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Serotypes and Virulence Gene Profiles of Shiga Toxin-Producing Escherichia coli Strains Isolated from Feces of Pasture-Fed and Lot-Fed Sheep. Steven P. Djordjevic, 2004.Shiga toxin-producing Escherichia coli (STEC) strains possessing genes for enterohemolysin (ehxA) and/or intimin (eae), referred to here as complex STEC (cSTEC), are more commonly recovered from the feces of humans with hemolytic uremic syndrome and hemorrhagic colitis than STEC strains that do not possess these accessory virulence genes . Ruminants, particularly cattle and sheep, are recognized reservoirs of STEC populations that may contaminate foods destined for human consumption . We isolated cSTEC strains from the feces of longitudinally sampled pasture-fed sheep, lot-fed sheep maintained on diets comprising various combinations of silage and grain, and sheep simultaneously grazing pastures with cattle to explore the diversity of cSTEC serotypes capable of colonizing healthy sheep . A total of 67 cSTEC serotypes were isolated, of which 21 (31.3%), mainly isolated from lambs, have not been reported . Of the total isolations, 58 (86.6%) were different from cSTEC serotypes isolated from a recent study of longitudinally sampled healthy Australian cattle (M . Hornitzky, B . A . Vanselow, K . Walker, K . A . Bettelheim, B . Corney, P . Gill, G . Bailey, and S . P . Djordjevic, Appl . Environ . Microbiol . 68:6439-6445, 2002) . Our data suggest that cSTEC serotypes O5:H–, O75:H8, O91:H–, O123:H–, and O128:H2 are well adapted to colonizing the ovine gastrointestinal tract, since they were the most prevalent serotypes isolated from both pasture-fed and lot-fed sheep . Collectively, our data show that Australian sheep are colonized by diverse cSTEC serotypes that are rarely isolated from healthy Australian cattle . Involvement of Two Putative Alternative Sigma Factors in Stress Response of the Radioresistant Bacterium Deinococcus radiodurans. Amy K. Schmid, 2002. The Streptococcus pneumoniae cia Regulon: CiaR Target Sites and Transcription Profile Analysis. Thorsten Mascher, 2003.The ciaR-ciaH system is one of 13 two-component signal-transducing systems of the human pathogen Streptococcus pneumoniae . Mutations in the histidine protein kinase CiaH confer increased resistance to beta-lactam antibiotics and interfere with the development of genetic competence . In order to identify the genes controlled by the cia system, the cia regulon, DNA fragments targeted by the response regulator CiaR were isolated from restricted chromosomal DNA using the solid-phase DNA binding assay and analyzed by hybridization to an oligonucleotide microarray representing the S . pneumoniae genome . A set of 18 chromosomal regions containing 26 CiaR target sites were detected and proposed to represent the minimal cia regulon . The putative CiaR target loci included genes important for the synthesis and modification of cell wall polymers, peptide pheromone and bacteriocin production, and the htrA-spo0J region . In addition, the transcription profile of cia loss-of-function mutants and those with an apparent activated cia system representing the off and on states of the regulatory system were analyzed . The transcript analysis confirmed the cia-dependent expression of seven putative target loci and revealed three additional cia-regulated loci . Five putative target regions were silent under all conditions, and for the remaining three regions, no cia-dependent expression could be detected . Furthermore, the competence regulon, including the comCDE operon required for induction of competence, was completely repressed by the cia system . Lipid II-Mediated Pore Formation by the Peptide Antibiotic Nisin: a Black Lipid Membrane Study. Imke Wiedemann, 2004.The antibiotic peptide nisin is the first known lantibiotic that uses a docking molecule within the bacterial cytoplasmic membrane for pore formation . Through specific interaction with the cell wall precursor lipid II, nisin forms defined pores which are stable for seconds and have pore diameters of 2 to 2.5 nm . Filamentous "Epsilonproteobacteria" Dominate Microbial Mats from Sulfidic Cave Springs. Annette Summers Engel, 2003.Hydrogen sulfide-rich groundwater discharges from springs into Lower Kane Cave, Wyoming, where microbial mats dominated by filamentous morphotypes are found . The full-cycle rRNA approach, including 16S rRNA gene retrieval and fluorescence in situ hybridization (FISH), was used to identify these filaments . The majority of the obtained 16S rRNA gene clones from the mats were affiliated with the "Epsilonproteobacteria" and formed two distinct clusters, designated LKC group I and LKC group II, within this class . Group I was closely related to uncultured environmental clones from petroleum-contaminated groundwater, sulfidic springs, and sulfidic caves (97 to 99% sequence similarity), while group II formed a novel clade moderately related to deep-sea hydrothermal vent symbionts (90 to 94% sequence similarity) . FISH with newly designed probes for both groups specifically stained filamentous bacteria within the mats . FISH-based quantification of the two filament groups in six different microbial mat samples from Lower Kane Cave showed that LKC group II dominated five of the six mat communities . This study further expands our perceptions of the diversity and geographic distribution of "Epsilonproteobacteria" in extreme environments and demonstrates their biogeochemical importance in subterranean ecosystems .
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