Prevalence and characterization of Salmonella isolated from raw vegetables in China

Raw vegetables have been associated with numerous foodborne Salmonella outbreaks; however, there is little epidemiological or molecular data on Salmonella contaminants of raw vegetables in China. Here, we investigated the prevalence and molecular characteristics of Salmonella isolates from raw vegetables in China. In total, 406 raw vegetable samples were collected covering most provincial capitals in China. The overall prevalence of Salmonella was 3.4% (14/406), with contamination levels of < 1 MPN/g. Coriander (7.8%, n = 90) and lettuce (6.0%, n = 83) showed the highest contamination rates. Among the 31 Salmonella isolates recovered from the 14 positive samples, 14 different serovars and 15 multilocus sequence typing patterns were identified. All of the identified serovars have previously caused infections in humans, with several also linked to raw vegetable-associated disease outbreaks. Of the 15 non-duplicate isolates, 7 (46.7%) were resistant to at least one class of antibiotics and 4 (26.7%) were multidrug-resistant. The highest rate of resistance was observed for nalidixic acid (33.3%). This study provides a systematical surveillance on prevalence of Salmonella in Chinese raw vegetables, and suggests that the Salmonella contamination of fresh vegetables is a potential risk to public health when they are eaten raw.