Escherichia coli O157:H7, a toxin-producing food and waterborne bacterial pathogen, has been linked to large outbreaks of gastrointestinal illness for more than two decades. E. coli O157 causes a wide range of clinical illness that varies by outbreak, although factors that contribute to variation in disease severity are poorly understood. Several recent outbreaks involving O157 contamination of fresh produce (e.g., spinach) were associated with more severe disease, as defined by higher hemolytic uremic syndrome and hospitalization frequencies, suggesting that increased virulence has evolved. To test this hypothesis, we developed a system that detects SNPs in 96 loci and applied it to >500 E. coli O157 clinical strains. Phylogenetic analyses identified 39 SNP genotypes that differ at 20% of SNP loci and are separated into nine distinct clades. Differences were observed between clades in the frequency and distribution of Shiga toxin genes and in the type of clinical disease reported. Patients with hemolytic uremic syndrome were significantly more likely to be infected with clade 8 strains, which have increased in frequency over the past 5 years. Genome sequencing of a spinach outbreak strain, a member of clade 8, also revealed substantial genomic differences. These findings suggest that an emergent subpopulation of the clade 8 lineage has acquired critical factors that contribute to more severe disease. The ability to detect and rapidly genotype O157 strains belonging to such lineages is important and will have a significant impact on both disease diagnosis and treatment guidelines.pathogens ͉ polymorphisms ͉ population genetics E nterohemorrhagic Escherichia coli (EHEC) includes a diverse population of Shiga toxin-producing E. coli that causes outbreaks of food and waterborne disease (1-3). EHEC often resides in bovine reservoirs and is transmitted via many food vehicles including cooked meat, such as hamburger (4) and salami (5), and raw vegetables, such as lettuce (6, 7) and spinach (8). In North America, E. coli O157:H7 is the most common EHEC serotype contributing to Ͼ75,000 human infections (9) and 17 outbreaks (3) per year.It is not clear why outbreaks of EHEC O157 vary dramatically in the severity of illness and the frequency of the most serious complication, hemolytic uremic syndrome (HUS) (10-12). The 1993 outbreak in western North America (4) and the large 1996 outbreak in Japan (13) had low rates of hospitalization and HUS (14, 15), whereas the 2006 North American spinach outbreak (8) had high rates of both hospitalization (Ͼ50%) and HUS (Ͼ10%). One hypothesis is that outbreak strains differ in virulence as a result of variation in the presence and expression of different Shiga toxin (Stx) gene combinations (16)(17)(18)(19).To assess the genetic diversity and variability in virulence among E. coli O157 strains, we developed a real-time PCR system for identifying synonymous and nonsynonymous mutations as SNPs (20-23). Although molecular subtyping methods, such as pulsedfield gel electrophoresis (PFGE), ...

A total of 868 isolates was screened from seven different collections of organisms from previous studies ± pyelonephritis in children aged 1±24 months; ®rst, second and recurring urinary tract infection (UTI) in women aged 18±39 years; UTI in women aged 40±65 years and peri-urethral and faecal isolates from women aged 18±39 years ± for the presence of 10 potential Escherichia coli UTI virulence genes. Previously reported differences between the frequency of these genes in UTI compared with faecal isolates were con®rmed and extended. A single virulence signature (strains containing aer, kpsMT, ompT, ®m and papG AD ) occurred in 29% of the pyelonephritic isolates, but in no more than 11% of the other collections. Peri-urethral isolates were found to have frequencies of these 10 genes that differed from those found for both UTI and faecal isolates.

Neisseria meningitidis is infrequently reported as a laboratory-acquired infection. Prompted by two cases in the United States in 2000, we assessed this risk among laboratorians. We identified cases of meningococcal disease that were possibly acquired or suspected of being acquired in a laboratory by placing an information request on e-mail discussion groups of infectious disease, microbiology, and infection control professional organizations. A probable case of laboratory-acquired meningococcal disease was defined as illness meeting the case definition for meningococcal disease in a laboratorian who had occupational exposure to an N. meningitidis isolate of the same serogroup within 14 days of illness onset. Sixteen cases of probable laboratory-acquired meningococcal disease occurring worldwide between 1985 and 2001 were identified, including six U.S. cases between 1996 and 2000. Nine cases (56%) were serogroup B; seven (44%) were serogroup C. Eight cases (50%) were fatal. All cases occurred among clinical microbiologists. In 15 cases (94%), isolate manipulation was performed without respiratory protection. We estimated that an average of three microbiologists are exposed to the 3,000 meningococcal isolates seen in U.S. laboratories yearly and calculated an attack rate of 13/100,000 microbiologists between 1996 and 2001, compared to 0.2/100,000 among U.S. adults in general. The rate and case/fatality ratio of meningococcal disease among microbiologists are higher than those in the general U.S. population. Specific risk factors for laboratory-acquired infection are likely associated with exposure to droplets or aerosols containing N. meningitidis. Prevention should focus on the implementation of class II biological safety cabinets or additional respiratory protection during manipulation of suspected meningococcal isolates.

BackgroundWhile Group B Streptococcus (GBS) human colonization and infection has long been suspected as originating from cows, several investigators have suggested that ongoing interspecies GBS transmission is unlikely due to genotyping data demonstrating that human and bovine-derived GBS strains represent mostly distinct populations. The possibility of ongoing transmission between humans and their livestock has not been systematically examined.Methodology/Principal FindingsTo examine ongoing interspecies transmission, we conducted a prospective cross-sectional cohort study of 68 families and their livestock. Stool specimens were collected from 154 people and 115 livestock; GBS was detected in 19 (12.3%) humans and 2 (1.7%) animals (bovine and sheep). Application of multilocus sequence typing (MLST) identified 8 sequence types (STs or clones), with STs 1 and 23 predominating. There were 11 families in which two members submitted stools and at least one had GBS colonization. In 3 of these families, both members (consisting of couples) were colonized, yielding a co-colonization rate of 27% (95% CI: 7%–61%). Two of these couples had strains with identical MLST, capsule (cps) genotype, susceptibility, and RAPD profiles. One couple co-colonized with ST-1 (cps5) strains also had a bovine colonized with the identical strain type. On multivariate analysis of questionnaire data, cattle exposure was a predictor of GBS colonization, with each unit increase in days of cattle exposure increasing the odds of colonization by 20% (P = 0.02). These results support interspecies transmission with additional evidence for transmission provided by the epidemiological association with cattle exposure.Conclusions/SignificanceAlthough GBS uncommonly colonizes livestock stools, increased frequency of cattle exposure was significantly associated with human colonization and one couple shared the same GBS strains as their bovine suggesting intraspecies transmission. These results set the framework for GBS as a possible zoonotic infection, which has significant public health implications.