Bacteriology Flashcards
What are the differences between prokaryotes and eukaryotes, when it comes to:
-Amount of chromosomes
-Gene structure
-Organelles
-Type of ribosome
-Nucleus
-Prokaryotes are haploid (n), as opposed to eukaryotes, which are diploid (2n)
-Prokaryotic genes don’t contain introns, eukaryotic genes (usuallly) do
-Prokaryotes lack mitochondria, ER or a Golgi apparatus, all of which are present in eukaryotic cells
-Prokaryotes use 70S ribosomes, whereas eukaryotes use 80S ribosomes
-Prokaryotes don’t have a nucleus, eukaryotes are nucleated
Which three ways to microbes have to transfer mobile genetic elements?
-Transduction via phages
-Transfection -> cell dies and another cell takes up the DNA
-Conjugation via plasmids
What are phages?
Phages, or bacteriophages, are viruses that infect bacteria
What is a plasmid?
A circular piece of extrachromosomal DNA
What is the difference between conjugable and mobilizable plasmids?
Conjugagable plasmids contain the machinery to develop a conjugation pillar, whereas mobilizable plasmids need to use the conjugation pillar created by other plasmids
What is the function of the toxin-antitoxin system of plasmids? How does it function?
Toxin-antitoxin systems serve to make sure only daughter cells that inherit plasmids can survive
It works as follows: plasmids produce a stable toxin and an unstable antitoxin -> if a daughter cell does not inherit the plasmid, the production antitoxin wil cease and it will succumb to the toxins
What is mutualism (ecology)
Coexistence in which both organisms benefit
What is commensalism (ecology)
Coexistence in which one organism benefits, and the other is not harmed or helped
What is parasitism (ecology)
Coexistence in which one organism benefits while the other gets harmed
What is quorum sensing?
A communication system that influences the behaviour of a group of bacteria
True or false: quorum sensing communication can cross the species barrier
True -> quorum sensing systems can influence bacteria of other species (for instance: inhibit their growth)
In what kind of processes is quorum sensing usually involved?
Processes that make up the virulence factors of the bacterium
What is a biofilm?
A slimy, extracellular polymeric substance, containing DNA, polysaccharides and proteins
Why are biofilms advantageous for bacteria?
Bacteria within the biofilm receive lower concentration of antibiotics and have to be less metabolically active
What are virulence factors?
Factors that make it easier for the bacterium to adhere to cells, invade the host, evade host defences or gain nutrition -> all involved in causing disease
Wat are endotoxins?
Lipopolysaccharides (LPS) found in the cell wall of Gram- bacteria -> can cause septic/endotoxic shock
What are exotoxins?
Substances secreted (mostly) by Gram+ bacteria, that can interfere with host metabolism (disregulate immune system, degrade connective tissue)
What are superantigens?
Antigens that activate TCR’s/BCR’s regardless of their specificity, causing a huge inflammatory response
Which three factors make the respiratory tract the most common site for infection by pathogens?
- Direct contact with the outside world
- Largest epithelial surface
- Frequent breathing -> frequent exposure
Which three infections can be caused by haemophilus influenzae?
- Epiglottitis
- Meningitis
- Otitis media
Is haemophilus influenzae Gram+ or Gram-?
Gram- coccobacillus
Which two major categories or H. influenzae are there?
- Capsulated: groups A-F -> regist phagocytosis
- Uncapsulated = non-typeable
Which group of H. influenzae is best known for causing disease in humans?
H. influenzae group B (Hib)
What are the two epidemiological shift that are currently happening in epiglottitis infections? What is their cause?
- From children to elderly (>55) (mostly males), because children are vaccinated against Hib
- From capsulate tot non-typeable Hib-infections (NTH-infections; unencapsulated), caused by vaccination against capsulated H. influenzae
Why was the first Hib-vaccination, that was solely aimed at the polysaccharide polyribosylribitol phosphate of Hib, not effective?
It had an age-dependent response that was inconsistent <2 years -> target group of the vaccine
What is the conjugate Hib-vaccine? What is the function of the added components?
Vaccine with Hib polysaccharides + carrier protein antigens
The carrier protein antigens stimulate the immune response against the vaccine, specifically T-dependent immunity
In some cases, viral infections lead to a more advantageous environment for bacteria. Which factors constitute this favourable environment? (3)
- Changes to epithelial surfaces and epithelial integrity
- Effects on the immune systems (tuned towards virus and thus less effective in fighting of bacteria)
- Metabolic effects on the cells (mitochondria influenced)
Which targets of antibiotics are known? (5)
- Cell wall synthesis inhibition
- Inhibition of protein synthesis
- Inhibition of nucleic acid synthesis
- Anti-metabolites
- Disruption of membranes
What are the antibiotic resistance mechanisms? (4)
- Efflux pumps
- Immunity & bypass, for instance lowering of permeability
- Target modification
- Inactivating enzymes
Which of the following sample properties affect sensitivity of tests, and which specificity?
-Solid (and thus requiring grinding)
-Fluid (viscosity)
-Sterile or contaminated with microbiota
-Volume required for accurate testing
-Accesibility of sample
-Willingness of patient
-Presence of test inhibitors
-Solid (and thus requiring grinding) affects sensitivity
-Fluid (viscosity) affects sensitivity
-Volume required for accurate testing affects sensitivity
-Accesibility of sample affects sensitivity
-Willingness of patient affects sensitivity
-Presence of test inhibitors affects sensitivity
-Sterile or contaminated with microbiota affects specificity
Which phenotypic properties can help identify bacteria? (6)
-Antibiotic growth inhibition
-Biochemistry
-Antibody/antigen reactions
-Size and form
-Proteins
-Genomes/genes
What are the advantages and disadvantages of microscopy?
Advantages:
-Direct observation of microorganisms
-Relatively cheap
-Easy to perform
-Catch all technique
Disadvantages:
-Catch all technique (for instance causing false positives)
-Lack of sensitivity
-Special stains, chemicals or techniques required
Which phenotypic characteristic is investigated with (bacterial) cultures?
Growth characteristics, with the goal to obtain the organism in its pure form
Why would we want to obtain (bacterial) pathogens in their pure form using culturing?
It allows for:
-Pathogen identification
-Antibiotic resistance profiling
What is an easy way of selecting which bacteria grow in bacterial culture?
Modifying growth conditions to suit certain bacteria, through:
-Modifications to the agar
-Growing temperature
-Aerobic/microaerophilic/anaerobic
What is shown using Gram staining?
The thickness of the peptidoglycan layer (Gram+/Gram- bacteria)
What is Ziehl Neelson staining used for?
Mycobacteria
What is an example of antibody-antigen reactions in the identification and diagnostics of bacteria?
Latex particle agglutination (for instance for S. aureus)
Which three tests are used to test antibiotic susceptibility?
- Broth dilution
- Disk diffusion
- E-strip
How does broth dilution work?
- Suspension of bacteria added to tubes containing an increasing dilution of antibiotic
- Tubes incubated and read out to determine the MIC -> the minimal concentration that inhibits bacterial growth
What is the MIC (antibiotics)?
Minimal inhibitory concentration -> the minimum concentration that is needed to inhibit bacterial growth
How can broth dilution be used to determine the MBC?
Material from incubated tubes are put on an agar plate, after which the following can happen:
-If the antibiotic or the concentration of antibiotic in the tube was only inhibitory, bacteria will resume growth on the agar plates
-If the antibiotic or the concentration of antibiotic was lethal to bacteria, no growth will occur on the agar plates
What is the MBC (antibiotics)?
Minimal bacteridical concentration -> the minimum concentration that is needed to kill bacteria
How does disk diffusion work?
- Colony is spread out on an agar plate, after which disks with different antibiotics are placed
- Antibiotic diffuses into the agar -> if the bacterium is sensitive a certain diameter around the disks won’t show any bacterial growth
- The diameter of the zone can be used to determine sensitivity
How does the E-strip test work?
- A strip with an increasing concentration of antibiotic is places on an agar plate incubated with bacteria
- Bacterial growth will be inhibited from a certain concentration onwards -> this can be read from the strip
Which technique can be applied when bacteria are not culturable?
PCR/NGS for genotype testing
What are the advantages of PCR in bacterial diagnostics? (4)
- Very sensitive
- Very specific
- Usually based on specimen type
- Generates 100’s of millions of specific PCR-products
What is point-of-care testing?
Medical diagnostic tests at or near the point of care (as opposed to in a diagnostics lab)
What are the advantages of point-of-care testing?(9)
- Portability
- Lower cost
- Less sample required
- Less reagents
- Decentralized testing
- Faster turnaround
- Improved healthcare
- Interoperability
- Open/expanding market
What are the disadvantages of point-of-care testing? (3)
- Low throughput
- Possibly lower sensitivity/specificity
- Not always accepted by end users (doctors)
