Characteristics of heterotrophic endophytic bacteria in four kinds of edible raw vegetables: species distribution, antibiotic resistance, and related genes

This study aimed to explore antibiotic resistance characteristics and species of heterotrophic endophytic bacteria (HEB) in four kinds of edible raw vegetables, including radishes, lettuces, onions, and tomatoes. A total of 144 HEB were isolated and tested for resistance to sulfamethoxazole (SMZ), tetracycline (TET), cefotaxime (CTX), and ciprofloxacin (CIP), and their species were identified by 16S rRNA gene sequencing. Antibiotic resistance genes (ARGs) and class I integron in antibiotic-resistant isolates were analyzed by polymerase chain reaction. The results showed radishes had the highest, while tomatoes had the lowest concentration of antibiotic-resistant HEB. SMZ and CTX were predominant antibiotic-resistant phenotypes in HEB. The multi-resistant phenotypes, the combinations SMZ-TET-CTX and SMZ-TET-CIP, accounted for 9.34% of all antibiotic-resistant phenotypes, mainly in radishes and lettuces. Bacillus, Pseudomonas, Staphylococcus, and Stenotrophomonas showed resistance to two antibiotics and existed in more than one kind of vegetable, and were the main carriers of sul1, sul2, blaTEM, and intI1 genes. Therefore, these four genera were considered potential hosts of ARGs in edible raw vegetables. The study provides an early warning regarding health risks associated with ingesting antibiotic-resistant bacteria through raw vegetable consumption.