Cutaneous microenvironment of human immunodeficiency virus (HIV)-seropositive and HIV-seronegative individuals, with special reference to Staphylococcus aureus colonization.

A cross-sectional quantitative study of cutaneous bacterial and yeast flora at seven body sites in 99 human immunodeficiency virus-seropositive and 50 seronegative military personnel was performed. Statistically significant differences in carriage rates were only observed for Staphylococcus aureus on the foreheads of seropositive individuals. Seronegative individuals demonstrated staphylococcal carriage rates 1.3 to 2 times as great as those of historical controls (defined as healthy individuals not receiving any medications) at five of six body sites. We conclude that seropositive military personnel do not exhibit statistically significant elevations in densities and carriage rates of the microorganisms examined (except Staphylococcus aureus), relative to seronegative individuals. Seropositive individuals may be predisposed to staphylococcal carriage. The elevated staphylococcal carriage rates of military personnel undergoing basic training warrants a formal evaluation of the impact of training exercises on cutaneous flora. The information gained may serve to limit the spread of infection during training exercises and battlefield conditions.

Effects of topical erythromycin on ecology of aerobic cutaneous bacterial flora.

We have demonstrated previously that application of topical erythromycin, an antibiotic commonly used for the treatment of acne, results in an increased density of cutaneous erythromycin-resistant (Emr) coagulase-negative staphylococci; however, it is unknown if this increase results in an overall higher density of total cutaneous staphylococci or if upon cessation of erythromycin use, Emr coagulase-negative staphylococci remain at an increased density compared with the pretreatment density. To investigate this, 2% erythromycin or vehicle was applied to each subject's forehead (n = 225) twice a day by laboratory personnel for a period of 6 weeks. Samples were obtained for culture from the forehead, anterior nares, and back of the subjects at baseline and at weeks 6, 9, and 12 of the study. Cultures were performed on differential media. Plates into which erythromycin was incorporated (8 micrograms/ml) were used to identify Emr coagulase-negative staphylococci. The species of all Emr coagulase-negative staphylococci were determined, and an antibiogram for 16 antibiotics was obtained. The baseline prevalence of Emr coagulase-negative staphylococci on the forehead and nose was about 80% at the two study sites, whereas that on the back was 50%. The baseline density of Emr coagulase-negative staphylococci on the forehead, nose, and back was approximately 20% of the total flora. Following 6 weeks of erythromycin treatment, the prevalence of Emr coagulase-negative staphylococci on the forehead and nose was nearly 100% and the densities were 73 and 62%, respectively; the prevalence and density for the back were 78 and 42%, respectively. The most prevalent erythromycin resistance gene expressed by the Emr coagulase-negative staphylococci was ermC. There was no increase in the numbers of Staphylococcus aureus, gram-negative rods, or yeasts, nor was there increased resistance to any other antibiotic except clindamycin. The density of total aerobic organisms also remained static. There were no changes in the prevalence or density of Emr coagulase-negative staphylococci in the vehicle group. A statistically significant decrease in the prevalence and density of Emr coagulase-negative staphylococci in the erythromycin group was observed within 3 weeks posttreatment and by 6 weeks posttreatment, the prevalence and density returned to baseline values. These data demonstrate that the increased prevalence and density of Emr coagulase-negative staphylococci as a result of topical 2% erythromycin use are transient on both population and individual levels.

Replicate plating: does it increase reliability?

As a part of a clinical study to evaluate the antibacterial effect of a topically applied erythromycin gel, microbiological specimens were taken from two groups of patients: one group using 2% erythromycin gel and the other group using a placebo gel. These specimens were plated in triplicate using a common source on bacteriological media using standard procedures. After the appropriate incubation times, the numbers of aerobic and anaerobic organisms were counted separately from each of three plates. A comparison of the bacterial colony counts from the replicate plates showed a high degree of similarity for each type of organism. Tests for treatment differences in organism counts were performed based on single, double and triplicate plating. The results obtained were almost identical, suggesting that replicate plating from a common source is no more accurate than single plating. The only apparent advantage of this type of replicate plating is heightened confidence in the reliability of bacterial counts from single plates.

A new method for in vivo evaluation of antimicrobial agents by translocation of complex dense populations of cutaneous bacteria.

Previously, we described methods for measuring in vivo antimicrobial activity in which the resident bacterial flora of the forearm is expanded by occlusion with an impermeable plastic film, test agents are applied and quantitative cultures are obtained at varying time points. This methodology allows for an in vivo quantitative assessment of antimicrobial effects directed against a dense flora comprised primarily of staphylococci. This method may not be applicable to situations in which there is a high density of multiple species of bacteria. We describe herein new methods which permit in vivo determination of antimicrobial activity against a dense, mixed flora. Swabs moistened with a dilute nonionic detergent are used to remove bacteria from the subject's axilla or groin which are then translocated to the subject's forearm. Occlusion of the forearm with a large, sterile plastic chamber provides the necessary humid environment to yield a dense flora (10(5)-10(6) CFU) consisting of gram-positive cocci, gram-positive coryneforms and gram-negative rods. In this manner, multiple test sites are created on each forearm allowing for the simultaneous evaluation of multiple antimicrobial agents in a single subject. This method allows for the evaluation of the immediate, as well as sustained, in vivo bactericidal effect of an antimicrobial agent against a dense mixed flora with quantitative cultures obtained at varying time points after application of the test agent. Furthermore, ecological pressures which select for resistant organisms or allow for an overgrowth of nonsensitive bacteria can be evaluated by determining the composition of the flora after single or repeated applications of a test agent. The testing methodologies described herein can provide relevant information regarding the antimicrobial effectiveness of an agent in a variety of situations such as use against the axillary flora (including its utility as a deodorant), use as a perineal cleanser for critically ill, hospitalized patients and use in situations where a dense mixed flora exists, e.g. stasis ulcers and infected intertriginous dermatoses.

Antibiotic resistance patterns in coagulase-negative staphylococci after treatment with topical erythromycin, benzoyl peroxide, and combination therapy.

Antibiotic resistance of the resident cutaneous bacterial flora is a well recognized consequence of systemic antibiotic therapy. In this study, we followed the development of antibiotic resistance of coagulase-negative staphylococci (CNS), the most numerous aerobic bacteria found on the skin surface, during treatment with three topical antimicrobial agents used to treat acne vulgaris. Groups of 20 subjects received either topical erythromycin, benzoyl peroxide or a combination of the two for 16 weeks. After 12 weeks of treatment with erythromycin, the aerobic flora was dominated by S. epidermidis which was completely resistant to erythromycin. In addition there was an increase in resistance to clindamycin and tetracycline. Treatment with benzoyl peroxide and the combination of erythromycin and benzoyl peroxide resulted in a significant reduction in the number of aerobic bacteria without any change in the resistance pattern to erythromycin or other antibiotics.

Qualitative and quantitative changes in cutaneous bacteria associated with systemic isotretinoin therapy for acne conglobata.

Quantitative cultures in 40 patients treated with systemic isotretinoin demonstrated a significant reduction in the anaerobic diphtheroid, Propionibacterium acnes within one month of therapy and a continued suppression during 5 months of treatment. This reduction persisted after discontinuation of isotretinoin therapy despite a return of sebum excretion to pretreatment levels. Surface aerobic bacteria showed a significant reduction in the total number of organisms and significant qualitative changes. Gram negative bacteria were sharply reduced in both the anterior nares and skin while Staphylococcus aureus recovery increased significantly.