Scanning electron microscopic study of virulent Yersinia pestis and Yersinia pseudotuberculosis type 1

Virulent Yersinia pestis was grown on heart infusion blood agar and examined by scanning electron microscopy, exposing the fraction 1 envelope antigen on cell surfaces as a lumpy coating that spilled into the surrounding milieu. The amount of antigen depended on both the duration and temperature of incubation. Comparison of the cultures grown at 37 degrees C for 24, 48, and 72 h with those grown at 22 degrees C for identical periods demonstrated that the antigen increased in amount with the length of incubation, and that the overall production of antigen was much greater of 37 degrees C than at 22 degrees C. These experiments visually confirmed the findings of our previous immunological studies. Moreover, we established that the closely related, virulent organism Y. pseudotuberculosis bears no such antigenic coating at any temperature or incubation period. In addition, the emergence of multiple flagella was noted when Y. pseudotuberculosis was grown at 22 degrees C in a liquid medium, whereas Y. pestis remained without these organelles. These observations preceptibly corroborated the absence of fraction 1 envelope antigen and the presence of flagella, respectively, for distinguishing Y. pseudotuberculosis from Y. pestis.

Immunity in plague: protection of the vervet (Cercopithecus aethips) against pneumonic plague by the oral administration of live attenuated Yersinia pestis

Protection against pneumonic plague by the oral administration of a live, attenuated Yersinia pestis vaccine, EV76 (Paris) F, was evaluated in the vervet (Cercopithecus aethips). Six animals were vaccinated with a dose of 1.175 X 10(9) colony-forming units (cfu); all tolerated the dose and developed antibodies to Fraction I of Y. pestis. Three immunized animals were challenged with an inhaled dose of 3.2 X 10(6) cfu (160 LD50 [50% lethal dose]) of virulent Y. pestis strain 195/P and two survived; the other three received a challenge dose of 4.9 X 10(6) cfu (245 LD50) and one survived. The three surviving monkeys had high titers of antibody to Fraction I. At necropsy of the animals that succumbed to the challenge infection, almost complete consolidation of the lungs was apparent, and sizable effusions were present in the thoracic cavities. Indeed, the striking pathology indicated the severest form of pneumonic plague. Since it can be assumed that the animal surviving challenge with the larger inoculum would have survived the smaller dose, we conclude that the immunization procedure protected half of the vervets that were exposed to challenge.

Diagnosis of plaque: an analysis of the Yersin-Kitasato controversy

Images

Priming of Macaca cynomolgus philippinensis with purified antigen of Brucella melitensis before injection of Rev. I vaccine

In experiments designed for study of bacteremia and serologic response of Macaca cynomolgus philippinensis to vaccination with a soluble antigen (fraction I) of Brucella melitensis and the live Rev. I vaccine strain, fraction I and Rev. I were administered both four weeks apart and simultaneously. One of three monkeys given the vaccines four weeks apart and two of three monkeys vaccinated with fraction I and Rev. I in a single injection developed transient bacteremia, as shown by blood cultures. Both methods of vaccination induced significant titers of antibody to B. melitensis, and vaccinated monkeys were protected against subsequent challenge with a virulent strain of B. melitensis.

Immunity in plague: protection induced in Cercopithecus aethiops by oral administration of live, attenuated Yersinia pestis

A live, attenuated Yersinia pestis vaccine, designated EV76 (Paris) F, was pathogenic in Cercopithecus aethiops when administered parenterally. Although an oral dose of 10(9) colone-forming units of the vaccine was nonfatal to vervets, a transient but severe gastrointestinal disturbance resulted in four of 12 animals. Seven immunized vervets were protected against intradermal challenge. The remaining five vervets without serologic reactions and five untreated controls died from typical bubonic (septicemic) plague within seven days. General reactions after vaccination were not predictive of later-developing immunity, which appeared to correlate with the production of Fraction I-specific antibodies. Marked differences in immunity were noted with two methods of vaccine administration (incorporation into bananas and dropping into the mouth). This finding supported the prior observation that the oral mucosa is the major portal of entry for this strain of vaccine. Local reactions in the buccal cavity after feeding were negligible. Thus this strain of Y. pestis is a nonlethal, effective weapon against bubonic plague in a susceptible species.

Yersinia pestis: correlation of ultrastructures and immunological status

Ultrastructural identification and localization of the fraction 1 "envelope" antigen in the plague bacillus Yersinia pestis were the primary objectives of this brief study. The antigenicity of extra-cellular material between the bacilli in undisturbed cultured colonies and that of the pathogen per se were measured and correlated by means of the semi quantitative complement fixation method after incubation for 72 h at 37 C. When the amount of extracellular substance in wild-type T1 (virulent) bacteria was compared by electron microscopy with that in avirulent strains of Y. pestis, with and without passage through guinea pigs, we found that the material of interest was greatly attenuated or even absent in colonies that had not been passed through animals, whereas passage markedly augmented production of the material. We also explored the requirement for larger quantities of Ca(2+) and Mg(2+) in the culture media and discovered that without these ions production of the extracellular material was limited. These observations support the hypothesis that this extracellular substance between cultured Y. pestis bacilli of various strains represents the source of the fraction 1 envelope antigen.

An evaluation of Pasteurella pestis fraction-1-specific antibody for the confirmation of plague infections

Owing to the relatively long duration of specific serum plague antibodies in the host, the serological diagnosis of plague has substantial advantages over the conventional method of isolation of the causative agent. For the performance of both the complement-fixation (CF) and passive haemagglutination (HA) tests, the use of highly purified, specific Fraction 1 antigen is essential, and its preparation is discussed in this paper. Although both tests measure the same antibodies, the passive HA test is the more sensitive and constitutes the most effective means of detecting recovery from plague infection in nature. The CF test is nevertheless invaluable for such purposes as determining the antibody content of sera from immunized or infected hosts, indicating the amount of Fraction 1 developed by strains of Pasteurella pestis in cultures and therefore present in a vaccine, or detecting and estimating the amount of Fraction 1 antigen in extracts prepared from infected animal tissues and therefore for the field diagnosis of wild rodent plague after contamination or decomposition of rodents' carcasses.

Studies on Immunization against Plague

The tested vaccines were all atoxic, except that after intracutaneous injection of 0.2 ml of 3.26 × 109 organisms/ml with adjuvant, a hard papule persisted for a few weeks.

The potency ratio as tested in mice increased according to the number of organisms in the vaccine. The Al(OH)3 adsorbed vaccine appeared to be three times as effective as the aqueous one.

In guinea pigs, the protective single dose is about 1.5 × 109 organisms. Given in two equal doses, 0.652 × 109 to 6.52 × 109 organisms effectively protect all the animals. However, the group given the large dose had better antibody titers and developed smaller buboes after infection. About 1.0 × 109 organisms, given in two basic immunization doses with 1 booster, also revealed a stronger immune reaction and smaller buboes. These findings suggest that the frequency of small doses of vaccine is likewise important in that the use of small doses can be compensated for by more frequent inoculations. One sensitizing dose for basic immunization is adequate to prepare for the booster effect, as demonstrated in both the guinea pig and primate experiments.

A total dose of 4.89 × 109 organisms protected 90% of the guinea pigs when challenged by the intranasal route.

In primates, a total dose of 4.89 × 109 and 8.15 × 109 organisms protected all animals from a challenge dose of 9.9 × 106 195/P organisms given intraperitoneally.

In the animal experiments, the degree and duration of immunity was largely determined by the antigenic stimulation, enhanced by the aluminum adjuvant effect. The effective antigenic range of the tested vaccine preparations was relatively broad. When a good potential immunity exists in the host, an increase in antibody production can be obtained with a small booster dose.

Experimental Comparison of the Immunogenicity of Antigens in the Residue of Ultrasonated Avirulent Pasteurella Pestis with a Vaccine Prepared with Killed Virulent Whole Organisms

Several P. pestis cell wall antigens were prepared by repeated ultrasonation, and their toxicity and immunogenicity were studied and compared with killed virulent whole organism vaccine by means of toxicity, serologic and immunogenicity tests in guinea pigs and mice. The antigenic components were determined with the gel diffusion test. Preparation of the residue antigens requires a large quantity of starting material and is complicated in comparison with the preparation of killed whole organism vaccine. The solubility of the final material was less than that reported elsewhere.

Only a small amount was available for toxicity tests, and this was toxic to neither mice nor guinea pigs. Guinea pigs inoculated with TJW or E. V. 76 in distilled water preparations had rather severe local reactions. The immunogenicity of the tested vaccines was satisfactory and similar except in a few tests in which the whole organism vaccine was superior to the others. In the test system, in which the interval between immunization and challenge was rather short, the antibody response expressed in serologic tests was not pronounced, but in some instances it gave a rough prediction of immunity. The virulence antigens V and W did not play an essential role in these tests. The immunity was directly related to Fraction I antibody. The administration of the whole organism vaccine in oil adjuvant to guinea pigs enhanced and sustained Fraction I antibody formation.

The Immune Response of the Guinea Pig to the Antigens of Pasteurella Pestis

In experimental antiplague immunization the reaction of the guinea pig has been unique. Of greatest interest have been the difficulties in immunizing this animal either with aqueous suspensions of killed plague bacilli or with antigenic extracts of Pasteurella pestis, both highly immunogenic in the mouse, rat and monkey. The report that follows is an account of the development of the present conclusions about the immune response of this animal.

Materials and Methods. Strains of P. pestis. 1) Yreka, a virulent strain originally isolated from a fatal human infection in Yreka, California. 2) 195/P, a virulent strain from the Haffkine Institute in Bombay, India. It was originally isolated from a fatal pneumonic plague infection, and a sample of the culture was lyophilized and shipped to the Hooper Foundation. 3) Shasta, a virulent strain isolated from a fatal bubonic infection in 1951. 4) 111, a virulent strain isolated from a fatal pneumonic infection in Madagascar.

Studies on Immunization Against Plague

A study of the diffusible antigens of P. pestis was undertaken, adapting a technique of double diffusion in gels first developed by Elek and by Ouchterlony. By testing combinations of P. pestis strains and fractions and P. pseudotuberculosis strains against anti-P. pestis gamma globulin, two antigen-antibody precipitation reactions common to both organisms were demonstrated, and the P. pestis-specific Fraction I and Fraction II (toxin) reaction zones were identified. The study confirmed previous laboratory findings that the avirulent but antigenic A1122 strain possesses a moderate amount of Fraction I, and the avirulent, nonantigenic 14 and TRU strains possess almost no Fraction I, and that strain 14 is toxic and strain TRU is essentially atoxic.

There was no indication of an antigen-antibody reaction specific for virulent P. pestis strains.

The method of double diffusion in gels appears to be a highly precise one for qualitative analysis of antigens and may be found useful for comparative studies of heterologous but closely related species and for studying the factors related to cross immunity.

Studies on Immunization Against Plague

A hemagglutination test has been developed for the protein component of Pasteurella pestis, by application of a technique described by Boyden. This test and the polysaccharide hemagglutination test previously described are highly selective for either the protein or the polysaccharide of P. pestis, and the serum response is highly specific. The polysaccharide test is valuable for research, while the protein test is excellent for both diagnosis and research. Various virulent and avirulent P. pestis strains and preparations were compared by means of these and other serologic tests, and a working hypothesis of the antigenic structure of the plague bacillus and the relationship of structure of the plague bacillus to virulence and immunogenicity is outlined. The polysaccharide fraction does not affect phagocytosis and is not a protective antigen for either mice or guinea pigs, but it provokes a specific serologic reaction. The protein fraction is a protective antigen directly affecting phagocytosis.

Studies on Immunization Against Plague. V. Multiplication and Persistence of Virulent and Avirulent Pasteurella Pestis in Mice and Guinea Pigs

Some avirulent strains of Pasteurella pestis progressively decrease in numbers in host tissue without indication of multiplication, but viable bacilli can still be found up to the 6th to the 9th days after inoculation. Other strains maintain their numbers well for 5 or 6 days and are then progressively eliminated. Some strains multiply and definitely increase in numbers before being overcome and the tissue sterilized. With the avirulent strains studied, at no time were bacilli cultured from the blood later than 15 minutes after injection.

Those strains which are effective in stimulating development of immunity in mice may be the ones that, even though incapable of extensive multiplication, are rich in soluble envelope antigen or may be the ones that, although less productive of envelope antigen, have the capacity to multiply and to attain numbers adequate to provide necessary quantities of envelope antigen.

Studies on Immunization Against Plague

A hemagglutination test has been developed for P. pestis. The antigen is contained in old broth cultures, in extracts of killed and dried organisms and in alcohol-precipitated envelope antigens, but not in the protein fractions soluble in 0.25 saturation of ammonium sulfate solution or in those isolated by precipitation of soluble extracts by 0.3 or more saturated ammonium sulfate. The crude antigen has a low nitrogen content and is likely to be a polysaccharide.

The use of the hemagglutination test or of the inhibition of hemagglutination may be valuable in ascertaining the identity of plague antigens. The hemagglutination antigen appears not to play an important role as a protective antigen in plague.

Studies on Immunization Against Plague

A procedure for the complement-fixation test with plague Fraction I as antigen and specific high-titered antiplague (by preference anti-Fraction I) serum as antiserum has been described.

Examples of the use of the method are given: the determination of Fraction I plague antigen in the bacteria and in tissue extracts of carcasses of mice and guinea pigs that had died of experimental plague. Antibodies to Fraction I were detected in convalescent human sera, in sera of guinea pigs immunized with various living avirulent plague organisms, and of rabbits and monkeys immunized with Fraction I. The titers obtained are in direct agreement with values determined by precipitation, agglutination, immunization and passive mouse-protection tests.

The complement-fixation tests, besides being a valuable addition to research plague studies, also acts as a liaison test for evaluation of plague vaccines, estimation of degree of immunity, determination of potency of antiplague sera, confirmation of recent infection with Pasteurella pestis and help in the positive identification of plague bacilli.