Microbiology Flashcards
1
Q
Where are the following pathogens found and are they eukaryotes or prokaryotes?:
- Protozoa
- Fungi
- Bacteria
- Viruses
A
- Protozoa = found in single celled animals, eukaryotes
- Fungi = found in higher plant-like organisms, eukaryotes
- Bacteria = they are generally small and single celled, prokaryotes
- Viruses = very small, obligate parasites, non-living
2
Q
Eukaryote vs Prokaryote:
- Size
A
Eukaryote - 5-50mms (larger)
Prokaryote - 0.5-10mms (smaller)
3
Q
Eukaryote vs Prokaryote:
- Structure
A
Eukaryote - frequently multicellular complex which is compartmental
Prokaryote - usually single celled and relatively simple
4
Q
Eukaryote vs Prokaryote:
- Type of chromosome and DNA
A
Eukaryote - linear chromosomes, histones, introns and exons
Prokaryote - single circular chromosome with gene structure
5
Q
Eukaryote vs Prokaryote:
- Ribosomes
A
Eukaryote - 80S ribosomes
Prokaryote - 70S ribosomes
6
Q
Eukaryote vs Prokaryote:
- Cellular structure and cell cycle
A
Eukaryote - no wall or flexible cell wall. Cell cycle is mitosis/meiosis
Prokaryote - rigid cell wall. Cell cycle is rapid cell cycle
7
Q
Nucleoid:
- What does it contain?
- How is DNA replicated?
- How are chromosomes organised?
A
- DNA and proteins, no nuclear membrane and chromosomes are single circular molecules. Also contains DNA segregation machinery
- Via DNA dependent RNA polymerase
- By gyrases and extra chromosomal replicons often exist
8
Q
What is the cell wall made up of?
A
Peptidoglycan and has a repeated polysaccharide structure
9
Q
Cell wall in gram negative vs gram positive organisms
A
Gram negative - single layer. Outer membrane, periplasm then thin peptidoglycan layer
Gram positive - many layers of peptidoglycan ‘roped’ together
10
Q
Role of lipopolysaccharide
A
Has a structural role and antigen and bacterial toxin
11
Q
Things required for prokaryotic growth
A
Food, temperature, hydrogen ion concentration, osmotic protection, oxygen
12
Q
4 things that can be used to classify microorganisms
A
Appearance/structural features, growth requirements, enzyme/metabolic tests, molecular tests
13
Q
Appearance/structural features in classifying microorganisms
A
Shape, size, arrangement, Cell wall (gram +ve/-ve)
14
Q
Growth requirements in classifying microorganisms
A
Aerobic/anaerobic, requirement for blood products, sensitivity to inhibitory agents
15
Q
Enzyme/metabolic tests in classifying microorganisms
A
Coagulase test, catalase test, haemolysis (streptococci ONLY), biochemical profiling
16
Q
Molecular tests in classifying microorganisms
A
Immunological test, DNA sequencing, protein profiling
17
Q
What can microscopy tell about a microorganism?
A
If its a pure culture or polymorph, its shape, sizing and grouping, structures, staining
18
Q
Shapes of bacteria
A
Cocci, bacilli, spiral-shaped
19
Q
Divisions of cocci
A
1 plane - diplococcus or chains
3 planes - clumps/clusters
20
Q
Vibrio
A
Slightly curved rod. Gram negative
21
Q
Spiral shaped microorganisms - rigid and flexible
A
Rigid - spirillum
Flexible - spirochaete
22
Q
Spores
A
Inert structures that are resistant to physical and chemical challenge
23
Q
Gram stain
A
Process which shows retention of crystal violet/iodine complex by gram positive bacteria
24
Q
Gram stain procedure
A
- Prepare a heat fixed film of bacteria on a glass slide
- Stain with crystal violet for 1 minute then rinse with water
- Treat with Gram’s iodine for 1 minute then rinse with water
- Briefly decolourize with acetone or ethanol
- Counter stain with basic fuchsin or safranin for 1 minute then rinse with water
- Blot dry and view under oil immersion
25
What colour to gram positive and gram negative microorganisms stain?
Positive = purple, negative = pink
26
Examples of microorganisms which don't stain with the gram stain procedure
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Mycobacterium tuberculosis (causes TB) has a waxy cell wall which doesn't take up the stain
Treponema pallidum (causes syphilis)
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27
Aerobic
Grow in oxygen/air
28
Obligate aerobes
Require oxygen
29
Obligate anaerobes
Killed by oxygen
30
Facultative anaerobes
Tolerate oxygen
31
Capnophillic
Prefer high CO2 levels
32
Selective media
A media that selects for the growth of specific prokaryotes. Presence of specific substances permits the growth of one organism over another
33
Examples of selective media
Mannitol salt agar, salmonella-shigella
34
Differential media
Incorporation of chemicals produces visible changes in colonies that facilitate identification
35
Alpha hemolysis
Greening of colonies, partial hemolysis
36
Beta hemolysis
Yellowing of colonies, partial hemolysis
37
Gamma hemolysis
No haemolysis
38
What does matrix assisted laser desorption ionisation time of flight do?
- Generates a series of ions from a sample dependent on its constituents
- Separates the ions according to their mass and charge
- Detects the spectrum of proteins released from a sample resulting in a characteristic signature
39
How do pathogens cause damage to the host cell?
- Adhere, colonise and invade
- Evade host defences
- Multiply and complete life cycle
- Exit the host
40
Virulence
The capacity of a microbe to cause damage to the host
41
Pathogen
A harmful organism which produces a pathology
42
Endogenous and exogenous
Endogenous - microorganisms which from within a system
| Exogenous - not part of the normal flora
43
Opportunistic pathogen
An organism which causes infection when an opportunity/change in natural immunity arises
44
Contaminant
An organism that is growing in a culture by accident
45
Examples of fungal infections
Candida spp. (yeast (budding), from skin infection to Candidaemia)
Aspergillu spp. (moulds, causes infection in immunocompromised)
46
Examples of protozoal infections
Leishmaniasis, malaria, toxoplasma, GI infections
47
2 pathogenic, anaerobic gram negative cocci
Neisseria meningitis - commonest cause of bacterial meningitis
Neisseria gonorrhoea - causes gonorrhoea
48
Coliforms:
- Do they grow in aerobic or anaerobic conditions?
- Are they normal/abnormal?
- How are they differentiated from each other?
- Grow best aerobically but can also grow anaerobically
- Many of them are part of the normal gut flora
- They are differentiated by biochemical reactions, serotyping and O antigens and H antigens
49
What are coliforms?
Coliform is a term used to describe species of gram negative bacteria that look like E.coli on gram film and when cultured on blood agar
50
How do coliforms cause infection? Give examples of infections that can cause
Any coliform that gets into a normally sterile site can cause a serious infection e.g. urinary tract infections, peritonitis and biliary tract infections
51
What is the first line antibiotic for the treatment of infections caused by coliforms?
Gentamicin
52
Why do patients with coliform sepsis become very unwell very quickly?
Because of the endotoxin that is released from the gram negative wall when the bacteria die
53
Steps in sepsis
1. Small vessels become 'leaky' and lose fluid into the tissues
2. Lower volume requires heart to work harder to maintain oxygenation of tissues (↑HR)
3. Poor tissue oxygen perfusion means blood supply to less essential organs is shut down to maintain supply to the brain
4. Blood clotting system is activated causing blood clot in tiny vessels, using up all clotting factors and increased risk of haemorrhage
54
What is the most significant pathogenic streptococci?
Group A streptococci
55
Most important group in non-haemolytic streptococci
Enterococci (commonest cause of UTI)
56
Which groups of patients are most likely to get MRSA?
Elderly, immunocompromised, those in ICU, burns patients, dialysis patients, surgical patients and patients on dialysis
57
Microorganism that is the most common cause of skin, soft tissue and wound infection
Staph aureus
58
Clostridioides:
- What are they?
- Where are they found?
- What concerning things do they produce?
- Gram positive anaerobic bacilli
- They are found as part of the normal gut flora of man in animals and are found in faeces and soil
- They produce spores that can survive outside the body for many months and exotoxins that can cause severe tissue damage
59
What does C. difficile cause?
Antibiotic associated diarrhoea. It proliferates in absence of normal flora
60
Structure in icosahedral symmetry
Made up of repeated subunits, 3 building blocks required apex, edge and centre of face
61
How do viruses enter a cell?
- Viruses interact with specific receptors on the cell membrane and attach via lock and key mechanism
- They enter by the fusion of viral and cell membranes or endocytosis
- Uncoating - viral nucleic acid released from the capsid
- This produces new viral proteins
- Nucleic acid and proteins are packed together
- The virus is released from the target cell
62
Ways viruses can be released from target cells
- Via the reverse of entry, a piece of host membrane ends up around the capsid
- By budding - mature progeny virus is released with envelope derived from host cell membrane
- Lysis
63
Cell structures targeted by antibiotics
Cell wall, bacterial ribosomes, other bacterial structures/enzymes
64
Possible targets for antivirals
- Enzymes involved in viral nucleic acid replication or protein synthesis
- Uncoating
- Attachment/entry process
- Release stage
65
Rational drug design
The use of detailed molecular analysis of viral targets to design a molecule that might inhibit its function
66
What happens in immunity against virus infections?
Cytotoxic T lymphocytes can recognise proteins on the surface as being foreign and will signal the infected cell to undergo apoptosis to prevent formation of further mature virus
67
Viral persistence
Viral may become quiescent (no active replication)
Viruses may reactivate
Viruses may remain continually active for years - chronic infection
68
How is virus infection confirmed in the laboratory?
By detecting the antibody response against the virus or by detecting the presence of the virus itself
69
How can recent infection be differentiated from past infection?
Detection of virus specific IgM antibodies
Detection of rising titre of IgG antibodies
Detection of very high titre of IgG antibodies
70
Virus detection methods that are currently in use
PCR, antigen detection
71
Bacteriostatic vs bactericidal
Bacteriostatic - inhibit growth of bacteria
| Bactericidal - kill bacteria
72
Ideal antibiotic in relation to the following:
- Toxicity
- Inhibition or killing of bacteria
- Half life
- Tissue distribution
- Side effects
- How it is administered
- Minimal toxicity
- Bactericidal
- Long half-life
- Appropriate tissue distribution
- No adverse drug interactions/side effects
- Oral or parenteral preparations
73
How can absorbable antibiotics be secreted from the body?
In the urine or via the liver, biliary tract and into the faeces
74
How can drugs be administered?
Orally, intravenously or (rarely) intramuscularly
75
When will an antibiotic reach peak serum levels if given orally vs intravenously?
Orally - 1 hour
| IV - 15 mins
76
Commonly prescribed cell wall antimicrobials
Penicillin, cephalosporins, glycopeptides
77
Target of beta lactams
Penicillin binding proteins
78
Penicillins:
- End in what?
- Side effects
- Narrow or broad spectrum?
- Excretion?
- Safe in pregnancy?
- End in -cillin
- Very few side effects
- Range from narrow to broad spectrum
- Excreted rapidly in the kidneys
- Safe in pregnancy
79
Limitations of penicillin
Patients can be hypersensitive (allergic), they are excreted rapidly via kidneys (results in frequent dosing), increasing resistance
80
Gram positive penicillins
Flucloxacillin
81
Gram positive and gram negative penicillins
Amoxicillin and co-amoxiclav
82
Gram negative penicillins
Temocillin
83
3 principle compounds of penicillin and their administration
Benzylpenicillin - IV
Phenoxymethyl penicillin - oral
Benzathine penicillin - IM
84
What is amoxicillin challenged by?
Spread of beta lactamases (enzymes that destroy beta lactam ring)
85
Benefit the combination of antimicrobials
Extends the range of bacteria that can be treated
86
Flucloxacillin prescribed to treat which type of infections?
It is very narrow spectrum and is useful for streptococci and staphylococci only
87
What does the polar side chain on piperacillin do?
Enhances penetration into gram negative bacteria
88
What is temocillin?
Beta-lactamase resistant form of penicillin that is largely restricted to coliforms and is active against ESBL-producing organisms
89
Cephalosporins:
- What do they inhibit?
- Long or short half-life?
- How are they excreted?
- Side effects?
- Safe in pregnancy?
- Inhibit cell wall synthesis and are bacteriocidal
- They have a longer half-life in plasma
- Excreted via the kidneys and urine
- Very few side effects
- Safe in pregnancy
90
Are cephalosporins narrow or broad spectrum?
Broad-spectrum
91
Why are cephalosporins avoided in many hospitals?
They kill off the normal gut bacteria and allows the overgrowth of Clostridium difficile, which causes nasty gastroenteritis
92
Examples of glycopeptides
Vancomycin, teicoplanin (both given IV)
93
How do glycopeptides work?
- Bind to peptide side chains and prevent incorporation into the cell wall
- Blocks access to substrate PBP
- Inhibits peptoglycan synthesis
- Reduces cross-linking and activity of lytic enzymes weaken bacterial wall
THEY ARE BACTERICIDAL
94
Glycopeptides:
- How are they excreted?
- Narrow or broad spectrum?
- Via the kidneys and in the urine
| - Narrow spectrum - gram +ve only
95
Why are vancomycin avoided in patients with kidney failure?
Toxic levels can build up in the blood and cause further kidney damage
96
How do antibiotics that inhibit protein synthesis work?
They attach to bacterial ribosomes
97
Are antibiotics that inhibit protein synthesis bactericidal or bacteriostatic?
Bacteriostatic - usually protein synthesis of the bacteria can resume when the antibiotic is removed with the exception of aminoglycosides
98
Examples of antibiotics that target protein synthesis
Aminoglycosides (gentamicin), tetracyclines (doxycycline) and macrolides (erythromycin)
99
Gentamicin:
- How is it given?
- How does it work?
- Gram positive or gram negative infections?
- How is it excreted?
- Given IV (occasionally IM) as not absorbed by the gut
- Binds to ribosomes (30s) inhibiting protein synthesis. Bactericidal
- Works against gram negative infections
- Excreted in urine
100
Toxicity and side effects of gentamicin
Toxic - causes damage to the kidneys and CN VIII, causes dizziness and deafness so level in the blood must be monitored regularly
101
Tetracyclines:
- Mode of action
- Spectrum of activity
- Adverse effects
- When is use restricted?
- Actively transported into the cell, binds to 30s subunit and prevents attachment of tRNA to receptor sited
- Broad spectrum
- Destruction of normal intestinal flora resulting in increased secondary infections, staining and impairment of structure of bones and teeth
- Use is restricted in children and pregnancy
102
Examples of macrolides
Erythromycin, clarythromycin, azithromycin
103
How are macrolides excreted?
Through the liver, biliary tree and gut
104
Antibiotics that affect nucleic acids
Metronidazole, trimethoprim, fluoroquinolones
105
Common side effects of antibiotics
Nausea, vomiting and diarrhoea, renal and CN VIII damage (gentamicin), tendonitis (ciprofloxacin), interactions with alcohol (metronidazole)
106
Why are antibiotics often given in combination?
To cover a broad range of possible infecting organisms, to prevent the development of resistance, for the synergistic effect of combination
107
4 antibiotics are that are generally avoided as they are associated with an increased risk of C.difficile
Cephalosporins
Co-amoxiclav
Ciprofloxacin
Clindamycin
108
Natural antimicrobial resistance
Target not present, target not accessible, metabolism, developmental structure/state
109
Biofilms
Organisms resistant to antimicrobial agents and host defences
110
Persistor cells
Dormant cells that form spontaneously within a biofilm and are resistant to antimicrobials
111
Resistance
Drug is no longer active against an entire population of cells
112
How does resistance come about?
Genetic variation, selective pressure, evolution resistance, gene transfer
113
Ways gene transfer can occur horizontally between bacteria
Natural competence, bacteriophage, sex pili
114
Cross resistance and multiple resistance
Cross resistance - single mechanism. Affects closely related antibiotics
Multiple resistance - mechanisms. Affects unrelated antibiotics
115
Mechanisms of antimicrobial drug resistance
Altered permeability, inactivation, altered target site, replacement if a sensitive pathway
116
What are the following resistant to?:
- Penicillinase
- Beta-lactmase
- Carbapenemase
- Early penicillins i.e. amoxicillin
- All the penicillins
- All the penicillins, all cephalosporins and all carbapenems
117
Chain of infection
Infectious microbe → reservoir (where microbe lives and replicates) → portal of exit (where microbe leaves reservoir) → modes of transmission → portal of entry → susceptible host → infectious microbe
118
Ways to interrupt transmission
Sterilisation/disinfection
Isolation/PPE
Decontamination
Vaccination
119
5 ways any infection can spread (5 Is)
Inhalation, ingestion, inoculation (direct and indirect), mother to infant, intercourse
120
Standard control of infection precautions
Hand hygiene, sharps management, clinical waste, PPE, respiratory etiquette, body fluid spillages, environmental cleanliness, laundry, clean equipment, patient placement
121
6 steps of hand hygiene
1. Palm to palm
2. Palms over dorsum
3. Fingers interlaced
4. Backs of fingers to palms while fingers interlaced
5. Rotational rubbing of thumbs in opposite palms
6. Rotational rubbing of clasped fingers in palms
122
5 moments for hand hygiene
Before patient contact, before aseptic task, after body fluid exposure risk, after patient contact, after contact with patient surroundings
123
Droplet precautions
Single room, ensuite shower/toilet, gloves, apron or fluid resistant gown, mask, eye protection, vaccination (where possible, incl. staff)
124
Disinfection
Process by which the number of organisms are reduced to a level that is considered safe
125
Methods of disinfection
Hot water and detergent, hypochlorite, chlorohexadine, povidone iodine, ethanol
126
Sterilisation
Process by which all microorganisms are killed or removed to render the object incapable of causing infection
127
Methods of sterilisation
Heat (autoclave), chemical, radiation, filtration
128
How does an autoclave kill microorganisms?
By coagulating and denaturing enzymes and structural proteins
129
Multiple factors influencing disease transmission
Agent (infectivity, resistance, virulence etc), Environment (weather, housing, geography, food, air quality etc), Host (age, sex, genetics, behaviour, nutritional status, health status)
