This study explores relative levels of stxl and fur gene expression under antibiotic-stressed and control (non-stressed) Escherichia coli O157:H7 using real-time polymerase chain reaction (PCR) cycle threshold (CO value comparisons among replicates at designated time points of growth. Our data indicate that E. coli O157:H7 under the subinhibitory concentration(SIC) level of chloramphenicol decreases fur expression in early stationary phase cultures by 50% compared to non-stressed cells, but increases stxl expression by 35-50% during the log-to-stationary phase transition. Since the enterohemorrhagic E. coli stxl gene is negatively regulated by the fur gene product or results indicate that a separate fundamental transcriptional regulatory mechanism is functional in cultures grown under subinhibitory stress, such as antibiotic exposure. These data could support the clinical results obtained from treatment of EHEC-mediated toxicoinfections with antibiotics which have resulted inducing EHEC to prematurely produce cytotoxins within the host and speed the course of hemorrhagic colitis (HC) and/or hemolytic uremic syndrome (HUS). / Department of Biology

Escherichia coli O157:H7 is an enteric pathogen that can cause severe gastrointestinal disease, sometimes leading to hospitalization and death. These bacteria have a variety of virulence factors that can be encoded for on pathogenicity islands (PAIs). The goal of this study was to characterize specific E. coli O157:H7 PAI deletion mutants using three methods: Phentotype Microarrays (PM), growth curves and survival curves were used to elucidate possible roles for the PAIs. Results from the PM study suggest that PAIs have a role in carbon substrate utilization; i.e., four of the O-island (OI) deletion mutants (OI-87, 98, 102 and 172) and an S-Loop (SL-72) deletion mutant exhibited differences in substrate utilization (gains and losses in utilization) compared to parental O157:H7 strains EDL933 (OI) and Sakai (SL), respectively. All of the mutants with the exception of the OI-135 mutant exhibited differences in level of substrate utilization for substrates shown to have important roles in the bacterium. Cell growth results showed that three OI deletion mutants (OI-55, 87 and 102) and the SL (SL-72) mutant exhibited a difference in rate of growth compared to the parental strains. Cell viability results showed that seven of the OI deletion mutants (OI-51, 55, 98, 108, 135, 172 and 176) exhibited different rates of decline in cell number when transferred to sterile water compared to the parental strain. The results show that removal of PAIs from E. coli O157:H7 can affect carbon utilization, growth and survival demonstrating the importance of PAIs in the ecology of these bacteria. / xx, 208 leaves : ill. (some col.) ; 29 cm