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Principles > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What are the three domains into which life is split?

A
  1. Bacteria
  2. Archaea
  3. Eukaryotes
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2
Q

What are the main pathogens that can affect humans?

A
  • Bacteria
  • Viruses
  • Fungi
  • Protozoa
  • Prions
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3
Q

What is “virulence”?

A

The level of infectivity of a pathogen

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4
Q

A bacterial cell wall is composed of ___________

A

Peptidoglycan

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5
Q

What is peptidoglycan

A

The main constitute of a bacterial cell wall

It is essentiall a suger caging - repeating polysaccharide stucture with peptide cross links - providing a rigid structure and barrier

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6
Q

Which two types of bacterial cell wall exist?

A

Gram positive

Gram negative

(There are also bacteria without a cell wall)

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7
Q

How are gram positive and negative bacteria differentiated?

A

By performing a gram stain

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8
Q

What is a gram stain?

A

A test used to differentiate between gram positive and negative bacteria.

Crystal violet dye is used to stain the cell wall - specificially the peptidoglycan layer

The extent to which the dye is retained determines the type of bacteria

Gram positive - thick peptidoglycan layer - stay purple

Gram negative - thin peptidoglycan layer - turns pink

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9
Q

Gram positive bacteria have a _____ peptidoglycan layer allowing them to deal with ______ internal pressures.

A

Thick

Higher

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10
Q

Of both gram positive and negative which of the two has a larger periplasmic space?

A

Gram negative

(They have two different periplasmic spaces)

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11
Q

Which bacteria class has two membranes?

A

Gram negative

(Outer and plasma)

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12
Q

What exists on the outside of gram negative bacteria that confer antigenic properties?

A

Lipid polysaccharides (endotoxins)

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13
Q

Besides having antigenic properties, what other important characteristic do lipid polysaccharides possess?

A

They have bacterial toxin properties which cause damage to neighboring cells and evoke an inflammatory response

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14
Q

Why are gram positive bacteria more susceptible to antibiotics?

A

The outside peptidoglycan layer can act as a target for antibiotics such as penicillin

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15
Q

What happens when antibiotics bind to the peptidoglyan layer of gam positive bacteria?

A

The peptide cross links within peptidoglycan are broken down

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16
Q

What are flagella and fimbriae (pili)?

A

Extracellular proteinaceous extensions

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17
Q

What are some of the functions of flagella and fimbriea?

A
  • Increase bacterial surface area
  • Can act as a syringe to inject proteins and RNA into cells
  • Passage of DNA from one bacterium to another - horizontal gene transfer
  • Motility (only flagella)
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18
Q

What 5 key factors so bacteria require to grow and thrive?

A
  1. Food (C, O, H, N, salts and vitamins etc.)
  2. Correct temperature
  3. pH
  4. Osmotic pressure
  5. Oxygen content
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19
Q

What are aerobic bacteria?

A

Bacteria that require oxygen to grow

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20
Q

What are microaerophiles?

A

Bacteria that only require minimal oxygen to grow

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21
Q

What are facultative anaerobes?

A

Bacteria that can use oxygen if it is available, but do not require it to function

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22
Q

What are obligate anaerobes?

A

Bacteria that do not require oxygen at all

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23
Q

What are the stages in the chain of infection?

A
  1. Infectious microbe
  2. Reservoir
  3. Portal of exit
  4. Mode of transmission
  5. Portal of entry
  6. Susceptible host
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24
Q

What are the only 5 ways in which infection can be spread?

A
  1. Inhalation
  2. Ingestion
  3. Inoculation (vaccination or artifical introduction) - direct or indirect
  4. Mother to infant - vertical transmission
  5. Intercourse - STI or STD
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25
Q

In what 5 situations (clinically) is hand washing necessary?

A
  1. Before patient contact
  2. Before aseptic task
  3. After bodily fluid exposure
  4. After patient contact
  5. After contact with patient surroundings - when leaving zone
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26
Q

What are black bags for?

A

General/domestic waste

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27
Q

What are orange bags for?

A

Clinical waste

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28
Q

For serious airbourne pathogens, those infected should be kept within a ________ ________ room

A

Negative pressure

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29
Q

What is the definition of disinfection?

A

Any process by which the level of microorganisms is reduced to a safe level

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30
Q

What is the definition of sterilisation?

A

A process by which all microorganisms are killed or removed to render the object incapable of causing infection

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31
Q

What are the three bacterial shapes?

A
  1. Bacilli
  2. Cocci
  3. Spiral shaped
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32
Q

In what two ways can cocci divide?

A
  1. In two planes - produce chains
  2. In three planes - produce clusters
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33
Q

All bacilli are gram _________ bacteria

A

Positive

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34
Q

What bacterium causes the disease cholera?

A

Vibrio chlolera

(Vibrio family of 34 members)

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35
Q

What are rigid spiral bacteria called?

A

Spirillum

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36
Q

What are flexible spiral bacteria called?

A

Spirochaete

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37
Q

How are the flagella utilised differently between spirullum and spirochaete?

A

Spirillum - tufts at each end to aid movement

Spirochaete - within periplasm causign cork-screw motion - efficient at travelling through secretions

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38
Q

What are fusiform bacteria?

A

Bacteria with a thin strand structure that play a part in the natural gut flora

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39
Q

Why are fusiform bacteria potentially dangerous?

A

By crossing the placenta in pregancy, they can cause still births and even cancer

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40
Q

With gram positive bacteria there is only one type of membrane, what is it?

A

Cytoplasmic membrane

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41
Q

In a gram stain, what happens if the stain is clear?

A

There is no cell wall

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42
Q

During a gram stain, why is it important to keep the time constant when removing the stain?

A

Eventually all the stain will be removed from any bacterial type

43
Q

What is selctive media?

A

This is a growth medium that contains specific nutrients for a specific type of microbe to grow over others

44
Q

What is differential media?

A

Allows all types of bacteria to grow and contains a range of nutrients, but allows for differentitaion between bacterial species

45
Q

How can streptococcus be identified?

A

Through levels of haemolysis shown by bacteria

46
Q

What is haemolysis?

A

Destruction of red blod cells

47
Q

What is alpha haemolysis?

A

Partial haemolysis - greening of colonies

48
Q

What is beta haemolysis?

A

Total haemolysis - the most aggressive

49
Q

What is gamma haemolysis?

A

No haemolysis

50
Q

Describe polymerase chain reaction (PCR)

A

Primers bind to specific DNA segments of interest

Successful binding meads to amplification of the DNA target which replicates many times

Real-time PCR uses fluorescence and allows the amplification response to be monitored

51
Q

What is multi locus sequence typing (MLST)?

A

This allows sequences of bacterial DNA and entire genomes to be sequenced and uploaded to a database

This allows previously sequenced sections to be matched to newly scanned sequences

52
Q

What is MALDI-TOF?

A

Matrix assisted laser desorption ionisation time of flight

This profiles the protein components in a sample

The sample is ionised and travels in vacuum

The componenets will travel at different speeds and deflect to different degrees based on their charge and mass providing a classic signature

53
Q

Microorganisms can be classed depending on where they originate in relation to the body. What are these classifications?

A
  • Endogenous - originate from within the body
  • Exogenous - originates outwith host
54
Q

What are commensal organisms?

A

Organisms that are endogenous, part of the natural flora and often form mutalistic relations with the host

55
Q

What are opportunistic organisms?

A

Exogenous organisms that infect the host when there is an opportunity such as immunocompromisation

56
Q

What are contaminants?

A

Organisms that enter a culture by accident - can be confusing

57
Q

Fungal infections are generally associated with which two groups?

A
  1. Moulds - e.g. aspergillus
  2. Yeast - e.g. candida spp
58
Q

Aerobic gram negative cocci appear in which formation?

A

Diplococci

59
Q

What are the two (out of 10) pathogenic aerobic gram negative cocci species?

A
  1. Neisseria meningitidis - can cause meningitis
  2. Neisseria gonorrhoea - can cause gonorrhoea
60
Q

What are coliforms?

A

Gram negative bacteria - rod shaped and non-spore forming

Can grow either anerobially or aerobically - better aerobically

Many part of the natural bowel flora

Should not enter sterile areas as can cause disease e.g. peritonitis, UTI, biliary tract infection etc

61
Q

What is the first line antibiotic used for any infection caused by coliforms?

A

Gentamicin

62
Q

What is it on the outside of gram negative bacteria that stimulates the immune system?

A

Lipopolysaccharides (endotoxins) composed of O antigens and lipids

63
Q

Why can it be advantageous for gram negative bacteria to stimulate the immune system?

A

Vascularity, available nutrients and protein production can increase

64
Q

Describe the mechanism of fever production

A
  1. Endotoxin interacts with macrophages to stimulate immune response and cytokine release
  2. Cytokines cause adverse effects of sepsis and travel to the hypothalamus
  3. Prostaglandin E is produced which means the body perceives itself as cold
  4. Shivering is stimulated which generates heat and rasies the body temperature
65
Q

Describe the process of sepsis

A
  • Small blood vessels become leaky meaning fluid is lost into tissues - due to inflammation
  • This causes hypovolaemia
  • Blood pressure is reduced
  • Organ perfusion becomes inadequate and organ shutdwon may occur
  • Blood clotting system activates leading to clot formation
  • Clotting factors become used up leading to haemorrhage
66
Q

When will septic shock occur?

A

After cell death lipopolysaccarides are released (causing inflammation), yet this also happens with valid treatment

But, due to the sudden disintegration of many cells septic shock will occur due to the huge immune response initiated

67
Q

What is group A streptococci?

A

The most pathogenic streptococci

68
Q

What is the most important group of non-haemolytic streptococci?

A

Enterococci

(enterococcus faecalis and faecium)

69
Q

What is Clostridium spp and why is it hard to treat?

A

Gram positive anaerobic baccili - part of normal bowel flora

Spores are produced - can live outside body

Endotoxins produced can cause severe body damage

Antibiotic resistant (spore production) and general resistance

70
Q

What are the two main classes of antiobiotic that related to their function?

A
  1. Bacteriostatic - inhibits growth
  2. Bacteriocidal - kills bacteria
71
Q

What are narrow spectrum antibiotics?

A

Antibiotics which are very specific in the bacteria that they target

72
Q

Which types of antibiotics will target the cell wall?

A
  • B lactam (includes penicillins)
  • Glycopeptide
73
Q

Describe how penicillin halts cell wall production

A

Peptide cross links exist in the cell wall

These are formed from D alanine to D alanine terminal proteins

Such terminal proteins are formed when transpeptidase cleaves this dipeptide, releasing energy and creating the bond

Penicillin resembles a terminal protein such as this and can bind irreversible to transpeptidase which halts cell wall production

74
Q

What are beta lactam antibiotics?

A

Antiobiotics containing the beta-lactam ring in their molecular structure

Common in penicillins, co-amoxiclav, cephalosporins etc.

75
Q

Name a penicillin which targets gram positive bacteria well

A

Flucloxacillin

(IV or oral)

76
Q

Name 3 penicillins which can target either gram positive or negative bacteria

A
  1. Amoxicillin
  2. Co-amoxiclav (amoxicillin/clavulanic acid)
  3. Tazocin (Tazobactam/piperacillin)
77
Q

What are the 3 forms of penicillin?

A
  1. Benzylpenicillin (penicillin G) - IV
  2. Phenoxymethyl penicillin (penicillin V) - oral
  3. Benzathine penicillin - IM
78
Q

What is flucloxacillin commonly prescribed for?

A

Skin infections from staph and strep

Deals with gram positive bacteria

79
Q

What is the purpose of clavulanic aid in co-amoxiclav?

A

B lactamases are microorganisms that destroy the B lactam ring of antibiotics including amoxicllin renderinging them useless

Clavulanic acid inhibits B lactamases which allows the B lactam ring to remain intact.

Essentially co-amoxiclav is a “work around” to allow amoxicillin to work where it wouldn’t normally

80
Q

What is special about temocillin?

A

It is resistant to B lactamases

It will generally target coliforms

81
Q

Cephalosporins are very attractive antibiotics due to their bacteriostatic and bacteriocidal properties as well as being B lactamase resistant. However, what is their major disadvantage?

A

They are broad spectrum so cause damage to the natural flora

This clears the environment for dangerous bacteria which they cannot kill

They remove the competition for harmful bacteria

82
Q

Do glycopeptide antibiotics possess a B lactam ring in their structure?

A

No

83
Q

Give two examples of glycopeptides

A
  1. Vancomycin
  2. Teicoplanin
84
Q

How do glycopeptides function?

A
  • They bind to the end of peptides
  • This prevents peptide binding proteins such as transpeptidase from binding to their substate (the protein)
  • Proteins cannot be incorporated into the cell wall
  • Peptidoglycan cannot be synthesised
  • Cross links are reduced and the cell wall is weakened
85
Q

Why can glycopeptides only function on gram postitive bacteria?

A

The outer membrane in gram egative bacteria blocks any activity they could have on the peptidoglycan layer

86
Q

Describe how antibiotics can target bacterial protein synthesis

A

Human ribosomes are different to bacterial ribosomes

Antibiotics are taken into bacterial cells by active transport

They bind to the 30S subunt and prevent tRNA from binding at receptor sites

The chain of elonagtion is inhibited

87
Q

What type of antibiotic is gentamicin and why is it bactericidal?

A

Aminoglycoside

Gentamicin targets protein synthesis

When it binds to the 30S subunit in the ribosome, it inhibits protein sythesis

This binding is permanent so bacteria die

88
Q

What is the mode of action for the tetracyclines?

A

They are transported into the cell and bind to the 30S subunit of the ribosome.

This blocks tRNA binding sites and stops chain elongation

They are bacteriostatic

89
Q

Give an example of a tetracycline antibiotic

A
  • Doxycycline
  • Tetracycline
  • Minocycline
90
Q

What is the mode of action for macrolides?

A

They are taken into cells and bind to the 50S subunit in bacterial ribosomes

They can be lipophilic antibiotics and can easily pass through cell membrane to “find” bacteria hiding from the immune system

91
Q

Give an example of a macrolide antibiotic

A
  1. Erythromycin
  2. Clarithromycin
  3. Azithromycin
92
Q

Describe how quinolone work

A

They bind to the alpha subunit of DNA gyrase and prevent supercoiling of DNA which indrectly inhibts DNA synthesis

They are bactericidal

93
Q

What is an example of a fluroquinolone?

A
  • Ciprofloxacin
  • Levofloxacin
94
Q

Why is the use of fluroquinolones very restricted?

A

They are broad spectrum

95
Q

Why is folic acid required by bacterial cell and which antibiotics can prevent its synthesis?

A

Required to syntheiss key cell components

Sulphonamides and trimethoprim

96
Q

What are the serious side effects of gentamicin?

A

Renal damage and damage to cranial nerve VIII

97
Q

Which antibiotics are associated with increased risk of C diff?

A
  • Cephalosporins
  • Co-amoxiclav
  • Ciprofloxacin
  • Clindamycin
98
Q

What is a biofilm?

A

A protective layer around a microorganism that allows it to grow in different environments

99
Q

What are persistor cells?

A

Cells that are extremely resisatnt to antibiotics

This is because they are encased within biofilms and cannot be targeted by antibiotics when in a dormant or inactive state - which they often are

100
Q

What are some methods that bateria use for horizontal gene transfer?

A
  • Transformation - genetic material is released into the extracellular space
  • Transduction - via bacteriophages (viruses that use bacteria to replicate within)
  • Conjugation - exchange of plasmids through direct comtact via sexual pilus
101
Q

What are the two different types, or stages, of resistance?

A
  1. Cross resistance - resistant to single antibiotic(s) using the same mechanism
  2. Multiple resistance - resistant to multiple unrelated antibiotics
102
Q

What is MRSA?

A

Methicillin Resistant S. aureus

A “superbug”

It has an altered target site, so is difficult to treat

103
Q
A

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