Fungal Cell Membrane and Identification

Introduction to Microbiology

• Candida albicans is a fungus, not a bacterium.
• In SARS-CoV-2, the spike protein is used in vaccine development and is involved in the binding and entry step of the virus life cycle.
• The presence of a lipid structure called an envelope is used to classify viruses.
• Prion diseases can affect both humans and animals and are sometimes spread to humans by infected meat products.
• The protein that prions are made of is found throughout the body and is encoded by the host's DNA.
• Prokaryotic cells do not have a nuclear membrane.
• Gram-positive cells have a thick layer of peptidoglycan, while gram-negative cells have a thin layer of peptidoglycan sandwiched between the surface and plasma membrane.
• If a fungus grows as a single cell, it is called a yeast.
• Tinea infections are common dermatologic fungal infections that affect different parts of the body, such as the scalp, arms, legs, and trunk.

Fundamentals of Bacteriology

• The periplasmic space is a "bag of enzymes" that can degrade macromolecules, protect against toxic intruders, and gather essential nutrients.
• An unknown organism with a thick peptidoglycan, no capsule, and no flagella would have a Gram stain that is purple.
• Lipid A is a component of the lipopolysaccharide of the outer membrane of Gram-negative bacteria and can trigger a host immune response, leading to septic shock.
• Spirochetes move by flexing and spinning movements using the axial filament.
• Integral proteins allow the passage of solutes across the cell membrane.
• Plasmids are small, circular, double-stranded DNA molecules that can be transferred through conjugation, transformation, or transduction.
• Peroxidase is an enzyme that allows bacteria to grow near the surface of a solid media by breaking down reactive oxygen species (ROS).
• Transduction is the process of transferring DNA to another bacterium through a bacteriophage.

Microbiology and Parasitology

• Endospores can survive extreme heat, lack of water, and exposure to many toxic chemicals and radiation due to their low water content and large amount of calcium dipicolinate.
• In the stationary phase, microbial cells are smaller, have different enzymes, and fewer ribosomes.
• Gram-positive bacteria are characterized by the presence of teichoic acids.
• Bacterial capsules are composed of polysaccharides/polypeptides and play a role in bacterial virulence, but do not contribute to growth and multiplication.
• The components of cross-linkages in the cell wall are D-glutamic acid, D-alanine, and meso-diaminopimelic acid (DAP).

Fundamentals of Mycology

• Fungi are traditionally named based on their teleomorph state.

• The black fungi associated with COVID-19 belong to the phylum Mucoromycotina, which produces sexual spores known as zygospores.### Fungi

• Asexual spores are produced at the top of sporangiophore and are released when the sporangium is ruptured.

• Zygospores are formed inside a sac-like structure and are diploid spores.

• Chlamydospores are spherical spores formed from the thickening of a hyphal cell at the cross walls.

Medically Relevant Fungi

• Ascomycota is the phylum of fungi with the most number of medically-relevant species.
• Examples of medically-relevant fungi in Ascomycota include Pneumocystis, Candida, Aspergillus, Penicillium, and Sporothrix.

Cutaneous Mycosis

• Cutaneous mycosis is suspected if annular plaques with central clearing are present.
• On microscopy, narrow hyphae with parallel walls are expected.

Fungal Structures

• Aspergillus sp. produces acute angle branching hyphae in tissue on histopathology.
• Histopathology is more sensitive than KOH smear for deep fungal infections.

Fungal Cell Membrane

• Ergosterol is the main component of the fungal cell membrane.

Fungal Culture Media

• Cycloheximide is used to control the growth of saprobic fungi in fungal culture media.

Coenocytic Hyphae

• Coenocytic fungi are aseptate and have imperforate, sparse to none septa in hyphae.
• This allows for the isolation of cytoplasmic material.

Yeast Cells

• Yeast cells reproduce by budding and produce round, pasty or mucoid colonies.

Dimorphic Fungi

• Dimorphic fungi exist as molds in the environment and yeast in the host.

Endemic Fungi

• Blastomyces dermatitidis is an example of an endemic fungus.

Viruses

• Viruses are microscopic, intracellular parasites that are not living outside their host cells.
• Bacteriophages are viruses that infect bacteria, which are prokaryotes.
• Viral structure consists of capsids and envelope, but not ATPase.

Viral Life Cycle

• Steps in the viral life cycle include attachment and entry, transcription of viral genes, translation of viral proteins, virion assembly, and budding.

Testing Viral Viability

• The best way to test viral viability and infectivity is through visualization of cytopathic effect.

Hepatitis B Virus

• Hepatitis B virus is a gap-dsdDNA virus that converts its genome to dsDNA and removes the protein and mRNA.

(+) ssRNA Viruses

• SARS-CoV-2 is a (+) ssRNA virus that synthesizes (-) ssRNA from the dsRNA genome through the viral polymerase.
• (+) ssRNA is copied to (-) ssRNA to make more (+) ssRNA strands.

(-) ssRNA Viruses

• Influenza virus is a (-) ssRNA virus that makes (+) ssRNA from the (-) ssRNA genome.

Immune System

• The first line of defense of the immune system is innate immunity.
• Adaptive immunity is specific for the pathogen and confers protective immunity to reinfection with the same pathogen.

Vaccination

• The basis for vaccination is the immune system's capability for memory and specificity, which is the function of adaptive immunity.

Antigens

• Antigens are any non-self substance that can interact with immune cells or components.

Pattern Recognition Receptors

• Innate immunity responds quickly but has a limited number of germline-encoded pattern-recognition receptors (PRRs).### Statement Analysis
• Statement A: Bactericidal, cleaves glycosidic bonds in bacterial cell walls, true
• Statement B: Chief cells produce hydrochloric acid, false (parietal cells produce hydrochloric acid)
• Statement 1: Alternative complement pathway is activated by recognition of certain PAMPs, true
• Statement 2: C3b and C5b are inflammatory mediators, true (C3b tags pathogen for phagocytosis, C5b interacts with C6-9 to form Membrane Attack Complex)
• Statement A: Eosinophils contain major basic protein against helminthic infections, true
• Statement B: Kupffer cells in the liver and microglial cells in the brain are tissue resident macrophages, true
• Statement A: NK cells recognize injured and infected cells, true (induce apoptosis)
• Statement B: Type 1 IFN inhibits viral protein synthesis, true (increases defenses by inhibiting viral replication)

Complement System

• IgM is the most effective complement activator, activates classical complement pathway
• TGF-Beta induces production and secretion of IgA
• IgE triggers mast cell degranulation
• IgG is the most effective opsonin for phagocytosis by neutrophils
• IgA is involved in the activation of complement by the lectin pathway or alternative pathway

Vaccines

• Rabies is an inactivated vaccine, not a live attenuated vaccine
• Fully immunized child by 12th month: 1 dose BCG, 3 doses pentavalent vaccine, 3 doses OPV, 1 dose measles/MMR vaccine

Plasma Membranes

• Functions as a selectively permeable barrier
• Made of phospholipid bilayer

MHC

• MHC I presents peptide antigens from intracellular proteins
• MHC II presents endocytosed extracellular proteins
• MHC I is for intracellular pathogens or cytosolic proteins

Helper T Cells

• TH1 cells combat intracellular pathogens, not extracellular
• TH2 cells secrete IL-4, IL-5, and IL-13
• TH17 cells, when dysregulated, can lead to autoimmunity
• Treg cells are activated by both IL-10 and TGF-β

Parasitology

• Definitive host: where the adult parasites live
• Intermediate host: where the parasite goes through preliminary development
• Paratenic host: carrier host that carries the parasite around, but no development occurs
• Biological vector: essential in the life cycle, such as mosquitoes for W. bancrofti
• Phoretic vector: carries the parasite but is not essential in the life cycle, such as cockroaches carrying Ascaris and Trichuris eggs

Soil-Transmitted Helminths

• Ascaris lumbricoides causes Loeffler's syndrome, which manifests as allergies during the pulmonary phase
• Hookworms (N. americanus and A. duodenale) cause pulmonary symptoms and Loeffler's syndrome due to pulmonary migration
• Ascaris can lead to intestinal obstruction as a possible complication
• Kato-Katz method is used to diagnose soil-transmitted helminthiasis
• Trichuris trichiura clinical consequences include abdominal pain, diarrhea, dysentery, and rectal prolapse