PubMed Health⌕ Search

Biomedical subjects

James R Johnson

Publications and source records attributed to James R Johnson.

At least 73 records · Page 4Linked to original sources
PubMed2004

Detection of the Escherichia coli group 2 polysaccharide capsule synthesis Gene kpsM by a rapid and specific PCR-based assay.

A rapid and simple PCR-based assay for detection of the group 2 capsule synthesis gene kpsM of Escherichia coli was designed and validated. When combined with the published group 2 primers (kpsIIf, 5'-GCGCATTTGCTGATACTGTTG-3'; kpsIIr, 5'-CATCCAGACGATAAGCATGAGCA-3'), the new primers (the kpsIIf primer and a new reverse primer K2r, 5'-AGGTAGTTCAGACTCACACCT-3') allowed specific identification by exclusion of the heretofore elusive K2 kpsM variant. The primers yielded the predicted amplicon when multiplexed with other primers and used under varied assay conditions, including a range of concentrations of individual reaction mixture ingredients and of annealing temperatures (from 54 to 64 degrees C).

Bacterial Capsules↗
PubMed2004

Rapid and specific detection of Escherichia coli clonal group A by gene-specific PCR.

PCR primers specific for the recently described antimicrobial resistance-associated Escherichia coli clonal group A (CGA), a widespread cause of drug-resistant urinary tract infections in the United States, were devised on the basis of a novel single-nucleotide polymorphism identified within the housekeeping gene fumC, i.e., C288T. In comparison with two reference PCR-based fingerprinting methods, ERIC2 PCR and random amplified polymorphic DNA (RAPD) analysis, a PCR assay incorporating the new primers provided 100% sensitivity and 100% specificity for the detection of CGA among 138 diverse clinical and reference E. coli isolates. E. coli reference (ECOR) strain 47 was shown to be a member or a close relative of CGA (by ERIC2 PCR and RAPD analysis, respectively) and yielded a positive assay result. The new CGA-specific PCR assay, which exhibited interlaboratory reproducibility and stability under various experimental conditions, should allow the rapid and specific detection of CGA by any laboratory equipped for diagnostic PCR.

DNA Primers↗
PubMed2004

Rapid and specific detection of the O15:K52:H1 clonal group of Escherichia coli by gene-specific PCR.

Primers specific for Escherichia coli O15:K52:H1 were devised based on a novel single-nucleotide polymorphism identified within the housekeeping gene fumC, i.e., G594A. In experiments comparing various reference typing methods, the new primers provided 100% sensitivity and specificity for the O15:K52:H1 clonal group, including 162 diverse clinical and reference E. coli isolates.

Base Sequence↗
PubMed2004

Intestinal population dynamics of UTI-causing Escherichia coli within heterosexual couples.

From October 1999 to July 2001, a prospective cohort study was conducted to assess the intestinal Escherichia coli population dynamics of 23 sexually active couples. We tested the hypothesis that intestinal persistence and predominance of specific E. coli strains, co-colonization of sex partners with the same E. coli strain, and the intestinal diversity of fecal E. coli, contribute to recurrent urinary tract infection (UTI). E. coli isolates causing UTI, asymptomatic bacteriuria (ABU), or intestinal co-colonization were evaluated by ERIC2 PCR and compared with strains recovered exclusively from stool samples with respect to intestinal persistence, predominance, and diversity. Contrary to our hypothesis, UTI-causing strains exhibited similar levels of intestinal persistence and predominance as did fecal strains, and UTI episodes were not associated with shifts in fecal E. coli diversity. In contrast, intestinal co-colonization strains exhibited greater persistence and predominance than did fecal strains and were more likely to cause ABU, and co-colonization episodes were associated with significantly increased fecal E. coli diversity. Nonetheless, intestinal co-colonization strains were not associated with UTI. These findings suggest that E. coli strains involved in co-colonization may be more important contributors to intestinal E. coli dynamics than to UTI pathogenesis.

Adolescent↗
PubMed2003

Phylogenetic origin and virulence genotype in relation to resistance to fluoroquinolones and/or extended-spectrum cephalosporins and cephamycins among Escherichia coli isolates from animals and humans.

In Escherichia coli infection, the implications of fluoroquinolone (FQ) and extended-spectrum cephalosporin plus cephamycin (AmpC) resistance for phylogenetic origin and virulence potential are undefined, as is the influence of ecological context on these associations. Accordingly, 106 E. coli isolates exhibiting FQ and/or AmpC resistance and 98 susceptible isolates were compared with regard to phylogenetic background and virulence profiles, stratified by host group (104 predominantly extraintestinal human isolates and 100 predominantly intestinal cattle and swine isolates). Although resistant isolates exhibited significant shifts in phylogenetic distribution and virulence profiles, human and animal isolates exhibited different phylogenetic shifts, and only among human isolates did resistance predict reduced virulence. Evidence for similar strains being resistant versus susceptible was scant. The O15:K52:H1 clonal group and the closely related "clonal group A" featured prominently among resistant and susceptible human isolates, respectively. Thus, in E. coli, antibiotic resistance predicts phylogenetic background and virulence potential in a complex, context-dependent fashion.

Animals↗
PubMed2003

Microbial virulence determinants and the pathogenesis of urinary tract infection.

The most frequent and best-studied agent of urinary tract infection (UTI) is Escherichia coli, which serves as a useful model pathogen for understanding microbial virulence in relation to UTI pathogenesis. The E. coli strains that cause most UTIs and other extraintestinal E. coli infections represent a highly specialized subset of the total E. coli population. The enhanced virulence potential of such strains, which collectively are known as uropathogenic E. coli or extraintestinal pathogenic E. coli (ExPEC), is thought to be caused mainly by their multiple virulence factors. These virulence factors include diverse adhesins, siderophores, toxins, polysaccharide coatings, and other properties that assist the bacteria in avoiding or subverting host defenses, injuring or invading host cells and tissues, and stimulating a noxious inflammatory response. Although the true evolutionary basis for ExPEC is unknown, the virulence factors of ExPEC serve as useful epidemiologic markers and in the future may provide effective targets for anti-UTI interventions.

Adhesins, Escherichia coli↗
PubMed2003

Medical and economic impact of extraintestinal infections due to Escherichia coli: focus on an increasingly important endemic problem.

Escherichia coli is probably the best-known bacterial species and one of the most frequently isolated organisms from clinical specimens. Despite this, underappreciation and misunderstandings exist among medical professionals and the lay public alike regarding E. coli as an extraintestinal pathogen. Underappreciated features include (i) the wide variety of extraintestinal infections E. coli can cause, (ii) the high incidence and associated morbidity, mortality, and costs of these diverse clinical syndromes, (iii) the pathogenic potential of different groups of E. coli strains for causing intestinal versus extraintestinal disease, and (iv) increasing antimicrobial resistance. In this era in which health news often sensationalizes uncommon infection syndromes or pathogens, the strains of E. coli that cause extraintestinal infection are an increasingly important endemic problem and underappreciated "killers". Billions of health care dollars, millions of work days, and hundreds of thousands of lives are lost each year to extraintestinal infections due to E. coli. New treatments and prevention measures will be needed for improved outcomes and a diminished disease burden.

Bacteremia↗
PubMed2003

Isolation and molecular characterization of nalidixic acid-resistant extraintestinal pathogenic Escherichia coli from retail chicken products.

Fluoroquinolone use in poultry production may select for resistant Escherichia coli that can be transmitted to humans. To define the prevalence and virulence potential of poultry-associated, quinolone-resistant E. coli in the United States, 169 retail chicken products from the Minneapolis-St. Paul area (1999 to 2000) were screened for nalidixic acid (Nal)-resistant E. coli. Sixty-two (37%) products yielded Nal-resistant E. coli. From 55 products that yielded both Nal-resistant and susceptible E. coli, two isolates (one resistant, one susceptible) per sample were further characterized. Twenty-three (21%) of the 110 E. coli isolates (13 resistant, 10 susceptible) satisfied criteria for extraintestinal pathogenic E. coli (ExPEC), i.e., exhibited >or=2 of pap (P fimbriae), sfa/foc (S/F1C fimbriae), afa/dra (Dr binding adhesins), iutA (aerobactin receptor), and kpsMT II (group 2 capsule synthesis). Compared with other isolates, ExPEC isolates more often derived from virulence-associated E. coli phylogenetic groups B2 or D (74% versus 32%; P < 0.001) and exhibited more ExPEC-associated virulence markers (median, 10.0 versus 4.0; P < 0.001). In contrast, the Nal-resistant and -susceptible populations were indistinguishable according to all characteristics analyzed, including pulsed-field gel electrophoresis profiles. These findings indicate that Nal-resistant E. coli is prevalent in retail poultry products and that a substantial minority of such strains represent potential human pathogens. The similarity of the Nal-resistant and -susceptible populations suggests that they derive from the same source population, presumably the avian fecal flora, with Nal resistance emerging by spontaneous mutation as a result of fluoroquinolone exposure.

Animals↗
PubMed2003

High-frequency secondary mutations after suicide-driven allelic exchange mutagenesis in extraintestinal pathogenic Escherichia coli.

Frequent unintended secondary mutations occurred in extraintestinal pathogenic Escherichia coli strains CP9, CFT073, and RS218 during suicide plasmid-mediated, putatively specific deletions of hlyA, papG allele III, and iha. Pulsed-field gel electrophoresis and PCR analyses demonstrated genomic alterations and/or unintended loss of defined virulence genes (papG, the F7-2 papA allele, iutA, sat, hlyD, and cnf). Caution is warranted when attributing the observed phenotypic changes to the intended mutation.

Alleles↗