Food waste as a vector of foodborne and opportunistic pathogens: A study on microbial contamination in an urban area.

Food waste (FW) management in urban areas raises concerns about potential health risks. This study quantified Escherichia coli, assessed the prevalence of six pathogenic bacteria (Campylobacter spp., Salmonella spp., Listeria monocytogenes, Klebsiella pneumoniae Kp1, Acinetobacter baumannii, and Pseudomonas aeruginosa), and analyzed the genomic content of 39 L. monocytogenes isolates in FW collected from 27 sites in the Rennes area (Brittany, France). Sampling was conducted four times (once per season) at apartment buildings (AB), canteens, restaurants, and food shops. E. coli was detected in 91.3 % of samples (10 to 1.9 × 10⁶ cfu/g), with no correlation to physicochemical parameters (pH, moisture, organic matter, TKN, NH4+/TKN). Salmonella spp. and Campylobacter spp. were not detected. The prevalence of L. monocytogenes in FW ranged from 8 % in canteens to 55.6 % in AB, and that of K. pneumoniae Kp1 from 31.3 % in food shops to 44 % in canteens. A. baumannii and P. aeruginosa were less frequent (≤ 16.7 % and ≤ 11.1 %). Antibiotic resistance was rare. One K. pneumoniae isolate from a canteen was resistant to cefpodoxime. Four A. baumannii isolates from one AB were resistant to three aminoglycosides, and one exhibited multidrug resistance. Most L. monocytogenes clonal complexes (CCs) were associated with food or environmental sources, with CC121 being the most common. Four and three isolates belonged to hypervirulent CC1 and CC4, respectively. Overall, these results demonstrate the persistence of pathogenic bacteria in stored FW and emphasize that citizen-driven composting, when carried out without hygienic precautions, may represent an underestimated risk to public health.