Consecutive isolation of homologous strains of methicillin-resistant and methicillin-susceptible Staphylococcus aureus from a hospitalized child.
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.
Lawrence
C
C
Service de Bactériologie-Virologie-Hygiène, Hôpital Henri Mondor, Université Paris XII, Créteil, France.
Cosseron
M
M
Durand
P
P
Costa
Y
Y
Leclercq
R
R
D001483:Base Sequence; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D015931:Intensive Care, Neonatal; D016106:Methicillin Resistance / Q000235:genetics*; D008969:Molecular Sequence Data; D012641:Selection, Genetic; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*