Chapter 20: Gram-Negative Bacterial Pathogens

Introduction

Gram-negative bacteria are a diverse group of pathogens responsible for a wide range of infectious diseases. Their cell wall structure, characterized by an outer membrane containing lipopolysaccharide (LPS), contributes to their virulence and resistance to certain antibiotics.

• Neisseria spp.: Includes Neisseria meningitidis (meningitis) and Neisseria gonorrhoeae (gonorrhea).

• Bordetella pertussis: Causes whooping cough; virulence factors include pertussis toxin.

• Haemophilus influenzae: Can cause meningitis, pneumonia, and epiglottitis; capsule is a key virulence factor.

• Pseudomonas aeruginosa: Opportunistic pathogen, especially in immunocompromised patients; produces exotoxins and biofilms.

• Campylobacter spp.: Causes gastroenteritis; associated with contaminated food.

• Salmonella typhi: Agent of typhoid fever; invades intestinal mucosa.

• Yersinia pestis: Causes plague; transmitted by fleas, has antiphagocytic factors.

• Escherichia coli: Various strains cause diarrhea, urinary tract infections; some produce Shiga toxin.

Key Features:

• Signs and symptoms vary by species (e.g., fever, diarrhea, respiratory distress).

• Virulence factors: LPS, capsules, toxins, pili, and secretion systems.

• Epidemiology: Transmission via respiratory droplets, contaminated food/water, or direct contact.

Example: Neisseria meningitidis causes meningitis, presenting with fever, headache, and neck stiffness. Its capsule helps evade immune detection.

Chapter 21: Pathogenic Vibrios, Spirochetes, Chlamydias, and Rickettsias

Introduction

This group includes bacteria with unique morphologies and life cycles, often associated with specific diseases and transmission routes.

• Treponema pallidum: Spirochete causing syphilis; transmitted sexually.

• Helicobacter pylori: Causes peptic ulcers; produces urease to survive stomach acid.

• Rickettsia spp.: Obligate intracellular pathogens; cause diseases like Rocky Mountain spotted fever.

• Vibrio cholerae: Causes cholera; produces cholera toxin leading to severe diarrhea.

• Chlamydia trachomatis: Causes trachoma and sexually transmitted infections; obligate intracellular.

Key Features:

• Signs and symptoms: Ulcers, rashes, diarrhea, conjunctivitis.

• Virulence factors: Toxins, ability to invade host cells, immune evasion.

• Epidemiology: Often transmitted via vectors (ticks, lice), sexual contact, or contaminated water.

Example: Vibrio cholerae infection leads to "rice-water" stools due to cholera toxin-induced fluid loss.

Chapter 22: Pathogenic Fungi

Introduction

Pathogenic fungi can cause superficial, subcutaneous, or systemic infections, especially in immunocompromised individuals.

• Trichophyton: Causes dermatophytosis (ringworm).

• Candida albicans: Causes candidiasis; can affect mucous membranes and skin.

• Coccidioides immitis: Causes coccidioidomycosis (Valley fever); inhaled spores infect lungs.

• Histoplasma capsulatum: Causes histoplasmosis; found in soil contaminated with bird or bat droppings.

Key Features:

• Signs and symptoms: Skin lesions, respiratory symptoms, systemic illness.

• Virulence factors: Ability to grow at body temperature, spore formation, immune evasion.

• Epidemiology: Transmission via inhalation of spores, direct contact.

Example: Candida albicans can cause oral thrush in immunocompromised patients.

Chapter 23: Pathogenic Protozoa and Helminths

Introduction

Protozoa and helminths are eukaryotic pathogens responsible for significant morbidity worldwide, often transmitted via contaminated water, food, or vectors.

• Protozoa:

  • Naegleria fowleri: Causes primary amoebic meningoencephalitis.

  • Trichomonas vaginalis: Causes trichomoniasis, a sexually transmitted infection.

  • Trypanosoma spp.: Includes agents of sleeping sickness and Chagas disease.

  • Giardia lamblia: Causes giardiasis, a diarrheal illness.

  • Entamoeba histolytica: Causes amoebic dysentery.

• Helminths:

  • Taenia spp.: Tapeworms causing intestinal infections.

  • Ascaris lumbricoides: Roundworm causing ascariasis.

  • Enterobius vermicularis: Pinworm causing enterobiasis.

Key Features:

• Signs and symptoms: Diarrhea, abdominal pain, neurological symptoms.

• Virulence factors: Cyst formation, immune modulation, tissue invasion.

• Epidemiology: Transmission via contaminated water, food, or direct contact.

Example: Giardia lamblia infection leads to malabsorption and watery diarrhea.

Chapter 24: Pathogenic DNA Viruses

Introduction

DNA viruses are responsible for a variety of human diseases, ranging from mild to severe. They replicate using host cell machinery and often establish latent infections.

• Human Herpes Virus 1-5: Includes herpes simplex viruses (oral/genital herpes), varicella-zoster virus (chickenpox/shingles), cytomegalovirus, Epstein-Barr virus (mononucleosis), and human herpesvirus 5.

• Papillomavirus: Causes warts and is associated with cervical cancer.

• Hepatitis B: Causes hepatitis B; transmitted via blood and body fluids, can lead to chronic liver disease.

Key Features:

• Signs and symptoms: Skin lesions, jaundice, fever, lymphadenopathy.

• Virulence factors: Ability to evade immune response, latency, oncogenic potential.

• Epidemiology: Transmission via direct contact, sexual contact, blood, or vertical transmission.

Example: Hepatitis B virus infection can progress to chronic hepatitis and hepatocellular carcinoma.

General Information about Pathogen Groups

Overview

Each group of pathogens—bacteria, fungi, protozoa, helminths, and viruses—has unique characteristics affecting their transmission, pathogenesis, and epidemiology.

• Bacteria: Prokaryotic, reproduce by binary fission, possess diverse virulence factors.

• Fungi: Eukaryotic, reproduce by spores, can be opportunistic.

• Protozoa: Unicellular eukaryotes, often form cysts for survival.

• Helminths: Multicellular eukaryotes, complex life cycles.

• Viruses: Acellular, require host cells for replication, can integrate into host genome.

Comparison Table: Main Features of Pathogen Groups

Additional info: Students should be familiar with the signs, symptoms, epidemiology, and pathogenic mechanisms (virulence factors/structures) for each listed organism and the diseases they cause.