Effects of Low Concentrations of Antibiotics on Escherichia coli Adhesion
The Influence of Antibiotics on the Host-Parasite Relationship
We have previously shown that subinhibitory concentrations of antibiotics may infliience the adhesion of Escherichia coli SS142 to human epithelioid tissue culture cells. This report shows that these effects are not limited to E. coli SS142 or to our tissue culture system. Most of the 10 E. coli strains studied showed decreased adhesion to Intestine 407 tissue culture cells after growth in 25% of the minimum inhibitory concentration of streptomycin, tetracycline, trimethoprimsulfametrole,
... sulfametrole, chloramphenicol, and clindamycin. Nalidixic acid at 25% of the minimum inhibitory concentration caused an increase of adhesion. The hemagglutinating activity of the five hemagglutinating strains and the adhesiveness of E. coli SS142 to human buccal cells were similarly affected by low concentrations of the above-mentiQned antibiotics. We conclude that E. coli adhesion to human epithelioid tissue culture cells is a valid model of bacterial adhesion because of its high accuracy and reproducibility. We have recently described and characterized an in vitro assay for measuring bacterial adhesion to the human epithelioid tissue culture cell line, Intestine 407 (2, 9, 10). The adhesiveness of Escherichia coli SS142 was found to be reduced in this assay system after growth in subinhibitory concentrations of tetracycline, trimethoprim-sulfametrole, and clindamycin (9). A reduction ofE. coli adhesion was also observed by others in different model systems after growth in the presence of several antibiotics (1, 3, 7) . In this report, we compare the effects of various antibiotics on the adhesion to tissue culture cells of several E. coli strains. We demonstrate that E. coli adhesion is affected in a strain-specific manner, but that some antibiotics are more likely to change bacterial adhesiveness than others. Furthermore, we show a general correlation between the effects on adhesiveness observed in our tissue culture model, in a hemagglutination assay, and in human buccal cell adhesion. These correlations underline the usefulness of our tissue culture model for studies on bacterial adhesion. Our results also provide further evidence for a participation of bacterial protein structures in the process of E. coli adhesion, thus confirming existing concepts of the mechanism of E. coli adhesion (6). MATERIALS AND METHODS Medi and solutions. Minimal essential medium and calf serum were from GIBCO Laboratories, Glasgow, Scotland. Brain heart infusion (BHI) broth and agar were obtained from BBL Microbiology Systems, Cockeysville, Md. HEPES (N-2-hydroxyethylpiperazine-N'-2ethanesulfonic acid)-buffered Hanks solution (HEPES-Uanks) and phosphate-buffered saline were composed as described previously (9). Bacterial sdran. Ten E. coai strains of different pathogenic origin which adhered to Intestine 407 tissue culture cells Were selected fbr this study (Table 1) . The strains were maintained on brain heart infusion (BHI) agar plates at 4C after overnight growth at 37°C and were subcultured weekly. Tissue culture cells. The cell line Intestine 407 (ATCC CCL6) was obtained from Flow Laboratories, Irvine, Scotland, and were maintained in minimal essential medium containing 10%o calf serum in a 5% CO2 atmosphere at 370C as described previously (9) .