium sp. in raw milk biofilms

Abstract

The low temperatures used during raw milk storage in processing plants, while intended to inhibit microbial growth, fail to prevent psychrotrophic bacteria from colonizing surfaces and forming biofilms. Assessing the diversity of the bacterial community can provide insight into the ability of cold-adapted milk contaminants to develop biofilms during refrigeration. Therefore, biofilms were formed on stainless steel surfaces, at 4 °C using the CDC biofilm reactor at 60 rpm, from three raw milk samples collected at different times. The bacterial diversity and relative abundance of genera in each sample and in its corresponding biofilm were investigated through 16S rRNA gene sequencing. The results revealed that the genera Pseudomonas and Chryseobacterium were predominant in milk (46.36 % and 19.20 %) and biofilm (45.29 % and 24.19 %), whereas Janthinobacterium spp. was predominant exclusively in biofilms, reaching a relative abundance of 25.13 % though barely detectable in raw milk (0.016 %). Furthermore, the most abundant OTU of Janthinobacterium genus matched with J. lividum. On CDC biofilm reactor, J. lividum ATCC 14487 bacterial density reached 5.27 ± 0.45 log cfu/coupon after 5 days of incubation in sterile milk at 4 °C. Cross-streak antagonism tests further demonstrated that J. lividum can coexist in biofilms with Gram-negative strains, particularly Pseudomonas spp. These findings indicate that multi-species biofilms can form during the refrigeration phase of raw milk. They emphasize the risk associated with strains that, although initially present in minimal concentrations, can become predominant within such biofilms, potentially leading to dairy product spoilage.