| Description |
The discovery of new antibiotics, the extensive therapeutic use of antibiotics, and the appearance of antibiotic-resistant organisms in individuals with no history of exposure to antibiotics have made it increasingly important that we know how the antibiotics functions. If antibiotic modes of action against the microbial cell were understood, the antibiotics, singly or in combination, could be used more efficiently. Knowledge gained in antibiotic studies of the vulnerability of pathogenic bacterial cells could be used to develop better, less toxic, and less expensive chemotherapeutic agents than are now available. Very few reports on the mechanism of action of one of the newer drugs, aureomycin, have appeared in the literature. The properties of wide bacterial spectrum, high potency in low concentrations, lox toxicity, and failure to yield highly resistance mutants after antibiotic exposure have made in a useful and powerful therapeutic tool. The physical, chemical and pharmacological properties of aureomycin have been well characterized, but relatively nothing is known about its mode of action. The trend in antibiotic research has been toward the interpretation of mechanisms of action in terms of interference with some pathway essential in the metabolism of the particular organism involved. Utilization of organisms resistant to antibiotics ahs been one method employed in studies of antibiotic action. In this problem aureomycin resistance was developed in Micrococus pvogenes var. aureus, and aureomycin-sensitive organism often involved in infection, by subculturing the organism in media containing increasing concentrations of aureomycin. Comparisons between aureomycin-resistant and aureomycinsensitive strains were made on the following bases: fermentation of carbohydrates; production of hydrogen sulfide; hemolysin, coagulase, pigment; liquefaction of gelatin; reduction of nitrates to nitrites; acidification and coagulation of litmus mild; gram-staing characteristics; growth curves; and oxygen uptake. Sixty or more daily subcultures were made of six organisms identified as Micrococcus pyogenes var. aureus in semisynthetic media containing increasing concentrations of aureomycin. Daily subcultures were also made of the same six strains in aureomycin-free semisynthetic broth. Increases in aureomycin-resistance as demonstrated by tube dilution sensitivity tests were approximately 17-fold for organism #1, 12-fold for organisms #2 and #5(2), 14-fold for organism #3, 18-fold for organism #4, and 6-fold for organism #6. Organism #5(1) displayed the greatest increase in resistance, 128-fold. Control organisms transferred 67 times in aureomycin-free semisynthetic broth demonstrated not increase to 2-fold increases in resistance to aureomycin. After 30 tranfers in auereomycin-free broth, most of the induced-resistant organisms lost about one-half of their acquired resistance to aureomycin. Organism #3(1) dropped from nearly a 130-fold increase to a 7-fold increase in resistance. Aureomycin-resistant strains retained the characteristic gram-positive staining reaction of staphylococci. Resistan organisms revealed no differences from their aureomycin-sensitive parent strains in fermentation reactions indicating utilization of glucose, glactose, lactose, maltose, mannitol, and saccharose. They continued to cause reduction of nitrate to nitrite, reduction of methylene blue, and production of small amounts of hydrogen sulfide. Differences between aureomycin-resistant strains and their sensitive parent strains in their ability to liquefy gelatin, coagulate milk, and yield coagulase were not always consistent. Loss of beta hemolytic activity by organisms #5(1) and #5C was distinctive. These two organisms also exhibited loss of typical orange pigmentation characteristic of M. pyogenes var. aureus. All aureomycin-resistant organisms but one demonstrated increased oxygen uptake on a glucose phosphate buffer substrate when compared to the sensitive parent strains. Organism #5(1)R showed less oxygen uptake than any of the orginal cultures. With the addition of qureomycin to the dextrose substrate there was increased oxygen uptake in resistant organisms and decreased oxygen uptake by sensitive organisms and organism #5(1)R. Growth curves of aureomycin-resistant and aureomycin-sensitive strains were similar, with the exception of organism #5(1)R. The most resistant organism, #5(1)R, exhibited a much prolonged lag phase when compared with the organism from which it was derived |
