MICROM 442 ch 8-10 Flashcards
-broth microdilution
-disk diffusion
-gradient strips (Etests)
phenotypic testing methods
-PCR
-Sequencing
genotypic testing methods
-antibody-based detection (lateral low immunochromatographic assays)
-microscopy + machine learning
other testing methods
-“gold standard”
-double dilutions of antibiotics in each well + standard inoculum of bacteria into each well
-measure MIC e.g. 2µg/mL
broth dilution
-automated, high-output formats for clinical testing
-multiwell can fit many antibiotics
-colorimetric or fluorescent indicators to read bacterial growth
-instruments with automated readers»>
Antibiotic susceptibility testing (AST)/phenotypic -> broth microdilution
-bacteria lawn
-nitrocellulose strip with continuous gradient of bacteria
-measure MIC where ellipse of growth inhibition meets the strip
-interpret MIC according to same ranges as broth dilution
AST/phenotypic -> gradient strips (Etests)
-bacterial lawn
-paper disks with antibiotic placed on top
-antibiotics diffuse into agar
-standard single concentration used for each antibiotic
-does NOT give MIC
-does give S, I, R
AST/phenotypic -> disk diffusion
-for genes with good predictive value ie correlate with phenotypic
-look for presence/abscence of resistant gene
-vanA and vanB for VRE
-mecA for MRSA
-look for presence/absence of mutation associated with resistance e.g. rpoB for rifampin-resistant mycobacterium tuberculosis
AST/genotypic -> PCR
genotypic methods struggle more with predicting MIC which is
sometimes neeeded for theraputic dosing
sometimes genotype does not easily predict phenotypic resistance in particular
GN organisms may harbor multiple, complicated, resistance mechanisms including mutations involving membrane permeability
-to detect PBP2a from staphylococcus aureus
-mecA encodes PBP2a
-PBP2a positive = MRSA
-quick results directly from colony
antibody-based detection -> (lateral flow immunochromatographic assays)
-image bacteria challenged with antibiotic
-use machine learning to correlate growth patterns with susceptibility or resistance
digital microscopy
standardization for accurate AST determined by:
-FDA
-clinical & laboratory standards institute
-European committee on antimicrobial susceptibility testing
Reproducibility between labs and methods
-strict quality control standards
-guidelines for variable like media, drug concentration, incubation conditions (metabolism effects)
Ranges determined by many factors:
-pharmocokinetic/pharmacodynamic parameters
-site of infection (eliminated/spread differently)
wild-type MIC conditions
-clinical outcome studies (expected survival of patient at certain MIC)
-re-reviewed and revised every so often
site of infection
-some drugs [x] in urine
-some drugs inactivated by surfactants in the lungs
-some drugs are better/worse for penetrating the blood brain barrier
treatment considerations
-administration
-therapeutic drug monitoring informs dosing
-interxns with other drugs
-toxic side effects
-coverage for infections with multiple organisms
-site of infection
-allergies
administration
inhalation, topical, IV, oral
toxic side effects
-nephrotoxicity (kidneys)
-ototoxicity (deafness)
empiric therapy
broad-spectrum antibiotics
targeted therapy
narrow-spectrum antibiotics
meropenem is a
broad-spectrum antibiotic
ampicillin is a
narrow-spectrum antibiotics
local antibiograms can help
guide empiric treatment and are HOSPITAL SPECIFIC
antibiograms track
% susceptibility for the most common organisms
other treatment considerations:
SOURCE CONTROL
-surgically draining an abscess
-removing infected hardware (prosthetic devices, catheters, central lines, BIOFILMS!!)
-removing infected tissue (necrotic tissue + amputation)
Infections prevention and control
major hospitals have formal infection prevention and control programs led by nurses and physicians with certification or special training
tracking hospital-associated infections
-hospital environment
-patient to patient or patient to employee
-hospital procedures
standard precautions
-hand hygiene, disinfection, PPE
transmission-based precautions
-isolation and contact precautions
-resistant organism screen
-VRE, MRSA, multi-drug resistant organisms
surveillance and public health
-tracking and surveillance
-outbreak investigations -> contact tracing and sequencing
-diagnostic testing
higher rates of enerobacteriales bacteria in…
areas with lower median incomes, lower high school education diplomas, less insurance coverage, limited English proficiency
IMP
imipenem-resistant metallo-beta-lactamase
cefiderocol has a
siderophore portion which binds free iron
gram positive cocci (GPC)
-most form chains
-diplococci
-bullet-shaped/ lancet shaped
GPC
-aerotolerant anaerobe
-obligate fermenter
-does not respire only ferments
catalase negative
distinguish from other GPC
species differentiation of GPC
-hemolysis on blood agar
-cell wall (lancefield) antigens
-biochemical tests, antimicrobial susceptibility, etc.
streptococcus
alpha-hemolysis -> GREEN
-viridans group streptococci common normal oral microbiota occasional opportunists
-streptococcus pneumoniae
group A streptococcus (GAS)
-beta-hemolysis
-streptococcus pyogenes
-YELLOW
Other streptococci (S. bovis group)
NO HEMOLYSIS
Cell wall (lancefield) antigens
-species specific carboydrate antigens
-GAS vs GBS
GBS
streptococcus agalactiae
streptococcus pneumoniae
-GP cocci
-alpha hemolytic on blood agar
-polysaccharide capsule -> MAJOR VIRULENCE FACTOR
-100 different serotypes
Viriddans group streptococci (VGS)
-GP cocci in pairs/short chains
-can be alpha, beta or non-hemolytic
-bad taxonomy!
-S. MUTANS GROUP WHAT WE CONCENTRATE ON
catalse test used to
distinguish streptococci from other species
pneumococcal disease
refers to disease caused by streptococcus pneumoniae or pneumococcus
pneumococcal disease causes a range of diseases like
-mild: ear infections, sinusitis
-serious: pneumonia, meningitis, bloodstream infections
pneumococcal pneumoniae
most common cause of community-acquired (CA) pneumonia in older adults; infants at risk
pneumococcal pneumoniae symptoms
cough, fatigue, fever, chills, sweats, shortness of breath
symptoms of PP worse for smokers, people with asthma, respiratory issues and
often follows viral respiratory infections e.g. influenza
transient (bacteremia)
immune system not working so bacteria overcomes it
transient (bacteremia)
sepsis, septic shock
pneumococcal disease causes
-bacteremia
-meningitis
meningitis
-swelling in protective lining around brain and spinal cord
-children and elderly more susceptible
streptococcus pneumoniae is what type of anaerobe
aerotolerant
streptococcus pneumoniae has a polysaccharide capsule and
100 antigetically distinct serotypes
streptococcus pneumoniae is naturally
COMPETENT, takes up DNA from environment
streptococcus pneumoniae THIN capsule when
binding to host cells (colonizes in the nasopharynx mucosal surfaces)
streptococcus pneumoniae THICK capsule when
breaking through capsule of nasal epithelium
pneumolysin (Ply)
-produced as soluble toxin monomer -> binds to membrane cholesterol -> forms large pores by oligomerization of up to 50 monomers (30nm)
-kills cells directly
-can induce an inflammatory response
s. pneumoniae is extracellular or intercellular pathogen?
EXTRACELLULAR
disease occurs when
bacteria gain access to sterile sites
s. pneumoniae transmission
-direct: respiratory droplets, aerosols, coughing, sneezing
-indirectly via fomite -> objects
-increased mucus production e.g. during viral infections and allergies
s. pneumoniae role of pneumolysin
induces inflammation in nasopharynx -> inc. in mucus production
s. pneumoniae capsule is required for
-invasion -> prevents phagocytosis by INHIBITING OPSONIZATION
-prevents complement and Fc from interacting with receptors of phagocytic cells ie evading host defenses
s. pneumoniae role of pneumolysin in pathogenesis
-damages mucociliary escalator -> inhibits cilia beating -> holes
-disrupts alveolar epithelium and adema fluid accumulates in alveolar space -> fluid build up
-recruitment of inflammatory cells
-damages cells in BBB -> meningitis
s.pneumoniae diagnosis
-gram stain
-antimicrobial susceptibility
-blood agar (alpha-hemolytic)
-blood, CSF, sputum, etc.
-urine antigen test detects C polysaccharide (present in all serotypes)
viridan group streptococci -> s. mutans and s. sorbinus are
-early colonizers of oral cavity, main contributors to dental caries (cavities)
-uses sucrose to produce glucans (EXC polysacchar.) which enhances attachment to tooth enamel
-grow well in low pH
infective endocarditis parthenogenesis
-pathogens gain access to bloodstream
-rapidly adhere to injured or inflamed valve surface
-pathogens grow on/in endothelium -> vegetation forms on valve
-vegetation can embolize/move elsewhere and colonize other parts of body
