Biomedical subjects

K Ramotar

Publications and source records attributed to K Ramotar.

26 records · Page 2Linked to original sources

PubMed1994

Methicillin-resistant Staphylococcus aureus in tertiary care institutions on the Canadian prairies 1990-1992.

OBJECTIVE: To review experience with methicillin-resistant Staphylococcus aureus (MRSA) in tertiary acute-care teaching hospitals on the Canadian prairies. DESIGN: Retrospective review for a 36-month period, 1990 through 1992. SETTING: Five tertiary acute-care teaching hospitals in three Canadian prairie provinces. METHODS: MRSA isolates and susceptibility were identified through the clinical microbiology laboratory at each institution. For each patient, data collected included duration of institutional residence prior to isolation, patient ethnic background, age, sex, and antimicrobial susceptibility. Epidemiologic typing of strains used restriction fragment length polymorphism analysis by pulsed-field gel electrophoresis. RESULTS: Two hundred fifty-nine MRSA isolates were identified in 135 patients during the 36 months, with substantial institutional variation in number of isolates. No consistent increase in yearly numbers of isolates was apparent. Patients usually had MRSA identified at admission (62%); only one of five centers had the majority of isolates acquired nosocomially. Patients with MRSA present at admission were more frequently of aboriginal (First Nations) ethnicity (62% compared with 14% of nosocomial; P < 0.001). Pulsed-field gel electrophoresis of 167 isolates from 135 patients revealed 46 different strains with little interprovincial or interinstitutional identity of strains. CONCLUSIONS: MRSA isolated in patients in tertiary care institutions in these three Canadian provinces usually is acquired prior to admission. A disproportionate number of isolates are identified in aboriginal Canadians. Epidemiologic typing was consistent with a polyclonal origin of MRSA in this geographic area.

Adult↗

PubMed1994

Risk factors for acquiring ampicillin-resistant enterococci and clinical outcomes at a Canadian tertiary-care hospital.

The number of ampicillin-resistant enterococci (ARE) was noted to be increased at our teaching hospital. To determine the risk factors for acquiring this organism and to compare clinical outcomes, over a 5-month period 38 patients infected or colonized with ARE were compared with 76 patients, infected or colonized with ampicillin-susceptible enterococci (ASE). Risk factors included nosocomial acquisition, duration of hospitalization, admission to a medical service, prior antimicrobial therapy, and combination therapy for at least 7 days. The mortality rate of patients infected or colonized with ARE was higher than that of patients infected or colonized with ASE (34 versus 14%; P = 0.03), but most deaths did not appear to be related to enterococcal infection. Over a 2-year period, 16 patients with ARE bacteremia were also compared with 23 patients with ASE bacteremia. The risk factors associated with ARE bacteremia also included nosocomial acquisition, duration of hospitalization, and prior antimicrobial therapy. The mortality of patients with ARE bacteremia was also higher than that of patients with ASE bacteremia (81 versus 30%; P = 0.003), with most deaths being due to the underlying disease or a complication of it. Typing of ARE isolates by pulsed-field gel electrophoresis showed that two genotypes predominated in our institution. A prolonged hospital stay, exposure to multiple antimicrobial agents, and perhaps nosocomial transmission are important factors in acquiring ARE. The presence of ARE may also be a marker for poor outcome.

Adolescent↗

PubMed1992

Alteration of the carbohydrate binding specificity of verotoxins from Gal alpha 1-4Gal to GalNAc beta 1-3Gal alpha 1-4Gal and vice versa by site-directed mutagenesis of the binding subunit.

Verotoxin 1 (VT-1) and Shiga-like toxin II (SLT-II) bind to the glycosphingolipid (GSL), globotriaosylceramide (Gb3), whereas pig edema disease toxin (VTE) binds to globotetraosylceramide (Gb4) and to a lesser degree Gb3. Amino acids important in the GSL binding specificity of VT-1 and VTE have been identified by site-directed mutagenesis. One mutation, Asp-18----Asn, in VT-1 resulted in binding to Gb4 in addition to Gb3 in a manner similar to VTE. Several mutations in VTE resulted in the complete loss of GSL binding; however, one mutation resulted in a change in the GSL binding specificity of the VTE B subunit. The double mutation Gln-64----Glu and Lys-66----Gln (designated GT3) caused a selective loss of Gb4 binding, effectively changing the binding phenotype from VTE to VT-1. Both wild-type VTE and GT3 were purified to homogeneity and binding kinetics in vitro were determined with purified GSLs from human kidney. The cell cytotoxicity spectrum of the mutant toxin was also found to be altered in comparison with VTE. These changes were consistent with the GSL content of the target cells.

Amino Acid Sequence↗

PubMed1990

Characterization of Shiga-like toxin I B subunit purified from overproducing clones of the SLT-I B cistron.

The cistron encoding the B subunit of Escherichia coli Shiga-like toxin I (SLT-I) was cloned under control of the tac promoter in the expression vector pKK223-3 and the SLT-I B subunit was expressed constitutively in a wild-type background and inducibly in a lacIq background. The B subunit was located in the periplasmic space, and less than 10% was found in the culture medium after 24 h incubation. Polymyxin B extracts contained as much as 160 micrograms of B subunit/ml of culture. B subunit was purified to homogeneity by ion-exchange chromatography followed by chromatofocusing. Cross-linking analysis of purified native B subunit showed that it exists as a pentamer. In gels containing 0.1% SDS the native protein dissociated into monomers. B subunit was found to have the same glycolipid-receptor-specificity as SLT-I holotoxin. Competitive binding studies showed that B subunit and holotoxin had the same affinity for the globotriosylceramide receptor. We conclude that this recombinant plasmid is a convenient source of large amounts of purified SLT-I B subunit, which could be used for biophysical and structural studies or as a natural toxoid.

Antibodies, Monoclonal↗

PubMed1990

Modification of the glycolipid-binding specificity of vero cytotoxin by polymyxin B and other cyclic amphipathic peptides.

Polymyxin B, an amphipathic cyclic decapeptide produced by Bacillus polymyxa, is routinely used in the extraction of the components from the periplasmic space of gram-negative bacteria. Vero cytotoxin 1 (VT1) is an Escherichia coli-elaborated subunit toxin which binds to the glycolipid globotriosylceramide (Gal-alpha 1-4-Gal beta 1-4-Glc-ceramide [Gb3]) and has been strongly implicated in the etiology of the hemolytic uremic syndrome and hemorrhagic colitis. We now show by in vitro glycolipid-binding assays that in the presence of low concentrations of polymyxin B, globotetraosylceramide (GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc-ceramide [Gb4]) is also recognized by both the VT1 B (binding) subunit and holotoxin. Melittin, a 26-amino-acid cyclic peptide of similar amphipathic nature, produced the same effect, whereas a hydrophobic blocking agent did not. Triton X-100 did not increase binding of VT1 to Gb4 but prevented glycolipid binding in toto at concentrations above 0.5%. Caution is therefore advised in the analysis of VT1 glycolipid binding in the presence of amphipathic peptides.

Bacterial Toxins↗

PubMed1989

Dietary deficiency of phylloquinone and reduced serum levels in febrile neutropenic cancer patients.

In 34 cancer patients with 40 neutropenic febrile episodes requiring broad-spectrum antimicrobial therapy, detailed dietary assessments revealed that deficient and severely deficient phylloquinone intakes (less than or equal to 70 and less than or equal to 25 micrograms/d) were identified during 88% and 38% of all days recorded, respectively. Serum phylloquinone levels and serial prothrombin times (PT) drawn in a similar group of 32 patients revealed that an elevated PT (greater than or equal to 2 s beyond control) was significantly associated (p less than 0.01) with a serum phylloquinone level of less than 4.4 nmol/L. Patients on antimicrobial regimens that suppressed menaquinone-producing intestinal microflora and that contained an N-methylthiotetrazole (NMTT) moiety had an elevated PT significantly more often than did patients receiving antimicrobial agents that preserved the microflora and contained no NMTT moiety (3 of 10 vs 10 of 11, respectively; p = 0.02 Fisher's exact). These data suggest that these patients have a profound deficiency of oral vitamin K intake that may be further augmented by antimicrobial therapy.

Agranulocytosis↗

PubMed1984

Hypoprothrombinemia in febrile, neutropenic patients with cancer: association with antimicrobial suppression of intestinal microflora.

Serial, twice-weekly prothrombin times were determined in 108 febrile, granulocytopenic patients with cancer who were prospectively randomized to receive empiric antimicrobial therapy with moxalactam plus ticarcillin (M/T) or tobramycin plus ticarcillin (T/T). Thirty of 54 patients given M/T and 13 of 54 patients given T/T developed prothrombin times that were greater than or equal to 2 sec beyond control values (P less than .001) after a mean of 6.5 days of antimicrobial therapy. Serious bleeding episodes were more frequent in the group given M/T than in that given T/T (10 and two patients, respectively; P less than or equal to .05). Serial quantitative stool cultures revealed that both Escherichia coli and Bacteroides species were suppressed by greater than or equal to 5 log10 in eight of nine patients given M/T and in three of nine given T/T (P less than .05, Fisher's exact test). A significant reduction of the population of E. coli and Bacteroides fragilis, organisms that are major producers of bacterially synthesized menaquinones, was associated with a high incidence of hypoprothrombinemia. These observations support the hypothesis that menaquinones may play an important physiological role in the maintenance of blood coagulation during episodic dietary deficiency of phylloquinone.

Anti-Bacterial Agents↗

PubMed1984

Production of menaquinones by intestinal anaerobes.

Ninety intestinal organisms (71 isolates from fecal samples of neutropenic patients with cancer or from various sites in patients with intraabdominal infections and 19 control strains) were examined by reverse-phase thin-layer chromatography for their ability to produce menaquinones in vitro. Menaquinones were found in all of 24 organisms of the Bacteroides fragilis group. Two other Bacteroides species, Bacteroides disiens and Bacteroides bivius, also produced menaquinones. A single isolate of Bacteroides species lacked menaquinones. These constituents were found in all of five strains of Escherichia coli, all of four strains of Klebsiella pneumoniae, five of eight strains of Propionibacterium species, two of five strains of Eubacterium species, and the one strain each of Arachnia propionica and Veillonella parvula tested. No menaquinones were detected in organisms of the genera Fusobacterium, Clostridium, Bifidobacterium, Lactobacillus, Actinomyces, Peptococcus, or Peptostreptococcus. These findings suggest that E. coli, Bacteroides species, and some gram-positive, anaerobic, non-spore-forming bacilli produce menaquinones that may be a source of vitamin K in patients who are deprived of exogenous vitamin K1.

Actinomycetaceae↗