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J B Robbins

Publications and source records attributed to J B Robbins.

At least 73 records · Page 4Linked to original sources
PubMed1995

Perspective: hypothesis: serum IgG antibody is sufficient to confer protection against infectious diseases by inactivating the inoculum.

The theory proposed is that a critical level of specific serum IgG is sufficient to confer protection against infectious diseases by inactivating the inoculum of the pathogen. This theory relies heavily on evaluation of licensed vaccines and includes the following: Measurement of serum antibodies only reliably predicts the efficacy of vaccines, according to regulatory agencies. Serum IgG antibodies alone account for the protection conferred by passive immunization. "Herd" immunity conferred by vaccines on viral and bacterial diseases is best explained by serum antibodies that inactivate the inoculum on mucosal surfaces, thus reducing the pathogen's transmission. Once the disease is manifest, serum antibodies induced by active immunization will neither relieve symptoms nor eliminate the pathogen; specific IgG must be present when the host encounters the pathogen in order to confer protective immunity. Information about the initial pathogen-host contact is vital, whereas knowledge of the symptomatology of the disease may not be essential for vaccine development.

Antigens↗
PubMed1995

Characterization of a human monoclonal immunoglobulin M (IgM) antibody (IgMBEN) specific for Vi capsular polysaccharide of Salmonella typhi.

A search for human monoclonal antibodies to protective antigens of bacteria revealed an immunoglobulin M lambda chain [IgM(lambda); designated IgMBEN] reactive with the Vi capsular polysaccharide of Salmonella typhi. Vi, a linear homopolymer of alpha(1-->4)GalApNAc that is O acetylated at C-3, is a licensed vaccine for typhoid fever. Immunologic properties of IgMBEN were compared to those of burro globulin prepared by intravenous injections of S. typhi (B339-340). IgMBEN and B339-340 yielded identical precipitin lines with Vi by double immunodiffusion. IgMBEN and B339-340 produced similar precipitation results with Vi and its derivatives prepared by de-O-acetylation, carboxyl reduction, and removal or replacement of the N-acetyl at C-2 with O-acetyl. B339-340 yielded maximal precipitation with Vi (0.41 mg of antibody per ml with 1.4 micrograms of Vi); next was carboxyl-reduced, O-acetylated Vi, which precipitated 0.325 mg of antibody per ml with 2.5 micrograms of Vi. IgMBEN yielded maximal precipitation with de-O-acetylated, carboxyl-reduced Vi (approximately 11.0 mg of antibody per ml with approximately 1.3 micrograms of antigen); next were de-O-acetylated Vi (9.89 mg/ml) and Vi (9.19 mg/ml). The precipitin curves and equivalence points of these three antigens were similar. Pneumococcus type 1, which contains GalApNAc, did not precipitate with Vi or its derivatives. These slight differences in specificity between IgMBEN and B339-340 were related to our proposed structure of Vi. We plan to use IgMBEN as a reference for measurement of vaccine-induced Vi antibodies.

Antibodies, Monoclonal↗
PubMed1995

Comparative immunogenicity of conjugates composed of Escherichia coli O111 O-specific polysaccharide, prepared by treatment with acetic acid or hydrazine, bound to tetanus toxoid by two synthetic schemes.

Escherichia coli O111, of various H types and virulence factors, causes enteritis throughout the world, especially in young children. This O type is found rarely in healthy individuals. Serum antibodies to the O-specific polysaccharide of O111 lipopolysaccharide (LPS) protect mice and dogs against infection with this E. coli serotype. The O111 O-specific polysaccharide is composed of a pentasaccharide repeat unit with two colitoses bound to the C-3 and C-6 of glucose in a trisaccharide backbone; this structure is identical to that of Salmonella adelaide (O35), another enteric pathogen. Nonpyrogenic O111 O-specific polysaccharide was prepared by treatment of its LPS with acetic acid (O-SP) or the organic base hydrazine (DeA-LPS). The O-SP had a reduced concentration of colitose. These products were derivatized with adipic acid dihydrazide (ADH) or thiolated with N-succinimidyl-3(2-pyridyldithio) propionate (SPDP). The four derivatives were covalently bound to tetanus toxoid (TT) by carbodiimide-mediated condensation or with SPDP to form conjugates. Immunization of BALB/c and general-purpose mice by a clinically acceptable route showed that DeA-LPS-TTADH, of the four conjugates, elicited the highest level of LPS antibodies. Possible reasons to explain this differential immunogenicity between the four conjugates are discussed.

Acetates↗
PubMed1994

Clinical and serological responses following primary and booster immunization with Salmonella typhi Vi capsular polysaccharide vaccines.

Clinical and serum antibody responses following intramuscular injection of two formulations of Salmonella typhi Vi capsular polysaccharide (Vi) were assessed in a double-blind evaluation. Healthy adults were randomly assigned to receive a 25 micrograms dose of liquid (Vi-Liq; n = 182) or freeze-dried Vi vaccine (Vi-Lyoph; n = 55), or placebo (n = 86). Erythema and/or induration > or = 1 cm in diameter at the injection site developed in 13/182 (7%) of Vi-Liq and 3/55 (5%) of Vi-Lyoph recipients (not significant, n.s.). Fever (oral temperature > or = 100 degrees F (37.8 degrees C)) occurred in < 2% of vaccinees. The frequencies of rises of fourfold or greater and of maximal Vi antibody levels were similar in the two vaccine groups. Fourfold or greater rises in serum Vi antibody levels (RIA) developed in 53% of Vi-Lyoph and 60% of Vi-Liq recipients by 1 week (n.s.), and 98 and 93%, respectively, by 1 month (n.s.). The frequencies of adverse reactions and mean Vi antibody levels following booster immunization with Vi-Liq 27 to 34 months after primary immunization (n = 55) were similar to those observed following primary immunization, although subjects given a booster dose were more likely to develop local reactions > or = 1 cm in diameter than those given a first dose (10/55 versus 13/182, p = 0.013 by the chi 2 test). Primary and booster immunizations with the Vi vaccines are well tolerated in healthy adults; mean Vi antibody levels remain significantly elevated for up to 34 months after primary immunization.

Adolescent↗
PubMed1994

Safety, immunogenicity and an open, retrospective study of efficacy of a monocomponent pertussis toxoid vaccine in infants.

One hundred forty-five infants were vaccinated with 25 micrograms of pertussis toxoid (NICHD-Ptxd) at 3, 5 and 7 or at 3, 5 and 12 months of age. One month after the third vaccination all had high serum IgG and neutralizing antibodies (antitoxin) against pertussis toxin. Vaccination at 3, 5 and 12 months resulted in higher antibody titers than vaccination at 3, 5 and 7 months. Sera obtained from 109 children at 3 years of age showed a decline of antibodies, but all had detectable antibodies. Adverse reactions were confined to local redness and swelling, which exceeded 2 cm after 17% of all injections. When the children were 3 years old, a comparison was made of the incidence of clinical pertussis in 142 of the 145 vaccinated children and in 284 age-matched controls living in the same areas. Information on symptoms of pertussis was obtained from the parents during telephone interviews. None of the vaccinated children had clinical pertussis, defined as a 6-week course of paroxysmal cough with whooping attacks or vomiting, whereas 57 controls (20%) had experienced these symptoms. Sixteen vaccinated children were exposed to pertussis in the household. Two of them had laboratory-verified Bordetella pertussis infections with cough of 2 and 4 weeks, respectively, without whooping attacks or vomiting, whereas 14 did not develop a cough. The study shows that NICHD-Ptxd is immunogenic in infants and that it most likely confers a high degree of protection against pertussis.

Antibodies, Bacterial↗
PubMed1994

Qualitative and quantitative analyses of the antibody response elicited by Haemophilus influenzae type b capsular polysaccharide-tetanus toxoid conjugates in adults with IgG subclass deficiencies and frequent infections.

Twenty-one IgG subclass-deficient adult patients with repeated infections of the respiratory tract, were immunized with Haemophilus influenzae type b capsular polysaccharide (HibCP) covalently bound to tetanus toxoid (TT). Specific immunoglobulin and IgG subclasses to HibCP and TT were quantified; the biological activities of HibCP antibodies were also investigated. Most patients showed an antibody response similar to that observed in healthy adults, and the bactericidal activity related to the post-immunization levels of HibCP antibodies. No relation was found between immunoglobulin isotype deficiency, the clinical symptoms and the IgG subclass responsiveness, and no relation was observed between HibCP and TT antibody responses. Our data indicate that some, but not all, patients with recurrent infections and IgG subclass deficiency have an abnormal serum antibody response to polysaccharide and protein epitopes of Hib-TT conjugate vaccine. Analysis of the antibody response after vaccination with HibCP-TT conjugate vaccine did not seem to predict the clinical course of such patients.

Adult↗
PubMed1994

Comparison of conjugates composed of lipopolysaccharide from Shigella flexneri type 2a detoxified by two methods and bound to tetanus toxoid.

Shigella flexneri type 2a lipopolysaccharide (LPS) was detoxified with acetic acid (O-SP) or with hydrazine (DeALPS). DeALPS, but not O-SP, retained part of its lipid A. Both gave an identical line of precipitation with typing antiserum by double immunodiffusion, and both had low levels of LPS activity by the Limulus amoebocyte lysate assay. O-SP had an M(r) of approximately 17,000. DeALPS had two components of M(r)s approximately 30,00 (major and approximately 10,000 (minor). Adipic acid hydrazide derivatives of O-SP and DeALPS were conjugated to tetanus toxoid (TT), purified by gel filtration through CL-6B Sepharose, and designated O-SP-TT and DeALPS-TT, respectively. Saccharide (2.5 micrograms) as O-SP, DeALPS, or their conjugates was injected subcutaneously into 5-week-old mice three times 2 weeks apart. The mice were bled before the second injection and 7 days after the second and third. O-SP alone did not elicit immunoglobulin M (IgM) or IgG LPS antibodies. DeALPS elicited low levels of IgM LPS antibodies after the third injection only. Two of three lots of O-SP-TT induced significant levels of IgM LPS antibodies after the third injection. One O-SP-TT lot elicited IgG LPS antibodies after the second injection, and all three lots elicited significant levels of IgG after the third. DeALPS-TT induced low levels of anti-LPS IgM and IgG only after the third injection. The geometric mean antibody titers of both immunoglobulin classes induced by O-SP-TT were higher than those induced by DeALPS-TT. By these criteria, O-SP provided a more immunogenic saccharide than DeALPS for S. flexneri type 2a conjugates.

Animals↗
PubMed1994

Laboratory and preliminary clinical characterization of Vi capsular polysaccharide-protein conjugate vaccines.

To improve its immunogenicity for children and adults and to make it suitable for routine immunization of infants against typhoid fever, the capsular polysaccharide of Salmonella typhi (Vi) was bound to the B subunit of the heat-labile toxin (LT-B) of Escherichia coli or the recombinant exoprotein A (rEPA) of Pseudomonas aeruginosa. The conjugates elicited higher levels of antibodies (micrograms per milliliter of serum) in mice and in guinea pigs than did Vi and, unlike Vi alone, elicited booster antibody responses in both species. In adult volunteers, Vi-LT-B and Vi-rEPA, respectively, elicited higher levels of antibodies than Vi alone after the first injection (4.74 versus 1.77 and 4.91 versus 1.77; P < 0.005) and 26 weeks later (2.32 and 2.69 versus 0.54; P < 0.04); a second injection of the conjugates did not elicit a booster response of Vi antibodies. None of the 51 vaccinees had fever or significant local reactions. Vi-rEPA elicited slightly higher levels of Vi antibodies than did Vi-LT-B at all intervals after injection, but these differences were not significant. Each conjugate elicited antibodies to its carrier protein. The antibody responses elicited in adults by Vi bound to LT-B and rEPA are similar to those of other polysaccharide-protein conjugates. These conjugates promise to be an improved Vi vaccine. Studies of Vi conjugates with adults and infants in areas where typhoid is endemic are planned.

Adolescent↗
PubMed1994

Preparation, characterization, and immunological properties in mice of Escherichia coli O157 O-specific polysaccharide-protein conjugate vaccines.

Escherichia coli O157 causes severe enteritis and the extraintestinal complication of hemolytic-uremic syndrome, with their highest incidence occurring in children. We postulated that serum immunoglobulin G (IgG) antibodies to the O-specific polysaccharide of lipopolysaccharide (LPS) may confer protective immunity to enteric pathogens by inducing bactericidal reactions against the ingested organisms in the jejunum (J. B. Robbins, C. Chu, and R. Schneerson, Clin. Infect. Dis. 15:346-361, 1992; S. C. Szu, R. Gupta, and J. B. Robbins, p. 381-394, in I. K. Wachsmuth, P. A. Blake, and O. Olsvik, ed., Vibrio cholerae, 1994). Because polysaccharide-protein conjugates induce serum IgG antibodies in infants, we bound the O-specific polysaccharide of E. coli O157 to proteins. E. coli O157 LPS, treated with acetic acid or hydrazine, was derivatized with adipic acid dihydrazide and bound to proteins by carbodiimide-mediated condensation. Conjugates of these adipic hydrazide derivative were prepared with bovine serum albumin, formalin-treated exotoxin C of Clostridium welchii (Pig Bel toxoid), or Pseudomonas aeruginosa recombinant exoprotein A. The conjugates had low levels of endotoxin and elicited serum antibodies with bactericidal activity to the O157 LPS. The largest increase in LPS antibodies was of the IgG class. Clinical evaluation of E. coli O157-toxoid conjugates is planned.

ADP Ribose Transferases↗
PubMed1994

Synthesis and some immunologic properties of an O-acetyl pectin [poly(1-->4)-alpha-D-GalpA]-protein conjugate as a vaccine for typhoid fever.

Pectin, a plant polysaccharide, is mostly a linear homopolymer of poly(1-->4)-alpha-D-GalpA with < 5% neutral sugars: its molecular size has a broad distribution around 400 kDa, and the degree of esterification is < 5%. The structure of the capsular polysaccharide of Salmonella typhi (Vi) differs from pectin in that it is N acetylated at C-2 and O acetylated at C-3, and has a molecular size of approximately 2 x 10(3) kDa. There is no serological cross-reaction between pectin and Vi. Pectin, when O acetylated at C-2 and C-3, is antigenically identical to Vi in double immunodiffusion. Unlike Vi, O-acetylated pectin (OAcPec) is not immunogenic in mice, probably because of its comparatively low molecular weight. After storage at 3 to 8 degrees C for 3 months, there was no change in the O-acetyl content or the M(r) of OAcPec. At 60 degrees C, the M(r) of OAcPec declined more rapidly than that of Vi. OAcPec conjugated to tetanus toxoid elicited Vi antibodies in mice, and reinjection elicited a booster response. The levels of Vi antibodies elicited by OAcPec-tetanus toxoid conjugates were lower than those elicited by Vi conjugates, but these differences were not statistically significant. OAcPec has some advantages because it can be measured by standardized colorimetric assays and because it forms more soluble conjugates with proteins than does Vi. One disadvantage is that its glycosidic bond is not as stable as that of Vi. The use of a plant polysaccharide, pectin, as an immunogen for prevention of a systemic infection caused by a capsulated pathogen (S. typhi) provides a novel approach to improve the preparation and immunogenicity of polysaccharide-based vaccines.

ADP Ribose Transferases↗
PubMed1993

Binding of the O-antigen of Shigella dysenteriae type 1 and 26 related synthetic fragments to a monoclonal IgM antibody.

Shigella dysenteriae type 1 possesses an O-antigen whose repeating unit is -->3)-alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->2)-alpha-D-Galp -(1-->3)-alpha-D- GlcpNAc-(1-->, where Rhap is rhamnopyranosyl, Galp is galactopyranosyl, and Glcp is glucopyranosyl. Using ligand-induced protein fluorescence change, we have measured the affinities of a monoclonal murine IgM for 26 fragments of, or related to, the structure of the O-polysaccharide and of the IgM Fab for the intact O-specific bacterial polysaccharide. Synthetic saccharides used were methyl glycosides to ensure an anomerically defined pyranosyl ring conformation. The galactosyl residue is the only monosaccharide of the antigenic epitope that shows quantifiable binding: approximately 3.0 kcal/mol of binding free energy, depending on the structure and conformation of the fragment it is a part of. Addition of an alpha-(1-->2)-linked rhamnosyl residue increases the free energy of binding significantly. We propose this rhamnopyranosyl-alpha-(1-->2)-galactopyranosyl disaccharide to be the basic determinant of the Shigella O-polysaccharide. Further extension (by linkages as in the natural antigen) of this oligosaccharidic ligand toward the upstream end (in an oligo- (or poly-)saccharide, such as A-->B-->C-->D-->E-->m, where A, B, C, D, and E are sugars and m is any moiety, such as methyl, we define A as the glycosyl- or upstream terminus, and E as the glycoside- or downstream terminus) by rhamnosyl and N-acetylglucosaminyl moieties improves the binding only minimally. The antibody is quite specific for the rhamnosyl-alpha-(1-->2)-galactosyl sequence but less so for the nature of the attachment to the galactosyl residue on the downstream side. Measurements using IgM Fab and the intact O-specific polysaccharide show that the antibody can bind internal segments on the antigen chain. The free energy of binding of this antibody for the disaccharide determinant varies from -delta G of 4.7 to 5.1 kcal/mol, depending on its flanking residues.

Animals↗
PubMed1993

Synthesis of a tetrasaccharide donor corresponding to the O-specific polysaccharide of Shigella dysenteriae type 1.

O-(2,4-Di-O-benzoyl-3-O-chloroacetyl-alpha-L-rhamnopyranosyl)-(1--> 2)-O-(3,4,6-tri-O-benzoyl-alpha-D-galactopyranosyl)-(1--> 3)-O-(2-acetamido-4,6-di-O-acetyl-2-deoxy-alpha-D-glucopyranosyl)-(1--> 3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (1) was synthesized in a stepwise manner, using the following monosaccharide units: 2-(trimethylsilyl)ethyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside, 2-azido-4,6-O-benzylidene-3-O-chloroacetyl-2-deoxy-beta-D-glucopyranosyl chloride, methyl 3,4,6-tri-O-benzoyl-2-O -(4-methoxybenzyl)-1-thio-beta-D-galactopyranoside, and 2,4-di-O-benzoyl-3-O-chloroacetyl-alpha-L-rhamnopyranosyl chloride. Compound 1 corresponds to a complete tetrasaccharide repeating unit of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1.

Carbohydrate Sequence↗
PubMed1993

Laboratory and clinical evaluation of conjugate vaccines composed of Staphylococcus aureus type 5 and type 8 capsular polysaccharides bound to Pseudomonas aeruginosa recombinant exoprotein A.

The synthesis, standardization, and immunogenicity in young outbred mice and clinical evaluation in adult volunteers of investigational vaccines designed to induce serum antibodies to the type 5 and type 8 capsular polysaccharides (CPs) of Staphylococcus aureus are described. Conjugates composed of the type 5 CP and a sonicated preparation of a high-molecular-weight type 8 CP bound to a nontoxic recombinant protein derived from Pseudomonas aeruginosa exotoxin A (rEPA) were synthesized. The conjugates were nontoxic and elicited serum CP antibodies after two subcutaneous injections into young outbred mice; a third injection elicited a booster response. The lower-molecular-weight type 8 CP was not immunogenic in the mice, and the high-molecular-weight type 8 CP elicited low levels of antibodies without a booster effect. In the volunteers, neither the conjugates nor the type 8 CP alone caused significant local reactions or fever. The conjugates elicited type-specific antibodies of both the immunoglobulin M (IgM) and IgG classes after the first injection; a second injection 6 weeks later did not stimulate a booster effect. The high-molecular-weight type 8 CP alone, injected once only, elicited levels of IgG and IgM type-specific antibodies similar to those of the conjugate. The vaccine-induced CP antibodies were mostly of the IgG1 and IgG2 subclasses and had opsonophagocytic activity. The conjugates elicited IgG antibodies to the native exotoxin A with neutralizing activity. In summary, the type 5 and type 8 conjugates were safe and elicited biologically active antibodies to both the CP and rEPA components.

ADP Ribose Transferases↗
PubMed1993

Primum non nocere: a pharmacologically inert pertussis toxoid alone should be the next pertussis vaccine.

The objective of a vaccine for pertussis is to prevent the paroxysmal cough with its complications. Prevention of the paroxysmal cough should prevent transmission of B. pertussis. Clinical studies indicate that a critical level of antitoxin confers protection against pertussis and that the long-lived protective immunity that follows pertussis is best explained by the presence of antitoxin. Vaccine-induced protective immunity can be mediated by a critical level of antitoxin alone. In addition to preventing pertussis with vaccines, we predict this level of antitoxin will also exert epidemiologic control (herd immunity) by inhibition of colonization with B. pertussis and by prevention of the paroxysmal cough which will reduce transmission of this pathogen. Lastly, a pertussis toxoid need not have detectable pharmacologic activity to exert its protective actions: residual activity could exert a deleterious effect on glucose metabolism and exert immunomodulating effects. Accordingly the new pertussis vaccine should contain inactivated pertussis toxoid alone and there is no need to include other components. Several candidates could serve as a satisfactory pertussis toxoid. The admonition to physicians given by Hippocrates, Primum non nocere (first of all do no harm), should be heeded by those responsible for the development and use of the new pertussis vaccine.

Adult↗
PubMed1993

Countercurrent immunoelectrophoresis for diagnosis of acute bacterial pneumonia in Chinese children.

Countercurrent immunoelectrophoresis (CIE) with H. influenzal type b(Hib) and Pneumococci Omni antisera was performed on serum and concentrated urine and pleural fluid samples from 100 patients with acute pneumonia in Beijing Children's Hospital. Thirty-one patients were investigated by bacteriologic techniques (blood culture and pleural fluid culture). CIE was positive in 29/100 (29%) of cases of Hib, 13/100 (13%) of cases for pneumococci. Overall, bacterial causes of pneumonia were diagnosed by CIE in 41/100 (41%) cases. Antigens were detected in 5/90 (5.6%) serum samples, in 36/87 (41.5%) concentrated urine samples, and in 1/2 (50%) samples of pleural fluid. Only one Hib strain was found by pleural fluid culture. The contamination rate of bacterial culture in this group was high (5/31 cases, 16.1%). Therefore, traditional bacteriologic techniques are of very limited value for diagnosing pneumonia in Chinese children. The results showed that bacterial pathogen, especially Hib and Pneumococci, are very common and important causes of pediatric pneumonia in China.

Antigens, Bacterial↗
PubMed1992

Production of monovalent antisera by induction of immunological tolerance for capsular typing of Streptococcus pneumoniae.

Hyperimmune and high-titered polyclonal pneumococcal antisera, specific for cross-reactive types within groups, were produced in adult rabbits. Purified capsular polysaccharide was injected intravenously into adult rabbits. One week later, these rabbits were given multiple intravenous injections of formalin-inactivated pneumococci of the cross-reactive type by an established method. Each of the resultant antisera were specific for the cross-reactive type indicating that the previous injection of the polysaccharide had induced epitope-specific tolerance. This method was successful for production of antisera against pneumococcal types 6A, 6B, 9N, 9V, 19F and 19A. Polyclonal rabbit pneumococcal antisera have some advantages over murine monoclonal antibodies for serologic studies and this method should be applicable for producing type-specific antibodies to cross-reactive polysaccharides of clinical interest. Further, this method is simpler and generally produces higher titered monovalent (factor) reagents than absorbed antisera.

Animals↗
PubMed1992

Hypothesis for vaccine development: protective immunity to enteric diseases caused by nontyphoidal salmonellae and shigellae may be conferred by serum IgG antibodies to the O-specific polysaccharide of their lipopolysaccharides.

Immunoprophylaxis for bacterial enteric diseases is hindered because the protective immune mechanism(s) against nontyphoidal salmonellae or shigellae in humans are not established. On the basis of the similarities between the clinical signs, epidemiology, pathogenesis, and pathology of as well as protective immunity to salmonellae and shigellae, we propose that serum IgG antibodies to the O-specific polysaccharide (O-SP) of their lipopolysaccharides (LPSs) will confer protective immunity to these two pathogens. Critical to this notion is that (1) the virulence of these two pathogens requires full expression of their LPS; (2) active or passive immunization with serum IgG O-SP antibodies confers protection of mice against Salmonella typhimurium (there are no comparable data for humans); and (3) in humans, convalescence from shigellosis confers type (O-SP) -specific protective immunity, and indirect evidence shows a correlation between the level of serum LPS antibodies and resistance to shigellosis. We designed conjugate vaccines to elicit high levels of long-lived serum IgG O-SP antibodies to nontyphoidal salmonellae and shigellae to test this hypothesis.

Animals↗