Chlamydia and Legionella Quiz

Atypical Bacteria Part 1

• Atypical bacteria are either intracellular or extracellular
• Intracellular atypical bacteria consist of Chlamydia, Legionella, Mycobacterium, Rickettsiales, and Leptospira
• Extracellular atypical bacteria consist of Mycoplasma, Spirochetes (Borellia and Treponema)

Chlamydia and Chlamydophila

• Common human pathogens
• Do not gram stain
• Cellular characteristics similar to gram-negative bacteria, with an outer membrane and LPS
• Obligate intracellular pathogens, cannot be cultured on agar or broth
• Require cell culture for isolation
• Once thought to be viruses but contain both DNA and RNA
• Make their own macromolecules and are energy parasites, using host ATP
• Exist in two forms: elementary bodies (EB) and reticulate bodies (RB)
• EB are metabolically inactive and infectious
• RB are metabolically active and non-infectious

Chlamydia Life Cycle

• EB attach to cell receptors
• Within 1-6 hours the transcription of DNA begins
• Within 8 hours, RNA and protein synthesis occurs in EB
• Within 12 hours the host DNA synthesis declines, and RBs produce their own macromolecules of DNA, RNA and protein
• EB reorganize into RBs which undergo binary fission (24 hours)
• Continued multiplication
• Further reorganization of RB to EB
• Low infectivity

Important Members of the Chlamydia Group

• Chlamydia trachomatis: causes ocular infections, genital infections, and neonatal infections. Many serotypes make vaccine creation difficult
• Chlamydophila pneumoniae: causes respiratory infections.
• Chlamydia psittaci: a bird pathogen that causes psittacosis (flu-like illness) in humans.

Chlamydia Virulence Factors

• Intracellular replication in epithelial cells (not macrophages).
• Safe from complement, antibodies, and phagocytes
• Prevent fusion of endosomes with lysosomes
• Endosome becomes an inclusion body for RBs where they replicate
• Mechanisms for nutrient uptake from cytoplasm to the inclusion body of replicating RBs.
• Transporter proteins (e.g., Inc A) are inserted into the inclusion body membrane, forming secretion systems
• Secretion systems act as “molecular straws” taking nutrients from the cytoplasm and transport bacterial molecules into the host cell cytoplasm, inhibiting apoptosis while RBs divide.
• Proteins secreted via bacterial secretion systems into the cytoplasm also inhibit MHC Class I expression, decreasing antigen presentation to CD8 cells.

Chlamydia Pathogenesis

• Elementary bodies enter epithelial cells (conjunctiva and urogenital tracts)
• Organism replicates
• Infected cells secrete inflammatory mediators (IL-1, IL-8) causing acute, then chronic inflammation
• Manifestations from chronic inflammation because of tissue reorganization and scarring.
• Infected cells stimulated with gamma-IFN temporarily halt RB replication but don’t kill them
• May lead to chronic infection with disease re-expression later

Chlamydia Trachomatis Isolates

• Chlamydia trachomatis exists as 15 serovariants subdivided into two biovars:
  • Trachoma (ocular tropic strains A, B, Ba, C)
  • Genitourinary tract tropic (D, E, F, G, H, I, J, K)
  • Invasive lymphogranuloma venereum (L1, L2, L3)

Disease Associations of Chlamydia Trachomatis

• Trachoma: ocular infection
• STI- Genital discharge and perinatal infections
• Urethritis, cervicitis, pelvic inflammatory disease, neonatal infections
• (Estimated to cause 4 million new infections in US/yr)
• Most common bacterial STD in US
• Individuals frequently co-infected with N. gonorrhoeae
• Serotypes D-K
• STI- Lymphogranuloma venerium (L1, L2 and L3)

Chlamydia Transmission

• Human pathogen; no animal or environmental reservoirs
• Transmitted by direct contact with infected secretions
• Trachoma: Spread from infected eye by contaminated fingers or flies
• Newborn conjunctivitis: Passage down birth canal of mother with genital infection
• Genital infections and lymphogranuloma venereum transmitted by sexual contact

Trachoma

• Caused by different serovars vs genital infections with C. trachomatis
• Primarily a disease of people in developing countries characterized by crowding, poor sanitation, and poverty
• Transmitted from person to person on hands
• Begins as follicular conjunctivitis with diffuse inflammation
• Repeated infections lead to chronic inflammation, eyelid turning inward and abrasion of the cornea causing corneal ulceration and vision loss
• Very painful and debilitating
• Leading cause of preventable blindness worldwide (7 million people)

Urogenital Infections Associated with C. trachomatis

• Begins as urethritis or cervicitis
• Both associated with purulent discharge
• If untreated, can progress to:
  • Males: Prostatitis or epididymitis
  • Females: Endometritis, pelvic inflammatory disease (salpingitis)
• May lead to infertility

Neonatal Infections Associated with C. trachomatis

• Transmitted from infected mother to newborn via the vaginal canal
• Organisms contaminate infant's eyes and nasopharynx
• Leading to ophthalmia neonatorum, inflammation, hyperemia, purulent ocular discharge
• Leading to pneumonia

Chlamydophila pneumoniae

• Common infection in adults (200,000–300,000 cases/year)
• Most infections are asymptomatic
• Common in crowded conditions (schools, military barracks)
• Transmitted by person-to-person via inhalation of respiratory droplets
• Incubation: 3–4 weeks
• Clinical manifestations: atypical (walking) pneumonia
• Mild or asymptomatic
• Often not associated with fever
• Symptoms may resemble pharyngitis, bronchitis, persistent non-productive cough

Legionella pneumophila

• Gram-negative cell wall structure; does not pick up gram stain well
• Bacteria coccobacilli in tissue, pleomorphic in culture
• Over 50 species with 70 serogroups
• L. pneumophila serotypes 1 & 6 lead to over 90% of human infections
• Aquatic saprophytes living in biofilms and amoebae in water
• Found in various natural/man-made water sources (showers, fountains, spas, etc.)
• Transmitted in water mist (inhaled)
• Survive high temps. and treatments like chlorine

Legionella Associated Diseases

• Legionnaire's disease/Legionellosis: cause of community-acquired and hospital-acquired pneumonia.
  • ~10,000 reported cases/yr in US
  • More common in the elderly and others with risk factors like smoking, renal/liver disease, diabetes, immune suppression, cancer, AIDS, transplantation, corticosteriod use
• Pontiac Fever: Mild self-limiting febrile illness(fever, chills, myalgia, malaise)

Legionella Pathogenesis

• Infection through inhalation.
• Phagocytosis by alveolar macrophages; inhibit formation of phagolysosome surrounding the phagosome with materials from the endoplasmic reticulum.
• Incubation period: 2–10 days, abrupt onset of fever, chills, non-productive cough, headache
• Multisystem disease, involving GI tract (abdominal pain, diarrhea), liver (elevated LFTs), kidneys (electrolyte disturbances), and CNS
• No person-to-person transmission

Diagnosis of Legionellosis

• Clues to diagnoses:
• Pneumonia with pulmonary and non-pulmonary symptoms
• Negative sputum gram stain
• PCR
• Urine antigen test
• Culture – best sample is bronchoalveolar lavage grown on buffered charcoal yeast extract agar (BCYE)

Prevention of Legionella Infections

• If source is identified, treatments include superheating water to 70–80°C.
• Install copper-silver ionization units to produce metallic ions that kill microbes.
• Hyperchlorination NOT recommended as organisms are tolerant of chlorine in water.

Mycobacterium TB

• Acid-fast, aerobic rods, with a waxy coat that makes them resistant to drying and chemicals.
• Important for survival in/out of the body
• Does not gram stain
• Has a peptidoglycan layer
• Species of importance include:
• M. tuberculosis (TB)
• M. leprae (leprosy)
• M. intracellulare

Global TB Impact

• One of the leading causes of death globally.
• Approximately one-third of the world's population is infected.
• Estimated 8 million new cases yearly
• 1.5–3.0 million people die from TB annually
• One of the most common causes of death from infectious disease globally.
• Antibiotic resistance is a major problem.

Persons at Risk for TB in the US

• Foreign-born persons from TB-endemic areas (SE Asia, Africa)
• Close contacts of suspected TB patients
• Residents/employees of congregate settings (homeless shelters, prisons)
• People with HIV/AIDS
• Injection drug users
• Medically underserved / low-income populations

TB Pathogenesis

• Infection by inhalation of droplet nuclei
• Bacteria gain access to lungs and replicate within alveolar macrophages
• Replication is very slow
• Outcome depends on the strength of the host's immune response.
• Latent infection
• Active infection - Pulmonary - Non-pulmonary (disseminated involving multiple tissues/ organs)

Overview of TB Pathogenesis

• Primary lesion
• M. tuberculosis
• T cell
• Foamy giant cell
• Infected macrophage
• Firm caseous core inhibiting bacterial growth
• Persisting mycobacteria in lesion-free tissue
• Lymph nodes
• Persisting mycobacteria in primary lymph node lesions and lesion-free lymph nodes
• Post-primary disease
• Cavitating lesion

Latent TB Infections

• Immune-competent
• Bacteria are contained by a strong cell-mediated response, forming granulomas
• 90% of initial infections result in latent infection
• Granulomas may become calcified nodules (Gohn complex) over time.
• Bacteria within granulomas remain viable for years/decades without replicating.

Active TB Infections

• Active TB develops from initial infection (primary TB) or reactivation of latent infections (secondary TB)
• Primary TB: majority develop miliary TB (progressive, disseminated disease) usually in infants or children, immunocompromised individuals—pulmonary TB only occurs in about 6%
• Secondary TB (reactivated):
• Immune suppression allows latent TB to reactivate
• Granulomas break down releasing organisms
• Pulmonary TB results from reactivation in most cases

Primary vs. Reactivated Pulmonary TB

• Pulmonary disease may follow primary infection (~rare) or reactivation (most common) in adults
• Primary infection resulting in pulmonary disease is more common in children than adults
• Reactivated disease most often follows infection of an immune competent adult.

Manifestations of Reactivated Pulmonary TB

• Insidious onset of fever, night sweats, weight loss, anorexia, malaise, weakness
• Cough often productive of blood-streaked sputum
• Apical and posterior segments of upper lobes are most often affected
• In reactivated pulmonary disease, cavitary lesions may be seen on CXR

Miliary (Non-Pulmonary) TB

• Seen in children with primary infection
• Increasingly common in TB patients co-infected with HIV
• Infected macrophages can carry the organism hematogenously throughout the body
• Multiple organs can be affected:
• Lymphadenitis
• Meningitis
• Pott disease
• Chronic arthritis
• Genitourinary involvement
• Gastrointestinal involvement (GIT)

Diagnosis of TB

• Acid-fast stain of sputum (45-80% sensitivity)
• Sputum sample for nucleic acid detection
• NA detection using RNA probes and/or PCR can detect the presence of M. tuberculosis.
• Results in 1–2 days; <50–80% sensitive if smear-negative; >95% sensitive if smear-positive
• Culture (gold standard) takes 2-6 weeks, done to assess antibiotic sensitivity
• CXR for cavitary lesions
• TB skin test (PPD), injected intradermally. Within 48 hrs, a positive lesion is erythematous and indurated, measuring the area of induration. Can detect latent or active infection.
• Interferon gamma release assay (more consistent results compared to skin test); blood collected and T cells separated, incubated with TB antigens. Assay for production of IFN-γ

Mycobacterium avium complex (MAC)

• Group of mycobacteria that cause similar diseases
• Includes M. avium and M. avium intracellulare
• Ubiquitous in soil and water.
• Injects multiple species of birds and mammals (with or without causing disease)
• Causes serious disseminated disease in severely immunocompromised individuals (AIDS, cancer, or transplant patients).

MAC Disseminated Infection Pathogenesis

• Disseminated MAC occurs only in severely immunocompromised individuals/patients
• Enters body via ingestion or inhalation.
• Crosses mucosal epithelium and infects resting macrophages.
• Infected macrophages carry the organism throughout the body (lymph nodes, liver, spleen, bone marrow, and other sites)
• Organism replicates to very high numbers within macrophages in various tissues.
• Infected macrophages secrete cytokines, resulting in a cytokine storm.

Treatment of TB

• Use directly observed therapy to assure compliance.
• Treat latent TB for 9 months with a 2-drug regimen.
• Treat active tuberculosis as follows: Isolate with no identified resistance, use 4-drug regimen for the first 2 months, followed by 4–7 months with a 2-drug regimen.
• Resistance to anti-TB drugs is common, especially multidrug and extensively drug-resistant strains in some areas of the world
• Drug resistance is a serious issue.

Test your knowledge on the transmission, symptoms, and virulence factors of Chlamydia trachomatis and Chlamydophila pneumoniae. This quiz includes questions about their life cycles, host interactions, and diagnostic challenges related to pneumonia. Perfect for students studying microbiology and infectious diseases.