The viable populations of seven species of bacteria were reduced 17% to 99% by treatment with a 3% suspension of human cerumen of the soft or "wet" type. Species tested for susceptibility to cerumen were Staphylococcus aureus, Staphlylococcus epidermidis, Streptococcus pyogenes, Propionibacterium acnes, Corynebacterium spp, Escherichia coli, and Serratia marcescens. The reduction depended upon the species of bacterium and the age of the culture. Pathogenic species appeared to be more susceptible than others, while cultures in logarithmic growth were more susceptible than stationary phase cultures to the bactericidal activity of wet cerumen. There appeared to be little difference in the bactericidal activity between the two lots of cerumen used. The bactericidal activity of wet cerumen was found to be quite similar to that of dry cerumen as reported earlier in the literature.
An agar disk elution method using round well plates, supplemented MuellerHinton agar, and commercial drug disks is described for susceptibility testing of Mycobacterium marinum and the rapidly growing mycobacteria to antibiotics and sulfonamides. By this method, 14 of 14 strains of M. marinum were susceptible to rifampin, doxycycline, minocycline, and trimethoprim-sulfamethoxazole. Identical results were obtained with Middlebrook 7H10 agar and drugs prepared from standard powders. With 58 isolates of Mycobacterium fortuitum and Mycobacterium chelonei, this method had a 92% correlation with broth minimal inhibitory concentration determinations for cefoxitin and >98% for doxycycline, kanamycin, amikacin, and the sulfonamides. Sixty-nine percent of isolates of M. chelonei susceptible to amikacin on supplemented Mueller-Hinton agar were resistant on 7H10 agar, and 15 of 16 M. chelonei isolates susceptible to erythromycin in broth were resistant by disk elution when an endpoint of no growth was used with either agar. The agar disk elution method offers a practical method for testing of most antibacterial agents against these mycobacterial species.
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