Relation of lipid content and exotoxin production to virulence of Corynebacterium pseudotuberculosis in mice

Twenty-five isolates of Corynebacterium pseudotuberculosis from lesions of caseous lymphadenitis in goats were examined for cell wall lipid content, exotoxin production, and virulence in mice. The mean percentage of lipid content was 6.52% and significant (P less than 0.005) differences were demonstrated between some isolates. Exotoxin in broth culture filtrates of the 25 isolates was measured by the staphylococcal beta-hemolysin inhibition (BHI) test and a radioassay for phospholipase D. All isolates were positive for exotoxin in both tests and 1 isolate had higher activity than the others. Because the correlation between the BHI test and radioassay was poor, it may be that the radioassay detects only enzymatically active exotoxin, whereas the BHI test detects active and inactive exotoxin. All isolates were virulent in mice at 2 dosage levels used to produce subacute-chronic and acute disease. Differences in virulence among isolates were detected only at the lower dosage level. There was a direct relationship between percentage of lipid and induction of chronic abscessation in mice, but not between lipid content and mortality. Although exotoxin production in vitro could not be related quantitatively to virulence, the results of inoculating mice with bacterial cells and broth culture supernatant were consistent with a role for exotoxin in disease.