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ABSTRACTWhile the differential association of Escherichia coliO157 genotypes with animal and human hosts has recently been well documented, little is known about their distribution between countries and how this might affect regional disease rates. Here, we used a 48-plex single nucleotide polymorphism (SNP) assay to segregate 148 E. coliO157 isolates from Australia, Argentina, and the United States into 11 SNP lineages. We also investigated the relationship between SNP lineages, Shiga toxin (Stx) gene profiles, and total Stx production. E. coliO157 isolates clearly segregated into SNP lineages that were differentially associated with each country. Of the 11 SNP lineages, seven were detected among isolates from a single country, two were detected among isolates from all three countries, and another two were detected only among U.S. and Argentinean isolates. A number of Australian (30%) and Argentinean (14%) isolates were associated with novel, previously undescribed SNP lineages that were unique to each country. Isolates within SNP lineages that were strongly associated with the carriage of stx2aproduced comparatively more Stx on average than did those lacking the stx2asubtype. Furthermore, the proportion of isolates in stx2a-associated SNP lineages was significantly higher in Argentina and the United States than Australia (P< 0.05). This study provides evidence for the geographic divergence of E. coliO157 and for a prominent role of stx2ain total Stx production. These results also highlight the need for more comprehensive studies of the global distribution of E. coliO157 lineages and the impacts of regionally predominant E. coliO157 lineages on the prevalence and severity of disease.

ABSTRACTThe genetic diversity of Vibrio choleraeO1 strains from Argentina was estimated by random amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE). Twenty-nine isolates carrying the virulence genes ctxA, zot, ace, and tcpAappeared to represent a single clone by both typing methods; while 11 strains lacking these virulence genes exhibited several heterogeneous RAPD and PFGE patterns. Among the last group, a set of isolates from the province Tucuma´n showed a single RAPD pattern and four closely related PFGE profiles. These strains, isolated from patients with diarrhea, did not produce the major V. choleraeO1 virulence determinants, yet cell supernatants of these isolates caused a heat-labile cytotoxic effect on Vero and Y-1 cells and elicited significant variations on the water flux and short-circuit current in human small intestine mounted in an Ussing chamber. All these effects were completely abolished by incubation with a specific antiserum against El Tor hemolysin, suggesting that this virulence factor was responsible for the toxic activity on both the epithelial cells and the small intestine specimens and may hence be involved in the development of diarrhea. We propose “Tucuma´n variant” as the designation for this new cluster of cholera toxin-negative V. choleraeO1 strains.

ABSTRACTBetween 9 October and 12 November 1996, an outbreak of bloody diarrhea occurred in the neonatal nursery ward of the Policli´nico Neuque´n, in Neuque´n, a city in the southwestern region of Argentina. Seven patients of the intermediate care unit were affected. Isolates of Escherichia coliO18ac:H31 that were non-lactose and -sorbitol fermenting were recovered from outbreak cases. Although the strains were negative for a number of virulence factors typically found in diarrheagenic groups of E. coli, all isolates from the present neonatal outbreak possessed the enterohemolysin gene, ehl1. All isolates showed resistance to the antibiotics ampicillin and chloramphenicol. These isolates showed a low adherence property in HeLa cells without any recognizable pattern. In order to evaluate the outbreak dissemination in the neonatology ward, a prevalence study was conducted on 13 November. Stool specimens were obtained from 16 neonates hospitalized in the sector and from 33 medical staff members. E. coliisolates with identical biochemical characteristics of the outbreak strain were recovered from 11 of 16 inpatients and from 4 of 33 staff members during the prevalence study. A total of 15 E. colistrains recovered both from the outbreak and the prevalence study were processed by random amplified polymorphic DNA (RAPD)-PCR and pulsed-field gel electrophoresis (PFGE). By RAPD-PCR 14 of 15 strains showed patterns with 85 to 100% similarity, and by PFGE these strains were identical, each showing a unique pattern with 15 bands between 40 and 400 kb. One strain isolated from a nurse during the prevalence study presented a pattern not related to the others, and this was characterized as E. coliO81:HNM resistant to ampicillin only and negative for all the virulence factors studied. This outbreak occurred despite strict regulations in place to prevent cross-infection in the hospital. Postoutbreak prevalence studies were performed weekly thereafter without detecting new cases.

ABSTRACTIn a follow-up study, enterotoxigenic Escherichia coli(ETEC) infections in 145 children from two communities located in northeastern Argentina were monitored for 2 years. The occurrence of diarrhea was monitored by weekly household visits. Of 730 fecal specimens collected, 137 (19%) corresponded to diarrheal episodes. ETEC was isolated from a significantly higher proportion of symptomatic (18.3%) than asymptomatic (13.3%) children (P= 0.04541). Individuals of up to 24 months of age were found to have a higher risk of developing ETEC diarrhea than older children (odds ratio [OR], 3.872; P= 0.00021). When the toxin profiles were considered, only heat stable enterotoxin (ST)-producing ETEC was directly associated with diarrhea (P= 0.00035). Fifty-five percent of the ETEC isolated from symptomatic children and 19% of the ETEC isolated from asymptomatic children expressed one of the colonization factors (CFs) investigated, i.e., CF antigen I (CFA/I), CFA/II, CFA/III, and CFA/IV; coli surface antigens CS7 and CS17; and putative CFs PCFO159, PCFO166, and PCFO20, indicating a clear association between diarrhea and ETEC strains that carry these factors (P= 0.0000034). The most frequently identified CFs were CFA/IV (16%), CFA/I (10%), and CS17 (9%). CFs were mostly associated with ETEC strains that produce ST and both heat-labile enterotoxin and ST. Logistic regression analysis, applied to remove confounding effects, revealed that the expression of CFs was associated with illness independently of the toxin type (OR, 4.81;P= 0.0003). When each CF was considered separately, CS17 was the only factor independently associated with illness (OR, 16.6; P= 0.0151). Most CFs (the exception was CFA/IV) fell within a limited array of serotypes, while the CF-negative isolates belonged to many different O:H types. These results demonstrate that some CFs are risk factors for the development of ETEC diarrhea.