Very little information about the production of virulence factors by avian E. coli strains exists in Saudi Arabia, so the existence of APEC strains in KSA poultry farms must be investigated by epidemiological surveys, with particular attention to virulence factors of serotype isolates.
Corynebacterium pseudotuberculosis is a Gram positive facultative intracellular organism causing caseous lymphadenitis (CLA) in sheep and goats. The disease characterized by chronic suppurative BV6 and significant economical losses to the sheep industries worldwide (Paton et al., 2003; Dorella et al., 2006).
C. pseudotuberculosis causes a characteristic acute disease in buffaloes known as Oedematus skin disease (OSD). The disease is endemic in Egypt and is characterized by the development of diffused swellings in the skin of the hind quarter, fore limbs, belly and brisket regions. These lesions usually affect the lymph nodes which become enlarged and inflamed and filled with pus. At first is filled with serous fluid then turned to sac of pus due to contamination with other bacteria as staphylococci, streptococci, E. coli and Pseudomonas. The disease is characterized by high morbidity and low mortality and the badly treated cases died. OSD is a terrible disease for farmers and veterinarians; it causes severe economical losses due to the necessary surgical intervention, expensive medication, reduction in the milk production and lowering of work activity of the affected animals (Selim, 2001). In human infections caused by C. pseudotuberculosis most commonly occur by the occupational exposure, ingestion of raw milk from goat and cow’s milk (Peel et al., 1997).
The majority of studies have employed formalin inactivated toxoid vaccines derived from phospholipase D (PLD) rich C. pseudotuberculosis culture supernatants and these have conferred varying levels of protective immunity in both sheep and goats (Narin et al., 1977 and Eggleton et al., 2005). In the present investigation two combined vaccines prepared from formalin inactivated whole cells of biovar 1 (sheep origin) in each dose, the second vaccine is composed of inactivated whole cells of biovar 2 (buffalo origin) in combination with rPLD. These vaccines will be used for vaccination of sheep and buffaloes and protective efficacy was assessed by virulent strains locally isolated from sheep with CLA or buffaloes with OSD.
Materials and methods
In the present investigation, this is the first report describing immunizations of sheep with bacterins prepared from nitrate positive C. pseudotuberculosis strain isolated from buffaloes (biovar 2) and challenged with virulent biovar 2 isolate. No significant difference in protection efficacy of both vaccines could be observed in challenged sheep either challenged with virulent biovar 1 or biovar 2. All vaccinated sheep were completely protected against challenge. At the same time control non vaccinated groups either challenged with biovar 1 (sheep origin) or biovar 2 (buffalo origin) showed the development of chronic symptoms of CLA characterized by production of caseous abscess either in external or internal lymph nodes.
These results indicated that C. pseudotuberculosis either of biovar 1 or biovar 2 induced the same lesion which can be attributed to the same virulence factor i.e. PLD possessed by both biovars. Vaccination with a combination of rPLD and killed whole-cells resulted in complete protection against challenge (Fontaine et al., 2006). Our findings are in consistence with our finding about complete protection of combined rPLD and killed whole cells. The results of our study would tend to support the findings of pervious authors (Cameron, 1972 and Cameron and Fuls, 1973).
Interestingly, both PLD and the formalin inactivated whole cell vaccines prevented dissemination of challenge bacteria beyond the site of inoculation to essentially equivalent extents. Cell mediated immunity can be attributed to rPLD which activate macrophages in vaccinated animals. The role of rPLD in activation of macrophages has been shown in immune model (El-Enbaawy et al., 2005).