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Two avian strains of Pasteurella multocida, a vaccine strain and a virulent field isolate, were investigated to determine their propensity to release endotoxin from the cell surface. Both organisms released comparable amounts of endotoxin when plasma complement proteins were present, however the virulent strain did so without the loss of viability that occurred in the vaccine strain. Blocking complement activity decreased the ability of plasma to elicit endotoxin release from the bacteria. When the cells were treated with divalent metal chelators such as trans-1, 2-diaminocyclohexane-N,N,N1,N1-tetraacetic acid (CDTA), more endotoxin was released from the vaccine strain than from the virulent isolate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of purified lipopolysaccharide (LPS) from both strains revealed virtually identical patterns. Both had patterns considered typical of rough LPS. Challenge studies in 8 weeks old turkeys showed that the field strain induced endotoxemia of longer duration than the vaccine strain and produced greater mortality.

Twenty-four isolates of Pasteurella multocida from clinical cases of fowl cholera and the Clemson University vaccine strain were surveyed for the presence of potential virulence markers. Membrane proteins, enzymatic activity of the membrane proteins, and carbohydrate fermentation patterns were also determined to demonstrate phenotypic relationships within the groups. Few differences were found in these phenotypic characteristics among the isolates. Almost all the organisms produced siderophore and were hemolytic on turkey red blood cells. No extracellular enzyme or bacteriocin activity was detected and little antibiotic resistance was found. However, many organisms contained plasmids and demonstrated some degree of resistance to complement. Both characteristics were correlative markers in Pasteurella multocida isolated from birds with fowl cholera.

The concentration of EDTA-Tris (3.22 mM EDTA and 0.05 M Tris) used as a lavage to treat otitis externa, cystitis or other persistent infections in dogs and cats, was found to prevent the growth of Pseudomonas aeruginosa, Staphylococcus aureus and beta streptococci when present in growth media. Pseudomonas aeruginosa was rapidly lysed in this solution. Escherichia coli and Proteus vulgaris grew in the presence of EDTA-Tris, but to a lesser extent than the controls without these compounds. Minimal inhibitory concentrations (MIC) for 8 antimicrobial agents with and without EDTA-Tris were determined for E. coli and P. vulgaris. A potentiation effect on E. coli (greater than 50% decrease MIC) was observed when EDTA-Tris was combined with penicillin, oxytetracycline or chloramphenicol. A similar effect was observed with P. vulgaris when combinations of EDTA-Tris plus gentamicin, oxytetracycline, polymyxin-B or triple sulfa were used. The results of this study indicate that EDTA-Tris appears to have merit in selected cases of otitis externa, cystitis or other persistent infections where lavage might be used.

Ethylene diamine tetra-acetic acid disodium salt (3.22 mM) and Tris (hydroxymethyl aminomethane) (50 mM) was found to cause potentiation of antibiotic actions and/or increased uptake of antibiotics when assessed by bacterial inhibition kinetic studies and uptake of radiolabeled antibiotics. Solutions of EDTA-Tris potentiate the effect of tetracycline, dihydrostreptomycin and penicillin when reacted with Escherichia coli. A similar effect was observed for tetracycline when incubated with Proteus vulgaris and penicillin, chloramphenicol, dihydrostreptomycin and tetracycline when incubated with Pseudomonas aeruginosa. These effects were noted by decreasing bacterial counts in the bacterial inhibition kinetic studies and increased uptake of radiolabeled antibiotics.

Solutions of ethylenediaminetetraacetate (EDTA)-tris combined with antibiotics have been shown to be effective in treating selected cases of persistent bacterial infections. Basic techniques in microbial genetics, including mating frequencies, chemical elimination of R plasmids, isolation of plasmid DNA and agarose gel electrophoresis, were used to determine if EDTA-tris has a curing effect on an R plasmid as part of its clinical action. Results of this study indicated that EDTA-tris by itself eliminated an antibiotic resistance marker from a clinical isolate of Escherichia coli and when combined with another chemical curing agent altered the isolate's mating frequency.