INTEGRATED AQUATIC ANIMAL HEALTH STRATEGIES
Location: Aquatic Animal Health Research
Title: Attempt to develop live attenuated bacterial vaccines by selecting resistance to gossypol, proflavine hemisulfate, novobiocin, or ciprofloxacin
Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2013
Publication Date: April 6, 2013
Citation: Wei Pridgeon, Y., Klesius, P.H., Aksoy, M.Y. 2013. Attempt to develop live attenuated bacterial vaccines by selecting resistance to gossypol, proflavine hemisulfate, novobiocin, or ciprofloxacin. Vaccine. 31:2222-2230.
Interpretive Summary: To develop attenuated bacteria vaccines, four chemicals (gossypol, proflavine, hemisulfate, novobiocin, and ciprofloxacin) were used to modify 38 bacteria isolates. Gossypol failed to attenuate any bacteria. Proflavine hemisulfate was able to attenuate bacteria, but failed to provide significant protection to fish. Novobiocin and ciprofloxacin were able to attenuate some Gram-positive bacteria, but resistant bacteria failed to offer protection higher than 70%. Novobiocin and ciprofloxacin were able to attenuate some Gram-negative bacteria, but only one (novobiocin-resistant Edwardsiella tarda 30305) was relatively safe and highly efficacious.
In an attempt to develop attenuated bacteria as potential live vaccines, four chemicals (gossypol, proflavine hemisulfate, novobiocin, and ciprofloxacin) were used to modify the following four genera of bacteria through chemical-resistance strategy: 1) Aeromonas hydrophila (9 isolates); 2) Edwardsiella tarda (9 isolates); 3) Streptococcus iniae (9 isolates); and 4) S. agalactiae (11 isolates). All bacteria used in this study were able to develop high resistance to gossypol. However, only some bacteria were able to develop resistance to proflavine hemisulfate, novobiocin, or ciprofloxacin. When the virulence of resistant bacteria was tested in tilapia or catfish, none of the gossypol-resistant isolate was attenuated, whereas majority of the proflavine hemisulfate-resistant isolates were attenuated. However, all proflavine hemisulfate-attenuated bacteria failed to provide significant protection to fish. Eight novobiocin- or ciprofloxacin- resistant Gram-positive bacteria (S. agalactiae and S. iniae) were found to be attenuated. However, none of them offered protection higher than 70%. Of seven attenuated novobiocin- or ciprofloxacin- resistant Gram-negative isolates (A. hydrophila and E. tarda), only one (novobiocin-resistant E. tarda 30305) was found to relatively safe and highly efficacious. When E. tarda 30305-novo vaccinated Nile tilapia were challenged by its virulent E. tarda 30305, relative percent of survival of vaccinated fish at 14- and 28- days post vaccination (dpv) was 100% and 92%, respectively. Similarly, E. tarda 30305-novo offered 100% protection to channel catfish against challenges with virulent parent isolate E. tarda 30305 at both 14- and 28- dpv. Our results suggest that the development of live attenuated bacterial vaccines that are safe and efficacious is challenging, although it is feasible.