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. 2017 Jul 31;7(1):6946.
doi: 10.1038/s41598-017-07312-7.

Mitigation of a nitrate reducing Pseudomonas aeruginosa biofilm and anaerobic biocorrosion using ciprofloxacin enhanced by D-tyrosine

Ru Jia  1 , Dongqing Yang  1 , Dake Xu  2 , Tingyue Gu  3
Affiliations

Mitigation of a nitrate reducing Pseudomonas aeruginosa biofilm and anaerobic biocorrosion using ciprofloxacin enhanced by D-tyrosine

Ru Jia et al. Sci Rep. .

Abstract

Pseudomonas aeruginosa (PA) is a ubiquitous microbe. It can form recalcitrant biofilms in clinical and industrial settings. PA biofilms cause infections in patients. They also cause biocorrosion of medical implants. In this work, D-tyrosine (D-tyr) was investigated as an antimicrobial enhancer for ciprofloxacin (CIP) against a wild-type PA biofilm (strain PAO1) on C1018 carbon steel in a strictly anaerobic condition. Seven-day biofilm prevention test results demonstrated that 2 ppm (w/w) D-tyr enhanced 30 ppm CIP by achieving extra 2-log sessile cell reduction compared with the 30 ppm CIP alone treatment. The cocktail of 30 ppm CIP + 2 ppm D-tyr achieved similar efficacy as the 80 ppm CIP alone treatment in the biofilm prevention test. Results also indicated that the enhanced antimicrobial treatment reduced weight loss and pitting corrosion. In the 3-hour biofilm removal test, the cocktail of 80 ppm CIP + 5 ppm D-tyr achieved extra 1.5-log reduction in sessile cell count compared with the 80 ppm CIP alone treatment. The cocktail of 80 ppm CIP + 5 ppm D-tyr achieved better efficacy than the 150 ppm CIP alone treatment in the biofilm removal test.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Sessile cell counts, specific weight losses and pH. (a) Sessile cell counts after the 7-day biofilm prevention test with different treatment chemicals in the culture medium. (Error bars represent standard deviations, statistical reference point n = 4). (b) Weight losses of coupons (bars) and pH values (circles) of the culture medium at the end of the 7-day biofilm prevention test. (Error bars represent standard deviations, statistical reference point n = 6).
Figure 2
Figure 2
SEM images of PA biofilms on C1018 after the 7-day biofilm prevention test with: (a) no treatment (control), (b) 2 ppm D-tyr, (c) 30 ppm CIP, and (d) 30 ppm CIP + 2 ppm D-tyr. (Scale bars in the small inserted images are 50 μm).
Figure 3
Figure 3
CLSM images of PA biofilms (Dimensions: X = 224 µm, Y = 224 µm) on C1018 after the 7-day biofilm prevention test with: (a) no treatment (control) (biofilm thickness = 76 µm), (b) 2 ppm D-tyr (biofilm thickness = 74 µm), (c) 30 ppm CIP (biofilm thickness = 34 µm), and (d) 30 ppm CIP + 2 ppm D-tyr (biofilm thickness = 10 µm). The calculated numbers of live/dead cells are shown in (e) and (f). (Error bars represent standard deviations, statistical reference point n = 6).
Figure 4
Figure 4
SEM pit images on coupon surfaces after the 7-day biofilm prevention test with: (a) abiotic control, (b) no treatment, (c) 2 ppm D-tyr, (d) 30 ppm CIP, and (e) 30 ppm CIP + 2 ppm D-tyr. (Scale bars in the small inserted images are 50 μm).
Figure 5
Figure 5
IFM pit depth profile of coupons after the 7-day biofilm prevention test with: (a) abiotic control, (b) no treatment, (c) 2 ppm D-tyr, (d) 30 ppm CIP, and (e) 30 ppm CIP + 2 ppm D-tyr. (Scale bars in the small inserted images are 50 μm).
Figure 6
Figure 6
Sessile cell counts after the 3-hour biofilm removal test. (Error bars represent standard deviations, statistical reference point n = 4).
Figure 7
Figure 7
CLSM images of PA biofilms (Dimensions: X = 224 µm, Y = 224 µm) after the 3-hour biofilm removal test in the pH 7.4 PBS buffer containing: (a) no treatment (control) (biofilm thickness = 72 µm), (b) 5 ppm D-tyr (biofilm thickness = 69 µm), (c) 80 ppm CIP (biofilm thickness = 49 µm), and (d) 80 ppm CIP + 5 ppm D-tyr (biofilm thickness = 28 µm). The calculated numbers of live/dead cells are shown in (e) and (f). (Error bars represent standard deviations, statistical reference point n = 6).
Figure 8
Figure 8
Procedures of the PA biofilm mitigation tests: (a) the 7-day biofilm prevention test in anaerobic vials, and (b) the 3-hour biofilm removal test in the anaerobic chamber.
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