BM211 (Microbiology) - Block B (Lectures and Workshops)

Hyphae

A multicellular network of fungi

Conidia

Asexual spores produced by hyphae that extend above the surface

Acid fast (property)

When certain bacteria cannot be decolourised using acids as part of laboratory procedures

Lysozyme

An enzyme that catalyses the degradation of some bacterial cell walls

Wall teichoic acids (WTAs)

Teichoic acids that are covalently bound to the peptidoglycan layer

Lipoteichoic acids (LTAs)

Teichoic acids that are embedded and extend out of the membrane layer in gram positive bacteria

Sacculus

The boundary that envelopes a bacterial cell wall

Mycelia

Compact tufts formed by hyphae

Chitin

Proteins that make up fungal cell walls

Mycorrhizae

Symbiotic relationship between fungi and plant roots that help the plant roots obtain nutrients like phosphorus

Fruiting bodies (Overview)

Macroscopic reproductive structures produced by some fungi

Fruiting bodies/sporocarp (examples)

Mushrooms, and puffballs

Mycoses

Disease caused by fungus

Basidiospores

Sexual reproductive spores produced by basidiomycota fungi

Basidiomycota

Filamentous fungi composed of hyphae that reproduce sexually

Basidiocarp (or basidioma)

Complex multicellular fruiting body of basidiomycete fungi, often associated with toadstools

Asexual fungal reproduction

Growth and spread of hyphal filaments, asexual production of spores, simple cell division

Sexual fungi reproduction

Sexual spores can originate from the fusion of two haploid cells to form one diploid, spores are resilient. Can usually reproduce 5-6 times before aging

Fungal phylogeny

Fungi share a more recent common ancestor with animals than any other euaryotes

How long ago did fungi/animals diverge

estimated 1.5 BYA

Chytridiomycetes (Chytrids)

Earliest diverging line of fungi, commonly found in soil and freshwater. Killed off mass amphibians

Amphibian death

Caused by chytridiomycosis, the fungus burrows into the skin of amphibians and drains nutrients to degrade the skin (“flesh eating”)

Zygomycetes

Known for food spoilage, all are coenocytic and form zygospores. Often infect immunocompromised individuals

Coenocytic

A multicucleate cell which can result from multiple nuclear divisions

Glomeromycetes

Small group of fungi that have major ecological importance, forms endomycorrhizae with roots of plants. Cannot grow independently of a plant

Endomycorrhizae

Symbiotic fungi that penetrate plant root cells to form arbuscules enhancing nutrient uptake

Ascomycetes

Used in baking yeast and common moulds, found in aquatic environments. Decompose dead plant material. Makes alcohol

Saccharomyces Cerevisae

Flourish in habitats with sugars (e.g. bread, wine), can infect immunocompromised patients

Candida albicans

Yeast infection cause by an overgrowth of candida

Basidiomycota (club fungi)

Over 30,000 described species. Recognisable as mushrooms and toadstools. Undergo vegetative and sexual reproduction

Four main fungi divisions

Chytridiomycota, Zygomycota, Ascomycota, Basisiomycota

Hyphal growth

Exponential as each unicellular organism divides (1>2>4>8 etc)

Spitzenkorper (overview)

located at the hyphal tip, acts as a vesicle supply centre crucial for regulating growth and morphology

Gram stain (overview)

Allows differentiation based on bacterial cell walls, created by Hans Christian Gram who developed the method in 1884

Dichotomous keys

A tool that can be used to identify organisms such as plants animals and fungi

Gram staining steps

Cells are fixed to slide, crystal violet stains cells (1 min), iodine is added which binds stain to gram-positive cells, wash with ethanol, add safranin counterstain

Gram-positive cells

Turn purple when treated with violet stain, do not change

Gram negative cells

Ethanol washes off purple stain, safranin counterstain turns them pink

Gram stain exceptions

Gram-variable cells stain inconsistently (due to error, age, or structural issue), gram-intermediate present as a mix of both

Gram positive phyla

Actinobacteria, firmicutes, tenericutes

Actinobacteria (actinomycetota)

Identified by high GC content genomes

Firmicutes (bacillota)

IDentified by low GC content genomes

Tenericutes

Phylogenetically related but lack cell walls so do not stain

Other classifications

Monoderm, diderm

Monoderm

Monoderm bacteria have a single cytoplasmic membrane and thick peptidoglycan layer (typically gram positive

Diderm bacteria

Possess inner and outer membranes with thin peptidoglycan in between (typically gram negative)

Gram positive cell envelope (outside-in)

Polysaccharide capsule, S-layer, thick peptidoglycan layer, teichoic acids, cell membrane (phospholipid bilayer), additional structures

polysaccharide capsule

Present on many but not all bacteria, offers protection against immune evasion and resistance to desiccation

S layer

present on many but not all bacteria, offers protection, membrane stabilisation, adhesion, etc

thick peptidoglycan layer (function)

offers cell shape, resistance to osmotic pressure. Highly conserved and essential; major target of innate immune system

Teichoic acids (basic overview)

negatively charged, provides cell wall flexibility

Teichoic acid structure

Repeating glycerol or ribitol units linked with phosphodiester bonds. Can be substituted with sugars, and amino acid/sugars

Teichoic acids (capability)

Forms complexes with divalent cations (Mg2+, Ca2+). Role’s poorly understood

Cell envelope diversity

Diversity in bacteria can be revealed by electron microscopy and fine structure, notable examples are mycobacteria and mycoplasma

Cell membrane (phospholipid bilayer)

Offers permeability, ion gradient

Additional structures

e.g. Pili, flagella; offers motility

Peptidoglycan (AKA murein) (Structure)

Basic conserved structure; glycan chains with amino acid cross-links. constantly remodelled, cleaved to allow insertion fo new subunits

L-form bacteria

Lacks peptidoglycan, can be isolated for many species in lab culture. May play a role in pathogenesis (controversial)

Peptidoglycan (chemotypes)

Chemotypes are variants in structure

Peptidoglycan (chemotype examples)

Changes to glycan backbone; N-deacetylation, N-glycolylation, O-acetylation, amino acid side chain, amount of cross linking

(peptidoglycan) Glycan chain

Repeating units of N-acetylglucosamine and N-acetylmuramic acid

(peptidoglycan) peptide crossbridges

Often D-amino acids, meso-diaminopimelic acid (varied by species)

(peptidoglycan) cross-linking reactions

Transpeptidase, and transglycosylase. Catalysed by penicillin binding proteins (PBPs) — major antibiotic targer

Mycobacterial cell envelope

Do not stain well in gram stain due to waxy mycolic acids

Acid fast staining

Differential staining technique used to identify mycobacteria

Arabinogalactan

Polysaccharide, links peptidoglycan to mycolic acids

Mycoplasma

Genus of bacteria that lack a cell wall (peptidoglycan) making them antibiotic resistant. Extremely small, and pleimorphic

Pleimorphic

Describes cells or microorganism that vary in appearance rather than being uniform.

What makes a bacteria pathogenic?

Specific virulence factors that allow them to multiply in their host or vector without being killed or expelled by the host’s defences

Gram-positive actinomycetota (examples)

Corynebacterium diphtheriae, mycobacterium spp., streptomyces scabiei, nocardia spp.

Corynebacterium diptheriae

Gram positive, known for causing diptheria, toxigenic strains acquire the diphtheria gene from bacteriophage

Mycobacterium spp.

Acid-fast, rod-shaped, known for causing leprosy, tuberculosis.

Streptomyces scabiei

Multicellular filamentous aerobic gram-positive bacteria, known for causing scabs on potatoes (and other root veg)

Nocardia spp.

Filamentous partially acid-fast, known for causing nocardiosis in immunocompromised people

Gram-positive bacillota (example)

staphylococcus aureus, streptococcus spp., enterococcus spp., listeria monocytogenes., bacillus spp., clostridium spp.

Staphylococcus aureus

Non-motile, non-spore forming coccus-shaped anaerobe. Known for causing diseases (e.g. endocarditis, skin infections, etc).

Methicillin-resistant Staphylococcus aureus

A major concern in hospital environments, resistant to many common antibiotics

Streptococcus spp.

Non-motile, non-spore forming coccus-shaped anaerobe. Has two groups (A and B)

Group A strep

Can cause strep throat, scarlet fever, cellulitis, necrotising fasciitis

Group B strep

Can cause pneumonia, meningitis in newborns, some streptococci cause dental caries

Competent bacteria

Capable of taking up and incorporating exogenous DNA from their surroundings

Enterococcus spp.

Facultative anaerobes, short chains, non-spore forming. Can cause UTIs, meningitis, endocarditis.

Listeria monocytogenes

Non-spore forming motile rod shaped. Known for causing listeriosis. Can grow at 4*c and is a problem in refrigerated foods (found in raw milk, deli meats, etc)

Bacillus spp.

Rod-shaped spore-forming, known for anthrax and food poisoning. The toxins made are not destroyed when food is cooked

Clostridium spp.

Rod-shaped spore forming, known for food poisoning, botulism, tetanus

Bacteria in humans

Can be beneficial, firmicutes in the gut, streptococci in the mouth lactobacilli in the vagina

Gastrointestinal anthrax

Bacillus anthracis spores are ingested and germinate in the host digestive tract

Inhalation anthrax

The deadliest, spores are inhaled and germinate in the host respiratory tract

cutaneous anthrax

Bacillus anthracis spores enter an open wound

How is anthrax generally acquired

via andling infected animals, contaminated animal products

Endospores

Dormant touch non-reproductive structures produced by bacillota

Bacillus sporolation - vegetative cycle (stage 1)

Cells differentiate to form endospores, divide asymmetrically to produce 2 cell types

Bacillus Sporulation steps

Vegetative cycle, engulfment, cortex formation, spore coat, maturation, cell lysis, germination

Mature bacillus spores

Metabolically dormant and resistant to heat as well as other environmental stresses

Exotoxin

A toxin secreted by bacteria (i.e. not a physical part of the bacterial cell)

AB toxin

A= active part, B= bindng part

Protective antigen (PA)

Binds to eukaryotic cells and forms a pore (heptamer) for translocation of LF and EF into the cell

Lethal factor (LF)

Adenylate cyclase, lethal in lab animals when co-injected with PA

Edema factor (EF)

Endoprotease (causes edema in lab animals when co-injected with PA)

Listeriosis

Can cause mild-severe intestinal illnesses, if infection spreads causes invasive listeriosis (fever, flu symptoms, can cause miscarriage)