Microbiology Quiz: Enterococcus

Objectives of the Lecture

• Ability to identify common diagnostic factors of infectious disease, including labs, symptoms, and imaging studies.
• Understanding of pathogen identification and susceptibility testing application in case scenarios.
• Distinction between microbial infection, contamination, and colonization.
• Definitions of empiric, definitive, and prophylactic antimicrobial prescribing with case applications.
• Knowledge application in antimicrobial prescribing principles to select appropriate cases.
• Identification of significant features of select microorganisms.

Signs and Symptoms of Infection

• General Vital Signs:
  • Hyperthermia (> 38°C) and possible hypothermia (< 36°C).
  • Tachycardia (> 100 bpm) and tachypnea (> 20 rpm).
  • Hypotension (SBP < 100 mmHg).
• General Symptoms: Headache, nausea/vomiting, fatigue, and myalgia.
• Site-Specific Symptoms:
  • Meningitis: mental status changes, confusion, blurred vision, and stiff neck.
  • Sinus infection: runny nose, congestion, and dental pain.
  • Pneumonia: cough, shortness of breath, and chest pain.
  • GI infections: abdominal pain, diarrhea, and bloody stools.
  • UTI: dysuria, urgency, and hematuria.
  • Skin infections: redness, swelling, and purulent discharge.

Imaging Studies

• Primarily site-specific imaging used for diagnosis, including X-rays, CT scans, MRIs, ultrasounds, and echocardiograms.

Laboratory Findings

• Complete Blood Count (CBC):
  • White Blood Cell (WBC) count indicating leukocytosis (> 12,000 cells/mm³) or leukopenia (< 4,000 cells/mm³).
  • Differential providing percentages of WBC subtypes that may indicate specific conditions or infections.
• Common WBC Responses:
  • Neutrophilia indicates infection; bandemia (increased immature neutrophils) suggests heightened infection levels.
  • Monocytosis may indicate certain infections and diseases; lymphocytosis is often viral; eosinophilia suggests parasitic infections.

Additional Laboratory Findings

• Erythrocyte Sedimentation Rate (ESR):
  • Normal ranges for males (0 to 20 mm/h) and females (0 to 30 mm/h); used as a non-specific inflammatory marker.
• C-Reactive Protein:
  • Elevated levels indicate inflammation; important to monitor in infections.

Susceptibility Testing

• Determination of in vitro susceptibilities of microorganisms to antimicrobials through methods like Kirby-Bauer disk diffusion, showing zones of inhibition.
• Minimum Inhibitory Concentration (MIC) testing identifies the lowest antibiotic concentration preventing bacterial growth.

MIC Breakpoints

• Published by CLSI & EUCAST to classify isolate-antibiotic pairs as susceptible, intermediate, or resistant.
  • Susceptible (S): Effective against the bacteria.
  • Intermediate (I): Limited effectiveness; may require higher doses.
  • Resistant (R): Not effective; alternative antibiotics needed.

Culture Timeline

• Steps of microbial culture from specimen collection to susceptibility testing results typically take 72 hours.

Identification of Pathogens

• MALDI-TOF: Rapid identification method for pathogens.
• Antibody & Antigen Detection: Useful for specific infections.

Key Microorganisms

• MRSA: Methicillin-resistant Staphylococcus aureus characterized by altered penicillin-binding proteins.
• Streptococcus:
  • Grouped by hemolytic properties (alpha, beta, gamma) with common infections including pneumonia and skin infections.
• Enterococcus: Common gut flora; includes challenging bacteria like E. faecium, often resistant to treatments.
• Clostridium: Anaerobic and spore-forming, including pathogens like C. difficile, known for causing serious gastrointestinal diseases.
• Enterobacteriaceae: Important group of gram-negative rods, common in UTIs; relationships with antimicrobial resistance, notably ESBLs and CRE.
• Pseudomonas aeruginosa: Multi-drug resistant organism associated with various nosocomial infections.