Background/Objectives: Listeria monocytogenes is a foodborne pathogen that can infect both humans and animals and cause noninvasive gastrointestinal listeriosis or invasive listeriosis. The objectives of this study were to determine the genetic diversity of L. monocytogenes; the genes associated with its resistance to antibiotics, benzalkonium chloride (BC), and cadmium chloride (CdCl₂); and its biofilm formation. Methods: A total of 132 fresh fruits (44 samples) and vegetables (88 samples) were selected for this study. The genetic diversity of the isolates and the genes associated with their antibiotic resistance were determined using PCR amplification; meanwhile, their levels of susceptibility to antibiotics were determined using the agar diffusion method. Their levels of resistance to BC and CdCl₂ were determined using the minimum inhibitory concentration method, and their capacity for biofilm formation was evaluated using the crystal violet staining method. Results: A total of 17 L. monocytogenes strains were collected: 12.8% (17/132) from fresh fruits and vegetables in this study. The isolates of L. monocytogenes belonged to phylogenetic groups I.1 (29.4% (5/17); serotype 1/2a) and II.2 (70.5% (12/17); serotype 1/2b); strains containing Listeria pathogenicity islands (LIPIs) were also identified at prevalence rates of 100% for LIPI-1 and LIPI-2 (17/17), 29.4% for LIPI-3 (5/17), and 11.7% for LIPI-4 (2/17). The antibiotic susceptibility tests showed that the L. monocytogenes isolates exhibited six different multiresistant patterns, with multiple antibiotic resistance (MAR) index of ≥0.46 (70.5%; 12/17); additionally, the genes Ide, tetM, and msrA, associated with efflux pump Lde, tetracycline, and ciprofloxacin resistance, were detected at 52.9% (9/17), 29.4% (5/17), and 17.6% (3/17), respectively. The phenotypic tests showed that 58.8% (10/17) of cadmium-resistant L. monocytogenes isolates had a co-resistance of 23.5% (4/17) to BC. Finally, all strains of L. monocytogenes exhibited moderate biofilm production. Conclusions: The results of this study contribute to our understanding of the persistence and genetic diversity of L. monocytogenes strains isolated from fresh fruits and vegetables; in addition, their resistance to CdCl₂, which is correlated with co-resistance to BC disinfectant, is helpful for the food industry.

Staphylococcus aureus is a foodborne pathogen that affects animals and humans. The persistence of this pathogen in the environment is associated with its ability to form biofilms and/or develop resistance mechanisms to antibiotics and sanitizers. A total of 67 S. aureus strains collected from food contact surfaces (FCSs) made of stainless steel and FCS-polypropylene used in dairy industries in Jalisco, México, were selected for this study. The genetic diversity and genes indicating antibiotic resistance were determined using PCR; antimicrobial susceptibility, resistance to cadmium chloride (CdCl₂), and the minimum inhibitory concentration (MIC) of benzalkonium chloride (BC) were determined using the agar diffusion method and broth microdilution. Additionally, the effects of BC treatment on biofilm removal were evaluated. A total of 41.7% of the strains were MRSA [SCCmec Types II (20.8%), V (13.4%), and IV (7.4%)], and 58.2% were MSSA. Genes encoding antibiotic resistance—ermC (2.9%), ermA (2.9%), ermB (10.4%), aacA-aphD (10.4%), tetM (17.9%), and blaZ (88%)—were detected. A phenotypic test showed that 62.6% of the strains were cadmium-resistant S. aureus (>400 µg/mL CdCl₂), and the MICs of 97% of isolates lay between 1.56 and 25 µg/mL BC. Treatment with BC + MR (100 µg/mL + 1% milk residues) led to a smaller reduction in biofilm (2.11–2.25 log₁₀ cfu/cm²; p < 0.05) compared to BC (3.75–4.03 log₁₀ cfu/cm²; at 5–10 min). MSSA and MSRA can develop biofilms that harbor mechanism resistance-associated genes, which are a public health hazard and a food safety concern.

Background/Objectives: Listeria monocytogenes is a foodborne pathogen that can infect humans and animals, causing non-invasive gastrointestinal listeriosis or invasive listeriosis. The objectives of this study were to determine: the genetic diversity of L. monocytogenes; the genes associated with the resistance to antibiotics, benzalkonium chloride (BC), and CdCl₂, and biofilm formation. Methods: Seventeen strains of L. monocytogenes isolated fresh fruits and vegetables were selected for this study. Genetic diversity and the genes associated with antibiotic resistance were determined by PCR amplification. Susceptibility to antibiotics were determined using the agar diffusion method. Resistance to BC and CdCl₂ was determined using the minimum inhibitory concentration method. Capacity for biofilm formation was evaluated using the crystal violet staining method. Results: This study demonstrates that the isolates of L. monocytogenes belong to serotypes 1/2a (29.4%) and 1/2b (70.5%). Potential hypervirulent strains containing 70.5% Listeria pathogenicity island 1 (LIPI-1-2), 17.6% (LIPI-1-3), and 11.7% (LIPI-1-4) were also identified. Antibiotic susceptibility tests show that L. monocytogenes exhibit six different multiresistant patterns with a MAR index of ³ 0.46 (70.5%); besides, the gen Ide, tetM, and msrA were detected in 52.9%, 29.4%, and 17.6%, respectively, associated with efflux pump Lde, tetracycline and ciprofloxacin resistance. Phenotypic test shows that 58.8% cadmium-resistant L. monocytogenes have a co-resistance to BC of 23.5%. Subsequently, all strains of L. monocytogenes exhibited moderate biofilm. Conclusions: This study contributes to the persistence and genetic diversity of strains L. monocytogenes isolated fresh fruits and vegetables; in addition, resistance to CdCl₂ and correlation with co-resistance to BC disinfectant used in the food industry.