Lecture 8 Chlamydia and Tuberculosis and MAC

What are the unique traits of Chlamydia?

Obligate intracellular pathogen (can’t make its own ATP → “metabolic parasite”). Once thought to be a virus due to its small size (0.45 μm), but it's a Gram-negative-like bacterium with no rigid peptidoglycan (just a thin, cross-linked outer membrane ring).

What are the two key stages of the Chlamydia life cycle?

1. Elementary Body (EB)
2. Reticulate Body (RB)

Describe the Elementary Body (EB) – The "Extra-tough Bullet".

• Environmentally Resistant: Yes, due to cross-linked membrane proteins. Can survive outside a host.

• Infectious Form: Yes. This is the form that is passed from person to person.

• Capabilities: Binds to host cells, gets internalized, but DOES NOT replicate. Metabolically inactive.

Describe the Reticulate Body (RB) – The "Replicating Body".—the

• Environmentally Resistant: No, it's fragile (no cross-linked membrane proteins).

• Infectious Form: No, non-infectious.

• Capabilities: Metabolically active, replicates by budding/fission inside the host cell. This is the form that causes the disease to progress. It uses host ATP.

What cell types does C. trachomatis infect and why?

Infects specific non-ciliated epithelial cells (urethra, endocervix, fallopian tubes, conjunctiva). Access is gained through minute abrasions/lacerations. It avoids intracellular killing by preventing lysosome fusion.

What are the main diseases and serovars of Chlamydia trachomatis?

• Serovars A, B, Ba, C: Trachoma (eye infection → blindness).

• Serovars D-K (most common in US): Oculogenital disease (STD, conjunctivitis, infant pneumonia).

• Serovars L1, L2, L2a, L3: Lymphogranuloma Venereum (LGV) (invasive STD, buboes).

Which Serovars of Chlamydia trachomatis are most common in the US?

Serovars D-K

What are the symptoms of urogenital Chlamydia in women?

80% ASYMPTOMATIC! Symptomatic: mucopurulent discharge, cervicitis (red cervical erosions), painful urination. Untreated can lead to PID, endometriosis, and sterility.

What are the symptoms of urogenital Chlamydia in men?

Most are symptomatic. Purulent discharge, painful urination. It's the most common cause of "non-gonococcal urethritis." It can be mistaken for gonorrhea (must test for both!).

How is Chlamydia diagnosed? What is the GOLD STANDARD?

Gold Standard: Nucleic Acid Amplification Test (NAAT). It is the MOST SENSITIVE test, performed on urine or swabs.

• Culture: Most specific, but low sensitivity (requires tissue culture).

• Cytology (PAP smears): NOT reliable.

• Direct Antigen Detection: Detects MOMP or LPS, less specific.

What is the treatment for Chlamydia?

• All partners must be treated

• Preferred: Doxycycline for 7 days (genital, LGV is 21+ days).

• Pregnant/Allergic: Azithromycin (1 dose).

• Adult Ocular: Single oral dose of azithromycin OR tetracycline eye ointment for 6 weeks.

• Neonatal: Erythromycin or azithromycin for 10-14 days.

What is the "ACID-FAST" trait of Mycobacteria?

Their cell wall is rich in mycolic acids (lipids, waxy), so they are NEITHER Gram+ nor Gram-. They resist decolorization with acid-alcohol, requiring special stains like Carbolfuchsin (Ziehl-Neelsen)

How fast do Mycobacteria grow?

VERY SLOWLY. Generation time is 12-40 hours. Visible colonies take 2-40 days on solid media.

What is the most common mycobacterial disease in US AIDS patients?

Mycobacterium avium complex (MAC)

What is the most common mycobacterial disease worldwide in immunocompromised patients?

Tuberculosis (M. tuberculosis).

What is the commonly most reported STD in the US?

oculogenital disease

What environment do mycobacteria grow in?

Aerobic

Do mycobacteria form spores?

Non-spore formers and have slightly curved rods

How are Serovars differentiated from each other?

antigenic differences in major outer membrane protein: MOMP

What is the catalase result for Mycobacterium?

 catalase +

Is reinfection possible with Chlamydia?

No long-lasting immunity; reinfection can be more servere

What are the lesions for LGV Chlamydia?

Lesions in lymph nodes → necrotic, inflammation, MAJOR CONCERN is rupture

What are the lesions for non-LGV Chlamydia?

trachoma: small bumps on underside of EYELID

What is an oculogenital transient in Chlamydia?

small painless genital papules, pustules, or shallow ulcers

What are the three stages of LGV: lymphogranuloma venereum?

1- painless, 2- inflammation, and 3- proctitis or proctocolitis

What is a Trachoma in C. trachomatis?

conjunctivitis with diffuse inflammation: BLINDNESS RISK!!

What is adult inclusion trachoma caused by in C. trachomatis?

genital infective strains

What is neonatal trachoma caused by in C. trachomatis?

exposed at birth (pus/discharge)

What disease in infants is caused by C. trachomatis?

 Infant pneumonia: onest 2-3 weeks after birth

Can a C. trachomatis urogenital infection happen after treatment for gonorrhea?

Yes, longer incubation time and antibiotics for gonorrhea do not kill Chlamydia

What happens during the first stage of LGV: lymphogranuloma venereum?

painless, small lesion/ulcer at sight of infection (3-30 days after infection)

What happens at 2nd stage of LGV: lymphogranuloma venereum?

inflammation and swelling of inguinal lymph node: buboes (2-6 weeks after 1^st stage painful, danger of rupture)

What happens at 3rd stage of LGV: lymphogranuloma venereum?

 proctitis or proctocolitis occurs (often years later)

perirectal abscesses, genital elephantiasis- SEVERE swelling, thickening → disfigured genitals

What is Proctitis?

inflammation of lining of rectum

What is Proctocolitis?

Proctitis and the lowest portion of your colon

Where are Mycobacterium found?

Free living saprophyte (in the soil or dead decaying matter) or animal hosts

What two molecules are not usually found in the cell walls of Mycobacterium?

LPS and Teichoic Acids

What two molecules are found on Mycobacterium that are not usually found on the cell wall of bacteria?

Lipoarabinomannan and Arabinogalactan

What type of pathogen is Mycobacterium tuberculosis?

 Intracellular pathogen: lifelong RESPIRATORY infections

Who is the only reservoir for M. tuberculosis?

Humans

How is M.tuberculosis spread?

 Spread by person to person contact: inhale infected aerosols

What type of immune response determines the clearance of M. tuberculosis?

The CELLULAR immune response (mediated by leukocytes/T cells), not the humoral (antibody) response.

Scenario: A person is exposed to a LOW bacterial load of M. tb. What happens?

Infection is cleared more readily by the cellular immune system (leukocytes). The immune system can handle a small number of invaders effectively

Scenario: A person is exposed to a HIGH bacterial load of M. tb. What happens?

Clearance is impaired. The intense immune response leads to significant inflammation, causing tissue damage and CAVITIES FORM IN THE LUNGS (a hallmark of severe TB).

What is a Ghon complex?

It is the hallmark of latent TB infection.

• A calcified granuloma (walled-off clump of immune cells) surrounded by chronic inflammation.

• It physically "walls off the bacteria" to stop its spread.

• CRITICAL POINT: The bacteria inside are still ALIVE, just dormant.

What happens to most Ghon complexes?

Most Ghon complexes resolve on their own and cause no further problems.

What is the DANGER of a Ghon complex?

The latent bacteria can reactivate if they are released from the granuloma (e.g., if the immune system becomes compromised). This causes active TB disease to develop long after the initial infection

What is the progression of Pulmonary TB symptoms over time?

• Early Stage (Non-specific): Fever, malaise, night sweats, cough. Easily mistaken for other illnesses.

• Late Stage: Uncontrollable coughing (can last 3+ months), producing bloody sputum (from lung cavities) or purulent sputum. Patient is HIGHLY contagious due to coughing.

Why is the sputum bloody in active TB?

Cavities form in the lungs due to inflammation and tissue damage. These erode into blood vessels, causing hemoptysis (bloody sputum).

At what stage is a TB patient most contagious to others?

When they have an active, uncontrollable cough generating infectious aerosols (late-stage pulmonary TB).

What does "Miliary" or "Extrapulmonary/Disseminated TB" mean?

TB bacteria have escaped the lungs and spread through the bloodstream to other organs.

What organs can Miliary TB affect?

• Meninges (TB meningitis)

• Kidneys

• Brain

• Spine (Pott's disease)
  → Plus any other organ.

Can both Pulmonary and Miliary TB be fatal?

YES. Both CAN BE FATAL if left untreated or in immunocompromised patients.

What is another name for the Tuberculin Skin Test?

The Mantoux test (or tuberculin Tine test).

What does the Tuberculin Skin Test actually detect?

It shows EXPOSURE ONLY. It does NOT differentiate between latent infection or active disease.

What is injected during the Tuberculin Skin Test?

Purified M. tuberculosis cell wall proteins.

What type of immune reaction causes a positive skin test result?

A Delayed Type Hypersensitivity (DTH) reaction. Sensitized T cells at the injection site react, causing hardening and redness.

What is the hardened, raised area at the injection site called?

Induration. It is measured in millimeters at 48 hours to determine exposure likelihood.

When should the Tuberculin Skin Test be performed after suspected exposure?

Approximately 3-4 weeks after exposure (allows time for T cell sensitization).

How do you interpret a positive Tuberculin Skin Test in a young person (<18 years)?

A positive result suggests possible ACTIVE infection. Follow-up is ALWAYS necessary.

Why might an older person have a positive Tuberculin Skin Test even without active disease?

It could be from:

• Previous TB disease

• BCG vaccination (history of receiving the TB vaccine) → Causes a FALSE POSITIVE

Besides skin testing, how is TB exposure or disease confirmed?

Chest X-ray, TB Blood Test (IGRA), Lab Detection of Acid-Fast Bacteria, Molecular Probes

What are the main limitations of Sputum Smear Microscopy?

• Requires technical expertise to perform and read correctly.

• Insensitive (can miss cases, especially with low bacterial load).

What is the hallmark limitation of TB Culture?

It is SLOW!

• Solid Media (Lowenstein-Jensen): 4-6 weeks for visible colonies.

• Liquid Media (Middlebrook): 1-2 weeks for growth.

What does Serology show for TB? What are the two main types?

• It only shows EXPOSURE, not active disease.

• Two main types:

  1. Tuberculin Skin Test (Mantoux) - DTH reaction.

  2. Interferon-Gamma (IFN-γ) Release Assay (IGRA) - e.g., QuantiFERON-TB GOLD (blood test, no cross-reaction with BCG).

What are the main limitations of Nucleic Acid Amplification Tests (NAATs) for TB?

• Requires specialized lab facilities, practices, and training.

• Expensive.

What does the Cepheid Xpert MTB/RIF test detect?

It detects M. tuberculosis AND drug resistance (specifically to Rifampin/Rifampicin), all in one rapid test.

What is the Accuprobe test, and what is its key advantage?

• Detects rRNA of M. tuberculosis.

• Recommended by the CDC for identifying growth from liquid cultures.

• Key Advantage: Reduces identification time from 2-6 weeks down to < 2 hours.

What is the Mycobacterium tuberculosis Direct (MTD) assay?

A nucleic acid amplification test (NAAT) that identifies M. tb directly from sputum samples.

• Key Advantage: Very quick – result in 3.5 hours.

What are Line Probe Assays (LPAs) and what do they detect?

A rapid PCR test performed directly on sputum samples.

• Detects M. tuberculosis AND drug resistance, specifically to Rifampicin and Isoniazid.

• Turnaround Time: 24-28 hours.

Is the a vaccine for M. tuberculosis?

No vaccine

What are the 4 first-line drugs for treating active TB?

1. Isoniazid

2. Rifampin

3. Ethambutol

4. Pyrazinamide

What is the standard duration and drug combination for TB treatment?

• First 2 months (Intensive Phase): All 4 drugs (RIPE) taken daily.

• Next 4 months (Continuation Phase): Isoniazid + Rifampin only.

• Total Duration: 6 months.

What defines Multi-Drug Resistant TB (MDR-TB)?

The M. tuberculosis strain is resistant to the two most powerful first-line drugs: Isoniazid AND Rifampin.

How does drug resistance arise in M. tuberculosis?

Through spontaneous mutations on the bacterial chromosome.

What practices increase the likelihood of developing MDR-TB?

• Monotherapy (using a single drug to treat).

• Erratic drug administration (poor patient compliance).

• Suboptimal doses (prescribing too little).

• Poor drug absorption by the patient.

What two species make up the Mycobacterium avium complex (MAC)?

1. M. avium

2. M. intracellulare
   (They are grouped together as MAC because they are closely related).

Where is MAC found in the environment?

It is ubiquitous (everywhere!)

• Water

• Soil

• House dust

What is the geographic and host range of MAC?

• Found worldwide.

• Infects a large number of animals, birds, and insects.

What type of infections does MAC cause?

• Primarily lung infections that resemble Tuberculosis.

• Can become disseminated (spread throughout the body).

• Key Point: Disseminated disease is more common in non-AIDS immunocompromised patients (whereas MAC in AIDS patients is the most common mycobacterial disease).

What are the proposed portals of entry for MAC?

1. Respiratory tract (inhalation)

2. GI tract (ingestion)

What is the MOST LIKELY route of acquisition for MAC in immunocompromised (AIDS) patients?

Ingesting contaminated water (not respiration/inhalation, which is more common for the lung disease in non-AIDS patients).

What are the key symptoms of disseminated MAC infection?

• Fever

• Malaise

• Diarrhea

• Weight loss

What happens when MAC disease disseminates?

No organ is spared. The widespread infection can lead to organ failure.

How is disseminated MAC infection diagnosed?

By finding thousands of bacteria per ml of blood and in tissue samples (high bacterial load in the body).

What tests are positive for MAC and not for M. tuberculosis?

Tellurite (black ppt), Converts niacin to nicotinic mononucleotide

What tests are negative for MAC and not for M. tuberculosis?

Nitrate, Urease

Which tests are positive for both MAC and M. tuberculosis?

Slow growth and catalase

What disease does Mycobacterium leprae cause?

Leprosy (Hansen's disease)

What are the fundamental microbiological traits of M. leprae?

• Acid-fast bacilli (stains with carbolfuchsin).

• Obligate intracellular pathogen (cannot live outside host cells).

• CANNOT be cultured on artificial media (must be grown in live animals like armadillos or mouse footpads).

What determines the manifestation and severity of leprosy?

It depends entirely on the patient's immune response.

What are the two polar types of leprosy?

1. Tuberculoid Leprosy (milder, paucibacillary).

2. Lepromatous Leprosy (severe, multibacillary).

What cells does M. leprae have a specific affinity for?

• Macrophages

• Schwann cells (cells of the peripheral nerves)

How does M. leprae interact with Schwann cells?

1. Binds to laminin on the Schwann cell surface.

2. Gets internalized.

3. Undergoes slow replication.

4. Causes inflammation and ultimately axon death (nerve damage).

What determines the extent of damage in leprosy?

The extent of the patient's cell-mediated immune response

(Tuberculoid Leprosy) Describe the immune response, bacterial load, and disease severity.

• Immune Response: STRONG cell-mediated response, LOW antibody levels.

• Bacterial Load: LOW → Paucibacillary (few bacilli).

• Disease Severity: MILD disease (Tuberculoid leprosy).

(Lepromatous Leprosy) Describe the immune response, bacterial load, and disease severity.

• Immune Response: WEAK cell-mediated response, HIGH antibody levels.

• Bacterial Load: HIGH → Multibacillary (many bacilli).

• Disease Severity: SEVERE disease (Lepromatous leprosy).

What causes the tissue destruction in Lepromatous Leprosy?

Damage is due to loss of sensation, specifically the loss of the sense of pain.

• IMPORTANT: The disease does NOT cause flesh to rot. Repeated unnoticed injuries and infections lead to tissue damage.

What is the treatment for leprosy?

Short, simple, and available to all.

• Dapsone (a sulfa drug) + Rifampin

• Cures after single treatment (multi-drug therapy regimen)

What are the reservoirs and sources of M. leprae infection?

• Infected humans (primary reservoir).

• Nine-banded ARMADILLOS (animal reservoir, especially in the US).

• Transmission: Requires long-term exposure to a person shedding bacteria in large numbers (lepromatous cases).