Infectious Agents Flashcards
1
Q
What are viruses?
A
Viruses are not cellular organisms. They are packets of genetic material and proteins without any of the structures that distinguish prokaryotes and eukaryotes
2
Q
What does a virus require to grow that bacteria does not?
A
Bacteria can grow on their own whereas a virus requires a host to grow
3
Q
What 5 categories are living things divided into?
A
Living things are divided into five kingdoms: animal, plant, fungi, protist and monera.
4
Q
Arrange the 3 in order starting from the smallest to biggest: bacteria, virus, protozoans
A
Protozoans –> Virus –> Bacteria
5
Q
What are the structures in bacteria?
A
- Cell envelope
- Plasma membrane
- Pilli
- Naked chromosomal and plasmid DNA (plasmid for resistance)
- Ribosomes
- Flagellum
- Capsule (made of sugar and acts as a cell wall)
“Cells Please Play Naked, Really Fucking Cool”
A generalized bacterium, a prokaryote, lacks a nucleus and membrane-bound organelles, possessing a cell wall, a cell membrane, cytoplasm, ribosomes, and a nucleoid region containing DNA, with some having additional structures like flagella or pili
6
Q
What is the purpose of a bacterial capsule?
A
Protects the bacteria from the host’s immune system so that more bacteria invade the body
7
Q
What is the purpose of Flagella?
A
Aids mobility of the bacteria through propella - have sensors to swim down a gradient to an area of nutrients etc.
8
Q
What is the purpose of Pili/Fimbriae?
A
Pili/Fimbriae – help bacteria stick to surface to stop them being washed out
9
Q
What’s another word for Pili?
A
Fimbriae
10
Q
What is the size of bacterium?
A
1 micrometer diameter and 3-10 micrometers in length
11
Q
What is Chlamydia (bacteria, virus or protozoan)?
A
Bacteria
12
Q
What are the basic characteristics of bacteria?
A
- Genus/species – Bacteroides fragilis
- Light microscope -1um diam./ 3-10um length
- Prokaryotic cells – divides by binary fission
- Doubling time – 20 min for E.coli
- Cell wall differentiates – Blue/purple (positive), red (negative) (gram positive or negative)
13
Q
What is the genus/species of bacteria?
A
Bacteroides fragilis
14
Q
What size are bacteria?
A
1um diam./ 3-10um length
15
Q
How does bacteria divide?
A
Prokaryotic cells – divides by binary fission
16
Q
What is the doubling time in E. coli?
A
20 minutes
17
Q
What are the cell wall differences in bacteria?
A
Blue/purple (positive), red (negative)
18
Q
What does the species name often tell us?
A
The name of the disease it causes
19
Q
What is pathogenicity?
A
The degree to which a microorganism can cause disease
20
Q
What is another word for pathogenicity?
A
Virulence
21
Q
What is a pathogen?
A
Organism that causes or is capable of causing disease
22
Q
What is Commensal?
A
Organism which colonises the host but causes no disease in normal circumstances (can cause disease if in specific area; nonpathogenic bacteria)
23
Q
What is an Opportunist Pathogen?
A
Causes disease only in the absence of normal host resistance/if host defences are compromised
24
Q
What is Virulence/Pathogenicity?
A
The degree to which a given organism is pathogenic
25
What is Asymptomatic Carriage?
When a pathogen is carried harmlessly at a tissue site where it causes no disease
26
Which parts of your body are open to bacterial colonisation?
Any mucosal surface e.g. stomach, skin, buccal cavity etc.
27
Which parts of the body are sterile?
Blood, gall bladder, lungs, kidney → initiates an inflammatory response if bacteria is present
28
What is Bacterial Morphology/how is it classified?
- Shape, size and aggregation e.g. cocci, rods, clumps, chains, pairs
- Cell wall structure – Gram positive/ Gram negative
- Other structures – capsule, spore, flagella, pili
29
What makes up the gram positive bacterial cell envelope?
- Purple, single cytoplasmic membrane made of phospholipids
- Made of peptidoglycan (short chain of peptides linked to 2 sugars) → sort of cell's skeleton - antibiotics target this
- Some have a capsule
Phospholipid membrane but outside of this membrane they have a large area called peptidoglycan (two sugars linked to a peptide = chain like structure around the membrane) which is attached through triflic acid
30
What makes up a gram negative bacterial cell envelope?
- Inner cytoplasmic membrane
- Outer membrane
- Lipopolysaccharide (endotoxin) on the outside of the outer membrane
Phospholipid bilayer, have a small petridoglycan layer and also have a second membrane which is called the outer membrane. Space between inner and outsider layer is periplasmic space. On outer leaflet of gram negative cell wall you have lipopolysaccharide (LPS) which our immune system has recognised and so it goes into overdrive which causes inflammatory cascades.
LPS is toxic which is why it is also called Endotoxin
31
What is a prokaryotic cell?
A cell without a nucleus or membrane bound organelles (still has DNA)
32
What is the purpose of a bacterial capsule?
Protects the bacteria from the host's immune system so that more bacteria invade the body
33
What makes the difference between gram positive or gram negative?
Variations in cell wall = Gram positive or negative
34
How do we grow bacteria?
- Agar medium (media; grow bacteria on this jelly-like structure ), broth (liquid medium for growing bacteria)
- Aerobic (growth in oxygen), anaerobic (growth without oxygen), facultative (either)
- Shape of colony – diameter, edge, domes or flat
- Effect on medium – haemolysis (Streptococcus), pigment production (Pseudomonas), acid from sugar e.g. lactose (Escherichia coli)
35
What is the growth rate of bacteria of:
- Most viruses
- E.coli, S.Aureus etc
- Mycobacterium tuberculosis
- Fungi (candida albicans)
- Mycobacterium leprae
- Most viruses
Situation: Cells
Doubling time: <1 hour
- E.coli, S.Aureus etc
Situation: Broth or solid media
Doubling time: 20 - 30 mins
- Mycobacterium tuberculosis
Situation: Broth or solid media
Doubling time: 24 hours
- Fungi (candida albicans)
Situation: Broth or solid media
Doubling time: 30 mins
- Mycobacterium leprae
Situation: Broth or solid media
Doubling time: 2 weeks
36
What are Antibiotics?
- Many groups, split on chemical structure and mode of action such as penicillins and tetracyclines
- Can be either Bactericidal or Bacteriostatic
- Activity determined by Minimum Inhibitory Concentration (MIC) – the lower the MIC the more active the drug
37
What is Bactericidal?
Has the capacity to kill bacteria
38
What is Bacteriostatic?
Inhibit or stop the growth and reproduction of bacteria, but do not necessarily kill them.
39
What is Antibiotic Sensitivity Stokes Method?
he Stokes method, a disc diffusion technique, is used to determine antibiotic susceptibility by comparing a test organism with a sensitive control strain on the same plate, allowing for simultaneous evaluation under identical conditions
40
What is Antibiotic Sensitivity?
Antibiotic sensitivity, also known as antibiotic susceptibility, is a test that measures how susceptible bacteria are to different antibiotics. It helps doctors choose the best antibiotic to treat an infection.
41
What is Antibiotic Resistance?
- Most common mechanism is via enzyme – beta-lactamase (ESBL)
- Widespread and often indiscriminate use has led to multiresistant organisms (selection)
42
What has become antibiotic resistant?
- Several bacteria now very resistant (MRSA) and difficult to treat
- Greater reliance now on infection control and/or vaccines
43
Genetic variations in bacteria can be due to what?
Mutations
- Base substitution
- Deletion
- Insertion
Gene Transfer
- Transformation (e.g. via plasmid)
- Transduction (e.g. via phage)
- Conjugation (e.g. via sex pilus)
44
What is a Plasmid?
A plasmid is a small, circular, double-stranded DNA molecule that exists independently of a cell's chromosomal DNA, commonly found in bacteria and some other organisms, and can replicate independently.
45
Why are plasmids bad?
Plasmids are crucial carriers of genes, including those conferring antibiotic resistance and virulence, facilitating their spread among bacteria, posing a significant threat to human health. They have antibiotic or virulence determinant genes.
46
What is Bacterial Conjugation?
Bacterial conjugation is a process that allows bacteria to share genetic material with each other. It's a type of sexual reproduction in bacteria.
47
What are some healthcare-associated infection implications for the NHS?
- 300,000 HAIs per year in UK
- Costs NHS £1 billion
- Major impact on mortality and morbidity increasing length of stay and cost
- Increasing problem in community settings such as nursing and residential homes
48
What is MRSA (Methicillin-Resistant Staphylococcus Aureus)?
- A group of several bacteria that are now very resistant to antibiotics and are difficult to treat
- Caused wounds/bacteraemia can spreads through hands/fomites
- Treatment is Vancomycin plus topicals if necessary
49
What is C.Difficile?
- Bacteria that causes hospital-acquired diarrhoea and colitis
- Spread by hands and/or environmental surface
- Usually gained after taking a course of antibiotics
50
What hygiene measures can we use to reduce spread of MRSA?
- Clean hands before and after touching patients
- Hands cleaned with soap and water, or alcohol gel or hand rub
- Wear gloves and aprons when caring for a patient with MRSA
- A patient with MRSA may be moved to a room on their own or into a separate area for people who have MRSA or other infections`
51
How do we avoid getting c/difficile?
- Wash hands thoroughly with soap and water before preparing/eating food, after handling raw food, after going to the toilet, after visiting hospitals and care homes
- Take antibiotics only when necessary
- Wash all dirty clothes, bedding, towels of infected patients in washing machine on hottest cycle.
- Clean toilet seats, flush handles, taps, after use with detergent and hot water
52
What is Chlamydia Trachomatis?
- Related to Chlamydophila pneumoniae and C.psittaci
- Obligate intracellular bacterium
- Produces elementary and reticulate bodies that can be seen by light microscope
- Have a unique development cycle
- Can only divide in human cells like (but not being) a virus
- Grown in tissue culture
- Detected by molecular methods
- Treated with tetracycline or azithromycin
53
What are the 3 groups of chlamydia trachomatis?
Serovars A-C = Trachoma Serovars
D-K = NGU/Conjunctivitis Serovars
L1-L3 = Lymphogranuloma venereum
54
What is the Chlamydia life-cycle?
- Entry
- Differentiation to RB (reticulate body)
- Multiplication of RBs
- Differentiation to EBs (elementary body)
- Inclusion
- Release of EBs
- Attachment of EBs
- Entry
55
What are inclusion bodies in Chlamydia/Bacteria?
In bacteria, inclusion bodies are dense, amorphous protein aggregates, often formed when bacteria are forced to produce large amounts of a foreign protein, and they can be found in both the cytoplasm and periplasm
56
What are the basic characteristics of viruses?
- DNA (Herpes) or RNA (HIV)
- Require electron microscope to be seen (25 – 150nm)
- Several morphological forms
- No metabolic systems – requires tissue culture
57
What is the structure of the virus?
The simplest virions consist of two basic components: nucleic acid (single- or double-stranded RNA or DNA) and a protein coat, the capsid, which functions as a shell to protect the viral genome from nucleases and which during infection attaches the virion to specific receptors exposed on the prospective host cell.
- Virion: the intact virus particle
- Capsid: the protein coat
- Capsomeres: the protein structural units which make up the capsid
- Nucleic acid genome: either DNA or RNA
58
What are some non-living characteristics of viruses?
- They are acellular, that is, they contain no cytoplasm or cellular organelles.
- They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery. In other words, viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell.
- The vast majority of viruses possess either DNA or RNA but not both.
59
What are some living characteristics of viruses?
- They reproduce at a fantastic rate, but only in living host cells.
- They can mutate.
60
How do Viruses grow?
- Many different types of cells used for culture – growth determined by cytopathic effect (CPE)
- Growth recognised by unique appearance e.g. adenonvirus –grape-like clusters
- Also by antibody neutralisation and erythrocyte agglutination
61
What is RNA?
Ribonucleic acid (RNA) is a molecule that carries genetic information and is present in all living cells. It's similar to DNA, but RNA is usually single-stranded, while DNA is double-stranded.
62
How do viruses grow?
- Many different types of cells used for culture – growth determined by cytopathic effect (CPE)
- Growth recognised by unique appearance e.g. adenonvirus –grape-like clusters
- Also by antibody neutralisation and erythrocyte agglutination
63
What is a viral capsid?
A capsid is the protein shell of a virus, enclosing its genetic material.
A viral capsid is the protein shell that encases a virus's genetic material (DNA or RNA), protecting it and facilitating its entry into host cells.
64
How do we lab diagnose a virus?
- CPE
- Electron microscopy - morphology
- Serology – antibody tests e.g. ELISA looking for >4 fold rise in titre
- Molecular tests such as PCR and commercial DNA/RNA detection systems
65
What is ELISA?
ELISA, or enzyme-linked immunosorbent assay, is a laboratory technique used to detect and measure the presence and amount of a specific substance, like antibodies, antigens, proteins, or hormones, in a sample, often blood or other bodily fluids
66
What is Protozoa?
- Eukaryote (3-2000um)
- Contains nucleus, no cell wall
- Unicellular, often in soil and water
- Life cycle, trophozoite and cyst stages
- Examples, Acanthamoeba, Toxoplasma gondii
