title: Nonstable Staphylococcus aureus Small-Colony Variants Are Induced by Low pH and Sensitized to Antimicrobial Therapy by Phagolysosomal Alkalinization.
abstract: BACKGROUND
  Staphylococcus aureus-infected patients treated with antibiotics that are effective in vitro often experience relapse of infection because the bacteria hide in privileged locations. These locations include abscesses and host cells, which contain low-pH compartments and are sites from which nonstable S. aureus small-colony variants (SCVs) are frequently recovered.
  
  
  METHODS
  We assessed the effect of low pH on S. aureus colony phenotype and bacterial growth, using in vitro and in vivo models of long-term infection.
  
  
  RESULTS
  We showed that low pH induced nonstable SCVs and nonreplicating persisters that are capable of regrowth. Within host cells, S. aureus was located in phagolysosomes, a low-pH compartment. Therapeutic neutralization of phagolysosomal pH with ammonium chloride, bafilomycin A1, or the antimalaria drug chloroquine reduced SCVs in infected host cells. In a systemic mouse infection model, treatment with chloroquine also reduced SCVs.
  
  
  CONCLUSIONS
  Our results show that the acidic environment favors formation of nonstable SCVs, which reflect the SCVs found in clinics. They also provide evidence that treatment with alkalinizing agents, together with antibiotics, may provide a novel translational strategy for eradicating persisting intracellular reservoirs of staphylococci. This approach may also be extended to other intracellular bacteria.
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Nadja
authors.initials: N
authors.lastname: Leimer
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Carole
authors.initials: C
authors.lastname: Rachmühl
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Miguel
authors.initials: M
authors.lastname: Palheiros Marques
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Anna Sophie
authors.initials: AS
authors.lastname: Bahlmann
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Furrer
authors.affiliation: Institute of Food, Nutrition, and Health, ETH Zurich, Switzerland.
authors.forename: Fritz
authors.initials: F
authors.lastname: Eichenseher
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Kati
authors.initials: K
authors.lastname: Seidl
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Matt
authors.affiliation: Institute of Food, Nutrition, and Health, ETH Zurich, Switzerland.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Loessner
authors.affiliation: Division of Surgical Intensive Care, University Hospital Zurich, University of Zurich.
authors.forename: Reto A
authors.initials: RA
authors.lastname: Schuepbach
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology.
authors.forename: Annelies S
authors.initials: AS
authors.lastname: Zinkernagel
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002738:Chloroquine / Q000494:pharmacology; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018942:Macrolides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D010588:Phagosomes / Q000737:chemistry*; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000254:growth & development / Q000502:physiology*
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D000643:Ammonium Chloride; D002738:Chloroquine; C040929:bafilomycin A1
keywords: Staphylococcus aureus; antimicrobial therapy; intracellular persistence; relapsing infections; small colony variants