Abstract
Poultry products such as eggs provide essential nutrients to the human body and thus play vital roles in the human food network. Salmonella is one of the most notorious foodborne pathogens and has been found to be prevalent in eggs. To better understand the characteristics of Salmonella in eggs, we investigated the prevalence of Salmonella spp. in 814 fresh eggs collected from poultry farms and retail marketplaces in Yangling, Shaanxi Province, China. The serotype, genotype, and antibiotic susceptibilities of 61 Salmonella isolates recovered from the eggs were analyzed. The average detection rate of Salmonella-positive eggs was 5.6%, with 6.6% of the eggs collected from poultry farms and 5.1% from marketplaces. Thirteen serotypes were identified from the 61 isolates, among which Salmonella Typhimurium (24.5%) and Salmonella Indiana (22.9%) were the most prevalent serotypes. Other dominant serotypes included Salmonella Thompson (13.1%) and Salmonella Enteritidis (11.4%), with the remaining nine serotypes detected at low rates (1.6–4.9%). All the Salmonella isolates tested were resistant to sulfisoxazole (100.0%). The majority (77.1%) of the isolates were resistant to nalidixic acid, amoxicillin-clavulanate, and ampicillin, while nearly two-thirds (63.9–68.9%) were resistant to trimethoprim–sulfamethoxazole, kanamycin, tetracyclines, and chloramphenicol. The rate of resistance to ciprofloxacin was 40.1%; the resistance rates to streptomycin, ceftiofur, and ceftriaxone ranged from 21.3 to 26.2%; and those to gentamicin, amikacin, and cefoxitin were relatively low (3.3–16.4%). Forty-nine (80.3%) Salmonella isolates exhibited resistance to multiple antibiotics, 20 (32.8%) of which were resistant to at least 10 antibiotics. Subtyping by pulse-field gel electrophoresis revealed a close genetic relatedness of Salmonella isolates from poultry farms, in striking contrast to the high diversity of the isolates obtained from marketplaces. Isolates of the same serotype always shared identical genotype and antibiotic resistance profiles, even the ones that were recovered from eggs sampled at different locations and times. These findings indicate that diverse Salmonella spp. with high rates of multidrug resistance are prevalent in fresh eggs in the study area. More attention should be paid to egg production, transportation, and storage to prevent foodborne outbreaks caused by Salmonella.
Highlights
Salmonella spp. are notorious foodborne pathogens that can cause diarrhea in humans and animals (Cowen et al, 2016)
Among the three poultry farms, no Salmonella-positive eggs were detected from farm F, only one (0.9%) Salmonella-positive egg was detected in farm X, while 19 (21.6%) were detected in farm C
The average detection rate of Salmonella-positive eggs in poultry farms, supermarkets, and wet markets in Yangling (5.6%) was higher than those reported in Shandong Province (2.1%, 49/2342) and Hebei Province (4.8%) (Li et al, 2018; Yang et al, 2019); it was much lower than the detection rates in some conventional farms in Sichuan Province (12.2%) and Jiangsu Province (17.4%, 160/920), China (Li et al, 2013; Hai et al, 2020)
Summary
Salmonella spp. are notorious foodborne pathogens that can cause diarrhea in humans and animals (Cowen et al, 2016). There are approximately 9.38 million cases of Salmonella infections and 15,000 deaths from the infection worldwide every year (Patchanee et al, 2017). The outbreak of foodborne diseases caused by the consumption of eggs contaminated with Salmonella remains severe worldwide. According to reports from the United States Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC), there were 52 foodborne outbreaks in Missouri in 2015 due to eggs contaminated by Salmonella Oranienburg. The outbreak was tracked down to Rose Acre Farms’ Hyde County farm in North Carolina and 207 million eggs were recalled around the United States (FDA, 2019a)
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