In vitro effect of chlorhexidine and amikacin on oral gram-negative bacilli from bone marrow transplant recipients

Prophylactic use of chlorhexidine (CHX) mouthrinses has been shown to benefit the oral health status of bone marrow transplant recipients and other immunosuppressed persons and to reduce systemic complications of oral origin. However, a problem that often emerges with these patients is oropharyngeal and lower respiratory tract colonization by opportunistic aerobic or facultative gram-negative bacilli (GNB). Trends in four studies indicated that CHX rinses may predispose these persons to oral colonization by GNB such as the enterobacteria, Klebsiella pneumoniae and Enterobacter cloacae. Since GNB are generally susceptible to broad-spectrum aminoglycoside antibiotics such as amikacin, the in vitro sensitivities of K. pneumoniae, E. cloacae, Pseudomonas aeruginosa, and Escherichia coli ATCC reference strains and K. pneumoniae and E. cloacae oral clinical isolates to combinations of CHX and amikacin were determined by means of a disk diffusion sensitivity assay on Mueller-Hinton agar. The amikacin minimum inhibitory concentrations for all GNB tested were much lower (≤4.69 to ≤9.37 μg/ml) than those for CHX (≤18.75 to ≤300 μg/ml), and combinations of CHX and amikacin gave larger growth inhibition zones than CHX alone. No antibacterial antagonism between CHX and amikacin was found, and their solubilities were compatible. Therefore use of topical amikacin in conjunction with CHX rinses may reduce oral colonization by GNB in severely immunocompromised patient populations.