Elastolytic activity among Aeromonas spp. Using a modified bilayer plate assay.

A total of 166 isolates of Aeromonas, representing diverse geographical regions and originating from various sources, were evaluated for the ability to produce elastase by using a bilayer elastin agar medium (BEAM) plate assay. The degree of elastase activity of individual strains was roughly assessed by measuring the clear area beneath or peripheral to the colony and recorded as 1+, 2+, or 3+. Of the 166 aeromonads tested, 53 (32%) were found to produce elastase, of which 26 (49%) were 3+, 21 (40%) were 2+, and 6 (11%) were 1+. All but one A. hydrophila (n = 45) were observed to produce elastase (98%). One of three A. schubertii strains as well as one isolate of Aeromonas group 501 were elastase positive. All 3+ elastolytic activity was associated with A. hydrophila only. Elastase activity was not detected even after prolonged incubation with A. veronii biogroup sobria (n = 26), A. caviae (n = 57), A. veronii biogroup veronii (n = 4), A. media (n = 1), and A. eucrenophila (n = 1). In addition to its value as a reliable indicator of elastase production for eventual use in virulence assays, we have found that the detection of elastase using the BEAM plate serves as a very useful phenotypic marker for the major, clinically important Aeromonas spp.

Colonization of professional divers by toxigenic Vibrio cholerae O1 and V. cholerae non-O1 at dive sites in the United States, Ukraine and Russia.

Vibrio cholerae, recognized as the causative agent of epidemic cholera, was isolated from healthy professional divers and from water samples collected at dive sites in the United States, Ukraine and Russia. Swabs of nose, ear and throat of divers and their tank regulators, i.e. the divers and their diving gear, were taken before and after routine dives. Blood samples were collected before and 30-60 days after each dive to measure IgG and IgA titers against the whole cell antigen of V. cholerae O1. Nine strains of V. cholerae O1 and nine strains of V. cholerae non-O1 were isolated during this study. These isolates were identified by conventional biochemical tests and indirect fluorescent antibody staining methods, using fluorescein isothiocyanate-labeled monoclonal antibody, COLTA, prepared against the 'A' antigenic factor of the lipopolysaccharide of V. cholerae O1, and serotyped by slide agglutination. Seven of the nine strains of V. cholerae O1 isolated and successfully cultured during the studies, were toxigenic by enzyme-linked immunosorbent assay and polymerase chain reaction. Analyses of IgG and IgA antibodies of the divers showed that most of the divers had prior exposure to V. cholerae O1. V. cholerae serotype non-O1 strains isolated during the study were found to be non-toxigenic.

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.

Development and evaluation of a rapid, simple, sensitive, monoclonal antibody-based co-agglutination test for direct detection of Vibrio cholerae 01.

Cholera epidemics caused by Vibrio cholerae 01 continue to represent a major public health concern in many developing countries. A rapid and simple test kit for the detection of V. cholerae 01 has been developed. The kit, CholeraScreen is a monoclonal antibody-based, co-agglutination test and is used directly with stool specimens. It does not include culturing the specimen and is performed without the need for sophisticated laboratory equipment. Specificity of the test was demonstrated, using 118 reference cultures, to which cross-reactions were not observed. Preliminary results of field trials carried out in Guatemala and Bangladesh demonstrated that the test is equally sensitive as conventional culture methods in detecting V. cholerae and, in many cases, more sensitive. The CholeraScreen test is simple, specific, and does not require culturing procedures, making it suitable for direct detection of cells of V. cholerae in clinical specimens, even in the field. Also, the test requires less than five minutes to complete.

Evaluation of radiolabeled and colorimetric DNA probes in comparison with an antigen screening assay for the detection of Salmonella from poultry farms.

A total of 48 environmental drag-swab samples from various poultry farms were tested for the presence of Salmonella spp. by culture, an enzyme-linked immunosorbent assay-based Salmonella antigen screening (SAS) assay, and two DNA probes (radiolabeled and colorimetric). The radiolabeled DNA probe was allowed to hybridize with culture-positive samples (n = 8) and was found to detect Salmonella spp. in all cases (100%). Both of the probes, subsequently hybridized with culture-negative samples (n = 8), were observed to yield good agreement (91%) with the culture findings. The remaining samples (n = 32) were tested by the SAS assay, and where there was no agreement between the culture and SAS, samples were further examined by the DNA probes. Results using both probes agreed with those obtained by culturing the samples but did not agree with the SAS assay result when the ratio of samples tested to samples positive (S/P) cutoff value used was 0.5.

Serum antibody responses of divers to waterborne pathogens.

To assess the significance of exposure of divers to waterborne pathogens, specific immunoglobulin G serum antibody responses to Pseudomonas and Aeromonas isolates recovered from dive sites from the respiratory tracts of nine experienced divers and seven diving trainees working in the Chesapeake Bay area over a 6- to 18-month period were measured. A significant increase in the frequency of isolation of these organisms from respiratory surfaces both groups of divers after each dive was noted, with the divers' ears being the predominant recovery site (48%; P < 10(-8), chi-square). The acute serum responses of the majority of experienced divers (83%) showed evidence of preexisting antibody to these potential pathogens, whereas the acute serum response of only 32% of naive divers showed such evidence (P < 10(-8), chi-square). Six months into their training, the rate of seroresponse of the trainees to organisms recovered after their first dives increased to 61% (P = 0.003, chi-square), suggesting that repeated exposure in necessary for generation of a specific systemic immunologic response. The rate of acquisition of a new seroresponse to recovered organisms was approximately 12% per dive for both groups of divers, suggesting that there is continuous exposure to, and infection with, new strains present in the water during dives. These data suggest that, in cases in which systemic antibody is important for protection, there are various levels of susceptibility to waterborne potential pathogens in both experienced and inexperienced divers.

Occurrence of haemolysin producing Aeromonas species in the aquatic environment.

A total of 532 environmental isolates of motile aeromonads were evaluated for their ability to produce haemolysins. Of those isolates tested, 68 (12.5%) and 18 (3.4%) were found to be alpha and beta haemolytic, respectively. Aeromonas caviae was found to be alpha haemolytic (3.8%) for the first time. Isolates of Aeromonas which were either alpha or beta haemolytic on plate assay also produced detectable amounts of haemolysin in cell free broth assay.

A novel kit for rapid detection of Vibrio cholerae O1.

We report on the development and testing of a novel, rapid, colorimetric immunodiagnostic kit, Cholera SMART, for direct detection of the presence of Vibrio cholerae O1 in clinical specimens. Unlike conventional culture methods requiring several days to complete, the Cholera SMART kit can be used directly in the field by untrained or minimally skilled personnel to detect V. cholerae O1 in less than 15 min, without cumbersome laboratory equipment. A total of 120 clinical and environmental bacterial strains, including both O1 and non-O1 serotypes of V. cholerae isolated from samples collected from a variety of geographical regions, were tested, and positive reactions were observed only with V. cholerae O1. Also, results of a field trial in Bangladesh, employing Cholera SMART, showed 100% specificity and 96% sensitivity compared with conventional culture methods. Another field trial, in Mexico, showed that Cholera SMART was 100% in agreement with a recently described coagglutination test when 108 stool specimens were tested.

Cholera toxin gene polymerase chain reaction for detection of non-culturable Vibrio cholerae O1.

Cholera enterotoxin is a major antigenic determinant for virulence of Vibrio cholerae O1 which can enter into a viable but non-culturable (N-C) state, not detectable by conventional culture methods, yet remain capable of producing enterotoxin and potentially pathogenic. PCR was applied in the current study to detect the chilera toxin (ctx) gene of N-C cells, thus eliminating the necessity of culture. Sets of oligonucleotide primers were designed, based on the ctxAB operon of V. cholerae O1, to detect the presence of the ctx gene. DNA from both culturable and N-C cells of V. cholerae O1 was amplified by PCR using sets of primers flanking 302-, 564- and 777-bp fragments of the ctx gene. The PCR method employed was capable of detecting the ctx gene in N-C V. cholerae in aquatic microcosms and in diarrheal stool samples from three patients who had distinct clinical symptoms of cholera but were culture-negative for V. cholerae O1 and non-O1 and enterotoxigenic Escherichia coli. Forty cycles of a two-step reaction (30 s each at 94 and 60°C) were optimal and more time efficient than a three-step PCR described previously. The procedure, from the point of heating microcosms or broth culture samples to observation on gels, requires < 4 h to complete.

Evaluation of the monoclonal antibody-based kit Bengal SMART for rapid detection of Vibrio cholerae O139 synonym Bengal in stool samples.

A monoclonal antibody-based test, Bengal SMART, was developed for rapid detection of Vibrio cholerae O139 synonym Bengal directly from stool specimens. The test, which takes about 15 min to complete, was used to screen 189 diarrheal stool specimens. The results were compared with those of a monoclonal antibody-based coagglutination test (COAT) and the conventional culture methods used as the "gold standard" for detection of V. cholerae O139. The Bengal SMART test showed a sensitivity of 100% and a specificity of 97% in comparison with the gold standard. It also fared better than COAT, which had a sensitivity of 96% for rapid detection of V. cholerae O139 synonym Bengal. These results show that Bengal SMART is suitable for use in field settings for rapid diagnosis of cholera caused by V. cholerae O139.

Development and testing of monoclonal antibody-based rapid immunodiagnostic test kits for direct detection of Vibrio cholerae O139 synonym Bengal.

We report on the development and testing of two monoclonal antibody-based rapid immunodiagnostic test kits, BengalScreen, a coagglutination test, and Bengal DFA, a direct fluorescent-antibody test, for direct detection of Vibrio cholerae O139 synonym Bengal in clinical and environmental specimens. The BengalScreen test requires less than 5 min to complete and can be used in the field. Bengal DFA, being more sensitive than BengalScreen, requires only one reagent and less than 20 min for detection and enumeration of V. cholerae O139 synonym Bengal. In tests for specificity, all 40 strains of V. cholerae O139 reacted with both test kits, whereas 157 strains of heterologous species examined did not, yielding 100% specificity in this study. A field trial was conducted in with both BengalScreen and Bengal DFA, and the results were compared with those obtained by conventional culture methods. BengalScreen demonstrated a sensitivity of 95%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 94%. Results obtained by Bengal DFA, on the other hand, were 100% sensitive and 100% specific and yielded 100% positive and negative predictive values compared with culture methods. In a second evaluation, 93 stool specimens from Mexico that were negative for V. cholerae O139 by culture were also tested with both the BengalScreen and Bengal DFA kits. None of the 93 specimens were positive for V. cholerae O139 by both tests. A concentration method was optimized for screening of environmental water samples for V. cholerae O139 synonym Bengal with rapid test kits. BengalScreen results were unequivocally positive when water samples contained at least 2.0 x 10(3) CFU/ml, whereas Bengal DFA demonstrated an unequivocally positive reaction when the water sample contained at least 1.5 x 10(2) CFU/ml. When Bengal DFA was compared with conventional culture methods for enumeration of V. cholerae O139 synonym Bengal organisms, no difference was observed.