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Relationship between Phenotypic and Genotypic Florfenicol Resistance in Escherichia coli. Randall S. Singer, 2004.This study evaluated the relationship between florfenicol resistance and flo genotypes in 1,987 Escherichia coli isolates from cattle . The flo gene was detected in 164 isolates, all of which expressed resistance to florfenicol at MICs of  256 µg/ml . The florfenicol MICs for all isolates that lacked flo were
 16 µg/ml .
Increased Serum Resistance in Klebsiella pneumoniae Strains Producing Extended-Spectrum ß-Lactamases. H. Sahly, 2004.The aim of this study was to determine whether there is an association between serum resistance, O serotypes, and the production of extended-spectrum ß-lactamases (ESBLs) in Klebsiella pneumoniae . Ninety ESBL-producing and 178 non-ESBL-producing K . pneumoniae isolates gathered in five European countries were O serotyped and tested for sensitivity to the serum's bactericidal effect . The frequency of serum-resistant isolates was higher among ESBL-producing strains (30%; 27/90 isolates) than among non-ESBL-producing strains (17.9%; 32/178 isolates) (P = 0.037; odds ratio [OR] = 1.96; 95% confidence interval [95% CI] = 1.08 to 3.53) . Although O1 was the most common O serotype in both Klebsiella groups, its frequency among ESBL-producing strains was significantly higher (59%; 53/90 isolates) than among non-ESBL producers (36%; 64/178 isolates) (P = 0.0006; OR = 2.5; 95% CI = 1.52 to 4.29) . Furthermore, the prevalence of the O1 serotype was higher among serum-resistant strains of both ESBL-producing (74%; 20/27isolates) and non-ESBL producers (75%; 24/32 isolates) than among serum-sensitive ESBL producers (52.4%; 33/63 isolates) and non-ESBL producers (27.4%; 40/146 isolates) . Serum resistance among ESBL-producing strains (36%; 17/47 isolates) versus non-ESBL-producing strains (16%; 27/166 isolates) was also significantly higher after the exclusion of clonal strains (P = 0.0056; OR = 2.9; 95% CI = 1.41 to 6.01) . Sixteen ESBL types were detected, among which the frequency of serum resistance was significantly lower among the SHV-producing strains (9/48 isolates) than among the TEM producers (16/35 isolates) (P = 0.016; OR = 3.65; CI = 1.3 to 9.7) . Curing ESBL-coding plasmids did not influence the serum resistance of the bacteria; all six plasmid-cured derivatives maintained serum resistance . The present findings suggest that ESBL-producing strains have a greater pathogenic potential than non-ESBL-producing strains, but the linkage between O serotypes, serum resistance, and ESBL production remains unclear at this stage . Horizontal Transfer of Segments of the 16S rRNA Genes between Species of the Streptococcus anginosus Group. Leo M. Schouls, 2003.The nature in variation of the 16S rRNA gene of members of the Streptococcus anginosus group was investigated by hybridization and DNA sequencing . A collection of 708 strains was analyzed by reverse line blot hybridization . This revealed the presence of distinct reaction patterns representing 11 different hybridization groups . The 16S rRNA genes of two strains of each hybridization group were sequenced to near-completion, and the sequence data confirmed the reverse line blot hybridization results . Closer inspection of the sequences revealed mosaic-like structures, strongly suggesting horizontal transfer of segments of the 16S rRNA gene between different species belonging to the Streptococcus anginosus group. Southern blot hybridization further showed that within a single strain all copies of the 16S rRNA gene had the same composition, indicating that the apparent mosaic structures were not PCR-induced artifacts. These findings indicate that the highly conserved rRNA genes are also subject to recombination and that these events may be fixed in the population . Such recombination may lead to the construction of incorrect phylogenetic trees based on the 16S rRNA genes . Intraspecific Diversity of Vibrio vulnificus in Galveston Bay Water and Oysters as Determined by Randomly Amplified Polymorphic DNA PCR. Meilan Lin, 2003.Randomly amplified polymorphic DNA (RAPD) PCR was used to analyze the temporal and spatial intraspecific diversity of 208 Vibrio vulnificus strains isolated from Galveston Bay water and oysters at five different sites between June 2000 and June 2001 . V . vulnificus was not detected during the winter months (December through February) . The densities of V . vulnificus in water and oysters were positively correlated with water temperature . Cluster analysis of RAPD PCR profiles of the 208 V . vulnificus isolates revealed a high level of intraspecific diversity among the strains . No correlation was found between the intraspecific diversity among the isolates and sampling site or source of isolation . After not being detected during the winter months, the genetic diversity of V . vulnificus strains first isolated in March was 0.9167 . Beginning in April, a higher level of intraspecific diversity (0.9933) and a major shift in population structure were observed among V . vulnificus isolates . These results suggest that a great genetic diversity of V . vulnificus strains exists in Galveston Bay water and oysters and that the population structure of this species is linked to changes in environmental conditions, especially temperature .
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