HACEK Pathogens

Question 1

What are the HACEK pathogens?

Answer 1

Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella

Normal part of the oral-pharyngeal microbiota

Most common gram-negative cause of endocarditis among people who do not use IV drugs

Treatment choice is cephalosporin and ceftriaxone

Question 2

Describe Haemophilus Influenzae

Answer 2

Colonizes URT in the first few months of life

Requires blood factors for growth

Capsulated or Uncapsulated

Question 3

Which strains of H. influenzae cause mucosal surface infections?

Answer 3

Uncapsulated or non-typable

Localized infections
OM, sinusitis, bronchitis and pneumonia

Question 4

Which strains of H. influenzae cause invasive disease?

Answer 4

Encapsulated strains - composed of polyribitol phosphate (PRP)

Can express one of six polysaccharide capsules

H. influenzae type B acocunts for 95% of all strains that cause invasive disease

Question 5

How does H. influenzae overcome nonspecific mucociliary defenses?

Answer 5

OMP P2 and P5 promote binding to mucous

LPS - damages ciliated cells

Adhesins and Pili

IgA proteases

Question 6

How do uncapsulated strains of H. influenzae cause disease?

Answer 6

Direct movement of organisms to the site of infection.

E.g. sinuses, eustachian tubes, bronchi

Question 7

How is H. influenzae transmitted?

Answer 7

Person to person through respiratory droplets

Children 6-18 months are highest risk

Question 8

How is a H. influenzae infection diagnosed?

Answer 8

Blood culture in children with suspected disease

CSF, pleural fluid, and sputum cultures

Gram stain - gram negative

Question 9

What is H. influenzae treated with?

Answer 9

Third generation cephalosporins

Conjugated PROP vaccine

Antibiotic prophylaxis for close contacts with rifampin

Question 10

What are the three general mechanisms of antibiotic resistance?

Answer 10

Decreased entry

Altered target

Destroy antibiotic

Question 11

What is the major mechanism of antibiotic resistance in gram-negative pathogens?

Answer 11

B-Lactamases

Question 12

What are the main types of B-lactamases?

Answer 12

Penicillinases

Extended-spectrum B-lactamases - inactivates most except carbapenems

Carbapenemases

Question 13

What are three characteristics of all Clostridium?

Answer 13

Spore forming

Obligate anaerobes

Form toxins

Question 14

What is the mechanism of C. tetani toxin?

Answer 14

Travels to spinal cord and blocks glycine and GABA release by inhibitor neurons

Acts on Renshaw cells

Question 15

What are the symptoms of C. tetani infection?

Answer 15

Spasm, muscle contraction, rigidity

Classic: Lockjaw, Risus sardonicus (forced grin)

Question 16

What is the treatment for C. tetani?

Answer 16

Wound debridement

Metronidazole

Tetanus immune globulin

Benzos or NM blockers until toxin wears off

Question 17

What is the mechanism of Botulinum toxin?

Answer 17

Works at NMJ

Prevents ACh release, inhibiting muscle contraction

Results in flaccid paralysis

Question 18

What are the three types of botulism?

Answer 18

Food - toxin ingestion, undercooked food

Infant - spores, growth in infant intestine (contaminated honey)

Wound - infection with C. botulinum

Question 19

How does Botulism present?

Answer 19

Symptoms appear 12-48hrs after ingestion

3 D’s: Diplopia, dysphagia, dysphonia

Question 20

What is the treatment for botulism?

Answer 20

Antitoxin to block circulating toxin

Can’t block toxin already in nerves

Supportive care, toxin washout

Question 21

What is C. perferingens?

Answer 21

Widespread in nature/soil

Infects dirty wounds and causes food poisoning

Causes gas gangrene (clostridial myonecrosis)

Traumatic wound with vascular compromise

Question 22

What is alpha toxin?

Answer 22

Produced by C. perferingens

Destroys muscle tissue and causes hemolysis

Phospholipase that acts on lecithin and degrades cell membrane

Question 23

What is myonecrosis?

Answer 23

Necrotizing infection of muscle

Most often due to C. perfringens, C. speticum, C. histolyticum or C. sordellii

Usually associated with local trauma

Gas is always found in the skin

Question 24

How does myonecrosis present?

Answer 24

Severe pain at injury site within 24hrs

Skin tense and tender, fever, hypotension, shock

Diagnosis: gas at injury site on imaging, crepitus

Treatment: Surgical debridement plus BS antibiotics

Question 25

What differentiates food poisoning by C. perferingens and S. aureus/B. cereus?

Answer 25

Ingested spores of C. perferingens produce toxin, causing late onset (8-22 hours)

S. aureus has preformed toxin, early onset

Question 26

What is C. difficile?

Answer 26

Ubiquitous spores in nature

Ingestion not harmful with normal GI flora

Causes antibiotic-associated colitis - antibiotics alter normal gut flora

Non invasive disease via toxin

Question 27

What two toxins are produced by C. diff?

Answer 27

Toxin A - enterotoxin, watery diarrhea

Toxin B - Cytotoxin, cell necrosis/fibrin deposition

Both bind to GI cells and are internalized

Question 28

What is the presentation, diagnosis, and treatment for C. diff colitis?

Answer 28

Massive watery diarrhea

Stool detection of toxin A and B

Treat with metronidazole and oral vancomycin

Question 29

What is Listeria?

Answer 29

Found in soil

Facultative intracellular organism

Move from cell to cell to avoid extracellular response

In adults, from contaminated food

In neonates, transplacental or vaginal transmission

Question 30

What does Listeria cause?

Answer 30

Gastroenteritis - usually self limited

Meningitis - elderly or newborns

Infection in pregnancy causes bacteremia in 3rd trimester

Question 31

What is granulomatosis infantiseptica?

Answer 31

Severe in utero infection from Listeria

Disseminated abscesses and/or granulomas

Multiple organs affected

Most babies stillborn or dies soon after birth