1104/10/23

Mycoplasma

:Author:Gunjan Mehta,

Assistant Professor,Dept. of Biotechnology,

Shree M. & N. Virani Science College, Kalawad Road, Rajkot- 360005

:Author:Gunjan Mehta,

Assistant Professor,Dept. of Biotechnology,

Shree M. & N. Virani Science College, Kalawad Road, Rajkot- 360005

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OutlineOutline

Structure Classification Multiplication Clinical manifestations Epidemiology Diagnosis Control

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Pleuropneumonia organism

The mycoplasmas are essentially bacteria lacking a rigid cell wall during their entire life cycle, although they are also much smaller than bacteria. The first organism of this type was associated with pleuropneumonia of cattle, and was originally called the pleuropneumonia organism (PPO).

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General Characteristics smallest known free-living organisms. Because of the absence of cell walls, they do

not stain with the Gram stain, and they are more pleomorphic and plastic than eubacteria.

Giemsa stain– they appear as tiny pleomorphic cocci, short rods,

short spirals, and sometimes as hollow ring forms. Their diameter ranges from 0.15 u to 0.30 u.

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Mycoplasma very small (0.2 x 0.8 um)

– pass through a 0.45 um filter No Cell wall: plasma membrane only

– resistant to antibiotics that interfere with the integrity of cell wall; penicillins, cephalosporins, vancomycin, bacitracin

susceptible to tetracycline, erythromycin

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Structure The cell is enclosed by a limiting membrane

which is more similar to that of animal cells than that of bacterial cells because of sterols present in the membrane.

The cytoplasm contains ribosomes,but lacks mesosomes. There is no nuclear membrane.

In some strains, amorphous material on the outer surface of the membrane suggests the existence of a capsule.

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Mycoplasma requires sterols for growth, can be

grown on laboratory media most are facultatively anaerobic

– Exception M. pneumoniae replication controversial

– replication time 1-6 hours

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Mycoplasma pneumoniae AKA Eaton’s agent

– aerobic but very slow growing extracellular pathogen: attaches to

respiratory epithelium by an attachment factor called P1

interacts with a glycoprotein receptor on the epithelial cell surface

ciliostasis is followed by epithelial cell destruction

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Clinical Syndrome Pneumonia

– walking pneumonia frequently confused with virus infection

– primary atypical– clinical

Tracheobronchitis Pharyngitis

– differential diagnosis from Strep throat

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Children most susceptible

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No Seasonal Incidence

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Urethritis 1/2 of urethral infections not

caused by Chlamydia or N. gonorrhoeae.

Caused by– Mycoplasma hominus– Ureaplasma

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Infection of Tracheal ring Organ culture

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Destruction of host due to release of hydrogen

peroxide and superoxide anion.

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Laboratory diagnosis Culture:

– fried egg colonies on medium containing sterols

– Most mycoplasmas require a rich medium containing a sterol and serum proteins for growth.

Serology:– Complement Fixation test,

Hemagglutination

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Laboratory Diagnosis Culture Mycoplasma from sputum,

mucous membrane swabbings or other specimens

direct inoculation into liquid or solid media containing serum, yeast extract and penicillin to inhibit contaminating bacteria.

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Cultural Characteristics Despite the lack of a cell wall, they do not

require a medium of very high osmotic pressure.

On solid media, they form minute, transparent colonies. – looks like a fried egg. The different strains vary

in their growth rate may take from two days to several weeks to

form a colony.

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Fried Egg Colonies

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Fried Egg Colonies Stain intensely with

neutral red or tetrazolium or methylene blue.

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serology: complement fixation

on acute and convalescent serum. patient’s serum heated to 56C to eliminate

complement combine patient’s serum and known

Mycoplasma antigen in presence of added complement. Mix.

Incubate - add indicator system– Red cells and anti-red cell antibody– hemolysis occurs if complement is unused.

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Hemagglutination Cold agglutinins to human O

erythrocytes. hemabsorption & B-hemolysis of

guinea pig red blood cells.

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Identification conclusively identified by staining

its colonies with fluorescein-labelled antibody.

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M. pneumoniae Nucleic Acid Probes

specific recombinants to oligonucleotide sequences that are only found in Mycoplasma pneumoniae.

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L Forms Some bacteria readily give rise

spontaneously to variants that can replicate in the form of small filterable protoplasmic elements with defective or absent cell walls.

These organisms, called L-forms, can also be formed by many species when cell wall synthesis is impaired by antibiotic treatment or high salt concentration.

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L Forms vs Mycoplasma contain a rigid cell wall, at least at

one stage of their life cycle no sterols in their cytoplasmic

membrane.

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Pleuropneumonia-like organisms

Several organisms with similar morphological characteristics and cultural properties have been isolated. These are commonly referred to as pleuropneumonia-like organisms or PPLO. A certain group of mycoplasmas produce extremely tiny colonies on agar plates, and are called the T-strains.

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Metabolism The parasitic mycoplasmas have

truncated respiratory systems, lacking quinones and cytochromes.

Another indication for the simplicity of the electron transport chain is the finding that the reduced nicotinamide adenine dinucleotide (NADH) oxidase activity is cytoplasmic.

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Arginine dihydrolase Pathway pathway Complex electron transport chains

are usually membrane bound, since they depend on the spatial organization of their components. Ruling out oxidative phosphorylation as an ATP-generating system leaves only two proven ways of ATP generation, both based on substrate level phosphorylation. The major source for ATP is the arginine dihydrolase pathway.

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Metabolism A few species derive their energy from the

degradation of glucose or the hydrolysis of urea.

All species synthesize DNA, RNA, lipids and proteins.

Not known if they can synthesize amino acids. Those species that require sterols incorporate

these sterols (mainly cholesterol) into the cell membrane up to concentrations of 65%.

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Multiplication In the absence of a rigid cell wall, the

pattern of replication is quite different from that of typical bacteria, whose division starts with the formation of a well-defined septum.

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Life cycle- PPLO Mycoplasma

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Fragmentation of filaments

mechanism of division in mycoplasmas is controversial, sequential microscopic observation suggests that new elementary particles arise by fragmentation of filamentous cells containing several discrete DNA components.

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Thank you!!