Mycoplasmas are the smallest free-living organisms that lack cell walls. They colonize humans and can cause diseases. The two medically important genera that infect humans are Mycoplasma and Ureaplasma. Mycoplasma pneumoniae is a major cause of atypical pneumonia while Ureaplasma urealyticum and Mycoplasma hominis can cause nongonococcal urethritis. Mycoplasmas are difficult to culture and require complex media with sterols. They are treated with antibiotics like tetracycline and erythromycin.

1. Mycoplasmas

2. Classification
• Order Mycoplasmatales
• Family Mycoplasmataceae;
2 medically important genera:
•Mycoplasma
•Ureoplasma

3. 200 species; 16 colonize humans and 5
associated with diseases
• Mycoplasma
M. pneumoniae
M. hominis
M. genitalium
M. fermentans
• Ureaplasma
U. urealyticum

4. Morphology and Physiology
• The smallest free-living organisms
• Pass through some filters used to
remove bacteria
• Lack of a cell wall
• Multiple shapes including round, pear
shaped and even filamentous
-------- highly pleomorphic, resistant to
penicillin, cephalosporins, vancomycin,
sensitive to tetracycline, erythromycin.

5. • Require complex media
• Require sterols for growth
and for membrane synthesis,
use glucose as a source of
energy (ureaplasmas require
urea)
----cell membrane contains sterols -
rigid
• Grow slowly (3 weeks) by
binary fission and produce
"fried egg" or “T strain” (tiny
strain) colonies on agar
plates

6. Small, fried-egg-like colonies (except
M. pneumoniae)

7. Structure
• Three layer membranes
Outer and inner: proteins and saccharide
Middle: 1/3 cholesterol
• dsDNA, has ribosomes, no endoplasmic
reticulum (ER)

8. Mycoplasmas Bacterial L- form
1.Genetically unrelated to bacteria Related to the original bacteria
2.Steroids Steroid-free
3.Stablein general medium Hypertonic medium
4.Colonies small (0.1-0.3mm) Larger colonies (0.5-1.0mm)
5. Low turbidity turbidity
The differences between Mycoplasmas and Bacterial L- form

9. Pathogenesis
Adherence factors
• Adherence proteins are one of the major
virulence factors
• Adhesin localizes at tips of the cells and
binds to sialic acid residues on host
epithelial cells

10. Specialized tip organelle

11. Extracellular pathogen;
infect and colonize
mucous membrane; do
not invade other tissues.
Pathogenesis
M. pneumoniae adheres to
sialated glycoprotein receptor
at the base of cilia (and on
surface of RBC) by means of
P1 antigen.

12. M. pneumoniaeM. pneumoniae adherenceadherence
Tip organelle contains large
amounts of P1 adhesin and
other tip adhesins necessary for
adherence to respiratory
epithelium.
Other adhesins also identified

13. PathogenesisPathogenesis
Toxic Metabolic Products
• The intimate association provides an
environment in which toxic metabolic
products accumulate and damage host
tissues
• Products of metabolism : hydrogen
peroxide and superoxide -- oxidize host
lipids
• Inhibit host cell catalase

14. ? The mechanism of cellular damage is
unknown (produce peroxidase and
hemolyze RBC?)
• Causes ciliostasis, destroy cilia and ciliated
epithelial cells; breakdown clearance
activity, lead to LRT infection and persistent
cough.
PathogenesisPathogenesis

15. Pathogenesis
Immunopathogenesis
• M. pneumoniae is a superantigen
Activate macrophages and stimulate
cytokine production and lymphocyte
activation ;
can attract inflammatory cells and
induce cytokine secretion (TNF, IL-1, IL-
6).
• Host factors contribute to pathogenesis

16. Organism Disease
M. pneumoniae
Upper respiratory tract disease,
Tracheobronchitis, atypical pneumonia
M. hominis
Pyelonephritis, pelvic inflammatory
disease, postpartum fever
M. genitalium Nongonococcl urethritis (NGU)
U. urealyticum Nongonococcl urethritis (NGU)

17. M. Pneumoniae
• Need 10-20% Serum to culture in pH 7.8-8.0
• Pathogenesis: P1 protein, capsule and saccharide
• Spread by nasal secretions in close contact via
aerosolized[e 'r s la z] droplets amongə ɒ ɒ ɪ
classmates or family members
• Worldwide disease with no seasonal incidence
• Most common in school-age children (5-10y) and
young adults , but all age groups are susceptible

18. • Cause tracheobronchitis
• Cause “primary atypical pneumonia”
•long duration
• Antibodies play a role in controlling
infection, particularly sIgA
• Delayed type hypersensitivity

19. Clinical disease
• Cause mild URT disease, low-grade fever,
malaise, headache, dry and nonproductive
cough, persist for > 2 weeks
• 10% patients develop LRT symptoms:
tracheobronchitis, atypical (walking)
pneumonia
• Secondary complication: otitis media,
erythema multiforme (Stevens-Johnson
syndrome), myocarditis, pericarditis

21. U. urealyticum, M. hominis, and M.
genitalium
• Infants (females) are colonized with the agents at birth
• Only a small proportion of prepubertal children remain
colonized
• The incidence of genital mycoplasmas is associated
with sexual activity
• Sexually active men and women 15% with M. hominis and 45-
75% with Ureaplasma

22. • U. urealyticum and M. genitalium: cause
nongonococcal urethritis
• M. hominis: implicated as a cause of pyelonephritis,
pelvic inflammatory disease, and postpartum fever

23. Lab diagnosis
• Culture of mycoplasmas is not routinely attempted, and
relatively insensitive
• M. pneumoniae can grow in special medium with animal serum
(sterols), yeast extract, glucose, and penicillin. Colonies have a
“mulberry-shaped”.
• M. hominis requires arginine for growth. Colonies have a fried-
egg appearance.
• Ureaplasma requires urea for growth
• Microscope: no cell well, stain poorly, no value

24. Serology - M. pneumoniae
• Complement fixation test : high false-positive rate
• ELISE for detection of IgM and IgG Abs
• Nonspecific reaction to outer membrane glycolipids : cold
agglutinins:
• IgM Abs that bind the I antigen on human RBC at 4°C) develop in
65% of the patients - a test frequently used to confirm the
diagnosis.
• False-positive seen in infections with Epstein-Barr virus,
cytomegalovirus, and adenovirus.

25. Rapid bedside testRapid bedside test
correlates with titrescorrelates with titres
ofof >>1/321/32
Cool to 4Cool to 400
C for a fewC for a few
minutesminutes
Reverses on warming toReverses on warming to
373700
CC
Cold agglutininsCold agglutinins

26. Treatment
• M. pneumoniae: erythromycin,
tetracycline (also good for
chlamydia)
• Ureaplasma: use erythromycin,
resistant to tetracycline
• M. hominis: resistant to
erythromycin and tetracycline, use
clindamycin

27. Chlamydia

28. Family Chlamydiaceae
3 medically important species
Genus Chlamydia:
C. trachomatis
Genus Chlamydophilia:
C. pneumoniae
C. psittaci

29. Characteristics
• Small obligate intracellular parasites
• Contain DNA, RNA and ribosome and make
their own proteins and nucleic acids, unable
to make their own ATP
• Have special growth cycle and replicate by
binary fission
• Possess a rigid cell wall similar to gram-
negative bacteria
• Sensitive to antibiotic
Respond to wide-spectrum antibiotics, but not to
penicillin (lack peptidoglycan)

30. A. Elementary bodies (EB)
• small (0.3 ～ 0.4 µm) infectious form
• a rigid outer membrane
• resistant to harsh environmental
conditions outside of eukaryotic host
cells
• bind to receptors on host cells
• initiate infection.
Special Growth CycleSpecial Growth Cycle

31. B. Initial body or Reticulate bodies (RB)
• non-infectious intracellular form
• metabolically [,met 'b l k]activeə ɒ ɪ
replicating form
• Have fragile membrane, easy to
broken

33. ChlamydiaChlamydia
inclusion bodyinclusion body

34. Comparison of chlamydial elementary
bodies and reticulate bodies
Characteristic Elementary body Reticulate body
Size
Morphology
Infectivity to host
RNA:DNA ratio
Metabolic activity
Trypsin digestion
Projections and rosettes
0.2 ～ 0.3μM
rigid
Infectious
1:1
Relatively inactive
Resistant
Few
1 μM
Fragile, pleomorphic
Non-infectious
3:1 (↑ ribosomes)
Active, replicating Sensitive
More

35. Chlamydia trachomatis
• Only infects human epithelial cells (Except Biovar
mouse)
• Three biovars (biological variants):
•Biovar Trachoma (14 Serologic
types)
•Biovar lymphogranuloma
venereum, LGV (4 serologic types)
•Biovar mouse

36. Pathogenesis and Immunity
• Infects non-ciliated columnar epithelial cells
• Stimulate the infiltration of polymorphonuclear cells and
lymphocytes which leads to lymphoid follicle formation and
fibrotic changes
• Cells destruction / host inflammatory response
• Infection does not stimulate long lasting immunity
• Reinfection results in an inflammatory response and
subsequent tissue damage

37. Treatment and prevention
• Tetracycline
• Erythromycin
• Sulfonamides
• Vaccines are of little value and are
not used.
• Treatment coupled with improved
sanitation to prevent reinfection is the
best way to control infection.

38. 1. Chlamydia trachomatis
• Infections only occur in humans
• Two biovars (trachoma and LGV) and
19 serotypes (antigen differences in MOMP)
Serotypes Disease
A to C Trachoma
D to K Urethritis, cervicitis
Inclusion conjunctivitis
Neonatal conjunctivitis
Infant pneumonia
L1 to L3 Lymphogranuloma venereum

39. Pathogenesis
• EBs enter the body via minute abrasions and
lacerations
• Primarily infect nonciliated columnar, cuboidal, or
transitional epithelial cells (urethra, endocervix,
endometrium, fallopian tube, anorectum,
respiratory tract, conjunctiva)
• LGV biovar replicate in mononuclear
[m nə n'ju kliər] phagocytesɒ ʊ ː in lymphatic
system (formation of granuloma, abscesses, or
sinus tracts in LN draining the site of primary
infection)

40. Pathogenesis
• Destruct cells during replication
• Infection stimulates a severe inflammatory response
(neutrophils, lymphocytes and plasma cells).
• No long-lasting immunity after infection
• Re-infection induces a vigorous inflammatory
response with subsequent tissue damage (blindness
and sterility).

41. Trachoma
• A chronic suppurative['s pjə re t v] eye diseaseʌ ˌ ɪ ɪ
caused by serotypes A,B,Ba,C.
• Follicular conjunctivitis →scar →corneal
ulceration →pannus formation (invasion of
vessels into the cornea,) →blindness
• Endemic in the Middle East, North Africa, and
India (dry and sandy regions); predominantly in
children. Leading global causes of blindness
(500 million infected, 7 to 9 million blinded).
• Transmission: eye-to-eye by droplet, hands,
contaminated clothing, flies.

42. • worldwide primarily in areas of poverty and
overcrowding
• 500 million people are infected worldwide
and 7 - 9 million people are blind as a
consequence
• Infections occur most commonly in children
• The organism can be transmitted by
droplets, hands, contaminated clothing,
flies, and by passage through an infected
birth canal

43. • Chronic infection or repeated infection
Chlamydial
kerato-conjunctivitis

44. Urogenital infections
• Venereal infections caused by serotypes of D to K.
• The most common sexually transmitted bacterial disease
in U.S. 2.8 million new cases annually, largely in males
(50 million worldwide).
• In women: 80% asymptomatic; bartholinitis, cervicitis,
pelvic inflammatory disease, which can lead to sterility and
ectopic pregnancy.
• In men: 25% asymptomatic; nongonococcal urethritis
(NGU)

45. Nongonococcal Gonorrhea
urethritis
1. Mild 1. Severe
2. Slow and prolonged 2. Acute
3. Dysuria is mild 3. Severe dysuria
4. Urethral discharge is 4. Purulent
clear or white, thin discharge
and mucoid

46. Nongonococcal Urethritis (NGU)
Urethritis caused by pathogens other than
gonococcus
• C. trachomatis (35-50% of cases)
• Ureaplasma urealyticum (10-30% of cases)
• Mycoplasma hominis
• Gardnerella vaginalis
• Trichomonas vaginalis
• Candida albicans
• Herpesvirus hominis (?)
• Cytomegalovirus (?)

47. Adult Inclusion Conjunctivitis
• Acute follicular conjunctivitis with
mucopurulent discharge
• Mostly occur in sexually active adults
(18-30 yr) with genital infection with
serotypes A, B, Ba, D to K.
• Auto-inoculation, oral-genital contact

48. Newborn Inclusion Conjunctivitis
• 25% infants acquired from
mothers with active genital
infections
• Long (>12 months) disease
course if untreated and are at
risk for C. trachomatis
pneumonia

49. Infant Pneumonia
• A diffuse interstitial pneumonia
• Occur in 10-20% infants that
exposed to the pathogen at
birth
• Rhinitis → staccato cough
(afebrile)

50. Lymphogranuloma venereum (LGV)
• A chronic sexually transmitted disease caused by
C. trachomatis L1, L2, L2a, L3.
• More common in men, with male homosexuals
being the major reservoir.
• Small, painless lesions at site of infection
(genitalia). Fever, headache, myalgia.
• Swelling of regional lymph nodes (inguinal
nodes), painful buboes , rupture.
• Proctitis is common in women.
• Resolve spontaneously or progress to ulceration
or genital elephantiasis .

51. Iodine-stained Chlamydia trachomatis inclusion
bodies (arrows)

52. Chlamydial urethritis (elementary bodies in direct
smear of urethral cell, fluorescein antibody stain)

53. Laboratory diagnosis
• 1. Cytology
• Examination of stained cell scrapings for the presence of inclusion bodies
• 2. Culture
• the most specific method for diagnosis
• cultures of susceptible cells
• iodine-staining inclusion bodies
• 3. Serology
• Detection of high titer IgM antibodies is indicative of a recent infection

54. 2. Chlamydophilia pneumoniae
• Was first isolated from the conjunctiva of a child in Taiwan
- TWAR stain.
• An important cause of bronchitis, pneumonia and
sinusitis.
• Infection is common, especially in adults and
transmitted person-to-person by respiratory secretions.

55. Clinical disease
• Most infections are asymptomatic or mild - persistent
cough.
• Can’t be differentiated with other atypical pneumonia -
M. pneumoniae, Legionella pneumophila, and
respiratory viruses.
• Detected in atherosclerotic lesions in blood vessels.
However, the role in the development of atherosclerosis
is not clear. (Koch’s postulate)

56. Lab diagnosis
• Diagnosis is difficult
• Do not grow in cell lines
• NAATs are OK for use.
• Complement fixation test (not
specific) or MIF test (specific)

57. Rickettsia

58. General Characteristics
• Small obligate intracellular coccobacilli
• Gram negative (poorly), better stained with
Giemsa (Blue)
• Have cell wall, bigger than virus but smaller than
bacteria
• Have DNA and RNA
• Have an ATP transport system that allows them to
use host ATP
• Arthropod reservoirs and vectors ( e.g., ticks,
mites, lice or fleas).
• Sensitive to antibiotics

59. Structure:
Similar with Gram negative bacteria
Cell wall: outer membrane
peptidoglycan
lipopolysaccharide (LPS)
Microcapsule and polysaccharide
Two antigenically distinct groups:
 LPS: heat-stable, cross-reactive with somatic antigens
of non-motile Proteus species (Weil-Felix test)
 Outer membrane protein: heat-unstable, species-specific

60. Pathogenic Mechanism
Materials
：
Mechanism
：
Local lymph or micro blood vessels
Endothelial cells, micro blood vessels
in whole body
Fever, rash, headache, etc
(1st
bacteremia)
(2nd
bacteremia)
Endothelial cells, micro blood vessels
Endotoxin and Phospholipase A
Bites or faeces of arthropod
Targets:

61. Replication

62. Five genera in this class cause human
diseases:
Rickettsia
Bartonella
Coxiella (does NOT cause skin
rash)
Ehrlichia
Orientia

63. Disease Organism Vector Reservoir
Rocky
Mountain
spotted fever
R. Rickettsii Tick Tick, wild rodents
Scrub typhus R.
Tsutsugamushi
Laval Mite
(chiggers)
Mites, wild rodents
Epidemic
typhus
R. Prowazekii Louse Humans, squirrel
fleas, flying
squirrels
Murine
typhus
R. Thphi Flea Wild rodents
Q fever Coxiella
Burnetii
None Cattle, sheep,
goats, cats
Diseases Caused by the Rickettsia

65. Rickettsia rickettsii in endothelial cells of a blood
vessel from a patient

66. Spotted fever
• Have a restricted geographic distribution; Rocky
mountain spotted fever (RMSF) is the prototype
of the group, caused by R. rickettsii.
• Organisms are maintained in hard ticks (wood
tick and dog tick) by transovarian transmission.
• Transmitted to humans by ticks (need 24-48h to
establish infection).
• High fever, chills, headache, skin rash (>90%,
extremities to trunk)
• GI symptoms, respiratory failure, encephalitis,
renal failure.

69. • Diagnosis is urgent, because the prognosis
depends on the duration of illness. (identify key
clinical signs – rash)
• Culture: tissue culture or embryonated eggs (danger)
• Microscopy: Giemsa stain; FA for biopsy tissue
specimens (rapid and specific)
• Serology: Microimmunofluorescence (MIF), detect
antibodies against MOMP and LPS antigens
• Molecular diagnosis: PCR, not species-specific

70. O

71. Epidemic (louse-borne) typhus
• R. prowazekii transmits from man to man by
human head and body lice.
• Humans are the primary reservoir (lice die 2 to 3
wk after infection).
• Epidemics occur among people living in crowded,
unsanitary condition - war, famine, or natural
disaster.
• High fever, severe headache, chills, followed by a
generalized skin rash; complications: myocarditis
and CNS involvement.

72. R. Prowazekii
Louse
Human Human
Louse
Epidemic typhus

73. o

74. Endemic (murine) typhus
• R. typhi transmits to man from
rodents reservoir hosts by rat flea.
• Endemic all over the world,
primarily in warm, humid areas.
• Fever, severe headache, chills, skin
rash (50%) on chest and abdomen

75. R. Typhi
Rodent
Flea Rat Tick Flea Human
Rodent
Murine typhusMurine typhus
(much milder than epidemic typhus)(much milder than epidemic typhus)

76. Diagnosis:
• IFA test
T/P/C:
• Tetracyclines, doxycycline,
Chloramphenicol
• Pest control
• No vaccine

77. O

78. Scrub typhus
• A rickettsial disease caused by Orientia
tsutsugamushi
• Transmitted to humans by red mites (chiggers)
• Organisms are maintained in mites by
transovarian transmission.
• Endemic in eastern Asia, Australia, and Japan.
• Fever, severe headache, skin rash (<50%),
spread centrifugally to extremities.
• Generalized lymphadenopathy, splenomegaly,
CNS complication, heart failure

79. R. Tsutsugamushi
Eggs Adult stage Nymphal stage
Nymphal stage Adult stage Eggs
Rats Nymphal stage Nymphal stage Human
Scrub typhus
Chigger

80. T/P/C:
• Prompt treatment with
tetracyclines, doxycycline,
chloramphenicol
• Avoid exposure to chiggers
• No vaccine

82. Q fever
• Most infections are mild or asymptomatic
• Acute disease:
• Pneumonia - high fever, severe headache, chill,
myalgias, resemble “atypical pneumonia”
• Granulomatous hepatitis, hepatosplenomegaly,
• Chronic disease: subacute endocarditis with long
incubation period and poor prognosis

83. Diagnosis
Serologic tests (IFA, ELISA, CF)
• Acute Q fever: IgM and IgG are developed
against phase II antigen.
• Chronic Q fever: antibodies against both phase
I and II antigens are elicited.
(phase I antigen: weak antigenic)

84. T/P/C:
• Doxycycline for prolonged
period
• Vaccine is available (single
dose with no booster
immunization for uninfected
people)

85. Bartonella Henselae
• Cat scratch disease (CSD)
• Weil-Felix reaction negative
• Infection by cats or dogs
• “Parinaud” Eye-Lymph node syndrome
The eye looks red, irritated, and painful,
similar to conjunctivitis.

86. Immunity
• Cellular immunity is important, and humoral
immunity is helpful.
• Persons become immune to further infection
following recovery from the disease.

87. Diagnosis and Prevention
 Microscopy
 Serological Test (Weil-Felix reaction, ELISA, IF,
PCR)
 Breaking the infection chain ( controlling and
killing the intermediate hosts and reservoir
hosts)
 Inactivated vaccine has protective effect
 Chloromycetin, tetracycline are helpful for
therapy, sulphonamides are not administered
(increasing the penetrating of the vessel).

88. Exercises:
Elementary body Reticulate body
Weil-Felix test cold agglutinins
Mycoplasmas Chlamydia
Rickettsia
1.Describe the difference between mycoplasmas and
bacterial L-form ？
2.Describe the difference between chlamydial
elementary bodies and reticulate bodies ？
3.Describe the pathogenic mechanism of Chlamydia?