Safety of temperature sensitive mutant Mycoplasma gallisepticum vaccine

Abstract

A temperature sensitive (ts) vaccine strain designated ts-11 was selected after exposure of a low passage culture of the immunogenic Australian field isolate (strain 80083) of Mycoplasma gallisepticum to 100 mg/ml of N-methyl-N-nitro-N-nitrosoguanidine. Viable counts (assayed as colour changing units (CCU)/25 microliters) of a thawed stock culture of ts-11 were typically log10 3 to log10 5 higher when incubated at 33 degrees C (the permissive temperature) than duplicate viable counts incubated at 39.5 degrees C (the restrictive temperature). Doses of approximately 2 x 10(7) CCU of ts-11 caused no gross lesions or loss of egg production when inoculated into the air sacs of susceptible chickens and no clinical or pathological signs of sinusitis when inoculated into the infraorbital sinuses of susceptible turkey poults, whereas the parent strain 80083 was demonstrably pathogenic. However, 1 of 10 poults inoculated intra-abdominally with approximately 2 x 10(7) CCU of ts-11 did show signs of mild airsacculitis. Eight-week-old pullets were vaccinated by eye drop with up to 1.4 x 10(7) CCU of ts-11 and simultaneously subjected to several stressful management practices, without apparent ill effects. Administration by coarse aerosol of 5 ml of ts-11 vaccine/25 day-old broilers, with or without 25 doses of infectious bronchitis virus vaccine caused no obvious signs of respiratory disease. The non virulent ts phenotype was maintained after 3 passages of strain ts-11 in chickens. Chickens vaccinated 3 weeks previously with ts-11 or with strain 80083 were placed in contact with susceptible chickens for a period of 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

GapA+ Mycoplasma gallisepticum ts-11 has improved vaccine characteristics

“…It has been established that the ts-11 strain of M. gallisepticum does not colonize the air sacs (Whithear et al, 1990b), so isolation from the air sacs and production of air sac lesions were not expected in unchallenged birds. There were no visible air sac lesions in birds vaccinated with GapA + M. gallisepticum ts-11 or Vaxsafe M. gallisepticum ts-11 at 3 or 5 weeks after inoculation.…”

“…The ts-11 strain was selected for its ability to multiply in the upper respiratory tract to an extent sufficient to stimulate long-term protective immunity, but not at core body temperature (Whithear et al, 1990b). In this experiment, Vaxsafe M. gallisepticum ts-11 was reisolated from the tracheas of 4/24 birds (groups 5 and 8) in broth, whereas GapA + M. gallisepticum ts-11 was reisolated from 11/26 birds (groups 6 and 9).…”

Development of aMycoplasma gallisepticuminfection model in turkeys

“…The droplet size delivered by this apparatus has been determined previously as between 1 and 10 μm, with the majority of particles <5 μm at an air flow of 15 l/min (Whithear et al, 1996). Aerosols of M. gallisepticum delivered to chickens using this method have induced lesions consistently in the air sacs and the trachea, indicating that there is infection of the upper and lower respiratory tract (Whithear et al, 1990(Whithear et al, , 1996Gaunson et al, 2000Gaunson et al, , 2006. The strain comparison study described here was carried out in order to identify the more appropriate strain for the infection model.…”

“…To demonstrate the safety and efficacy of any vaccine candidate, a reproducible infection model is needed, such as the aerosol exposure method developed in our laboratory previously to test vaccine safety and efficacy in chickens using the M. gallisepticum Ap3AS wild-type strain (Whithear et al, 1990(Whithear et al, , 1996. Such a model has not been developed for turkeys.…”

Phenotypic and antigenic variation of Mycoplasma Gallisepticum vaccine strains

“…The strain was selected after exposure passage of an immunogenic Australian field isolate (strain 80083) of MG to N-methyl-nitro-N-nitrosoguanidine (22). This strain was found to be poorly transmitted from vaccinated to unvaccinated birds and showed little or no virulence for chickens and turkeys (21).…”