Garlanda 2 Flashcards
what should you consider when giving antimicrobial drugs
- spectrum of action
- growth of microbial populations
- phases of microbial growth
susceptibility testing can be done
qualitatively, semiquantitatively, or using nuclei acid based methods
what is synergy testing
testing to determine the effect of combining different antimicrobials
3 tests for antimicrobial testing
- diffusion susceptibility test (aka kirbey bauer)
- Min inhibitory concentration test
- Min bactericidal concentration test
how are results of qualitative tests given
susceptible (S)
intermediate (I)
resistant (R)
what influences results of qualitative methods
pharmacokinetic, pharmacodyniamc, clinical and microbiological data
Eg of synergism between two antimicrobial agents
amoxillin-clavulanic acid and aztreonam
MIC test
is broth dilution test, where a standard amount of microorganisms are incubated with serial diluation of antimicrobial agents. the turbidity indicates bacterial growth
How are results of MIC given
sensitive (s)
intermediate (i)
resistant (r)
nonsusceptible
what is the Etest
it combines diffusion susceptibility and MIC tests (A plastic strip contains a gradient of the drug of interent). note that multiple antimicrobials can be tested at once on one plate
what is MBC test
A semiquantitative space/ Where
samples from clear MIC tubes are tranferred in drug free growth medium. Broth dilution is the godl standard. It is used to discriminate bactericidal from bacteriostatic concentration of a drug
nucleic acid based methods are for
detecting known resistance genes.
E.g. mecA and mecC for oxacillin resistant in S. aureus. (if present then its resistant to most B lactam drugs)
- carbapenemase genes in carbapenem resistant enterobactericeae
the present of resistant genes means they uniformely confer in vivo resistance T/F
F
nucleic acid methods are preferred for diagnosis of MDR TB
t
define bacterial persistence
is when persistent cells do not proliferate in the presence of bactericidal agent, they are temporarily in a slow or non growing state, they are tolerant to bactericidal antibiotics. This contributes to the failure to treat chronic and relapsing infections
Steps of bacterial persistance
(1) Bacterial persisters can arise stochastically in unstressed bacterial cultures.
(2) Environmental insults (i.e., starvation, oxidative and acid stress, heat shock)
provoke persister cell formation.
(3) Social engagement through quorum sensing promotes persister cell formation.
(4) Heterogeneous and diffusion-limited biofilm microenvironments enhance
persistence.
(5) Host-pathogen interaction also induces formation of persisters.
what is cross resistance
it occurs when drugs are similar in structure, and the resistance to one drug confers resistance to a similar drug
what are the 3 types of media for culturing viruses
- media with mature organisms
- embryonated eggs
- cell cultures
recognition of viral growth in cell culture is done with
- cytopathic effect (morphological changes), inclusion bodies
- hemadsorption
explain the cytopathic effect
a syncytium formation can occur in the case of measles virus, or there than be inclusion bodies present in a rabies patient
know difference btw hemadsorption and hemagglutination
hemadsorption is when a virus infects cells expressing hemaglutinin and RBC’s attach to it
Hemagglutination is when RBC clump together into a lattice formation
which viruses use enzyme immunoassay
EBV, HEPB, HEPE, HIV, human T lymphotropic virus
serological tests are for which viruses
hepA and hepD
nucleic acid based test are used for which viruses
HIV
immunological tests use
antigens or antibodies (note that if the testing is delayed the specimen should be frozen or refrigerated to prevent overgrowth)
which antibody rises first
IgM (IgG is the longer lasting one)
serological tests are used to
monitor the spread of infection within a population, and establish the diagnosis of a disease
spectrum of action definition
the # of different pathogens a drug acts against
name a narrow spectrum drug
penicillin
name a broad spectrum drug
tetracyclin
Steps of binary fission
chromosome replication
cell elongation, chormosomes pushed apart
new cytoplasmic wall/septum
cell separation or cluster
phases of microbial growth
lag (adaptation to new environment)
log (is the target for drugs, metabolic rate is high)
Stationary phase (the pop size is constant bc nutrients are depleted and wastes accumulate. Metabolic rate declines)
Death phase (cells die at a faster rate than they are produced)
T/F susceptibility tests always predicts tx outcome
F
what is synergy testing
testing to determine the effect of combining different antimicrobials
MIC explained
same amount of bacteria is given different amount of antimicrobial. And then turbidity is tested to evaluate bacterial growth
The major limitation for conventional AST
is the low sensitivity since they sense the change in bacterial pop but measuring optical density
MIC is mainly used for
isolates of bacterial, including mycobacteria, anaerobes, fungi esp Candida
T/F MIC can tell you the achievable tissue concentration of the free drug
T
Designations of S, I, and R derived from the MIC study correlate
with achievable serum, plasma, or urine concentrations of free
drug.
microfluid techniques
microfluidic systems made it possible to
push the time requirements for culture-based ASTs to 1–3 h by
minimizing the bacterial incubation chamber to the single-cell level
and increasing the signal to background ratio in detecting the
variation of proteomes, metabolomes, genomes and/or
transcriptomes.
• The only information needed to determine antibiotic susceptibility
is whether the pathogen is dividing after the antibiotic is added.
• Therefore, some microfluidic-based methods have been developed
to observe bacterial division at early stages.
• The physical confinement of the pathogen in micro-channels allows
rapid ASTs on a time scale comparable to the doubling time of the
bacteria.
Microfluidic technologies for rapid antibiotic susceptibility tests (ASTs) at
the single-cell level, including both phenotypic analysis (microfluidic-based
single bacterial culture) and gene-based antimicrobial resistance (AMR)
detection (droplet digital analysis).
