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Pathology > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Normal flora of the skin

A
  • Coagulase-negative staphylococci

- Diptheroids

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2
Q

Normal flora of the nostrils

A
  • Staphylococcus aureus
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3
Q

Normal flora of the oral cavity

A
  • Streptococci

- Anaerobes

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4
Q

Normal flora of the upper respiratory tract

A
  • Viridans streptococci
  • Diptheroids
  • Anaerobes
  • Commensal neisseria
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5
Q

Normal flora of the lower GI tract

A
  • Coliforms
  • Faecal enterococci
  • Anaerobes (bacteroides, clostridia)
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6
Q

Normal flora of the anterior urethra

A
  • Skin flora

- Faecal flora

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7
Q

How does commensal infection occur

A
  • If an organism breaches the defence of a site where it is not commensal (e.g. E.coli is normal in the gut, but can breach the urinary tract)
  • Normal flora altered by broad-spectrum antibiotics
  • ‘Replacement’ pathogens resulting from antibiotics
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8
Q

List the sources of wound infection

A
  • Direct inoculation
  • Airborne contamination
  • Haematogenous spread
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9
Q

Why should skin shaving occur immediately before surgery and not more in advance

A

Doesn’t give time for staphylococci to colonise small lacerations in the skin

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10
Q

Where does MRSA typically colonise

A
  • Inguinal
  • Perineal
  • Axillary
  • Anterior nares
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11
Q

How may MRSA present

A
  • Pneumonia
  • Line sepsis
  • Surgical site infection
  • Intra-abdominal sepsis
  • Osteomyelitis
  • Toxic shock syndrome
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12
Q

How are MRSA carriers treated

A
  • Antiseptics e.g. mupirocin to nose
  • Antiseptic soap and shampoos
  • 3 weeks treatment
  • Check swabs at 3 days and 3 weeks after use of antiseptics
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13
Q

How are MRSA patients treated

A
  • Barrier nurse
  • Vancomycin or Teicoplanin are most often used
  • Linezolid is a new alternative
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14
Q

What is a conventional pathogen

A

Pathogen that may cause infection in the previously healthy person

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15
Q

What is a conditional pathogen

A

Pathogen that causes infection in those who have a predisposition to infection

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16
Q

What is a opportunistic pathogen

A

Pathogen that is usually of low virulence but will cause infection in the immunocompromised patient

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17
Q

What shape are bacilli

A

Rods

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18
Q

What shape are cocci

A

Spherical

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19
Q

What colour are gram-positive

A

Blue

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20
Q

What colour are gram-negative

A

Pink

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21
Q

What are coagulase-positive staphylococci known as and what is their significance

A
  • Staphylococcus aureus

- More likely to cause infection than coagulase-negative staphylococci

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22
Q

What infections is staphylococcus aureus typically responsible for

A
  • Superficial infections = boils, abscesses, styes, conjunctiviitis, wound infection
  • Deep infection = septicaemia, endocarditis, osteomyelitis, pneumonia
  • Food poisoning
  • Toxic shock syndrome
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23
Q

What infections are Staphylococcus epidermidis associated with

A

Infection in association with foreign bodies:

  • Prosthetic valves
  • Pacemakers
  • Prosthetic joints
  • IV lines
  • Peritoneal dialysis
  • Vascular grafts
  • Breast implants
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24
Q

Is staphylococcus epidermidis coagulase negative or positive

A

Negative

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25
Q

Staphylococcus may cause pneumonia with what histological features

A

Cavitating lesions

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26
Q

Consequences of staphylococcus aureus endotoxin

A

Causes rapid onset of symptoms

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27
Q

How does PVL-producing staphylococcus aureus spread

A

Associated with community-acquired infections:

  • Contact sports
  • Sharing towels
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28
Q

What antibiotics are active against S. aureus

A
  • Penicillin (90% resistant)
  • Flucloxacillin (active against beta-lactamase-producing organisms)
  • Erythromycin
  • Clindamycin
  • Fusidic acid
  • Cephalosporins
  • Vancomycin
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29
Q

How are streptococci and enterococci classified

A

Lancefield groups - on the basis of polysaccharide antigens on their surface

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30
Q

What species of streptococci are responsible for sepsis

A

Beta-haemolytic strains where colonies completely lyse the blood cells on a cultured plate

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31
Q

What does strep pyogenes cause

A
  • Necrotising fasciitis
  • Wound infection with cellulitis and lymphangitis
  • Tonsilitis and pharyngitis
  • Peritonsillar abscess (quinsy)
  • Otitis media
  • Mastoiditis
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32
Q

How should strep pyogenes be treated

A
  • All are sensitive to penicillin

- Clindamycin may be used second-line

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33
Q

Significance of enterococcus faecalis

A

Causes:

  • UTIs
  • Abdominal wound infections
  • May be isolated from the bile in acute cholecystitis
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34
Q

How are enterococci managed

A
  • Sensitive to ampicillin
  • Moderately resistant to penicillin
  • Resistance to cephalosporins
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35
Q

How does Viridans streptococci appear on culture plates

A

Alpha-haemolysis on blood-containing plates with a green discolouration (hence viridans)

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36
Q

Significance of Viridans streptococci

A

Can colonise abnormal heart valves causing endocarditis

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37
Q

What is streptococcus pneumoniae

A
  • Pneumococcus

- Encapsulated diplococci

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38
Q

What may streptococcus pneumoniae cause

A
  • Lobar pneumonia
  • Chronic bronchitis
  • Meningitis
  • Sinusitis
  • Conjunctivitis
  • Septicaemia (especially in splenectomy patients)
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39
Q

What is clostridium perfringens associated with

A

Gas gangrene

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40
Q

What is clostridium difficile associated with

A

Pseudomembranous colitis

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41
Q

How is C. diff diagnosed

A

Detection of toxin in stool

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42
Q

Which antibiotics specifically predispose to C. diff

A
  • Cephalosporins
  • Quinolones
  • Clindamycin
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43
Q

How is C. diff treated

A
  • Metronidazole in mild cases

- Vancomycin in more serious cases

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44
Q

E.coli causes sepsis in

A
  • UTI
  • Wound infection
  • Peritonitis
  • Biliary tract infections
  • Septicaemia
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45
Q

What is Proteus spp associated with

A

Staghorn calculi and UTI

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46
Q

What toxin does E.coli produce

A

Viratoxin

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47
Q

Clinical features of salmonella infection

A
  • Headache, fever, arthralgia
  • Relative bradycardia
  • Abdominal pain
  • Rose spots on the trunk
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48
Q

How is salmonella typically transmitted

A

Infected meat (especially poultry) and eggs

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49
Q

Clinical features of Shigella spp

A
  • Dysentery
  • Shigella soneii causes mild illness
  • Shigella dysentriae produces endotoxin and severe illness
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50
Q

What causes HUS

A

E.coli 0157

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51
Q

Features of campylobacter

A
  • Most common cause of acute infective diarrhoea
  • Usually infects caecum and terminal ileum
  • Local lymphadenopathy is common
  • May mimic appendicitis
  • Birds are a reservoir
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52
Q

How is Vibrio cholera transmitted

A
  • Contaminated water

- Seafood

53
Q

How does cholera present

A
  • Sudden onset effortless vomiting

- Profuse watery diarrhoea

54
Q

Which patients are most susceptible to pseudomonas infection

A
  • Burns

- Malignancies

55
Q

What does pseudomonas colonise

A
  • Catheters
  • ET tubes
  • Vascular grafts
56
Q

What are non-capsulated strains of Haemophilus influenzae associated with

A
  • Exacerbations of COPD

- Bronchiectasis

57
Q

What are capsulated strains of Haemophilus influenzae associated with

A

Severe illness in children:

  • Meningitis
  • Epiglottitis
  • Osteomyelitis
  • Orbital cellulitis

Post-splenectomy sepsis

58
Q

How is H. pylori transmitted

A
  • Faecal-oral
  • Oral-oral
  • Iatrogenic e.g. endoscopes
59
Q

What conditions are associated with H. pylori

A
  • Gastritis
  • Peptic ulceration
  • Gastric lymphoma
  • Gastric cancer
60
Q

SIRS criteria

A
  • Temp >38 or <36
  • Tachy >90bpm
  • Tachypnoea >20 or PaCO2 <4.25
  • WBC >12 or <4
61
Q

Describe Stage 1 of SIRS

A

Result of local insult, the local environment produces cytokines which:

  • Provoke and inflammatory response
  • Promote wound repair
  • Recruit reticuloendothelial cells
62
Q

Describe Stage 2 of SIRS

A
  • Cytokines are released into the circulation
  • Macrophages and platelets are recruited
  • Growth factor is produced
  • Acute phase response is controlled by a decrease in pro-inflammatory mediators and release of endogenous antagonists
63
Q

Describe Stage 3 of SIRS

A
  • Occurs if homeostasis is not restored
  • Massive systemic reaction and cytokines become destructive
  • Dysfunction of various distant organs
64
Q

Define septic shock

A

Severe sepsis with refractory hypotension

65
Q

Define sepsis

A

SIRS resulting from documented infection

66
Q

Define MODS

A

Diagnosed dysfunction of two or more organ systems

67
Q

How may mortality be predicted in sepsis

A

Proportional to the number of organs that are failing

68
Q

Define a boil (furuncle)

A

Infection of a hair follicle

69
Q

Define a stye (hordoleum)

A

Infection in a hair follicle on an eyelid

70
Q

Define a carbuncle

A

Group of boils interconnected in the subcutaneous tissue by tracts

71
Q

What bacteria is typically responsible for boils, styes, carbuncles

A

S. aureus

72
Q

Describe Erysipelas

A
  • Spreading infection of the skin due to strep pyogenes

- Presents as a red, raised indurated area of skin with sharp demarcation

73
Q

Describe Necrotizing fasciitis

A
  • Infection spreads along fascial planes, causing extensive necrosis
  • Overlying skin becomes devoid of its blood supply and turns purple/black
74
Q

Where does Meleney’s gangrene occur

A

Site of abdominal surgery or accidental abrasion of the skin

75
Q

Define lymphangitis

A

Non-suppurative infection of lymphatic vessels that drain an area of cellulitis

76
Q

How does lymphangitis present

A
  • Red, tender streaks along the lines of lymphatics

- Spreads from site of cellulitis to regional lymph nodes

77
Q

What causes tetanus

A
  • C. tetani

- Produces neurotoxin that blocks the inhibitory activity of spinal reflexes

78
Q

How does tetanus present

A
  • Facial spasm produces trismus
  • Lockjaw
  • Arching of neck and back from spasm
  • Neck stiffness
79
Q

Define an abscess

A

A localised collection of pus, walled off by a barrier inflammatory reaction

80
Q

How many air changes per hour do theatres undergo

A

15 per hour (3 of which are fresh air)

81
Q

Describe air movement in theatres

A
  • Filtered with HEPA filter

- Enters at ceiling height and leaves at floor level

82
Q

When are laminar airflow systems required

A

Arthroplasty

83
Q

Define ‘clean’ surgery

A

An operation carried out through a clean skin incision under sterile conditions, where the GI/GU/respiratory tracts are not breached

84
Q

Define ‘clean-contaminated’ surgery

A

An operation carried out under sterile conditions with breaching of a hollow viscus other than the colon, where contamination is minimal

85
Q

Define ‘contaminated’ surgery

A

An operation carried out where contamination has occurred e.g. opening of colon, open fracture, bites

86
Q

What is the wound infection rate in contaminated surgery

A

15%

87
Q

Define ‘dirty’ surgery

A

Operation carried out in the presence of pus or a perforated viscus

88
Q

Risk of wound infection in dirty surgery

A

> 25%

89
Q

How does alcohol work in skin preparation

A

Denatures proteins

90
Q

Mechanism of action of chlorhexadine

A
  • Causes bacterial cell wall disruption
  • Bactericidal
  • Most active against gram-positive organisms
91
Q

How long does chlorhexadine have an effect

A

6 hours

92
Q

Difference between disinfection and sterilisation

A

Sterilisation is the complete destruction of all viable microorganisms, including spores, cysts and viruses

93
Q

What are destroyed in autoclave

A

Bacteria, fungi, spores, viruses

94
Q

What monitors the efficacy of autoclave

A

Brown’s tube

95
Q

Role of Bowie-Dickie test

A

Identifies when equipment is appropriately sterilised

96
Q

Why is moist heat better than dry heat

A

Penetrates material better and denatures the protein of the cell walls of micro-organisms

97
Q

What is used to sterilise endoscopes and some laparoscopic items

A

Glutaraldehyde solution

98
Q

Which antibiotic is first-line in animal and human bite injuries

A

Co-Amoxiclav

99
Q

When is Co-amoxiclav useful as a prophylactic antibiotic

A

Bowel, hepatobiliary, and GU surgery

100
Q

When is Cefuroxime useful as a prophylactic antibiotic

A

Used in combination with metronidazole in colorectal and biliary surgery

101
Q

Precautions to be aware of with Cephalosporins

A
  • <10% of those who are penicillin allergic are also allergic to cephalosporins
  • Those with renal impairment will require dose adjustment
  • Mild transient rise in liver enzymes may occur
102
Q

List the common macrolides

A
  • Erythromycin

- Clarithromycin

103
Q

What are the first choice antibiotics for severe gram negative infections

A

Aminoglycosides e.g. Gentamicin

104
Q

What are the side effects of aminoglycosides

A
  • Ototoxicity

- Nephrotoxicity

105
Q

What type of antibiotic is Ciprofloxacin

A

Quniolone

106
Q

What is Ciprofloxacin typically used for

A
  • UTIs (especially those that are catheter related)
  • Prostatitis
  • Skin and soft tissue with P. aeruginosa
  • Gram negative chest infections
107
Q

What common drug does Ciprofloxacin potentiate

A

Warfarin

108
Q

What is Metronidazole active against

A
  • Anaerobes - e.g. bacteroides, clostridia

- Protozoal organisms - e.g. Entamoeba histolytica, Giardia lamblia

109
Q

What antibiotic causes ‘red man syndrome’

A

Vancomycin

110
Q

When is Clindamycin used in surgery

A

Skin and soft tissue infections where penicillin is not an option or severe streptococcal cellulitis including necrotising fasciitis

111
Q

Define intrinsic (innate) antibiotic resistance

A

Occurs when the organism lacks the target site for the agent or is impermeable to the antibiotic

112
Q

Define acquired antibiotic resistance

A

Refers to organisms that were previously susceptible to the agent in question

113
Q

Antibiotic prophylaxis in biliary tract surgery

A

Co-amoxiclav

114
Q

Antibiotic prophylaxis in colorectal surgery

A

Cefuroxime and Metronidazole

115
Q

Antibiotic prophylaxis for GU surgery

A

Co-amoxiclav or Gentamicin

116
Q

Antibiotic prophylaxis for limb amputation

A

Penicillin

117
Q

Antibiotic prophylaxis for GU instrumentation

A

Co-amoxiclav and Gentamicin

118
Q

Which antibiotics inhibit cell wall formation

A
  • Penicillins

- Cephalosporins

119
Q

Which antibiotics inhibit protein synthesis

A
  • Aminoglycosides
  • Chloramphenicol
  • Macrolides
  • Tetracylines
  • Fusidic acid
120
Q

Which antibiotics inhibit DNA synthesis

A
  • Quinolones
  • Metronidazole
  • Sulphonamides
  • Trimethorpim
121
Q

Which antibiotics inhibit RNA synthesis

A

Rifampicin

122
Q

What type of virus is Hepatitis B

A

Double-stranded DNA virus

123
Q

What percentage of Hep B patients become chronic carriers

A

10%

124
Q

Serology for Hep B infected persons and carriers

A
  • HBsAg

- Anti-HBcAg

125
Q

What does the presence of HBeAg imply

A

High levels of circulating viral DNA and this high infectivity

126
Q

What serology implies vaccination to Hep B

A

Anti-HBsAg in isolation

127
Q

What type of virus is Hepatitis C

A

Single-stranded RNA virus

128
Q

What is the treatment for Hepatitis C

A
  • Interferon-alpha

- Ribavirin

Pathology (7 decks)

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