Quantitative and qualitative changes of the cutaneous aerobic bacterial flora upon 20 sites on the backs of each three healthy subjects were examined before and after one site was occluded, using skin flora maps as a tool. Major local alterations were found to affect the carriage of micro-organisms in distant surrounding areas. Staphylococcus epidermidis was the most successful competitor. Furthermmore, some sites appeared to act as retricted reservoirs for specific types of micro-organisms whereas other areas were less limited in their support of flora.
The colonization and survival of Bacitlus species, members of the cutaneous microbial community of humans, were investigated by applying spores of Bacillus licheniformis to the forearms of volunteers. Four strains were tested, including the bacitracin producer ATCC 10716 and its bacitracin-negative mutant. Germination occurred within 24 h. Significant differences in survival population and duration were found among the test strains; however, ATCC 10716 and its mutant produced statistically similar survival curves. In general, an inoculum density of 104 colony-forming units per cm2 allowed survival for at least 2 weeks. Individual variation was extreme, for one subject harbored bacilli for over 2 months and another eliminated the microorganism within 3 days. Individuals could be differentiated into long-term (>21 days) and short-term (<14 days) carriers. Eight of the 11 volunteers (73%) inoculated with ATCC 10716 carried it for 2 weeks, and 5 subjects (45%) continued to support the bacilli for 3 weeks. Spreading of the organism to other regions of the body occurred, but bacilli were not detected in these areas beyond 6 days.
A procedure of replica plating is described whereby all isolated colonies of Micrococcaceae can be identified with relative ease and rapidity. The method is as accurate as the recommended procedure, but permits a more complete and economical analysis of cutaneous flora in large-scale surveys. In this system, Baird-Parker carbohydrate medium was found somewhat superior to standard medium as was incubation at 35 degrees C instead of the customary 30 degrees C. Baird-Parker's broth medium for acetoin production yielded more positive results than did commercial medium, although the reactions were less distinct. However, an agar acetoin test medium was found as good or perhaps even better than Baird-Parker's medium. The classification schemes of Baird-Parker and Bergey's Manual were contrasted in the analysis of data.
To determine whether antibiotic production might be ecologically advantageous in the survival of Bacillus species on human skin, we applied spores of a bacitracin-producing strain of Bacillus licheniformis (ATCC 10716) to the forearms of 11 volunteers. Three additional strains of B. licheniformis which did not synthesize antibiotics, including a mutant of ATCC 10716, were used in subsequent control trials. Samples of flora were taken from inoculated and control (opposite forearm) sites during the colonization period, generally 3 weeks. Although population densities were unaltered, changes in the carriage, composition, and bacitracin sensitivity of resident flora were related with the presence of ATCC 10716 only, which suggests that microbial interactions are important in bacillus colonization and in maintenance of normal flora. Interactions were examined in vitro by comparing growth curves of representative skin bacteria, including isolates of Staphylococcus epidermidis, Staphylococcus saprophyticus, Micrococcus luteus, and a large-colony diphtheroid, grown individually, in mixed culture with each other, and together in presence of each test strain of B. licheniformis. We observed some diminution of growth of M. luteus and the diphtheroid in the first mixed culture, and the diphtheroid was completely retarded in common culture with ATCC 10716. Lesser antibiotic effects were seen on the cocci, whose rank of sensitivity was similar to that in vivo. The growth of the diphtheroid was enhanced in mixed culture with those strains of bacilli which lack antibiotic activity.
Viable aerobic mesophilic bacteria are not evenly distributed on the skin of the volar forearm. An increase in the size of the area sampled did not result in a proportional increase in the number of the viable aerobic mesophilic bacteria recovered.
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