Influence of ciprofloxacin on Salmonella pathogenicity island-1 gene invA

Objective To analyze the gene variations and mutations of Salmonella pathogenicity island-1(SPI-1) gene invA in different Salmonella serovars and ciprofloxacin-resistant strains,and the influence of ciprofloxacin on growth of Salmonella. Methods The minimal inhibitory concentrations(MICs) for ciprofloxacin were determined using the standard broth microdilution method in 40 Salmonella strains of 6 Salmonella enterica serovars. The ciprofloxacin-resistant Salmonella strains were induced from ciprofloxacin-susceptible strains with ciprofloxacin by multiple-passage selection. The invA genes were sequenced and compared in different Salmonella strains. The growing capacity of ciprofloxacin-resistant and ciprofloxacin-susceptible strains was compared as well. Results The invA gene was detected in all the 40 Salmonella strains,but the base variations belonging to silent muations were observed in different serovars. No gene deletion or mutation was observed in invA in ciprofloxacin-resistant strains,the growing capacity of Salmonella induced with ciprofloxacin was obviously weakened.Conclusion The invA gene variations in different serovars showed the evolution of virulence in Salmonella. Ciprofloxacin may not induce gene sequence variation or delection of SPI-1 gene invA,but decrease the growth of Salmonella.