Gram+ and Gram- Structures Flashcards
A 2 year old girl is brought to the ED. She is lethargic and has a fever of 105 F. Blood cultures reveal gram positive alpha-hemolytic cocci that are sensitive to optochin. Which of the following virulence factors is contributing to this girl’s illness?
A. Escherichia coli lipopolysaccharide
B. Depurinating exotoxin
C. O-acetylated peptidoglycan
D. Staphylococcal protein A
E. Streptococcal superantigen
C.
Streptococcal pneumoniae is a gram+ diplococci organism that is optochin-sensitive, which is useful in distinguishing it from optochin-resistant strains such as Strep Viridans. Its main virulence factors are its antiphagocytic capsule and o-acetylated peptidoglycan, which is highly inflammatory, collects in joints, and is difficult for the body to degrade.
(Superantigens, on the other hand, are proteins secreted by staph aureus and strep pyogenes that cause toxic shock syndrome - a massive cytokine sharknado resulting in high fever, hypotension and rash.)
most common cause of meningitis (green-cap meningitis)
strep pneumoniae
this iron-containing enzyme is present in high concentrations in neutrophilic granules and is a major host defense against extracellular bacteria
myeloperoxidase (MPO)
this is what makes the green color in strep related meningitis - it is the oxidation state of iron in damaged tissues
All of the following are true of gram-positive bacterial cells EXCEPT:
A. they usually contain a polysaccharide antiphagocytic capsule
B. they contain a thick highly bridged peptidoglycan layer of N acetyl glucosamine and N acetyl muramic acid
C. they contain an outer membrane composed of teichoic and lipoteichoic acid
D. they have haploid chromosomes and episomes
E. pathogenic cocci do not have flagella
C.
These cells contain the adhesins teichoic acid and lipoteichoic acid as a component of their cell walls, but do not have an outer membrane.
pieces of foreign DNA, which were once bacteriophages but no longer move around, that carry genes of virulence
pathogenicity islands
most gram+ cells’ antiphagocytic capsules are polysaccharides, with this notable exception, which has a poly D-glutamic acid capsule
bacillus anthracis
an example of fimbria, this protein resides on the surface of group A strep bacteria, creating a fuzzy later that aids in adhesion to host tissues
M protein (or other MSCRAMMs)
this motile gram+ rod causes neonatal and fetal sepsis and meningitis
listeria monocytogenes
All of the following are true of spores EXCEPT:
A. they are an inert, heat, and dry resistant gram+ structure
B. they are found in Clostridium under aerobic conditions and Bacillus under anaerobic conditions
C, they secrete tetanus toxin during their vegetative state
D. they produce an exotoxin so toxic that it must be biologically inactivated as an immunogenic toxoid in order to vaccinate
E. they contain dipicolinic acid and Ca++ in their coating to confer resistance
B.
The opposite is true. See picture below of Clostridium tetani spores. Note their tennis racket appearance.
identify the organisms shown below:
bacillus spores
All of the following are true of Streptococcal pneumoniae EXCEPT:
A. its capsule is a target for vaccines
B. it is an extracellular pathogen and cannot live inside a PMN
C. along with Haemophilus influenzae it is the most common cause of otitis media
D. it is considered a two-dimensional pathogen, in that it both makes a toxin and has other disease-causing characteristics
E. it belongs to a strain of organisms that is more invasive than stapholococcus
D.
This is true of staph aureus. Strep pneumoniae is a one-dimensional pathogen whose major virulence factor is its capsule.
All of the following are true of Neisseria meningitidis EXCEPT:
A. contains an antiphagocytic capsule
B. may cause gram-negative shock
C. has pili for attachment to host cells
D. its endotoxin binds the TLR2 receptor to promote the secretion of inflammatory cytokines
E. contains lipid A as part of its cell wall
D.
N. meningitidis contains the endotoxin LPS as part of its cell wall, which uses TLR4 as its receptor, promoting the recruitment of highly inflammatory cytokines.
Gram+ bacteria contain LTA peptides that interact with TLR2.
When gram- bacterial cells are lysed by the immune system, fragments of their cell walls containing this highly toxic component are released into systemic circulation, causing fever, diarrhea, and endotoxic shock
lipid A (LPS/LOS)
During a meningitis outbreak at a school, all students were immediately vaccinated against the offending organism, N. meningitidis group C, including one affected student, who very shortly later died. Why did this vaccine not protect the patient?
IgM takes 4-5 days to appear in circulation after initial pathogen exposure
what is the current national protocol for managing meningitis outbreaks?
vaccination AND the antibiotic rifampin, which inhibits bacterial RNA synthesis and has good mucosal penetration
Note: meningitis is spread by intimate contact and cannot be aerosolized
