Antifungals + Antibiotics Flashcards
What is mycosis?
Plural mycoses, in humans and other animals, an infection caused by any fungus that invades the tissues, causing superficial, subcutaneous, or systemic disease
How many classes of antifungals are available?
four
What are the critical fungus pathogens according to WHO?
Cryptococcus neoformans
Candida auris
Aspergillus fumigatus
Candida albicans
What are the traditional antifungal classes?
Echinocandins- disruption of cell wall
Polyenes- disrupt cell membrane
Azoles- target ergosterol biosynthesis
Allyamines- inhibit ergosterol synthesis
Flucytosine- inhibits nucleic acid synthesis
What are echinocandins?
Echinocandins are a class of antifungal compounds produced by the fungus Glarea lozoyensis
These compounds target the fungal cell wall by inhibiting synthesis of beta 1,3 glucan, a critical component of the cell wall. This disruption weakens the cell wall and leads to cell death
What are caspofungin and micafungin used for?
They are echinocandins
To treat fungal infections including candidemia, candida peritonitis, and other fungal infections
What is an example of a polyene?
Nystatin is an antifungal compound produced by the bacterium Streptomyces nourcei
What is nystatin used to treat?
Treats topical fungal infections
When was Nystatin discovered?
Nystatin, the first polyene antibiotic, discovered in the 1950’s by Hazen and Brown
Nystatin is a polyene macrolide antibiotic produced by Streptomyces noursei
How was Nystatin discovered?
Dr Hazen’s initial discovery of a promising new bacterium found in a soil sample obtained from a friends dairy farm
She named the bacterium Streptococcus noursei after the wife of the farm owner. Hazen and Brown then characterised the antifungal agent and named it nystatin after the New York State Health Department
What is Terbinafine?
Terbinafine is a synthetic allylamine but was isolated as an active compound F12 from the culture media of Streptococcus spp
What is onychomycosis?
is a chronic nail disorder consisting of a fungal infection that causes physical and psychosocial discomfort to patients
What is Amphotericin B?
It is derived from the bacterium Streptomyces nodosus, which is commonly associated with soil. It’s been used as an antifungal drug. It works by binding to fungal cell membranes and forming pores, causing leakage of cellular contents and cell death
How does Nystatin work?
Nystatin binds to ergosterol, a component of fungal cell membranes, leading to membrane disruption and cell death
How does Griseofulvin?
Griseofulvin is an antifungal compound derived from certain species of Penicillum and other fungi. It’s used to treat fungal infections of the skin, hair and nails. It works by disrupting the mitotic spindle formation during fungal cell division, inhibiting fungal growth
Can fungals be resistant to Echinocandin?
Resistance to echinocandins is conferred by mutations in FKS (Glucan Synthase) genes, which encode the catalytic subunit of the beta glucan synthase complex
What are the stages in producing new antifungal drugs?
Stage 1- drug discovery- 10,000 compounds
Stage 2- Pre-clinical development- 250 compounds
Stage 3- Clinical development- 5 compounds
Regulatory approval- 1 compound
What is the SPOTi assay used for?
To test antifungal susceptibility
How can AI help find antifungal drugs?
New AI based screens for new antifungal compounds or peptides: repurposing previous antifungals, screening genomes from new sources and using non-traditional antifungals such as antifungal peptides
What are antibiotics?
May be defined as a compound that kills bacteria or stops bacterial growth, although some definitions state antibiotics are compounds from living compounds, usually micro-organisms, that act against bacteria
Why are antibiotics produced by bacteria?
As a survival mechanism e.g. to kill/prevent the growth of competitor organisms and are usually products of secondary metabolic pathways
What is the human history of antibiotics?
Long history using natural sources to resolve infections infections, e.g. ancient Egyptians used mouldy bread, many societies used plant extracts
Early 1900’s: discovery by Paul Enrlich that arsenical compounds could treat syphillis and that certain chemical dyes were bactericidal
Further development by Gerhard Domagk led to use of the sulphonamide drugs, of which the first was Prontosil in 1935
How was penicillin discovered?
Discovered by Alexander Fleming, 1928, and St Mary’s Hospital, London
Plate of Staph aureus became contaminated with mould
Fleming tried to repeat the observation an failed
What conditions were present when penicillin was discovered?
Mould bacteria interaction occurred only:
- with certain Penicillium spp
- when both are growing slowly
- within narrow pH range
- on surface culture
- penicillin highly unstable and difficult to purify
How was penicillin developed to be what it is today?
Considerable problems with purification and stability
Howard Florey and Ernst Chain credited with turning penicillin into a life saving drug
Up to 500 litres per week needed of the Penicillium supernatant for filtering and testing
Chromatography used for purification, with subsequent testing of penicillin in animals and humans
Production increased rapidly by 1944, used extensively since
Side effects can include headaches, nausea and diarrhoea
What are the types of penicillin?
Natural penicillin: natural product from penicillium culture. Very narrow spectrum, which was expanded by chemical modification
Semi-synthetic: Created to avoid problems including:
- Penicillin resistance
- Acid tolerance
- Enables oral use rather than intravenous
How is industrial penicillin produced?
Mutant forms of Penicillium chrysogenum used, enabling selection higher yielding strains
Currently, submerged liquid fermentation used (10-12 tons of mycelia used to incoculate a 120,000 litre fermenter)
What are the three distinct phases in industrial penicillin production?
- Rapid mycelia growth (30-40 hours) in corn-steep liqour substrate
- Penicillin production via fed batch fermentation (5-7 days). Precursors for appropriate side chain added to the fermentation
- Fermentation is chilled, filtered penicillin purified by solvent extraction
Mycelia collected and used for animal feed
What is the classification of antibiotics based on?
Based on (1) structure or (2) target molecules- mode of action
What are the five major groups of antibiotics based on target?
Bacterial cell wall
Bacterial plasma membrane
Protein synthesis
DNA or RNA synthesis
Metabolic targets
What are the problems with antibiotics now?
Pace of discovery of new ‘natural’ antibiotics stalled, as few novel antibiotic types discovered in last three decades. Many natural antibiotics have been modified chemically to get around the problem of resistance and also extend spectrum of use
Inappropriate use driving resistance to antibiotics e.g. use in agriculture
Why is there little incentive to develop new antibiotics?
Profits low as antibiotics only prescribed for 1-2 weeks, and likely to have limited life span because of resistance
How big a problem is anti-microbial resistance (AMR)
AMR a leading cause of death worldwide, killing about 3500 people daily
>1.2 million died in 2019, AMR estimated to kill more people than HIV/AIDS or malaria
What alternatives to antibiotics have been identified?
Tier 1: Clinical development
Antibodies
Probiotics
Lysins
Bacterophages
Immunstimulation
Vaccines
Tier 2: Preclinical development
Anti-microbial peptides (AMPs)
What do antibodies, probiotics and phage lysins do?
Antibodies: bind to and inactivate pathogen
Probiotics: live microorganisms that may confer a health benefit to the host. Defined mixtures of bacteria may provide therapeutic/prophylactic therapies
Phage lysins: bacteriophage enzymes which destroy cell walls of target bacteria
What do bacteriophages, immune stimulation and vaccines do?
Bacteriophages: infect and kill bacteria, can be used in low doses as they replicate when their host bacterium is present
Immune stimulation: proposed as a potential approach with antibiotic therapy. Targeted interventions could be devised once these mechanisms are understood
Vaccines: can reduce infection incidence considerably, and thus reduce need for antibiotics.
What are Antimicrobial peptides?
Natural antimicrobial defence
Diverse group of low molecular mass proteins with broad spectrum antibacterial activity
Heterogenous structures, but usually amphipathic and cationic
Animals: located in phagocytes or epithelial surfaces
One of earliest developed molecular effectors of innate immunity
Where are AMP’s found?
Found in nearly every species studied
Now > 2,000 known
Relatively few taxa examined
No systematic form of nomenclature
What is the structure of the AMP’s?
prepropiece- conserved
active peptide- variable
Why are AMP’s important?
Important effectors on innate immunity, can also interact with adaptive components
Can interact and/or synergize with other immune molecules- lower concentrations of individual peptides required
Chemotactic, can up regulate cytokines and complement components, assist in wound repair
How are AMP’s stored?
Clustering of cationic and hydrophobic domains
AMP’s may be expressed constitutively and stored before release at site or time of need
In some cells/tissues, AMP expression induced by micro-organisms
What are the advantages of natural AMP’s?
Small, bioactive peptides, widely found throughout animal kingdom
Broad spectrum activity, many are multi-functional
High concentrations can be achieved in topical creams
What are the disadvantages of natural AMP’s?
Sensitive to protease activity, therefore most advantageous as topical applications
Can be expensive to synthesize and produce at large scale
Oral peptide medications- low bioavailability
What is the possible mode of delivery of AMP formulations?
Nanocarriers
Large surface area for absorption/encapsulation of AMPs
Prevent peptide adhesion
Nanostructured materials allow for creation of formulations for possible delivery of peptides to specific tissues
Enable time controlled release
How do AMP’s work?
Antimicrobial peptides (AMPs) kill microbes by disrupting their membranes, interfering with metabolism, or targeting intracellular components. They often form pores or break apart microbial cell membranes, leading to cell death
