Evaluating packaged ice safety using culture-based and metagenomic methods

Ice can serve as a vector for microbial contamination, presenting potential risks to public health. This study aimed to evaluate the microbial quality and safety of commercially available ice in Manitoba as well as to characterize the microbiome of ice cubes and assess the presence of antimicrobial resistance (AMR) genes. Samples from five different brands, four non-International Packaged Ice Association (IPIA)-accredited and one IPIA-accredited brand, were collected from retail stores between May and August 2024. Ice samples were tested using membrane filtration for total plate count, Escherichia coli , coliforms, Pseudomonas , yeasts, moulds and Enterococcus and screened for Listeria monocytogenes and Salmonella . Separate filtration samples were collected for metagenomic analysis. Membrane filtration results showed that 12.8% of samples from non-IPIA-accredited brands failed to meet IPIA standards for total coliforms, whereas 100% of samples from the IPIA-accredited brand complied. All samples tested negative for foodborne pathogens when conventional culture-based methods were used. However, metagenomic sequencing revealed the presence of pathogen-associated DNA. A diverse resistome was identified across all brands, including the IPIA-accredited sample, with genes conferring resistance to β -lactams, aminoglycosides and biocides. Recovered Pseudomonas isolates were identified as Pseudomonas lactis , a psychrotrophic species capable of growth at refrigeration temperatures. Biofilm assays demonstrated that recovered P. lactis formed biofilms at both 4 and 10 °C, with significantly greater biofilm formation observed at 4 °C. Our findings demonstrate consistent compliance among the IPIA-accredited brand, while variability and failures occurred among non-accredited producers. The detection of cold-adapted, biofilm-forming bacteria such as Pseudomonas spp., which can reduce sanitizer efficacy and protect co-existing micro-organisms, including potential pathogens harbouring AMR genes, highlights the need for targeted environmental monitoring using key indicator organisms such as Pseudomonas spp. Broader adoption of IPIA standards could strengthen microbial control practices and enhance consumer protection within the Canadian packaged ice industry.