Microbiology Final (only recent info)

Define Biofilm

 A biofilm is a structured microbial community attached to a surface and encased in self-produced extracellular polymeric substances (EPS) (polysaccharides, proteins, DNA). Biofilms are important in natural and clinical settings, influencing processes like nutrient cycling and antibiotic resistance.

What are the selective Advantages of Biofilms

Biofilms provide enhanced protection from environmental stresses, increase nutrient access, and promote cell-to-cell communication, contributing to improved survival and growth. They also facilitate persistence against antimicrobials and increase genetic diversity through horizontal gene transfer.

Examples of biofilms

include dental plaque, microbial mats, and biofilms on medical implants.

Effects of biofilms

Biofilms can lead to chronic infections, contribute to industrial clogging and corrosion, and cause contamination of medical equipment. Additionally, they play a positive role in bioremediation and wastewater treatment by aiding in the breakdown of pollutants.

Define  Quorum Sensing

Cell-to-cell communication using signaling molecules (autoinducers) that regulate gene expression in response to population density.

Vibrio Fischeri

• Free-living cells → no light
  
  

In high density (e.g., in squid light organ), autoinducer (AHL) concentration rises → activates lux genes → bioluminescence

What is Quorum sensing’s role in infection?

• Staphylococcus: Quorum sensing regulates toxin production, biofilm dispersal (agr system).
  
  

• Pseudomonas aeruginosa: Uses quorum sensing to form biofilms, resist antibiotics, and produce virulence factors.

Communicable

Can spread from host to host (e.g., flu)

Serogroup

group of microbes with shared antigenic features

Pathogenic

Capable of causing disease

Reservoir

Habitat where pathogen lives (e.g., water, animals)

Vector

Organism that transmits pathogens (e.g., mosquito)

Host

Organism harboring the pathogen

Cholera (Vibrio cholerae)

• Characteristics: Gram– curved rod, motile, facultative anaerobe
  
  

• Pathogenicity: Produces cholera toxin → stimulates cAMP → massive fluid loss
  
  

• Symptoms: "Rice water" diarrhea, dehydration, electrolyte imbalance
  
  

• Epidemiology: Fecal-oral, waterborne, endemic in poor sanitation areas
  
  

• Biofilm Link: Enhances environmental survival & transmission in aquatic environments

Basic features of fungi

Eukaryotic, heterotrophic, reproduce via spores, have chitin walls

Structures of fungi

• Cell wall: Chitin

• Membrane: Ergosterol

• Hyphae: Filaments

• Mycelium: Network

• Spores: Reproductive units

Roles of fungi in nature

Decomposers, symbionts (e.g., mycorrhizae), pathogens

Types of mycoses

• Superficial (skin/hair)

• Cutaneous (nails)

• Subcutaneous (under skin)

• Systemic (organs)

• Opportunistic (immunocompromised)

Fungal immune evasion strategies

Capsules, phenotypic switching, blocking phagocytosis, enzyme secretion

Purpose of WHO Fungal Priority Pathogen List (2023)

Identify high-risk fungi for diagnostics, treatment, and R&D focus

Key fungal pathogens and traits

• Cryptococcus neoformans: Encapsulated, causes meningitis

• Candida albicans: Dimorphic, thrush/systemic infections

• Candida auris: Drug-resistant, nosocomial

• Histoplasma spp.: Dimorphic, lung infection from bat/bird droppings