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Disease Mechanisms > Microbiology - Bacteria > Flashcards

Microbiology - Bacteria Flashcards

1
Q

How can bacteria be studied?

A

Light microscopy

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2
Q

What type of genetic material do bacteria contain?

A

DNA and RNA

Single double-stranded chromosome

Plasmids (circular DNA) in cytoplasm

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3
Q

What are the main parts of a bacterium?

A

Cell membrane

Cell wall

(Capsule)

Flagellae (movement)

Pili/Fimbrae (adhesion)

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4
Q

How can bacteria be classified according to shape?

A

Coccus

Bacillus

Spirochaetes

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5
Q

How can Gram stain be used to differentiate between Gram +ve and Gram -ve cocci/bacilli?

A

Gram positive = purple

Gram negative = pink

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6
Q

Describe the Gram +ve cell wall

A

Thick layer of peptidogycan

Outer cytoplasmic membrane

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7
Q

Describe the Gram -ve cell wall

A

Inner membrane

Thin peptidoglycan layer

Outer membrane

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8
Q

Why is Gram staining important?

A

Leads us towards likely infecting organism

Many antibiotics work on bacterial cell wall - different antibiotics for Gram +ve and Gram -ve

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9
Q

Give two examples of organisms which don’t stain well with Gram stain?

A

Mycobacterium tuberculosis - waxy coat

Treponema pallidum (spirochaete causing syphilis)

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10
Q

What do bacteria require for growth?

A

Food (any organic matter)

Moisture

Correct temperature (37C for most human pathogens)

Correct pH (around pH7.4 for most human pathogens)

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11
Q

How quickly can a bacterial population double its population under ideal growth conditions?

A

Every 20 minutes

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12
Q

Describe the four phases of the bacterial growth curve

A

Lag phase (bacteria maturing, not ready to divide)

Log phase (binary division)

Stationary phase (growth rate = death rate)

Death phase (bacteria run out of nutrients and die)

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13
Q

Describe an aerobic bacteria

A

One which grows in the presence of air.

May grow anaerobically, but less well.

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14
Q

What is a microaerophilic bacteria?

A

One which grows in an atmosphere with reduced oxygen concentration and enriched CO2

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15
Q

What is an anaerobic bacteria?

A

One which can only grow in the absence of oxygen

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16
Q

What is an exotoxin?

A

A toxin (enzyme) produced inside the cell and exported from it.

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17
Q

Which sort of bacteria mainly produce endotoxins?

A

Gram +ve

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18
Q

What is an endotoxin?

A

Part of the bacterial cell wall.

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19
Q

Which type of bacteria usually produce endotoxins?

A

Gram -ve

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20
Q

What are two effects of toxins on the body?

A

Interact with immune cells causing release of cytokines

Damage to red and white blood cells causing leaky blood vessels - hypotension, affect blood clotting > sepsis

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21
Q

What is LPS?

A

Lipopolysaccharide

It is found in the other membrane of Gram -ve bacteria and is an endotoxin

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22
Q

What type of bacteria form spores?

A

Gram +ve bacilli

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23
Q

Give two examples of bacteria that form spores.

A

Clostridium sp (e.g. C. diff)

Bacillus sp (e.g. anthrax)

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24
Q

What are spores?

A

Inactive forms of bacteria that can survive adverse conditions for many years.

They cannot replicate.

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25
Q

Which diagnostic methods are used for bacterial infections?

A

Microscopy - Gram stained film

Culture

Detection of Antigen (e.g. urine sample)

Detection of Antibody in blood (serology)

Molecular methods (PCR) - organism’s DNA or RNA

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26
Q

Which bacteriology tests can be returned with the same day?

A

Gram film

PCT

Serology (if not batched)

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27
Q

How long does culture and antibiotic sensitivity testing take?

A

48 hours

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28
Q

How long does TB culture take?

A

4 - 12 weeks

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29
Q

Which Gram +ve cocci grow in chains?

A

Streptococci spp

Enterococcus sp

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30
Q

Which Gram +ve cocci produce α-haemolysis?

A

Strep. pneumoniae

Strep. viridans

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31
Q

Describe Strep. pneumoniae, what infections does it produce?

A

Gram +ve

Aerobic

Coccus

Chains

α-haemolysis

Pneumonia, Meningitis

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32
Q

Describe Strep. viridans, what infections does it produce?

A

Gram +ve

Coccus

Aerobic

Chains

α-haemolysis

Endocarditis

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33
Q

Which Gram +ve cocci cause β-haemolysis?

A

Group A Strep (Strep. pyogenes)

Group B Strep

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34
Q

Describe Strep. pyogenes, what infections does it cause?

A

Gram +ve

Coccus

Chains

Aerobic

β-haemolysis

Throat, skin infections

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35
Q

What infection does Group B strep cause?

A

Neonatal meningitis

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36
Q

What is β-haemolysis?

A

Complete haemolysis

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37
Q

What is α-haemolysis?

A

Partial haemolysis

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38
Q

Which Gram +ve cocci, growing in chains, do not produce haemolysis?

A

Enterococcus sp.

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39
Q

What infection does Enterococcus sp produce?

A

UTI

It is a gut commensal

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40
Q

Describe Enterococcus sp.

A

Gram +ve

Coccus - chains

Aerobic

Non-haemolytic

Gut commensal

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41
Q

Can Streptococcus and Enterococcus grow anaerobically?

A

Yes.

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42
Q

How are strains of Streptococcus and Enterococcus differentiated?

A

By the type of haemolysis they produce on blood agar plate.

43
Q

Which antibiotic is usually used to treat Streptococcus pneumoniae?

A

Penicillin

44
Q

Where are the Strep. viridans group normally found as commensals?

A

Upper Respiratory Tract

Bowel

Vagina

45
Q

Which are the most pathogenic streptococci?

A

Group A and Group B

those causing β haemolysis - caused by (exo)toxins that lyse red blood cells

46
Q

Which infections are caused by Strep. pyogenes?

A

Streptococcal sore throat (tonsilitis)

(with rash = scarlet fever)

Skin & soft tissue infections - necrotising fasciitis

Perperal sepsis - pregant and recently post natal women

47
Q

Which antibiotics would be used to treat Group A strep infections?

A

Penicillin

Amoxicillan

48
Q

Which antibiotics are Enterococci usually sensitive to?

A

Most are sensitive to amoxicillin

Most are resistant to penicillin

49
Q

Describe the Staphylococci

A

Gram +ve

Coccus - clusters

Aerobic, but can grow anaerobically

50
Q

How is Staph aureus distinguished from the other staphylococci?

A

Coagulase test.

Staph. aureus - coagulase +ve

51
Q

What type of commensals are the coagulase -ve Staphs?

A

Skin commensals

52
Q

How do the coagulase negative staphs cause infections of prosthetic joints, heart valves, IV catheters?

What is the difficulty with such infections?

A

Produce surface polysaccharide slime that allows them to stick to plastic and other artificial material.

Hard to treat with antibiotics

53
Q

Where is Staph. aureus normally found?

A

Nose

Upper Respiratory Tract

54
Q

What type of toxins are produced by Staph aureus?

A

Different strains produce different (exo)toxins.

Toxic shock syndrome toxin

Panton-Valentine leukocidin

Enterotoxins

55
Q

What do the terms MSSA and MRSA mean?

A

Meticillin-sensitive Staph. aureus - sensitive to flucloxacillin

Meticillin-resistant Staph. aureus - resistant to all penicillins and cephalosporins

(+ others)

56
Q

Which infections are caused by Staph. aureus?

A

Commonest cause of skin, soft tissue and wound infection

Commonest cause of bone & joint infection

Food poisoning (enterotoxin-producing only)

57
Q

What is the preferred antibiotic treatment of Staph. aureus (MSSA) infection?

A

Flucloxacillin

58
Q

What is bacteraemia?

A

Bacteria in the bloodstream

59
Q

What may occur if a patient has bacteraemia?

A

Sepsis

Infection may spread elsewhere in body resulting in

disseminated infection

abcess formation

60
Q

What is the commonest cause of bacteraemia?

A

Staph. aureus

61
Q

Describe the Neisseria spp bacteria

A

Gram -ve

Coccis - diplococci

Aerobic

62
Q

What infections are caused by Neisseria spp. bacteria?

A

Neisseria gonorrhoeae - gonorrhoea

Neisseria meningitidis - meningitis

63
Q

What are the coliforms?

A

Gram -ve bacilli

Look like Escherichia coli (E. coli) on Gram film and when cultured on blood agar

64
Q

How are the coliforms distinguished?

A

Biochemical reactions

Antigenic structure of cell wall (serotyping)

O antigens - cell wall

H antigen - flagella

65
Q

Where are the coliforms often found?

A

Gut commensal

66
Q

Name some gut commensal coliforms.

A

E. coli (most strains)

Klebsiella spp

Enterobacter spp

Proteus spp

67
Q

Name some gut pathogens

A

Salmonella spp

Shigella spp

Verotoxin producting E. Coli - VTEC - O157, O104

68
Q

Which antibiotic is the first line treatment for infections caused by coliforms?

A

Gentamicin

69
Q

Why do patients with coliform sepsis because unwell very rapidly?

A

Endotoxin is released from Gram -ve cell wall when the bacteria die

70
Q

Which Gram -ve bacilli are strict aerobes?

A

Pseudomonas aeruginosa

Legionella pneumophilia (Legionnaire’s disease)

71
Q

Which Gram -ve bacilli are spiral or curved?

A

Vibrio cholera

Campylobacter spp

Helicobacter pylori

72
Q

Which Gram -ve (cocco)bacillus is the most common cause of chest infection?

A

Haemophilus influenzae

73
Q

Which bacteria are strict anaerobes?

A

Clostridium spp

Bacteroides spp

74
Q

Describe Clostridium spp bacteria

A

Gram +ve

Anaerobic

Bacillus

Normal bowel flora - found in faeces & soil

Produces spore

Produce exotoxins

75
Q

Which anaerobic Gram +ve bacteria is associated with antibiotic diarrhoea, especially in the elderly?

A

Clostridium difficile

76
Q

Which Gram +ve anaerobic bacteria causes gas gangrene, a severe soft tissue infection following wound contamination?

A

Clostridium perfringens

77
Q

Which Gram +ve anaerobic bacteria causes tetanus?

A

Clostridium tetani

78
Q

Describe Bacteroides spp

A

Gram -ve

Anaerobic

Bacillus

Normal bowel flora, normally non-pathogenic, cause infection in sterile sites such as peritoneum and biliary tract

79
Q

What is the first line treatment for infections caused by anaerobic bacteria?

A

Metronidazole

80
Q

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

A

Gentamicin

81
Q

How are mycobacteria classified by staining?

A

Acid Fast Bacilli (AFB)

Acid-Alcohol Fast Bacilli (AAFB)

82
Q

Give two examples of spirochaetes

A

Treponema pallidum - syphilis

Borrelia burgdoferi - Lyme disease

83
Q

Do spirochaetes stain with Gram stain?

A

No

84
Q

How do you choose an antibiotic?

A

Site of infection - likely organisms

Orally or IV

Allergies

Local guidelines

85
Q

Which antibiotics are less likely to cause C. diff infection?

A

Narrow spectrum

86
Q

Why are antibiotics sometimes given in combination?

A

Cover a broad range of organisms

Prevent development of resistance

Synergistic effect

87
Q

How do antibiotics work?

A

Attacking bacterial cell wall

Attacking bacterial ribosome

Acting on bacterial DNA

88
Q

Which antibiotics act on bacterial cell wall?

A

Penicillins

Cephalosporins

Glycopeptides

89
Q

Name four antibiotics in the penicillin group.

On which part of the bacteria do they act?

A

Penicillin

Flucloxacillin

Amoxicillin

Co-amoxiclav

Bacterial cell wall

90
Q

Name a cephalosporin

On which part of the bacteria does it act?

A

Ceftriaxone

Bacterial cell wall

91
Q

Name a glycopeptide antibiotic.

On which part of the bacteria does it act?

A

Vancomycin

Bacterial cell wall

92
Q

Which penicillins can be used to treat Gram +ve organisms?

A

Penicillin (IV, oral)

Flucloxacillin (IV, oral)

93
Q

Which penicillins can be used to treat Gram -ve organisms?

A

Penicillin

Amoxicillin

Co-amoxiclav

94
Q

Which antibiotics inhibit protein synthesis?

A

Macrolides

Tetracyclines

Aminoglycosides

95
Q

Name three macrolide antibiotics.

On which part of the bacteria do they act?

A

Clarythromycin

Azithromycin

Erythromycin

Inhibit protein synthesis

96
Q

Name a tetracycline antibiotic.

On which part of the bacteria does it act?

A

Doxyclycline

Inhibits protein synthesis

97
Q

Name an aminoglycoside.

On which part of the bacteria does it act?

A

Gentamicin

Inhibits protein synthesis

98
Q

Which antibiotics act on bacterial DNA?

A

Metronidazole

Trimethoprim (+ sulphonamide = co-trimoxazole)

Fluoroquinolones (Ciproflaxacin)

99
Q

How does genetic variation in bacteria result?

A

Mutation

Gene transfer

100
Q

What are the three mechanisms of gene transfer in bacteria?

A

Transformation

Conjugation

Transduction

101
Q

How are genes transferred through transformation?

A

DNA released by dead bacteria is taken up by living bacteria and incorporated into either plasmids or the bacterial chromosome

102
Q

How are genes transferred through conjugation?

A

Bacterial sex

Sex pilus transfers plasma DNA from one bacteria to another

103
Q

How are genes transferred through transduction?

A

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

104
Q

What aspects of antibiotic therapy lead to resistance?

A

Unecessary antibiotics

Sub-therapeutic dosing

Exposure to low concentrations of antibiotic in environment

Disease Mechanisms (9 decks)

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