HACEK Pathogens Flashcards
What are the HACEK pathogens?
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
Describe Haemophilus Influenzae
Colonizes URT in the first few months of life
Requires blood factors for growth
Capsulated or Uncapsulated
Which strains of H. influenzae cause mucosal surface infections?
Uncapsulated or non-typable
Localized infections
OM, sinusitis, bronchitis and pneumonia
Which strains of H. influenzae cause invasive disease?
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
How does H. influenzae overcome nonspecific mucociliary defenses?
OMP P2 and P5 promote binding to mucous
LPS - damages ciliated cells
Adhesins and Pili
IgA proteases
How do uncapsulated strains of H. influenzae cause disease?
Direct movement of organisms to the site of infection.
E.g. sinuses, eustachian tubes, bronchi
How is H. influenzae transmitted?
Person to person through respiratory droplets
Children 6-18 months are highest risk
How is a H. influenzae infection diagnosed?
Blood culture in children with suspected disease
CSF, pleural fluid, and sputum cultures
Gram stain - gram negative
What is H. influenzae treated with?
Third generation cephalosporins
Conjugated PROP vaccine
Antibiotic prophylaxis for close contacts with rifampin
What are the three general mechanisms of antibiotic resistance?
Decreased entry
Altered target
Destroy antibiotic
What is the major mechanism of antibiotic resistance in gram-negative pathogens?
B-Lactamases
What are the main types of B-lactamases?
Penicillinases
Extended-spectrum B-lactamases - inactivates most except carbapenems
Carbapenemases
What are three characteristics of all Clostridium?
Spore forming
Obligate anaerobes
Form toxins
What is the mechanism of C. tetani toxin?
Travels to spinal cord and blocks glycine and GABA release by inhibitor neurons
Acts on Renshaw cells
What are the symptoms of C. tetani infection?
Spasm, muscle contraction, rigidity
Classic: Lockjaw, Risus sardonicus (forced grin)
What is the treatment for C. tetani?
Wound debridement
Metronidazole
Tetanus immune globulin
Benzos or NM blockers until toxin wears off
What is the mechanism of Botulinum toxin?
Works at NMJ
Prevents ACh release, inhibiting muscle contraction
Results in flaccid paralysis
What are the three types of botulism?
Food - toxin ingestion, undercooked food
Infant - spores, growth in infant intestine (contaminated honey)
Wound - infection with C. botulinum
How does Botulism present?
Symptoms appear 12-48hrs after ingestion
3 D’s: Diplopia, dysphagia, dysphonia
What is the treatment for botulism?
Antitoxin to block circulating toxin
Can’t block toxin already in nerves
Supportive care, toxin washout
What is C. perferingens?
Widespread in nature/soil
Infects dirty wounds and causes food poisoning
Causes gas gangrene (clostridial myonecrosis)
Traumatic wound with vascular compromise
What is alpha toxin?
Produced by C. perferingens
Destroys muscle tissue and causes hemolysis
Phospholipase that acts on lecithin and degrades cell membrane
What is myonecrosis?
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
How does myonecrosis present?
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
What differentiates food poisoning by C. perferingens and S. aureus/B. cereus?
Ingested spores of C. perferingens produce toxin, causing late onset (8-22 hours)
S. aureus has preformed toxin, early onset
What is C. difficile?
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
What two toxins are produced by C. diff?
Toxin A - enterotoxin, watery diarrhea
Toxin B - Cytotoxin, cell necrosis/fibrin deposition
Both bind to GI cells and are internalized
What is the presentation, diagnosis, and treatment for C. diff colitis?
Massive watery diarrhea
Stool detection of toxin A and B
Treat with metronidazole and oral vancomycin
What is Listeria?
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
What does Listeria cause?
Gastroenteritis - usually self limited
Meningitis - elderly or newborns
Infection in pregnancy causes bacteremia in 3rd trimester
What is granulomatosis infantiseptica?
Severe in utero infection from Listeria
Disseminated abscesses and/or granulomas
Multiple organs affected
Most babies stillborn or dies soon after birth
