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Emergence of Multidrug-Resistant Salmonella enterica Serovar Typhi in Korea. Kyungwon Lee, 2004.A chloramphenicol-resistant strain of Salmonella enterica serovar Typhi was first noted in Korea in 1992, when a resistant isolate was detected in a returned traveler . Continued isolation of multidrug-resistant (MDR) strains thereafter in other settings prompted a retrospective analysis of laboratory records and phenotypic and genotypic analyses of 12 chloramphenicol-resistant isolates . Among these, one isolate was resistant only to chloramphenicol, and the other isolates were also resistant to ampicillin and co-trimoxazole . MDR was transferred by conjugation from 9 of the 11 isolates . PCR showed that all isolates had an incompatible group HI1 plasmid, and oriT was detected in 10 isolates, which included strains with an unsuccessful transfer of resistance . All of the ampicillin-resistant isolates had a ß-lactamase band of pI 5.4 and blaTEM alleles . A PCR amplicon from an isolate showed that the sequences were identical to those of blaTEM-1, suggesting that all isolates had a TEM-1 ß-lactamase . All isolates had class 1 integrons: 10 isolates had integrons of ca . 1.2 kb with dhfr7 gene cassettes, and 1 isolate had an integron of ca . 2.3 kb with aacA4 and blaOXA-1-like gene cassettes . The pulsed-field gel electrophoresis patterns of 7 of 11 MDR isolates were identical and indistinguishable from those reported for isolates in India and Indonesia . In conclusion, some of the MDR strains in Korea are related to those in other Asian countries . Susceptibility testing became necessary for selection of antimicrobial agents for the optimal treatment of patients with the emergence of MDR Salmonella serovar Typhi in Korea . Two Chlorocatechol Catabolic Gene Modules on Plasmid pJP4. Michael Schlömann, 2002. Ribosylnicotinamide Kinase Domain of NadR Protein: Identification and Implications in NAD Biosynthesis. Oleg V. Kurnasov, 2002.NAD is an indispensable redox cofactor in all organisms . Most of the genes required for NAD biosynthesis in various species are known . Ribosylnicotinamide kinase (RNK) was among the few unknown (missing) genes involved with NAD salvage and recycling pathways . Using a comparative genome analysis involving reconstruction of NAD metabolism from genomic data, we predicted and experimentally verified that bacterial RNK is encoded within the 3' region of the nadR gene . Based on these results and previous data, the full-size multifunctional NadR protein (as in Escherichia coli) is composed of (i) an N-terminal DNA-binding domain involved in the transcriptional regulation of NAD biosynthesis, (ii) a central nicotinamide mononucleotide adenylyltransferase (NMNAT) domain, and (iii) a C-terminal RNK domain . The RNK and NMNAT enzymatic activities of recombinant NadR proteins from Salmonella enterica serovar Typhimurium and Haemophilus influenzae were quantitatively characterized . We propose a model for the complete salvage pathway from exogenous N-ribosylnicotinamide to NAD which involves the concerted action of the PnuC transporter and NRK, followed by the NMNAT activity of the NadR protein . Both the pnuC and nadR genes were proven to be essential for the growth and survival of H . influenzae, thus implicating them as potential narrow-spectrum drug targets . Distribution of Biosurfactant-Producing Bacteria in Undisturbed and Contaminated Arid Southwestern Soils. Adria A. Bodour, 2003.Biosurfactants are a unique class of compounds that have been shown to have a variety of potential applications in the remediation of organic- and metal-contaminated sites, in the enhanced transport of bacteria, in enhanced oil recovery, as cosmetic additives, and in biological control . However, little is known about the distribution of biosurfactant-producing bacteria in the environment . The goal of this study was to determine how common culturable surfactant-producing bacteria are in undisturbed and contaminated sites . A series of 20 contaminated (i.e., with metals and/or hydrocarbons) and undisturbed soils were collected and plated on R2A agar . The 1,305 colonies obtained were screened for biosurfactant production in mineral salts medium containing 2% glucose . Forty-five of the isolates were positive for biosurfactant production, representing most of the soils tested . The 45 isolates were grouped by using repetitive extragenic palindromic (REP)-PCR analysis, which yielded 16 unique isolates . Phylogenetic relationships were determined by comparing the 16S rRNA gene sequence of each unique isolate with known sequences, revealing one new biosurfactant-producing microbe, a Flavobacterium sp . Sequencing results indicated only 10 unique isolates (in comparison to the REP analysis, which indicated 16 unique isolates) . Surface tension results demonstrated that isolates that were similar according to sequence analysis but unique according to REP analysis in fact produced different surfactant mixtures under identical growth conditions . These results suggest that the 16S rRNA gene database commonly used for determining phylogenetic relationships may miss diversity in microbial products (e.g., biosurfactants and antibiotics) that are made by closely related isolates . In summary, biosurfactant-producing microorganisms were found in most soils even by using a relatively limited screening assay . Distribution was dependent on soil conditions, with gram-positive biosurfactant-producing isolates tending to be from heavy metal-contaminated or uncontaminated soils and gram-negative isolates tending to be from hydrocarbon-contaminated or cocontaminated soils .
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