Category:Mycoplasmas

Overview

• Pathogens belong to the Mycoplasma and Ureaplasma genera
• Cause many diseases especially respiratory diseases of farm animals including contagious bovine pleuropneumonia
• Can be involved in mastitis and conjunctivitis in cattle
• Implicated in respiratory and urinary tract diseases in dogs and cats
• Non-pathogenic mycoplasmas present in the rumen
• Live on mucous membranes of oronasal cavity, conjunctiva and intestines
• Stress factors and concurrent disease may predispose to tissue invasion
• Usually host-specific
• Limited survival in the environment

Characteristics

• Smallest free-living prokaryotic organism
• Pleomorphic organisms
• Have no peptidoglycan cell wall
• Susceptible to dessication, heat and disinfectants
• Require enriched media containing animal protein, sterol and a source of DNA for growth
• Colonies have a fried egg appearance
• Most are facultative anaerobes

Pathogenesis and pathogenicity

• Mycoplasmas adhere to host cells and produce toxins
• Some adhere to neutrophils and macrophages and prevent phagocytosis
• Mycoplasmas induce proliferation of macrophages and [[monocytes]], and release of cytokines such as TNF and interleukins
• Cause damage to cilia in the respiratory tract leading to pneumonia
• Molecular mimicry allows some mycoplasmas to avoid the host immune response and may initiate immune-mediated disease

Diagnosis

• Samples can be tested for the presence of mycoplasmas by fluorescent antibody techniques, peroxidase techniques and PCR
• Biochemical profiles such as urease production can be used for identification
• Ureaplasmas produce urease, whereas Mycoplasmas do not metabolise urea
• Serolgy is required for specific identification including complement fixation tests, ELISA, agglutination tests and haemagglutination-inhibition tests
• Growth inhibition tests using specific antisera can be used as well as fluorescent antibody tests

Other mycoplasmas

• M. bovis, M. dispar and Ureaplasma can be involved in Enzootic pneumonia of calves
• M. ovipneumoniae is implicated in enzootic pneumonia of lambs
• M. felis may be involved in mild respiratory infection
• Mycoplasmas may cause lymphocytic chronic inflammation (peribronchiolar and perialveolar cuffing)
• Cause peritonitis in sheep, peritonitis in goats and peritonitis in pigs