Fastidious Gram-Negative Rods Flashcards
Module 2
What is the biology of Haemophilus influenzae?
a significant human pathogen; invasive strains are almost always encapsulated and type B; transmission is via respiratory route; gram stain is a pleomorphic gram-negative bacillus; they are fastidious and require one or both factors supplied by red blood cells
What factors does H. influenzae need?
X factor or V factor for growth
What do non-encapsulated strains of H. influenzae cause?
otitis media, bacterial conjunctivitis, and sinusitis
What diseases does H. influenzae cause?
prior to Hib vaccine it was most common cause of: meningitis in kids under 6, bacterial conjunctivitis, and bacterial epiglottitis; second most common cause of: otitis media in kids, and acute sinusitis; causes bronchitis, cellulitis, and pneumonia
H. influenzae Case Study
A couple brings their crying 6-year-old son to the ER; he is crying, holding his head, and repeatedly saying “it hurts”. He complained of an earache the night before, slept poorly, and refused to eat breakfast complaining both his ears and head hurt. He stayed home from school and became increasingly drowsy. He vomited twice in two hours and his temp is 101.8 F. On exam, he has a bulging left eardrum with pus behind it. His neck is stiff. The parents reveal he is healthy but has not yet completed his childhood vaccinations.
How do we test for H. influenzae?
take a specimen from respiratory, CSF, blood, or ear aspirate then culture (REQUIRES chocolate agar and CO2 enrichment) or use molecular detection
What other species of Haemophilus are relevant?
H. influenzae biogroup aegyptius, H. ducreyi, and H. parainfluenzae
What is H. influenzae biogroup aegyptius?
a species that causes pink eyes (purulent and contagious)
What is H. ducreyi?
agent of venereal disease chancroid (or soft chancre), with an ulcer on the genitals
What is H. parainfluenzae?
normal flora of the upper respiratory tract; accounts for 75% of H. flora in the oropharynx
What is the biology of Bordetella pertussis?
1) has an affinity for epithelial cells of nasopharynx and produces and exotoxin
2) small, gram-negative rods or coccobacilli
What diseases does Bordetella pertussis cause?
whooping cough mainly in infants and children that is highly communicable
How is Bordetella pertussis spread?
respiratory droplets; colonizes the mucous membranes of the respiratory tract; prevent through immunization
Bordetella pertussis Case Study
A 5-year-old male was brought to the ER with 10-day history of choking spells. The spells began with repetitive coughing and progressed to his turning red and gasping for breath. In the 2 days before, he had 3 episodes of vomiting during his choking spells. On physical exam, his pulse and respiratory rates were elevated. The chest X-ray was clear and there was no evidence of tracheal abnormalities. His WBC was elevated (16,000).
How do we test for B. pertussis?
take a specimen from nasopharynx (using calcium alginate or Dacron swab NOT cotton) then culture (requires Regan Lowe media and is a strict aerobe) or use molecular detection
What is the biology of Legionella pneumophila?
1) “pneumo” meaning lung and “philos” meaning loving
2) lives in aquatic environments
3) thin, gram-negative bacilli
4) causes Legionnaires disease
What diseases does L. pneumophila cause?
human infection is ‘chance infection’ via water distribution systems, serious pneumonia with possible involvement of kidneys, heart, and rectum
What are the risk factors for L. pneumophila?
smoking, heavy drinking, underlying illness like diabetes and immunosuppression, we see more often in males, mortality rate is 10-15%
How do we test for L. pneumophila?
specimen of respiratory tract or urine for antigen test then culture (on BCYE), use direct fluorescent antibody stain, molecular detection, or urine antigen test
What is the biology of Brucella spp.?
1) several pathogenic species
2) small, gram-negative coccobacilli
3) zoonosis (transmitted to man from an animal)
4) humans are infected by contact with animals
5) transmitted by ingestion of raw mild, direct contact, or inhalation
What are the pathogenic species of Brucella?
B. abortus which is found in cattle, B. melitensis which is found in goats and sheep, and B. suis which is found in pigs
What disease does Brucella cause?
undulant fever where symptoms include chills, fever, sweating, weakness, fatigue, and weight loss
How does Brucella spread?
it is an intracellular parasite that is ingested by circulating monocytes and is then transported to lymph nodes and then to spleen / liver
What is the biology of Francisella tularensis?
1) tiny, gram-negative coccobacilli
2) cottontail rabbit is a common reservoir
3) humans usually infected by direct cutaneous inoculation or from tick or deer fly bite
4) highly infectious, only requires 10-40 organisms to become infected
5) high morbidity
What disease does Francisella tularensis cause?
tularemia an acute, febrile disease characterized by rapid onset and flu-like symptoms; fever, chills, headache, myalgia (muscle pain), lymph node swelling, and ulcer at site of inoculation
How do we test for F. tularensis?
take a specimen then use serology or culture (requires special media)
What is the biology of Pasteurella multocida?
1) associated with animals; normal flora in their respiratory tract
2) gram-negative coccobacilli
What disease does Pasteurella multocida cause?
cellulitis with lymphadenitis, often from dog/cat bites or scratches
How do we test for P. multocida?
take a specimen from wound or blood culture then culture using sheep blood/chocolate agar
What is P. multocida susceptible to?
penicillin, this is odd for a gram-negatitve rod
What is another way to think about fastidious gram-negative rods?
Haemophilus and the Ellas
How can we distinguish between the rods?
Legionella = typically longest
Brucella = short rod
Francisella = so small it looks like a dot
