title: Phenotypic resistance in mycobacteria: is it because I am old or fat that I resist you?
abstract: OBJECTIVE
  We aimed to explore the phenomenon of phenotypic resistance to antimycobacterial antibiotics and to determine whether this was associated with cell age or the presence of lipid bodies.
  
  
  METHODS
  The accumulation of lipid-body-positive [lipid-rich (LR)] cells was followed using cell staining and flow cytometry. LR cells of Mycobacterium smegmatis, Mycobacterium marinum, Mycobacterium fortuitum and Mycobacterium bovis (BCG) were separated from non-lipid-body-containing [lipid-poor (LP)] cells and their MBCs determined. We also compared the MBCs for LR and LP cells from 'old' and 'young' cultures.
  
  
  RESULTS
  The LR cells of all species were more resistant to antibiotics than LP cells. For BCG, the susceptibility ratios were as follows: rifampicin, 5×; isoniazid, 16.7×; ethambutol, 5×; and ciprofloxacin, 5×. Phenotypic resistance was found in LR cells irrespective of cell age.
  
  
  CONCLUSIONS
  We have shown that phenotypic antibiotic resistance is associated with the presence of lipid bodies irrespective of cell age. These data have important implications for our understanding of relapse in mycobacterial infections.
authors.affiliation: Medical and Biological Sciences Building, University of St Andrews, North Haugh, St Andrews, Fife KY16 9TF, UK rjhh@st-andrews.ac.uk.
authors.forename: Robert J H
authors.initials: RJ
authors.lastname: Hammond
authors.affiliation: Medical and Biological Sciences Building, University of St Andrews, North Haugh, St Andrews, Fife KY16 9TF, UK.
authors.forename: Vincent O
authors.initials: VO
authors.lastname: Baron
authors.affiliation: Medical and Biological Sciences Building, University of St Andrews, North Haugh, St Andrews, Fife KY16 9TF, UK.
authors.forename: Katarina
authors.initials: K
authors.lastname: Oravcova
authors.affiliation: Medical and Biological Sciences Building, University of St Andrews, North Haugh, St Andrews, Fife KY16 9TF, UK.
authors.forename: Sam
authors.initials: S
authors.lastname: Lipworth
authors.affiliation: Medical and Biological Sciences Building, University of St Andrews, North Haugh, St Andrews, Fife KY16 9TF, UK.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Gillespie
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D066292:Lipid Droplets / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009161:Mycobacterium / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D009164:Mycobacterium Infections / Q000382:microbiology; D010641:Phenotype
chemical_list: D000900:Anti-Bacterial Agents