Screening and characterization of Salmonella Typhi isolates persisting within gallbladder of patients undergoing cholecystectomy for chronic cholelithiasis

摘要

Salmonella Typhi chronically infects the gallbladder and is considered as a predisposing factor for gallbladder cancers. We screen for any Salmonella Typhi isolates present in the gallbladder of 155 patients undergoing cholecystectomy for chronic cholelithiasis in two different regions within the country. Along with microbiological identification, we develop a multiplex PCR assay to speciate the Salmonella spp. Characterisation studies involve determining tolerance to bile, quantifying biofilm forming ability and antibiotic susceptibility testing using disc diffusion assay. Eight (10.66%) of 75 patients (100%) from region in North India (New Delhi) were positive for S .Typhi on culture compared to two (2.5%) of 80 patients from other region in South (Goa). All the isolates had a minimum inhibitory concentration to bile of 4% with minimum bactericidal concentration varying between 4%-6%. Crystal violet assays revealed that the gallbladder isolates showed a quicker and better biofilm masses. Multi-drug resistance (MDR) is common among Salmonella strains but a few gallbladder isolates from the typhoid endemic region possessed a concern with its resistance to fluroquinolones. All the isolates were susceptible to ceftriaxone indicating its possible use in treatment of chronically infected individuals. It was seen that supplementing the media with sub-lethal bile concentrations did enhance the biofilm forming ability of the organism without any significant alterations in the drug resistant patterns. Furthermore, growth in sub-lethal bile concentration also induced similar changes in total protein profiles in all the gallbladder isolates.