title: Effect of L. plantarum cell-free extract and co-trimoxazole against Salmonella Typhimurium: a possible adjunct therapy.
abstract: BACKGROUND
  Frequent and indiscriminate use of antibiotics has led to the development of multi-drug resistant bacterial strains. It necessitates the exploitation of alternative therapeutic strategies. In order to reduce the dose of antibiotic required and to decrease the associated side effects, the present study was aimed at evaluating the synergism, if any, between a conventional antibiotic, co-trimoxazole (CTZ)) and cell free supernatant (CFS) of a probiotic (L. plantarum) against S. Typhimurium NCTC 74. This antimicrobial combination was selected on the basis of antibiotic susceptibility pattern of Salmonella and L. plantarum.
  
  
  METHODS
  The synergy was evaluated in terms of size of zone of inhibition, fractional inhibitory concentration index, time-kill assay (in-vitro) as well as macrophage functions (ex-vivo).
  
  
  RESULTS
  The concentration producing the same or higher antibacterial effect (size of zone of inhibition) was reduced to half when both the agents were used in combination with respect to the concentrations required when used separately. CTZ and CFS exhibited synergetic activity against Salmonella by checkerboard microtitre test and the time-kill test. Ex-vivo studies demonstrated a significantly higher intracellular killing of bacteria by macrophages treated with CFS (80 AU/ml) + (CTZ) (2 μg/ml) as compared to when treated with both separately at higher concentrations. Significant reduction in the extent of lipid peroxidation and nitrite levels generated by macrophages in presence of CFS and CTZ, in conjunction, further substantiated the synergistic efficacy of the combination.
  
  
  CONCLUSIONS
  The antimicrobial efficacy of this combination indicates that it may serve as the basis in developing alternative strategies to combat Salmonella infections.
authors.affiliation: Department of Microbiology, Basic Medical Sciences Block, Panjab University, Sector-14, Chandigarh-160014, India. rishipraveen@yahoo.com
authors.forename: Praveen
authors.initials: P
authors.lastname: Rishi
authors.forename: Simran
authors.initials: S
authors.lastname: Preet
authors.forename: Prabhjot
authors.initials: P
authors.lastname: Kaur
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001685:Biological Factors / Q000737:chemistry / Q000494:pharmacology*; D002478:Cells, Cultured; D004357:Drug Synergism; D006801:Humans; D048191:Lactiplantibacillus plantarum / Q000737:chemistry; D017737:Macrophages, Peritoneal / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D019936:Probiotics / Q000737:chemistry / Q000494:pharmacology*; D012480:Salmonella Infections / Q000188:drug therapy / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000187:drug effects*; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001685:Biological Factors; D015662:Trimethoprim, Sulfamethoxazole Drug Combination