Tracking the Transfer of Antimicrobial Resistance Genes from Raw Materials to Sourdough Breads

Abstract

The main hypothesis of the present work is that raw materials used in bread making are able to transfer ARGs to processed breads. Four flours and four semolinas were purchased from supermarkets and processed into breads using a dried sourdough starter. All raw materials and fermented doughs were investigated for their microbiological characteristics. The levels of yeasts and lactic acid bacteria (LAB) increased up to 107 CFU/g. The values of pH decreased to 4.54 – 4.86 while total titratable acidity increased inversely. All unprocessed and processed samples, including breads, were analysed by a molecular approach to detect bacterial and fungal DNAs and 17 antibiotic resistance genes for penicillins, macrolides, tetracyclines, and chloramphenicol. The operational taxonomy units (OTUs) identified from unprocessed wheat milling products, fermented doughs and baked products mainly belonged to Acetobacteraceae. Enterococci were present in all doughs. After baking, Enterococcus and Acetobacteraceae relative abundance (RA) % decreased. DNA analysed for fungal composition showed that Kazachstania humilis dominated dried sourdough starters and doughs and its DNA was also detected at high RA % in baked products. The search for ARGs revealed that all samples analyzed did not show resistance to penicillins, chloramphenicol, and macrolides but three of the semolinas included in this study (S1, S3 and S4) and the corresponding doughs (SD1, SD3 and SD4) were positive for tet(A) and tet(B) resistance genes. Although only tet(A) gene was detected in barely one bread sample (SB3), the main hypothesis was accepted and breads can be associated to the dissemination of ARGs.

Keywords: Antibiotic resistance genes, fermentation, Lactic Acid Bacteria, sourdough, Wheat, yeasts