Intro to ID Flashcards
What are systemic signs of infection used in diagnosing SIRS?
1) Temp >38°C or <36°C, 2) HR >90 BPM, 3) RR >20 RPM, 4) WBC >12,000 or <4,000 or >10% bands. At least two are needed for SIRS.
What does a ‘left shift’ in WBC differential indicate?
An increase in immature neutrophils (bands), typically seen during bacterial infections.
What is the normal range of procalcitonin and its significance?
Normal PCT <0.05 mcg/L. A level >0.5 mcg/L suggests bacterial infection and supports antibiotic use.
What are key radiographic tests used to confirm infection?
X-ray, CT, MRI, bone scans, and echocardiography (TTE/TEE).
Differentiate between colonization and infection.
Colonization: pathogen present without causing symptoms or immune response. Infection: pathogen causes tissue damage and symptoms.
What gram stain and morphology results identify Staphylococcus aureus?
Gram-positive cocci in clusters; catalase-positive, coagulase-positive.
What are the four main mechanisms of bacterial resistance?
1) Enzymatic inactivation, 2) Altered target sites, 3) Efflux pumps, 4) Reduced permeability (porin loss).
Which beta-lactamase class includes ESBLs, and what is the treatment of choice?
Ambler Class A; treatment: Carbapenems (e.g., meropenem).
Define bactericidal vs. bacteriostatic activity.
Bactericidal: kills bacteria (preferred in severe infections). Bacteriostatic: inhibits bacterial growth without killing.
What is the key PK/PD parameter for beta-lactams?
Time above MIC (fT>MIC); aim for ≥40-70% of dosing interval.
What are the key steps to establish the presence of an infection?
1) Clinical signs and symptoms, 2) Lab findings (WBC, ESR, CRP, PCT), 3) Radiologic evidence, 4) Microbial culture and diagnostics.
What are the five main types of laboratory white blood cells and their roles?
Neutrophils: bacterial defense; Lymphocytes: viral/fungal/TB; Monocytes: macrophages; Eosinophils: parasites/allergy; Basophils: hypersensitivity.
What are the categories of Gram-positive cocci and their key species?
Clusters (Staph aureus, CoNS); Pairs/chains (Strep pneumoniae, viridans strep, Group A/B strep, Enterococcus).
What are Gram-positive bacilli examples and their oxygen requirements?
Aerobic: Bacillus, Corynebacterium, Listeria. Anaerobic: Clostridium, Cutibacterium, Actinomyces.
Differentiate aerobic Gram-negative lactose fermenters vs. non-fermenters.
Lactose fermenters: E. coli, Klebsiella, Enterobacter. Non-fermenters: Pseudomonas, Acinetobacter, Proteus, Morganella.
Which organisms are identified as atypical bacteria?
Chlamydia spp., Legionella, Mycoplasma pneumoniae, Spirochetes (Treponema, Borrelia).
What are the main mechanisms of antimicrobial resistance?
1) Enzymatic inactivation (e.g., beta-lactamases), 2) Altered target sites (e.g., PBPs), 3) Efflux pumps, 4) Decreased permeability (porin loss).
What resistance genes are associated with MRSA and VRE?
MRSA: mecA gene (PBP2a); VRE: vanA or vanB gene (D-Ala-D-Lac/Ser change).
What are the four Ambler classes of beta-lactamases?
Class A: ESBLs, KPC; Class B: MBLs (NDM, VIM, IMP); Class C: AmpC; Class D: OXA-type.
What treatment is preferred for ESBL-producing organisms?
Carbapenems are first-line. Piperacillin/tazobactam may be used only for urinary sources.
What is the significance of AmpC beta-lactamases?
Inducible resistance that may lead to derepression with certain antibiotics. Treat with cefepime, carbapenems, or non-β-lactams.
