Rapid identification of cholera vibrios with fluorescent antibody

Evaluation of enrichment media for improved PCR-based detection of V. cholerae and V. vulnificus from estuarine water and plankton

AIMS

Pathogenic Vibrio spp., including V. cholerae and V. vulnificus, are commonly found along the estuaries of the south-east United States; however, it is often difficult to recover these species directly from environmental samples. Pre-enrichment assays are commonly used to improve the detection of pathogenic vibrios from environmental sources. Here, we evaluated a novel enrichment procedure using freshly collected and autoclaved natural estuarine water amended with 1% peptone (designated as estuarine peptone water, EPW) and compared it to traditional alkaline peptone water (APW) for detection by PCR of V. cholerae and V. vulnificus.

METHODS AND RESULTS

Of the 50 samples collected in total, V. cholerae DNA was detected in APW 10% of the time and in EPW 40% of the time. Likewise, the cholera toxin gene (ctxA) was detected in 4 vs 18% of the samples using APW and EPW, respectively. Conversely, APW showed improved recovery for V. vulnificus relative to EPW with respective detection frequencies of 46 and 20%. Results showed similar patterns across different sample types (water and plankton).

CONCLUSIONS

While enrichment in traditional APW was adequate for the recovery of Vibrio vulnificius, use of sterile estuarine water amended with peptone significantly improved the detection of V. cholerae and the virulence gene ctxA from estuarine sources.

SEROLOGICAL GROUPING OF ACTINOMYCES BY MEANS OF FLUORESCENT ANTIBODIES

Slack, John M. (West Virginia University, Morgantown), Ann Winger, and Dane W. Moore, Jr. Serological grouping of actinomyces by means of fluorescent antibodies. J. Bacteriol. 82:54-65. 1961.-Serological groups A, B, C and D of actinomyces were established using fluorescent antibody techniques. One hundred and thirty-eight cultures were included in the study. Eighty-nine were classed in group A, 15 in B, 13 in C, and 21 in D. The isolates were from patients and animals with actinomycosis and from healthy human beings. There was no correlation between source of the isolate and serological group. Furthermore, no one species could be placed exclusively in one group although the majority of those designated as Actinomyces bovis were in group A. Seventeen anaerobic diphtheroids and seven Corynebacterium acnes isolates were placed in group A. One diphtheroid was in each of groups B and D. On this basis it is suggested that these organisms be included in the genus Actinomyces.Additional species of Corynebacterium as well as Lactobacillus Propionibacterium, Streptomyces, and Nocardia did not fluoresce with any of the group antisera.

Direct immunofluorescence assay for rapid environmental detection of Vibrio cholerae O1

An immunofluorescence assay for direct detection of V. cholerae O1 was developed using polyclonal antibodies raised against outer membrane proteins (OMPs) of V. cholerae O1. Production of OMPs varied with growth media used; maximum production was found in tryptic soy broth. The detection system was specific because no cross-reactivity was observed with other bacteria including V. cholerae O139, E. coli, S. dysenteriae and Salmonella enterica subsp. enterica serovar Typhi. The technique was able to detect 240 CFU/mL of V. cholerae O1 suspended in phosphate-buffered saline. The assay coupled with bacterial enrichment in APW for 6 h detected as few as 5 CFU of V. cholerae in spiked samples. Moreover, a 2-h incubation of enriched bacterial cells in 0.1% yeast extract with 10 ppm nalidixic acid enhanced the bacterial size and helped in morphological identification of V. cholerae. Among 32 potable water samples from afflicted hand pumps and wells collected from a cholera-plagued area 12 were found to be contaminated with V. cholerae by immunofluorescence assay as well as by conventional culture methods. The proposed method could thus be employed in environmental surveillance of V. cholerae O1.

Identification and strain differentiation of Vibrio cholerae by using polyclonal antibodies against outer membrane proteins

Cholera is caused only by O1 and O139 Vibrio cholerae strains. For diagnosis, 3 working days are needed for bacterial isolation from human feces and for biochemical characterization. Here we describe the purification of bacterial outer membrane proteins (OMP) from V. cholerae O1 Ogawa, O1 Inaba, and O139 strains, as well as the production of specific antisera and their use for fecal Vibrio antigen detection. Anti-OMP antisera showed very high reactivity and specificity by enzyme-linked immunosorbent assay (ELISA) and dot-ELISA. An inmunodiagnostic assay for V. cholerae detection was developed; this assay avoids preenrichment and costly equipment and can be used for epidemiological surveillance and clinical diagnosis of cases, considering that prompt and specific identification of bacteria is mandatory in cholera.

Cholera

Despite more than a century of study, cholera still presents challenges and surprises to us. Throughout most of the 20th century, cholera was caused by Vibrio cholerae of the O1 serogroup and the disease was largely confined to Asia and Africa. However, the last decade of the 20th century has witnessed two major developments in the history of this disease. In 1991, a massive outbreak of cholera started in South America, the one continent previously untouched by cholera in this century. In 1992, an apparently new pandemic caused by a previously unknown serogroup of V. cholerae (O139) began in India and Bangladesh. The O139 epidemic has been occurring in populations assumed to be largely immune to V. cholerae O1 and has rapidly spread to many countries including the United States. In this review, we discuss all aspects of cholera, including the clinical microbiology, epidemiology, pathogenesis, and clinical features of the disease. Special attention will be paid to the extraordinary advances that have been made in recent years in unravelling the molecular pathogenesis of this infection and in the development of new generations of vaccines to prevent it.

Cholera DFA: an improved direct fluorescent monoclonal antibody staining kit for rapid detection and enumeration of Vibrio cholerae O1

An improved fluorescent monoclonal antibody staining kit, Cholera DFA, for direct detection and enumeration of Vibrio cholerae O1 has been developed, employing a highly specific anti-A antigen monoclonal antibody, COLTA, labeled with fluorescein isothiocyanate (FITC). An optimized quantity of anti-photobleaching agent is used in a glycerol mounting medium to retard the rapid fading of immunofluorescent stained cells during fluorescent microscopy, thus enabling prolonged inspection of individual fields, as well as improved photographic recording of results without loss of fluorescence intensity. When tested for specificity, all 30 strains of V. cholerae O1 reacted with Cholera DFA, whereas 100 heterologous species examined did not, yielding 100% specificity for all strains examined in this study. A field trial was conducted in Bangladesh, employing Cholera DFA and the results were compared with those obtained by conventional culture methods. Of 44 diarrheal stool specimens tested, Cholera DFA was positive for V. cholerae O1 in all culture-positive stool specimens and negative for all culture-negative stool specimens. The procedure is sensitive and highly specific, as well as simple, i.e., less complex than the indirect fluorescent assay, requiring only one reagent and less than 30 min to complete the staining process, while retarding rapid fading that often occurs with fluorescent microscopy.

Screening of aquatic samples for Vibrio cholerae serotype O1 by a dot-blot method and a latex agglutination test

A dot-blot, enzyme-linked immunosorbent method and a latex agglutination test were studied for their abilities to detect Vibrio cholerae serotype O1 in aquatic samples by testing artificially contaminated water as well as samples from natural potential sources. Water samples were preenriched with alkaline peptone and then enriched with Monsur peptone water. For the dot-blot test, enriched cultures of organisms in a small portion of the Monsur peptone water were transferred to a polyvinylidene difluoride membrane with a microfiltration apparatus. The enzyme-linked immunosorbent assay was performed by using biotin-labeled antibodies and avidin-biotin-peroxidase complex; brown dots developed in the wells that contained serotype O1 vibrios. Latex agglutination tests were performed by mixing 1 drop of the culture in Monsur with 1 drop of reagent coated with monoclonal antibody specific for antigen A. The sensitivities and specificities of the methods were compared with those of the colony-blot method, which identified individual colonies of V. cholerae O1 in mixed bacterial cultures on isolation media. Our results indicate that the dot-blot method is as sensitive as the colony-blot method and is useful for screening for V. cholerae serotype O1 even in specimens that are heavily contaminated with non-O1 vibrios.

Detection of Vibrio cholerae with monoclonal antibodies specific for serovar O1 lipopolysaccharide

Six hybridoma cell lines, each of which produced a monoclonal antibody (MAb) against Vibrio cholerae O1 lipopolysaccharide (LPS), were established. Each MAb was active serologically by both enzyme-linked immunosorbent assay (ELISA) and the slide agglutination test. In the ELISA, each MAb was tested against 7 O1 and 9 non-O1 LPS preparations. Three MAbs reacted with both Inaba and Ogawa serovars (A antigen), two MAbs reacted with the Ogawa serovars only (B antigen), and one MAb reacted with the Inaba serovars only (C antigen). Each MAb was also tested in the ELISA against whole-cell preparations of 37 O1 and 52 non-O1 V. cholerae serovars, 20 heterologous Vibrio species, and 37 heterologous bacterial species. The MAbs reacted with V. cholerae O1 cells only, except for one anti-A antigen MAb which reacted weakly with five V. cholerae non-O1 serovars and Serratia marcescens. Each anti-A antigen MAb was labeled with fluorescein isothiocyanate (FITC) and tested by direct immunofluorescence against selected O1 and non-O1 serovars. Each MAb-FITC conjugate, when tested alone, exhibited O1-specific fluorescence; however, mixtures of the MAb-FITC dramatically enhanced fluorescence intensity on O1 cells. This finding was also visualized by immunoelectron microscopy on both thin-sectioned and negatively stained O1 cells by using an anti-mouse immunoglobulin-colloidal gold conjugate. These results suggest that the A antigen can be described by more than one epitope and that a superior serotyping reagent can be prepared from a defined mixture of MAbs.

Rapid diagnosis of cholera by coagglutination test using 4-h fecal enrichment cultures

A simple, rapid, and reliable method to detect Vibrio cholerae in fecal specimens would assist in the management of cases of severe diarrhea, especially since most such cases occur in areas with minimal laboratory facilities. A coagglutination test was used to detect V. cholerae antigen in bile-peptone broth incubated with feces. In the technique, Staphylococcus aureus Cowan 1 coated with anti-V. cholerae O1 antiserum was tested with cultures incubated for 4 h. When 165 specimens were tested, the sensitivity, specificity, and accuracy of the test, compared with standard culture methods, were 97, 99, and 98%, respectively. These promising results were better than those of dark-field microscopy using the same specimens, and the test was logistically easy to perform. The coagglutination test using enrichment broth culture of feces is a simple and rapid method which may be used to confirm a diagnosis of cholera.

Rapid detection of Vibrio cholerae O:1 by motility inhibition and immunofluorescence with monoclonal antibodies

Monoclonal antibodies against the group and type specific antigens of Vibrio cholerae O:1 lipopolysaccharide were used for the rapid detection of Vibrio cholerae strains by motility inhibition and immunofluorescence. Motility inhibition of live Vibrio cholerae O:1 was obtained with group specific monoclonal antibodies. Monoclonal antibodies against the type specific antigens B (Ogawa) and C (Inaba) inhibited motility of strains of homologous serotypes only. Indirect immunofluorescence of heatfixed bacteria with monoclonal antibodies and fluorescein-isothiocyanate conjugated rabbit anti-mouse immunoglobulin was also shown to be suitable for the rapid detection of Vibrio cholerae O:1. Both tests were highly specific and no cross-reactions were observed with strains of non-O:1 vibrios, Escherichia coli or Salmonella spp. tested. However, a weak fluorescence of some Ogawa strains was observed when high concentrations of Inaba specific monoclonal antibodies were used.

Vibrio cholerae flagellar antigens: a serodiagnostic test, functional implications of H-reactivity and taxonomic importance of cross-reactions within the Vibrio genus

Serodiagnostic tests for all serotypes of Vibrio cholerae using H-antisera were investigated. Activity motile cell lines of 155 stock and international reference cultures of human, animal, fish, and halophilic Vibrios, Aeromonas, Comomonas, Pseudomonas, Salmonella, and Escherichia were investigated. Without exception, all cholera vibrios (including the NAG serotypes) reacted with H sera. Positive reactions were obtained specifically (a) within 2 hrs at 52 degrees C in the tube test using thick formalized suspensions and H antisera at optimal proportion titre and (b) within 30 sec by slide agglutination of fresh cultures. The other vibrios investigated reacted similarly with their homologous H antisera. 2. The rapid diagnostic techniques of fluorescent antibody labeling or immobilization were unsuccessful, V. cholerae flagella being refractive to H sera in these tests. V. cholerae was, however, sensitive in a type-specific manner to O antisera. These and related observations suggest that O antigen has a functional role in Vibrio motility. 3. Interspecies H cross-reactions between V. cholerae and fish and animal vibrios which correlated with bacteriologic similarity, were demonstrated. O antigens of these vibrios were strain specific. Cross-absorption analysis indicated that the H antigens of vibrios were characteristic and homogenous within the species, and therefore a potentially important taxonomic criterion of Vibrio species.

RAPID IDENTIFICATION OF VIBRIO CHOLERAE BY DARKFIELD MICROSCOPY

This article describes a rapid, simple and reproducible method for detecting Vibrio cholerae in diarrhoeal patients. The method involves darkfield examination of a liquid stool specimen or a rectal swab immersed in broth and immobilization of V. cholerae by the addition of specific vibrio antisera. The authors state that in 80% of cases a definitive diagnosis is available within five minutes. There is no need for elaborate equipment or long training of technicians and the method is easily performed by one person in the field.

Comparison of methods for the rapid recognition of cholera vibrios

A comparison was made of three methods of bacteriological diagnosis during the outbreak of cholera due to Vibrio El Tor in the Republic of the Philippines in the last quarter of 1961. Although the disease was clinically indistinguishable from cholera caused by V. cholerae the etiological agent was a haemolytic, cholera-related vibrio which differed in some respects from what is classically regarded as V. cholerae. Of the three techniques evaluated, the selective-enrichment/fluorescent-antibody technique provided the most rapid and the greatest number of positive results in the 481 specimens examined in parallel. The oblique-light technique was second in sensitivity and rapidity, while the gelatin-agar method also had some advantages.

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Enteropathogenic E. coli were sought routinely by the fluorescent antibody technique, using monovalent and polyvalent conjugates (rhodamine sulfonyl· chloride, fluorescein and rhodamine isothiocyanate). In 2061 stool specimens examined with monovalent antibody to E. coli 0127:B8, there were 61 false positives, 14 of which were from previously known cases of E. coli 0127:B8 infection, and 33 specimens that were negative by fluorescence but positive on culture. In 457 stool specimens examined with polyvalent antiserum, there were 15 false positives, five of which came from cases previously infected by the corresponding serotypes, and there were 20 specimens negative by fluorescence but positive on culture. The disagreement amounted, therefore, to 4.6% in the former instance and 7.6% in the latter. This fluorescent technique permits rapid sufficiently precise detection of enteropathogenic E. coli in stools.