Download Cell wall deficient bacteria

Mycoplasmas and Cell Wall
Defective Bacteria
Mycoplasmas

smallest known free-living organisms

Due to their smallest size, originally
thought to be viruses, but differ in
i) Contain both RNA and DNA
 ii) Can synthesize proteins by their own
enzymes
 iii) Can multiply on their own

Classification
For many years thought to be viruses
 Nowdays classified as atypical bacteria because
they lack the cell wall
 At least 15 spp are thouhgt to be of human
origin, only 4 spp are of medical importance

Spp.
Disease
M.pneumoniae
. atypical pnuemoina
M.hominis
. postpartum fever
. pelvic inflamatory diseases
Ureaplasma urealyticum
. non gonococcal urethritis
. lung diseases in premature
infants of low birth weight (LBW)
M.genitalium
. Urethral infections
General characterisitcs
Smallest organisms that can be free living 125250 nm in size

Highly pleumorphic because of lack of rigid cell
wall

Completely
resistant
to
penicillin
cephalosporins because of lack of cell wall

and
Can reproduce in cell free media, on agar
produce colonies of fried egg appearance


Have affinity for mammalian cell membrane
Morphology

Stain poorly with bacteria stain (gram stain), but
stain well with Giemsa stain

They lack cell wall so:
Highly pleomprphic
Not stained with gram stain
Can’t be killed by penicillin

On Giemsa stain they appear as tiny
pleomorphic cocci, short rods, short spirals, and
sometimes as hollow ring forms. Their diameter
ranges from 0.15 µ to 0.30 µ
Growth and Cultural Characteristics

Cannot be studied by usual bacteriologic
methods because of the small size of their
colonies and delicacy due to lack of rigid cell wall

Facultative anaerobes except for M.pneumoniae
that are strict aerobe

Grows better on H2 and N2 with 10% CO2

Most grow at 370C. Generation time slow, 1-6
hrs

Use glucose as energy source

Many strains grow in heart infusion
peptone broth with 2% agar, pH 7.8 and
animal serum or 30% ascitic fluid added

Mycoplsama contain sterols in their cell
membrane, so their growth requires the
addition of serum or cholestrol to the
medium to produce sterols, Ureaplasma
reqiure urea

After 2-6 days of incubation, produce
small colonies that have freid- egg
appearance
Pathogenesis

Pathogenic Mycoplasma have polar tips
structures-mediate adherence to host cells

Direct cytotoxicity through generation of
hydrogen
peroxide
and
superoxide
radicals

Cell lysis-by antigen antibody reactions/
chemotaxis and action of mononuclear
cellls
Medical importance

Part of normal flora of mouth, genitourinary
tract especially females

i) Asymptomatic
Many infections
asymptomatic.
due
to
Mycoplsmas
are
Medical importance

ii) Mycopasma pneumoniae and
pneumonia (walking pneumonia)
atypical
M.pneumoniae is a prominant cause of a typical
pneumonia especially in persons 5-20 years of
age
 transmitted by infected respiratory secretions
 Incubation period 1-3 wks
 Generally mild disease, but can range from
asypmtomatic infection-serious pneumonitis
Complications-neorologic, hemolytic anaemia, skin
lesions

Medical importance

iii) Mycoplsma hominis

uterine tube infections (salpingitis and
tubo-ovarian abscesses) 10%


post abortal or post partum fever(10%)
Occasionally arthritis
Medical importance

IV) Ureaplasma urealyticum

Common in female genital tract

Attributed to some cases
gonococcal urethritis in men

Associated with lung disease in premature
LBW infants

Weak evidence correlates U.urealyticum to
infertility
of
non
Medical importance

V) Mycoplasma genitalium

Attributed to some cases of non acute and
chronic non-gonococcal urethritis in men

In females, M.genitalium has been
associated with cervicitis, endometritis
salpingitis and infertility
Diagnosis
Specimen include,
blood,sputum,nasopharyngial or urethral
exudates
Direct staining is of limited use. For direct
detection in clinical specimen :
. IF
. PCR
Culture is difficult and time consuming
Diagnosis
Serology (most widely used)
Detection of IgM or rising titer of IgG by ELISA or
CFT (acute and convalescent phase sera are
necessary to demonstrate a fourfold rise in the CF
antibodies)
Cold agglutinins at a titer of 1/128 or higher =
acute infection (Heamoaglutination)
Cold
agglutinins?
Positive in?
Specific?
o Certain antigens on human red blood cells are identical to
Mycplasma pneumonia antigens. So, antibodies to
mycoplasma cross react with human red blood cells causing
them to agglutinate at 4 degree but not at 37 degree
o Positive in 50 % of cases
o Not specific. Positive in other diseases like viral infections &
malaria
Treatment

Lack of cell wall make organisms resitant to
antimicrobials acting on cell wall e.g penicillines,
cephalosporins and vancomycin

Sensitive to antimicrobials that inhibit protein
synthesis e.g. tetracyline, erythromicin ,
azithromycin and chloramphenical
Other Cell wall- defective bacteria
(L-forms bacteria)

First isolated in 1935 by Emmy Klienburger who named them Lforms (Lister Institute in London where she was working)

Don’t occur naturaly and not genetically related to mycoplasma

Usually result from
Spontaneous mutation
Effects of chemicals
Enzymes (lysozymes)
Antibiotic treatment
Other Cell wall- defective bacteria
(L-forms bacteria)

Two types:
Protoplast (stable L-forms) usually derived from gram
positive bacteria in which the cell wall is completely
destroyed.They can’t be reverted to their original morphology.
Spheroplast (unstable L-forms) usually derived from gram
negative bacteria in which cell wall is not completely destroyed;
they retain some outer membrane material and can revert to
their original morphology.
Their role in disease is uncertain; may be responsible for the
recurance of the infection after antimicrobial treatment.
L Forms vs Mycoplasma

contain a rigid cell wall, at least at one
stage of their life cycle

no sterols in their cytoplasmic membrane