Mollie E. McBride

Physiological and environmental control of Gram negative bacteria on skin.

The relative importance of the environment versus the physiology of the host in the control of Gram negative bacteria on skin has been examined by two experimental designs.

A new Brevibacterium sp. isolated from infected genital hair of patients with white piedra

A new aerobic gram-positive non-sporeforming bacillus has been isolated from infected genital hair of patients with white piedra in association with Trichosporon beigelii. This species has been characterised morphologically, nutritionally, by DNA base composition, cell-wall analysis and cellular fatty-acid profile on the basis of 14 isolates. The G+C content of DNA is 63.05 mol%. Cell walls possess meso-diaminopimelic acid (Type IV) and the sugars glucose, galactose, xylose and ribose; mycolic acids are not present. The species has a distinct colonial and microscopic morphology, is strongly proteolytic and produces methanethiol. These findings and the cellular fatty-acid profile are compatible with the genus Brevibacterium. A new species is proposed based on the following characters: colonial and microscopic growth and morphology; conditions for rod-to-coccus cycle; ribose utilisation; and tellurite reduction. The type strain has been named Brevibacterium mcbrellneri E2cr (ATCC 49030). The strong proteolytic properties may be the mechanism of pathogenesis.

White piedra: evidence for a synergistic infection

To determine the relative roles of coryneform bacteria and Trichosporon beigelii in the pathogenesis of genital white piedra, scrotal hair from 10 subjects was studied. Hairs were examined by light microscopy to determine the relative proportions of each organism, and were also cultured for coryneforms and yeasts. Histologically, hair nodules from five out of nine cases showed a mixture of yeasts and bacteria, four had bacteria alone, and none showed yeast alone. Five strains of T. beigelii were cultured, two strains of Saccharoniyces cerevisiae and 22 strains of coryneforms. The isolates were tested for synergism by a plate‐overlay method. Growth of coryneforms occurred over and around sections of the plate inoculated with T. beigelii but not around the control yeast, S. cerevisiae. There were strain differences in the stimulatory response of both T. beigelii and coryneform strains. In reverse experiments coryneforms did not enhance growth of T. beigelii. It was concluded that white piedra is a mixed infection caused by the synergistic action between T. beigelii and a specific coryneform bacteria resulting in invasion of the hair cuticle and cortex.

Prevalence of Trichosporon beigelii. Colonization of normal perigenital skin.

Although the natural habitat of Trichosporon species is considered to be the soil, the role of normal skin in the carriage of Trichosporon beigelii is unknown. The purpose of this study was to determine the prevalence of T. beigelii colonization on normal perigenital skin. Inguinal skin scrapings were obtained from 322 asymptomatic volunteers. There were 261 males and 61 females ranging in age from 18 to 89; 136 were white, 134 were black, and 52 were Hispanic. Specimens were cultured on Sabourauds glucose agar containing 500 micrograms ml-1 chloramphenicol, and incubated at 23-26 degrees C for up to 4 weeks. The overall incidence of T. beigelii colonization was 12.4%. However, this varied with patients age, sex, race and socioeconomic background. The highest prevalence (27.1%) was found in black males who attended a Veterans Affairs hospital. The prevalence was lowest in females (1.6%), and no patients who attended a private clinic were colonized. It was concluded that T. beigelii colonizes normal skin with some regularity.

Correlations between epithelial cells and bacterial populations in bacteriological skin samples

The purposes of this study were to determine whether the variability in populations of skin bacteria observed between individuals is related to the number of epithelial cells removed during the skin scrubbing procedure and also whether any particular group of microorganisms can be directly associated with epithelial cells. Foreheads of 31 subjects were sampled using the cup scrubbing method, and bacterial populations were quantified as: total anaerobes, aerobes, Propionibacterium spp., aerobic coryneforms, and Micrococcaceae. Epithelial cells were counted in a haemocytometer. Correlation coefficients were positive between total bacterial populations and epithelial cell counts, with the largest values of 0.64 for Propionibacterium spp., 0.58 for Micrococcaceae, and 0.15 for aerobic coryneforms. High epithelial cell counts were always associated with high bacterial populations, but high bacterial counts occurred, in some instances, with low epithehal cell counts; epithelial cells are not, therefore, responsible for variations in bacterial populations in all cases. Stained smears of epithelial cells from subjects from whom aerobic coryneforms were not cultured showed microcolonies of presumptive anaerobic diphtheroids, closely associated with epithelial cells. These findings and the high correlation between Propionibacterium spp. and epithelial cells suggests a re‐examination of the location of anaerobes in the stratum corneum.

Cutaneous Microflora of Patients with Repeated Skin Infections

The microflora of normal skin in 16 patients with repeated staphylococcal and streptococcal skin infections was examined to determine whether abnormalities existed which would indicate a protective role for the indigenous flora against colonization by pathogens. Five sites‐hands, feet, axilla, groin and back‐were examined quantitatively and qualitatively and compared with a control group. Total populations of indigenous flora were significantly higher from patients with repeated skin infections of the back, axillae and feet. The frequency of isolation of different species from normal skin was comparable between the control and experimental groups, with the exception of the incidence of Staphylococcus aurcus and Proteus species which were isolated only from patients with repeated skin infections. Gram‐negative bacteria were isolated with comparable frequency between the two groups, but patients with repeated skin infections tended to carry gram‐negative bacteria on multiple sites. It was concluded from the high population of indigenous flora and the types of microorganisms present that the microflora of normal skin did not appear to protect patients with repeated skin infections against colonization by pathogens. The presence of high populations of Staphylococcus aurcus on the normal skin of patients with repeated skin infections would appear to be the most important contributing factor.

THE EFFECTS OF SELENIUM AND TELLURIUM COMPOUNDS ON PIGMENTATION OF GRANULES OF TRICHOMYCOSIS AXILLARIS

Trichomycosis axillaris is a condition characterized Ijy die formation of granules surrounding the liair of the axilla and pubis. An excellent review of the early literature has been documented by Crissey et al.2 Three colors of the grantiles have been described; the most common, yellow; and less frequently, red and black. In tlie early literature evidence has been presented that different etiological agents were responsible for the formation of different pigmentation. ̂ Micrococci have been described as the causative organism of red granules, filamentous organisms resembling Nocardia have been associated with tlie black type, and corynebacteria have been isolated from the yellow variety.2 In a more recent study-̂ the same tliree species of corynebacteria were consistently isolated from specimens of trichomycosis axillaris, regairdless of the

Experimentally Induced Cutaneous Infections in Man

The experimental production of disease often permits a better understanding of etiologic factors than can be obtained by clinical study. The variables encountered in clinical infection and the difficulties encountered with terminology point to the need for experimental models. The development of model infection systems is important not only in elucidating the factors involved in the pathogenesis of spontaneous infection but also because models would be useful in testing antimicrobial formulations.