Non-Culturable Bacterial Agents

  • Definition of Non-Culturable Bacterial Agents:

    • Obligate intracellular bacteria that are non-culturable or extremely difficult to culture.

    • Organisms from various genera are characterized by very small size and obligate intracellular parasitism, making them challenging to cultivate.

Chlamydiaceae Family

  • Chlamydia trachomatis

    • Several serotypes:

    • Types A, B, C: Cause chronic infections; notably chronic eye infection (trachoma), which may lead to blindness.

    • Types D-K: Associated with urethritis and pelvic inflammatory disease (PID), potentially leading to ectopic pregnancy or infertility; often subclinical, especially in women.

    • Neonatal effects:

    • Neonatal pneumonia and neonatal conjunctivitis, acquired during passage through an infected birth canal.

    • Structural characteristics:

    • Obligate intracellular bacteria with NO peptidoglycans in their cell wall.

    • Life cycle:

    • Dimorphic life cycle with two forms:

      • Elementary Body (EB): Spore-like form.

      • Reticulate Body (RB): Vegetative, metabolically active form.

    • Diagnosis methods:

    • Lab tests including Nucleic Acid Amplification Tests (NAATs), Enzyme-Linked Immunosorbent Assay (ELISA), and culture in cell lines specific for Chlamydiae.

Chlamydophila Genus

  • Chlamydophila psittaci

    • Reservoir: Primarily found in birds, especially parrots.

    • Disease: Causes psittacosis, an atypical pneumonia that can spread systemically.

  • Chlamydophila pneumoniae

    • Known as walking pneumonia, characterized as atypical (interstitial) pneumonia.

    • Transmission occurs via aerosols.

Summary Table of Chlamydiaceae

Species

Serotype

Natural Host

Diseases in Humans

Chlamydia trachomatis

A, B, C

Humans

Trachoma, cervicitis, urethritis, proctitis, conjunctivitis, neonatal pneumonia, lymphogranuloma venereum

Chlamydophila psittaci

Primarily A

Birds and non-human mammals

Atypical pneumonia (psittacosis)

Chlamydophila pneumoniae

Humans

Acute respiratory disease

Rickettsiaceae Family

  • Definition:

    • Obligate intracellular bacteria that cannot be seen under a light microscope and cannot be cultivated in artificial media.

  • Transmission:

    • Zoonotic with geographical dependence.

    • Spread through arthropod vectors (ticks, mites, fleas, lice) or animal reservoirs.

    • Humans primarily acquire infections via arthropod bites with the exception of Coxiella burnetii, which can be inhaled or ingested (product of animal birth).

  • Symptoms (Rickettsia Triad):

    • Headache, fever, rash.

  • Diagnostic Methods:

    • Microscopy using Giemsa stain and serological tests.

Principal Rickettsioses

Rickettsial Agent

Diseases

Reservoir in Nature

Transmission

Geographic Distribution

Rickettsia rickettsii

Rocky Mountain spotted fever

Ticks

Tick bite

North and South America

Rickettsia conorii

Boutonneuse fever

Ticks

Tick bite

Southern Europe, Africa and Asia

Rickettsia prowazekii

Epidemic typhus

Humans, flying squirrels

Louse feces

Worldwide

Rickettsia typhi

Recrudescent typhus

Humans

Flea feces

Worldwide, especially in the tropics and subtropics

Orientia tsutsugamushi

Scrub typhus

Chiggers

Chigger bite

Asia, Oceania, and northern Australia

Ehrlichia chaffeensis

Monocytotropic ehrlichiosis

Deer, goats, dogs

Tick bite

North America, Africa, Asia

Anaplasma phagocytophilum

Granulocytotropic anaplasmosis

Deer, elk, wild rodents

Tick bite

North America and Eurasia

Coxiella burnetii

Q fever

Cattle, sheep, goats, other livestock

Aerosol from infected birth products

Worldwide

Detailed Rickettsiaceae Information

  • Rickettsia rickettsii

    • Disease: Rocky Mountain spotted fever.

    • Symptoms: Rash typically starts on palms and soles of feet.

  • Rickettsia typhi

    • Disease: Endemic typhus.

    • Symptoms: Rash starts centrally and spreads outwards, not affecting palms and soles.

  • Rickettsia prowazekii

    • Disease: Epidemic typhus.

    • Transmission via human body lice.

  • Ehrlichia species

    • Disease: Ehrlichiosis.

    • Symptoms: Fever, headache, fatigue, muscle aches occurring 1-2 weeks post-tick bite; usually no rash.

    • Primary vector in the U.S.: Lone star tick (Amblyomma americanum).

  • Coxiella burnetii

    • Disease: Q fever.

    • Symptoms: Flu-like symptoms including abrupt fever, profuse perspiration, interstitial pneumonia; lasts 1-2 weeks.

    • Transmission: Inhalation of aerosolized spores or ingestion of raw milk from infected animals.

    • Characterized as a spore former and has a negative Weil-Felix reaction.

Weil-Felix Test

  • Definition:

    • An agglutination test for the diagnosis of rickettsial infections.

    • Based on the presence of antigenic cross-reactivity between Rickettsia spp. and certain Proteus spp. serotypes.

  • Mechanism:

    • Rickettsial infections lead to antibodies that cross-react and agglutinate indicating a positive Weil-Felix reaction.

  • Procedure:

    • A small amount of the patient's serum is placed on a solid surface; a drop of the desired antigen is added and mixed. Visible agglutination is indicative of a positive result.

    • All rickettsial infections yield a positive Weil-Felix reaction, while Coxiella burnetii presents a negative result.

Spirochetes

Treponema

  • Treponema pallidum

    • Classification: Gram-negative spirochete (spiral-shaped), highly mobile.

    • Disease: Venereal syphilis.

  • Treponema pallidum pertenue

    • Disease: Yaws (non-venereal endemic syphilis).

    • Characteristics: Tropical skin infection starting with a round, hard swelling (2-5 cm).

  • Treponema pallidum endemicum

    • Disease: Bejel (non-venereal endemic syphilis).

    • Transmission: Mouth-to-mouth via shared utensils.

    • Geographic prevalence: Eastern Mediterranean, North and West Africa.

  • Treponema carateum

    • Disease: Pinta (non-venereal endemic syphilis).

    • Characteristics: Skin lesions and discoloration due to direct non-sexual contact affecting exposed areas of skin, such as the face and extremities.

Summary Table for Treponema

Agent

Transmission

Geographic Location

Disease

Clinical Manifestations

Age Group

T.pallidum subsp. pallidum

Sexual contact or congenital

Worldwide

Venereal syphilis

Refer to text above page

All ages

T.pallidum subsp. pertenue

Traumatized skin to infected lesion

Humid, warm climates

Yaws

Skin papules, nodules, ulcers

Children

T.pallidum subsp. endemicum

Mouth to mouth (utensils)

Arid, warm climates

Endemic nonvenereal syphilis

Skin/mucous patches, papules, macules, ulcers

Children

T.carateum

Traumatized skin to infected lesion

Semiarid, warm climates

Pinta

Skin papules, macules

Primarily children and adolescents

Borrelia

  • Transmission:

    • Via tick or louse bite.

  • Borrelia burgdorferi

    • Disease: Lyme disease.

    • Vector: Ixodes ticks (associated with deer).

    • Notes: Most common vector-borne disease in North America and Europe and an emerging issue in northern Asia.

  • Symptoms Progression:

    • Stage 1 (days to months post-tick bite): Fever, headache, fatigue, depression, erythema migrans.

    • Stage 2 (weeks to months post-tick bite): Neurologic symptoms including bilateral Bell’s palsy, cardiac issues, migratory arthralgia (migrating joint pain).

    • Stage 3 (months to years post-tick bite): Chronic monoarthritis (especially of the knee), potential for subacute encephalitis.

Leptospira

  • Description:

    • Question-marked shaped bacteria, associated with tropical diseases.

  • Leptospira interrogans

    • Transmission: Acquired through contact with water contaminated by rodent urine.

    • Pathways: Ingestion of contaminated water or via breaks in skin, eyes, or mucous membranes.

    • Severe forms can lead to jaundice, kidney failure, and bleeding (known as Weil's disease).

  • Leptospirosis

    • Phase 1: Symptoms include fever, chills, headache, with an asymptomatic phase possible.

    • Phase 2: Symptoms involve meningitis, liver damage (jaundice), and renal failure.

Quick Check Questions

  1. Which bacteria has an avian reservoir (e.g. parrots)?

    • Answer: Chlamydophila psittaci

  2. Which bacteria is found in water contaminated by rodent urine?

    • Answer: Leptospira interrogans

  3. Which bacterium gives a negative Weil-Felix reaction?

    • Answer: Coxiella burnetii

  4. Which non-venereal endemic tropical syphilis is found in the MENA region?

    • Answer: Treponema pallidum endemicum (Bejel)

  5. Which endemic typhus is transmitted by rat fleas and characterized by a rash that starts centrally and spreads outwards?

    • Answer: Rickettsia typhi