Gram positive bacteria

Question 1

What is the first line treatment for Osteomyelitis (Staphylococcus aureus infection?

Answer 1

Flucloxacillin for 6 weeks.

Iff penicillin allergy -> clindamycin.

Add fusidic acid and rifampicin for initial 2 weeks.

Question 2

What is meticillin-resistant S. aureus treated with?

Answer 2

Vancomycin.

Question 3

Staphylococci can be grouped based on what test?

Answer 3

Coagulase test.

Coagulase is an enzyme produced by bacteria that clots blood plasma. The fibrin clot around the bacteria may protect from phagocytosis.

Question 4

What is the most important coagulase +ve Staphylococci?

Answer 4

S. aureus

Question 5

What is the most important coagulase -ve Staphylococci?

Answer 5

S. epidermidis (important opportunistic pathogen).

Question 6

What is the normal habitat for Staphylococci?

Answer 6

Nose and the skin.

Question 7

How does S. aureus spread?

Answer 7

By aerosol and touch.

Question 8

What do we mean by carriers and shedders?

Answer 8

Carriage of S. aureus varies and can be either permanent or transient and the host can be a shedder, releasing large numbers of bacteria, or a non-shedder.

Question 9

List the virulence factors for S. aureus:

Answer 9

Pore-forming toxins (in some strains): alpha-haemolysin, Panton-Valentine Leucocidin.

Proteases: exfoliatin

TSS toxin

Protein A

Question 10

The PVL toxin:

Answer 10

Produced by many of the community MRSA strains and causes haemorrhagic pneumonia. It is encoded by a pro-phage gene that is incorporated into the bacterial genome.

Question 11

Alpha-haemolysin:

Answer 11

At low concentration induces apoptosis in cells by allowing exchange of monovalent ions across the cell membrane. At high concentration it binds to the lipid membrane and causes massive necrosis.

Question 12

Exfoliatin:

Answer 12

Causes scalded skin syndrome. It is a glutamate-specific serine protease that degrades the cadherin desmoglein I. This is present in desmosomes suprabasally.

Question 13

TSS toxin:

Answer 13

Is a super antigen rather similar to the erythrogenic toxin of S.pyogenes.

Question 14

Protein A:

Answer 14

Surface protein which binds Ig’s in wrong orientation.

Question 15

MRSA resistant to:

Answer 15

Beta-lactams, gentamycin, erythromycin, tetracycline.

Question 16

What are the pyogenic diseases caused by S. aureus?

Answer 16

Wound infections, Abscesses (boils and carbuncles), impetigo, septicaemia, osteomyelitis, pneumonia, endocarditis.

Question 17

What are the toxin mediated diseases causes by S. aureus?

Answer 17

Scalded skin syndrome, TSS, food poisoning.

Question 18

S. epidermidis

Answer 18

Ability to form persistent biofilms.

Question 19

S. saprophyticus

Answer 19

Haemagglutinin for adhesion and urease.

Question 20

Streptococcus pyogenes

Answer 20

Beta-haemolytic (Group A), facultative anaerob, penicillin sensitive.

Gram positive cocci in chains.

Question 21

What are the three types of haemolysis?

Answer 21

Beta: complete (Streptococcus pyogenes = Haemolysins O and S).

Alpha: partial, greening. (S. intermedius)

Gamma: no lysis (Some Streptococcus mutans).

Question 22

Alpha haemolysis is due to..

Answer 22

The production of hydrogen peroxide, which reacts with haemoglobin to form the green compound met-haemoglobin.

Question 23

Beta haemolysis is due to…

Answer 23

to the production of two pore-forming toxins – streptolysin O and S. Streptolysin O is oxygen sensitive and is very antigenic.

Question 24

Sero-grouping (Lancefield)

Answer 24

Based on CHO cell surface antigens.

Lancefield A-H and K-V.
Antiserum to each group added to a suspension of bacteria = clumping indicates recognition.

Question 25

What is an example of Group A pathogen?

Answer 25

Streptococcus pyogenes

Question 26

What is an example of Group B pathogen?

Answer 26

Streptococcus agalactiae. (Neonatal infections).

Question 27

Streptococcus pyogenes virulence factors:

Answer 27

Exported factors, toxins and surface factors.

Question 28

Streptococcus p. exported factors:

Answer 28

Enzymes: - Hyaluronidase = spreading - Streptokinase = breaks down clots - C5a peptidase = reduces chemotaxis

Question 29

Streptococcus p. toxins:

Answer 29

Streptolysins O and S: binds cholesterol Erythrogenic toxin: SPeA - exaggerated response. (Streptococcal pyrogenic exotoxins A) there is also C. Scarlet fever.

Question 30

Streptococcus p. surface factors:

Answer 30

Capsule: hyaluronic acid M protein (surface protein) encourages complement degradation, basically antiphagocytic.

Question 31

What are the infections caused by Streptococcus p.?

Answer 31

Wound infections (cellulitis, puerperal fever) Tonsillitis and pharyngitis Otitis media Impetigo Scarlet fever

Question 32

What are the complications of Strep. p. infections?

Answer 32

Rheumatic fever and glomerulonephritis.

Question 33

Streptococcus pneumoniae

Answer 33

Commensal in the oro-pharynx in about 30% of the population.

Question 34

What infections can be caused by Streptococcus pneumoniae?

Answer 34

Pneumonia, otitis media, sinusitis, meningitis

Question 35

What are the predisposing factors for Strep. pneu. infections?

Answer 35

Impaired mucus trapping (viral infections). Hypogammaglobulinaemia. Asplenia (spleen produces tuftsin, enhances phagocytosis).

Question 36

Viridans group streptococci

Answer 36

Term used to describe oral streptococci. Can be alpha- or non-haemolytic.

Question 37

What infections can be caused by the viridans group?

Answer 37

Some cause dental caries and abscesses. Infective endocarditis (S. sanguinis, S. oralis).

Question 38

What are the members of the milleri group?

Answer 38

S. intermedius, S. anginosus, S. constellatus. Cause deep organ abscesses in the brain and liver for example.

Question 39

List Gram positive bacilli:

Answer 39

Listeria monocytogenes Bacillus anthracis (spore forming) Corynebacterium diphtheriae (thick greyish pseudo membrane on tonsils). Clostridia (spore forming, survive the environment, produces toxins)

Question 40

What are the three syndromes associated with anthrax?

Answer 40

Cutaneous - blister with black centre (eschar) Inhalation - respiratory sepsis Ingestion - severe gastroenteritis

Question 41

Examples of the clostridia group:

Answer 41

C. tetani, C. botulinum, C difficile

Question 42

C. tetani

Answer 42

Tetanus. Risus sardonicus or rictus grin Toxin inhibit GABA neurotransmission and cause muscle contractions and spasms progressing from head down.

Question 43

Tetanus

Answer 43

The first few signs and symptoms are: Neck stiffness Sore throat Difficulty opening the mouth The latter is due to masseter spasm. Later, more muscle groups become involved, in a roughly descending manner. Contraction of facial muscle groups, giving rise to trismus and the rictus of tetany, known generally as the risus sardonicus. Descending patterns of muscle rigidity, progressing from the head, down Characteristic spasms: Flexion and adduction of the arms Extension of the legs Opisthotonos Potentially, these spasms could involve the larynx and the diaphragm, and therefore ventilation may become necessary They are intermittent, and they may be spontaneous or triggered by touch, visual, auditory, or emotional stimuli. The muscle contraction during these spasms is of such strength that bones may break and tendons may be avulsed from their insertion sites. Autonomic dysfunction This takes somewhat longer to develop Typically, it manifests as an increase in sympathetic tone - hypertension, tachycardia, ileus and urinary retention. After the respiratory failure, this autonomic madness is what actually kills people. These signs and symptoms all arise from the effect of tetanus toxin on synaptobrevin, a protein which faciliates the binding of neurotransmitter vesicles to the presynaptic membrane. The consequence is a cessation of neurotransmission - particularly of GABA.

Question 44

Botulism

Answer 44

Food or wound borne Botulinum toxin causes paralysis spreading from head to body.

Question 45

C. difficile

Answer 45

ABx associated diarrhoea and pseudomembranous colitis.