Microbiology Study Guide: Bacterial and Viral Pathogens, Eukaryotic Microbes, and Cell Division

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: $\text{CG pairs: 3 bonds; AT pairs: 2 bonds}$

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

Pathogen	Disease	Transmission	Prevention
Corynebacterium diphtheriae	Diphtheria	Airborne droplets	DTaP vaccine
Bordetella pertussis	Pertussis (Whooping cough)	Airborne droplets	DTaP vaccine
Varicella Zoster Virus (VZV)	Chickenpox, Shingles	Airborne, direct contact	Varicella vaccine
Measles virus	Measles (Rubeola)	Airborne droplets	MMR vaccine
Rubella virus	German Measles (Rubella)	Airborne droplets	MMR vaccine

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