ARB and ARGs survived from the extremely acidity posing a risk on intestinal bacteria in an in vitro digestion model by horizontal gene transfer

Abstract Background: Antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs) have been considered as emerging contaminants, which even might be closely related to human health.Methods: To investigate the disease-producing risk of ARB and the horizontal gene transfer (HGT) risks of both extracellular ARGs (eARGs) and intracellular ARGs (iARGs), an in vitro digestion model was established to simulate the process of ARB and ARGs going through digestive tract. CTC/DAPI-FCM assay was used to study the survival of ARB during digestion, and the changes of genes (including tetA, tetG, tetM, sul1, sul2, bla EBC, bla FOX, intI1 and 16S rRNA) were determined by QPCR.Results: The results showed that ARB were mostly affected by pH of gastric juice. About 99% ARB (total population of 2.45 × 109–2.54 × 109) were killed by the gastric juice of pH 2.0 for the severely damage of bacterial cell membrane, but more than 80% ARB (total population of 2.71 × 109–3.90 × 109) were still alive with intact cell membrane when the pH of gastric juice increased to 3.0 and above. ARGs, intI1 and 16S rRNA could be detectable even at extreme pH when most bacteria died. The eARGs (accounting for 0.03%–24.56% of total genes) were less than iARGs obviously. The eARGs showed greater HGT potential than that of iARGs, suggesting transformation occurs more easily than conjugation. The transfer potential followed the order as: tet (100%) > sul (75%) > bla (58%), related to the high correlation of intI1 with tetA and sul2 (p < 0.01). Moreover, gastric juice of pH 1.0 could decrease the transfer frequency of ARGs by 2–3 order of magnitude compared to the control, but still threatening human health.Conclusions: Under the treatment of digestive juice, ARGs still have high gene horizontal transfer potential, suggesting that food-borne ARB pose a risk of ARGs horizontal transfer to intestinal bacteria.