[Show abstract][Hide abstract] ABSTRACT: Phage typing and DNA macrorestriction fragment analysis by pulsed-field gel electrophoresis (PFGE) were evaluated for use in the epidemiological subtyping of Escherichia coli serogroup O157 strains isolated in Ontario, Canada. Among 30 strains isolated from patients with sporadic cases of infection, 22 distinct XbaI macrorestriction patterns were identified and 17 strains exhibited unique PFGE patterns. In contrast, phage typing identified only seven different phage types and 17 strains belonged to the same phage type. A total of 25 phage type-macrorestriction pattern combinations were identified among the strains from patients with sporadic cases of infection. PFGE subtyping differentiated between unrelated strains that exhibited the same phage type, and in one group of strains, phage typing differentiated between strains of the same PFGE subtype. Both typing procedures correctly identified outbreak-related isolates as belonging to the same type in four separate outbreaks. Each outbreak strain was characterized by a distinct macrorestriction pattern, while phage typing subdivided the outbreak strains into only three different types. A small percentage of outbreak-related isolates had PFGE patterns that differed slightly (one or two DNA fragment differences) from that of the outbreak strain. On the other hand, each isolate from the same outbreak belonged to the same phage type as that of the outbreak strain. We conclude that phage typing and PFGE fingerprinting represent complementary procedures for the subtyping of E. coli serogroup O157 and that the combined use of these procedures provides optimal discrimination.
Journal of Clinical Microbiology 07/2000; 38(6):2366-8. · 4.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The utility of phage typing, pulsed-field gel electrophoresis (PFGE), and plasmid profile analysis was compared, to differentiate between Canadian Escherichia coli O157:H7 strains of human (n = 27) and cattle (n = 24) origin. The diversity indices for phage typing, plasmid analysis and PFGE were 0.85, 0.69 and 0.93, respectively. PFGE and phage typing were also applied to study the role of direct transmission of E. coli O157:H7 from cattle to humans on isolates collected from two separate farm outbreaks. PFGE showed that more than one E. coli O157:H7 strain with varying PFGE DNA subtype profiles, may be responsible for an outbreak, and that more than one E. coli O157:H7 subtype may be circulating on a particular farm at any one time. To our knowledge, this is one of the first reports where PFGE typing was used to verify the direct transmission of E. coli O157:H7 from cattle to humans.
Epidemiology and Infection 09/1999; 123(1):17-24. · 2.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Shigella is an important cause of diarrheal disease in children in developing countries. The increasing prevalence of antibiotic-resistant strains has stimulated interest in the use of multivalent Shigella vaccines. Because Shigella vaccines under development are based on eliciting immunity to O antigens, monitoring the distribution of serotypes in defined target populations is critical. We initiated health center-based surveillance in a poor semirural community in Colina, Santiago (7489 children <60 months of age) to determine the age-specific incidence of Shigella disease and the responsible serotypes.
Surveillance was maintained at the 2 health centers during warm seasons (November 1 through April 30) for 4 successive years (1994 to 1998). Shigella was recovered from 54 of 243 cases of dysentery (22%) and from 215 of 3966 cases of nondysenteric diarrhea (5.4%) (P < 0.001). The peak mean annual incidence of shigellosis occurred among children 12 to 47 months of age (9.0 to 12.6 cases/10(3) children), although the incidence in infants (5.2/10(3)) and children 48 to 59 months of age (6.2/10(3)) was also substantial. During the 1995 through 1996 season, an age-matched healthy control was cultured for every child <60 months of age with diarrhea. Shigella isolation from cases (34 of 576, 5.9%) was >8-fold higher than controls (4 of 576, 0.7%) (P < 0.01). Four serotypes, Shigella sonnei (45%), Shigella flexneri 2b (19%), S. flexneri 2a (14%) and S. flexneri 6 (11%), accounted for 89% of all cases.
Shigella remains an important pediatric pathogen in Santiago. The serotype distribution from Colina, which closely resembles data from a population-based surveillance study in Santiago in the mid-1980s, demonstrates a remarkable degree of serotype stability in Santiago during a 15-year period.
[Show abstract][Hide abstract] ABSTRACT: Helcococcus kunzii, a nonvirulent member of the human skin flora, has recently been implicated in causing infections in immunosuppressed patients. We report a case of breast abscess associated with H. kunzii in an immunocompetant patient and discuss the criteria used in its identification and our observations of susceptibility testing for this species.
Journal of Clinical Microbiology 09/1998; 36(8):2377-9. · 4.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In September 1994, a complaint was registered at a public health unit concerning a cheese product. In addition, public health laboratories in Ontario reported an increase in the number of isolates of Salmonella berta from patients with diarrhoeal illness. A clinical, environmental and laboratory investigation was initiated to determine the nature of this outbreak. Isolates of Salmonella berta were compared using large fragment genomic fingerprinting by pulsed-field gel electrophoresis (PFGE). By late October, 82 clinical cases had been identified including 35 confirmed, 44 suspected and 3 secondary. The investigation linked illness to consumption of an unpasteurized soft cheese product produced on a farm and sold at farmers' markets. Subtyping results of patient, cheese and chicken isolates were indistinguishable, suggesting that the cheese was contaminated by chicken carcasses during production. The outbreak illustrates the potential role of uninspected home-based food producers and of cross-contamination in the transmission of foodborne bacterial pathogens.
Epidemiology and Infection 02/1998; 120(1):29-35. · 2.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Streptococcus iniae is a pathogen in fish, capable of causing invasive disease and outbreaks in aquaculture farms. During the winter of 1995-1996 in the greater Toronto area there was a cluster of four cases of invasive S. iniae infection in people who had recently handled fresh, whole fish from such farms.
We conducted a prospective and retrospective community-based surveillance for cases of S. iniae infection in humans. To obtain a large sample of isolates, we studied cultures obtained from the surface of fish from aquaculture farms. Additional isolates were obtained from the brains of infected tilapia (oreochromis species). All the isolates were characterized by pulsed-field gel electrophoresis (PFGE).
During one year, our surveillance identified a total of nine patients with invasive S. iniae infection (cellulitis of the hand in eight and endocarditis in one). All the patients had handled live or freshly killed fish, and eight had percutaneous injuries. Six of the nine fish were tilapia, which are commonly used in Asian cooking. Thirteen additional S. iniae isolates (2 from humans and 11 from infected tilapia) were obtained from normally sterile sites. The isolates from the nine patients were indistinguishable by PFGE and were highly related to the other clinical isolates. There was substantial genetic diversity among the 42 surveillance isolates from the surface of fish, but in 10 isolates the PFGE patterns were identical to those from the patients with S. iniae infection.
S. iniae can produce invasive infection after skin injuries during the handling of fresh fish grown by aquaculture. We identified a clone of S. iniae that causes invasive disease in both humans and fish.
New England Journal of Medicine 09/1997; 337(9):589-94. · 54.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent policies of early discharge of postpartum mothers and their infants has raised concerns of possible decreased sensitivity in Guthrie bacterial inhibition assay (BIA) phenylketonuria (PKU) screening resulting in missed cases. In order to assess the potential impact of early discharge from hospital on neonatal screening for PKU and its variants, we performed 18 standard BIA screening tests on 11 newborn infants with the disease. Blood spot samples were collected from 1 to 24 h after birth and were analyzed at the Ontario Ministry of Health newborn screening laboratory according to the routine screening protocol. Except for one 4-hour postnatal sample from an infant with 'non-PKU mild hyperphenylalaninemia' (MHP) all blood samples showed phenylalanine levels > or = 240 mumol/l, irrespective of the age of the baby. During our 29 year experience with neonatal PKU screening (3.9 million infants tested), employing a cutoff blood phenylalanine of 240 mumol/l in blood spots obtained at > or = 24 h of age, only two biological false negative (one confirmed) tests were discovered in infants subsequently shown to have classical PKU: another three false negative tests were discovered in sibs of infants with MHP. The sensitivity of the screening test was 99.2% for infants with classical and mild PKU. Ascertainment of patients with MHP is unknown and is very likely incomplete. Over a 3-year period (1992-4) the specificity of the test was 99.9% for those screened after 24 h. The positive predictive value was 12.8%. Although early discharge may have an impact on other screened diseases, we conclude, from our studies, that early discharge may not affect the detection of infants with classical and mild (atypical) PKU, but would probably increase the number of infants with MHP missed using the BIA and a cutoff level of 240 mumol/l. Because of our experience and that of others, we recommend that neonates be at least 12 h of age before initial BIA PKU screening be carried out. To confirm this recommendation further prospective studies should be initiated.
Early Human Development 01/1997; 47(1):87-96. · 1.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Enterohemorrhagic Escherichia coli (EHEC) strains detected with DNA probes (for virulence plasmid and Shiga-like toxins) from subjects with hemolytic-uremic syndrome (n = 19) or diarrhea (n = 41) or asymptomatic carriers (n = 29) were examined for sorbitol fermentability, as were enterotoxigenic (n = 40), enteropathogenic (n = 40), and enteroinvasive (n = 40) E. coli and urinary tract infection (n = 40) strains and normal flora E. coli strains (n = 40). Sorbitol negativity was common only in EHEC, particularly among strains from severe clinical infections. All 19 EHEC strains from patients with hemolytic-uremic syndrome, irrespective of O:H serotype or Shiga-like toxin genotype, were sorbitol negative.
Journal of Clinical Microbiology 09/1995; 33(8):2199-201. · 4.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Yersinia enterocolitica has emerged as an enteropathogen associated with several types of human infections that often require antimicrobial therapy, but little is known about the antimicrobial susceptibilities of pathogenic strains isolated from humans in Canada. To determine the present patterns of antimicrobial susceptibility, to identify changes in these patterns that occurred during the past two decades, and to investigate the relationships between O serotypes and patterns of susceptibility, we tested a total of 1,105 pathogenic Y. enterocolitica strains isolated during 1972 to 1976, 1980, 1985, and 1990 for their susceptibilities to 22 antimicrobial agents. Susceptibility testing was performed by using a single breakpoint concentration in agar procedure. The results showed that all strains were susceptible to ciprofloxacin and piperacillin, and 98% or more of the strains from each period were susceptible to trimethoprim, sulfamethoxazole, cotrimoxazole, tetracycline, chloramphenicol, cefamandole, cefotaxime, aztreonam, and four aminoglycosides. In contrast, all strains were nonsusceptible to erythromycin, furazolidone, and clindamycin and 90% or more of the strains from each period were nonsusceptible to ampicillin, carbenicillin, ticarcillin, and cephalothin. Strains belonging to serotypes O:3, O:5,27, and O:8 had different patterns of susceptibility to ampicillin, carbenicillin, ticarcillin, and amoxicillin-clavulanic acid. No major difference in susceptibility was observed between any of the groups of human or animal strains included in the study, but nonsusceptibility to tetracycline increased from 0.4% in 1985 to 2% in 1990 in human strains isolated in those years. Our results indicate that between 1972 and 1990 there was no marked decrease in susceptibility to agents commonly used for therapy among pathogenic Y. enterocolitica strains isolated in Canada.
Antimicrobial Agents and Chemotherapy 10/1994; 38(9):2121-4. · 4.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The distribution of the Escherichia coli attaching and effacing (eae) gene in strains of verotoxin-producing E. coli (VTEC) isolated from cattle and humans was studied. The majority of strains isolated from humans with bloody diarrhoea or HUS and cattle with severe diarrhoea were eae positive (82 and 83% respectively). In contrast, 59% of VTEC isolated from asymptomatic cattle were eae negative and of the remaining 41% that were eae positive, the majority were serotype O157. H7. The nucleotide sequence of the 3' end of the eae gene of enteropathogenic E. coli (EPEC) of serotype O55. H7 was found to be almost identical to that of serotype O157. H7. Specific primers are described which detect the eae sequences of VTEC serotypes O157. H7, O157. H-, and EPEC serotypes O55. H7 and O55. H-. The nucleotide sequence of the 3' end of the eae gene of serotype O111. H8 differed significantly from that of O157. H7. Primers were developed to specifically identify the eae sequences of VTEC serotypes O111. H- and O111. H8. We conclude that whereas the majority of VTEC associated with disease in cattle and humans possess the eae gene, the gene itself may not be necessary to produce haemorrhagic colitis and HUS. Sequence heterogeneity in the 3' end of eae alleles of VTEC permits specific identification of subsets of these organisms.
Epidemiology and Infection 07/1994; 112(3):449-61. · 2.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Restriction fragment length polymorphisms (RFLPs) of genomic DNAs from 49 clinical isolates of Shigella sonnei were analyzed by using a modified restriction endonuclease analysis procedure to investigate the genetic variability of this species. After cleavage with the restriction enzyme HaeIII or RsaI, DNA samples were electrophoresed in polyacrylamide gels and the RFLP patterns were visualized by silver staining. The results showed that among 20 strains associated with sporadic cases of infection in three Canadian provinces, 15 distinct RFLP patterns were revealed by HaeIII digestion and 12 distinct patterns were revealed by RsaI digestion. In contrast, the RFLP patterns of individual isolates within six groups of epidemiologically related isolates were identical to each other but distinct from those of unrelated isolates, and these patterns could be used to determine the genetic relationships between isolates associated with separate outbreaks of shigellosis. Our results indicate that the modified restriction endonuclease analysis technique represents a rapid, reproducible, and highly discriminatory method for the molecular typing of this species.
Journal of Clinical Microbiology 07/1994; 32(6):1427-30. · 4.23 Impact Factor