Module 6: Microbiology Flashcards
are viruses living organisms? why/why not?
they are not, because:
- Consist only of DNA or RNA and protein
- Are incapable of independent reproduction
- Are smaller than any cell (~0.1 m)
- Have no cell membrane
- Do not have ribosomes
- Have few enzymes for metabolism
properties of virus?
- Infect bacterial, plant and animal cells
- Are large, inert systems consisting of nucleic acid (DNA or RNA) and protein
- No cell wall, ribosomes, mitochondria or nucleus. Thus, cannot produce energy or synthesize proteins
*Incapable of independent replication and require living host
they are “obligate intracellular parasites”
what are the classifications of a virus?
- Type of nucleic acid: DNA or RNA
- Arrangement of nucleic acid: Double-stranded or single-stranded & Linear or circular
- Structure of the virus particle: Enveloped / “naked”
- Symmetry of capsid
- Icosahedral
- Helical
- complex
What is the 6 steps of the viral lifecycle?
- Attachment to host cell surface
- Penetration into host cell cytoplasm
- Uncoating to release viral genome
- Replication of viral genomes, mRNA and proteins
- Assembly of viral components
- Maturation and release of progeny viruses through host
membranes
Describe the pathogenic consequences of viral infection
The cell dies by rupturing during a virus release (cell commits suicide), this process is called apoptosis. The infected cell loses function and is transformed by virus
Give examples of viral diseases
HPV (DNA), AIDS, fever, COVID (RNA)
Describe the basic structure of a fungus
- Thick carbohydrate cell wall
- Phospholipid bilayer of cell membrane
- Moulds - multicellular fungi consisting of long, branched filaments called
hyphae that form a tangled mass called mycelium. - Yeast - Single cell fungi that multiply by budding and division
- Dimorphic fungi - Moulds at room temperature but yeast at body temperature
Describe the different types of fungal infections and give medically relevant examples of each type
- Superficial mycoses (most common)
* Fungus grows on body surfaces e.g., Skin, hair, nails,
mouth
* Example: Athlete’s foot, thrush, ringworm - Subcutaneous mycoses
* Fungus grows in the deeper layers of the skin
* Example: Madura foot - Systemic mycoses
* Fungus grows/spreads into internal organs
* Example: histoplasmosis, systemic candidiasis
Describe the three different types of parasites and give medically relevant examples of each type
- Helminths (worms)
- e.g. pinworm - Protozoa
- e.g. plasmodium which causes malaria - Arthropods - lives outside host but feeds on hosts blood/tissue
- e.g. ticks, mites, lice, fleas
what are the benefits and harms of microorganisms?
Benefits:
- Commensals/Normal regional flora
o Stimulate the immune system
o Recycling of elements
o Food production
o Beer, wine, cheese etc
o Therapeutics
o Vaccines, antibiotics
o Pest control
o Gene therapy & Biotechnology
Harms:
o Infectious disease
o Pathogens
o Opportunistic pathogens
o Antimicrobial resistance
o Allergens
o Food spoilage
o Contamination
what are the four host-microbe relationships and describe them?
o Commensalism: One organism benefits, the
other not harmed
o Mutualism: Both organisms benefit and
depend on each other
o Parasitism: One organism benefits, the other
is adversely affected
o Opportunism: A change in living relationship
resulting in parasitism
what are Koch’s postulates?
- the suspected pathogen must be present in all cases of the disease and absent from healthy animals
- the suspected pathogen must be grown in pure culture
- cells from a pure culture of the suspected pathogen must cause disease in a healthy animal
- the suspected pathogen must be reisolated and shown to be the original
what is an infectious disease?
caused by infectious agent with infection in one person being transmitted to others
Describe the features that differentiate Gram-positive and Gram-negative bacteria.
Gram positive bacteria has a thick peptidoglycan layer and a plasma membrane, whereas, gram negative bacteria peptidoglycan layer is thin and has an outer and inner membrane.
They also stain differently, gram positive stains blue/purple whilst gram negative stains pink/red.
Describe bacterial reproduction, growth phase and how to measure bacterial growth
Bacterial cells undergo Binary Fission to reproduce a cell into two parts which involves:
* DNA replication to get two copies
* Moving of the DNA strands to opposite ends of the cell
* Splitting of the cell in the middle into two separate bacteria that has the same genetic material
Replication results in an exponential increase in cell number
Lag Phase: Initial adaptation to conditions
Logarithmic Phase: Exponential increase in cells
Stationary Phase: Rate of cell division equals cell death.
Death Phase: Decrease in cell numbers.
Measuring bacterial growth: Turbidity is a direct indication of growth that can be measured using a spectrophotometer.
Describe how the healthcare environment contributes to the incidence of infectious disease
Promotes atypical/resistant organisms compared to community-acquired
* Older & more vulnerable hosts
* Multiple routes of infection—frequent contact
between patients-carers
* Use of antimicrobials
- Constant environmental pressure is selective
for resistant organisms
- Promoted by ease of genetic transfer in bacteria
Describe what is meant by MRSA, its key virulence factors and pathophysiology
MRSA is Methicillin-resistant Staphylococcus aureus. Its key virulence factors are toxins and it is gram positive
Describe other significant bacterial HCAIs
Clostridioides difficile
- gram positive
- found in feces of neonates and infants
- transmission: fecal-oral
Major virulence factors—exotoxins
* Enterotoxin
- Targets enterocytes, causes disruption in signaling pathways → changes in cell shape/integrity
→ induces apoptosis
* Cytotoxin
- Similar to enterotoxin but with disruption of tight junctions
Cell damage
* Diarrhea
* Pseudomembranous colitis e.g. inflammatory cells form a viscous exudate
Incidence in Australia: ~4/10 000 patient days
Describe the basic antibiotic modes of action
Classes of antibotics are:
* Cell metabolism
* Cell wall synthesis
* Protein synthesis
* Nucleic acid synthesis
* Cell membrane function
- Only targets pathogen and not the host (antibiotics/antivirals etc.) – selective for the microbial target
- Narrow spectrum (doesn’t affect normal flora), selective toxicity (few side effects), routes of
administrations, good distribution to site of infection, emergence of resistance is slow - Can also aid host immune system (vaccines)
Describe bacterial antibiotic resistance mechanisms
- Production of enzymes: Enzymatic inactivation of antibiotic
* Example: beta-lactamases of Gram-positive and Gramnegative bacteria, aminoglycoside-modifying enzyme - Alteration in the bacterial cell binding sites: Changing binding site of penicillin binding proteins (PBPs)
for Gram-positive and Gram-negative bacteria
* Changing ribosomal binding site of aminoglycosides in P.
aeruginosa - Change in membrane permeability: * Reduced antibiotic accumulation through the mutation or loss
of outer membrane channels e.g. loss of outer membrane
porins in P. aeruginosa - Producing alternate metabolic pathways/drug efflux pump: * Expression of efflux systems to actively extrude drugs out of
the cell e.g. Tetracycline efflux from many Gram-negative
bacilli - Biofilm formation: * Biofilm-embedded cells demonstrate a markedly higher
tolerance to antimicrobial agents than planktonic bacteria e.g.
uropathogenic E. coli
Describe what human practices can lead to antibiotic resistance and what can be done to prevent it
*Antibiotic dosage is too low
*Poor prescribing
*Use of broad-spectrum antibiotics
*More common in hospitals than in the wider
community
*Antibiotics prescribed to patient with viral infection
*Poor prescribing
*Patient does not complete course of antibiotics
*Poor patient adherence
what are the different types of antimicrobials?
Anti-parasitic (eukaryotic)
* Danger of side-effects because we are eukaryotes too!; target unique part of life cycle
* E.g. anti-helminth (worm)—Combantrin; anti-malarial—quinine
Anti-fungal
* Also eukaryotic! Difficult to find unique targets; target membrane integrity (ergosterol)
* E.g. canesten, Lamisil
Anti-viral
* Target unique function—normal nucleic acid synthesis; often involves inhibiting host cell enzymes –
side effects
* E.g. Zovirax
Anti-bacterial
* AKA antibiotic
transfer of resistance genes?
- Transformation
- Transduction
- via bacteriophage
- Conjugation
- Bacterial “mating”
- Transposition
- Through transposons
what are the potential routes for infection and environment factors?
Potential routes of infection include:
* Airborne transmission (suspended particles)
* Respiratory droplets
* Direct/indirect contact
* Faecal-oral
* Vector-borne (bites; not generally the cause of
hospital transmission)
* Sexual (not generally the cause of hospital
transmission)
Surfaces
* Door handles
* Taps
* Toilet seats etc.
Instruments
* Respirators
* Ultrasound probes etc.
Medical supplies
* Bandages
* Surgical instruments
* Ultrasound gel etc.
Describe the difference between sterilization and disinfection, and give an example method to achieve each of these
Sterilisation—the killing or removal of all viable organisms, including spores
* Endospores—survival strategy for Clostridium spp. and Bacillus spp.
e.g. heat, irradiation
Disinfection—the killing of many but not all microorganisms
* Reduction of bacterial load
* Decrease likelihood of reaching infective dose
e.g. pasteurisation, filtration, chemical disinfectants
Describe the additional infectious disease risks associated with the health care environment
- Concentration of vulnerable and/or infective persons
- Repeated contact with equipment, carers/therapists/other staff
- Reservoir of non-typical pathogens/highly resistant organisms
Can lead to: - Nosocomial ( = hospital) acquired infections
- More recently — HCAI ( = health care associated infections
Outline the infection control methods in place in health care settings
Standard precautions
* Hand hygiene
* Use of PPE where appropriate
* Includes environmental controls—waste management; routine cleaning; spill management
Additional precautions
* Contact precautions
* droplet precautions
* Airborne precautions
Further considerations for multi-resistant organisms (MROs)
Describe why in-patients are more vulnerable
In the community, susceptible hosts include:
* Young, old, pregnant, immunocompromised
In hospital, additional factors increasing host susceptibility:
* Underlying disease e.g. cancer, diabetes, cardiovascular disease
* Trauma e.g. burns
*Invasive procedures = easier access to normally sterile sites
* Treatment e.g. cytotoxic (cancer) drugs, steroids (immunosuppressing
Describe approaches to aid in-patients in resisting infection
Three approaches:
1. Exclude sources of infection from the hospital
environment
2. Interrupt the transmission of infection from source to
host
3. Increase host resistance to infection
Reduce risk of post-operative infection by:
* Minimising length of operation
* Adequate wound drainage
* Preventing pressure sores, chest infections etc. using
active physiotherapy
Care of invasive devices e.g. catheters, IV lines, nasogastric
tubes
* Easily contaminated by patient’s own skin flora
