Gram-Negative Rods Overview

Gram-Negative Rods

• Other gram-negative rods covered include Haemophilus, Pseudomonas, Brucella, and Chlamydia species.
• Objectives include describing the clinical significance of infections, identifying organisms, explaining pathogenicity, and outlining the laboratory identification processes.
• Haemophilus species are gram-negative coccobacilli or rods.
• They require hemin (X factor) and NAD+ (V factor) for growth.
• Haemophilus influenzae type B (Hib) causes severe disease; non-encapsulated types are less severe and part of normal respiratory flora.
• H. influenzae is a common cause of meningitis in children.
• Haemophilus species are identified by isolation from sterile sites (blood, CSF, or synovial fluid), rapid diagnosis, and growth on chocolate agar (X, V factors).
• Prevention involves vaccination and antibiotics.

Pseudomonas Species

• Pseudomonas species are motile, encapsulated, and obligate aerobes.
• They are found in soil, water, plants, and animals.
• They can colonize without causing disease but can cause opportunistic infections (e.g., nosocomial infections).
• Pseudomonas aeruginosa is a primary human pathogen that can grow in water-containing vessels, laboratory water baths, and wet IV tubing.
• Pseudomonas aeruginosa pathogenesis begins with attachment and colonization, followed by tissue damage from adherence and colonization, production of toxins, and extracellular products.
• Localized and systemic infections can occur.
• Clinical significance includes localized infections (respiratory, gastrointestinal, and CNS), ranging from pneumonia and diarrhea to meningitis.
• Identification involves blood agar plates, MacConkey plates, and biochemical/diagnostic tests.
• Treatment is challenging due to antibiotic resistance, necessitating combinations of antibiotics, especially for immunocompromised individuals.

Brucella Species

• Brucella species are animal pathogens causing zoonotic infections (transmission from animals to humans).
• Transmission is often associated with animal contact or consumption of contaminated products (dairy, meat).
• Brucellosis includes B. abortus (cattle) and other species, with transmission to humans by animal contact and consumption of contaminated animal products or inhaling aerosols.
• Infection routes include skin cuts, gastrointestinal tract, and inhalation of aerosols.
• The causative organism spreads via lymphatic systems into various body organs.
• Clinical symptoms include incubation for 5 days to several months. Flu-like symptoms and undulant fever (temperatures repeatedly rise and fall) are common.
• Complications include GI tract, skeletal, neurological, cardiac, and pulmonary involvement.
• Identification involves detailed patient history, samples from blood, body fluids, or tissues cultured on blood agar, and treatment with combinations of antibiotics.

Neisseria gonorrhoeae

• Gram-negative, aerobic cocci (diplococci) are sexually transmitted.
• Transmission is by sexual contact or during childbirth through an infected birth canal.
• Attachment to host cells is facilitated by pili.
• Resistance to phagocytosis is attributed to lipooligosaccharide (LOS) and opacity proteins.
• Infections can take place in the genitourinary tract (males may exhibit painful urination with yellow discharge; females may have a greenish-yellow discharge and possible salpingitis, pelvic inflammatory disease, or infertility risks).
• Symptoms of rectal infection include constipation, painful defecation, and purulent discharge (prevalent among homosexual men).
• Infections and complications can be treated with cephalosporins, and treatment for partners is recommended.

Treponema pallidum

• Treponema pallidum is a sexually transmitted spirochete, a gram-negative bacterium, with a corkscrew or helical shape.
• Syphilis occurs in three stages: primary (chancre at inoculation site), secondary (rash, papules, and other systemic symptoms), and tertiary (gummatous lesions and organ damage).
• Congenital syphilis can lead to severe fetal or neonatal complications.
• Transmission includes sexual contact and transplacental transmission (congenital syphilis).
• Diagnosis involves dark-field microscopy, immunofluorescence, and serological tests (ELISA).
• Treatment requires penicillin.

Chlamydia Species

• Chlamydia species are gram-negative, obligate intracellular parasites.

• They have a unique life cycle with infectious elementary bodies and reproductive reticulate bodies.

• Infection occurs through cell entry and avoiding lysosome fusion, and multiplication through binary fission.

• Chlamydia trachomatis causes infections in the genitourinary tract and eyes (e.g. urethritis, cervicitis, epididymitis, or conjunctivitis).

• Chlamydia trachomatis (LGV) causes lymphogranuloma venereum, with painful inguinal or perirectal lymph node swelling.

• Chlamydia trachomatis (Trachoma) leads to chronic eye infections and blindness.

• Chlamydia psittaci causes psittacosis (ornithosis), a zoonotic disease affecting the lower respiratory tract.

• Chlamydia pneumoniae causes pneumonia, often asymptomatic.

• Diagnosis involves PCR, culture (tissue culture), and antibody detection (immunofluorescence).

• Treatment involves antibiotics (e.g., erythromycin, azithromycin, or doxycycline).

This quiz covers the clinical significance, pathogenicity, and identification processes of various gram-negative rods, including Haemophilus and Pseudomonas species. Learn about their growth requirements, disease implications, and laboratory diagnostics. Perfect for those studying microbiology and infectious diseases.