Lecture 6 Gram positive cocci

Question 1

What are the important genera of gram positive cocci?

Answer 1

Staphylococcus

Streptococcus

Enterococcus

Question 2

What is the catalase test?

Answer 2

A test to tell whether a bacterium is staphylococcus or streptococcus/enterococcus

Question 3

How is a catalase test performed?

Answer 3

Hydrogen peroxide and if bubbles are produced its a staph if not its strepto

Question 4

What is a coagulase test?

Answer 4

Coagulase converts fibrinogen to fibrin.

Rabbit plasma is mixed with the bacteria and if it coagulates it is a coagulase positive test

Question 5

What are the 3 important human pathogens from the staphylococcus genus?

Answer 5

Staphylococcus aureus

Staphylococcus epidermis

Staphylococcus saprophyticus

Question 6

How is staph aureus distinguished from other staph species? What are other species called?

Answer 6

Positive coagulase test other species are coagulase negative staphylococci.

Question 7

What percentage of people are carriers of staph aureus?

Answer 7

20 - 40% of the population are carriers

Question 8

Where are staph aureus typically found?

Answer 8

anterior nares

Question 9

What kind of disease does staph aureus cause?

Answer 9

Chronic skin infections such as folliculitis, boils and minor wound infections

It can also be a virulent pathogen if it enters the bloodstream it can be fatal.

Can cause septicaemia

Osteomyelitis

Septic arthritis

Bursitis

Organ abscesses

Question 10

What is folliculitis?

Answer 10

infection of hair follicules

Question 11

how is septicaemia diagnosed?

Answer 11

aerobic and anaerobic bottles are used to culture bacteria

Question 12

What kind of locations can organ abscesses be found in?

Answer 12

Epidural abscess can be near spinal canal

Brain abscesses

Psoas abscesses

Lung abscesses

Question 13

What are some non-pyogenic diseases caused by staph aureus?

Answer 13

Staphylococcal Scalded Skin Syndrome

Staph toxic shock syndrome

Staph food poisoning

Question 14

Where are coagulase negative staph cocci typically found?

Answer 14

Staph epidermis

Question 15

Can Staphylococcus epidermis cause disease?

Answer 15

It’s very low in virulence but when there is a breach in the skin they can cause infection.

Question 16

What is the most common coagulase negative cocci?

Answer 16

Staph epidermis

Question 17

What kind of infections are caused by coagulase negative staphylococcus?

Answer 17

Infections of intravenous (or intra-arterial cannulas)

Prosthetic heart valves

Prostetic joint infection

Infection of orthopaedic pins, plates, screws, and wires

Meningitis with foreign devices

Question 18

What is the virulence factor of staph epidermis?

Answer 18

Extracellular polysaccharides or slime. Biofilm formation on foreign device

Question 19

Where do coagulase negative staphylococci typically cause infections that are relevant for orthopaedic treatment of joints?

Answer 19

They commonly cause infection on prosthesis.

Question 20

Where do staph saprophyticus typically cause infection?

Answer 20

In the Urinary tract it is second only in prevalence to Escherichia coli

Question 21

How is classification of streptococcus started?

Answer 21

Starts with the way they haemolyse blood agar.

Question 22

How are streptococcus species different in haemolysing blood agar?

Answer 22

Certain bacteria can produce hamolysins:

Alpha-haemolytic streptococci use alpha haemolysis sometimes called viridians streptococci

Beta haemolytic streptococci produce beta haemolytic streptococci

Question 23

What are the 3 kinds of haemolysis in streptococcus?

Answer 23

Beta (blood is dissolved agar is transparent)

Alpha (partial haemolysis of agar with olive green tinge)

Gamma haemolysis (no haemolysis)

Question 24

How can beta haemolytic streptococci be further classified?

Answer 24

According to antigenic differences in cell wall carbohydrates

Question 25

What is the lancefield grouping system?

Answer 25

Streptococci have C carbohydrates in their cell wall and they are antigenically distinct. 20 different groups within the genus determined by the difference in these carbohydrates.

Question 26

What are the particularly important Lancefield groups?

Answer 26

Lancefield group A also known as streptococcus pyogenes Lancefield group B also known as streptococcus agalatiae

Question 27

How many beta haemolytic streptococci are there and how do they differ?

Answer 27

There are 20 lanefield groups and they differ by the differences in C carbohydrates in their cell wall

Question 28

What are the types of complications that can result from primary infection with a beta haemolytic group A streptococcus (streptococcus pyogenes)?

Answer 28

Suppurative complications that are pus forming Non-suppuratives that are toxin or immune mediated

Question 29

What does primary infection with beta haemolytic group A streptococci look like?

Answer 29

Pharyngitis and tonsillitis. If it infects the skin it causes cellulitis, erysipelas and impetigo

Question 30

What are the types of suppuratives complications that can result from group A beta haemolytic streptococci?

Answer 30

Peritonsillar abscess Retropharyngeal abscess sinusitis Otitis media Mastoiditis Necrotising fasciitis

Question 31

What are some non-suppuratives complications that can result from group A beta haemolytic streptococci?

Answer 31

Scarlet fever Toxic shock syndrome (rarely) Rheumatic fever Acute glomerulonephritis

Question 32

How does pharyngo-tonsillitis look?

Answer 32

Red appearance and pus rom tonsils (this is known as strep throat)

Question 33

What is a perintonsillaer abscess (quinsy)?

Answer 33

Abscess in the tonsils making them enlarge

Question 34

What is mastoiditis?

Answer 34

Swelling behind the ear and redness and pain. Caused by bacteria travelling up the mastoid tube into the back of the ear and causing infection in bone behind the ear.

Question 35

What happens if mastoiditis is left untreated?

Answer 35

It can travel to the brain and cause meningitis

Question 36

What is impetigo?

Answer 36

Superficial outer keratin layer and is usually seen in school children because it is very contagious.

Question 37

What is erysipelas?

Answer 37

Superficial epidermal layer infected and raised. It contains sharp borders

Question 38

What is cellulitis?

Answer 38

Subcutaneous tissue is infected and reddened.

Question 39

Who is cellulitis typically seen in?

Answer 39

Elderly

Question 40

What is necrotising fasciitis?

Answer 40

Rapidly spread destructive infection along fascial planes causing necrosis of muscle and subcutaneous tissue

Question 41

What is scarlet fever?

Answer 41

Follows a pharyngitis is S. pyogenes is carrying pyrogenic exotoxin

Question 42

What are the common symptoms of scarlet fever?

Answer 42

Strawberry tongue and a rash

Question 43

What is rheumatic fever?

Answer 43

Patients develop antibodies against their own tissues. Polyarthritis subcutaneous nodules Erythema marginatum (a unique skin rash) Chorea (writhing movement of limbs) Carditis (including damage to heart valves)

Question 44

Who is rheumatic fever commonly seen in?

Answer 44

Endemic in poor socioeconomic conditions.

Question 45

What is post streptococcal glomerulonephritis?

Answer 45

An inflammatory disease of the glomeruli caused by desposition of immune complexes acute renal damage often occurs which resolves

Question 46

What are the features of post streptococcal glomerulonephritis?

Answer 46

High BP Haematuria Proteinuria Oedema

Question 47

Where are group B haemolytic streptococcus normally found?

Answer 47

In the vagina as part of the normal microbiome

Question 48

What do group B haemolytic streptococci do that is harmful?

Answer 48

They can cause serious infection of the mother and the neonate Premature labour and rupture of membranes

Question 49

How is group B haemolytic streptococcus infection found and treated?

Answer 49

Screened for carriage during pregnancy and treated with IV amoxicillin during labour

Question 50

What infections are caused by group B beta haemolytic streptococcus in the mother?

Answer 50

Maternal infections such as: Postpartum endometritis Post caesarean section bacteraemia Urinary Tract Infections

Question 51

What infections are caused by group B beta haemolytic streptococcus in the infant?

Answer 51

Septicaemia pneumonia Meningitis

Question 52

Where are alpha haemolytic streptococci commonly found?

Answer 52

Oropharyngeal, gastrointestinal and genital tract commensal flora Organised into species groups

Question 53

Is classification of alpha haemolytic streptococci easy?

Answer 53

No it is complicated and controversial. All species are organized into species groups: Bovis, anginosis, mitis, mutans, and salivarius groups

Question 54

What kind of infections do alpha haemolytic streptococcus cause?

Answer 54

Bacteraemia Infective endocarditis Abscess, particularly of orofacial area, pulmonary and pleural, intra-abdominal pain. (they are common abscess causing organisms) Dental carries

Question 55

What are the virulence factors of alpha haemolytic streptococci in dental carries?

Answer 55

glycosyltransferases convert sucrose into insoluble glucans Glucans then adhere to dental enamel and form the basis of dental plaque or tartar. (biofilm) Acid production, demineralisation of the tooth then causes initiation of caries

Question 56

What strain of alpha haemolytic streptococcus is associated with endocarditis and bacteraemia? What else should be checked for if these conditions are present?

Answer 56

Streptococcus Bovis which is also associated with colonic malignancy

Question 57

What is streptococcus pneumonia?

Answer 57

The pneumonia causing streptococcus which is a highly virulent pathogen.

Question 58

Where is pneumococcus typically carried?

Answer 58

In the upper respiratory tract of 5 - 10% of the population

Question 59

Name an important virulence factor for pneumococcus?

Answer 59

Its capsule which has 80+ antigenically distinct serotypes

Question 60

What does pneumococcus commonly cause?

Answer 60

Meningitis and pneumonia

Question 61

Where are enterococcus commonly found?

Answer 61

commonesals of bowel

Question 62

What are the main species of enterococcus?

Answer 62

E. faecalis and E. facium

Question 63

Which of the 2 enterococcus species are less commonly encountered?

Answer 63

E. faecium

Question 64

What are the typical infections of enterococcus?

Answer 64

``` Intra-abdominal infections Urinary tract infections Soft tissue infections Bacteraemia Endocarditis ```

Question 65

What is a problem with Enterococcus species?

Answer 65

They are very resistant to antibiotics; in particular E. faecium

Question 66

How can enterococci be identified?

Answer 66

They agglutinate with lancefield group D antiserum