The phenogenetic and phylogenetic relationships among 7 identified strains of C. pseudotuberculosis isolated from sheep were checked by PCR specific primers demonstrated with random amplified polymorphic DNA – polymerase chain reaction (RAPD – PCR) by using five arbitrarily primers. C pseudotuberculosis isolates were distinguished according to the banding patterns of their amplified DNA on agarose gel. The variation can be used for diagnostic differentiation among C. pseudotuberculosis strains. Differences were observed in RAPD patterns between the 7 isolates and this may be due to the presence of novel serovars of this microorganism.

Clinical examination of 380 rearing sheep revealed that 30 animal were suffering from skin abscesses with an incidence of (7.89%). Bacteriological examination of 30 swabs from affected sheep revealed isolation of 30 isolates of C. pseudotuberculosis (48.39%) , 18 isolates of S. aureus (29.03%) and 14 isolates of S. aureus subsp. anaerobius (22.58).The isolated bacteria were identified morphologically and biochemically.The results of animal pathogenicity test showed that C. pseudotuberculosis isolates were 100% pathogenic to guinea pigs and 80% of S.aureus isolates were pathogenic to mice, while all isolates of S. aureus subsp. anaerobius were pathogenic to mice. The dead animals showed haemorrhage and symptoms of septicaemia, C. pseudotuberculosis, S.aureus and S. aureus subsp. anaerobius were reisolated from the dead animals. Antimicrobial sensitivity of C. pseudotuberculosis , S. aureus and S. aureus subsp. anaerobius isolates to some antimicrobial agents which usually used in farms showed that from 90% to 100% of C. pseudotuberculosis isolates were sensitive to erythromycin, amoxicillin, tetracycline ,streptomycin, ampicillin and rifampicin while S. aureus isolates (from 55% to 66%) were sensitive to rifampicin,tetracycline ,erythromycin and streptomycin, while S. aureus subsp. anaerobius isolates were moderately resistant to all used antimicrobial agents.

Out of 63 bacteriologically examined sanguineous fluids samples which were collected from Oedematous Skin Disease (O.S.D.) lesions, 37 isolates of C. pseudotuberculosis (C.p.) were recovered. The sensitivity tests revealed that isolates were highly sensitive to trimethoprim + sulphamethoxazole, amoxycillin, gentamicin and enrofloxacin. Diphtheria toxin (DT) produced by C. pseudotuberculosis of buffalo was determined by using the double immunodiffusion technique, it was applied on concentrated exotoxins which was prepared from C.p. isolates against Diphtheria toxin antiserum, its results were 15 (40.54%) positive and 22 (59.46) %) negative to presence of DT. Virulence of isolates having only phospholipase D ( PLD) or both PLD and DT was assayed by S/C inoculation of exotoxines prepared from isolates in guinea pigs, 15(40.54%) guinea pigs died within 18 hours while 22 (59.46%) guinea pigs died during 48 hours. An important point in this investigation that there have been very rare previous reports describing the production of DT by local isolates of C. pseudotuberculosis of buffalo.