Prevalence, Serotype, Antibiotic Susceptibility, and Genotype of Salmonella in Eggs From Poultry Farms and Marketplaces in Yangling, Shaanxi Province, China

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 .

Genomic Investigation of Antimicrobial-Resistant Salmonella enterica Isolates From Dead Chick Embryos in China

“…These isolates were subjected to antimicrobial susceptibility assay and further genomic characterization. The positive rate found in this study was lower than that observed in eggs collected from poultry farms in Yangling, Shaanxi province (6.6%) (Li et al, 2020a ), and Shandong province (Zhao et al, 2021 ) and higher than that obtained by Li et al (0.5%) across China in 2016 (Li et al, 2020b ).…”

Prevalence and Antimicrobial Resistance of Salmonella Isolated From Dead-in-Shell Chicken Embryos in Shandong, China

“…Serotyping is an effective approach to evaluating modes of transmission to develop strategies for preventing disease spread within poultry facilities (30). We found that S. Thompson, which is a member of Salmonella serogroup C1 commonly associated with disease in humans (31) and isolated in poultry and poultry eggs (8,28,32), was the most prevalent isolate in the present study. This is in contrast to studies in Shanghai and Sichuan that had identified S. Enteritidis as the most common serovar in commercial chicken farms (25,33), while S. Indiana was found to be dominant in Shandong (34), and S. Weltevreden was dominant in Central Vietnam (35).…”

“…We found that S . Thompson, which is a member of Salmonella serogroup C1 commonly associated with disease in humans ( 31 ) and isolated in poultry and poultry eggs ( 8 , 28 , 32 ), was the most prevalent isolate in the present study. This is in contrast to studies in Shanghai and Sichuan that had identified S .…”

“…In this study, we collected Salmonella isolates from 6.7% of analyzed chicken embryos, and the positive rate was similar to the eggs collected from poultry farms in Yangling (6.6%) ( 28 ) but lower than that from commercial chicken farms in China ( 25 , 29 ). These differences in Salmonella isolation rates may be attributable to regional or seasonal differences, or to variations between studies with respect to the techniques used to collect samples.…”

Characteristics of Salmonella From Chinese Native Chicken Breeds Fed on Conventional or Antibiotic-Free Diets

“…Among the 14 antibiotics used in this study, the resistance rates of all Salmonella isolates to 11 antibiotics in conventional chicken were higher than those from chickens fed on antibiotic-free diets. The average MDR rate (20.2%, 22/109) of Salmonella isolates from chickens fed on antibiotic-free diets was significantly lower than the rates of 100% among 63 isolates examined by Yang et al (19) from conventional farms in a similar geographical region, and also lower than that from other poultry farms in China (43). These data indicated that the use of antibiotics may promote the development of MDR Salmonella (44).…”