Microbiology Legend Cycle 29 Organims 6 Mycoplasma

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MICROBIOLOGY LEGEND

CYCLE 29 ORGANIMS 6

MYCOPLASMA

Mycoplasma, the smallest organisms capable of self-replication was first isolated by Roux and Nocard from cattle with contagious bovine pleuropneumonia in 1898. Subsequent isolates from other sources were termed pleuro-pneumonia-like organisms. Members of the class Mollicutes (Latin: mollis means soft and cutin skin), they are characterised by their absence of a cell wall and are therefore refractory to treatment with β- lactam class antibiotics. All Mycoplasma require lipid precursors for plasma membrane synthesis. Mycoplasma is a species of gram-negative bacteria that is a common inhabitant of the human oropharynx and also a cell culture contaminant. It is usually non-pathogenic but it can cause infections in leukemic or immunosuppressed patients.

Like viruses they pass through filters that retain bacteria, but except for the cell wall, possess all other cellular constituents of bacteria. Unlike cell-wall deficient bacteria, they fail to revert to bacteria when cultured under appropriate conditions. Despite superficial cultural similarities, the Mycoplasma comprise a heterogenous group of micro-organisms differing from each other in DNA composition, metabolic reactions, nutritional requirements, antigenic composition and host specie specificity.

They are divided into 3 taxonomic families: The Mycoplasmataceae and Spiroplasmataceae, both requiring cholesterol for growth and non-cholesterol-dependent Acholeplasmataceae. Included in the family Mycoplasmataceae are the Mycoplasma species which do not hydrolyse urea and the genus Ureaplasma, strains of which produce abundant quantities of urease.

There are 51 recognised species in the genus Mycoplasma. 10 Mycoplasma species have been detected in the clinical laboratory. Mycoplasma pneumonia is the cause of primary atypical pneumonia. Mycoplasma salivarian and Mycoplasma orale are common inhabitants of the oropharynx, particularly in individuals with poor oral hygiene, whereas Mycoplasma buccale is a less frequent oropharyngeal colonizer. Mycoplasma is ubiquitous in nature as saprophytes and/or parasites of plants and animals. Mycoplasma species also cause contamination of cell cultures, interfering with their metabolic processes and slowing their rate of growth.

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Mycoplasma infection in a cell culture Mycoplasma orale incubation for seven days on Mycoplasma Experience solid Mycoplasma medium

The Mycoplasma appears to be host-specific, being communicable and potentially pathogenic only within a single host species. Mycoplasma has been cultivated from human mucous membranes and tissues, particularly from the genital, urinary and respiratory tracts. Mycoplasma is part of the normal flora of the mouth and can be grown from normal saliva, oral mucous membranes, sputum or tonsillar tissue. M. salivarium, M. orale and other Mycoplasma can be recovered from the oral cavities of many healthy adults, but an association with clinical disease is uncertain. M. hominis is found in the oropharynx of less than 5% of adults. M pneumonia in the oropharynx is generally associated with disease. Some Mycoplasma are inhabitants of the genitourinary tract, particularly in females. In both men and women, genital carriage of Mycoplasma is directly related to the number of lifetime sex partners.

Diagnostic Laboratory Tests  Specimens – consists of throat swabs, sputum, inflammatory exudates and respiratory, urethral or genital secretions.  Microscopic examination – direct examination of a specimen for Mycoplasma is useless.  Cultures – the material is inoculated onto special solid media and incubated for 3-10 days at 37°C

with 5% CO2 (under micro-aerophilic conditions), or in special broth and incubated aerobically. One or two transfers of media may be necessary before growth appears that is suitable for microscopic examination by staining or immuno-fluorescence. Colonies may have a “fried egg” appearance on agar.  Serology – antibodies develop in humans infected with Mycoplasma and can be demonstrated by several methods.

Treatment Many strains of Mycoplasma are inhibited by a variety of antimicrobial drugs, but most strains are resistant to penicillin, cephalosporin and vancomycin. Tetracycline and erythromycin are effective both in vitro and in vivo and are, at present, the drugs of choice in mycoplasmal pneumonia.

References 1. http://en.wikipedia.org/wiki/Mycoplasma 2. Clinical laboratory medicine, Volume 2001, Kenneth D. McClatchey 3. Medical Microbiology 20th edition, Brooks, Butel & Ornston

Questions 1. Discuss the morphological characteristics of the Mycoplasma. 2. Discuss the pathophysiology of Mycoplasma. 3. Discuss the diagnostic laboratory tests that can be used to identify this organism.

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