Gram- Rods [Part II] (Kirn) - 4/27/16 Flashcards
*Note: these Gram- Rods are not GI related but occur in people who are immunocompromised or have issues with innate/adaptive immune system
What are the three major categories of these pathogens and examples of each?
- Respiratory pathogens:
- Haemophilus
- Bordetella
- Legionella - Zoonotic
- Brucella
- Pasteurella
- Francisella
- Yersinia - Opportunistic
- Pseudomonas aeruignosa
Respiratory pathogen: Haemophilus influenzae
Special growth requirements
- NAD + hemin
- Chocolate agar (lysed blood cells)
Slender, pleiomorphic Gram- rods
Only colonizes/infects humans
Common in upper respiratory tract (unencapsulated) –> middle ear, sinuses, lungs
Spread by respiratory route
Virulence factors: Capsule, IgA protease, Fe acquisition mechanisms
Diseases:
- Otitis media
- Sinusitis
- Severe URT infection (epiglottitis)
- Pneumonia
- Meningitis
- Septic arthritis
Respiratory pathogen: Bordetella pertussis
Only colonizes/infects humans
Survives for only short periods in environment (basically someone has to cough on you) –> transmitted by coughing [spread by respiratory route]
2 week incubation Highly infectious, cold like prodrome, followed by period of paroxysms of coughing - Inspiratory "whoop" - Whooping cough - Vomiting, cyanosis, convulsions
Virulence factors: adhesins (promote attachment and prevent clearance by phagocytes)
- Filamentous hemagglutinin - binds integrins on ciliated epithelial
- Fimbriae - phase variation
- BrkA protein - complement resistance
Virulence factors: toxins (impair local clearance, systemic effects)
- Tracheal cytotoxin - stimulates IL-1 mediated killing of ciliated epithelial cells
- Adenylate cyclase toxin - inhibits phagocyte function
- Pertussis toxin - system effects such as lymphocytosis, sensitization to histamine and enhanced insulin secretion
Prevention:
- 3 component vaccine: DTwP (Diphtheria,
Tetanus, Whole cell pertussis)
- Due to concerns about reactogenicity, an acellular vaccine is currently used: DTaP - Diphtheria, Tetanus, acellular pertussis)
Respiratory pathogen: Legionella pneumophila
Causes respiratory infection in humans but unlike Haemophilus and Bordetella, it is acquired from an ENVIRONMENTAL source
Growth requirements:
- Highly fastidious
- BCYE agar (Buffer, charcoal, yeast extract, iron, cysteine, antibiotics)
Slender Gram- rod
Hard to see in stained sputum smears
Direct fluorescent antibody stain (limited utility)
Urine Ag test helpful for Serotype 1 infection
- Natural habitat: water
- Heavily colonizes warm bodies of water in the environment as well as potable (safe to drink) sources
- Multiples in protozoan (amoebae) host and in macrophages (actively blocks phagosome/lysosome fusion)
- Usual source of exposure is aerosal from water supply (A/C, water taps, shower heads)
- Hyperchlorination and high heat required to control growth
What are zoonoses?
Characteristics of zoonotic bacteria?
Pathogens transmitted from animals - directly or by insect vector (these come from LIVE animals.. not food) - do they have animals at home? Have they traveled to another country recently?
- Small, gram- rods or coccobacilli
- Little or no human to human transmission
- Multiply in phagocytes
- Some highly virulent
- Possible agents of bio-terrorism
Zoonotic: Brucella
- Small, gram- coccobacillus
- Source: livestock, unpasteurized dairy
- Systemic febrile illness
- Poses a significant threat to lab workers (can contract from holding agar plate too close to face)
Zoonotic: Pasteurella multocida
- Small, gram- coccobacillus
- Normal oral flora of domestic animals (cats and dogs)
- Causes “snuffles” (respiratory infection) in rabbits
- Infection associated with animal bites (wound infection)
- Rapidly progressive soft tissue infection
- Can disseminate widely
Zoonotic: Francisella tularensis
- Small, gram- coccobacillus
- Transmission from wild animals, especially rabbits (but no “snuffles”), by direct contact or via insect vector
- Very infectious
- High risk to lab workers (but only when its isolated on plates) but little human to human contact
Disease:
- Ulceroglandular lesion (broken skin contact)
- Oculoglandular lesion
- Oral or pharyngeal (Contaminated food)
- Respiratory infection (Aerosol inhalation)
Zoonotic: Yersinia pestis
Cause of bubonic plague (multiplies in lymph nodes which become enlarged –> buboes –> bacteria then spread to blood, lungs, and meninges… staining looks like safety-pin)
Transmitted from rodents to human by FLEA BITE
Transmission:
- Bacteria feed on blood in flea gut, secrete enzyme that causes blood to clot
- When flea feeds on human, intestinal blockage forces regurgitation of blood from prior meal
- Bacteria enter human host through bite wound
Virulence:
- Phagocyte paralysis
- Fe acquisition
- Capsule
Opportunistic: Pseudomonas aeruginosa
Ubiquitous in environment
- Present in soil, water, vegetation, biotic and abiotic surfaces
- Biofilm (bunch of bacteria living together - function like a multicellular organism in that the bacteria in the middle of the film do different things than the bacteria at the edge of the film)
- Opportunistic pathogen
- Multiple mechanisms of antimicrobial resistance
Gram- rod, polar flagella
Obligate oxidizer (doesn’t ferment anything), no acids from sugars on test media
Many isolates produce siderophores (pyoverdin)
Disease:
Community acquired infections in immunocompetent people
- Hot tub folliculitis, otitis externa (outer ear)
Nosocominal infections
- Burn victims, Intubated patients
Cystic fibrosis
- Chronic respiratory infection
Virulence factors:
- Extracellular polysaccharide
- Pili
- LPS
- Extracellular enzymes
- Exotoxin A
- Type III Secretion system
Other Gram Negative Rods:
Burkholderia spp.
- Burkholderia cepacia complex
- Burkholderia mallei
- Burkholderia pseudomallei
Stenotrophamonas maltophilas
Acinetobacter
