Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2013
Publication Date: N/A
Interpretive Summary: Escherichia coli O157:H7 (O157) are Shiga toxin-producing bacteria. Humans can become infected with these bacteria by consuming improperly cooked meats, such as ground beef, unpasteurized dairy products, and contaminated fresh produce and water. In healthy human adults, O157 bacteria generally produce self-limiting diarrhea that usually resolves without any medical intervention. However, in children and elderly individuals, infections with O157 bacteria lead to production of bloody diarrhea that could progress into kidney malfunction, and even death. Patients who recover from the disease could experience life-long kidneys and nervous system-related problems. The O157 bacteria produce Shiga toxins responsible for the serious consequences of O157 infections in humans. In addition, O157 bacteria produce several known and many yet unknown protein factors and other chemicals that promote survival and persistence of O157 bacteria in cattle, which are the major reservoirs of O157 bacteria. Cattle carry O157 bacteria in their intestines and therefore shed these bacteria in their feces. Cattle feces are the major risk factor for the contamination of animal hides and carcasses in slaughter plants leading to the downstream contamination of meat products. Thus, a concerted approach is needed to identify protein/non-proteins factors and chemicals, and the mechanism by which these various types of factors promote colonization and fecal shedding of O157 in cattle. We have determined that two different sets of protein factors work in concert to control and enhance the ability of O157 bacteria to “swim” in their growth environment, presumably including cattle intestines. Ability of these bacteria to swim or move around efficiently appears to be critical for O157 bacteria to colonize and persist in cattle intestine. The complete understanding of the role and the mechanism by which these two sets of protein factors promote swimming motility of O157 in cattle intestines would aid in designing and testing of novel interventions for reducing colonization and persistence of O157 in cattle, the outcome critical for reducing the risks of downstream contamination of meats, produce, water, and human infections.
Technical Abstract: In a recent study we demonstrated that in comparison to the wild-type enterohemorrhagic Escherichia coli (EHEC) O157:H7, a motility-compromised hha deletion mutant with an up-regulated type III secretion system and increased secretion of adherence proteins showed reduced fecal shedding in cattle. In addition to the importance of hha in a positive regulation of motility, a two-component quorum-sensing pathway encoded by the qseBC genes has been shown to activate bacterial motility in response to mammalian stress hormones epinephrine (E) and norepinephrine (NE) as well as bacterially produced autoinducer-3. In this study, we demonstrate relative contributions and hierarchy of hha, a member of the Hha/YmoA family of nucleoid-associated proteins, and qseBC in expression of the wild-type motility phenotype in an isolate of EHEC O157:H7 strain 86-24 in the absence or in response to norepinephrine. By using single (Delta hha or Delta qseC) and double (Delta hha qseC) deletion mutants we show that the hha gene has a predominant positive regulatory effect in comparison to QseBC in the expression of wild-type motility phenotype by EHEC O157:H7. We also demonstrate that Hha is hierarchically dominant over QseBC in transcriptional activation of motility by showing that the transcription of qseC in the hha mutant was significantly reduced compared to the parental and hha-complemented strains.