tailieunhanh - Chapter 130. Streptococcal and Enterococcal Infections (Part 1)

Harrison's Internal Medicine Chapter 130. Streptococcal and Enterococcal Infections Streptococcal and Enterococcal Infections: Introduction Many varieties of streptococci are found as part of the normal flora colonizing the human respiratory, gastrointestinal, and genitourinary tracts. Several species are important causes of human disease. Group A Streptococcus (GAS, S. pyogenes) is responsible for streptococcal pharyngitis, one of the most common bacterial infections of school-age children, and for the postinfectious syndromes of acute rheumatic fever (ARF) and poststreptococcal glomerulonephritis (PSGN). Group B Streptococcus (GBS, S. agalactiae) is the leading cause of bacterial sepsis and meningitis in newborns and a major cause of endometritis and fever. | Chapter 130. Streptococcal and Enterococcal Infections Part 1 Harrison s Internal Medicine Chapter 130. Streptococcal and Enterococcal Infections Streptococcal and Enterococcal Infections Introduction Many varieties of streptococci are found as part of the normal flora colonizing the human respiratory gastrointestinal and genitourinary tracts. Several species are important causes of human disease. Group A Streptococcus GAS S. pyogenes is responsible for streptococcal pharyngitis one of the most common bacterial infections of school-age children and for the postinfectious syndromes of acute rheumatic fever ARF and poststreptococcal glomerulonephritis PSGN . Group B Streptococcus GBS S. agalactiae is the leading cause of bacterial sepsis and meningitis in newborns and a major cause of endometritis and fever in parturient women. Enterococci are important causes of urinary tract infection nosocomial bacteremia and endocarditis. Viridans streptococci are the most common cause of bacterial endocarditis. Streptococci are gram-positive spherical to ovoid bacteria that characteristically form chains when grown in liquid media. Most streptococci that cause human infections are facultative anaerobes although some are strict anaerobes. Streptococci are relatively fastidious organisms requiring enriched media for growth in the laboratory. Clinicians and clinical microbiologists identify streptococci by several classification systems including hemolytic pattern Lancefield group species name and common or trivial name. Many streptococci associated with human infection produce a zone of complete P hemolysis around the bacterial colony when cultured on blood agar. The P-hemolytic streptococci can be classified by the Lancefield system a serologic grouping based on the reaction of specific antisera with bacterial cell-wall carbohydrate antigens. With rare exceptions organisms belonging to Lancefield groups A B C and G are all P-hemolytic and each is associated with characteristic .