Microtiter bacterial hemagglutination technique for detection of Shigella antibodies

Prospective study of the association between serum antibodies to lipopolysaccharide O antigen and the attack rate of shigellosis

A means for determining immune status against shigellosis would significantly improve the design and evaluation of interventional and other epidemiologic studies. Previous case-control studies have indicated the potential role of humoral antilipopolysaccharide antibodies. To test this proposition, 190 soldiers serving in a field unit were monitored prospectively for 2.5 months for shigellosis. Blood samples were taken at the beginning of the follow-up period and tested for serological evidence of prior exposure to Shigella sonnei and Shigella flexneri. The risk for acquiring S. sonnei shigellosis was 3.7 times higher for individuals lacking homologous antibodies (P less than 0.02). The risk for acquiring S. flexneri shigellosis was 2.4 times higher for individuals lacking antibodies, although a low attack rate for S. flexneri resulted in numbers too small to achieve statistical significance. While the importance of the serum antilipopolysaccharide antibodies in protection against the disease remains unclear, these findings demonstrate that they are strong markers of acquired immunity. Serological markers should be incorporated in epidemiologic studies of shigellosis and in the design and evaluation of future trials of potential anti-Shigella vaccines.

Immunoglobulin M, A, and G antibody response to lipopolysaccharide O antigen in symptomatic and asymptomatic Shigella infections

The antilipopolysaccharide antibody response in sera obtained from subjects involved in 10 outbreaks of shigellosis occurring in Israeli military field units was determined by an enzyme-linked immunosorbent assay and a passive hemagglutination test. Both tests were found to be sensitive and specific for the diagnosis of shigellosis. A significant antibody response was detected in 73 to 82% of the symptomatic and 48 to 60% of the asymptomatic subjects during the Shigella sonnei and Shigella flexneri outbreaks. Fifty percent of the symptomatic and none of the asymptomatic subjects showed a significant antibody response in the Shigella boydii outbreaks. An examination of the kinetics of the antibody levels over a 10-week period after the onset of disease revealed that immunoglobulin A (IgA) levels were highest 2 weeks after infection and had declined to initial levels within 2.5 months. In contrast, IgG levels at the late convalescent stage were half those measured at early convalescence, still being about twice as high as the initial titers. Although the IgM levels showed a pattern similar to that of IgA, their elevation at the early convalescent stage was less pronounced. We conclude that the detection of an increase in the level of the IgA fraction appeared to be the best indicator for recent symptomatic, as well as symptomatic, infections due to Shigella organisms.

Anatomical and immunological responses of rabbit gallbladders to bacterial infections

To study the sequential morphological and immunological response of the rabbit gallbladder to bacterial infection and to compare the inflammatory responses with different pathogens, gallbladders were infected with Streptococcus faecalis and two strains of Escherichia coli, one of which produced enterotoxin. Gallbladder infection was produced either by intravenously injecting bacteria into rabbits with a small liver infarct or by injecting bacteria directly into the gallbladder of normal rabbits. The percentage of gallbladders infected intravenously with a nonenterotoxigenic E. coli strain was 86% at 1 week, 70% at 3 weeks, and 15% at 6 weeks. Epithelial necrosis and leukocyte infiltration were prominent 1 week after infection. At 3 and 6 weeks after infection, there was crypt distortion and increased mucus secretion in the epithelium as shown by periodic acid-Schiff staining. The lamina propria was infiltrated with mononuclear cells, many of which were plasma cells. Myofibroblasts (contractile fibroblasts) were also identified on transmission microscopy, In addition to these changes, toxigenic E. coli produced subepithelial capillary dilation in the villus core. Morphological changes (excluding toxin-associated changes) were related to the duration of infection rather than to the specific species of infecting bacteria. Infected gallbladders studied by immunofluorescence had a greater than 50-fold increase in plasma cells compared with control cells. In addition, the number increased with the duration of infection. Immunoglobulin A cells were the major cell type in gallbladders infected by intravesical injection, whereas immunoglobulin G cells predominated in gallbladders infected intravenously. The gallbladder appears to mount a local immune response to bacterial infection.

Immunity to enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli strains represent the most frequent etiological agent of travelers diarrhea. Challenge studies with several of these strains were undertaken in volunteers to evaluate the mechanisms of disease-induced immunity. Seventeen students and other community volunteers were given 10(6) or 10(8) organisms of E. coli B7A (O148:H28), which produces heat-labile and heat-stable enterotoxins. Ten individuals developed diarrheal illness closely resembling natural travelers diarrhea; of these ten, rises in titer of serum antitoxin and anti-O antibody occurred in eight (80%). Eight of the volunteers who developed diarrhea in the first test agreed to undergo rechallenge 9 weeks later with 10(8) B7A organisms. Only one of these eight "veterans" developed diarrhea versus seven of twelve controls given the same challenge (P = 0.05). Despite clinical protection, all "veterans" excreted B7A after rechallenge. Four controls who developed diarrhea during the homologous B7A rechallenge test were rechallenged 9 weeks later with 10(9) organisms of E. coli strain E2528-C1 (O25:H-), which produces only heat-labile enterotoxin and possesses a different O, H, and pili antigen composition than B7A. Three of four "veterans" and two of six controls developed comparable diarrhea. These studies demonstrate that prior disease due to enterotoxigenic E. coli confers homologous immunity against subsequent challenge, and the operative mechanism apparently is not bactericidal and is not mediated by serum anti-O antibodies. Heterologous protection was not conferred where the only common antigen was heat-labile enterotoxin, indicating that serum infection-derived antitoxin to heat-labile enterotoxin also is not protective.

Escherichia coli strains that cause diarrhoea but do not produce heat-labile or heat-stable enterotoxins and are non-invasive

Three enteropathogenic Escherichia coli (E.P.E.C.) strains (O127:K63:H6, O128:K67:H2, and O142:K86:H6) isolated from outbreaks of infantile diarrhoea and one strain from the "normal" colonic flora (E. coli HS) of a healthy adult were fed in doses of 10(6), 10(8), and 10(10) organisms in NaHCO3 to adult volunteers. The strains, which had been stored for 7--9 years, gave negative results in sensitive tests for heat-labile (L.T.) enterotoxin (Y-1 adrenal-cell test), heat-stable (S.T.) enterotoxin (infant mouse assay), invasiveness (guineapig eye test), and gross fluid accumulation (infant rabbit assay). Two strains (O142 and O127) caused diarrhoea. L.T. or S.T. enterotoxins were not found in E. coli stool isolates from individuals with diarrhoea and no one had a rise in L.T. antitoxin titre; the findings suggest that L.T. and S.T. enterotoxins were not involved in pathogenesis of the diarrhoea. Non-invasive E.P.E.C. strains probably induce diarrhoea by a mechanism (presumably an enterotoxin) distinct from L.T. or S.T. enterotoxins.

Diagnostic value of indirect hemagglutination in the seroepidemiology of Shigella infections

To evaluate the usefulness of the indirect hemagglutination (IHA) test in the epidemiological investigation of shigellosis, single serum specimens were tested from 50 patients with Shigella dysenteriae 1 (Shiga bacillus) infections, 103 asymptomatic contacts of these cases, 267 adult and 100 student control, and serum specimens collected during two outbreaks caused by S. sonnei and one outbreak due to S. flexneri 6. In patients with S. dysenteriae 1, 74% demonstrated titers of greater than or equal to 1:40, with 50% showing titers of greater than or equal to 1:160, whereas in the controls 10.4% had titers of greater than or equal to 1:40 and only 0.3% had titers of greater than or equal to 1:160. IHA titers in serum specimens collected from patients with S. sonnei and S. flexneri 6 were too low to be considered diagnostic for individual patients, but were useful in analysis of group results. Groups of ill individuals yielded titers significantly higher than non-ill groups; however, titers from ill groups were usually less than 1:40. The IHA test for S. dysenteriae 1 antibodies serves as a valuable adjunct to the diagnosis of Shiga bacillus dysentery. In our laboratory, an IHA titer of 1:40 or 1:80 is a "borderline positive." Shiga bacillus dysentery is strongly indicated when IHA titers are greater than or equal to 1:60.

Serum factors responsible for killing of Shigella

Eight strains of Shigella were tested for susceptibility to killing by seven normal human sera. Although there was a wide range of susceptibility between strains of bacteria, there was surprisingly little difference in the killing activity of individual sera and no relationship between antibody titres and killing capacity.

Bacteriolysis required small amounts of antibody, but as little as 0.02 mg of a 19S fraction from normal serum restored full killing capacity to 1 ml of antibody depleted serum. Neither 11S IgA nor Cohn fraction II restored the bacteriolytic ability. Both the early reacting complement sequence and the alternate C3 activating pathway appeared to participate in killing as indicated by the roles of C2 and C3PA. Killing occurred, but with reduced efficiency, when either of the two substances was missing. However, serum lacking both C2 and C3PA could no longer kill Shigella. Killing also required the presence of C3, and presumably some of the later components of complement are subsequently involved.

Characterization of an unusual strain of proteus rettgeri associated with an outbreak of nosocomial urinary-tract infection

An outbreak of nosocomial urinary-tract infection was caused by a strain of Proteus rettgeri that fermented lactose overnight and was resistant to all antimicrobial drugs tested. The nonmotile isolates shared an O (somatic) antigen that differed from those of wild-type P. rettgeri. The organisms proved markedly serum-sensitive. In rats, the isolates elicited an acute interstitial nephritis with associated transient bacteriuria. Attempts to transfer the lac(+) trait and drug-resistance markers to recipient strains of Escherichia coli K-12 failed; exposure of the isolates to acridine orange yielded small numbers of non-lactose-fermenting variants which, however, were still as drug-resistant as before. Epidemiological studies failed to uncover the source of this unique strain and appeared to indicate exogenous spread of infection.

Effect of cultural environment on the blood group activity of microorganisms

Blood group activity was proven to be a property of the bacterium per se which possesses it, although such activity was influenced by the cultural environment of the organism. High concentrations of peptones having blood group activity were able to transfer this activity to inactive organisms; however, the conferred activity was proportional to the concentration. As a result of the low concentrations, the blood group activity of peptones was eliminated upon incorporation in culture media, and the activity of the peptones had no effect on the blood group activity levels of microorganisms when grown in these media. Conversely, the vitamin content of culture media did affect blood group active organisms. Multiple vitamins in media decreased the activity levels by blocking the reactive sites of the active organisms on which activity detection depended. Blood group activity levels were highest in media of minimal or no vitamin content. Therefore, it can be concluded that a choice of cultural medium becomes an important factor in the quantitation of bacterial blood group activity.

Decreased 19S antibody response to bacterial antigens in systemic lupus erythematosus

The antibody response to immunization with Brucella and the levels of natural antibody to Escherichia coli and Shigella were compared in patients with systemic lupus erythematosus and control groups. After Brucella immunization, SLE patients showed a significantly lower antibody response in whole serum and in the macroglobulin antibody fraction separated by sucrose density gradient centrifugation. Sucrose gradient fractionation of natural antibodies to E. coli and a polyvalent Shigella antigen showed a significant decrease in macroglobulin antibody against four of the five E. coli antigens tested and the Shigella polyvalent antigen in SLE patients when compared with a group of normal individuals and a matched control group with pulmonary tuberculosis. Whole serum natural antibody titers against 5 of 13 Shigella antigens were significantly lower in the SLE patients when compared with the normal group, and against 7 of 13 when compared with the matched tuberculosis controls. Whole serum titers against 8 of 13 E. coli antigens were significantly lower in the SLE patients when compared with normal subjects. The observed decreased antibody response to bacterial antigens in SLE patients, occurring mainly in the macroglobulin fraction, is discussed in relation to the increased incidence of infection commonly observed in these patients.