Hee Young Kang

OBJECTIVES: Antimicrobial resistance and class 1 integrons found in Escherichia coli isolates from humans and animals in Korea were characterized. METHODS: E. coli isolates were examined for susceptibility to antimicrobial agents. Integrase genes were amplified. Gene cassette regions for classes 1 and 2 integrons were amplified and sequenced. Conjugal transfer and Southern hybridization were performed to determine the genetic localization of class 1 integrons. The clonal relationship of E. coli isolates carrying an identical cassette array was analysed by PFGE. RESULTS: Commensal E. coli isolates from animals were highly resistant to commonly used antimicrobial agents such as tetracycline, sulfamethoxazole, streptomycin, ampicillin and carbenicillin. Integrons were most prevalent in commensal E. coli isolates from poultry (44%), followed by clinical isolates from humans (33%), commensal isolates from swine (23%) and humans (13%). dfrA17-aadA5, dfrA12-orfF-aadA2 and aadA1 were found most frequently in E. coli isolates from humans, poultry and swine, respectively. Class 1 integrons were mostly located in conjugative plasmids. E. coli isolates carrying an identical cassette array were phylogenetically unrelated. CONCLUSIONS: The use of antibiotics is strongly associated with antimicrobial resistance. E. coli isolates from different sources may select a specific gene cassette by antibiotic selective pressure, which results in differences in class 1 integrons. The horizontal transfer of class 1 integrons through conjugative plasmids seems to be responsible for wide dissemination of a particular type of class 1 integron.

BACKGROUND: Melasma is associated with epidermal hyperpigmentation, weak basement membrane, vascular proliferation and increased numbers of mast cell. Tranexamic acid (TXA), a plasmin inhibitor, is reported to improve melasma when injected locally. However, the effects of oral and topical TXA on melasma have not been well studied and the underlying mechanism remains unclear. OBJECTIVES: To elucidate the effects of oral and topical TXA on melasma. METHODS: A clinical study was conducted with 25 women for 8 weeks from March to July 2010. Volunteers were instructed to take two TXA tablets three times a day and apply a TXA topical agent twice a day for 8 weeks. Skin pigmentation and erythema was measured using a Mexameter(®) during each visit and skin biopsies were collected from eight subjects before and 8 weeks after treatment. Fontana-Masson, anti-CD31, antitryptase and antitype IV collagen staining was performed. RESULTS: Twenty-two subjects completed the study and no serious adverse events occurred during the study period. The mean lesional melanin index (MI) scores decreased significantly. Interestingly, the MI scores for the perilesional skin increased. The erythema index scores of lesional and perilesional skin also showed a similar pattern. Histological analysis showed significant reduction of epidermal pigmentation, vessel numbers and mast cell counts. Type IV collagen staining was not observed in all specimens. CONCLUSION: TXA decreased epidermal pigmentation associated with melasma and also reversed melasma-related dermal changes, such as vessel number and increased numbers of mast cells.

Increasing evidence on the impact of the different wavelengths of sunlight on the skin demonstrates the need for tailored recommendations of sunscreen according to skin phototype and dermatoses, which is now possible due to advances in the filters and formulations of sunscreens. A selective literature search was performed by an international expert panel, focusing on the type of sunscreen to recommend for photoaging, skin cancers, photodermatoses, pigmentary disorders and skin inflammatory disorders. Protection against ultraviolet (UV)B is especially important for light skin as there is a high risk of sunburn, DNA damage and skin cancers. Darker skin may be naturally better protected against UVB but is more prone to hyperpigmentation induced by visible light (VL) and UVA. Protection against UVA, VL and infrared A can be helpful for all skin phototypes as they penetrate deeply and cause photoaging. Long-wave UVA1 plays a critical role in pigmentation, photoaging, skin cancer, DNA damage and photodermatoses. Adapting the formulation and texture of the sunscreen to the type of skin and dermatoses is also essential. Practical recommendations on the type of sunscreen to prescribe are provided to support the clinician in daily practice.

BACKGROUND: The pathogenesis of melasma has not yet been clearly demonstrated. We tried to determine whether the stem cell factor (SCF) and its receptor c-kit are involved in the mechanism of hyperpigmentation of melasma because this factor is highly implicated in the stimulation of melanocyte function in vitro and in vivo. OBJECTIVES: The present study was conducted to investigate the expression of SCF and c-kit on the lesions of melasma compared with nonlesional skin. PATIENTS/METHODS: Skin samples were obtained from lesional and nonlesional facial skin of 60 Korean women with melasma. Immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis was performed to determine the expression of SCF and c-kit in melasma. RESULTS: The expression of SCF was significantly increased at the lesional dermis compared with nonlesional dermis. However, there was no significant difference in the expression of SCF in lesional and nonlesional epidermis. The expression of c-kit was significantly increased at lesional epidermis compared with nonlesional skin. RT-PCR of SCF and c-kit mRNAs demonstrated increased expression of both types of transcripts in the lesional skin compared with nonlesional skin. CONCLUSIONS: These results suggest that the increased expression of SCF in the dermis and of c-kit in the epidermis play an important role in the mechanism of hyperpigmentation in melasma.