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Sixty-four verotoxin-producing (VT+) Escherichia coli strains were analyzed for VT1- and VT2-specific DNA sequences and for production of hemolysin. Strains of human origin were of the following serotypes: O157:H7 or H-, O111:H8 or H-, O26:H11, O114:H4, and rough:H7. Strains of serotypes O157:H7, O113:H21, O116:H21, and rough:H- were from cattle, while those of serotype O139:K12:H1 were from pigs. All 64 isolates carried either VT1 or VT2 or both genes. Sixty of the strains (93.8%) were hemolytic (Hly+). The three O139:K12:H1 strains examined produced alpha-hemolysin, as shown by their reaction with the alpha-hemolysin-specific monoclonal antibody h2A and by DNA hybridization with an alpha-hly gene probe. The remaining 57 Hly+ strains (95%) produced a different type of hemolysin (enterohemolysin), which is genetically and serologically unrelated to alpha-hemolysin. The two types of hemolysin are further distinguished by the appearance of the lysis zone on blood agar and by the time interval for the detection of hemolysis. In contrast to alpha-hemolysin, enterohemolysin can be detected only on blood plates containing washed erythrocytes. The frequent association of enterohemolysin with verotoxin production (89%) makes it useful as an epidemiological marker for rapid and simple detection of potential VT+ E. coli.

K88 antigen-negative enterotoxigenic Escherichia coli and non-enterotoxigenic strains isolated from piglets with diarrhea were examined for K99 antigen by agglutination tests after growth on Minca-IsoVitaleX (BBL Microbiology Systems, Cockeysville, Md.) agar medium. Of 64 K88-negative enterotoxigenic strains from as many piglets, 17 were found to be K99 positive. Of these, 10 were Swedish and 7 were of Norwegian origin. All 17 produced heat-stable enterotoxin detectable in the infant mouse assay, but only 2 gave positive ligated loop tests in 3- to 7-week-old piglets. Ligated loop tests in 5- to 12-day-old piglets were positive for each of the 15 K99-positive strains tested. Each of the Swedish K99-positive isolates was from a piglet of lesser than or equal to 7 days of age. One piglet harboring a K99-positive strain also harbored an O141:K88 enterotoxigenic strain producing only heat-stable enterotoxin. Five of the Swedish piglets yielding K99-positive isolates were from dams vaccinated wih a multicomponent bacterial vaccine containing K88 antigen. The K99 strains were O:K:H serotyped. The O serogroups represented were O8, O9, O64, O101, and O140. None of the 101 non-enterotoxigenic porcine isolates, representing 42 serogroups and non-O-groupable and rough strains, was found to be K99 positive. The findings indicate that so-called class 2 or atypical porcine enterotoxigenic E. coli should be routinely examined for the presence of K99 antigen.

Two hundred and ninety-four isolates of Escherichia coli, including 105 from blood cultures, 94 from stools of hospital inpatients, and 96 from rectal cultures of healthy young adults, were biotyped by using the API-20E system and tested for the presence of K1 antigen. The overall frequency of K1 strains was 14.2% and was similar among the three sources. Forty-eight biotypes were observed, but two-thirds of all isolates, including two-thirds of the K1 strains, belonged to only five biotypes. Among the five commonest biotypes, the distribution of K1 strains was nonrandom, since 23 of the 27 K1 strains belonged to only two biotypes. Analysis of the O and H antigens of K1 strains indicated that this correlation of biotype with K1 antigen was due to a restricted number of serovars ("clones") that were repeatedly isolated from the population studied. These serovas included O18:K1:H7, O1:121:H6 and O16:K1:H6. Although a statistically significant correlation between biotype and K1 antigen was observed, the correlation was not sufficiently great to alow biotyping to be of significant predictive value as a marker for the K1 antigen.

The incidence of enterotoxigenic Escherichia coli (ETEC) was investigated in 95 E. coli strains isolated from 48 infants with diarrhea in Santiago, Chile. By using standard biological assays and DNA-DNA hybridization procedures, ETEC was found in 31.2% of the cases: 14 strains produced heat-stable enterotoxin (ST) only, three strains produced heat-labile enterotoxin (LT) and ST, and two strains produced LT only. DNA probes detected all enterotoxin producers except one ST-producing strain. The ST strains hybridized with one or both of the human ST probes (ST Ib and ST A2). Two of the LT-ST strains hybridized with the ST Ia and ST Ib probes, and the third strain did not hybridize with any of the ST probes. Only the ST group expressed multiple resistance (85.7%) and colonization factor antigen I (CFA I) (92.8%); CFA II was found in two of three LT-ST strains. The O153:H45 serotype was found in 10 of 14 ST strains, and O6:K15:H16 was found in one LT strain and in two LT-ST strains. These findings suggest that ETEC, especially strains that produce ST, may be an important cause of diarrhea among Chilean infants.

The relationship between bacterial characteristics and the severity of urinary tract infection in adults has not been clarified. In this study, Escherichia coli strains (n = 178) were prospectively collected from women with community-acquired urinary tract infection. The isolates were identified by O:K:H serotype and characterized for adherence, hemolysin production, and serum bactericidal resistance. The patients had acute pyelonephritis with or without complicating factors and acute cystitis. Nine serotypes (O1:K1:H7, O1:K1:H-, O2:K1:H-, O4:K12:H1, O7:K1:H-, O9:K34:H-, O16:K1:H6, O16:K1:H-, and O75:K5:H-) comprised 65% of the strains in uncomplicated pyelonephritis, but were significantly less often encountered in complicated pyelonephritis or cystitis. Adherence was the single property most characteristic of the pyelonephritogenic clones. Adhesins specifically recognizing Gal alpha 1----4Gal beta-containing receptors occurred in 80% of strains in uncomplicated pyelonephritis, in 50% of strains in complicated infections, and in 37% of cystitis strains. Hemolysin production and serum resistance did not correlate with any disease pattern. Advanced age did not seem to reduce the selection of virulent E. coli to cause pyelonephritis. These results demonstrate in women a relationship between E. coli virulence and the severity of urinary tract infection analogous to that previously observed in pediatric populations and also illustrate the balance between host resistance and bacterial virulence in the urinary tract.