Consecutive isolation of homologous strains of methicillin-resistant and methicillin-susceptible Staphylococcus aureus from a hospitalized child

J Hosp Infect. 1996 May;33(1):49-53. doi: 10.1016/s0195-6701(96)90028-6.


A multiply resistant, methicillin-resistant Staphylococcus aureus was repeatedly isolated from the anterior nares of a premature neonate hospitalized in an intensive-care unit and treated with multiple courses of antibiotics. Two months following cessation of antibiotic therapy, a strain of S. aureus with a similar antibiotic resistance profile, but susceptible to methicillin, was isolated from three consecutive nasal swabs. Total DNA of the methicillin-susceptible and -resistant isolates was digested with SmaI and resolved by pulsed-field gel electrophoresis. The SmaI restriction profile of the susceptible isolate was similar to that of the resistant one except for the replacement of a 207-kb fragment by a 147-kb fragment. In Southern hybridization, a mecA-specific probe hybridized to the 207-kb SmaI fragment of the methicillin-resistant strain but not to DNA of the susceptible strain. These results suggest that loss of the mecA gene can occur in vivo when antibiotic selective pressure is removed.

Publication types

  • Case Reports

MeSH terms

  • Base Sequence
  • Humans
  • Infant, Newborn
  • Infant, Premature
  • Intensive Care, Neonatal
  • Methicillin Resistance / genetics*
  • Molecular Sequence Data
  • Selection, Genetic
  • Staphylococcal Infections / drug therapy
  • Staphylococcal Infections / microbiology*
  • Staphylococcus aureus / drug effects
  • Staphylococcus aureus / genetics
  • Staphylococcus aureus / isolation & purification*