Week 11: Pathogenic Fungi Flashcards
What are fungi?
Eukaryotes that contain a cell wall and produce spores
Fungi are very diverse and inhabit a wide variety of habitats, with at least 100,000 named species.
What is the estimated total number of fungal species?
Over 500,000
Only ~500 can cause mycosis in humans or animals.
What are unicellular fungi commonly known as?
Yeasts
Example: Saccharomyces cerevisiae – budding yeast or baker’s yeast.
What is tinea corporis and what causes it?
A skin disease caused by Microsporum canis
Lesions vary in size and location, commonly affecting scalp, face, and body.
What is superficial candidiasis usually caused by?
Candida albicans
Infections are normally relatively harmless.
What is invasive candidiasis and its impact?
A severe infection caused by Candida species with a very high mortality rate
It can occur in certain cases.
What are some species of Aspergillus and their effects?
Aspergillus flavus and Aspergillus fumigatus
Aspergillus flavus grows on important agricultural crops; Aspergillus fumigatus can cause allergic reactions or aspergillosis.
What are aflatoxins and their significance?
Strong carcinogens produced by many Aspergillus species
Example: aflatoxin B1.
Who first characterized penicillin?
Alexander Fleming
He discovered it was produced by Penicillium notatum.
What is the structure of Penicillin G?
Core structure specific for Gram-positive bacteria
Sensitive to β-lactamase produced by penicillin-resistant bacteria.
What is the role of sulfanilamide in antibiotic treatment?
It inhibits growth of certain bacteria by blocking folic acid biosynthesis
It is a competitive inhibitor of dihydropteroate synthetase (DHPS).
What is the mutation rate in E. coli?
1 × 10–9 to 1 × 10–10 per nucleotide
This leads to an average of 1 resistant cell per 500 bacteria.
How can bacteria acquire antibiotic resistance?
Through point mutations, plasmids, transposons, or horizontal gene transfer
Some resistance genes existed before the antibiotic era.
What are azole compounds used for?
To inhibit fungal growth by targeting cytochrome P450 enzyme 14α-demethylase
Example drugs include Clotrimazole and Fluconazole.
What is the mechanism of action for echinocandins?
Inhibit β-(1,3)-D-glucan synthase for cell wall synthesis
Important in treating fungal infections.
What is the target of antiviral treatments?
Specific viral processes without damaging host cells
Examples include fusion inhibitors and inhibitors of viral replication.
What is the function of restriction endonucleases in bacteria?
They cut double-stranded DNA at specific recognition sequences
This mechanism helps bacteria discriminate between foreign and their own DNA.
What is the significance of the ‘silver bullet’ concept?
Substances that specifically target vital metabolic functions of bacteria
It aims to minimize damage to host cells.
What happens when cell wall synthesis is inhibited in bacteria?
It can lead to bacterial death
Example: Penicillin inhibits cell wall synthesis.
What is the role of quorum sensing in new antibiotics?
Blocks communication in pathogens without affecting growth
This reduces the likelihood of developing resistance.
What is the primary mechanism of action for acyclovir?
Inhibits viral DNA polymerase
It is effective for HSV and varicella-zoster virus.
What are restriction endonucleases?
Enzymes that cut double-stranded DNA
They play a critical role in bacterial defense mechanisms.
What is the primary function of restriction endonucleases?
To cut DNA at or near specific recognition sequences
This allows bacteria to distinguish between foreign and their own DNA.
What does EcoRI stand for?
Escherichia coli, R class of endonuclease, 1st enzyme discovered
It is one of the most commonly used restriction enzymes in molecular biology.
What is the recognition sequence for EcoRI?
GAATTC
EcoRI cuts at this specific sequence.
What is the role of EcoRI methylase?
To methylate the recognition sequence GAATTC
Methylation protects the bacterial DNA from being cut by EcoRI.
Fill in the blank: EcoRV is a type of _______.
[restriction endonuclease]
What is the recognition sequence for EcoRV?
GATATC
This sequence is specifically cut by EcoRV.
What is the function of modification methylase EcoRV?
To methylate the recognition sequence GATATC
This modification helps in distinguishing between foreign and self DNA.
True or False: Restriction endonucleases can only cut DNA from foreign sources.
False
They can also cut their own DNA unless it is methylated.
What is one method bacteria use to discriminate between ‘foreign’ and ‘own’ DNA?
Methylation of specific recognition sequences
This prevents the restriction endonucleases from cutting the bacterial DNA.
What does the term ‘CRISPR-Cas’ refer to?
A system used by bacteria for adaptive immunity
It allows bacteria to remember and fight off past infections.
