Center for Biofilm Engineering
Abstract:
"Oxygen Limitation Contributes to Antibiotic Tolerance of Pseudomonas
aeruginosa in Biofilms"
04-019 The role of oxygen limitation in protecting Pseudomonas
aeruginosa strains growing in biofilms from killing by antibiotics was
investigated in vitro. Bacteria in mature (48-h-old) colony biofilms were poorly
killed when they were exposed to tobramycin, ciprofloxacin, carbenicillin,
ceftazidime, chloramphenicol, or tetracycline for 12 h. It was shown with
oxygen microelectrodes that these biofilms contain large anoxic regions. Oxygen
penetrated about 50 µm into the biofilms, which
averaged 210 µm thick. The region of active protein
synthesis was visualized by using an inducible green fluorescent protein. This
zone was also limited to a narrow band, approximately 30 µm
wide, adjacent to the air interface of the biofilm. The bacteria in
mature biofilms exhibited a specific growth rate of only 0.02 h-1.
These results show that 48-h-old colony biofilms are physiologically
heterogeneous and that most of the cells in the biofilm occupy an
oxygen-limited, stationary-phase state. In contrast, bacteria in 4-h-old colony
biofilms were still growing, active, and susceptible to antibiotics when they
were challenged in air. When 4-h-old colony biofilms were challenged under
anaerobic conditions, the level of killing by antibiotics was reduced compared
to that for the controls grown aerobically. Oxygen limitation could explain 70%
or more of the protection afforded to 48-h-old colony biofilms for all
antibiotics tested. Nitrate amendment stimulated the growth of untreated control
P. aeruginosa isolates grown under anaerobic conditions but decreased the
susceptibilities of the organisms to antibiotics. Local oxygen limitation and
the presence of nitrate may contribute to the reduced susceptibilities of P.
aeruginosa biofilms causing infections in vivo.
Borriello, G., E. Werner, F. Roe, A.M. Kim, G.D. Ehrlich and P.S. Stewart,
"Oxygen Limitation Contributes to Antibiotic Tolerance of Pseudomonas aeruginosa
in Biofilms," Antimicrob. Agents Chemother., 48(7):2659-2664 |
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