Mice were immunized against Salmonella typhimurium with graded doses of heat-killed (HK) and acetone-killed (AK) vaccines and then challenged by the oral or intraperitoneal routes with two doses of S. typhimurium. HK and AK vaccines gave good protection against an intraperitoneal challenge, but failed to protect against an oral challenge which is presumably the natural mode of infection. HK vaccine was as potent as AK vaccine in reducing the mortality rate among mice challenged by the intraperitoneal route but, unlike HK vaccine, AK vaccine was also able to reduce the infectivity rate. With a small intraperitoneal challenge dose it was observed that a gradual increase in vaccine dose is associated with a corresponding fall in mortality rate, but with a larger challenge dose an increase in vaccine dose was associated with a corresponding increase in mortality rates. It was concluded that the protective potency of this type of vaccine may partly depend upon the total amount of antigen in the animal, i.e. including both the vaccine and the challenge organisms, at a critical time after challenge.

During systemic treatment of mice with ampicillin or streptomycin, oral contaminations with exogenous bacterial species resulted in an abnormal colonization pattern. The contaminants persisted much longer and in much higher concentrations in the caecum of systemically treated mice than in control animals. Spread of the contaminant into the mesenteric lymph nodes and the spleen was found much more often in the antibiotic treated group. This, however, was only seen when the contaminant was ‘resistant’ to the antibiotic injected. The experiments suggest that the ‘CR-inducing species’ of the microflora live in close contact with the mucosa and therefore could be identical with the anaerobic tapered rods described by Savage & Dubos (1968).

The protection afforded by similar concentrations of different dengue virus serotypes against a subsequent challenge of West Nile virus was studied in hamsters. The New Guinea C strain of dengue 2 virus gave the best protection. It was found that the anamnestic neutralizing antibody response induced by the challenge West Nile virus against West Nile virus in hamsters, previously immunized with dengue 2 virus, might play a major role in the cross-protection observed in this system.

A study of diphtheria in Iran was undertaken during the summer of 1969. Diphtheria was found to be more common among the younger people and to reach its peak 3 months after the start of the school term, during the coldest period of the year. Owing to the liberal use of antibiotics a number of modified clinical cases were observed. Of the strains isolated, 89·7% were gravis, 1·3% intermedius and 9 % mitis. Phage typing of these strains showed that the mitis and intermedius strains could only be typed by adapted phages and the majority of gravis strains were phage type XIV, which is the epidemic type seen in other countries.

As the mass immunization campaign reduces the incidence of diphtheria in Iran, the epidemiological pattern of the disease will change as seen in the U.K. and U.S.A. It is, therefore, suggested that in the future further studies of diphtheria in Iran be undertaken in order to provide us with information about the changing epidemiological pattern of the disease.

Aerosol vaccination of mice with purified plain tetanus toxoid does not induce an immune response unless a suitable adjuvant is added.

Aluminium phosphate is without effect by aerosol treatment. Killed cells of Klebsiella pneumoniae, although effective, are unsatisfactory owing to the long inhalation period needed.

Killed Bordetella perussis cells were found to be an excellent adjuvant. A single aerosol treatment with a toxoid-B. pertussis mixture during a moderate exposure period evoked a considerable immune response. With repeated aerosol treatment of primed mice the addition of adjuvant is not required; booster treatment with plain toxoid is at least as effective.

Extracts from B. pertussis cells exert as good an adjuvant effect as the whole-cell vaccine. The remaining cell-wall debris also appears to be an active adjuvant.

In combination with constant doses of adjuvant (108B. pertussis cells), the 50 % protective doses (ED 50) of toxoid were determined by inhalation and by s.c. injection and were found to be 0·1875 and 0·0625 LFU respectively. This would imply that, as a result of the adjuvant action, the s.c. ED 50 is reduced by approximately a factor of 20; whereas the respiratory ED 50 is decreased by at least a factor of 100.

It is suggested that the much more pronounced adjuvant activity in aerosol immunization is associated with the induction of strong cell-mediated hypersensitivity in the respiratory tract.

Arguments in favour of biotyping of Enterobacteriaceae excreted in the faeces of isolated patients, as a method of investigating the efficiency of the isolation procedures, are presented as well as a technical outline of the procedure. The study included three kidney transplantation patients, five acute myeloid leukaemia patients and four healthy persons as controls.

The results show, apart from new colonizations during isolation, a difference in the mean number of contaminations and colonizations with different Enterobacteriaceae biotypes. It is concluded from these results, that the isolation procedures were not completely effective and that the AML patients studied had a decreased colonization resistance of their digestive tract. This was less evident in the kidney transplant group.

The colour-change and lead acetate tests for fermentation of d–, l–and m–tartaric acids and citric acid used in the Kristensen scheme for biotyping Salmonella typhimurium were found to be unreliable because, whatever the conditions of culture, they gave different results in replicate tests of the same strains. Many genotypically non-fermenting strains gave inconsistent reactions due to the emergence of fermenting mutant bacilli in some of their test cultures. No reliable test was found for the fermentation of citric acid.

A ‘turbidity’ test was found to give consistent and reliable results with the three tartaric acid isomers. It demonstrated fermentation by the significantly greater amount of growth obtained in a 24 hr. culture in Oxoid peptone water with added isomer than in a control culture without isomer. Lewis & Stocker's (1971) plate-inhibition test for fermentation of m–tartrate, which identifies m–tartrate-negative strains because m–tartrate inhibits their growth on citrate- or glycerol-containing minimal medium, was found to be as reliable as, and easier to read than, the turbidity test.

Use of the turbidity test for d–and l–tartrates and the plate-inhibition test for m–tartrate in biotyping 1435 strains of S. typhimurium showed that many strains had previously been mistyped by the lead acetate test and distinguished 16 new biotypes in addition to the 22 biotypes already recognized.

The incidence and acquisition of Candida albicans and other yeasts in two wards of a skin hospital is described. Carriage rates on the skin in hospital patients is higher than is generally supposed, and cutaneous sites may act as sources of infection with these organisms.

Four hundred and sixty-seven serum specimens from the female students at a residential college were examined for the presence of circulating antibody to human wart virus using the technique of counter-current immunoelectroosmophoresis. A significantly higher incidence of antibodies was found in students with a past history of plantar warts than in any other group. Antibody took several months to develop and was detectable in 20–30 % of the students up to 9 years after infection. From a few cases of multiple infection, it was shown that reinfection could occur in spite of the presence of circulating antibodies probably of the IgG class. The sensitivity of the test was compared with two recognized techniques for detection of wart virus antibodies, namely gel diffusion and passive haemagglutination.

The membrane methods described in Report 71 on the bacteriological examination of water supplies (Report, 1969) for the enumeration of coliform organisms and Escherichia coli in waters, together with a glutamate membrane method, were compared with the glutamate multiple tube method recommended in Report 71 and an incubation procedure similar to that used for membranes with the first 4 hr. at 30°C., and with MacConkey broth in multiple tubes. Although there were some differences between individual laboratories, the combined results from all participating laboratories showed that standard and extended membrane methods gave significantly higher results than the glutamate tube method for coliform organisms in both chlorinated and unchlorinated waters, but significantly lower results for Esch. coli with chlorinated waters and equivocal results with unchlorinated waters. Extended membranes gave higher results than glutamate tubes in larger proportions of samples than did standard membranes. Although transport membranes did not do so well as standard membrane methods, the results were usually in agreement with glutamate tubes except for Esch. coli in chlorinated waters. The glutamate membranes were unsatisfactory. Preliminary incubation of glutamate at 30° C. made little difference to the results.

The passive protection of mice against an intracerebral infection with Bordetella pertussis, by antiserum introduced directly into the brain with the infecting organisms, was compared with the protection afforded by intraperitoneal antiserum. The antibody effective by the intracerebral route is that which is adsorbed onto the infecting organisms, although it does not affect the viability of the organisms in vitro in the absence of complement.

Passive protection against organisms introduced intracerebrally takes place in one of two ways, depending on the size of the challenge: (1) after 3–4 days' growth, the growth rate declines so that the number of organisms does not reach the figure lethal for the mouse; (2) the organisms do not appear to multiply, as their numbers decline from the moment of injection, so that the brain is sterile after 2 days.

Many of the mice protected against a challenge of 50,000 organisms (ca. 100 LD50) by intraperitoneal or intracerebral antiserum recover by the first mechanism. The second mechanism operates after a smaller challenge of 5000 organisms (ca. 10 LD50), irrespective of whether the antiserum is given intracerebrally with the challenge, or intraperitoneally within several hours of challenge. Too much antiserum given intracerebrally with a 50,000 challenge, but not with a 5000 challenge, inhibits protection.

In some mice, virulent antibody-treated organisms which have not been killed, grow very slowly over a long period, but are eventually eliminated from the brain.

Poliomyelitis is an important problem of public health in warm-climate countries. Studies of serological responses to vaccination in these countries have given conflicting results but in many investigations the rates have been considerably less than in countries with temperate climates. In this study three possible factors influencing sero-conversion were investigated – the season of the year when vaccine was given, the social status of the mother (as indicated by the number of years of schooling) and the presence of non-poliomyelitis viruses (NPV) in the gut when vaccine was given.

Over 200 children about 2 months of age were included in the study. Each was given three doses of trivalent vaccine at 6-week intervals.

The sero-conversion rates of the groups fed in winter were excellent but were slightly less good in summer. The differences were greatest in children in the lower socio-economic groups and in children excreting other enteroviruses.

The conclusions are that, provided a potent vaccine is used, the factors which diminish the effectiveness of immunization in warm-climate countries can be overcome: (1) by giving three doses of trivalent vaccine; (2) by beginning vaccination at the earliest possible age (when enteroviruses are fewest); (3) by concentrating special attention on the lower socio-economic groups and if necessary by giving a reinforcing dose several months after the third dose has been given – preferably in the colder months.

Ninety-nine young Gambian children were studied for 61 weeks. About half of them had trachoma at the outset, and 80 % of the remainder acquired the disease while under observation. IgG trachoma antibody in the serum and IgG and IgA antibodies in the conjunctival secretions (CS) were titrated by an indirect immunofluorescence method. In serum samples obtained in capillary tubes the mean titre was slightly higher than in samples collected on filter paper. Sorum antibody at titres ↛ 1/10 was invariably associated with a clinical diagnosis of trachoma; it increased both in frequency and titre as the disease progressed, and was present in about half of those with Tr II. In CS, IgG antibody was present less often and at lower titres than in serum, and IgA antibody was detected even less frequently. There was some evidence of correlation between the titres of IgG and IgA antibodies in CS, but none for a relationship between the titres of the antibodies in serum and those in CS. Antibodies were almost never present in the absence of conjunctival follicles, but their titres were unrelated to the degree of follicular hyperplasia; there was no obvious relationship between the serological findings and corneal lesions. In children diagnosed clinically as trachoma, serum antibody was present in almost all those with conjunctival inclusions, and in a proportion of inclusion-negative subjects; the mean titre was much higher in the inclusion-positive group.

These findings do not settle whether CS antibodies are made locally, or are derived partly or wholly from the blood. They suggest that the indirect immunofluorescence test may be a useful diagnostic aid in trachoma, particularly in view of the rarity of false positive reactions; but there is at present little to choose between it and complement-fixation tests in terms of sensitivity.

Intravenous inoculation of Aspergillus fumigatus spores was used to study experimentally induced and natural resistance. Slight resistance resulted in increased survival time and higher resistance produced in addition a decreased infection rate.

Sublethal doses of living spores gave significant protection against challenge 3 weeks later, but large doses of heat-killed spores had no demonstrable effect.

Mice from one source showed a single, dramatic decrease in dose response to a deep-frozen strain of the organism over a period of 34 months. The dose response initially resembled that described by Scholer (1959) in which one million spores killed the majority of mice. The change was almost certainly due to an increase in resistance of the mice due to environmental factors, and the resistance was probably also effective against other strains of the organism. Although not proved, it seemed likely that the resistance was due to increased natural contact with A. fumigatus or related fungi. Possibly for a similar reason, mice of the same stock bred on different premises differed in their susceptibility to infection. The results indicated that environmental resistance-producing factors may have been operating simultaneously on a number of premises housing laboratory animals in south-east England. These findings may have significance in relation to the occurrence of natural aspergillosis of mammals and birds.

Of five A. fumigatus strains, four were of closely similar virulence; the fifth strain grew more slowly in vitro and was somewhat less virulent. Isolates from mice which died sporadically after small doses of spores were of no greater virulence than the inoculated strain. Although the susceptibility of mice aged 3 weeks was not uniform under all conditions, such animals were less resistant than young adult mice. Mice from six different sources showed only slight differences in susceptibility between each other, or from mice known to have developed a natural resistance.

Two methods are described for the extraction of enterotoxin from foods incriminated in incidents of staphylococcal food poisoning. Enterotoxin was detected serologically in 12 of 24 food samples from 20 separate incidents: eight samples contained enterotoxin A, three contained D and one both A and B. The amount of enterotoxin in nine foods, based on 100 % recovery, varied from 0·02 to 0·09 μg./g.

Data are also given on the numbers of Staphylococcus aureus isolated from samples of food from 39 food poisoning incidents. Colony counts varied between 7·5 × 105 and 9 × 109/g. with a median value of 7 × 107/g.

Sera from 203 Asian immigrants to the United Kingdom were examined for toxoplasma antibodies. The antibody titres were not significantly different from those found in the indigenous population although there was some indication that a higher domestic animal–human contact in Asia was associated with a higher positivity rate.

The intranasal inoculation of volunteers with living partially attenuated strains of influenza A and B viruses offers a new opportunity to determine the protective effect of serum haemagglutin-inhibiting antibody against a strictly homologous virus, under conditions where the time and dosage of the infective challenge can be controlled, the scoring of proven infections can be more precise and higher rates of infection can be achieved than in most natural epidemics.

In 1032 adult volunteers, whose serum HI antibody titre was determined immediately before virus challenge, there was a consistent inverse quantitative relationship between the HI titre and the likelihood of infection. The PD50 (50 % protective dose) of HI antibody was 1/18–1/36, but an unusual finding was that volunteers with no detectable pre-challenge antibody often seem to be less susceptible to infection than those with pre-challenge antibody in low titre.

In one group of volunteers challenged with an influenza B strain there was no evidence that pre-challenge antibody titres against viral neuraminidase had any significant protective effect against challenge infection.

The antibodies active in the Rose Bengal plate test (RBPT) for bovine brucellosis have been studied. The results of fractionation experiments showed that RBPT activity was associated with fractions containing immunoglobulin of the IgG1 class; other immunoglobulin classes were inactive in this respect although active in other tests. These results were confirmed by inhibition tests with specific antisera and by elution of the antibody from agglutinated RBPT antigen.

The major proportion of the serum complement-fixing activity was also present in the IgG1 fraction and it is suggested that the RBPT and CF reactions are probably mediated by the same antibodies.