Interactions of Trichophyton mentagrophytes and micrococci on skin culture.

Scanning electron microscopy was used to search for local or limited synthesis of antibiotics by a strain of Trichophyton mentagrophytes. Micrococcus luteus, which was susceptible to penicillin and to the dermatophyte when both were cultured on agar media, displayed morphological alterations of flattened walls, invagination, enlargement, and collapse in skin cultures with the fungus. Penicillinase did not neutralize these effects. A control strain of Staphylococcus spp with poor sensitivity to penicillin was resistant to the dermatophyte in all test systems. T. mentagrophytes showed positive tropism to the bacteria. Regional variation in fungal germination and antibiotic production, the limited yield of antibiotics, and the pattern of dermatophyte growth and alteration of bacterial morphology demonstrated the significant influence of microenvironment on antibiosis.

Uneven distribution of aerobic mesophilic bacteria on human skin.

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.

Survival of bacillus licheniformis on human skin.

The colonization and survival of Bacillus 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 10(4) 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 (greater than 21 days) and short-term (less than 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.

Interactions of Bacillus licheniformis ATCC 10716 and normal flora of human skin.

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.

Inhibition of diptheroid esterase by Micrococcus luteus.

Micrococcus luteus produced a diffusible, esterase inhibitory factor (EIF) which inhibited the activity of cutaneous diphtheroid esterases on Tween 80-CaCl2 agar media. Esterases of Staphylococcus, Micrococcus, Bacillus, and Serratia were not susceptible. EIF did not appear to combine with the substrate or to prevent enzyme synthesis; it was unable to reverse the precipitation of calcium oleate. The composition of the medium, especially peptones, influenced the production of EIF. EIF was synthesized in the absence of diphtheroids, but production required the presence of Tween. The interaction was observed on agar medium of pH 5.5-8.5, at 25-43 degrees C, under an atmosphere of 10-20% CO2, in the presence of urea, but not after the addition of NaCl or dextrose. Supernatants of broth cultures had to be concentrated to detect EIF. Crude dialyzed and concentrated preparations of EIF withstood 60 degrees C for 60 min but were inactivated after 100 degrees C for 10 min. EIF may possibly be associated with a lipoid substance, since it did not precipitate in ethanol.

Effects of occlusion upon population dynamics of skin bacteria.

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.