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Foundations of Medicine > Classifications of Pathogenic Bacteria: Gram Positive > Flashcards

Classifications of Pathogenic Bacteria: Gram Positive Flashcards

1
Q

What does it mean for a bacteria to be gram positive?

A

The cell wall of the bacteria has a thick layer of peptidoglycan

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2
Q

What is peptidoglycan?

A

Sugar network made from two major sugars:

N-acetylmuramic acid
N-acetylglucosamine

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3
Q

Why is peptidoglycan very important?

A

Forms the basis of gram staining - a method used to classify bacteria

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4
Q

What colour do gram positive bacteria appear under the microscope?

A

Purple

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5
Q

What are the five steps to gram staining?f

A

Applying a primary stain (crystal violet).

Adding a mordant (Gram’s iodine).

Rapid decolorization with ethanol, acetone or a mixture of both.

Counterstaining with safranin.

Dry slides and view under microscope

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6
Q

Why do gram positive bacteria stain purple?

A

The crystal violet is able to form complexes within the peptidoglycan, so the stain is retained.

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7
Q

What is another way bacteria can be classified?

A

Aerobic - grows in presence of oxygen
Anaerobic - grows in absence of oxygen

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8
Q

What are the main shapes a bacteria can take?

A

Cocci - round
Bacilli - rods

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9
Q

What are the two major forms of cocci bacteria?

A

Streptococci - in chains
Staphylococci - in clusters

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10
Q

How can streptococci be further divided up?

A

Appearance on blood agar

Alpha - haemolytic - partial destruction of surrounding red blood cells - turn blood agar green

β -haemolytic - compete destruction of surrounding red blood cells - turn blood agar clear

Non-haemolytic - no effect and no difference on blood agar

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11
Q

How can staphylococci be further divided up?

A

Whether they produce the enzyme coagulates or not

Coagulase +ve - tend to be pathogens or disease forming organisms eg Straph Aureus

Coagulase -ve - tend to be less pathogenic

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12
Q

How can bacilli be further divided up?

A

By size

Small
Large

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13
Q

How can anaerobic bacilli be divided up?

A

Most gram +ve anaerobic are bacilli eg clostridium group - C. diff.

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14
Q

What is a gram positive bacteria that effects the respiratory tract?

A

Streptococcus pneumoniae

Alpha-haemolytic streptococci

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15
Q

What is an example of a coagulase +ve gram +ve bacteria and what can it be broken up into?

A

Staphylococcus aureus
- MSSA
- MSRA

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16
Q

Where is staphylococcus aureus found and what can it cause?

A

Found: nose, axilla, pernieum

A major human pathogen that can cause wide range of diseases from boils/abscesses and soft tissue infections to septicaemia and osteymyelitis (inflammation of bone) .

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17
Q

When would you decolonise staphylococcus aureus?

A

Only in specific circumstances such as going into surgery, as it can be harmless when just colonising

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18
Q

What are typical anti-microbial susceptibility patterns of staphylococcus aureus?

A

Commonly penicillin resistant due to production of enzyme penicillinase - destroys the beta lactam ring and renders penicillin ineffective.

Some strains are methicillin resistant - synthetic penicillin

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19
Q

What are examples of coagulase-negative staphylococci?

A

S. epidemidis - main pathogen in catheter-related bloodstream infections
S. haemolyticus
S. saprophyticus - UTI and wirses in patients

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20
Q

What can S. lugdunensis, a coagulase negative, gram positive, staphylococci cause?

A

A harmless skin commensal to a life-threatening pathogen (as with infective endocarditis).

Behaves like Staphylococcus aureus.

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21
Q

What is key characteristic of coagulase negative staphylococci?

A

Form biofilms - bacteria adheres to a surface and forms a complex microbial community and there is released biofilm matrix.

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22
Q

What has the risk of forming biofilms?

A

Anything prosthetic:

Hip joints
Pacemaker wires
Prosthetic heart valves

23
Q

What can Streptococcus pneumoniae cause?

A

Pneumonia
Meningitis
Septicaemia (blood poising)

24
Q

What is a unique feature of Streptococcus pneumoniae?

A

Has a capsule that helps protect it from the host immune system

25
Q

What is viridans streptococci?

A

Another group of streptococci or alpha-hemolytic bacteria.

They typically colonise and
reside in the oral cavity.

26
Q

What can viridans streptococci produce?

A

Bacteremias and septicemia as an immunocompromised patients.

27
Q

How can β-haemolytic streptococci be further classified?

A

By carbohydrate surface antigens

Groups: A-G

Most important groups: A,B,F and D

28
Q

Discuss Group A, β-haemolytic streptococci

A

Streptococcus pyogenes aka “flesh eating” bugs

An example: Necrotizing fasciitis

It can cause devastating skin and soft tissue infections and septicemia with things progressing incredibly fast.

29
Q

Management of severe Group A, β-haemolytic streptococci

A

Antibiotics and surgery to remove effected tissue

30
Q

What is the most common Group A, β-haemolytic streptococci infection?

A

Sore throat pharyngitis

Called streptococcus pyogenes

31
Q

Discuss Group B, β-haemolytic streptococci infection

A

Often cause infection in neonates but also in older adults

Example: Streptococcus agalactiae

32
Q

How do neonates get Streptococcus agalactiae?

A

Genital tract carriage in women (common in 25% of women and is harmless)

Can cause neonatal sepsis such as meningitis and bacteraemia

33
Q

What would you do if a pregnant patient was positive for Group B, β-haemolytic streptococci?

A

Give antibiotics to prevent the transmission of the group B strep to the baby where the
baby might become infected
and subsequently develop disease.

34
Q

What underlying factors can make people more at risk of developing Streptococcus agalactiae?

A

Diabetes
Liver disease
Alcohol abuse
CVD
Malignancy

35
Q

What have group D streptococci been re-classified as?

A

Enterococcus

36
Q

What are the two main groups of Enterococcus?

A

Enterococcus faecalis
Enterococcus faecium

37
Q

What can Enterococcus cause?

A

Septicaemias and infective endocarditis

Less virulent than group A or B strep.

Often non-hemolytic although they can be beta-hemolytic.

38
Q

How is gram positive bacilli classified?

A

Aerobic
Anaerobic

39
Q

How would you describe the shape of the clostridium group of bacteria?

A

Large bacillli

40
Q

What is a clinically important gram-positive bacillus?

A

Clostridiodes Difficile
aka C. diff.

41
Q

Is C. diff anaerobic or aerobic?

A

Anaerobic

42
Q

How id C. diff diagnosed?

A

Difficult to culture
Diagnosed based off of the antigen that’s on the surface and if it produces a toxin.

43
Q

Do healthy people have C. diff?

A

Asymptomatic gut carriage in healthy people - 16% of adults and 66% of babies

44
Q

What can C. diff cause?

A

Diarrrgoea, associated with with toxin production.

Lead then on to toxic megacolon and can be fatal in rare circumstances.

Pseudomembranous colitis.

45
Q

What is a risk factor for C. diff?

A

Antibiotic use and anything that disrupts normal gut flora

46
Q

Key feature of C. Diff

A

Produces endospores or spores.

Bacteria goes into hibernation and these spores are very resistant.

Alcohol gel does not kill them - need soap and water.

47
Q

How does C. Diff spread?

A

When a patient has diarrhoea
they can stay on surfaces
for a prolonged period of time.

That together with hands can easily transmit infection to other patients.

48
Q

What does Clostridium perfringens cause?

A

Can contaminate food and cause gastroenteritis (Enterotoxin producing stains)

Can cause spores

Need to go to theatre in severe circumstances

Infected wounds may cause “gas gangrene”

49
Q

Where can clostridium perfringens be found?

A

Soil
In gut and faeces

50
Q

What is available for prophylaxis of clostridium tetani?

A

A vaccine

Antigenetically modified toxin

51
Q

What can clostridium tetani cause?

A

Toxin production by C. tetani causes tetanus

52
Q

What can bacillus anthracis cause?

A

Anthrax

53
Q

What bacteria can be found in botox?

A

Clostridium botulinum

Foundations of Medicine (56 decks)

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