Microbiology Flashcards
What percentage of the world’s deaths are caused by infections?
33%
What are the two major emerging threats related to infection in high-income countries?
- Healthcare-associated infections
2. Antibiotic resistance
List the four major types of micro-organisms which cause human infectious disease
- Viruses
- Bacteria
- Fungi
- Protists
In 1876, who established that microbes can cause disease?
Robert Koch
Koch’s postulates: #1
A specific ___________ is always associated with a given disease.
microorganism
Koch’s postulates: #2
The microorganism can be __________ from the diseased animal and __________ in pure culture in the laboratory.
isolated, grown
Koch’s postulates: #3
The cultured microbe will cause __________ when transferred to a healthy animal.
disease
Koch’s postulates: #4
The _______ type of microorganism can be isolated from the newly _________ animal
same, infected
Do prokaryotic cells have a nucleus?
No
Do prokaryotic cells have internal membranes?
No
How is prokaryotic DNA organised?
One circular chromosome in a nucleoid
Which type of cells contain extensive and specialised organelles- prokaryotic or eukaryotic?
Eukaryotic
How are bacteria named?
Genus, then species
In the strain of E.coli known as “0157:H7,” what do the “O” and “H” refer to?
Different antigens
Bacteria are most helpfully classified by shape and _________
staining
The ability to take up stain is based on the __________ and accessibility of cell wall ____________________.
thickness, peptidoglycans
List the four layers encapsulating gram negative prokaryotic cells (from outermost to innermost layer)
- Capsule
- Outer membrane
- Peptidoglycan layer
- Plasma membrane
Which two layers make up the bacterial cell wall?
The outer membrane and the layer of peoptidoglycan
Gram-positive bacteria have a uniformly dense cell wall consisting primarily of
peptidoglycan
Which types of bacteria have a very this peptidoglycan layer and an outer membrane?
Gram negative bacteria
An __________ is a toxic, heath stable lipopolysaccharide substance present in the outer membrane of gram negative bacteria that is released from the cell upon lysis.
Endotoxin
What type of bacteria have lipopolysaccharide?
Gram negative bacteria
Gram negative bacteria have what toxic substance in their outer membrane layer?
Lipopolysaccharide
Peptidoglycans have 3-5 amino acid proteins, which is significant because it makes them resistant to
enzymatic destruction
What kind of enzymes assist with cross-linking of peptidoglycans?
Transpeptidase enzymes
Which class of antibiotic prevents the cross-linking of peptides by binding bacterial transpeptidases?
Beta lactam antiobiotics (penicillin,s cephalosporins, carbapenems)
Which class of antibiotic is only effective in gram positive bacteria?
Glycopeptides (e.g. Vancomycin)
Bacterial capsules are made up of
polysaccharides
What is the medical importance of the bacterial capsule?
It “hides” the immunogenic cell wall
Immunity requires antibodies to the _______
capsule
Which part of the bacteria confers virulence?
The capsule
Mobile genetic elements code for ________ and antibiotic resistent _______.
toxins, genes
These are DNA sequences that are able to move location in the genome
Transposons
Circular “extrachromosmal” DNA that replicates independently.
Plasmids
This type of independently replicating DNA can be passed down to progeny or transmitted between bacteria
Plasmids
Non-replicating, dormant form of bacteria that are resistant to drying, temperature, disinfection, and digestion.
spores
Bacillus spp and Clostridium spp are two examples of bacteria that can form ________
spores
Name four examples of bacteria virulence factors:
1. ___________ molecules
adhesion
Name four examples of bacteria virulence factors:
2. ___________ to degrade host proteins
Enzymes
Name four examples of bacteria virulence factors:
3. Degrade ___________ mediators
immune
Name four examples of bacteria virulence factors:
4. _________ host cells
Lyse
Gene regulation - bacterial growth. Describe what happens in the lag phase of bacterial growth
- no increase in cell numbers
- Adjustment to new environment
- Gene regulation
Gene regulation - bacterial growth. Describe what happens in the log or exponential phase of bacterial growth
- Cell doubling
- Slope of curve = growth rate of that organism in that environment
- This is where the person would have either a superficial infection, or bacteraemia
Gene regulation - bacterial growth. Describe what happens in the stationary phase of bacterial growth
- Nutrients become depleted
- Metabolites build up
- Divison stops
- Gene regulation
- ABSCESS
Gene regulation - bacterial growth. Describe what happens in the death phase of bacterial growth
- Exhaustion of resources
- Toxicity of environment
Bacteria are most helpful classified by ________ and staining
shape
Shape of Streptococcus and Enterococcus bacteria?
Coccus/cocci = round
Shape of Enterobacter spp?
Bacillus/bacilli = rod-shaped; long
Shape of Vibrio cholera?
Vibrio = comma-shaped
Shape of Coccobacillus?
In between Coccus and Bacillus- oval
Shape of Campylobacter jejuni (spirilium)?
Rigid spiral
Shape of spirochete?
Coiled spirals
What are the three requirements for successful viral infection?
- Enough virus
- Cells accessible, susceptible, and permissive
- Local antiviral defense absent or overcome
List the 5 types of viral transmission:
- Horizontal (between members of the same species)
- Iatrogenic (Due to activity of a health care worker)
- Nosocomial (Infection occurs in hospital)
- Vertical (Transfer of infection between parent and offspring)
- Germ line (Agent transmitted as part of the genome - e.g. pro-viral DNA)
What is the most common route of entry for viral infections?
Respiratory tract
List the 5 methods of acquiring viral infections (body system “breach”)
- Respiratory tract
- Alimentary tract (eating, drinking, etc)
- Urogenital tract
- Eye
- Skin
Viral infections can be ________, __________ or _________.
acute, chronic, latent
This type of viral infection is characterised by a rapid onset of dz, a relatively brief period of symptoms, and resolution within days
acute
These types of viral infections are caused by pathogens with slow growth rates, promoting an infection that is persistent for long periods.
Chronic
This is an infection that is hidden, inactive, or dormant
Latent
Can latent infections be transmitted to another host, even without any visible signs of disease?
Yes
This is the capacity of a virus to cause disease in an infected host
Virulence
This is the amount of virus needed to kill 50% of infected animals
LD 50
How can virulence be quantified? (5)
- LD 50
- Mean time to death
- Mean time to appearance of sx
- Measurement of fever, weight loss
- Measurement of pathological lesions
Viral genes affecting virulence fall into four classes:
1. Those that affect the abilty of the virus to ______
replicate
Viral genes affecting virulence fall into four classes:
2. Those that modify the ______ _________ mechanisms
host’s defense
Viral genes affecting virulence fall into four classes:
3. Those that enable the virus to ______ in the host
spread
Viral genes affecting virulence fall into four classes:
4. Those which have intrinsic _______ _________ effects
cell killing
This describes that capability of a virus to infect a distinct group of cells in the host
Tropism
Tropism is determined by
the availability of virus receptors on the surface of a host cell.
A _________ host is a person who can become infected by an infectious agent.
susceptible
Name 5 risk factors that can accelerate risk of infection
- Age (< 6 months old, and in the elderly)
- Nutrition and sociocultural condition
- Open wounds/invasive procedures
- Suppressed immune system
- Presence and/or number of infectious organisms
A ________ cell or host is one that allows a virus to circumvent its defenses and replicate.
permissive
What is the most common type of test used to detect levels of antibodies?
Enzyme-linked immunosorbent assay (ELISA)
ELISA assays are usually _________, using a reaction that converts the substrate into a coloured product which can be measured using a plate reader.
chromogenic
Which type of serologic testing enables you to run multiple tests for different viruses simultaneously?
Automation and Random Access Analyser
Which testing method is the best of non-cultivable viruses?
Viral nucleic acid detection testing (PCR)
What is the most common type of viral nucleic acid detection test?
PCR
What type of serologic test for viral infections can also quantify viral load?
PCR
Explain concepts of viral prevention
- PPE: Gloves, masks
2. Vaccines, chemoprophylaxis, immunoprophylaxis
Which four common viruses are there currently no vaccines for?
- HIV
- HCV
- CMV
- EBV
HAART drugs are used to treat
HIV
Lamivudine is used to treat
HBV
Ribavarin and PEG intereron are used to treat
HCV
Tamiflu is used to treat
Influenza
Acyclovir is used to treat
HSV
Ganciclovir is used to treat
CMV
What are the 5 main methods used to diagnose infectious disease?
- Microscopy
- Bacterial culture
- Tissue culture
- Serology
- Molecular techniques (PCR)
What type of laboratory test is more sensitive for detecting very small numbers of bacteria- microscopy or culture?
Culture
What is the main strength of bacterial culture?
It’s good for bacteria you can _________ and ________.
stain, grow
What type of lab test is best for antiobiotic susceptibility testing?
Bacterial culture
Bacterial culture provides provisional identification of bacteria based on the bacteria’s ___________.
metabolism
What is the time frame to achieve results in a bacterial culture?
24 hours for provisional identification,
48 hours to get definitive information
What are the limitations of bacterial culture?
- Slow (definitive results take 48 hours)
- Labour intensive
- Some microorganisms are “unculturable,” such as syphilis
How is HIV mainly diagnosed?
Serology
This lab test can show the response of the immune system to pathogens
serology
Which type of lab testing is helpful in the detection of antibodies in viral infections?
Serology
In serology testing, how can you distinguish between acute and chronic infections? (hint: Antibodies)
The presence of different isotypes IgM vs IgG can distinuish between acute and chronic infection
Which two types of bacteria don’t stain well and are also difficult to culture? What is a better test to diagnose infections with these microorganisms?
Chlamydia and mycoplasm infections
Serology
What is the main limitation with serology testing, in terms of looking for antibodies?
Antibodies can take weeks to develop
This lab technique that takes a specific sequence of DNA and amplifies it to be used for further testing. It amplifies dsDNA molecules (fragments) with the same size and sequence by enzymatic method and cycling condition.
PCR
Four steps of PCR:
1. _______________ by heat
Denaturation
Four steps of PCR:
2. Annealing ________ to target sequence
primer
Four steps of PCR:
3. ___________ TAQ DNA polymerase synthesizes in the 5’ to 3’ direction
Extension
Four steps of PCR:
4. The first PCR cycle ends with _____ new DNA strands that are identical to original target
two
Which type of laboratory testing in helpful in determining the causative agent in viral encephalitis?
PCR
PCR testing has a good ___________ predictive value- a high probability that people with a negative test truly DON’T have the disease.
negative
Which lab technique is used to monitor viral load? (e.g. HIV or HCV)
PCR
Main limitation of PCR:
Can only be used to identify the presence or absence of a _________ pathogen or gene.
known
This type of culture may consist of a single cell, a population of cells, or a whole or part of an organ
Tissue culture
What type of culture is helpful in studying
- the cytopathic effects on cells
- expression of viral proteins detected at the cell surface
Tissue culture
What laboratory technique is used to differentiate bacteria by the chemical and physical properties of the cell walls?
Gram staining
Safranin or fuchsine is the counterstain that shows up as pink or red in what type of bacteria?
Gram negative bacteria
Name some examples of gram positive bacteria
- Staphylococcus
- Streptococcus
- Enterococcus
- Listeria
- Lactobacillus
Name some examples of gram negative bacteria
- E.coli
- Pseudomonas
- Chlamydia
- Yersinia pestis
Acid-fast stains such as Ziehl-Neelsen, or fluorescent stains such as auramine are used to identify what type of bacteria?
Mycobacteria
