Bacterial Pathogens Flashcards
To learn Forgie's bugs.
Haemophilus influenzae
- Small gram negative bacilli.
- LOS endotoxin.
- Outer membrane protein (OMP) and fimbriae for adhesion.
- IgA protease.
What is the difference between typable H. influenzae and non-typeable (ntHi) H. influenzae?
Typeable forms have a capsule which make them capable of bloodstream invasion. The capsule makes them resistant to phagocytosis. The ntHi lack this capsule and cannot cause bloodstream infection.
Which is the most dangerous type of H. influenza?
Haemophilus influenzae type B (HiB).
What are some of the clinical symptoms of typeable H. influenzae?
- Usually result from HiB.
- Bacteremia
- Meningitis
- Pneumonia (cough, fever, purulent sputum)
- Cellulitis
- Epiglottitis
What are some of the clinical symptoms of non-typeabe H. influenzae?
Nonencapsulated H. influenzae.
- Sinusitis & otitis media
- Pneumonia
- Purulent conjunctivitis (pink eye)
How is H. influenzae diagnosed?
Bacterial cultures from blood, sputum, and CSF. H, influenzae requires factor V and X from RBC for growth. Must be cultured on chocolate agar.
What drugs would be given to treat H. influenzae?
Amoxicillin - Clavulanate
or
Cefotaxime / Ceftriaxone
Staphylococcus aureus
- Gram positive cocci in clumps (grapes).
- Aerobic
- Protein A (prevent opsonization), coagulase, and catalase.
- Hyaluronidase, staphylokinase, lipase, and protease.
- Hemolysins, exfoliatin, enterotoxin, toxic shock (TSST-1).
What is the function of staphylokinase?
It breaks down blood clots allowing staphylococcus aureus to escape and spread from clots.
What does exfoliatin do?
It results in blistering on the skin known as “scalded skin syndrome”.
What does TSST-1 stand for? What bacteria causes it?
Toxic Shock Syndrome Toxin 1. It is released by staphylococcus aureus.
How is staphylococcus aureus infection diagnosed?
Swabs are taken from affected sites for gram stain and culture growth (Gram +ve cocci in bunches).
How is staphylococcus aureus treated?
- Drain any abscesses.
- Cloxacillin, first generation cephalosporins, clindamycin.
- MRSA is typically treated with vancomycin.
Describe the possible clinical presentations of S. aureus.
- 25% of people are asymptomatic carriers.
- Direct infections (folliculitis, impetigo, cellulitis, furuncles, carbuncles, abscesses).
- Bloodstream infections with abscesses forming due to seeding of distant sites.
- Several toxin mediated syndromes (food poisoning, scalded skin syndrome, toxic shock syndrome).
How is S. aureus spread?
Through droplet or direct contact.
How is H. influenzae spread?
Through direct contact.
Streptococcus pneumoniae
- Gram positive diplococci.
- Aerobic
- > 95 different polysaccharide capsules.
- IgA protease & Adhesins
What are some of the clinical presentations of Strep. pneumoniae?
- Pneumonia (fever, cough, purulent rusty sputum).
- Meningitis
- Otitis media (bulging gray or yellow tympanic membrane)
- Sinusitis
How is Strep. pneumoniae diagnosed?
Clinically, X-Ray, sputum, CSF and blood for gram stain and culture.
How is Strep. pneumoniae treated?
- High dose ampicillin or second generation cephalosporin.
- For meningitis vancomycin and cefotaxime should be given until CSF culture and sensitivity are returned.
Where is asymptomatic Strep. pneumoniae carried in humans?
The nasopharynx. Upto 50% of people are asymptomatic carriers of Strep. pneumonia.
Streptococcus pyogenes
- Gram positive cocci in chains.
- Aerobic
- Hyaluronic capsule.
- M protein, Protein F, DNase, hyaluronidase, SPE.
What are protein F, M protein, and SPE in the context of strep pyogenes?
Protein F: functions in adhesion.
M Protein: functions in adhesion and inhibits complement activation {MAJOR virulence factor}.
SPE: Strep pyrogenic exotoxin.
How is Strep. pyogenes spread?
Through direct contact or droplets.
Describe the clinical presentation of strep. pyogenes.
- Superficial: Impetigo, erysipelas, pharyngitis.
- Deep: Necrotizing fasciitis, bacteremia.
- Post streptococcal syndromes: acute rheumatic fever, glomerulonephritis, scarlet fever.
What are two symptoms of scarlet fever?
Sandpaper rash and strawberry tongue.
What is a symptom of post strep glomerulonephritis?
Tea coloured urine.
How is strep. pyogenes treated?
Penicillin, amoxicillin, erythromycin, first generation cephalosporin, TMP/SMX, and clindamycin are all effective.
How is strep. pyogenes diagnosed?
Swabs for gram stain or culture. The primary reason for treating strep throat is to prevent rheumatic fever.
What are some symptoms of rheumatic fever?
Arthritis, carditis, subcutaneous nodules, erythema marginatum, and chorea (neurological disorder resulting in quick jerky movements of the face and shoulders).
Bordetella pertussis {Whooping cough}
- Small gram negative bacillus.
- Aerobic
- Polysaccharide capsule.
- Filamentous hemagglutinin, fimbriae and pertactin for adhesion.
- PERTUSSIS TOXIN, adenylate cyclase toxin, tracheal toxin, dermonecrotic toxin, hemolysin.
What three stages present during most bordetella pertussis infections?
Catarrhal stage: Runny nose, low fever, cough.
Paroxysmal stage: coughing, mucous pooling in airways, fits of coughing {WHOOPING COUGH in children}.
Convalescent stage: Intermittent fits of coughing and possible secondary bacterial infections.
How does bordetella pertussis spread?
Droplet transmission between humans.
How is bordetella pertussis diagnosed?
Nasopharyngeal aspirate for DFA, PCR, and culture.
How would you treat bordetella pertussis?
- Macrolides will reduce the duration of symptoms and infectivity of the host.
- TMP/SMX
Clostridium botulinum
- Gram positive bacillus.
- Anaerobic.
- Botulinum toxin and spore formation.
How is Clostridium botulinum spread?
Spores are found in soil and water and subsequently contaminate meats, vegetables, and fish.
How is C. botulinum diagnosed?
- NO fever with descending symmetrical paralysis.
- Normal sensation and consciousness.
- Anaerobic cultures and toxin assay of serum, stool, and food.
How is C. botulinum treated?
- Supportive care with artificial ventilation.
- Trivalent antitoxin (against toxin types A,B,E).
- Penicillin antibiotics are effective against wound and infant botulism.
How does C. botulinum present clinically?
1) Generalized botulism (intoxication).
- Muscle weakness, diplopia, difficulty swallowing, speech problems, symmetrically descending paralysis. No fever, no sensory issues, and normal LOC.
2) Wound botulism.
- Wound directly contaminated with spores causes paralysis of limb. May result in generalized botulism.
3) Infant botulism.
- Ingestion of spores followed by poor feeding and then paralysis.
Clostridium difficile
- Gram positive bacillus.
- Anaerobic
- Exotoxins A & B.
- Spore formation.
- Flagella (H antigen)
How is C. difficile spread?
Through spores and fecal-oral transmission.
5% - 10% carry C. difficile asymptomatically.
How does C. difficile present clinically?
Pseudomembranous colitis may occur up to 10 weeks after an antibiotic course. Symptoms include (possibly bloody) diarrhea, fever, abdominal pain & cramping. Toxic megacolon may occur.
How is C. difficile diagnosed?
Diarrheal stool toxin assay & endoscopy for possible pseudomembranes.
How is C. difficile treated?
Stop offending treatments (antibiotics) and start oral metronidazole. Oral vancomycin is the secondary line of therapy.
Clostridium tetani
- Gram positive bacilli.
- Anaerobic
- Tetanus toxin, spore formation, flagella (H antigen), and hemolysin.
How is Clostridium tetani spread?
- Spores are found in soil and water. It may also be found in the GIT of both humans and animals.
- Wounds or bites may inoculate the spores into damaged tissue.
How does Clostridium tetani present clinically?
- Muscle spasm near the wound, 1-2 weeks later lockjaw or trismus occurs. Gradual involvement of other facial, and later body, muscles.
- Neonatal tetanus has very high mortality and presents with fever, rigidity, and weakness.
How is Clostridium tetani diagnosed?
Strychnine poisoning is in the differential. Many patients will not remember the dirty wound. Dental infections may cause trismus but the dental infection can be found and other symptoms will not be present.
What is trismus?
Reduced opening of the muscles of the jaw - lockjaw.
How is Clostridium tetani treated?
- Secure airway (cABC).
- Strychnine blood level.
- Wound history and possible debridement.
- Immunization status.
- Start TIG (tetanus immune globulin).
- Tetanus toxoid vaccine.
- Metronidazole
Corynebacterium diphtheriae
- Gram positive club shaped bacillus.
- Aerobic
- Does not have a capsule.
- Diptheria toxin (if infected with lysogenic phage).
- Storage granules (containing phosphate for energy).
How is Corynebacterium diphtheriae spread?
Respiratory droplets of direct contact with skin discharge from an infected patient or carrier.