Microbiology: Gram-Negative Bacteria Quiz

Gram - Bacteria

• LPS (Lipopolysaccharide) acts as an endotoxin, triggering an over-reactive immune response known as sepsis
• Sepsis is particularly dangerous when accompanied by bacteremia (bacteria in the blood)
• Gram-negative bacteria have a thin peptidoglycan layer that doesn't bind to the gram stain, making them appear pink.

Gram (-) Diplococci

• Neisseria is a genus of gram-negative diplococci.
• N. gonorrhoeae and N. meningitidis are two major species responsible for various infections.
• Pili are hollow tubes that extend from the bacterial cell and serve multiple functions:
  • Attachment: The pili act as suction cups, allowing the bacteria to adhere to surfaces.
  • Transfer of DNA: Enable the transfer of genes, including antibiotic resistance, between bacteria.
  • Motility: Facilitates short-distance movements for bacteria.
• Porin proteins inhibit neutrophil function and facilitate cell invasion.
• IgA protease is a protein that degrades IgA, an antibody found on mucosal surfaces.
• Capsules, often present on N. meningitidis, render bacteria slippery, making them less readily phagocytized by macrophages.

Gonorrhea

• Transmission: Occurs through sexual contact and can also be transmitted to the eyes during childbirth.
• Symptoms: Many cases are asymptomatic.
• Ping pong effect: Recurring infections can occur if a partner doesn't receive treatment and can become worse for individuals with repeated exposure.
• Complications: Can lead to chronic infections, sterility, and in rare cases, systemic infections affecting joints.
• Treatment: Antibiotics are effective but resistance is a growing concern.
• Prevention: Safe sex practices and education are critical for controlling the spread.

Meningitis

• Transmission: Primarily occurs through respiratory droplets.
• Symptoms: Many individuals are asymptomatic.
• Complications: Can lead to meningitis characterized by inflammation of the meninges, toxic shock, and in rare cases, systemic infections.
• Treatment: Antibiotics are the primary treatment, but resistance is a concern.
• Prevention: Vaccination against specific strains exists and can reduce the severity of infection.

Gram (-) Coccobacilus

• Haemophilus and Bordetella are genera of gram-negative coccobacili.

Haemophilus influenzae

• Facultative anaerobic and fermentative.
• Normal flora of the respiratory tract, but can cause infections in specific conditions.
• Virulence Factors:
  • Capsule: Provides protection against immune system cells.
  • Adhesions: Adhere to cells of the respiratory tract and can impair ciliary function, damaging the respiratory tract.
  • IgA proteases: Breakdown IgA, reducing its ability to fight infection.
• Transmission: Occurs through respiratory droplets.
• Treatment: Effectively treated with antibiotics, resistance is not a significant concern.
• Prevention: Vaccination against encapsulated strains is available.

Bordetella pertussis

• Strict aerobe and primarily affects humans.
• Virulence factors:
  • Adhesions: Allow the bacteria to attach to the respiratory tract, making them difficult to remove.
  • Exotoxins:
    • Local toxin: Blocks ciliary action, leading to tissue damage and increased risk of secondary infection.
    • Systemic toxin: Interferes with signaling pathways, resulting in increased respiratory secretions and mucus production.
    • Pertussis toxin: Inhibits cell signaling pathways, leading to higher mucus production and bacterial burden.
• Transmission: Occurs through respiratory droplets.
• Treatment: Antibiotics are effective, but early detection is crucial.
• Prevention: Vaccination is available to minimize the risk of infection.

Legionella pneumophila

• Facultative intracellular bacteria that can grow in ameba and alveolar macrophages.
• Virulence factors:
  • LPS mediates damage upon bacterial death.
  • Resistance to intracellular defenses: Can survive within cells without being destroyed.
  • Resistance to cleaning agents: Survival in water and resistance to bleach make it a potential public health threat.
• Transmission: Occurs through contaminated water, primarily mist or ice.
• Treatment: Antibiotics are effective, early detection is key.
• Prevention: Proper water filtration and sanitation are essential.

Yersinia pestis

• Natural host: Rats (asymptomatic)
• Zoonotic infection: Humans are a dead-end host.
• Virulence factors:
  • Resistance to phagocytic killing: Evasion of immune system cells.
  • Cytotoxins: Disrupt actin filaments and suppress cytokine production.
  • Plasmid encoded:
    • Capsule: Protection against phagocytosis.
    • Complement degrading genes: Prevents the formation of the membrane attack complex (MAC), a critical component of the immune response.
• Transmission: Primarily spread by fleas, but pneumonic plague can be spread from person to person.
• Treatment: Effective treatment with antibiotics.
• Prevention: Rodent control measures are critical for preventing transmission.

Pseudomonas aeruginosa

• Environments: Widespread in moist environments like soil, vegetation, water, and hospitals.
• Growth requirements: Minimal nutritional requirements, enabling it to thrive in a variety of environments.
• Virulence factors: Virulent, possessing a wide range of virulence factors:
  • Biofilms: Form protective layers that resist antibiotics and immune cells.
  • Capsules: Protect the bacteria from immune system cells.
  • Adhesions: Allow attachment to surfaces.
  • Exotoxins: Block protein synthesis.
  • Pigments: Produce toxic forms of oxygen and stimulate cytokine release.
  • Enzymes: Degrade various host components, like lipids and elastin.
  • Complement inhibition: Suppress the complement system, a crucial part of the immune response.
  • Neutrophil inhibition: Inhibit the function of neutrophils, immune cells.
• Transmission: Contact with contaminated materials, including fomites.
• Treatment: Requires combination therapy due to high intrinsic and acquired antibiotic resistance.
• Prevention: Good hygiene practices are essential for preventing infection.

Gram-Negative Curves (Vibrios, Commas)

• Flagella: Motility.
• Endotoxins: LPS contributes to sepsis.
• Secretion systems: Release toxins and virulence factors into the environment.

Vibrio cholerae

• Environment: Found in water and shellfish.
• Growth: Can thrive in water at a wide temperature range.
• Motility: Flagella allows movement in water and within hosts.
• Virulence factors:
  • Pilus: Adhesion and secretion of toxins.
  • Exotoxins:
    • Cholera toxin: Disrupts cellular regulation, leading to diarrhea and dehydration.
    • Other toxins: Can cause disease independently of cholera toxin.
• Transmission: Fecal-oral route, primarily through contaminated water.
• Treatment: Rehydration therapy and antibiotics are effective.
• Prevention: Sanitation and safe water sources are critical.

Campylobacter jejuni

• Normal flora: Found in poultry, but can cause disease in humans.
• Zoonotic infection: Human infection is usually caused by contaminated food.
• Virulence factors:
  • Molecular mimicry: Its antigens resemble human cell components, leading to an immune response that can cause inflammatory conditions.
• Transmission: Consumption of contaminated food, particularly poultry.
• Treatment: Usually self-limiting, but symptomatic treatment with fluid and electrolytes may be necessary.
• Prevention: Proper cooking of poultry and food safety practices are essential.

Helicobacter pylori

• Host: Restricted to humans.
• Virulence factors:
  • Motility: Allows movement within stomach lining and burrowing into ulcers.
  • Urease activity: Neutralizes stomach acid, creating a suitable environment for survival.
  • Adhesion proteins: Allow attachment to stomach cells.
  • Exotoxins: Contribute to damage in the stomach.
  • O antigen: Resembles human blood type O sugars, potentially contributing to immune evasion.
• Transmission: Fecal-oral route.
• Treatment: Antibiotics and proton pump inhibitors (though their use is being reevaluated).
• Prevention: Good hygiene habits and safe drinking water are important for prevention.

Spirochetes

• Gram (-) or Gram neutral: Stain weakly gram-negative due to their thin peptidoglycan layer.
• Genus: Borrelia and Treponema.

Borrelia burgdorferi

• Natural host: Mice and deer, transmitted by ticks.
• Zoonotic infection: Humans are a dead-end host.
• Vector: Ticks act as vectors, transmitting the bacteria between hosts.
• Bullseye rash (Erythema migrans): A classic symptom of Lyme disease.
• Virulence factors: No identifiable toxins, but antigenic variation of outer proteins contribute to immune evasion.
• Transmission: Tick bites, particularly in the summer months.
• Disease: Lyme disease can cause a spectrum of symptoms:
  • Erythema migrans: The classic bullseye rash.
  • Joint arthritis: Inflammation of joints, especially in the knees.
  • Neurological manifestations: Palsy and other neurological problems.
  • Cardiac complications: Heart problems.
• Treatment: Antibiotics are effective, but complete clearance can be challenging.
• Prevention: Tick control measures are essential for preventing Lyme disease.

Treponema pallidum

• Host: Exclusively infects humans.
• Virulence factors: Adhesions allow attachment to host cells, and the primary damage is often immune-mediated.
• Disease: Causes syphilis, a sexually transmitted infection with stages:
  • Tertiary syphilis: Immune-mediated tissue and organ destruction.
  • Neurosyphilis: Infection of the nervous system.
  • Cardiovascular syphilis: Infection of the cardiovascular system.
• Transmission: Sexual contact and vertically from mother to child.
• Prevention: Safe sex practices, education, and early detection are important for controlling syphilis.

Obligate Intracellular Bacteria

• Can only replicate inside host cells.

Gram (-) Rods

• LPS: Contain LPS, which can trigger an immune response.

Chlamydia trachomatis

• Host: Humans.
• Virulence factors:
  • Cell lysis: Breakdown of host cell membranes, releasing bacterial contents and triggering an inflammatory response.
  • Elementary bodies (EBs): Inert, spore-like form that is stable in the environment and allows transmission.
  • Reticulate bodies (RBs): Metabolically active and replicating form within host cells.
• Transmission: Sexually transmitted infection.
• Symptoms: Often asymptomatic but can lead to:
  • Epithelial damage: Damages cells of the vaginal tract and other mucosal areas.
  • Memory response: Repeated infections can lead to more severe symptoms.
• Treatment: Antibiotics are effective.
• Prevention: Safe sex practices and education are crucial for preventing transmission.

Rickettsia rickettsii

• Natural host: Rodents and hard ticks.
• Zoonotic infection: Humans are a dead-end host.
• Virulence factors:
  • Adhesions: Ability to adhere to host cells.
  • Cell lysis: Lyse infected cells, releasing bacteria and triggering an immune response.
• Transmission: Through bites of infected hard ticks.
• Symptoms: Rocky Mountain Spotted Fever, characterized by:
  • Rash: A distinctive spotted rash.
  • High fever:
  • Headaches:
  • Malaise: General feeling of discomfort.
• Complications: Can lead to damage of blood vessels (endothelial cells), resulting in organ failure.
• Treatment: Antibiotics are effective but early detection is crucial.
• Prevention: Control of rodent populations and tick bites are important for prevention.

Test your knowledge on the characteristics and pathogenicity of Gram-negative bacteria. This quiz covers various aspects including virulence factors, immune evasion, and clinical manifestations associated with these organisms. Perfect for microbiology students seeking to deepen their understanding of bacterial pathogens.