Unit 5- Microbiology & Prokaryotes Flashcards
How does prokaryotes differ from eukaryotes?
Prokaryotes have no membrane bound organelles, no nucleus and small in size.
What advantage does the simplicity of prokaryotic cells provide?
It allows for rapid growth and division due to a high surface area.
What is significant about antibiotics?
- Derived from soil microorganisms.
- Potent bacteriocides with high therapeutic index which means low toxicity to human cells but high toxicity to bacteria.
What is taxonomy?
The classification of organisms into ordered groups.
What is nomenclature?
The labelling of groups or individual members within those groups.
What are the levels of taxonomy for cellular living organisms?
Life, Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
What are the three domains of life?
Bacteria, Archaea, and Eukaryotes.
How are bacteria and archaea different despite both being prokaryotes?
- Bacteria have peptidoglycan in their cell walls.
- Archaea have a distinct evolutionary history based on mRNA sequencing.
What are the four kingdoms in the eukaryotic domain?
- Protista: Includes algae, Protozoa, and slime molds
- Fungi: Includes yeast (unicellular) and molds (multicellular).
- Animalia: Includes multicellular animals like parasites.
- Plantae: Includes multicellular plants that perform photosynthesis.
What characteristics are used to classify bacteria?
- Morphology
- Staining reactions
- Culturing characteristics
- Biochemical reactions
- Antigenic capability
- Nucleotide base composition (GC-ratio)
- Presence, location, & shape of an endospore
- Atmospheric preferences
What are the atmospheric preferences of bacteria?
- Anaerobos: Grow without oxygen
- Aerobes: Requires oxygen
- Facultative anaerobes: Tolerates hypoxia
- Microaerophiles: Prefer lower oxygen levels
- Capnophiles: Thrive in elevated carbon dioxide levels.
What is the structure of the bacterial genome?
A single circular double-stranded DNA molecule, sometimes with plasmids coding for non-essential functions.
What it is the bacterial capsule, and what is this function?
- A rigid cell wall surrounding the cell membrane, composed of loose polysaccharides.
- Maintains cell shape, protects phagocytosis, and contributes to virulence.
How does the composition of the bacterial capsule affect virulence?
Capsule composition varies across phyla, influencing bacteria’s ability to survive in the human body & evade immune responses.
What are fimbriae, and what is their function?
Hair-like structures protruding from bacterial cells involved in bacterial conjugation.
What are pili, and what role do they play in bacteria?
Structures used by bacteria to share and swap plasmids during conjugation, often transferring antibiotic resistance.
What are endospores, and why are they significant?
Dormant bacterial structures formed under unfavourable conditions; they are extremely resistant to heat, dehydration, radiation, & chemicals.
What is glycocalyx, and what are its types?
An outermost layer of prokaryotic cells made of polysaccharides/polypeptides. Types include:
* Slimes: Unorganised, loose, water-soluble, sticky, & essential for biofilm formation.
* Capsules: Organised, firmly attached, & protective.
What are the functions of glycocalyces?
- Protect the plasma membrane from stresses, desiccation, or chemicals.
- Help bacteria attach to surfaces, initiating disease.
- Aid in biofilm formation (slime only).
What are biofilms, and where can they form?
Aggregations of microorganisms embedded in a slime matrix, forming on living tissues (e.g. tooth paste) or non-living surfaces (e.g. catheters).
Why are biofilms more resistant to antibiotics and stresses?
Cells communicate via quorum sensing, coordinating actions like replication or secretion of harmful substances.
What is the composition of bacterial cell walls, an dhow does it differ from eukaryotes?
- Bacteria: Peptidoglycan’s (NAG & NAM connected by amino acid cross bridges).
- Eukaryotes: Pectin or cellulose (e.g. in fungi & plants).
What is the function of the bacterial cell wall?
Provides structural support, protecting the cell from osmotic pressure, drought & chemicals.
What is a pathogen?
A microorganism capable of causing disease in plants, animals, or insects.
What is pathogenicity?
The ability of a microbe to cause disease in a host organism.
Define virulence?
The degree of pathogenicity of a microbe, determined by its genetic, biochemical, or structural features.
Differentiate between obligate & opportunistic pathogens.
- Obligate pathogens: Always associated with disease.
- Opportunistic pathogens: Cause disease under specific conditions, such as when host defences are comprised.
What are the two mechanisms by which bacteria cause disease?
- Invasiveness: Ability to invade tissues, involving colonisation and evasion of host defences.
- Toxigenesis: Ability to produce toxins (exotoxins & endotoxins).
What is the difference between exotoxins & endotoxins?
- Exotoxins: Released from bacteria, acting at sites distant from growth.
- Endotoxins: Cell-associated, released when bacteria are lysed.
What are zoonoses?
Diseases transmitted from animals to humans.
How does the normal flora protect the host?
Competes with pathogens for colonisation sites & produces bacteriocins that suppress harmful organisms.
How does penicillin work?
Inhibits DD-transpeptidase, preventing peptidoglycan cross-linking in bacterial cell walls, leading to cell death.
What contributes to antibiotic resistance, such as MRSA?
Inappropriate antibiotic use & exposure to suboptimal antibiotic levels, leading to resistance mechanisms like B-lactamase production.
What are passive defence mechanisms of mucous membranes?
- Mucociliary Clearance: Respiratory tract removes pathogens.
- Tears: Contain lysozyme enzymes.
- Mucus: Provides alternative binding sites for pathogens.
Name three types of antimicrobial agents.
- Disinfectants: For non-living surfaces.
- Antiseptics: For living tissue.
- Antibiotics: Kill or inhibit microorganisms in the body.
What distinguishes viruses from other microorganisms/
- Small size: much smaller than bacteria.
- Genome: Contains only 1 type of nucleic acid (DNA/ RNA).
- Metabolically inert: Can only replicate inside host cells.
What is a virion?
The intact virus particle, comprising of a nucleic acid core & a protein coat (capsid).
What is the role of vaccination in virus prevention?
Provides adaptive immunity by exposing the body to antigenic material from the virus.
What is HIV, and what does it cause over time?
A single-stranded RNA retrovirus that eventually causes AIDS by denting the immune system.
What causes influenza, and what are its symptoms?
Caused by a family of RNA viruses and causes symptoms of common cold (runny nose, sore throat, muscle pains, headaches, coughing, fatigue, and variable body temperatures).
What causes chickenpox, and what are its symptoms?
Caused by the double-stranded DNA virus Varicella zoster virus & leads to red skin rashes that develop into itchy spots.
What is the typical treatment for chickenpox?
No treatment, but calamine lotion is may be used to soothe the skin.
What condition can Varicella zoster virus cause in adults, and how does it differ from chickenpox?
The virus can cause shingles in adults, which has similar but more intense and longer-lasting symptoms than chickenpox.
What causes oral and genital herpes?
Both are caused by strains of the double stranded DNA virus Herpes simplex virus.
What are the symptoms of a herpes outbreak?
Liquid-filled blisters appear on the skin, which burst to form painful sores.
What is used to treat herpes and how does it work?
No cure, but over-the-counter antiviral creams can speed recover during an outbreak, which inhibit viral DNA polymerase, limiting viral DNA synthesis.
What infections can Aspergillus moulds cause?
Can cause non-invasive infections like fungal sinusitis & invasive lung infections, especially in individuals with lung diseases.
How do polyenes like amphotericin treat fungal infections?
Polyenes bind to ergosterol in the fungal cell membrane, form channels, & cause electrolyte leakage.
Why is amphotericin treatment reserved for severe infections?
Amphotericin has high toxicity so it is used only for potentially fatal infections.
What are dermatophytes, & what infections do they cause?
Dermatophytes are moulds causing nail infections (onychomycosis) & skin infections.
How does terbinafine (Lamisil) treat dermatophyte infections?
Terbinafine inhibits fungal squalene epoxidase, blocking ergosterol production & compromising fungal cell membrane integrity.
What is candida, & what infections does it cause?
Candida is a genus of commensalism yeast-like fungi that causes oral & vaginal thrush & fungal septicaemia, with Candida albicans being the most common strain.
How is Candida treated?
- Polyenes nystatin: Applied as a cream, sucked as tablets or used as vaginal pessaries.
- Imidazoles (e.g. clortrimazole): Delivered topically & work like triangles to inhibit ergosterol synthesis.
What increases the prevalence of systemic fungal infections?
Widespread use of broad-spectrum antibiotics.
What is the cell wall of fungi made of?
Polysaccharides, polypeptides, and chitin.
What are the 3 growth forms of fungi?
- Unicellular (e.g. yeasts)
- Multicellular (e.g. moulds with hyphae & mycelium)
- Dimorphic (switch forms based on conditions)
What are the 4 classifications of Protozoa based on locomotion?
- Amoeba- cytoplasmic projections
- Flagellates- use flagella
- Sporozoa- non-motile as adults
- Ciliates- use cilia
What is the role of schizonts & merozoites in malaria?
Schizophrenic form in the liver & release merozoites that invade red blood cells.
How does quinine treat malaria?
It inhibits haem polymerase, causing parasitic death through haem poisoning.
What are 2 main groups of helminths?
- Nematodes (roundworms)
- Flatworms (trematodes & cestodes).
How are helminth infections commonly transmitted?
Poor hygiene, contaminated water, undercooked meat, or skin contact.
What causes schistosomiasis, and how is it treated?
Schistosoma trematodes; treated with praziquantel.
What role do Cyanobacteria play in ecosystem?
Responsible for most photosynthesis & oxygen production.
How does the micro biome benefit humans?
It regulates the immune system & aids digestion.
What is the difference between pathogenicity and virulence?
Pathogenicity: ability to cause disease
Virulence: degree of pathogenicity
Name 5 virulence factories used by microbes.
- Adhesion factors
- Biofilm formation
- Extracellular enzymes
- Toxins (exotoxins & endotoxins)
- Antiphagocytic factors.
How does endotoxins affect host?
Trigger immune response like fever, inflammation, & blood clotting.
What are exotoxins, & how are they classified?
Secreted toxins classified as cytotoxins, neurotoxins, or enterotoxins.
What are Antimicrobials?
Chemicals that either kill microbes or inhibit their growth.
What is selective toxicity in antimicrobials?
The ability of antimicribials to target microbial cells without harming host cells.
Why are antimicrobial drugs more abundant than anti-fungal, anti-protozoal, or antiviral drugs?
Pathogenic bacteria differ significantly from human cells, enabling selective toxicity. Fungi, Protozoa, helminths, & viruses share more similarities with human cells, making selective toxicity harder to achieve.
What are the main categories of antimicrobial mechanisms of action?
- Inhibition of cell wall synthesis
- Inhibition of protein synthesis
- Inhibition of general metabolic pathways
- Inhibition of nucleic acid synthesis.
- Disruption of cell membrane structure
What are beta-lactams, & how do they work?
Beta-lactams are bactericidal agents that inhibit cell wall synthesis & are effective against actively growing bacteria.
What are penicillins effective & ineffective against?
- Effective mainly against G+ve bacteria
- Ineffective agaist mycoplasma & ureaplasma ( no cell wall).
What are examples of gycopeptide antibiotics, & what do they target?
Vancomycin & bleomycin, which act mainly on G+ve bacteria.
How do aminoglycosides work?
They bind to the 30S ribosomal subunit, preventing the formation of an initiation complex with mRNA.
What’s re characteristics of aminoglycosides?
- Bactericidal & broad-spectrum
- Administered I.V or I.M. (Unstable in GIT)
- Poor tissue penetration
- Can cause ototoxicity & nephrotoxicity.
- Reserved for serious G-ve infections.
How do tetracyclines work, & what are their uses?
They inhibit the binding of aminoacyl-tRNA to the 30S ribosomal subunit, making them broad-spectrum & bacteriostatic. Used for acne, chlamydia, & syphilis in penicillin-allergic patients.
Hat are the side effects of tetracyclines?
Teeth discolouration, bone and nail formation issues in infants (only used in adults).
What is chloramphenicol, & hoe does it act?
A broad-spectrum, bacteriostatic agent that binds to the 50S ribosomal subunit, inhibiting peptide transferase.
What are the uses & side effects of chloramphenicol?
- Crosses blood-brain barrier (BBB); used for meningitis & brain abscesses.
- Severe side effects limit systemic use. Commonly used topically for bacterial conjunctivitis (eye drops).
What are macrolides, & how do they function?
Bacteriostatic agents that bind to the 50S ribosomal subunit & inhibit peptidyl transferase or translocation.
When are macrolides used?
In penicillin-allergic patients to treat G+ve bacteria & some bacilli.
What is the function of DNA replication inhibitors?
Inhibit DNA gyrase & topoisomerase II, which control bacterial DNA folding/unfolding.
What are the uses of DNA replication inhibitors?
Used for lower respiratory infections, sepsis, & in penicillin-allergic patients.
What are polymyxins, & how do they act?
They disrupt bacterial cell membrane structure, acting mainly against G-ve bacteria.
What are the limitations of polymyxins?
Not absorbed from the gut (cannot be given orally) & reserved for serious infections due to toxicity.
What is the role of hospitals infection control department?
- Advising on antibiotics for rare or difficult infections.
- Restricting certain antibiotics to prevent resistance.
- Providing advise on reducing infections & cleaning protocols.
- Recommending disinfectants & hygiene measures.
