Abstract
Cronobacter spp. are foodborne pathogens that can infect and cause life-threatening diseases in all age groups, particularly in infants and immunocompromised elderly. This study aimed to investigate the prevalence, antibiotic susceptibility, and molecular characteristics of Cronobacter spp. isolates in edible mushrooms collected from 44 cities in China. In total, 668 edible mushrooms were collected from traditional retail markets and supermarkets and were analyzed by quantitative methods, PCR-based serotyping, multilocus sequence typing (MLST), and antibiotic susceptibility testing. Among the 668 samples tested, 89 (13.32%) were positive for Cronobacter spp., and the contamination levels exceeded the 110 most probable number (MPN)/g in 13.48% (12/89) of the samples. Flammulina velutipes samples had the highest contamination rate of 17.54% (37/211), whereas Hypsizygus marmoreus samples had the lowest contamination rate of 3.28% (2/61). Ten serotypes were identified among 115 isolates, of which the C. sakazakii serogroup O1 (n = 32) was the primary serotype. MLST indicated that there was quite high genetic diversity in Cronobacter spp. and 72 sequence types were identified, 17 of which were new. Notably, C. sakazakii ST148 (n = 10) was the most prevalent, followed by C. malonaticus ST7 (n = 5). Antibiotic susceptibility testing revealed that the majority of Cronobacter spp. strains were susceptible to the 16 antibiotics tested. However, a portion of isolates exhibited relatively high resistance to cephalothin, with resistance and intermediate rates of 93.91 and 6.09%, respectively. One isolate (cro300A) was multidrug-resistant, with resistance to five antibiotics. Overall, this large-scale study revealed the relatively high prevalence and high genetic diversity of Cronobacter spp. on edible mushrooms in China, indicating a potential public health concern. To our knowledge, this is the first large-scale and systematic study on the prevalence of Cronobacter spp. on edible mushrooms in China, and the findings can provide valuable information that can guide the establishment of effective measures for the control and precaution of Cronobacter spp on edible mushrooms during production processes.
Highlights
Cronobacter spp. is a gram-negative, motile, rod-shaped, nonsporulating pathogenic bacterium belonging to the family Enterobacteriaceae (Barron and Forsythe, 2007)
Quantitative detection was conducted by an isolation and enrichment method according to the National Food Safety Standard of China Food microbiological examination: Enterobacter sakazakii (GB 4789.40-2010; National Standard of the People’s Republic of China, 2010) for powdered infant formula (PIF), as described previously, with some modifications (Xu et al, 2015; Ling et al, 2018)
The mean contamination level of L. edodes, P. ostreatus, and P. eryngii was lower than 2 most probable number (MPN)/g
Summary
Cronobacter spp. is a gram-negative, motile, rod-shaped, nonsporulating pathogenic bacterium belonging to the family Enterobacteriaceae (Barron and Forsythe, 2007). C. sakazakii, C. malonaticus, and C. turicensis have been proven relevant to human infections (Liu et al, 2013; Forsythe et al, 2014), and outbreaks have been reported in some countries (Caubilla-Barron et al, 2007; Patrick et al, 2014). Cronobacter spp. has been isolated from clinical samples, and from various foods, including cereals, meat, herbs, spices, salads, fruits, and vegetables, as well as their as well as derivative food products (Alsonosi et al, 2015; Ueda, 2017). The source of infections in adults is still unidentified (Joseph and Forsythe, 2012). An indepth understanding of the genetic diversity of Cronobacter spp. can effectively promote reliable source tracking of contaminated foods and enhance the resolution of surveillance
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