Title of Dissertation: CHARACTERIZATION AND MOLECULAR MECHANISMS OF ANTIMICROBIAL RESISTANCE IN FOODBORNE PATHOGENS Sheng Chen, Doctor of Philosophy, 2004 Dissertation directed by: Associate Professor Jianghong Meng Department of Nutrition and Food Science The emergence of antimicrobial resistance bacteria in both the medical and agricultural fields has become a serious problem worldwide. The u...

Twelve populations of Escherichia coli B all lost D-ribose catabolic function during 2,000 generations of evolution in glucose minimal medium. We sought to identify the population genetic processes and molecular genetic events that caused these rapid and parallel losses. Seven independent Rbs(-) mutants were isolated, and their competitive fitnesses were measured relative to that of their Rbs(+...

The objective was to develop and characterise in vitro Bartonella bacilliformis antibiotic resistant mutants. Three B. bacilliformis strains were plated 35 or 40 times with azithromycin, chloramphenicol, ciprofloxacin or rifampicin discs. Resistance-stability was assessed performing 5 serial passages without antibiotic pressure. MICs were determined with/without Phe-Arg-β-Napthylamide and artes...

The ability of sequential subcultures in subinhibitory concentrations of gemifloxacin, trovafloxacin, ciprofloxacin, gatifloxacin and moxifloxacin to select resistant mutants was studied in 16 pneumococci [eight with ciprofloxacin MICs (mg/L) 0.25-1; four with 8-16; four with 16-32]. Subculturing was done 50 times, or until mutants with elevated MICs (> or = 4 x) to the selecting drug emerged. ...

Genes acrAB encode a multidrug efflux pump in Escherichia coli. We have previously reported that transcription of acrAB is increased under general stress conditions (i.e. 4% ethanol, 0.5 M NaCl, and the stationary phase in Luria-Bertani medium). In this study, lacZ transcriptional fusions and an in vitro gel mobility shift assay have been utilized to study the mechanisms governing the regulatio...

The objective of this study was to evaluate collateral sensitivity and cross-resistance antibiotic-induced resistant Salmonella Typhimurium various antibiotics. S. ATCC 19585 (STWT) exposed ciprofloxacin, gentamicin, kanamycin, tetracycline induce antibiotic resistance, respectively, assigned as STCIP, STGEN, STKAN, STTET. susceptibilities the mutants cefotaxime, chloramphenicol, polymyxin B, s...

Mechanisms of antibiotic resistance were examined in nalidixic acid-resistant Salmonella enterica serovar Enteritidis field isolates displaying decreased susceptibility to ciprofloxacin and in in vitro-derived ciprofloxacin-resistant mutants (104-cip and 5408-cip). All field isolates harbored a single gyrA mutation (D87Y). Deletion of acrB and complementation with wild-type gyrA increased quino...

Escherichia coli K-12 strains are normally tolerant to n-hexane and susceptible to cyclohexane. Constitutive expression of marA of the multiple antibiotic resistance (mar) locus or of the soxS or robA gene product produced tolerance to cyclohexane. Inactivation of the mar locus or the robA locus, but not the soxRS locus, increased organic solvent susceptibility in the wild type and Mar mutants ...

The cydAB operon of Escherichia coli encodes cytochrome bd, a terminal oxidase in the aerobic respiratory chain. The high oxygen affinity of this oxidase explains its increased synthesis under low-oxygen conditions. Expression of the cydAB operon is controlled by the ArcA/ArcB two-component system and the oxygen-sensing transcriptional regulator Fnr. However, cydAB expression is still induced u...

OBJECTIVES Biocides are widely used to prevent infection. We aimed to determine whether exposure of Salmonella to various biocides could act as a driver of antibiotic resistance. METHODS Salmonella enterica serovar Typhimurium was exposed to four biocides with differing modes of action. Antibiotic-resistant mutants were selected during exposure to all biocides and characterized phenotypically...