In vitro and in vivo effect of antibiotics on catheters colonized by staphylococci.

An in vitro model was used to study whether and how catheter infections can be cured. Silastic catheters were "infected" with Staphylococcus aureus ATCC 25923 and Staphylococcus epidermidis KH11 and V2; these "infections" were then treated with 24, 48 and 96 h continuous infusions of various antimicrobial agents administered both as monotherapy and in combination. The Staphylococcus aureus strain was considerably more difficult to eliminate from catheters than were the Staphylococcus epidermidis strains. This experience gained in the laboratory was then applied in vivo to 16 episodes of catheter sepsis in seven children. Treatment for at least six days with imipenem/cilastatin combined with fosfomycin or an aminoglycoside successfully eliminated the pathogens isolated from 11 of the 16 episodes of infection. The broad-spectrum combination was chosen because it could not be assumed that individual pathogens would be sensitive to a single substance. Nine of the infected catheters could be retained in the patients. This experience suggests that it may be possible to successfully eliminate the colonization of central venous catheters by coagulase-negative staphylococci using the antimicrobial agents employed here.