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Isothiocyanates have been reported to exert antimicrobial activity. These compounds are found in a licensed native preparation of nasturtium (Tropaeoli majoris herba) and horseradish (Armoraciae rusticanae radix) which is used for treatment of upper respiratory and urinary tract infections. The aim of our investigation was to assess the antimicrobial activity of a mixture of the contained benzyl-, allyl-, and phenylethyl- isothiocyanates against clinically important bacterial and fungal pathogens including antimicrobial resistant isolates. Susceptibility testing was performed by agar-dilution technique. Isothiocyanates were mixed in proportions identical to the licensed drug. Minimum inhibitory- and minimum bactericidal concentrations were assessed. The Minimum inhibitory concentration90 was defined as the concentration which inhibited 90% of the microbial species tested. H. influenzae, M. catarrhalis, S. marcescens, P. vulgaris, and Candida spp. were found to be highly susceptible, with minimum inhibitory concentration90 -values ranging between ≤0.0005% and 0.004% (v/v) of total ITC. Intermediate susceptibilities were observed for S. aureus, S. pyogenes, S. pneumoniae, K. pneumoniae, E. coli and P. aeruginosa, with Minimum inhibitory concentration90 -values ranging between 0.004% and 0.125% (v/v), but with elevated Minimum bactericidal concentrations90-values (2-7 dilution steps above Minimum inhibitory concentration90). Low susceptibilities were determined for viridans streptococci and enterococci. Interestingly, both resistant and non-resistant bacteria were similarly susceptible to the test preparation.

The gastric and tracheal flora of 142 consecutive patients receiving stress ulcer prophylaxis were investigated, identifying identical isolates by typing. Furthermore, the growth pattern of normal respiratory bacteria and organisms causing ventilation pneumonia at different pH values and the in vitro effect of sucralfate and bismuth subsalicylate on these bacteria in simulated gastric fluid were studied. The results obtained were as follows: (1) with rising gastric pH bacterial counts in gastric aspirates, especially gram-negatives, increased significantly; (2) in 45 (31.7%) of the patients identical organisms were first isolated in gastric samples and one to two days later in tracheal secretions; (3) ventilation pneumonia was significantly more frequent in patients with high gastric pH; (4) pathogens causing ventilation pneumonia grew well in simulated gastric fluid at higher pH values, unlike normal respiratory organisms; and (5) sucralfate and bismuth subsalicylate showed antibacterial activity against frequent causative organisms of ventilation pneumonia.

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