High Temperature in Combination with UV Irradiation Enhances Horizontal Transfer of stx2 Gene from E. coli O157:H7 to Non-Pathogenic E. coli

Abstract

BackgroundShiga toxin (stx) genes have been transferred to numerous bacteria, one of which is E. coli O157:H7. It is a common belief that stx gene is transferred by bacteriophages, because stx genes are located on lambdoid prophages in the E. coli O157:H7 genome. Both E. coli O157:H7 and non-pathogenic E. coli are highly enriched in cattle feedlots. We hypothesized that strong UV radiation in combination with high temperature accelerates stx gene transfer into non-pathogenic E. coli in feedlots.Methodology/Principal Findings E. coli O157:H7 EDL933 strain were subjected to different UV irradiation (0 or 0.5 kJ/m2) combination with different temperature (22, 28, 30, 32, and 37°C) treatments, and the activation of lambdoid prophages was analyzed by plaque forming unit while induction of Stx2 prophages was quantified by quantitative real-time PCR. Data showed that lambdoid prophages in E. coli O157:H7, including phages carrying stx2, were activated under UV radiation, a process enhanced by elevated temperature. Consistently, western blotting analysis indicated that the production of Shiga toxin 2 was also dramatically increased by UV irradiation and high temperature. In situ colony hybridization screening indicated that these activated Stx2 prophages were capable of converting laboratory strain of E. coli K12 into new Shiga toxigenic E. coli, which were further confirmed by PCR and ELISA analysis.Conclusions/SignificanceThese data implicate that high environmental temperature in combination with UV irradiation accelerates the spread of stx genes through enhancing Stx prophage induction and Stx phage mediated gene transfer. Cattle feedlot sludge are teemed with E. coli O157:H7 and non-pathogenic E. coli, and is frequently exposed to UV radiation via sunlight, which may contribute to the rapid spread of stx gene to non-pathogenic E. coli and diversity of shiga toxin producing E. coli.

Cinnamon Oil Inhibits Shiga Toxin Type 2 Phage Induction and Shiga Toxin Type 2 Production in Escherichia coli O157:H7

“…In recent years, new STEC serotypes have emerged, culminating in the 2011 E. coli O104:H4 outbreak that involved more than 4,000 persons in 16 countries (43). E. coli O104:H4 appears to be an enteroaggregative E. coli (EAEC) acquiring stx via horizontal gene transfer (44), which can also occur between STEC and nonpathogenic E. coli (11), facilitating the spread of stx genes and increasing the pathogenic potential of STEC. Therefore, exploring an effective method to control Stx prophage activation and related Stx production in STEC is of great necessity.…”

“…Phage enumeration. PFU were determined as previously described (11,18). Since no detectable phage was found in the E. coli O157:H7 culture 6 h postsubculture in LB broth containing various concentrations of cinnamon oil, PFU were only analyzed at 12 h. Briefly, E. coli O157:H7 culture at 12 h after cinnamon oil treatment (4 replicates per treatment) was centrifuged at 10,000 ϫ g and 4°C for 5 min.…”

“…The activation of Stx prophage, phage DNA replication, and subsequent bacterial cell lysis results in Stx release (10). Importantly, released Stx phages are able to convert commensal E. coli into new Stx-producing E. coli (STEC) (11), facilitating the spread of STEC strains (12). Prophage induction can be caused by factors provoking SOS response, which activates the RecA protein, resulting in self-cleavage of the phageencoded cI repressor, initiation of phage transcription, and further the transcription of stx genes (13).…”

Shiga toxins and stx phages: highly diverse entities

“…Such factors include hydrogen peroxide (Wagner et al, 2001;Łoś et al, 2009, 2010, high temperature in combination with UV irradiation (Yue et al, 2012), EDTA (Imamovic & Muniesa, 2012), sodium citrate (Imamovic & Muniesa, 2012;Nejman-Faleń czyk et al, 2012), amino acid starvation (Nejman-Faleń czyk et al, 2012), phenethyl isothiocyanate (Nowicki et al, 2014), DNase colicins (Toshima et al, 2007), high hydrostatic pressure (Aertsen et al, 2005a), sodium chloride (Łoś et al, 2009;Harris et al, 2012), nitric oxide (Vareille et al, 2007), 60 Co irradiation (Yamamoto et al, 2003) Łoś et al, 2009;Nassar et al, 2013), as well as those antibacterials used as growth promoters in animal production (Köhler et al, 2000).…”

The effect of antimicrobials on verocytotoxin bacteriophage transduction under bovine rumen fluid and broth conditions

“…Indeed, the low overall production and isolation of transductants may be attributed to the combination of donor and recipient cell concentrations being lower than the threshold value required for their generation, due to the decrease in bacterial cell numbers observed in the presence of the different antibiotic treatments (Imamovic et al, 2009). Moreover, the free phages observed in our study may have had reduced capacity to infect bacterial cells (Yue et al, 2012;Martinez-Castillo and Muniesa, 2014). The higher transduction rates in LB broth may be explained by the impact of the matrix on this process.…”