Comparison ofin vivoandin vitromethods for pathogenicity evaluation formycoplasma gallisepticumin respiratory infection

Abstract

This study was designated to examine the pathogenicity of several strains of Mycoplasma gallisepticum (R, F, S-6, 227 and A5969) and laboratory derived substrains. Preliminary results indicated that the nine M. gallisepticum strains differed markedly in their pathogenicity for chickens. A comparison was made between various in vivo and in vitro methods for quantitative evaluation of pathogenicity. Reproducibility, convenience, and relevance to clinical observations were considered. Two in vivo tests were employed. In one case 2-week-old chickens were infected with M. gallisepticum by aerosol. Air sac lesion score, ability to reisolate M. gallisepticum from trachea and air sac, and serological response to M. gallisepticum were determined 2 weeks post infection. The second test was based on the ability to reisolate M. gallisepticum 3 days after intratracheal inoculation at different dose levels. In this way it was possible to calculate a median tracheal infection dose for each of the strains tested, a parameter which reflected their ability to colonise this organ. Scanning electron microscopy (SEM) was used to examine changes in the surface morphology of the infected trachea and photometric analysis of the SEM lesion was performed. Certain strains multiplied profusely in the trachea of healthy birds without causing detectable pathological changes. Chick tracheal ring (TR) cultures were used for estimating pathogenicity in vitro. In the standardised TR system a method for quantitative evaluation of mycoplasma-TR interaction was devised. The use of the TR system as a model for evaluating in vitro pathogenicity was rapid and less subject to environmental variation than the in vivo tests. The test was economical with respect to time, space and birds.

A modified live Mycoplasma gallisepticum vaccine to protect chickens from respiratory disease

“…The 6/85-and ts-11-based vaccines are reported to be safer than the F strain vaccine but do not afford the same level of protection [22,23,[28][29][30]. R high was previously reported to be avirulent for chickens [10] but the genetic changes associated with attenuation were only recently determined on a biochemical and molecular basis by Papazisi et al [11]. They reported that three proteins are absent in M. gallisepticum R high including the primary cytadhesin molecule, GapA.…”

“…Repetitive in vitro passage of this organism gave rise to a highly attenuated strain "R high " that produces little if any pathology in chickens, even when used at doses 10,000-fold higher than a pathogenic dose of R low [10]. Previous studies have demonstrated that mutations in M. gallisepticum R high resulted in the loss of expression of three proteins, e.g.…”

Effect of infection route and concurrent infectious bronchitis virus vaccination onMycoplasma gallisepticumdisease pathology in an experimental model

“…Another method that has been used to deliver MG to the respiratory system is through the use of aerosols (Rodriguez & Kleven, 1980;Levisohn et al, 1986). Intratracheal instillation was chosen as a similar means of infection without the need for specialized aerosol generation equipment.…”

“…Many infection model systems have been used, including those looking at disease status such as air sac and tracheal pathology (Rodriguez & Kleven, 1980;Levisohn et al, 1986;Nunoya et al, 1987), and those investigating production parameters such as egg production, egg quality, and weight gain (Branton & Deaton, 1985). Production parameter experiments generally require a significantly longer experiment, but the results are directly applicable to real-world conditions.…”

Complementary Randomly Amplified Polymorphic DNA (RAPD) Analysis Patterns and Primer Sets to Differentiate Mycoplasma Gallisepticum Strains

“…13,15,22 A variety of procedures have been used to differentiate this heterologous population. Cultural, immunologic, and bird inoculation characteristics of isolates have limited differentiation ability other than to classify isolates as variant MG. 1,10,14,20,21 Cellular protein profiles can differentiate strains; however, banding patterns are complex and influenced by culture and electrophoretic conditions. 7,17,19 Several procedures used to examine genomic characteristics of MG have demonstrated a wide degree of variability among strains.…”