Serological titres to Leptospira fainei serovar hurstbridge in human sera in Australia.

A set of 723 diagnostic sera from human patients, submitted for the microscopic agglutination test (MAT) for antibodies to a group of 6 leptospiral serovars, was also tested by MAT for antibodies to the recently-discovered Leptospira fainei serovar hurstbridge. MAT titres of > or = 128 to serovar hurstbridge were detected in 13.4% of these sera, and titres of > or = 512 in 7.2%. In contrast, none of 62 sera obtained from a control population of laboratory staff gave titres of > or = 128. The difference between the number of titres of > or = 128 given by the two groups of sera was highly significant (P < 0.01). The titres observed may have been due to cross-reactions with other leptospiral serovars, but this could not be demonstrated. An alternative explanation is that serovar hurstbridge is present in the human population.

Identification of enterotoxigenic Escherichia coli using alkaline phosphatase-labeled synthetic oligodeoxyribonucleotide probes.

Alkaline phosphatase-conjugated synthetic oligodeoxyribonucleic acid probes were used to detect enterotoxigenic Escherichia coli strains containing either the heat stable or heat labile toxin genes. Both of the synthetic probes detected as little as 5 ng of purified plasmid DNA bearing the appropriate toxin gene. In addition, both probes could detect 5 X 10(6) toxigenic bacteria by colony hybridisation. No cross reactivity was observed between probes. When 197 clinical isolates of Escherichia coli were examined for toxigenicity using bioassays, 13 heat stable and 17 heat labile toxin strains were identified. Of the 13 heat stable toxin strains, 12 were positive using the heat stable toxin synthetic probe (sensitivity, 92%; specificity, 98%) while 16 of 17 bioassay heat labile toxin positive samples were identified using the heat labile toxin synthetic probe (sensitivity, 94%; specificity, 97%). Alkaline phosphatase-conjugated synthetic probes with high sensitivity and specificity should provide a rapid means of identifying toxigenic Escherichia coli.

The use of ELISA and nonradioactive DNA hybridization assays for the detection of human cytomegalovirus.

A hybridization assay using a biotinylated DNA probe was compared to both ELISA and direct isolation methods for detecting human cytomegalovirus (HCMV). The biotin labeled HCMV AD 169 HindIII-O-DNA fragment was used in a dot-blot assay to screen for the presence of HCMV in 186 urine specimens obtained from kidney transplant patients. The biotinylated HCMV HindIII-O probe could detect 3 log10 TCID50 units of HCMV. Urine specimens were also examined for the presence of HCMV by either ELISA or direct isolation of virus in tissue culture. The HindIII-O fragment detected 12 of 20 culture positive samples (sensitivity, 60%). There were 5 samples which were probe positive and cell culture negative (specificity, 97%). The ELISA assay also detected 12 of 20 culture positive samples (sensitivity, 60%). Eight samples were ELISA positive, cell culture negative (specificity, 95%). Seven specimens were positive by all three criteria. Five specimens which were both ELISA positive and probe positive were cell culture negative. The ELISA positive, probe positive, culture negative specimens originated from patients who gave a culture positive specimen within 10 days of the original sample. The combination of probe and ELISA assays detected 16 of the 20 culture positive specimens (sensitivity, 80%). The combined use of biotinylated DNA probes and ELISA allows the detection of HCMV in urine specimens with good sensitivity and specificity.

Pseudoreplica electron microscopy for the detection of rotavirus: comparison with high-speed centrifugation electron microscopy and ELISA.

Three-hundred and sixty-three stool specimens from patients with diarrhoea were examined for rotaviruses to compare the sensitivity of the pseudoreplica technique (PSD-EM) to that of high-speed centrifugation EM (HSC-EM) in relation to a commercially available (Rotazyme, Abbott) enzyme-linked immunosorbent assay (ELISA). In ELISA-positive cases, both methods were of equal sensitivity. However, in borderline (+/-) and ELISA-negative specimens, PSD-EM detected 31 of 48 (64.6%) and 18 of 229 (8%) positive specimens respectively, compared to only 22 of 48 (45.8%) and one of 229 (0.4%) positives detected by HSC-EM. PSD-EM detected a significantly higher number of positives compared to HSC-EM (p less than 0.05). In view of its simplicity, sensitivity and the fact that a relatively large number of specimens could be processed compared to HSC-EM, we consider that PSD-EM is a much better procedure for routine screening and diagnosis of viral gastroenteritis than HSC-EM.