Mycobacteria, Mycoplasma, Actinomyces, Nocardia Flashcards
Mycobacteria Cell Wall
Peptidoglycan (similar to other Gram Positives)
High Lipid Content (60%)
LAM and Mycolic Acids form Waxy coat.
Hardy, Impenetrable, Hydrophobic
Acid-Fast Stain
Use Extreme measures (Heat, Penetrating Agents) to stain Mycobacteria.
Once in, the stain is Fast because the Mycobacterial Cell Wall is Impenetrable.
Acid-Fastness: Once Stained, Difficult to Decolorize.
Procedure:
1) Specimens (sputum, CSF) are Centrifuged
- -to concentrate the bacteria in the pellet, rather than in the supernatant fluid.
2) Slide is flooded with Carbol-Fuchsin (Red) dye, then Heated for 3-5 min.
3) Decolorized with Hydrochloric Acid in Alcohol.
4) Counterstained with Methylene Blue.
Mycobacteria tuberculosis
(MTB) (TB)
Bacteriology
Aerobic, Catalase Positive Rods (Bacilli).
Bacteriology:
–Grows Slowly (12-24 hr Generation time).
3-6 weeks to see Colonies.
–Due to Hydrophobic Cell surface, which causes them to clump and limits permeability of Nutrients into the cell.
–Resistant to Drying, Disinfectants, Acids, Alkalis.
(Book: susceptible to UV light and Heat, including Pasteurization)
Niacin Accumulation:
–Niacin is formed as a metabolic byproduct by all Mycobacteria, but some species possess an enzyme that converts free niacin to niacin ribonucleotide. MTB lacks this enzyme, and accumulates Niacin as a water-soluble byproduct in the culture medium.
(Recall that Niacin = Vitamin B2)
Mycobacteria tuberculosis
(MTB) (TB)
Infection Course
Primary Infection
1) Inhalation of TB in droplet nuclei.
(most often, Deposited in the peripheral alveoli of the Well-Ventilated Middle and Lower Lobes)
2) TB is Phagocytosed by Alveolar Macrophages.
3) Phagosome-Lysosome Digestive Mechanisms:
- -MTB *Inhibits Acidification of the Phagosome, which is necessary for the lysosomal enzymes to work.
- -MTB Cell Wall also blocks fusion of phagosome with lysosome.
- -Result: MTB multiplies within Phagosome of the Nonactivated Macrophage.
4) CD4+ TH1 cells are activated in response to mycobacterial antigens.
–TH1 cells secrete Cytokines: IFN-γ, TNF, IL-12
–Which activate Macrophages to kill ingested microbes.
–If Macrophage Activation is successful, disease is arrested. If unsuccessful, DTH results.
–These cytokines also attract CTLs and Macrophages, producing tissue injury due to release of digestive enzymes.
==> Granuloma results.
Granuloma:
= mixture of Macrophages, Lymphocytes, Fibroblasts.
Caseous Necrosis:
- -A form of Cell Death; cheese-like appearance.
- -Due to DTH.
In the Early stages of infection, MTB-laden Macrophages are transported in lymph vessels to Hilar Lymph Nodes draining the infected site.
–From there, TB can spread to other organs or other parts of the lung, including the apices. (Apex is most common part of lung with new foci)
Latent/Dormant TB:
1) Some of the organisms, when faced with oxygen and nutrient deprivation, enter a Dormant state (Latency) rather than dying.
Reactive (Adult) TB:
1) Dormant TB Reactivates at Aerobic sites
2) Auto-destructive DTH causes tissue damage: Granulomas and Caseous Necrosis
3) Necrosis causes Pulmonary Cavities
4) May occur in Lung and/or Other Organs: Kidneys, Bones, Lymph Nodes, Brain, etc.
5) Reactivation is Associated with
- -Age (Men over 50)
- -Immunosuppression
- -Malnutrition
- -Alcoholism
- -Diabetes
- -Depression
Mycobacteria tuberculosis
(MTB) (TB)
Symptoms
Symptoms:
Primary TB:
1) Fever
2) Malaise
3) May show infiltrates @ Midzone of Lung
Reactivation TB:
–Occurs in 10% of ppl recovering from Primary infection.
1) Cough is Universal Symptom
- -Dry, initially.
- -Sputum, as disease progresses.
- -Hemoptysis, later.
2) Fever
3) Malaise
4) Fatigue
5) Sweating
6) Weight Loss
7) Infiltrates in Lung Apices coalesce to form Cavities with progressive destruction of lung tissue.
8) Other organs may be involved.
Mycobacteria tuberculosis
(MTB) (TB)
Diagnosis
Diagnosis:
1) Tuberculin Test:
–Measures DTH to a Tuberculoprotein prep called
Purified Protein Derivative (PPD).
–Intradermal injection read 48-72 hours later.
–Positive Result: Erythema and induration, 10 mm or more.
–In U.S., positive test is Very strong evidence of TB infection (b/c low incidence and BCG is not used here).
__Positive result indicates that person has developed DTH through MTB infection, but does not imply that the disease is active. Could be past or current infection.
Foreigner with Positive PPD:
_May be due to BCG vaccine, which is a live vaccine.
_BCG is not recommended in U.S. b/c low incidence.
Patients on Immunosuppressive Drugs or with AIDS may Fail to React .
2) Chest X-ray and CT:
–In Active Pulmonary TB,
Infiltrates or Consolidations and/or Cavities often seen @ Upper Lungs.
3) Acid-Fast Stain:
- -Sensitivity 65%, False Negatives b/c # of organisms is often small (Low Yield).
- -False Positives, may be Other Mycobacteria.
4) Culture:
–Takes 3 weeks or longer to show visible colonies.
–Radiometric procedures are faster
–PCR/Nucleic Acid Amplification (NAA):
Higher Specificity (98%)
Sensitivity (70-80%)
Mycobacteria tuberculosis
(MTB) (TB)
Treatment
Treatment: 6-9 Months
- Because MTB grows slowly and because some may be dormant.
- Also b/c Difficult to penetrate.
Prolonged Treatment for HIV patients.
Initial Empiric Treatment:
- Start patient on 4 Drugs.
- -Resistance!!
Once susceptibility test results are available, can discontinue fourth drug and continue to use the drugs known to be fully active against that patient’s particular TB isolate.
First-Line:
1) Isoniazid (INH) (Mycolic Acid)
2) Rifampin (RIF) (RNA Polymerase)
3) Pyrazinamide (PZA) (Fatty Acid Synthesis)
4) Ethambutol (EMB) (LAM)
5) Streptomycin (30S Ribosome)
–Isoniazid and Rifampin are Active against Both Intracellular and Extracellular organisms.
–Isoniazid and Ethambutol act on the Mycolic Acid (Isoniazid) and LAM (Ethambutol) steps of Mycobacterial Cell Wall Synthesis.
–Pyrazinamide acts at the Acidic pH found within cells.
–Streptomycin is Only active against Extracellular organisms because it does not penetrate into cells.
Second Line: 1) Fluoroquinolones (DNA Gyrase) 2) Cycloserine (Peptidoglycan) 3) Para-Aminosalicyclic Acid (Folic Acid, Mycobactin) 4) Ethionamide (Peptide Synthesis?) 5) Kanamycin, Amikacin (30S Ribosome)
–Fluoroquinolones (e.g. Ciprofloxacin) are active against MTB and Penetrate well into Infected cells.
Mycobacterium Leprae
Leprosy) (Hansen’s Disease
Epidemiology:
_90% cases Immigrants
_California, Texas, Louisiana, Florida, New York
Transmission:
_Nasal Secretions
Pathogenesis:
_A phenolic glycolipid (PGL-1) binds to membrane of Scwann cells
Disease:
_Chronic Granulomatous Disease of the Peripheral Nerves and Superficial Tissues, particularly the Nasal Mucosa
Diagnosis:
_Acid-Fast Stain
Treatment:
_Dapsone + Rifampin
Tuberculoid Leprosy:
1) Macular Skin lesions
2) Intact Cell-Mediated Immunity
3) Non-Progressive Disease
4) Few Bacilli present
5) Non-contagious
Lepromatous Leprosy:
1) Nodular Skin Lesions
2) Deficient Cell-Mediated Immunity
3) Progressive Disease
4) Abundant Bacilli
5) Contagious
6) Causes Deformities, Loss of Nasal Bone
Mycoplasma and Ureaplasma
Bacteriology: --Lack Cell Wall --Plastic and Pleomorphic Pleomorphic b/c Lacks Cell Wall. --Membrane contains Cholesterol --Stains Poorly (B/c Lacks Cell Wall, so can't retain stain)
–Smallest free-living microorganism (invisible by Light microscopy)
Mycoplasma pneumoniae
Epidemiology:
- -Close Contact
- -or Exchange of Aerosols
- -Accounts for 40% of Community-Acquired Pneumonia
- -Accounts for 10% of all Cases of Pneumonia
- -Often in Teenagers (5-15 yrs)
- -Almost Always Benign
_________________
Pathogenesis:
1) Attaches to Bronchial Epithelial cells
2) Invades Host cells
3) Damage to Host cells:
_Metabolism Alteration (Competition for Precursors)
_Adherence interferes with Ciliary function
_Triggers Inflammatory reaction (Lymphocytes and Macrophages)
_Molecular Mimicry and Phenotypic Plasticity
_________________
Manifestations:
1) Tracheobronchitis, Primary Atypical Pneumonia
(Fever, Malaise)
_“Walking” Pneumonia
2) Pharyngitis (fever + sore throat) and Otitis are common (15%)
3) Rash (1/3 pts)
_Cold Hemagglutinins: IgM Antibodies that react with an altered antigen on RBCs
_________________
Diagnosis:
1) Serology: EIA
(Enzyme Immunoassay)
(EIA principle: Antigen, Antibody, Antibody-Conjugated Enzyme, Substrate)
2) PCR
(Cannot Gram stain b/c No Cell Wall!!!)
_________________
Treatment: Bacteriostatic
(DOC) 1) Macrolides: Erythromycin, Clarithromycin, Azithromycin
(DOC) 2) Tetracyclines: Doxycycline
(Alt) 3) Fluoroquinolones
(Beta-Lactams) Penicillin and Cephalosporins are INEFFECTIVE because LACKS CELL WALL.
Other Mycoplasmas
Mycoplasma genitalium:
_Common inhabitant of Genitourinary Tract
_Causes Urethritis,
_Associated with Pelvic Inflammatory Diseases (PID)
_Treatment: Erythromycin, Tetracycline
_________________
Mycoplasma hominis:
_Associated with Postpartum Fever
_Localized Abscesses in Immunocompromised patients
_Resistant to Erythromycin
_________________
Ureaplasma urealyticum:
_Produces Urease
_Acquired by Sexual Contact
_Associated with Urethritis, Mainly in Men
_Treatment: Tetracycline, Azithromycin, or Quinolones
Actinomyces and Nocardia
Fungi-like Bacteria:
_Show Filamentous Growth
Found in Nature (Soil, Mouth)
Actinomyces:
1) Gram+ Rods that Branch
2) Normal Flora
3) Anaerobic
4) @ Cervicofacial Area
5) Sulfur Granule
6) Non-Acid Fast
7) No Evidence of Immunity
Nocardia:
1) Gram+ Rods that Branch
2) Soil
3) Aerobic
4) @ Cutaneous, Pulmonary, Brain
5) sulfur granule is not common
6) Partial Acid-Fast
7) T Cell-Mediated Immunity
Actinomyces Bacteriology:
1) Gram Positive Rods that Branch
2) Normal Flora @ Mouth, Colon, Vagina
3) Anaerobic
4) A. israelii causes 3/4 of human Actinomycosis
Actinomycosis (Lumpy Jaw):
1) Rare infection disease
2) Infects Oral Cervicofacial area, Thorax, Abdomen, Pelvis
Nocardia Bacteriology:
1) Gram Positive Rods that show true Branching
2) Found @ Environment, Notably in Soil
3) Gram Stain: Poorly, Appear “Beaded”
4) *Partially Acid-Fast
5) *Aerobic!! (unlike Actinomyces)
Nocardiosis:
1) Pulmonary and Systemic
2) Disease caused by Bacteria Found in Soil and Water
3) Can affect Lungs, Brain, Skin
Actinomyces israelii
Bacteriology:
1) Gram Positive Rods that Branch
2) Normal Flora @ Mouth, Colon, Vagina
3) Anaerobic
4) A. israelii causes 3/4 of human Actinomycosis
_________________
Actinomycosis:
1) Cross Epithelial Barrier and cause Disease:
_B/c low oxygen exists beyond epithelial barrier, compared to in oral cavity. Thus, must reach this more anaerobic environment in order to thrive.
2) Formation of Inflammatory Sinuses, Ultimately Discharge to Surface
3) Sulfur Granules (mass of the filamentous bacteria solidified with exudates) are present in the Pus
_________________
Cervicofacial Actinomycosis:
1) Lumpy Jaw
2) Accounts for more than 50% Actinomycosis
3) Dental Caries is a Predisposing Factor
4) Infection may follow Tooth extractions or Dental surgery
5) Infection is rare (Antibiotics given after dental surgery to prevent infection by this bacteria)
_________________
Diagnosis:
1) Specimens obtained directly from lesions (Open Biopsy or Needle Aspiration)
2) Staining of Sulfur Granules
3) Anaerobic Culture
4) *CANNOT examine sputum b/c this is NORMAL FLORA.
_________________
Treatment:
1) High Dose Penicillin G for up to 6 months:
_B/c Difficult for drugs to Penetrate Sulfur Granule Clusters
2) Ampicillin, Doxycycline, Erythromycin, Clindamycin.
Nocardosis
Nocardia Bacteriology:
1) Gram Positive Rods that show true Branching
2) Found @ Environment, Notably in Soil
3) Gram Stain: Poorly, Appear “Beaded”
4) *Partially Acid-Fast
5) *Aerobic!! (unlike Actinomyces)
_________________
Epidemiology:
1) Inhalation of bacteria or Open Cut
2) 2 Major Forms: Pulmonary (N. asteroides) and Cutaneous (N. brasiliensis)
3) 500-1000 new cases in U.S.
4) Most Pulmonary Cases in Immunocompromised patients
_________________
Pathogenesis:
1) T Cell-Mediated Immunity is dominant
(Transplant patients, HIV, Pregnancy, Chemotherapy, some Cancer patients)
2) Pulmonary Forms: Secondary Abscesses in Brain (30%)
3) Cutaneous infection follows Minor Trauma
_________________
Manifestations:
1) Bronchopneumonia and Brain Abscess,
_Cough, Dyspnea, Fever
2) Subcutaneous Abscesses (Mycetoma)
_________________
Diagnosis:
1) Sputum: Gram Stain Positive for Branched Bacteria, Beaded
2) Weak Acid-Fastness is Characteristic
3) Growth on Blood Agar
_________________
Treatment:
_Sulfonamides
(Inhibit Folate Synthesis)
