48.
Antibiotic Pre-exposure Reduces the Ability to Detect Heat Production
of Bacteria in Biofilm
Christen Ravn, Ulrika Furustrand Tafin, Bertrand Betriséy, Søren Overgaard,
Andrej Trampuz
Infectious Disease Service Lausanne University Hospital; Infectious Disease
Service, Lausanne University Hospital; Infectious Disease Service, Lausanne
University Hospital; Department of Orthopaedic Surgery and Traumatology,
Odense University Hospital; Infectious Disease Service, Lausanne University
Hospital
Background:
Antibiotic treatment before collection of culture specimens
might reduce the ability to detect bacteria in prosthetic joint infections (PJI)
which can hamper specific antibiotic treatment.
Purpose / Aim of Study:
To investigate the suppressive effect of different
antibiotics in a well- established biofilm model of typical bacteria in PJI.
Materials and Methods:
Biofilms of Staphylococcus aureus (MSSA), S.
epidermidis (MRSE), Escherichia coli and Propionibacterium acnes were
formed on porous glass beads (Tafin, UF, 2012. Antimicrob Agents
Chemother 56(4):p.1885-91). After 24 hour incubation (72 hours for P. acnes)
of beads with bacteria, beads were exposed to vancomycin, flucloxacillin,
daptomycin or ciprofloxacin at increasing concentrations from 1-1024 times
the minimal inhibitory concentration (MIC). After 24 h of antibiotic exposure,
beads were sonicated to dislodge biofilm. The sonicate was investigated by
microcalorimetry to detect heat production as an indication of bacterial
presence in triplicate. The minimal heat inhibitory concentration (MHIC) was
defined as the lowest antibiotic concentration inhibiting heat production over
24
hours (72 hours for P. acnes).
Findings / Results:
Vancomycin clearly affected, but did not totally inhibit
heat production of staphylococci or P. acnes at any concentration up to 1024
mg/l. Flucloxacillin inhibited S. aureus only at 128 mg/l (512x MIC). In
contrast, daptomycin inhibited heat production of both S. aureus, S.
epidermidis and P. acnes at 128x, 64x and 32x MIC, respectively. E. coli was
inhibited by ciprofloxacin at 0.063 mg/l (8x MIC).
Conclusions:
With sonication and microcalorimetry we saw heterogeneous
effects of antibiotic exposure on the ability to detect heat production as an
expression of bacterial presence.
