|Kim, Gwang Hee - Kangwon National University|
|Oh, Deog Hwan - Kangwon National University|
Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2016
Publication Date: 9/5/2016
Citation: Kim, G., Fratamico, P.M., Breidt, F., Oh, D. 2016. Survival and expression of acid resistance genes in Shiga toxin-producing Escherichia coli acid adapted in pineapple juice and exposed to synthetic gastric fluid. Journal of Applied Microbiology. doi: 10.1111/jam.13223.
Interpretive Summary: Harmful bacteria known as Shiga toxin-producing Escherichia coli (STEC) found as food contaminants can cause serious illnesses and death. E. coli O157:H7 is an important STEC; however, in recent years, other types of STEC bacteria have caused illnesses similar to those caused by O157:H7. One reason why STEC O157:H7 is able to cause illness is because it is not easily inactivated when exposed to acidic conditions in certain foods and also the acidic conditions in the human gastrointestinal tract. Research was conducted to understand how STEC are able to tolerate acidic conditions in pineapple juice (PJ), a food with low pH, and if exposure to PJ causes the pathogens to become more tolerant to the acidic conditions in the GI tract. Results showed that STEC adapted in PJ at refrigeration temperature showed enhanced survival in synthetic gastric fluid compared to the control strains, and the expression level of certain genes involved in acid resistance also increased in PJ. In addition, some types of STEC were as resistant to acid as STEC O157:H7. Thus, exposure of STEC to acidic foods may increase the risk of foodborne illness caused by these bacteria.
Technical Abstract: Aims: The aim of this research was to examine relative transcriptional expression of acid resistance (AR) genes, rpoS, gadA and adiA, in O157:H7 and non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes after adaptation to pineapple juice (PJ) and subsequently to determine survival with exposure to synthetic gastric fluid (SGF). Methods and Results: Five pairs of strains, each consisting of one sensitive and one resistant strain belonging to five different STEC serogroups (O26, O103, O104, O111 and O157) (n=10) were used in this study. All strains were adapted in PJ (pH 3.8) stored at 4 degrees C and 20 degrees C for 24 h, and then the relative transcription levels of genes in all strains were quantified using a real-time quantitative-PCR assay. After adaptation in PJ, the STEC strains were exposed to SGF (pH 1.5 and 2.0) at 37 degrees C for 2 h. Generally, the STEC adapted in PJ at 4 degrees C displayed enhanced survival compared to adaptation at 20 degrees C and non-adapted controls with exposure to SGF. Moreover, resistant strains exhibited higher survival rates compared to sensitive strains. Adaptation at 4 degrees C resulted in significantly (P < 0.05) enhanced gene expression levels in PJ, and transcript levels of gadA were higher than rpoS and adiA genes. Conclusions: The up-regulation of AR genes due to adaptation in PJ at low temperature may increase survival in acidic environments such as the gastrointestinal tract. Some non-O157 STEC strains, including serotypes O103:H2 and O111:H8, showed relatively high AR levels, similar to those of STEC O157:H7. Significance and Impact of the Study: Induction of AR genes in acidic fruit juice, and potentially in other acidic foods may increase the risk of foodborne illness by non-O157 STEC serogroup.