Bacterial Biofilms and Pathogenesis

Biofilm Formation and Maturation

Biofilms are structured communities of microorganisms attached to surfaces and embedded in a self-produced extracellular matrix. They play a significant role in microbial survival and pathogenicity.

• Biofilm Stages: Initial attachment, microcolony formation, maturation, and dispersion.

• During biofilm maturation: Antibiotics are less effective due to the protective matrix and altered metabolic states of bacteria.

• Oral biofilms: Important in dental diseases such as caries and periodontitis.

• Microbial mats: Thick, layered biofilms found in aquatic environments, often composed of multiple microbial species.

Bacterial Diseases: Diphtheria and Pertussis

Diphtheria

Diphtheria is a serious respiratory disease caused by Corynebacterium diphtheriae. It primarily affects children and can be prevented by vaccination.

• Pathogen: Corynebacterium diphtheriae (airborne transmission).

• Pathogenesis: Produces exotoxin that causes a pseudomembrane in the throat, leading to suffocation and tissue destruction.

• Diagnosis: Isolation of C. diphtheriae from the throat.

• Prevention: DTaP vaccine (diphtheria toxoid).

• Treatment: Antibiotics; antitoxin available for acute cases.

• Trends: 100,000–200,000 cases and 15,000 deaths per year in the US before vaccines; cases declined rapidly after vaccine introduction in the 1940s.

Pertussis (Whooping Cough)

Pertussis is an acute, highly contagious respiratory disease caused by Bordetella pertussis, primarily affecting children.

• Pathogen: Bordetella pertussis (gram-negative, non-motile, obligate aerobe, forms capsule).

• Transmission: Airborne droplets; school-age children are most affected.

• Virulence Factors: Produces two toxins: tracheal cytotoxin (damages ciliated cells) and pertussis toxin (systemic effects).

• Stages of Disease:

  • Catarrhal stage: 1–2 weeks, resembles common cold.

  • Paroxysmal stage: 1–6 weeks, violent coughing fits, possible rib fractures.

  • Convalescence stage: 2–3 weeks, gradual recovery.

• Prevention: Acellular pertussis vaccine (part of DTaP).

• Trends: Cases declined after vaccine introduction; recent increases due to breakdown in herd immunity.

• New Strategies: Additional vaccination for teens, adults, pregnant women; public health campaigns.

Viral Diseases: Herpesviruses and Measles

Human Herpes Virus 3 (Varicella Zoster Virus, VZV)

VZV causes chickenpox (primary infection) and can reactivate later in life as shingles.

• Transmission: Airborne; highly contagious among children.

• Symptoms: Low-grade fever, rash; usually mild in children.

• Latency: Virus remains dormant in neurons; can reactivate as shingles (herpes zoster).

• Reversions: Virus can reactivate multiple times, but most reactivations are contained without symptoms.

Measles (Rubeola)

Measles is a highly infectious viral disease caused by a paramyxovirus, primarily affecting children.

• Transmission: Airborne; virus enters nose and throat.

• Symptoms: Fever, rash, cough, conjunctivitis; can cause immune suppression and secondary infections.

• Pathogenesis: Haemagglutinin protein causes cells to fuse (syncytia), infects lymphoid tissue.

• Prevention: MMR vaccine (measles, mumps, rubella).

• Trends: Cases declined after vaccination; resurgence in unvaccinated populations.

German Measles (Rubella)

Rubella is a mild viral infection but can cause severe birth defects if contracted during pregnancy.

• Transmission: Airborne; infects via endosome receptors.

• Prevention: Vaccination is the best prevention.

Bacterial Cell Division and Chromosome Segregation

DNA Replication in Bacteria

Bacterial DNA replication is a highly regulated process ensuring each daughter cell receives a complete chromosome.

• Origin of Replication (oriC): Specific DNA sequence where replication begins.

• AT-rich regions: Weaker hydrogen bonding (2 bonds) facilitates strand separation.

• DNA A box: Binding site for DnaA ATP, which initiates unwinding.

• Helicase (DnaB): Unwinds DNA after DnaA-mediated opening.

• SeqA: Binds hemimethylated DNA to regulate re-initiation.

Key Equations:

• Hydrogen bonds:

Chromosome Segregation Systems

• PAR System: DNA-binding proteins (ParA, ParB) and physical properties of chromosomes move DNA to cell poles.

• Tethered Old Chromosome: Anchored to cell pole; new cell gets pushed to the top during division.

Cell Division Machinery

• FtsZ Protein: Tubulin-like protein crucial for binary fission; forms a contractile ring at the cell center.

• FtsZ Complex: Anchors in the center, divides cells, and recruits other division proteins.

• Min System: Determines the cell midpoint for division; prevents FtsZ ring formation at cell poles.

• If Min system is nonfunctional: Unequal cell division occurs.

• If FtsZ is nonfunctional: Cell cannot divide properly and becomes elongated.

Eukaryotic Microbes and Protists

Genetic and Ecological Diversity

• Eukarya: Most genetically and ecologically diverse branch of life; includes multicellular and unicellular organisms.

• Multicellularity: Most eukaryotic cells are multicellular; all have complex cell structures and organelles.

• Acquisition of Mitochondria: Primary endosymbiosis event; secondary endosymbiosis led to further diversity (e.g., algae).

Protists and Pathogenic Eukaryotes

• Giardia: Parasitic protist with two nuclei; causes giardiasis via contaminated water. Exists as trophozoite (disease form) and cyst (infectious form).

• Trichomonas: Large genome; causes trichomoniasis.

• Trypanosoma brucei: Causes African sleeping sickness; transmitted by tsetse fly.

• Trypanosoma cruzi: Causes Chagas disease; transmitted by kissing bug.

• Leishmania tropica/L. mexicana: Transmitted by sandfly; causes cutaneous leishmaniasis.

• Visceral Leishmaniasis: Severe, often fatal disease affecting internal organs.

Other Eukaryotic Microbes

• Dinoflagellates: Marine/freshwater protists; some produce toxins, important coral symbionts.

• Diatoms: Silica cell walls; major component of plankton, phototrophic.

• Tardigrades: Water bears; highly resistant, can survive extreme conditions (including space).

Fungi

Fungal Biology and Roles

• Fungi: Eukaryotic, heterotrophic organisms; absorb nutrients and reproduce via spores.

• Roles: Decomposers, nutrient recyclers, some are pathogens.

• Cellular Forms: Some fungi are unicellular (e.g., yeast), others are multicellular (e.g., molds).

• Similarities to Bacteria: Some bacteria resemble fungi in appearance (e.g., actinomycetes).

Summary Table: Key Bacterial and Viral Pathogens

Additional info: Some explanations and context have been expanded for clarity and completeness based on standard microbiology knowledge.