TAILIEUCHUNG - Chapter 168. Infections Due to Mycoplasmas

Mycoplasmas, the smallest free-living organisms known, are prokaryotes that are bounded only by a plasma membrane. Their lack of a cell wall is associated with cellular pleomorphism and resistance to cell wall–active antimicrobial agents, such as penicillins and cephalosporins. The organisms' small genome limits biosynthesis and explains the difficulties encountered with in vitro cultivation. Mycoplasmas typically colonize mucosal surfaces of the respiratory and urogenital tracts of many animal species. Of the 17 species of mycoplasmas recovered from humans, most are commensals. . | Chapter 168. Infections Due to Mycoplasmas Mycoplasmas the smallest free-living organisms known are prokaryotes that are bounded only by a plasma membrane. Their lack of a cell wall is associated with cellular pleomorphism and resistance to cell wall-active antimicrobial agents such as penicillins and cephalosporins. The organisms small genome limits biosynthesis and explains the difficulties encountered with in vitro cultivation. Mycoplasmas typically colonize mucosal surfaces of the respiratory and urogenital tracts of many animal species. Of the 17 species of mycoplasmas recovered from humans most are commensals. Mycoplasma pneumoniae causes upper and lower respiratory tract infections. M. genitalium and ureaplasmas are established causes of urethritis and have been implicated in other genital conditions. M. hominis and ureaplasmas are part of the complex microbial flora of bacterial vaginosis Chap. 124 . The two biovars of Ureaplasma previously classified together as U. urealyticum have recently been separated into two species U. parvum and U. urealyticum. Mechanisms of Pathogenicity Adherence of mycoplasmas to the surface of the host cell is necessary for colonization and infection. Some pathogenic mycoplasmas are flaskshaped with specialized tips that enhance adherence. M. pneumoniae adheres via a network of interactive adhesins and accessory proteins and produces hydrogen peroxide which may cause injury to host cells. M. hominis metabolizes arginine with the production of potentially cytotoxic amounts of ammonia. Ureaplasmas have been placed in a separate genus because of their unique urease activity the metabolism of urea also produces ammonia. M. pneumoniae may evoke IgM autoantibodies that agglutinate human erythrocytes at 4 C. These cold agglutinins can cause anemia and other complications. Mycoplasma pneumoniae Epidemiology M. pneumoniae causes upper and lower respiratory tract symptoms in all age groups with the highest attack rates in 5- to .

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