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Principles > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What are prion proteins?

A

Infectious proteins with no DNA or RNA
Rare, but cause incurable brain infection
Cannot easily removed by sterilisation or disinfection

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2
Q

What are viruses?

A

RNA or DNA
Protein coat +/- lipid envelope
Obligate intracellular parasite

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3
Q

What are the diagnostic methods for parasites?

A

Viral cell culture
Antigen or antibody detection in blood (serology)
PCR to detect DNA or RNA

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4
Q

What are bacteria?

A 
Contain DNA and RNA 
One double strand chromosome, sometimes with extra plasmids
Cell membrane and cell wall +/- capsule 
Flagellae for movement 
Pili/fimbriae for adhesion
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5
Q

What are the bacterial shapes?

A 
coccus = round 
bacillus = rod shaped 
spirochaetes = spirals
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6
Q

What colour does gram positive stain?

A

Purple

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7
Q

What colour does gram negative stain?

A

Pink

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8
Q

What does a gram positive cell wall look like?

A

Thick layer of peptidoglycan

This will hold the purple colour

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9
Q

What does a gram negative cell wall look like?

A

Thin layer of peptidoglycan

Cannot hold the purple colour, so shows pink

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10
Q

Why does mycobacterium tuberculosis not stain well with gram stain?

A

Has a thick waxy coat which does not take up the stain

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11
Q

What is a pathogen?

A

A harmful organism

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12
Q

What is a commensal?

A

An organism that is part of the normal flora

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13
Q

What is an opportunistic pathogen?

A

An organism that will probably only cause infection in n immunocompromised individual

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14
Q

What is a contaminant?

A

An organism that has got into the culture by a accident

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15
Q

What is pathogenicity?

A

The ability of a microorganism to produce disease

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16
Q

What is virulence?

A

The degree of pathogenicity of an organism (how easily the organism can cause disease)

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17
Q

By which method to bacteria replicate?

A

Binary fission

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18
Q

how quickly can bacteria double their numbers in ideal growth conditions?

A

Every 20 minutes

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19
Q

What are the four stages of the bacterial growth curve?

A

Lag phase = DNA replication
Log phase = Exponential growth
Stationary phase = Rate of growth equal to rate of death
Death phase = Limited nutrients, so bacteria compete and some die

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20
Q

What is an exotoxin?

A

Mostly produced by gram positive bacteria

Usually produced inside the cell then exported from it

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21
Q

What is an endotoxin?

A

Mostly produced by gram negative bacteria

Part of the gram negative bacterial cell wall, released when bacterial cell dies

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22
Q

What are the diagnostic methods for bacteria?

A 
Microscopy (gram stained film)
Culture 
Detection of antigen 
Detection of antibodies in blood (serology)
PCR
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23
Q

What types of fungi are there?

A 
Moulds = Produce spores and hyphae
Yeasts = Reproduce through budding
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24
Q

What is the most common cause of mould infection in humans?

A

Aspergillus spp

usually in immunocompromised

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25
Q

What is the most common cause of fungal infection in humans?

A

Candida spp
Yeast
Stain as lage gram positive oval structures

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26
Q

What are the gram positive aerobic cocci?

A 
Streptococci = chains 
Staphylococci = clusters
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27
Q

How do you differentiate between streptococcus species?

A

Haemolysis seen on blood agar

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28
Q

What are the possible results of streptococcal haemolysis?

A

Alpha haemolysis = partial haemolysis, greenish discolouration around colony

Beta haemolysis = complete haemolysis, clearing around colony, most virulent

Gamma haemolysis = no haemolysis

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29
Q

What are the alpha haemolytic streptococci?

A

Streptococcus pneumoniae

Streptococcus “viridans”

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30
Q

What infections can be caused by Streptococcus pneumoniae?

A

Commonest cause of pneumonia

Also causes meningitis

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31
Q

Where would the Streptococcus “viridans” normally colonise and what infection can they cause if they reach a normally sterile site?

A

Common commensals of the URT, bowel and vagina

Endocarditis

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32
Q

What are the beta haemolytic streptococci?

A

Group A strep (Strep. pyogenes)

Group B strep

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33
Q

What infections can be caused by Group A Streptococcus (Strep. pyogenes)?

A

Streptococcal sore throat (tonsillitis) (+ rash gives scarlet fever)
Skin and soft tissue infections (e.g. necrotising fasciitis)
Puerperal sepsis (life threatening infection in pregnant and recently post natal women)

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34
Q

What are the non-haemolytic streptococci?

A

Most important are the enterococci (part of normal bowel flora)

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35
Q

What infection can be caused by the Enterococci?

A

Commonest cause of UTI

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36
Q

Which test is used to distinguish between Staphylococcus species?

A

Coagulase test

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37
Q

What are the possible results if a Staphylococcus coagulase test?

A

Coagulase positive

Coagulase negative

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38
Q

What is the one coagulase positive Staphylococcus?

A

Staphylococcus aureus

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39
Q

Which infections can be caused by Staphylococcus aureus?

A

Commonest cause of skin, soft tissue and wound infection
Commonest cause of bone and joint infection
Enterotoxin producing strains cause food poisoning
Staph. aureus bacteraemia

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40
Q

What are the coagulase negative Staphylococci?

A

Many species of skin commensals

Inc. Staph epidermidis

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41
Q

What infections can be caused by coagulase negative Staphylococci?

A

Prosthetic joint and heart valve infection

IV catheter infection

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42
Q

Which antibiotics can be used to treat Streptococcus pneumoniae?

A

Most UK strains still resistant to penicillin

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43
Q

Which antibiotics can be used to treat Group A Streptococci?

A

All strains still sensitive to penicillin and amoxicillin

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44
Q

Which antibiotics can be used to treat Enterococci?

A

Most trains still sensitive to amoxicillin (not penicillin)

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45
Q

What is the antibiotic of choice for Staphylococcus aureus?

A

Flucloxacillin

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46
Q

What are antibiotic resistant strains of Staphylococcus aureus resistant to?

A

MRSA

All penicillins, all cephalosporins, plus others

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47
Q

What is pyrexia?

A

Raised temperature (fever)

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48
Q

What is rigor?

A

Shivering attack as raised temperature drops

Sign of fever or pyrexia

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49
Q

Above which temperature is fever diagnosed?

A

> 38 degrees C

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50
Q

What causes sepsis?

A

Small blood vessels become leaky in severe infection and fluid is lost into the tissues
Lower blood volume leads to septic shock

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51
Q

What are the gram negative aerobic cocci?

A

Diplococci (appear in pairs)
Neisseria meningitidis
Neisseria gonorrhoeae

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52
Q

What infection can be caused by Neisseria meningitidis?

A

Commonest cause of bacterial meningitis

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53
Q

What infection can be caused by Neisseria gonorrhoeae?

A

Gonorrhoea

54
Q

What are the gram negative aerobic large bacilli?

A

Coliforms

Look like E.coli on gram film and blood culture

55
Q

How are the coliforms differentiated from each other?

A

Biochemical reactions

Antigenic structure of cell wall (serotyping)

56
Q

What are the gut commensal coliforms?

A 
Most E.coli spp.
Klebsiella spp.
Enterobacter spp.
Proteus spp.
Many more
57
Q

What are the gut pathogen coliforms?

A

Salmonella spp.
Shigella spp.
Verotoxin producing E.coli (E.coli O157, E.coli O104)

58
Q

What infections can be caused by the coliforms?

A

Any coliform in a normally sterile site, e.g.
UTI
Peritonitis
Biliary tract infection

59
Q

What is the first line antibiotic treatment for coliform infections?

A

Gentamicin

60
Q

What are the gram negative aerobic small bacilli?

A 
Pseudomonas aeruginosa 
Legionella pneumophila (Legionnaires' disease)
61
Q

What are the gram negative microaerophilic bacilli?

A

Spiral or curved Gram negative bacilli =
Vibrio cholerae
Campylobacter spp
Helicobacter pylori

62
Q

What infection is caused by Vibrio cholerae?

A

Cholera

63
Q

What infection is caused by Campylobacter?

A

Commonest cause of bacterial diarrhoea in the UK

64
Q

What infections can be caused by Helicobacter pylori?

A

Gastritis

Duodenal ulcers

65
Q

What is the gram negative aerobic small (cocco)bacillus and what infection does it cause?

A

Haemophilus influenzae

Common cause of chest infection

66
Q

What are the strict anaerobes?

A

Clostridium spp.

Bacteroides spp.

67
Q

What is the classification of the Clostridium spp?

A

Gram postive anaerobic bacilli

68
Q

What type of Clostridium spp. are there and what infections do they cause?

A

Clostridium difficile = Antibiotic associated diarrhoea

Clostridium perfringens = “Gas” gangrene

Clostridium tetani = Tetanus

69
Q

What is the classification of the Bacteroides spp?

A

Gram negative anaerobic bacilli

70
Q

What infections can be caused by the Bacteroides spp?

A

Usually non pathogenic

Only cause infection in sterile sites (e.g. peritoneum, biliary tract)

71
Q

What is the first line treatment for infections caused by anaerobes?

A

Metronidazole

72
Q

What are the Mycobacteria?

A

Have a thick waxy outer coat which does not take up Gram Stain
Stained by acid fast bacilli or acid-alcohol fast bacilli

73
Q

What infection can be caused by Mycobacterium tuberculosis?

A

TB

74
Q

What are the Spirochaetes?

A

Spiral shaped spectre that do not stain on gram stain
Treponema pallidum
Borrelia burgdorferi

75
Q

What infection is caused by Treponema pallidum ?

A

Syphilis

76
Q

What infection is caused by Borrelia burgdorferi?

A

Lyme disease

77
Q

How does genetic variation in bacteria occur?

A

Mutation

Gene transfer

78
Q

How do mutations in bacterial DNA cause genetic variation?

A

Rapid bacterial grwoth increases chance of genetic mutation
This leads to new variants of the organism
Many fail to survive, but rare strains can be successful

79
Q

What are the three methods of gene transfer?

A

Transformation
Conjugation
Transduction

80
Q

How does transformation lead to genetic variation?

A

DNA released from dead bacteria can be taken up by living bacteria and incorporated into palms or bacterial chromosome

81
Q

How does conjugation lead to genetic variation?

A

Bacterial “sex”

Sex pilus is produced by one bacteria through which plasmids DNA can be transferred

82
Q

How does transduction lead to genetic variation?

A

Viruses that infect bacteria can transfer bits of DNA from one bacteria to another

83
Q

What are the main mechanisms of antibiotic resistance?

A

Production of enzymes that destroy antibiotics
Altered antibiotic binding sites
Alteration of cel wall porins
Up-regulation of efflux pumps

84
Q

Which enzymes can be produced to destroy antibiotics?

A

Beta-lactamase = resistance to early penicillins like amoxicillin

Extended spectrum beta-lactamse = resistance to all penicillins and cephalosporins

Carbapenemase = resistance to all penicillins, all cephalosporins and carbapenems

85
Q

How do altered antibiotic binding sites cause antibiotic resistance?

A

Genetic mutation alters antibiotic binding sites

Antibiotics that cannot bind have no effect on bacteria

86
Q

Give an example of altered antibiotic sites leading to antibiotic resistance?

A

Alteration of penicillin binding protein on Staph aureus resulted in fluxloxacillin resistance (MRSA)

87
Q

How do changes to cell wall porins cause antibiotic resistance?

A

Alterations to porins may result in bacterial cell wall becoming impermeable to the antibiotic

88
Q

How does up regulation of efflux pumps cause antibiotic resistance?

A

Antibiotic is removed from the cell before it has time to act

89
Q

Give an example of up regulation of efflux pumps leading to antibiotic resistance?

A

Common mechanism of resistance in fungi e.g. Candida spp.

90
Q

Why must antibiotics be selectively toxic?

A

To kill bacteria without killing surrounding tissue

91
Q

What is the difference between bactericidal and bacteriostatic?

A 
Bactericidal = Kill bacteria 
Bacteriostatic = Inhibit bacteria growth
92
Q

By which three mechanisms can antibiotics work?

A

Acting on bacterial cell wall = Human cells do not have a cell wall

Affecting the bacterial ribosome = Structurally different from human ribosomes

Acting in bacterial DNA =
Structurally different from human DNA

93
Q

Which groups of antibiotics work on the bacterial cell wall?

A

Penicillins
Cephalosporins
Glyopeptides

94
Q

What are the advantages of the penicillins?

A

Safe, very few side effects
Narrow to broad spectrum
Excreted rapidly via kidneys
Safe in pregnancy

95
Q

What are the disadvantages of the penicillins?

A

Some patients are allergic - allergy to one means allergy to all of the family, and sometimes also cephalosporins
Frequent dosing needed due to rapid excretion

96
Q

What are the three forms of penicillin available?

A 
Benzylpenicillin (IV)
Phenoxymethyl penicillin (Oral)
Benzathine penicillin (IM)
97
Q

Which penicillin can only be used for gram positive organisms and why might it be prescribed?

A

Flucloxacillin (IV, Oral)
Only used for Staphylococci and Streptococci

Skin and soft tissue infection
Wound infection
Cellulitis

98
Q

Which penicillins can be used for gram positive and negative organisms?

A

Amoxicillin (IV, Oral)
Co-Amoxiclav (IV, Ora)
Tazocin (IV)

99
Q

Why is Co-Amoxiclav more effective than Amoxicillin?

A

Clavunic acid is a beta-lactamase inhibitor, and so prevents the destruction of amoxicillin

100
Q

Which penicillin can only be used for gram negative organisms and why might it be prescribed?

A

Temocillin (IV)
Only active against coliforms
Brought back due to increasing bacterial resistance
Still active against EBSL producing organisms

101
Q

What are the advantages of the cephalosporins?

A

Excreted via kidneys and urine
Few side effects
Safe in pregnancy

102
Q

What are the disadvantages of the cephalosporins?

A

Broad spectrum antibiotics, significantly affect the normal bowel flora
Increased risk of C.diff

103
Q

Give examples of the glycopeptides?

A

Vancomycin (IV)
Teicoplanin (IV)

Excreted via kidneys and urine

104
Q

What kinds of bacteria are the glycopeptides active against?

A

ONLY active against organisms with a gram positive cell wall

105
Q

Are penicillins bactericidal or bacteriostatic?

A

Bactericidal

106
Q

Are cephalosporins bactericidal or bacteriostatic?

A

Bactericidal

107
Q

Are glycolpeptides bactericidal or bacteriostatic?

A

Bactericidal

108
Q

Which groups of antibiotics inhibit protein synthesis?

A

The macrolides
The tetracyclines
The aminoglycosides
Others (clindamycin, chloramphenicol)

109
Q

Are macrolides bactericidal or bacteriostatic?

A

Bacteriostatic

110
Q

Are tetracyclines bactericidal or bacteriostatic?

A

Bacteriostatic

111
Q

Are aminoglycosides bactericidal or bacteriostatic?

A

Bactericidal

112
Q

Give examples form the macrolide family?

A

Erythromycin
Clarythromycin
Azithromycin

113
Q

How are the macrolides excreted?

A

Via the liver, biliary tract and into the gut

114
Q

Which macrolide is safe in pregnancy?

A

Erythromycin

115
Q

Which kinds of infections are macrolides useful in treating?

A

Infections in which bacteria hide from hot cell immunity by getting into the host cells
Macrolides are lipophilic

116
Q

Give an example of an aminoglycoside?

A

Gemtamicin (IV)

117
Q

Which organisms is gentamicin effective against?

A

Gram negative aerobes such as coliform and pseudomonas aeruginosa

118
Q

How is gentamicin excreted?

A

Via urine

119
Q

In what way is gentamicin toxic?

A

Damages kidneys and CN VIII, causing dizziness and deafness

Must monitor bloods carefully

120
Q

Which groups of antibiotics act on bacterial DNA?

A

Metronidazole
Trimethoprim (+/- sulphonamide)
Fluroquinolones

121
Q

Which infections are metronidazole used to treat?

A

True anaerobic infections

Some protozoal infections

122
Q

How can trimethoprim be administered?

A

On its own, orally

In combination with sulphamethoxazole, orally or IV, as co-trimoxazole (synergistic effect)

123
Q

Which bacteria is trimethoprim effective against?

A

Some Gram negative and some Gram positive bacteria

124
Q

How is trimethoprim excreted?

A

Via urine

125
Q

Give examples of Fluroquinolones?

A

Ciprofloxaxin (IV, Oral)

Levofloxacin (IV)

126
Q

Are fluroquinolones bactericidal or bacteriostatic?

A

Bactericidal

127
Q

How are fluroquinolones excreted?

A

Via urine

128
Q

Which antibiotic should you really not drink alcohol when taking?

A

Metronidazole

129
Q

What are the 4 C antibiotics?

A

Cephalosporins
Co-Amoxiclav
Ciprofloxacin
Clindamycin

130
Q

Why do we avoid use of the 4 C antibiotics?

A

Broad spectrum

Associated with increased risk of C.diff

Principles (13 decks)

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