Surveillance and examination of microbial contamination in ice cream in China

This study investigated the microbial contamination of ice cream in China. A total of 2887 ice cream samples were collected from different regions of China. Contamination by the aerobic plate count (APC), coliforms, and three foodborne pathogens, Listeria monocytogenes (L. monocytogenes), Staphylococcus aureus (S. aureus), and Salmonella spp., was detected in the samples. L. monocytogenes isolates were further analyzed for antibiotic susceptibility and multi-locus sequence typing (MLST). The results showed that APC was more than 105 colony forming units (CFU)/g in 6.10% (176/2887) and coliform was more than 102 CFU/g in 15.69% (453/2887) of all samples. The positive rates of S. aureus, L. monocytogenes, and Salmonella spp. were 0.66%, 0.62%, and 0.10%, respectively. Among these, S. aureus contamination was more than 102 CFU/g in two samples, and L. monocytogenes in the positive sample was in the range of 0.3-240 most probable number (MPN)/g, with a median of 4.3 MPN/g. The hygienic status of the packaged samples was much better than that of the bulk samples (P<0.05). Catering samples were more frequently and heavily contaminated than samples from retail and wholesale outlets (P<0.05). No significant differences were observed in samples bought from urban and rural areas (P>0.05). For 18 L. monocytogenes strains isolated from ice cream, the resistance rate of nine antibiotics was 5.56% (1/18). By MLST, the L. monocytogenes strains were classified into nine sequence types (STs), of which ST8 was the most common (six isolates). These results indicate that a potential health risk to the public may be caused by ice cream, particularly in susceptible populations.