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Notes: A miniaturized sensitive bioassay was used to detect tetracycline in open comedones following topical twice daily application of 0.22% tetracycline hydrochloride for a minimum of 4 weeks to the facial skin of patients with mild to moderate acne. The lower limit of detection was 4.8±0.8 ng per comedone or per 10 μl. Using this method. Ill of 155 open comedones from 15 patients were found to contain a detectable amount of tetracycline, ranging from 1.8 to 156.9 ng per comedone, and between 4.5 and 1140.1 ng per mg comedonal material. There was a significant effect of comedone weight on tetracycline content, with smaller comedones containing proportionately more tetracycline. The Spearman rank correlation coefficient was −0.5619 (P 〈 0.001). All III comedones in which tetracycline was detected contained sufficient drug to inhibit fully antibiotic-sensitive propionibacteria. However, conditions favourable to the selection and overgrowth of highly tetracycline-resistant strains (MIC ≥ 32 μg/ml) prevailed in at least 18.7% (29 of 155) of the comedones tested.

Notes: Topical formulations of erythromycin and benzoyl peroxide are popular and effective treatments for mild to moderate acne vulgaris. Use of the former is associated with resistance gain in both skin propionibacteria and coagulase-negative staphylococci, whereas use of the latter is not. We evaluated the efficacy of a combination of erythromycin and benzoyl peroxide against a total of 40 erythromycin-sensitive and -resistant strains of Staphylococcus epidermidis and skin propioni- bacteria in vitro. Using the checkerboard technique, five erythromycin resistant strains of Propionibacterium acnes were inhibited synergistically or additively by the combination. Complete mutual indifference was exhibited between the drugs against the remaining 35 strains. However, erythromycin resistant staphylococci and propionibacteria were inhibited by the same concentration of benzoyl peroxide as erythromycin-sensitive strains. These results suggest that, although the combination of erythromycin and benzoyl peroxide is not synergistic against the majority of erythromycin-resistant staphylococci and propionibacteria, the concomitant therapeutic use of both drugs should counteract the selection of erythromycin-resistant variants and reduce the number of pre-existing resistant organisms on the skin of acne patients.

Notes: The relationship between sebum excretion rate (SER) and clinical improvement was investigated in 255 acne patients treated For 6 months with either oral erythromycin (1 g/day), minocycline (100 mg/day), oxytetracycline (1 g/day) or cotrimoxazole (400 mg/day); topical therapy was 5% benzoyl peroxide. In all but the cotrimoxazole treated group, there was a significant correlation between a high SER and reduced clinical response. This was particularly evident in those patients with an SER of greater than 2–5 μg/cm2/min. These patients showed only 17% improvement compared with 100% improvement in those subjects with an SER of 1.0 μg/cm2/min or less. The presence of obvious seborrhoea in a patient who has failed to respond to an adequate 6–month course of antimicrobial therapy, should indicate the earlier rather than later use of isotretinoin for their acne.

Notes: Background Propionibacterium acnes is the target of antimicrobial treatments for acne vulgaris. Acquired resistance to erythromycin, clindamycin and tetracyclines has been reported in strains from diverse geographical loci, but the molecular basis of resistance, via mutations in genes encoding 23S and 16S rRNA, respectively, has so far only been elucidated for isolates from the U.K. Objectives To determine whether similar or different resistance mechanisms occur in resistant P. acnes isolates from outside the U.K. Methods The phenotypes and genotypes of 73 antibiotic-resistant strains of P. acnes obtained from the skin of acne patients in the U.K., U.S.A., France, Germany, Australia and Japan were compared. Antibiotic susceptibilities were determined by minimum inhibitory concentration (MIC) measurements, and polymerase chain reaction and DNA sequencing were used to identify mutations in genes encoding rRNA. Results Most erythromycin-resistant isolates (MIC90≥ 512 μg mL−1) were cross-resistant to clindamycin but at a much lower level (MIC90≥ 64 μg mL−1). As in the U.K., resistance to erythromycin was associated with point mutations in 23S rRNA in 49 of 58 strains. An A→G transition at Escherichia coli equivalent base 2058 was present in 24 strains. This gave a unique cross-resistance phenotype against a panel of macrolide, lincosamide and type B streptogramin antibiotics. Two further point mutations (at E. coli equivalent bases 2057 and 2059) were identified (in three and 22 isolates, respectively) and these were also associated with specific cross-resistance patterns originally identified in isolates from the U.K. However, nine of 10 erythromycin resistant-strains from Germany did not exhibit any of the three base mutations identified and, in six cases, cross-resistance patterns were atypical. Consistent with previous U.K. data, 34 of 38 tetracycline-resistant strains carried a base mutation at E. coli 16S rRNA equivalent base 1058. Tetracycline-resistant isolates displayed varying degrees of cross-resistance to doxycycline and minocycline, but isolates from the U.S.A. had higher MICs for minocycline (4–16 μg mL−1) than isolates from other countries and, in particular, Australia. All the P. acnes isolates resistant to one or more of the commonly used antiacne antibiotics were sensitive to penicillin, fusidic acid, chloramphenicol and the fluoroquinolone, nadifloxacin. All but one isolate (from the U.K.) were sensitive to trimethoprim. Conclusions This study shows that 23S and 16S mutations identified in the U.K. conferring antibiotic resistance in P. acnes are distributed widely. However, resistant strains were isolated in which mutations could not be identified, suggesting that as yet uncharacterized resistance mechanisms have evolved. This is the first report of high-level resistance to minocycline and is of concern as these strains are predicted to be clinically resistant and are unlikely to remain confined to the U.S.A. Epidemiological studies are urgently required to monitor how resistant strains are selected, how they spread and to ascertain whether the prevalence of resistance correlates with antibiotic usage patterns in the different countries.

Notes: Antibiotic-resistant propionibacteria are being isolated with increasing frequency from antibiotictreated acne patients. Minimum inhibitory concentrations (MICs) of three tetracyclines, extensively used in acne therapy, were determined for 46 resistant and 19 sensitive propionibacterial isolates. Sensitive strains were inhibited by ≤1 μ/ml of all three tetracyclines. For every resistant strain tested, the MIC of tetracycline exceeded that of doxycycline which, in turn, exceeded that of minocycline. The mean MIC for resistant strains was 20.61±4.56 μ/ml of tetracycline, 9.70±2.03 μ/ml of doxycycline and 1.95±0.35 μ/ml of minocyciine. In order to determine whether these strains could be inhibited by concentrations of minocycline achievable in vivo, serum levels of minocycline were determined in acne patients receiving either the recommended dose of 50 mg b.d. (20 males, 14 females), or twice this dose (21 males, 12 females). Serum levels were significantly higher (P〈0.001, Student's t-test) in patients receiving 100 mg b.d. Males on 50 mg h.d. had significantly lower serum levels than females on the same dose (P〈0.05. Student's t-test). For all patients, the mean serum level on high-dose minocycline was 246±0.45 μ/ml, compared with 1.38±0.30 μ/ml on the smaller dose. These results indicate that tetracycline-resistant propionibacteria should be considered clinically minocycline sensitive, if patients who harbour such strains are prescribed 100 mg b.d. The recommended dose of minocycline for treating acne, especially in male patients, should be re-assessed.

Notes: The effect of zinc and erythromycin on cultures inoculated with mixtures of different ratios of erythromycin sensitive (ES) and resistant (ER) Propionibacterium acnes cells was studied in vitro. Propionibacterium acnes ES outgrew P. acnes ER in the absence of erythromycin and zinc. At low levels of erythromycin ES outgrew ES. whilst the addition of 600 pg/ml zinc further reduced the growth of ER compared to ES Growth of ER and ES were similar at levels of erythromycin near the minimum inhibitory concentration (MIC) of ES cells. Concentrations above the MIC for Es cells inhibited ES but not ER cells. At the higher concentrations of erythromycin, the addition of 96 ng/ml zinc delayed the growth of ER cells, whilst the addition of 300 μg/ml zinc prevented the growth of ER cells. The combination of erythromycin and zinc, at appropriate concentrations, inhibits both ES and ER.

Notes: In a double-blind clinical study in ninety-four subjects a 1.5% (w/v) erythromycin lotion was as effective as 5% (w/v) benzoyl peroxide gel in significantly reducing the number of small inflamed lesions and the overall acne severity. However, benzoyl peroxide also significantly reduced the number of non-inflamed lesions whereas erythromycin had no effect on these lesions. This study supports the view that, although topical erythromycin is of value in the treatment of mild or moderate acne vulgaris, long established, safe and effective remedies should not be replaced by topical antibiotics until more comparative studies and investigations on bacterial resistance have been completed.

Notes: Background  Skin colonization by antibiotic-resistant propionibacteria is commonplace among acne patients globally. Increasing attention is now being paid to how resistance rates might be reduced to preserve the future efficacy of antibiotics, especially erythromycin and clindamycin in acne therapy.Objective  To assess the efficacy of oral isotretinoin in the control of antibiotic-resistant propionibacteria.Methods  Acne patients (72 in the U.K., 62 in the U.S.A.) colonized with high numbers of antibiotic-resistant propionibacteria were sampled before, during and 12 weeks after oral isotretinoin therapy. Propionibacterial samples were collected from five acne-prone skin surface sites using a detergent scrub method and from the anterior nares using moistened swabs. Total and antibiotic-resistant propionibacteria were enumerated by viable counting on media with and without selective antibiotics.Results  After 16 weeks of oral isotretinoin therapy, mean population densities of viable propionibacteria and variants resistant to erythromycin, clindamycin or tetracycline had fallen by more than 90% at all skin sites and in the nares. The sole exception was a smaller reduction in tetracycline-resistant strains on the lower back. In general, greater reductions were observed on skin than in the nares. By the end of the treatment period only three patients (all in Philadelphia) yielded no antibiotic-resistant strains from any site. Post-treatment, propionibacterial counts remained well below pretreatment levels but had begun to recover on the face and in the nares. The recovering propionibacterial population included both susceptible and resistant strains. Changes during and post-treatment at the two centres were similar but not identical.Conclusions  Oral isotretinoin effectively reduced skin and nasal colonization by antibiotic-resistant propionibacteria. However, viable populations of resistant isolates persisted post-treatment at multiple sites. Novel methods are required to eradicate antibiotic-resistant propionibacteria completely, especially from the nasal reservoir.