Infections caused by S. marcescens may be difficult to
treat because of resistance to a variety of antibiotics,
including ampicillin and first and second generation
cephalosporins [42]. Aminoglycosides have good activity
against S. rnarcescens, but resistant strains have-also
been reported recently [43]. As the killing effect of /?-
lactam antibiotics is time dependent, the length of time
the bacteria are exposed to antibiotic concentrations
above the MIC is an important parameter when
assessing likely clinical outcome. Data obtained from
a rabbit model suggest that if a P-lactam and
aminoglycoside are combined, the aminoglycoside
induces rapid killing and reduction of the inoculum,
while the p-lactam antibiotic prevents regrowth between
the doses of aminoglycosides [44].