Antimicrobial resistance patterns of Escherichia coli through the digestive tract of veal calves

The aim of the present study was to evaluate differences in resistance patterns of Escherichia coli in different parts of the digestive tract of veal calves. Therefore, after slaughter, the lower intestinal tract of 19 calves was sampled at five locations (duodenum, jejunum, cecum, colon, and rectum), and up to three E. coli isolates per sample underwent susceptibility testing for seven antimicrobial agents (gentamicin, amoxycillin + clavulanic acid, tetracycline, trimethoprim + sulfamethoxazole, ampicillin, nalidixic acid, and enrofloxacin), using the Kirby-Bauer disk diffusion method. Multiresistance (resistance to more than two compounds) was present in 93.5% of all isolates (n = 179). For gentamicin, nalidixic acid, and enrofloxacin, the percentage of resistant E. coli isolates was significantly lower in the duodenum and jejunum than in the cecum, colon, and rectum. For ampicillin, the percentage of resistance was significantly lower in the jejunum, compared to the other segments of the intestinal tract. For the other antimicrobials tested, no significant differences in the percentage of resistant isolates throughout the intestinal tract were detected. In conclusion, resistance among enteric E. coli from veal calves can reach high levels and prevalence depends on localization of sampling. These considerations should be taken into account when further fine-tuning sampling protocols for indicator bacteria.     

K-1 Antigen of Escherichia coli: Epidemiology and Serum Sensitivity of Pathogenic Strains

K-1 Escherichia coli are far more frequent in neonatal sepsis (36% of E. coli sepsis) and meningitis (80% of E. coli meningitis) than would be expected by the frequency of K-1 E. coli colonization in neonates (11 to 25%). There is no apparent parallel in cases of sepsis in adults. To study further this apparent age-related difference in virulence, E. coli K-1 clinical isolates were tested for their sensitivity to sera. Strains isolated from cases of neonatal meningitis were more sensitive to serum bactericidal activity than those from cases of neonatal or adult sepsis or adult meningitis (P < 0.01). Serum sensitivity did not appear to be determined by K or O antigens. Four isolates sensitive to serum bactericidal activity obtained from neonatal cerebrospinal fluid were killed by adult serum chelated with 0.05 M Mg(2+) ethyleneglycol-bis (beta-aminoethyl ether)-N,N-tetraacetic acid (EGTA), suggesting that the alternative pathway was activated. Although untreated neonatal sera killed these strains as well as adult sera did, EGTA-treated neonatal sera were less effective than EGTA-treated adult sera. This suggests that the alternative pathway function was not activated in neonatal sera. The bactericidal defect of neonatal EGTA-treated serum was partially corrected by addition of either A or B hyperimmune equine meningococcal antiserum.     

Increasing ciprofloxacin resistance among prevalent urinary tract bacterial isolates in Gaza Strip, Palestine

This article presents the incidence of ciprofloxacin resistance among 480 clinical isolates obtained from patients with urinary tract infection (UTI) during January to June 2004 in Gaza Strip, Palestine. The resistance rates observed were 15.0% to ciprofloxacin, 82.5% to amoxycillin, 64.4% to cotrimoxazole, 63.1% to doxycycline, 32.5% to cephalexin, 31.9% to nalidixic acid, and 10.0% to amikacin. High resistance to ciprofloxacin was detected among Acinetobacter haemolyticus (28.6%), Staphylococcus saprophyticus (25.0%),Pseudomonas aeruginosa (20.0%), Klebsiella pneumonia (17.6%), and Escherichia coli (12.0%). Minimal inhibitory concentration (MIC) of ciprofloxacin evenly ranged from 4 to 32 mu g/mL with a mean of 25.0 mu g/mL. This study indicates emerging ciprofloxacin resistance among urinary tract infection isolates. Increasing resistance against ciprofloxacin demands coordinated monitoring of its activity and rational use of the antibiotics.     

Quinolone-resistant uropathogenic Escherichia coli strains from phylogenetic group B2 have fewer virulence factors than their susceptible counterparts

The prevalence of 31 virulence factors was analyzed among nalidixic acid-susceptible and -resistant Escherichia coli strains from phylogenetic group B2. Hemolysin, cytotoxic necrotizing factor 1, and S and F1C fimbriae genes were less prevalent among nalidixic acid-resistant E. coli strains. Quinolone resistance may be associated with a decrease in the presence of some virulence factors.     

Characterization of multiple-antimicrobial-resistant Escherichia coli isolates from diseased chickens and swine in China

Escherichia coli isolates from diseased piglets (n = 89) and chickens (n = 71) in China were characterized for O serogroups, virulence genes, antimicrobial susceptibility, class 1 integrons, and mechanisms of fluoroquinolone resistance. O78 was the most common serogroup identified (63%) among the chicken E. coli isolates. Most isolates were PCR positive for the increased serum survival gene (iss; 97%) and the temperature-sensitive hemagglutinin gene (tsh; 93%). The O serogroups of swine E. coli were not those typically associated with pathogenic strains, nor did they posses common characteristic virulence factors. Twenty-three serogroups were identified among the swine isolates; however, 38% were O nontypeable. Overall, isolates displayed resistance to nalidixic acid (100%), tetracycline (98%), sulfamethoxazole (84%), ampicillin (79%), streptomycin (77%), and trimethoprim-sulfamethoxazole (76%). Among the fluoroquinolones, resistance ranged between 64% to levofloxacin, 79% to ciprofloxacin, and 95% to difloxacin. DNA sequencing of gyrA, gyrB, parC, and parE quinolone resistance-determining regions of 39 nalidixic acid-resistant E. coli isolates revealed that a single gyrA mutation was found in all of the isolates; mutations in parC together with double gyrA mutations conferred high-level resistance to fluoroquinolones (ciprofloxacin MIC, >/=8 microg/ml). Class 1 integrons were identified in 17 (19%) isolates from swine and 42 (47%) from chickens. The majority of integrons possessed genes conferring resistance to streptomycin and trimethoprim. These findings suggest that multiple-antimicrobial-resistant E. coli isolates, including fluoroquinolone-resistant variants, are commonly present among diseased swine and chickens in China, and they also suggest the need for the introduction of surveillance programs in China to monitor antimicrobial resistance in pathogenic bacteria that can be potentially transmitted to humans from food animals.     

Relationship between phylogenetic groups,antibiotic resistance and patient characteristics in terms of adhesin genes in cystitis and pyelonephritis isolates of Escherichia coli

Extraintestinal pathogenic Escherichia coli (E. coli) is considered as the main causative agent of urinary tract infections worldwide. The relationship between antimicrobial resistance, phylogenetic groups, patient characteristics and adhesin virulence genes are complex and not fully understood. In this study, among 146 urinary isolates of E. coli, phylogenetic groups and various adhesin virulence genes were examined with multiplex Polymerase Chain Reaction methods. Patient characteristics divided into sex, cystitis and pyelonephritis; community-acquired and hospital-acquired; complicated and uncomplicated infection. Antimicrobial resistance was also determined. The papAH gene was seen more often in pyelonephritis than cystitis and female than male patients. iha gene was more frequent in hospital-acquired infections than in community-acquired infections. sfa/focDE was more frequent in ampicillin, amikacin, gentamicin, nalidixic acid, norfloxacin, cefuroxime, ceftriaxone, cefazolin, cefotaxime, ciprofloxacin and trimethoprim/sulfamethoxazole susceptible and extended-spectrum β-lactamase (ESBL) and multi-drug resistance (MDR) negative isolates. focG was seen more often in nalidixic acid, norfloxacin, cefuroxime, ceftriaxone, ciprofloxacin susceptible and MDR negative isolates. fimH and papAH were more commonly observed in amoxicillin/clavulanic acid and cefotaxime susceptible isolates, respectively. iha and afa/draBC genes were more frequent in resistant isolates than the susceptible ones; for iha, in ampicillin, amoxicillin/clavulanic acid, nalidixic acid, cefuroxime, ceftriaxone resistant and ESBL and MDR positive isolates; for afa/draBC, in cefotaxime, cefuroxime, ciprofloxacin, trimethoprim/sulfamethoxazole resistant and ESBL and MDR positive isolates, this trend was observed. ST 131 E. coli virulence gene pattern has a direct effect on resistance profile. Isolates belong to that clonal group has MDR and commonly harbour afa/draBC and iha genes. Our findings may provide new insights into the relationships between pathogenesis, patient characteristics and resistance of E. coli UTI.     

Association between mortality of Escherichia coli meningitis in young infants and non-virulent clonal groups of strains

To identify factors associated with Escherichia coli meningitis (ECM) mortality in infants aged <3 months, the clinical, biological and bacterial characteristics of isolates from 99 cases of ECM were compared, including the phylogenetic group, multilocus sequence type, O serogroup and sequence O type (a combination of sequence type complex (STc) and O serogroup) and virulence genotype. All 99 isolates were susceptible to the initial antimicrobial treatment. The mortality rate (14%) was not influenced by term or post-natal age. Hypotension or seizures were the sole clinical predictive factors for fatal outcome (p <0.01), and abnormal initial trans-fontanellar ultrasound was associated with death (p 0.03). Seventy-seven isolates belonged to the common sequence O types (STc29^O1, STc29^O18, STc29^O45, STc301^O7, STc304^O16, STc697^O83, STc700^O1) causing neonatal meningitis. None of the phylogenetic groups and none of the virulence determinants were distributed differently between survivors and non-survivors, except that the aerobactin gene ( iucC ) was less frequent in lethal isolates (94% vs. 71%, p 0.02). Isolates belonging to rare sequence O types were more likely to be lethal (OR 4.3, p 0.01), although they induced a lower level of bacteraemia than common sequence O types such as STc29^O18 and STc29^O45 in a neonatal rat model. These results suggest that unidentified human genetic risk-factors may be more important than strain virulence in predicting ECM mortality.     

Molecular epidemiology of Escherichia coli causing neonatal meningitis

Escherichia coli is the second cause of neonatal meningitis which is a major cause of neonatal mortality and is associated with a high incidence of neurological sequelae. E. coli neonatal meningitis (ECNM) strains, as other extraintestinal pathogenic E. coli, mainly belong to the phylogenetic group B2 and to a lesser extent to group D, but are distributed in fewer clonal groups. One of these, the O18:K1:H7 clone is worldwide distributed meanwhile others such as O83:K1 and O45:K1 are restricted to some countries. Over the past few years, major progress has been made in the understanding of the pathophysiology of E. coli O18:K1:H7 neonatal meningitis. In particular, specific virulence factors have been identified and are known to be carried by ectochromosomal DNA in most cases. Molecular epidemiological studies, including characterization of virulence genotypes and phylogenetic analysis are important to lead to a comprehensive picture of the origins and spread of virulence factors within the population of ECNM strains. To date, all the known genetic determinants obtained in ECNM strains are not sufficient to explain their virulence in their globality and further studies on clonal groups different from the archetypal O18:K1:H7 clone are needed. These studies would serve to find common pathogenic mechanisms among different ECNM clonal groups that may be used as potential target for a worldwide efficacious prevention strategy.     

Patterns of mutations in target genes in septicemia isolates of Escherichia coli and Klebsiella pneumoniae with resistance or reduced susceptibility to ciprofloxacin

Thirty-two Escherichia coli and 21 Klebsiella pneumoniae septicemia isolates with varying degrees of resistance to ciprofloxacin were analyzed for the presence of point mutations within the quinolone-resistance target genes. The number of mutations observed in the resistant isolates agreed with the level of ciprofloxacin resistance in both species. Such isolates were also resistant to nalidixic acid. Isolates with borderline susceptibility to ciprofloxacin, on the other hand, behaved differently in the two species. In E. coli all the isolates harbored at least one mutation and these isolates were also resistant to nalidixic acid, while no mutations were detected in the K. pneumoniae isolates, and susceptibility to nalidixic acid was unpredictable. Therefore, nalidixic acid cannot be used as a class representative. Time-kill curve studies on an isolate with borderline susceptibility from each species showed higher degrees of resistance to ciprofloxacin in comparison to that of the wild-type E. coli. A previously unreported parC mutation, S57-->T, was detected in a resistant E. coli isolate and might expand the QRDR of this gene. Normalized resistance interpretations of histograms confirmed the setting of microbiological zone breakpoints for ciprofloxacin testing.     

Common virulence factors and genetic relationships between O18:K1:H7 Escherichia coli isolates of human and avian origin

Extraintestinal pathogenic (ExPEC) Escherichia coli strains of serotype O18:K1:H7 are mainly responsible for neonatal meningitis and sepsis in humans and belong to a limited number of closely related clones. The same serotype is also frequently isolated from the extraintestinal lesions of colibacillosis in poultry, but it is not well known to what extent human and avian strains of this particular serotype are related. Twenty-two ExPEC isolates of human origin and 33 isolates of avian origin were compared on the basis of their virulence determinants, lethality for chicks, pulsed-field gel electrophoresis (PFGE) patterns, and classification in the main phylogenetic groups. Both avian and human isolates were lethal for chicks and harbored similar virulence genotypes. A major virulence pattern, identified in 75% of the isolates, was characterized by the presence of F1 variant fimbriae; S fimbriae; IbeA; the aerobactin system; and genomic fragments A9, A12, D1, D7, D10, and D11 and by the absence of P fimbriae, F1C fimbriae, Afa adhesin, and CNF1. All but one of the avian and human isolates also belonged to major phylogenetic group B2. However, various subclonal populations could be distinguished by PFGE in relation to animal species and geographical origin. These results demonstrate that very closely related clones can be recovered from extraintestinal infections in humans and chickens and suggest that avian pathogenic E. coli isolates of serotype O18:K1:H7 are potential human pathogens.     

Extraintestinal pathogenic Escherichia coli as a cause of invasive nonurinary infections

Multiple Escherichia coli isolates from four adults with extraintestinal infections underwent molecular phylotyping and virulence profiling. A patient with secondary peritonitis had two low-virulence E. coli strains from phylogenetic groups A and D. In contrast, three patients with invasive extraurinary infections (septic arthritis/pyomyositis, nontraumatic meningitis/hematogenous osteomyelitis, and pneumonia) each had a single high-virulence phylogenetic group B2 strain resembling typical isolates causing urinary infection and/or sepsis, i.e., extraintestinal pathogenic E. coli.     

Identification of regions of the Escherichia coli chromosome specific for neonatal meningitis-associated strains

Specific virulence factors associated with the pathogenesis of Escherichia coli strains causing neonatal meningitis (ECNM), such as the K1 capsular polysaccharide, the S fimbriae, and the Ibe10 protein, have been previously identified. However, some other yet unidentified factors are likely to be involved in the pathogenesis of ECNM. To identify specialized unique DNA regions associated with ECNM virulence, we used the representational difference analysis technique. The genomes of two strains belonging to nonpathogenic phylogenetic group A of the ECOR reference collection were subtracted from E. coli strain C5, isolated from a case of neonatal meningitis. Strain C5 belongs to the phylogenetic group B2 as do the majority of ECNM. We have isolated and mapped 64 DNA fragments which are specific for strain C5 and not found in nonpathogenic strains. Of these clones, 44 were clustered in six distinct regions on the chromosome. The sfa and ibe10 genes were located in regions 2 and 6, respectively. A group of genes (cnf1, hra, hly, and prs) known to be present in a pathogenicity island of the uropathogenic strain E. coli J96 colocalized with region 6. The occurrence of these DNA regions was tested in a set of meningitis-associated strains and in a control group composed of non-meningitis-associated strains belonging to the same B2 group. Regions 1, 3, and 4 were present in 91, 82, and 81%, respectively, of the meningitis strains and in 40, 13, and 47% of the control strains. Together, these data suggest that regions 1, 3, and 4 code for factors associated with the ability of E. coli to invade the meninges of neonates.     

Both urinary and rectal Escherichia coli isolates are dominated by strains of phylogenetic group B2

To compare the genetic structures of uropathogenic and commensal Escherichia coli populations, a total of 181 urinary and rectal E. coli isolates were classified into intraspecies phylogenetic groups by PCR amplifications of phylogenetic markers. The genetic variability of these isolates within phylogenetic groups was further assessed by enterobacterial repetitive intergenic consensus (ERIC) typing. The distributions of 10 known virulence factors were also examined. In contrast with most reports, phylogenetic group B2 not only accounted for the majority of urinary isolates from young women with urinary tract infections (69%) but also was the dominant group among the rectal isolates from healthy young women (48%). Such difference may be explained by geographic variation, difference in host population characteristics, or differences in sampling method, or a combination of the three. Strains with known virulence factors most frequently belonged to phylogenetic groups B2 and D. Additionally, group B2 and D rectal isolates were more heterogeneous than urinary isolates. Two subclusters existed within group B2 strains by ERIC typing. These subclusters were not evenly distributed between rectal and urine isolates and differed in virulence gene distribution.     

Phylogenetic groups and virulence factors in pathogenic and commensal strains of Escherichia coli and their association with blaCTX-M

We compared the distribution of phylogenetic groups and nine virulence factors among the pathogenic (isolated from blood and urine) and commensal (isolated from feces of healthy individuals) strains of Escherichia coli, and also compared the occurrence of virulence factors according to the production of (bla)(CTX-M) among the pathogenic strains. A total of 550 non-duplicate E. coli isolates (145 from blood, 200 from urine, 205 from feces) were collected. Phylogenetic grouping and virulence genotyping were done by PCR for all isolates. For pathogenic strains, antimicrobial susceptibility tests and PCR for (bla)(CTX-M) were performed. The distribution of phylogenetic groups was similar between isolates from blood and urine: B2 (44.8%; 58.5%, respectively) > D (29.0%; 23.0%, respectively) > A (18.6%; 9.5%, respectively) > B1 (7.6% and 9.0%, respectively). Phylogenetic groups B2 and D were also frequent (22.9% and 21.0%, respectively) among isolates from feces. The prevalence of all virulence factors except S fimbrial adhesion was significantly higher in pathogenic strains than in commensal strains and they were most frequent in phylogenetic group B2. α-Haemolysin, yersiniabactin receptor, serum resistance-associated outer membrane protein (traT), and aerobactin receptor (iutA) were found to be independent predictors for pathogenicity, and of them, iutA and traT were significantly more common in (bla)(CTX-M-1 group) and (bla)(CTX-M-9 group,) respectively. Considering the possibility that these virulence genes, together with antimicrobial resistance genes, can spread to other strains, further study and ongoing surveillance seem to be required.     

Detection of decreased fluoroquinolone susceptibility in Salmonellas and validation of nalidixic acid screening test.

We evaluated 1,010 Salmonella isolates classified as fluoroquinolone susceptible according to the National Committee for Clinical Laboratory Standards guidelines for susceptibility to nalidixic acid and three fluoroquinolones. These isolates were divided into two distinct subpopulations, with the great majority (n = 960) being fully ciprofloxacin susceptible and a minority (n = 50) exhibiting reduced ciprofloxacin susceptibility (MICs ranging between 0.125 and 0.5 microg/ml). The less ciprofloxacin-susceptible isolates were uniformly resistant to nalidixic acid, while only 12 (1.3%) of the fully susceptible isolates were nalidixic acid resistant. A similar association was observed between resistance to nalidixic acid and decreased susceptibility to ofloxacin or norfloxacin. A mutation of the gyrA gene could be demonstrated in all isolates for which the ciprofloxacin MICs were >/= 0.125 microg/ml and in 94% of the nalidixic acid-resistant isolates but in none of the nalidixic acid-susceptible isolates analyzed. Identification of nalidixic acid resistance by the disk diffusion method provided a sensitivity of 100% and a specificity of 87.3% as tools to screen for isolates for which the MICs of ciprofloxacin were >/= 0.125 microg/ml. We regard it as important that microbiology laboratories endeavor to recognize these less susceptible Salmonella strains, in order to reveal their clinical importance and to survey their epidemic spread.     

Use of diagnostic microarrays for determination of virulence gene patterns of Escherichia coli K1, a major cause of neonatal meningitis

Forty Escherichia coli strains isolated primarily from neonatal meningitis, urinary tract infections and feces were screened for the presence of virulence genes with a newly developed microarray on the array tube format. A total of 32 gene probes specific for extraintestinal as well as intestinal E. coli pathotypes were included. Eighty-eight percent of the analyzed strains were positive for the K1-specific probe on the microarray and could be confirmed with a specific antiserum against the K1 capsular polysaccharide. The gene for the hemin receptor ChuA was predominantly found in 95% of strains. Other virulence genes associated with K1 and related strains were P, S, and F1C fimbriae specific for extraintestinal E. coli, the genes for aerobactin, the alpha-hemolysin and the cytotoxic necrotizing factor. In two strains, the O157-specific catalase gene and the gene for the low-molecular-weight heat-stable toxin AstA were detected, respectively. A total of 19 different virulence gene patterns were observed. No correlation was observed between specific virulence gene patterns and a clinical outcome. The data indicate that virulence genes typical of extraintestinal E. coli are predominantly present in K1 strains. Nevertheless, some of them can carry virulence genes known to be characteristic of intestinal E. coli. The distribution and combination of virulence genes show that K1 isolates constitute a heterogeneous group of E. coli.     

Phylogenetic groups and virulence factors of Escherichia coli strains causing pyelonephritis in children with and without urinary tract abnormalities

Escherichia coli isolates causing acute pyelonephritis in 93 children (25% with urinary tract abnormalities) were tested for nine virulence factors (papC, papGII, papGIII, sfa/foc, hlyC, cnf1, iucC, fyuA and iroN) and their phylogenetic groups were determined. Isolates lacking papGII were more frequent among patients with urinary tract abnormalities (58% vs. 10%, p 0.0003), as were non-virulent phylogenetic group A isolates (25% vs. 5%, p 0.043). Pyelonephritis caused by less virulent E. coli strains was more frequent among patients with significant urinary tract abnormalities. Further studies are required to determine whether screening for E. coli virulence factors may help to identify children warranting anatomical investigations.     

Antimicrobial resistance of Campylobacter spp. isolated from broiler flocks in Iceland 2001-2005

Minimum inhibitory concentrations of six antimicrobial agents were determined for one Campylobacter sp. isolate from each of the 362 Campylobacter-positive commercial chicken flocks in Iceland in the years 2001-2005. Of all isolates tested, 6.9% were resistant, although none were multiresistant. Resistance to ampicillin was most commonly observed (3.6%) followed by resistance to enrofloxacin (3%), nalidixic acid (1.9%), and oxytetracyclin (0.3%), with cross-resistance between enrofloxacin and nalidixic acid. All isolates were susceptible to erythromycin and gentamicin. Resistance rates among Campylobacter coli isolates (7/13 or 53.8%) were much higher than among Campylobacter jejuni isolates (18/349 or 5.2%), and resistance patterns differed. Resistant strains were compared using pulsed field gel electrophoresis. Macrorestriction with SmaI and KpnI restriction enzymes yielded 13 different pulsotypes, none of which indicated a predominant genotype. Specific pulsotypes with uniform resistance patterns arising on geographically separated farms indicate clonal dissemination. Although resistance levels were low and similar to that seen in the other Nordic countries, further research on this matter is needed as there is no antimicrobial selective pressure in chicken farming in Iceland.     

Virulence and antimicrobial resistance profiles among Escherichia coli strains isolated from human and animal wastewater

To gain insight into whether Escherichia coli isolated from humans and resistant to some common antimicrobial agents are derived from animals, 85 E. coli strains were selected by ERIC-PCR from human and animal wastewater samples. Phylogroup, pathogenicity islands (PAIs), resistance to quinolones, fluoroquinolones and presence of extended-spectrum beta-lactamases (ESBLs) were analyzed. Among the total, 55% were resistant to nalidixic acid and 38% to ciprofloxacin; 12% produced ESBLs. Chicken-derived strains were associated with quinolone and fluoroquinolone resistance and presence of ESBLs, while human strains were associated with susceptibility. Group B2 E. coli strains were associated with human origin, susceptibility to fluoroquinolones and presence of PAIs, whereas groups A, B1 and D showed a low virulence profile and a high level of antimicrobial resistance. In both human and animal wastewater, E. coli A, B1 and D were prevalent, and strains from both origins showed a similar virulence profile in each phylogroup. These findings led us to hypothesize that abusive antibiotic use in food animal production may promote the development of resistance among these intestinal E. coli phylogroups, which could later be transmitted to humans through the food supply. The low prevalence of E. coli group B2 in the animal gut may explain, at least in part, the absence of emergence of resistant B2 isolates.     

Fluoroquinolone-resistant uropathogenic Escherichia coli in Norway: evidence of clonal spread.

Prevalence, resistance profiles, virulence gene complements, and phylogenetic and clonal affinities of fluoroquinolone-resistant Escherichia coli from urinary tract infections (UTIs) in Norway were investigated. Of 7302 E. coli UTI isolates from 2003, 1.2% were fluoroquinolone-resistant; 35 of these fluoroquinolone-resistant isolates were included in the present study. The isolates were predominantly multiresistant, carried few virulence factors, and tended to belong to the less-virulent phylogroups A and B1. Although the isolates were genetically heterogeneous, there was evidence of a limited degree of clonal dissemination.