Isolation and Identification of Streptococci and Staphylococci

Isolation and Identification of Streptococci and Staphylococci

Introduction

Group A streptococcus (Streptococcus pyogenes) is an important organism of bacterial infections in both adults and children throughout the world. Impetigo is the most common bacterial skin infection in children. All cases of bullous impetigo are caused by Staphylococcus aureus and non-bullous impetigo are usually due to group A ß-hemolytic Streptococci, although recently in Japan group A ß-hemolytic streptococci andS. aureus are often simultaneously detected from many cases of non-bullous impetigo (Colford et.al 2005). The purpose of the present study is to examine how often streptococcal strains are detected from various infectious skin diseases, which strains are dominant in number on skin lesions of streptococcal impetigo, and the susceptibility of each isolate to various antimicrobial agents.

Materials and methods

Bacterial strains

Streptococci were isolated from various skin lesions at the Department of Dermatology, Okayama University Medical School, between March, 1994, and June, 1998 using Mitis Salivarius agar plates (Difco Laboratories, Detroit, MI, USA) and sheep blood agar plates (Nissui Pharmaceutical, Tokyo, Japan). Plates were incubated for 24 or 48 h at 37°C in air. Streptococcal strains were identified by positive growth on Mitis Salivarius agar plates, Gram staining, negative catalase test, property of hemolysis in sheep blood agar plates, and an api strep 20 (bioMérieux S.A., France). Bacterial colony showing ß-hemolytic streptococci was serologically group-typed (A, B, C or G) using the latex agglutination method (Denka Seiken, Tokyo, Japan). Some strains of S. pyogenes were classified by T-agglutination (Denka Seiken (Colford et.al 2005).

Streptococcal strains were classified into two groups of infective origin and Colonization origin. The strains of infective origin were isolated from infectious skin diseases as follows: cellulitis, abscess, Toe web infection, felon, paronychia, impetigo, blistering diatal dactylitis, and Secondary infections that had distinct inflammatory signs. The strains of colonization origin were isolated from skin diseases that had no distinct inflammatory signs (Kataja 2005). The strains other than streptococci grown on blood agar plates were simultaneously identified by routine methods.

Susceptibility tests

The minimum inhibitory concentrations (MICs) of ampicillin (ABPC; Meiji Seika, Tokyo), Cefditoren (CDTR; Meiji Seika), Cefdinir (CFDN; Fujisawa Pharmaceutical, Osaka, Japan), imipenem (IPM; Banyu Pharmaceutical, Tokyo), Minocycline (MINO; Lederly, Tokyo), Clindamycin (CLDM; Sigma, St. Louis, MO, USA), erythromycin (EM; Sionogi Pharmaceutical, Osaka), Gentamicin (GM; Sigma), Fusidic acid (FA; Sankyo, Tokyo), Ofloxacin (OFLX; Daiichi Pharmaceutical, Tokyo), Tosufloxacin (TFLX; Toyama, Tokyo), and Vancomycin (VCM; Eli Lilly Japan, Kobe, Japan) against 35 ß-hemolytic streptococci and 23 S. aureusstrains isolated from skin infectious diseases were determined by the broth microdilution method according to the guidelines of Japanese Society for Chemotherapy. Cation-supplemented Mueller-Hinton broth (Difco) was used as the growth medium, and 5% defibrinated horse blood (Japan Ram, Fukayasu, Hiroshima, Japan) was added as the growth medium in cases of streptococcal strains (Maruyama et.al 2001).

Results

Streptococci isolated from skin lesions

Seventy-three streptococcal strains isolated from various skin lesions between March, 1994, and June, 1998, are listed in Table 1 see appendices. Forty-one strains were of infective origin and 32 strains of colonization origin (Nishijima et.al 2004).

Streptococcal strains isolated from infectious skin diseases are listed in Table ...