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An enzyme-linked immunosorbent assay (ELISA) is described for the detection of a soluble Listeria monocytogenes serogroup 4 antigen in cerebrospinal fluid samples (CSFs). In the ELISA an anti-Listeria monoclonal antibody, immobilized onto assay wells, was used to capture antigen from CSFs, the captured antigen was then reacted with a fluorescein isothiocyanate (FITC) conjugate of the same anti-Listeria antibody, which was detected with a horseradish peroxidase conjugate of a monoclonal antibody to FITC. The presence of antigen was detected by an enhanced chemiluminescence assay using a camera luminometer. Antigen was detected in the CSFs taken from five out of seven patients with culture proven L. monocytogenes serogroup 4 central nervous system infections, and in none of the CSFs taken from 25 other patients.

Clinical information was collected on 722 cases of Listeria monocytogenes infections in humans occurring in Britain between 1967 and 1985. This series comprised 34% (248 cases) associated with pregnancy and 66% (474 cases) in non-pregnant adults and juveniles. The cases not associated with pregnancy comprised: 76% in patients with severe underlying illness (of which 34% had central nervous system infections, and 42% bacteraemia without involvement of the central nervous system); 21% in previously healthy individuals (of whom 18% had meningitis); and 3% in patients without bacteraemia or involvement of the central nervous system. Cases occurred most often in male patients over 40 years of age. The overall mortality was 44%. Overall, the pattern of infection has altered to a disease of higher incidence, affecting most often susceptible non-pregnant individuals and the unborn. An annual increase in incidence of listeriosis occurred in the autumn in all categories of patients.

Clinical information was collected on 722 cases of Listeria monocytogenes infections in humans occurring in Britain between 1967 and 1985: 248 cases (34%) were associated with pregnancy (maternal, foetal, and neonatal), and comprised 9 cases (4%) of maternal bacteraemia without infection of the foetus; 42 cases (19%) of intra-uterine deaths; 118 cases (54%) of neonatal infection diagnosed within 2 days post-partum; and 50 cases (23%) of neonatal infection diagnosed as ill after 2 days post-partum. An overall mortality of 50% was recorded. The cases unassociated with pregnancy are described elsewhere (see accompanying paper).

A direct immunofluorescence technique was developed using FITC conjugates of anti-listeria antibodies (CL2 and CL17). Using this technique Listeria monocytogenes (whole cells) were observed in post mortem tissue from 3 patients where listeriosis had been proven by the isolation of the bacterium, and also from a patient where listeriosis was suspected. Using one of these monoclonal antibodies (CL2) an indirect antigen capture ELISA was developed for the detection of soluble antigen. Soluble antigen was detected in cerebrospinal fluid (CSF) from 27% of patients infected with L. monocytogenes serogroup 4 and 2% of patients where listeriosis was suspected. The test was 100% specific in that antigen was not detected in 270 other CSF samples tested. Antigen was only detected in CSF samples taken within 7 days after onset of illness.

Two monoclonal antibodies which recognise serogroup specific cell surface antigens of Listeria monocytogenes are described. The antibodies were specific for Listeria (i.e. did not react with 87 strains of bacteria from 14 other genera). In an indirect immunofluorescent test the antibodies had similar specificities when tested against strains of L. monocytogenes from human infections grown under a number of different growth conditions, and serological reference strains. A direct immunofluorescent antibody test was developed, and similar specificities of the antibodies found with strains of Listeria which had been isolated from food and grown under 2 different growth conditions. This technique is also used to directly demonstrate Listeria in soft cheese.

A phage-typing system for Listeria monocytogenes is necessary to eludicate its transmission and spread. We describe the general characteristics of a phage-typing system for L. monocytogenes and its use in selected epidemiological studies. Previously 78.4% of 823 strains of Listeria isolated in France between 1958 and 1978 were typable with a set of twenty phages isolaged from lysogenic strains. We now use twenty-seven phages; six derived from serovars 1/2a and 1/2b, eight from 4b, and thirteen from 4ab, 3c, 5, 6a and 6b. We used this system to examine 186 strains isolated during and after an outbreak in the province of Anjou which occurred during 1975 and 1976. One hundred and eight of these strains were of one phage type (octal code 000 420 000). Using this system we confirmed two cases of cross-infection in hospital neonates in England. Our results show that the reproducibility of the technique and the discrimination of the system are satisfactory for routine use. However, further testing and development of this system are underway.

Soluble antigen was prepared from Listeria monocytogenes serovar 4b using a formamide extraction method. Antigenic material was detected in this extract by gel diffusion and ELISA using anti-Listeria monoclonal antibodies. Using this ELISA, antigen was detected in cerebrospinal fluid (CSF) during infection due to L. monocytogenes serovar 4b with wells coated with three of the monoclonal antibodies (CL1, CL2 and CL3). The antigen binding of CL3 was found to be greatly influenced by changes in ionic strength, and these properties were utilized in an affinity purification method. An analysis of the antigens was carried out using crossed immunoelectrophoresis and this indicated that the crude formamide extract contains a number of distinct antigens. A group of three antigens of differing electrophoretic mobilities were demonstrated in the affinity purified material.