Journal of Antimicrobial Chemotherapy (1987) 20, 815-823
© 1987 The British Society for Antimicrobial Chemotherapy
research-article |
The inhibitory effect of sodium alginate on antibiotic activity against mucoid and non-mucoid strains of Pseudomonas aeruginosa
aDepartments of Pediatrics and of Epidemiology and Public Health, Yale University School of Medicine New Haven, CT 06510, USA bDepartment of Bacterial Diseases, Walter Reed Army Institute of Research Washington, DC, 20012, USA cDepartment of Clinical Investigation, Walter Reed Army Medical Center Washington, DC, 20307, U.S.A.
accepted 28 July 1987
The exopolysaccharide of mucoid strains of Pseudomonas aeruginosa (MPA) is chemically similar to alginate, a common polysaccharide of seaweeds. Both polymers have been reported to decrease the diameter of the inhibition zones produced in antibiotic disc diffusion assays. In order to determine whether this phenomenon was due to reduced diffusion of the antibiotic in an agar matrix, or to inhibition of antibiotic activity by sodium alginate, we studied the effect of sodium alginate on the susceptibility of P. aeruginosa strains to antibiotics in disc diffusion assays, as well as in broth and agar dilution assays. Sodium alginate decreased the activity of the aminoglycoside antibiotics, amikacin and gentamicin, against two MPA strains and their non-mucoid derivatives in each of the assays. In broth dilution assays, increase of the calcium ion concentration likewise reduced aminoglycoside activity against P. aeruginosa, but not against Escherichia coli and Staphylococcus aureus. Sodium alginate caused no inhibition of the activity of piperacillin and carbenicillin. The reduction of aminoglycoside activity may have implications for the common failure of these antibiotics in the treatment of pulmonary infections caused by MPA in cystic fibrosis patients, but must be considered only an in-vitro phenomenon at present.