Lecture 8: Molecular Applications to Infectious Diseases Flashcards
Applications of Molecular
Analyses to Infectious Diseases…
- Qualitative detection
- Quantitative detection
- Microbial “identity” testing
- Genotyping/drug resistance
What are the controls used for PCR?
- Positive control: positive template
- Negative control: negative template
- Amplification control: omnipresent template unrelated to target
- Reagent blank: no template present
Advantages of Molecular Detection of Resistance to
Antimicrobial Agents…
- Mutated genes are strong evidence of resistance
- Rapid detection without culturing
- Direct comparison of multiple isolates in epidemiological
investigations
A molecular marker for identification of bacterial species***
-this gene (1,500 bp) is large enough for informatics purposes
16S rRNA
presence in almost all bacteria, often existing as a multigene family, or operons;
16S rRNA
the function of the 16S rRNA gene over time has not changed, suggesting that random sequence changes are a more accurate measure of _____________
time (evolution)
Overall, between 16S gene based and clinical identities, the study shows a
genus-level concordance rate of ___% and a species-level concordance rate of
____%.
96
87.5
The use of ______ gene sequencing in the clinical laboratory is becoming commonplace for identifying biochemically
unidentified bacteria or for providing reference identifications
for unusual strains
16S rRNA
What is pitfall with 16S rRNA gene sequencing?
- it has low phylogenetic power at the species level and poor discriminatory power for some genera
- For bacteria that are difficult to grow or identify
What is the “gold standard”
for proposed new species and for the definitive assignment of a strain with ambiguous properties to the correct taxonomic unit?
DNA-DNA hybridization
rapidly spreading outbreak of an infectious disease
Epidemic
a disease that sweeps across wide geographical areas
Pandemic
collection and analysis of environmental,
microbiological, and clinical data
Epidemiology
- An opportunistic, toxin-producing bacterial pathogen of the
gastrointestinal tract. - The most common cause of healthcare-associated diarrhea
Clostridum Difficile Infection
(CDI)
C difficile causes ___% to ___% of antibiotic-associated diarrhea and _____ % of pseudomembranous colitis cases.
25-30
> 95
Incidence has almost doubled since 1996, and the mortality rate is rising owing to emergence of a hypervirulent strain.
(027/NAP1/B1)
Clostridum Difficile Infection
Disease-causing C difficile strains produce 1 or both of 2 toxins, that are…
Toxin A is an enterotoxin and toxin B is a cytotoxin***
How do the C difficile toxins induce damage?
The toxins destroy cells and produce patches (colonized plaques) of inflammatory cells and decaying cellular debris inside the colon and
cause watery diarrhea
Ture or false:
other stains of C. diff produce neither toxin and are thought to colonize the colon without causing disease
true
What are the two different testing options for the detection of C difficile?
- An immunoassay to simultaneously assess for toxin and glutamate
dehydrogenase(GDH) as the presence of C. difficile antigen (sensitivity) - Nucleic acid amplification tests (NAAT) for C difficile toxin genes (test
code 16377).(Specificity)
Staphylococcal resistance to oxacillin/methicillin occurs when an isolate produces an altered penicillin-binding protein, PBP2a, which is encoded by the______ gene
mecA
-The variant penicillin-binding protein binds beta-lactams with lower avidity, results in resistance to this class of antimicrobial agents.
Strains that are oxacillin and methicillin resistant, historically termed methicillin-resistant S. aureus (MRSA), are resistant
to all __________.
ß-lactam agents
What is the antibiotic resistance gene?
mecA
What are tests for MRSA?
-Cefoxotin disk screen test
-Nucleic acid amplification tests, such as the polymerase chain
reaction (PCR (to detect mecA gene)
