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Y4 Infectious diseases > Principles > Flashcards

Principles Flashcards

1
Q

What are the 3 main shapes of bacteria ?

A
  1. Cocci spheres
  2. Bacilli (rods)
  3. Spiral-shaped (spirillium or spirochaete)
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2
Q

What is the purpose of gram staining bacteria ?

A
  • is a common technique used to differentiate two large groups of bacteria based on their different cell wall constituents.
  • The Gram stain procedure distinguishes between Gram positive and Gram negative groups by coloring these cells red (neg) or violet (pos)
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3
Q

What 2 bacterial organisms do not gram stain ?

A
  1. Mycobacterium tuberculosis - causes TB
  2. Treponema pallidum - causes syphilis
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4
Q

Define what each of these descriptors of bacteria mean:

  1. Aerobic
  2. Obligate aerboes
  3. Obligate anaerobes
  4. Faculatitve anaerobes
  5. Capnophilic
A
  1. Aerobic - grow in O2/air
  2. Obligate aerboes - require O2
  3. Obligate anaerobes - killed by O2
  4. Faculatitve anaerobes - tolerate O2
  5. Capnophilic - Prefer high CO2 levels
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5
Q

How are the 3 different types of streptococci differentiated ?

A

Streptococci are divided into three groups based on their hemolytic (red blood cell lysing) activity.

  1. In alpha hemolysis, the red blood cells remain intact, but the hemoglobin is converted to biliverdin. This causes dark greening of the blood agar plate.
  2. Beta hemolysis is a complete hemolysis of erythrocytes by the enzyme hemolysin. Clear zones will appear around the colonies on the blood agar plate. (Most pathogenic type)
  3. Gamma hemolysis = no hemolysis.
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6
Q

What is done when serological tests are done to assess infection by bacteria ?

A
  • Detect presence of specific IgM Ab to virus/ microbe
  • Which can identify specific Serotypes (strain) of bacteria
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7
Q

Define virulence

A

The capacity of a microbe to cause damage to the host.

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8
Q

Define pathogen

A

a harmful organism that produces a pathology

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9
Q

Define commensal

A

An organism that is part of the normal flora – often mutualistic relationship

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10
Q

Define what an opportunisitc pathogen is

A

An organism that causes infection when opportunity/ change in natural immunity arises – e.g. in an immunocompromised individual

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11
Q

Define what a contaminant is

A

An organism that is growing in a culture by accident

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12
Q

What are the 6 main different types of infectious agents

A
  1. Bacteria – Prokaryotic, single celled organisms
  2. Viruses – Non-living, obligate parasites
  3. Fungi – Eukaryotic single to multi-cellular infectious agents
  4. Protozoa – Amoeba, Plasmodium (malaria), Toxoplasma
  5. Parasites
  6. Prions – infectious proteins, nvCJD & BSE (cattle)
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13
Q

What are the 2 pathogenic aerobic gram neg cocci and there appearance

A
  • Neisseria meningitidis - commonest cause of bacterial meningitis
  • Neisseria gonorrhoeae - causes gonorrhoea

Appear as gram neg diplococci

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14
Q

What are the main guy commensal coliforms?

A

Enterobacteriacae:

  • Most strains of Escherichia coli
  • Klebsiella spp.
  • Enterobacter spp
  • Proteus spp

All gram neg bacteria

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15
Q

What are the main guy pathogens ?

A
  • Salmonella spp
  • Shigella spp
  • Verotoxin (VTEC) producing Escherichia coli – E. coli O157 & O104
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16
Q

What are coliforms ?

A
  • A species of Gram negative bacilli that look like Escherichia coli (E. coli) on Gram film and when cultured on blood agar
  • Many of them are part of normal bowel flora
  • Differentiated from each other by: – Biochemical reactions – Antigenic structure of cell wall (serotyping) – O antigens (cell wall) and H antigen (flagella)
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17
Q

How do coliforms cause infection ?

A

When they get into a normally sterile site can cause serious infection e.g. UTI, Peritonitis, Biliary tract infection

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18
Q

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

A

Gentamicin

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19
Q

Why do Patients with coliform (Gram-negative) sepsis become very unwell very quickly

A

Because of the endotoxin released from the Gram negative cell wall when the bacteria die

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20
Q

What body temp defines a fever?

A

38 degrees

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21
Q

What is the purpose of a fever when fighting an infection ?

A
  • Most human pathogens grow best at 37°C – growth starts to slow if temp increases
  • Raising the core temperature is an adaptive response and is considered to be beneficial in fighting infection
  • However, harm may also result from fever e.g febrile convulsions in young children
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22
Q

Describe the pathogenesis of sepsis

A
  1. Small blood vessels become “leaky” and lose fluid into the tissues
  2. Lower blood volume requires heart to work harder to maintain oxygenation of tissues (↑HR)
  3. Poor tissue oxygen perfusion mean blood supply to less essential organs (skin, kidneys, liver is shut down to try to maintain blood supply to brain
  4. Blood clotting system is activated causing blood clotting in tiny blood vessels→ uses up all clotting factors→ increased risk of haemorrhage
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23
Q

What are the 4 main groups of gram positive pathogenic bacteria ?

A

Streptoccus – Pneumonia, GAS, Oral Streps

Enterococcus – Enteric infections

Staphylococcus – Nosocomial & community – Skin infections & biofilms

Clostridia – Anaerobic bacilli

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24
Q

What are beta haemolytic streptococci further differentiated as ?

A

Using lancfield grouping

25
Q

What is the most significant pathogenic streptococci and what are the infections it is associated with ?

A

Group A streptococci (it is a beta haemolytic strep) (e.g. strep. pyogens) associated with:

  1. Streptococcal sore throat (Scarlet fever)
  2. Invasive diseases e.g. necrotising fasciitis
  3. Puerperal sepsis (infection of pregnant & post natal women)
26
Q

Define what pneumonia is

A

An acute inflammation of the lungs, often caused by inhaled pneumococci of the species Streptococcus pneumoniae. The alveoli and bronchiles of the lung become plugged with a fibrous exudate

27
Q

What is the main causative organism of pneumonia ?

A
  • Streptococcus pneumoniae (Part of normal upper resp tract flora in many people)

Note also causes severe meningitis

28
Q

What is the microscopic appearance of step. pneumoniae ?

A

Gram positive α-haemolytic cocci

29
Q

Are the majority of strains of step. pneumoniae still sensitive to penicillin ?

A

Yes - hence most treatment includes one

30
Q

What is the most important type of non-haemolytic streptococcus and what is the type of infection they commonly cause ?

A

Enterococci - Enterococcus faecalis, Enterococcus faecium

It is a bowel commensal but if it gets into a sterile site e.g. commonly cause UTI

31
Q

Most strains of E. faecalis are sensitive to what?

A

amoxicillin (but not to penicillin)

32
Q

There are some very antibiotic-resistant strains of E. faecium known as ?

A

“VRE” (vancomycin resistant enterococci) can cause “outbreaks” of infections in hospital

33
Q

What are the 2 main types of staphylococcus and what do they appear like under a microscope and how are they differentiated ?

A
  • Staph. aureus (coagulase pos) and Staph. epidermidis (coagulase neg)
  • They are Gram positive cocci
34
Q

What are the areas of the body commonly colonised by staph. aureus ?

A
  • Nostrils and perineum
  • It is an infection originating from both hospital (nasocomial) and the community
35
Q

What are the areas of the body commonly colonised by staph. epidermidis and where does it usually originate?

A

skin & mucous membranes

Originates - nosocomial infection/ immunocompromised.

36
Q

What is staph. epidermidis infections associated with ?

A

It is associated with foreign devices e.g. catheters

37
Q

Where does MRSA usually originate from and what patients are most affected by it?

A
  • Mainly nosocomial origin
  • Usually affecting elderly & immunocompromised, Intensive care units, Burns Patients, Surgical patients, Intravenous lines, Dialysis patients
38
Q

What type of infections does staph. aureus mainly cause

A
  • Commonest cause of skin, soft tissue and wound infection
  • Commonest cause of bone and joint infection
  • Also causes Food poisoning – enterotoxin-producing strains only
39
Q

Describe the natural progression of staph.aureus infections

A
  1. Multiplies at site of acquisition, causing local infection & inflammation, e.g. abscess
  2. Gets into bloodstream
  3. Bacteraemia (SAB)
  4. Disseminates to distant sites in the body
  5. Causing Sepsis (septicaemia) life threatening
  6. May cause abscesses in spleen, liver, kidneys etc.
40
Q

What is the typical appearance of clostridum spp. and where is it normally found in the body ?

A
  • Gram positive anaerobic bacilli
  • Part of normal bowel flora of man and animals – found in faeces and in soil.
41
Q

Why can clostridium spp. survive outside the body for many months ?

A

Because its spores can

42
Q

What are the 3 main types of clostridum spp. and what infections do they cause ?

A
  • Clostridium difficile – causes antibiotic-associated diarrhoea, esp. in the elderly
  • Clostridium perfringens – causes “ gas ” gangerene, a severe soft tissue infection following contamination of a wound
  • Clostridium tetani – causes tetanus, a usually fatal paralytic illness
43
Q

What are the 5 ways that infection can spread ?

A
  • Inhalation
  • Ingestion
  • Inoculation – direct & indirect
  • Mother to Infant – Vertical transmission
  • Intercourse – STI or STD
44
Q

Familiarise yourself what the main areas missed on hand washing

A
45
Q

What are the WHO 5 moments for hand hygiene ?

A
46
Q

What are the principles of Respiratory Hygiene/Cough Etiquette (i.e. when coughing or sneezing)

A
  1. Cover nose & mouth with disposable single use tissues when sneezing/coughing/wiping & blowing nose
  2. Dispose of hand tissue in waste bin
  3. Wash hands with soap & water after coughing/sneezing, contact with respiratory secretions.
47
Q

Define what sterilisation and disinfection is

A

Disinfection = Process by which the number of microorganisms are reduced to a level that is considered safe.

Sterilisation = the process by which all microorganisms are killed or removed to render the object incapable of causing infection e.g. autoclave

48
Q

What are the 2 mechanisms by which antibiotics can treat infections ?

A
  1. They can be bactericidal (kill bacteria)
  2. Or Bacterostatic (inhibit bacterial growth)
49
Q

What are the 2 types of antibiotic spectrum ?

A

Broad or narrow

50
Q

When given orally where are antibiotics absorbed from?

A

The small intestine and then spread to all parts of the body

51
Q

What are the 3 ways in which a antibiotic can target a bacteria ?

A
  1. Acting on the bacterial cell wall
  2. Affecting the bacterial ribosome
  3. Acting on bacterial DNA directly
52
Q

What are the 3 groups of antibiotics that target the bacterial cell wall ?

A
  1. Penicillins
  2. Cephalosporins
  3. Glycopeptides
53
Q

What is the specific mechanism of action of penicillins ?

A

Inhibits cell wall synthesis by preventing cross-linking of peptidoglycans and is bactericidal

54
Q

Do penicillins have many side effects ?

A

no

55
Q

What is the spectrum of action of the penicillins ?

A

Ranges from broad to narrow

56
Q

How are penicillins excreted ?

A

Via the kidneys

57
Q

Give some examples of penicillins

A

Any antiobitc with ‘cillin’ in its name

58
Q

What is the specific mechanism of action of Cephalosporins ?

A

The exact same as penciliins - It inhibits cell wall synthesis by preventing cross-linking of peptidoglycans and they are bactericidal

59
Q
A

Y4 Infectious diseases (7 decks)

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