Form variation in Escherichia coli K1: determined by O-acetylation of the capsular polysaccharide.

The chemical basis for the alternating antigenic change called form variation noted for the Escherichia coli K1-capsular polysaccharide has been shown by 13C nuclear magnetic resonance to be a result of random O-acetylation of C7 and C9 carbons of the alpha-2-8-linked sialic acid homopolymer. A serologic method (antiserum agar) was developed to identify and isolate the form variants. The O-acetyl positive and O-acetyl negative K1 polysaccharides had unique biochemical and immunologic properties. The O-acetyl-positive variants resisted neuraminidase hydrolysis in contrast to the susceptibility of the O-acetyl negative variant to this enzyme. In addition, O-acetylation altered the antigenicity of the O-acetyl polysaccharides. When injected as whole organisms, O-acetyl positive organisms produced anti-K1 -antibodies in rabbits specific for this polysaccharide variant. O-acetyl negative organisms were comparatively less immunogenic; however, antibodies induced by these organisms reacted with both K1 polysaccharide variants. Burros, injected with either variant, produced antibodies reactive with both K1 polysaccharides.

Escherichia coli K51 and K93 capsular polysaccharides are crossreactive with the group A capsular polysaccharide of Neisseria meningitidis. Immunochemical, biological, and epidemiological studies.

Eleven Escherichia coli strains, crossreactive with the capsular polysaccharide (CPS) of Neisseria meningitidis group A (GrA), were detected among 645 stool isolates from healthy families in Cairo, Egypt. 10 of these strains were of the O107:K93:H27 or O107:K93:SP serotypes and may be considered descendents of a single bacterium or as a clone. The remaining crossreactive strain was of the O7:K51:H18 serotype. None of the 11 strains produced enterotoxins and none were enteroinvasive. The purified CPS of these E. coli strains, as well as a polysaccharide (PS) from B. pumilis, strain Sh17, precipitated with equine GrA (H49) antiserum. A partial identity between the E. coli K93, K51 and Sh17 PS on the one hand and the GrA CPS on the other was observed by double immunodiffusion when reacted against the H49 antiserum. Four K93 strains and one K51 strain were found among 320 E. coli strains from patients at the Clinical Center, National Institutes of Health, and three K93 strains were found in 105 stool samples from children in Copenhagen. The data from these three surveys suggest that these crossreactive E. coli are common organisms and could serve as a stimulus for "natural" GrA CPS antibodies. Quantitative precipitation analysis showed that K51, K93, and Sh17 PS precipitated 25, 46.8, and 50% of H49 antibodies, respectively. Absorption of H49 antiserum with the GrA CPS removed its precipitating activity with the E. coli K93, K51, and Sh17 PS. Absorption of H49 antiserum with either K51 CPS or Sh17 PS removed the homologous crossreactivity only, whereas K93 CPS absorbed both K93 and K51 reactivities. Antibodies, raised by intravenous injection of formalinized E. coli K93 or K51 cells into rabbits, precipitated with GrA CPS and were bactericidal against GrA meningococci. The crossreaction between the E. coli K93 and the GrA CPS was unexpected since these two CPS are compositionally so dissimilar.

Complex formation between Escherichia coli lipopolysaccharide O antigen and capsular K antigen as detected by immunoelectrophoresis.

Many Escherichia coli of serotypes commonly found in the normal intestine and in extraintestinal diseases, and having capsular antigens of the low molecular group called group II, will, in simple saline extracts, produce complexes between some or all of the lipopolysaccharide molecules and some of the polysaccharide K molecules. Non-complex-forming and complex-forming strains with the same O and K can be found. The complexes are thermostable but are disrupted by some detergents. O-K complex formation may lead to misinterpretation of immunoprecipitation results; one example is the counter current technique used for K determination of E. coli. In this technique O antigen lipopolysaccharide may, when complexed to K polysaccharide, mimic a K antigen. The possible implications of O-K complex formation during the infection process, especially for antibody formation need to be examined.

Serum sensitivity of a diversity of Escherichia coli antigenic reference strains. Correlation with an LPS variation phenomenon.

One hundred and ninety-four E. coli O, K and H antigen reference strains and some strains of certain O:K types were examined for resistance to the bactericidal effect of normal human serum by the method of Olling. A strain was defined as serum-resistant when less than 50% and serum-sensitive when greater than 90% bacteria were killed. Fifty-seven reference strains were serum-sensitive, 21 of them produced K antigens which apparently had no protective role. Thirty-seven reference strains were serum-resistant, and 13 of these produced no K antigen; thus the O antigens might by themselves be protective in these cases. K- mutants of the serum-resistant O8:K87 strains were serum-sensitive, and the O9:K9 strain changed from being serum-resistant to being partly resistant when the K antigen was lost; mutants of the O6:K13 strain with no or a small amount of K13 were less resistant than the original K+ strain; similar mutants of the O22:K13 reference strain did not show any decrease in serum resistance. Strongly related to 022 is 083, and results with several 083 strains pointed to the importance of this O antigen for serum resistance. In an O83:K14 strain a spontaneous variation occurred in LPS from a few to many repeating units; this variation was accompanied by a change from serum sensitivity to serum resistance.

Two new Escherichia coli O groups: O172 from "Shiga-like" toxin II-producing strains (EHEC) and O173 from enteroinvasive E. coli (EIEC).

Two Escherichia coli strains were established as antigenic test strains for two new O groups, O172 and O173. The O172 strain (EHEC) which produces "Shiga-like" toxin II (verocytotoxin 2) was isolated from a case of haemorrhagic colitis while the enteroinvasive O173 strain (EIEC) originated from a child with diarrhoea.

Doxycycline prophylaxis of travelers' diarrhea in Honduras, an area where resistance to doxycycline is common among enterotoxigenic Escherichia coli.

Daily doxycycline (DX), known to be effective prophylaxis against travelers' diarrhea (TD) in areas of the world where enterotoxigenic Escherichia coli (ETEC) are sensitive to the drug, has not been extensively studied in geographic areas where antibiotic resistance is common. Therefore we studied 44 U.S. Peace Corps Volunteers during their first 5 weeks in Honduras, which is such an area. During the first 3 weeks, volunteers took daily either 100 mg DX or placebo (PL) in a double-blind, randomized fashion. All 22 taking PL developed TD during the first 3 weeks, compared to 7 of 22 (32%) taking DX (P less than 0.001; 68% protection). ETEC were isolated from 39% of episodes of TD. From the PL group, ETEC from 7 of 13 stool samples (54%) were resistant to DX, whereas from the DX group, ETEC from 10 of 11 stool samples were resistant (P less than 0.05). TD that developed in persons taking DX was also found to be less severe, as judged by length of illness (P less than 0.01) and frequency of stools (P less than 0.05). This study demonstrates that DX 1) significantly prevents TD even in areas where antibiotic resistance is common, although it does not prevent TD caused by docycycline -resistant ETEC, and 2) significantly diminishes the severity of illness.

PIP: This study analyzed the effect of doxycycline prophylaxis of travelers' diarrhea in Honduras, an area where antibiotic resistance is common among enterotoxigenic Escherichia coli (ETEC). 44 newly arrived US Peace Corps volunteers were given either 100 mg of doxycycline/day or a placebo. All 22 subjects who received a placebo developed travelers' diarrhea within 3 weeks compared to 7 of 22 subjects (32%) who received doxycycline. ETEC were isolated from 39% of the travelers' diarrhea episodes. In the placebo group, ETEC from 7 of 13 stool samples (54%) were resistant to doxycycline. In the doxycycline group, ETEC from 10 of 11 stool samples (91%) were resistant. Volunteers who took doxycycline had a shorter diarrheal illness than controls and a less severe disease, as measured by the peak numberof stools/day. No clinical adverse drug effects were noted. The protective effect of the drug lasted only while the drug was being taken. This study demonstrates that prophylactic doxycycline significantly reduces the severity of illness among those who experience travelers' diarrhea and can provide a 60-70% protection rate even in countries where ETEC are resistant to antibiotics. Antibiotic prophylasix should be viewed as a temporary measure, however, until safer and perhaps more effective methods such as vaccines or nonpharmacologic agents become available.

Clonal relationships among Escherichia coli serogroup 06 isolates from human and animal infections.

The clonal relationship of thirty E. coli strains of 0 antigen serotype 06 isolated from human, dog, pig or cow infections were investigated. Two main clones with serotypes 06 : H1 or 06 : H31, H- were identified. Isolates from humans, dogs, pigs and cows were found in both clones, indicating that animals are a possible source for human extraintestinal Escherichia coli strains. Two human ETEC (06 : H16) and two pig isolates (06 : H10) were not related to the 06 : H1 or 06 : H31, H- E. coli clones.

A comparative study of nosocomial and community-acquired strains of Escherichia coli causing bacteraemia in a Danish University Hospital.

In a previous study we found a considerably higher mortality rate in patients with nosocomial (NO) compared with community-acquired (CA) Escherichia coli bacteraemia. To establish whether this was due to host differences or to differences in the infecting bacteria, we compared 205 NO with 172 CA bacteraemic isolates of E. coli with respect to serotype, virulence factors and antimicrobial susceptibility. Overall the six most frequent O antigens were O18ac, O6, O1, O2, O15 and O75, respectively. The six most frequent capsular antigens were K1, K5, K52, K2, K7 and K34, respectively. No major differences were found regarding O-antigens, capsular antigens, production of haemolysin, P-fimbriation, serum sensitivity or antimicrobial susceptibility. Surprisingly we found 17 strains of serotype O15:K52:[H1] of both NO (eight) and CA (nine) origin with similar phenotypic characteristics to a strain causing a CA outbreak in London 1986-1987. Possibly the Danish and the English strains belong to the same clone. Our findings argue against the existence of a distinct NO flora. NO E. coli bacteraemia strains seem to originate primarily from the patients' own flora.

Escherichia coli bacteraemia in patients with and without haematological malignancies: a study of strain characters and recurrent episodes.

We compared serotypes, virulence factors and susceptibility to antibiotics of Escherichia coli strains isolated from 282 patients with bacteraemia. Thirty-five of these were neutropenic patients with haematological malignancy and 247 were patients with a normal or raised total white blood cell count and no haematological malignancy. Strains isolated from recurrent bacteraemia were also bio- and ribotyped. Overall, no significant difference was found between O serogroups, K antigens, serum sensitivity, production of haemolysin, expression of P-fimbriae and patterns of antibiotic susceptibility in the two groups of strains. The haematological patients more often than the non-haematological patients had an unknown focus of infection, recurrent bacteraemia, shorter intervals between recurrences and recurrences caused by identical strains. Despite a well-defined focus, six of eight non-haematological patients had recurrences with a strain different from the strain isolated in a previous episode. A possible connection between shorter intervals and recurrence with identical strains is discussed. We suggest that strains from recurrent E. coli bacteraemia are sent to a reference laboratory for serotyping and possibly ribotyping.

Unusual serotypes of Escherichia coli from piglet diarrhea in north Spain.

Eighteen strains of Escherichia coli isolated from piglet diarrhea were examined with a wide range of antisera and were found not to belong to the common serotypes found in this disease. Several different serotypes were found; nine strains belonged to O153, and an O group (not commonly associated with piglet diarrhea) belonged to four different serobiotypes.

Structural studies of the Escherichia coli K93 and K53 capsular polysaccharides.

The structures of the Escherichia coli K93 and K53 capsular polysaccharides have been investigated by chemical and spectroscopic methods. The repeating unit of both polymers was found to be----3)-beta-D-Galf-(1----f)-beta-D-GlcAp-(1. The O-5 and O-6 atoms of D-galactose are acetylated in the repeating unit of the K93 polymer, but only O-2 is acetylated in the K53 polymer. The K93 polysaccharide is cross-reactive with the Neisseria meningitidis Group A capsular polysaccharide (of known structure). The K53 polysaccharide, although structurally similar to that from K93 organisms, does not cross-react with the Group A polymer.

Cytotoxin activity on Vero cells among Escherichia coli strains associated with diarrhea in cats.

The role of Escherichia coli as a causative agent of diarrhea in cats was investigated. Isolates of E coli from healthy and diarrheic cats were serotyped and investigated for their biochemical characters, production of cytotoxin activity on Vero cells, heat-labile enterotoxin, heat-stable enterotoxin, and hemagglutination of erythrocytes from other animal species. None of 48 investigated strains produced heat-labile enterotoxin or heat-stable enterotoxin, nor did they agglutinate erythrocytes. Most strains were hemolytic and belonged to O-serotypes 2 and 6. Cytotoxin activity on Vero cells was significantly more common and produced in greater amounts among E coli strains isolated from diarrheic cats, and was neutralized by anti-Shiga-like toxin I serum.

Antibodies against core and O antigen epitopes of Escherichia coli O83 in rabbit antisera and in commercial human immunoglobulin.

An unexpected serological cross-reaction was detected between two common Escherichia coli O antigens: O83 and O6. It was found that the cross-reacting antibodies were induced by common core epitopes not exposed in naturally occurring smooth strains. Smooth O6 strains would, however, after prolonged immunization of rabbits provoke production of precipitating antibodies against this common core epitope. Routine rabbit O antisera of smooth test strains O1 to O171 did not contain antibodies to the core epitope. Core antisera could readily be produced with an R mutant of the O6 strain. Extracts or Lipopolysaccharides (LPS) of several of the E. coli commonly found in the normal intestine and in extraintestinal diseases would only precipitate in antisera containing anti-core epitope anti-bodies after treatment with deoxycholate or sodium dodecyl sulfate. Other E. coli such as J5 (O111), used extensively for production of antisera intended for protection against endotoxemia, did not react with antibodies against this common core epitope. Another unexpected observation was that normal commercial human immunoglobulin contained precipitating IgG antibodies to the E. coli O83 antigen commonly found in strains from neonatal meningitis and other extraintestinal infections. Significant amounts of precipitating anti-LPS antibodies against other common O antigens (O2, O4, O6, O75 etc.) could not be detected in normal immunoglobulin.

Escherichia coli serotyping and disease in man and animals.

Serotyping of Escherichia coli is useful, but complex, with 173 O antigens, 80 K antigens, and 56 H antigens, which can all be subdivided into partial antigens. The O, K, and H antigens can be found in nature in many of the possible combinations. The final number of E. coli serotypes is very high, 50,000-100,000 or more. The number of frequent pathogenic serotypes is, however, limited. Two main groups of such frequent serotypes are (i) serotypes from diarrhoeal disease and (ii) serotypes from extraintestinal disease. Serotypes from diarrhoeal diseases are mostly species specific, and could at present be used as epidemiological markers for bacterial clones equipped with special virulence markers, such as toxins and adhesins. Their O-antigen lipopolysaccharides may be regarded as virulence factors. These strains are not inhabitants of the normal intestine. Serotypes from extraintestinal diseases constitute a different set of clones, which are good colonizers of the intestinal tract, that under certain conditions succeed in invading host tissues. They are characterized by virulence factors different from those found in strains from diarrhoeal disease. Thus, the two groups of pathogenic E. coli are both composed of a limited number of clones for which the O:K:H serotypes are excellent, although not faultless, markers.

The clonal nature of enteropathogenic Escherichia coli strains.

Enteropathogenic Escherichia coli belonging to O groups O111 and O55 and isolated from cases of infantile diarrhea in 26 countries all over the world during 1950-1960 were examined for their outer-membrane protein (OMP) patterns; nine O:H serotypes of O111 and 11 serotypes of O55 were represented. Characteristic biotypes have earlier been described as closely associated with the most common O:H serotypes: O111:H2, O111:H12, O55:H6, and O55:H7. Different OMP patterns characterized each of the common O:H serobiotypes. The OMP patterns can be looked upon as another set of stable phenotypic characters in addition to the serotype antigens and the fermentative characters. The description of geographically widely spread, stable sero-/bio-/OMP types supports the concept that the typical enteropathogenic E coli strains also have a clonal connection.

Episome-carried surface antigen K88 of Escherichia coli. I. Transmission of the determinant of the K88 antigen and influence on the transfer of chromosomal markers.

Ørskov, Ida (Statens Seruminstitut, Copenhagen, Denmark), and Frits Ørskov. Episome-carried surface antigen K88 of Escherichia coli. I. Transmission of the determinant of the K88 antigen and influence on the transfer of chromosomal markers. J. Bacteriol. 91:69-75. 1966.-The transmission of the determinant of the Escherichia coli K88 antigen in mixed cultures of E. coli strains is described. The K88 factor could not be transferred by filtrates, nor could responsible phages or colicines be detected. Acriflavine was shown to "cure" the bacteria for the K88 antigen. Generally, the strains having acquired the K88 antigen also acquired the ability to transfer chromosomal markers, but this ability was in some cases retained by segregants which had lost the K88 antigen. Introduction into an F(+) strain caused reduction of the recombination frequency and disappearance of the f(+) antigen. Not all wild-type strains with the K88 antigen are genetic donors of this antigen, at least not to a discernible degree. It was concluded that the K88 antigen determinant is carried by an episome.