title: In vitro evaluation of the effect of linezolid and levofloxacin on Bacillus anthracis toxin production, spore formation and cell growth.
abstract: Owing to its ability to form spores and toxins, Bacillus anthracis is considered a bioterror agent. Although current therapeutic strategies can be effective, treatment does not prevent sporulation and toxin production.
  
  
  
  To quantify the combined effect of a protein synthesis inhibitor and a bactericidal agent on B. anthracis toxin production, sporulation and cell growth.
  
  
  
  Susceptibility and synergy titrations were conducted on B. anthracis Sterne and 03-0191 strains using linezolid and levofloxacin. The effect of antibiotic exposure on cell viability was evaluated using a continuous medium replacement model. In vitro static models were used to study the effect of linezolid and levofloxacin on sporulation and toxin production. Spores were quantified using the heat shock method. Toxin was quantified via commercial ELISA.
  
  
  
  Synergy titrations indicated that the combination was synergistic or indifferent; however, in all models antagonism was observed. In the spore model, linezolid resulted in the lowest sporulation rates, while combination therapy resulted in the highest. In the toxin model, linezolid prevented toxin production altogether.
  
  
  
  This study advances our understanding of the effects of combination therapy on B. anthracis infection. Used alone, linezolid therapy abolishes toxin production and reduces sporulation. These results suggest that studies using a step-wise approach using linezolid initially to stop sporulation and toxin production followed by levofloxacin to rapidly kill vegetative B. anthracis can be recommended.
authors: Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Canada umheadb@outlook.com.
authors: Breanne M
authors: BM
authors: Head
authors: Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Canada.|St Boniface Research Centre, Winnipeg, Canada.
authors: Michelle
authors: M
authors: Alfa
authors: Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg, Canada.
authors: Daniel S
authors: DS
authors: Sitar
authors: Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Canada.
authors: Ethan
authors: E
authors: Rubinstein
authors: Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Canada.|National Laboratory for HIV Immunology, JC Wilt Infectious Disease Research Centre, Public Health Agency of Canada, Winnipeg, Canada.|Department of Medical Microbiology, University of Nairobi, Nairobi, Kenya.
authors: Adrienne F A
authors: AF
authors: Meyers
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000942:Antigens, Bacterial / Q000096:biosynthesis*; D001408:Bacillus anthracis / Q000187:drug effects* / Q000254:growth & development; D001427:Bacterial Toxins / Q000096:biosynthesis*; D004357:Drug Synergism; D064704:Levofloxacin / Q000494:pharmacology*; D000069349:Linezolid / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D013171:Spores, Bacterial / Q000187:drug effects* / Q000254:growth & development
chemical_list: D000900:Anti-Bacterial Agents; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; C030325:anthrax toxin; D064704:Levofloxacin; D000069349:Linezolid