BM211 (Microbiology) - Block C (Lectures and workshops)

Defining feature of gram negative bacteria

The outer membrane, the peptidoglycan layer is much thinner (compared to G+)

Fimbriae

Short hair-like structures found on G- bacteria. Act as crucial organelles for adhesion

Flagella

Hair-like tail-shaped organelles used by organisms for motility to “swim” through liquids

Bacteria Capsules

Produced by gram negative bacteria, organised outermost polysaccharide layers as a protective shield

Conjugative Pili

Thin flexible filaments produced by donor bacteria (primarily G-) to facilitate bacterial conjugation (transfer of DNA)

Type 3 Secretion (T3SS)

(AKA injectisome), a syringe-like nano-machine used by G- bacteria to directly inject effector proteins into host cells.

Gram negative outer membrane

Firs line of defence, acts as a selective permeability barrier. Nutrients enter through protein channels, excludes large hydrophilic antibiotics

Gram negative bilayer

Asymmetric and consists of two types of lipids: phospholipids, lipopolysaccharides

Gram negative outer membrane proteins

B-barrel outer membrane proteins, lipoproteins

What kind of bacteria is (primarily) responsible for AMR?

Gram negative bacteria

Proteobacteria

Major phylum of G- bacteria, found in all major ecosystems

Proteobacteria in the human gut

Usually indicative of a dysbiotic microbiome, for example E. coli and Crohn’s disease

5 Classes of proteobacteria

alpha, beta, delta, gamma, epsilon

Alphaproteobacteria

nearly 1000 described species, many are obligate aerobes and facultative aerobes. Many are oligotrophic.

Alphaproteobacteria 6 orders

Rhizobiales, rickettsiales, rhodobacterales, rhodospirillales, caulobactereales, sphingomonadales

Alphaproteobacteria - Rickettsiales

Obligate intracellular bacteria mostly associated to arthropods, unable to synthesise certain metabolites and must obtain them from the host, some can infect mammalian hosts

Alphaproteobacteria caulobacterales

Caulobacter crescentus is a model for asymmetric cell division and cellular differentiation (stalked and swarmer daughter cells)

Betaproteobacteria

500 described species, much functional diversity.

Betaproteobacteria - 6 major orders

Burkholderiales, hydrogenophilales, methylophilales, niesseriales, nitrosomonadales, rhodocyclales

Betaproteobacteria - neisseria meningitidis

causes meningitis, common in young people. Causes infection in humans, severe and often fatl

Betaproteobacteria - neisseria gonorrhoeae

causes ghonorrhoea, approx 1 in 10 are asymptomatic. Concerning spread of drug-resistant strains

Betaproteobacteria - bordetella pertussis

Causes whooping cough, serious and highly infectious. Can be vaccinated and treated

Gammaproteobacteria - Enterobacteriales

Facultative aerobes, motile or nonmotile, possess relatively simple nutritional requirements

Enterobacteriales - 2 groups

Can be separated by the type and proportion of fermentation; mixed acid fermenters, 2,3-butanediol fermenters

Enterobacteriales mixed acid fermenters

Found in warm-blooded animals intestines. Some strains are pathogenic. e.g. E. coli, salmonella, shigella

Pathogenic E. coli

Colonizes various sites in human body, have distinctive virulence factors encoded on plasmids an bacteriophages

Enterobacteriales butanediol fermenters

Closely related organisms, two types; enterobacter (found in water, sewage), and klebsiella (found in soil and water)

Gammaproteobacteria - pseudomonadales

major cause of serious hospital and acquired infections associated with high levels of AMR and mortality. e.g. causes mortality in people with CF

Epsilonproteobacteria - campylobacter jejuni

Causes foodborne illness most commonly associated with undercooked poultry, pork, shellfish. Symptoms - diarrhea, fever, cramps. Cases increase in summer

Deltaproteobacteria key genera

bdellovibrio, myxococcus, desulfovibrio, geobacter, syntrophobacter

Deltaproteobacteria (overview)

sulfur/sulfate reducers, dissimilative iron reducers, bacterial predators

Deltaproteobacteria - bdellovibrio

Predates other bacteria, following primary contact with g- bacteria the bdellovibrio cell attaches to and penetrates into the prey periplasmic space.

Deltaproteobacteria - Myxoccocus Xanthus

“Wolf pack”, forms a swarm to glide across surfaces and obtain their nutrients by using extracellular enzymes to lyse other bacteria

Clinical syndromes associated with fungi

Mycotoxicoses, hypersensitivity, host colonisation

Mycotoxicoses

Fungi produce metabolites (alkaloids, toxins, psychotropic agents) often accidentally or recreationally ingested. Induced emesis (vomiting) is often first line of treatment

Ergot alkaloids

Spores associated with cereals (wheat, rye), causes convulsing and gangrene due to vasoconstriction. Middle ages epidemics referred to as st. anthonys fire

Psychotropic agents

Consumption of fungi for recreational purposes - psilocybin and psilocin (semi-synthetic derivatives include LSD)

Aflatoxin

Massive economic impacts, aspergillus flavus is the contamination of poultry. Causes necrosis of tissue in bloods, can also affect humans

Fungal hypersensitivity

High fungal spore counts in airs, when inhaled causes an overreaction of the immune system

Hypersensitivity pneumonitis (HP)

Immune mediated inflammatory lung disease triggered by breathing in environmental spores. Causes flu like syptoms

Pathogenic fungi

Only about 50 fungal species causes significant disease, e.g. ringworm, athletes foot

Dimorphic fungi

Exist as either yeasts or in filamentous form

Filamentous reproduction

Produce asexual spores (conidia) or sexual spores

Superficial mycosis

Fungus only infects the surface layer of skin hair or nails, very common and treatable. Fungi that cause this are collectively called “Dermatophytes”

subcutaneous mycosis

Infects deeper layers of skin, caused by different fungi to superficial. Mostly treatable with topical drugs. Forms crusty wart like lesions

Systemic mycosis

Most serious, infects internal organs. Often due to inhaling spores in immunocompromised individual (old/AIDS).

Opportunistic pathogens

Cause disease in those whose immune system can no longer fight off the fungi

Histoplasmosis

Widespread primary fungal infections common in midwest USA, inhaled spores germinate in the lungs

Coccidioidomycosis

Caused by dimorphic fungi common in south west USA, becomes airborne during rain. Causes pneumonia

Blastomycosis

Caused by blastomyces dermatitis (dimorphic) common in great lakes in North America. Fungus lives in rotten wood, if untreated causes skin lesions

Paracoccidioidomycosis

subtropical disease in south america, initially pulmonary, causes lesions on the face and extremities

Cryptococcosis

Caused by the yeast form of cryptococcus neoformans. Can occur in virtually any bodily organ. Seen in HIV patients (2nd most common opportunistic pathogen)

Candida Albicans

Dimorphic yeast, diseases include thrush (more serious in immunocompromised individuals). Has a highly dynamic genome, and posses biofilms

Pneumocytosis

Pneumonia, opportunistic infection

Antifungal drugs

Difficult to specifically treat as the cellular machinery is similar to that of humans, few drugs target fungi uniquely

Ergosterol inhibitors (overview)

An analogue of cholesterol in fungal plasma membranes, provides stability and shape.

Ergosterol inhibitors (two types)

Polyenes, azoles

Ergosterol inhibitor (mode of action)

Targets the unique fungal plasma membrane. Binds to ergosterol, depletes the membrane, destabilises fungal cell membranes leading to cell death

Echinocandins

Relatively new class of antifungal drugs, natural cyclic lipopeptides

Echinocandins (mode of action)

Inhibits the synthesis of glucan in the cell wall, prevents fungal cell wall synthesis

DNA synthesis inhinitors

Nucleic acid analogues that target candida and cryptococcus infections. Used in conjunction with other antifungals

DNA synthesis inhibitors (mode of action)

Inhibits enzymes required for DNA synthesis

Fungal products - metabolites

Enzymes, antibiotics, bioconversion, fuel, food

Biology-degredation

Removal of oil spills are heavy fuels in the sea, fungi cat utilise long-chain hydrocarbons

Fungi can remove what toxic chemicals from soil and water

Insecticides, herbicides, uranium oxides

Fungal primary metabolites (overview)

Formed during growth phase. Intermediates and end products of anabolism, uesd as cell building blocks. Products of catabolism

Fungal primary metabolites (examples)

Ethanol, yeast (saccharomyces cerevisae), lactic acid (aspergillus niger), citric acid (aspergillus niger)

Fungal secondary metabolites

Formed near the end of the growth phase, frequently near or in stationary phase

Citric acid production

Produced by aspergillus, from glycolysis and the TCA cycle

Citrate isolation

Purified by the addition of CaO to the culture broth. Precipitates the citrate. Filtered and then treated with sulfuric acid.

A. niger history

Citric acid producing strain isolated in 1917, and production began in 1919 by Pfizer

Penicillium (food)

Genus of fungi that ripens many cheeses - specifically roqueforti and glaucum are used for blue cheese

Fusarium venenatum

Quorn meat alternative grown by fermentation

Yeast extract

Marmite is made from saccharomyes cerevisae, by-product of beer breqing. Used for Vit B

Bakers yeast

Saccharomyces cerevisae, fermentation produces CO2 and helps dough rise

Alcohol

Fermentation means yeast turns sugars into alcohol

Louis Pasteur

Developed a reliable strain of brewers yeast in 1850s

Bioethanol

Alternative energy source to petroleum based fuels. Genetically engineered Saccharomyces yeasts to ferment xylose

Xylose

Major fermentable sugars present in cellulosic biomasses such as agriculture residues

Secondary metabolites

Not essential for growth, formation is highly dependent on conditions. Often produced in large amounts as a group of related compounds

Specialised metabolites/antibiotics

Complex organic molecules requiring a number of enzymatic reactions that don’t occur during the growth phase. Starting materials derived from primary metabolism.

Beta lactam antibiotics

Produced by penicillium, aspergillus, streptomyces, etc. can be natural or semi-synthetic (which have more desirable pharma properties).

Beta lactam ring

4 molecules (C3N) with an NH group, double bonded O group

Production of penicillins

Highly aerobic process, typically secondary metabolite fermentation. C- source becomes exhausted, inducing production. Very pH dependant

Statins

Aspergillus produce lovastatin, penicillum citrinum produces mevastatin. Both responsible for lowering cholesterol

Immunosuppressants

Tolypocladium inflatum produces cyclosporine used for arthritis, psoraisis, crohns disease, and organ transplants