Journal of Antimicrobial Chemotherapy, Vol 42, 227-232, Copyright © 1998 by The British Society for Antimicrobial Chemotherapy
C Konig, HP Simmen and J Blaser
Little is known about how many bacteria are present at an infectious focus
at the onset of antibiotic therapy. The number of cfu was determined in pus
and infected peritoneal fluids obtained from 41 patients. Pathogens were
detected in 71% of specimens. There were high concentrations of bacteria in
culture-positive samples, in both soft- tissue and peritoneal infections,
averaging 2 x 10(8) cfu/mL. These concentrations were much higher than the
standard inoculum size used in in-vitro susceptibility tests, 5 x 10(5)
cfu/mL. The impact of this discrepancy on antibacterial efficacy was
studied with amikacin, ciprofloxacin, imipenem and piperacillin against
Escherichia coli and Staphylococcus aureus. The inhibitory and bactericidal
activities of amikacin and ciprofloxacin determined with high inocula were
two to four times lower than with standard inocula, whereas the activity of
piperacillin was diminished at least 128-fold. Similar activity was
observed with these drugs in Mueller-Hinton broth and peritoneal fluid. The
bactericidal activity of imipenem was reduced in peritoneal fluid. Thus,
conditions prevailing at the infection site may compromise antibiotic
activity determined in vitro.
ORIGINAL ARTICLES
Bacterial concentrations in pus and infected peritoneal fluid-- implications for bactericidal activity of antibiotics
Department of Medicine, University Hospital Zurich, Switzerland.
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