The Association Between a Large Molecular Mass Plasmid and Virulence in a Strain of Salmonella pullorum

P. A. Barrow, M. A. Lovell
1988 Microbiology  
Eight strains of Salmonella pullorum isolated from epidemiologically independent cases of pullorum disease (bacillary white diarrhoea) in young chickens possessed at least one large molecular mass plasmid in addition to smaller molecular mass plasmids. The 85 kb large plasmid, designated pBLOOl, of one of these strains was 'tagged' with an ampicillin resistance marker by the insertion of transposon Tn3. The plasmid was eliminated by passage in nutrient broth containing acridine orange. It was
more » ... introduced into the strain from which it had been eliminated by mobilization using the F plasmid. Following oral inoculation of newly hatched Rhode Island Red chickens, the parent strain produced a high level of mortality (71%) with characteristic signs of pullorum disease. Following intramuscular inoculation of chickens of the same age, the bacterial LD5, was (log" c.f.u.) 3.38 & 0.43 (mean & SEM). The derivative lacking pBLOOl produced no mortality or morbidity when inoculated orally and the bacterial LD5, value increased to (log" c.f.u.) 5.54 f 0-28. This increase was statistically significant (x2 = 13.6, P < 0.01). Reintroduction of pBLOOl restored virulence as gauged by oral inoculation of chickens (62% mortality) and by the intramuscular bacterial LD" value (log, , c.f.u. = 3.78 & 0.25). These values were not significantly different to those produced by the parent strain (x2 = 0.59, P = 0-4 and x2 = 0-66, P = 0.5, respectively). Following oral Abbreviation : RIR, Rhode Island Red.
doi:10.1099/00221287-134-8-2307 pmid:3253408 fatcat:3mpnl4mubfanlko77vjv72sexq