Haemophilus paragallinarum causes infectious coryza in poultry, and a panel of monoclonal antibodies (Mabs) were established, which detect surface antigens of this bacterium. It was postulated that these Mabs could be used to detect antigenic differences between strains of H. paragallinarum used in infectious coryza (IC) vaccines, and isolates made from the field , from poultry vaccinated against IC. It has previously been reported that in South Africa there are three different Mab patterns that have been common to H. paragallinarum isolates for the past three decades. The effects of different growth conditions such as duration of incubation, inoculum size, levels of NAD or NaCI in the medium, and the pH of the medium on these Mab patterns were investigated. It was found that many different factors appear to influence the expression of the antigens detected by the panel of Mabs. It was found that at different stages during the growth cycles, the isolates could be classified into different Mab groups. It was also found that alteration of the inoculum size resulted in Mab-pattern switches. Addition of extra NaCI to the medium, in order to slow the growth rate, was found to result in Mab-pattern switches. pH was found to have signifcant effects on the levels of expression of the antigens detected by the Mabs, although these changes did not result in Mab-pattern switches. The effects of pH were also found to be highly strain dependent. The use of NAD, rather than sterile chicken serum, in the medium did not significantly alter the levels of expression of these antigens. Alterations of the growth conditions greatly affected the levels of expression of the antigens detected by the Mabs, and were highly strain dependent. It was not possible to predict the effects of a particular growth condition on a particular strain or isolate of H. paragallinarum.
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