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MycoplasmasMycoplasmas

A

group

of

the

smallest

organisms

that

can

be

freliving

in

nature,

Pass

bacterial

filter

and

also

grow

on

laboratormedia.

More

than

80

species,

belong

toMycoplasmatales

of

Mollicute.

3

families

can

bedivided:

Mycoplasmataceae

(require

external

cholesteroduring

growth,

contain

Mycoplasma

and

Ureplasmatwo

genera);

Acholeplasmataceae

(need

not

external

cholesteduring

growth);Spiroplasmataceae(canform

spiral

structure)BIOLOGICAL

FEATURESMotility:

Motile

by

possible

release

andreattachment

of

terminal

cell

organelle;

noflagella

present;

possess

a

proteinattachment

factor

termed

P1

that

interactswith

a

specific

cellular

receptor

and

allowsadherence

to

respiratory

epithelium.Respiration-Fermentation:

Aerobes-anaerobes.Culture

Most

aerobic;

require

10%-20%

human

oranimal

serum

added

to

basic

nutrientmedia

except

Acholeplasma;

typical

colonyshow

fried

egg

apperance.Many

species

are

part

of

the

normal

flora

These

organisms

are

a

frequent

cell

culturecontaminantThe

organisms

have

limited

biosynthetic

abilitthey

require

cholesterol

for

their

cell

membranand

can

generate

energy

via

the

breakdown

ofarginineUreaplasma

requires

urea

to

produce

anelectrochemical

gradient;

urea

is

converted

toammonia

to

produce

ATP.GENETICS

These

bacteria

have

the

smallestgenome

of

any

prokaryote

(

about

20%that

of

E.

coli)

and

the

lowest

G

Ccontent

(about

24%).ResistanceSensitive

to

osmotic

presssure

resistant

to

thallium

acetate醋酸亚铊in

a

concentration

of1:10000

which

can

inhibitbacteriaTransmissionM.

pneumoniae

is

spreadby

closecontact

via

aerosolized

droplets

andthus

is

most

easily

spread

in

confinedpopulations

(e.g.,

families,

schools,barracks).PATHOGENESISAdherence

factors

-

The

P1

Adhesin

localizesat

tips

of

the

bacterial

cells

and

binds

tosialic

acid

residues

on

host

epithelial

cellsnature

of

the

adhesins

in

the

other

specieshas

not

been

established.

Colonization

of

therespiratory

tract

by

M.

pneumoniae

results

inthe

cessation

of

ciliary

movement.Toxic

Metabolic

Products·

Immunopathogenesis:

most

children

areinfected

from

2

-

5

years

of

age

butdisease

is

most

common

in

children

5-15

yearsof

age.M.pneumoniaeprimary

atypicalpneumonia.Incubation:

1-3

weeksThis

disease

can

rangefrom

subclinical

tobronchopneumonia,

oftenwith

a

gradual

onset

andmild

to

moderate

severity.

Along

convalescence

(4-6weeks)

and

severalpossible

complications(CNS,

cardiac)

follow

acutedisease.Clinical

FindingsU.

urealyticum,

M.hominis,

M.genitaliumare

responsible

for

one

form

ofnongonococcal

urethritis.M.

hominis

is

associated

withpyelonephritis,

pelvic

inflammatorydisease

and

post-partum

fevers.HOST

DEFENSES·

Host

defenses

are

not

wellcharacterized

but

probably

involve

bothhumoral

and

cell

mediated

responses.EPIDEMIOLOGYMycoplasma

affect

a

specific

age

distribution(5-9

year

olds)

and

represent

8-15%

of

allpneumonias

in

school

age

children.Disease

occurs

worldwide,

is

endemic

insome

areas

and

is

spread

by

close

personalcontact

(schools,

families).U.

urealyticum

is

sexually

acquired.Antibody

titers

indifferent

agegroups.

Anti-mycoplasmapneumoniaeantibodies

indicatepneumonia

causedby

this

organismis

highest

in

the5-15

year

agegroupAcquired

Pneumonia

Caused

byMycoplasma

pneumoniaeMicrobiological

diagnosis

Specimens:throatswab,sputum,

genitalsecretion,

etc.Microscopy

-

This

is

not

particularly

usefulbecause

of

the

absence

of

a

cellwallbut

it

canbe

helpful

in

eliminatingotherpossiblepathogens.Culture-

Sputum(usuallyscant)

or

throatwashings

mustbesentto

the

laboratory

inspecialtransport

medium.

It

maytake2

-3

weeks

to

get

apositiveidentification.Cultureisessential

for

adefinitive

diagnosis.Complementfixation

testCold

agglutinins

-

Approximately

34%

-

68%

ofpatientswith

M.

pneumoniae

infectiondevelop

coldagglutinins.ELISA

-

There

is

a

new

ELISA

for

IgM

thathasbeen

used

for

diagnosis

of

acute

infection.CONTROL

Sanitary:

Avoidance

of

contacts,

ifpossible.

Immunological:

No

single

vaccine

isavailable.

Natural

resistance

followsinfection.

Chemotherapeutic:

Tetracycline,erythromycin

or

chloramphenicol

areeffective.Mycoplasma

and

L

Form

BacteriaMYCOPLASMAL-FORM

BACTERIANo

genetic

relationship

withbacteriaRelate

to

their

parent

bacteria

,sometimes

can

revertCholesterol

for

their

cellmembraneStable

in

ordinary

mediumNo

cholesterol

for

their

c