Mycoplasma (Woychik) - 5/2/16

Question 1

What are the four organisms associated with human disease?

Answer 1

Mycoplasma pneumoniae - URI, bronchitis, pneumonia

Sexually transmitted:
Ureaplasma urealyticum
Mycoplasma hominid
Mycoplasma genitalium

Men: nongonococcal urethritis
Women: bacterial vaginosis, cervicitis, pelvic inflammatory disease

Question 2

Mycoplasma General Characteristics:

Size & Cell Wall?

Answer 2

Smallest (size and genome) free-living organism - genome ~1/10 the size of E. coli

Highly polymorphic in shape - lack of rigid cell wall (NO PEPTIDOGLYCAN) - instead, they have a 3-layered cell membrane

• Completely resistant to penicillin and other antibiotics that attack cell wall
• Generally stains poorly or not at all (e.g., not visible by gram stain)

Question 3

Mycoplasma General Characteristics:

Antigenic determinants?

Answer 3

Because lack cell wall, major antigenic determinants = membrane glycolipids and proteins

Therefore, antibodies to mycoplasmas cross react with human tissues

Question 4

Mycoplasma General characteristics:

Colony morphology on agar plates?

Answer 4

M. pneumonia - dense mulberry shape, but can also be spherical

Colonies from other 3 species have characteristic fried egg appearance

Question 5

Mycoplasma General characteristics:

Fastidious nutritional requirements for growth?

Growth time?

Answer 5

Sterol-containing membranes (not present in other bacterias or viruses)

Sterols required for growth and membrane synthesis; since mycoplasma cannot synthesize them, a cholesterol source (serum) or cholesterol is added to medium

Very slow growing (e.g. M. pneumonia doubling time is over 6 hours)

Question 6

Mycoplasma pneumonia and atypical (or walking) pneumonia:

Transmission?

Who does it affect?

Pathogenesis?

Answer 6

Person-to-person by coughing, respiratory secretions

Prominent causative agent of pneumonia, especially in closed populations (military recruit camps, boarding schools, colleges)

Respiratory pathogenicity linked to high affinity of of M. pneumonia for respiratory epithelial cells:

• Attachment occurs at base of cilia and mediated by terminal organelle composed of adhesions + auxiliary proteins at one end of M. pneumonia and a glycoprotein on the surface of respiratory epithelial cells (act as receptor)
• Attachment leads to loss of ciliary action –> loss of cilia –> sloughing of the cell into lumen –> COUGH

Question 7

Atypical pneumonia:

Clinical characteristics?

Answer 7

Incubation period: 2-3 weeks (vs. 1-3 days for viral respiratory infections)

Typically gradual (occurring over several days) onset of fever, malaise, headache, cough (clinical hallmark)

Age-related incident of upper vs. lower respiratory infection noted:

• Age 3 or less –> primarily URI
• Age 5-20 –> bronchitis and pneumonia (this age group has highest attack rate)
• Older adults –> pneumonia

1-2 weeks into infection –> formation of cold agglutinins (IgM antibodies against an altered I antigen on all RBCs)
- IgM = pentamer –> can lead to lysis of RBCs

Question 8

Atypical pneumonia:

Laboratory Diagnosis?

Treatment?

Answer 8

Currently problematic!

Culturing M. pneumonia not practical; can take up to 2 weeks

• Cold agglutination = obsolete test (not specific or sensitive enough for diagnostic purposes)
• Serological tests often negative early in infection (7-10 days) so not reliable
• PCR-based = most specific and rapid

Treatment:
- Macrolides (bind to 50S ribosomal unit) b/c mycoplasma doesn’t have a cell wall