Activity of bacteriophage endolysins LP101_021 and PlyP100 against Listeria monocytogenes for Squacquerone soft cheese decontamination

Listeriosis, caused by Listeria monocytogenes, is a severe foodborne infection, particularly hazardous for pregnant women and immunocompromised individuals. In Europe, L. monocytogenes was the fifth most reported zoonotic agent in 2022, with outbreaks frequently linked to ready-to-eat (RTE) foods. Addressing food contamination with innovative antimicrobial strategies is critical to enhancing food safety and reducing public health risks. This study evaluated the efficacy of two bacteriophage-derived endolysins, LP101_021 and PlyP100, in reducing L. monocytogenes contamination in Squacquerone, a traditional Italian soft cheese made from whole cow's milk. Squacquerone samples were experimentally inoculated with approximately 6 log₁₀ cfu/g of L. monocytogenes strain Lm-ID11. The samples were then treated with either LP101_021 or PlyP100, and viable bacterial counts were monitored over time. Reductions in bacterial load were measured at 1 and 24 h post treatment to assess the effectiveness of each endolysin. Endolysin LP101_021 demonstrated a significant reduction in L. monocytogenes counts, decreasing bacterial loads by more than 3 log₁₀ cfu/g within 1 h, with sustained effects over 24 h. PlyP100 exhibited a more moderate impact, reducing bacterial counts by approximately 0.5 log₁₀ cfu/g after 1 h and 1.38 log₁₀ cfu/g after 24 h. By comparing the effects of those two endolysins, these findings highlight the rapid and effective antimicrobial action in particular of LP101_021 in cheese matrices. The study underscores the potential of bacteriophage endolysins as targeted antimicrobial agents for food safety applications. Their specificity allows the biocontrol of harmful pathogens without disrupting beneficial microbial communities, making them a promising alternative to conventional antimicrobial strategies. Furthermore, the effectiveness in reducing L. monocytogenes contamination in dairy products supports their potential integration in food processing and storage protocols, addressing the global challenge of antibiotic-resistant bacteria.