Detachment characteristics and oxacillin resistance of Staphyloccocus aureus biofilm emboli in an in vitro catheter infection model - PubMed (original) (raw)
Detachment characteristics and oxacillin resistance of Staphyloccocus aureus biofilm emboli in an in vitro catheter infection model
C A Fux et al. J Bacteriol. 2004 Jul.
Abstract
Catheter-related bloodstream infections due to Staphylococcus aureus are of increasing clinical importance. The pathophysiological steps leading to colonization and infection, however, are still incompletely defined. We observed growth and detachment of S. aureus biofilms in an in vitro catheter-infection model by using time-lapse microscopy. Biofilm emboli were characterized by their size and their susceptibility for oxacillin. Biofilm dispersal was found to be a dynamic process in which clumps of a wide range of diameters detach. Large detached clumps were highly tolerant to oxacillin compared with exponential-phase planktonic cultures. Interestingly, the degree of antibiotic tolerance in stationary-phase planktonic cultures was equal to that in the large clumps. The mechanical disruption of large clumps reduced the minimal bactericidal concentration (MBC) by more than 1,000 times. The MBC for whole biofilm effluent, consisting of particles with an average number of 20 bacteria was 3.5 times higher than the MBC for planktonic cultures. We conclude that the antibiotic resistance of detached biofilm particles depends on the embolus size and could be attributed to nutrient-limited stationary-phase physiology of cells within the clumps. We hypothesize that the detachment of multicellular clumps may explain the high rate of symptomatic metastatic infections seen with S. aureus.
Copyright 2004 American Society for Microbiology
Figures
FIG. 1.
Characteristics of an S. aureus biofilm growing in a glass flow cell. (A) Percent surface area coverage. (B) Thickness (micrometers). (C) Amount of detached biomass quantified by log total cell counts (○) and CFU per milliliter (•). Error bars represent 1 SD of the arithmetic mean (A and B) and the geometric mean (C).
FIG. 2.
Highly heterogeneous S. aureus biofilms. The biofilms consisted of discrete cell clusters (darker areas) separated by interstitial channels and voids (A). Time-lapse imaging documented the detachment of two large cell clusters (indicated by white arrows) from a 7-day-old biofilm over a 15-min interval (B and C). The nutrient flow direction is indicated by the black arrows. Scale bar, 100 μm.
FIG. 3.
Characterization of S. aureus biofilm emboli. (A) The size distribution of detaching particles is shown numerically (white bars) and as the total fraction of detached biomass (gray bars) for days 1 and 7. Error bars represent 1 SD. (B) Confocal image of a large clump containing ca. 107 CFU. Live cells (based on membrane integrity) are stained in green, and dead cells are stained in red. Field of view = 0.5 by 0.5 mm.
FIG. 4.
Log reduction of viable cells in response to increasing oxacillin concentrations. A dotted line marks a 3-log reduction in CFU of large clumps and therefore indicates the MBC. Intact detached clumps tested in fresh medium (•) and stationary-phase planktonic cultures tested in spent medium (▵) were highly tolerant to antibiotics. Mechanically disrupted large clumps (○) regained their antibiotic susceptibility. For exponential-phase planktonic cultures (□) and stationary-phase planktonic cultures in fresh medium (▪), the conventional MBC was 0.5 μg/ml. A dashed line represents the detection limit. Error bars represent 1 SD.
References
- Characklis, W. 1990. Biofilm processes, p. 195-232. In W. G. Characklis and K. C. Marshall (ed.), Biofilms. John Wiley & Sons, New York, N.Y.
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