Antibacterial and anti-biofilm activities of probiotic Lactobacillus plantarum against Listeria monocytogenes isolated from milk, chicken and pregnant women.

() is a foodborne pathogen that poses significant risks to public health and food safety. The present study aimed to identify the presence of spp. in various samples, including pasteurized milk, chicken fillets, and stool samples from pregnant women in Sharkia Governorate, Egypt. Additionally, the study identified the serotypes, virulence-associated genes, antimicrobial resistance patterns, and biofilm formation in isolates. Moreover, the antibacterial and anti-biofilm activity of ATCC 14917 () against isolates was investigated. A cross-sectional study was conducted from August 2021 to January 2022 to collect 300 samples of pasteurized milk, chicken fillets, and stool from pregnant women admitted to outpatient clinics of hospitals. The results showed that 32.7% of the samples were positive for spp., including (48.9%), (26.5%), (14.3%), (5.1%), and (5.1%). Among all isolates, , , , and virulence-associated genes were detected. However, the virulence genes , , and were found in 10 (38.5%), 8 (30.8%), and 25 (96.2%) isolates, respectively. The isolates classified into four serotypes (1/2a, 1/2b, 1/2c, and 4b), with 1/2a and 4b each identified in 30.8% of the isolates, while 1/2b and 1/2c were identified in 19.2% of the isolates. All isolates showed 100% resistance to streptomycin, kanamycin, and nalidix acid, and 92.3% of isolates showed gentamicin resistance. However, all isolates were susceptible to ampicillin and ampicillin/sulbactam. Multidrug resistance (MDR) was observed in 20 (76.9%) isolates. The biofilm formation ability of 26 isolates was evaluated at different incubation temperatures. At 4°C, 25°C, and 37°C, 53.8, 69.2, and 80.8% of the isolates, respectively, were biofilm producers. Furthermore, 23.1% were strong biofilm producers at both 4°C and 25°C, while 34.6% were strong biofilm formers at 37°C. Treating isolates with cell-free supernatant (CFS) reduced the number of biofilm-producing isolates to 15.4, 42.3, and 53.8% at 4°C, 25°C, and 37°C, respectively. CFS antibacterial activity was tested against six virulent, MDR, and biofilm-forming isolates. At a concentration of 5 μg/mL of CFS, none of the isolates exhibited an inhibition zone. However, an inhibition zone was observed against strains isolated from pasteurized milk and pregnant women's stools when using a concentration of 10 μg/mL. Transmission electron microscopy (TEM) revealed that CFS induced morphological and intracellular structural changes in . In conclusion, this study identified virulent MDR isolates with strong biofilm-forming abilities in food products in Egypt, posing significant risks to food safety. Monitoring the prevalence and antimicrobial resistance profile of in dairy and meat products is crucial to enhance their safety. Although CFS showed potential antibacterial and anti-biofilm effects against isolates, further research is needed to explore its full probiotic potential.