Induction of prophages by fluoroquinolones in Streptococcus pneumoniae: implications for emergence of resistance in genetically-related clones

PLoS One. 2014 Apr 9;9(4):e94358. doi: 10.1371/journal.pone.0094358. eCollection 2014.

Abstract

Antibiotic resistance in Streptococcus pneumoniae has increased worldwide by the spread of a few clones. Fluoroquinolone resistance occurs mainly by alteration of their intracellular targets, the type II DNA topoisomerases, which is acquired either by point mutation or by recombination. Increase in fluoroquinolone-resistance may depend on the balance between antibiotic consumption and the cost that resistance imposes to bacterial fitness. In addition, pneumococcal prophages could play an important role. Prophage induction by fluoroquinolones was confirmed in 4 clinical isolates by using Southern blot hybridization. Clinical isolates (105 fluoroquinolone-resistant and 160 fluoroquinolone-susceptible) were tested for lysogeny by using a PCR assay and functional prophage carriage was studied by mitomycin C induction. Fluoroquinolone-resistant strains harbored fewer inducible prophages (17/43) than fluoroquinolone-susceptible strains (49/70) (P = 0.0018). In addition, isolates of clones associated with fluoroquinolone resistance [CC156 (3/25); CC63 (2/20), and CC81 (1/19)], had lower frequency of functional prophages than isolates of clones with low incidence of fluoroquinolone resistance [CC30 (4/21), CC230 (5/20), CC62 (9/21), and CC180 (21/30)]. Likewise, persistent strains from patients with chronic respiratory diseases subjected to fluoroquinolone treatment had a low frequency of inducible prophages (1/11). Development of ciprofloxacin resistance was tested with two isogenic strains, one lysogenic and the other non-lysogenic: emergence of resistance was only observed in the non-lysogenic strain. These results are compatible with the lysis of lysogenic isolates receiving fluoroquinolones before the development of resistance and explain the inverse relation between presence of inducible prophages and fluoroquinolone-resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Southern
  • Chronic Disease
  • Ciprofloxacin / pharmacology
  • Disease Progression
  • Drug Resistance, Bacterial / drug effects
  • Drug Resistance, Bacterial / genetics*
  • Fluoroquinolones / pharmacology*
  • Humans
  • Lysogeny / drug effects
  • Mitomycin / pharmacology
  • Pneumococcal Infections / microbiology
  • Pneumococcal Infections / pathology
  • Polymerase Chain Reaction
  • Prophages / physiology*
  • Streptococcus pneumoniae / drug effects
  • Streptococcus pneumoniae / genetics*
  • Streptococcus pneumoniae / isolation & purification
  • Streptococcus pneumoniae / virology*
  • Virus Activation / drug effects*

Substances

  • Fluoroquinolones
  • Mitomycin
  • Ciprofloxacin

Grant support

This study was supported by grants BIO2008-02154, SAF2009-10824 and BIO2011-25343 from Plan Nacional and PI 0901904 by FIS of Ministerio de Economíy Competitividad. CIBER de Enfermedades Respiratorias (CIBERES) is an initiative of ISCIII. A.D. was supported by a grant from FPU of Ministerio de Educación, Spain. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.