G1: General Principles of Infectious Diseases

What are the gram-positive cocci?

• Staphylococcus spp.

• Streptococcus spp.

• Enterococcus spp.

What are the Staphylococcus spp.?

• S. Aureus

• S. Epidermidis

• S. Saprophyticus

What are the Streptococcus spp.?

• S. Pneumoniae

• Viridans-group Streptococci

• S. Pyogenes (group A)

• S. Agalactiae (group B)

• S. Gallolyticus (group D)

What are the Enterococcus spp.?

• E. Faecalis

• E. Faecium

What is Streptococcus pyogenes sensitive to?

• Amoxicillin

• Amoxiclav

• Ampicillin

• Azithromycin

• Cefaclor

• Clarithromycin

• Clindamycin

• Erythromycin

• Levofloxacin

• Penicillin

What are the gram-negative cocci?

• Neisseria spp.

  • N. Meningitidis

  • N. Gonorrhoeae

• Moraxella spp.

  • M. Catarrhalis

What gram-negative bacilli more likely to be lactose fermenting?

• Escherichia coli

• Klebsiella spp.

  • Klebsiella pneumoniae

  • Klebsiella oxytoca

What gram-negative bacilli is more likely to be non-lactose fermenting?

• SPACE:

  • Serratia marcescens

  • Pseudomonas aeruginosa

  • Acinetobacter baumannii

  • Citrobacter freundi (±)

  • Enterobacter cloacae (±)

• Coccobacilli:

  • Haemophilus influenzae

• Proteus mirabilis

What are the gram-positive anaerobes?

• Clostridium difficile

• Clostridium perfringens

• Peptostreptococcus spp.

• Propionibacterium acnes

What are the gram-negative anaerobes?

• Bacteroides fragilis

• Prevotella spp.

What is the acid fast bacilli?

Mycobacterium spp. (tuberculosis & nontuberculous mycobacteria)

What are the atypicals?

• Chlamydia spp. (trachomatis, pneumoniae)

• Mycoplasma pneumoniae

• Legionella pneumophila

What is the process of seeing the bugs under the microscope?

Culture draw

→ Incubation

→ Gram stain

→ Identification & susceptibilities

What is the minimum inhibitory concentration (MIC)?

Lowest concentration of antibiotic that inhibits visible growth of a microorganism

What do MIC values indicate?

Level of resistance of an organism to a specific antibiotic agent

• Resistant (R): high level resistance

• Intermediate (I): low level resistance

• Susceptible (S): little to no resistance

How do we know what MIC values correspond w/ susceptible, intermediate, & resistant?

• FDA breakpoints upon initial approval of antibiotic

• Clinical Laboratory Standards Institute (CLSI) establishes & re-assesses breakpoints based on:

  • In vitro microbiological assessment

  • Pharmacodynamics & pharmacokinetics of agents

  • Clinical trial outcomes

What is the CLSI M100 document?

Breakpoints reported for unique organism-antibiotic combinations as interpretive criteria

What is empiric therapy antibiotic selection?

Prior to, or during initial culture work up w/ gram stain

What is targeted/definitive therapy antibiotic selection?

Following final culture report w/ MICs & susceptibilities

What is rapid diagnostic testing?

• Rapid & accurate results on day 1

• Supports decisions for appropriate & targeted therapy 1-3 days earlier than conventional methods

What does purple mean in gram stain?

Gram-positive

What does pink mean in gram stain?

Gram-negative

What are sterile fluid fluids/tissues?

• Blood

• CNS

• Lower respiratory tract

• Most internal organs

What are non-sterile fluid fluids/tissues?

• Skin

• Upper respiratory tract

• Genitourinary tract (GU)

• Gastrointestinal tract (GI)

What happens w/ normal host flora going further down GI tract?

• Gram (+), aerobes, 10^1-2 organisms

• Gram (-), gram (+), aerobes & anaerobes, 10^4-7 organisms

• Gram (-), few gram (+), anaerobes > aerobes, 10^5-11 organisms

What is colonization?

Normal presence of microorganisms w/o causing infection

What is contamination?

Abnormal presence of microorganisms w/o causing infection (typically due to translocation)

What is infection?

A disease caused by germs that enter the body

What is blood culture contamination?

Significant pt care issue

What is the process of contaminating a blood sample?

Preparation: when a sterile field is breached

→ Collection set assembly: from bacteria on clinicians hands/surfaces

→ Venipuncture: when skin contaminants are drawn into specimen

→ Sample handling: when bacteria comes to reside on culture bottles

What do contaminated blood cultures lead to?

• Unnecessary utilization of laboratory resources

• Increased length of hospitalization & potential for needless hospital admissions

• Profound impact on costs

• Unnecessary antimicrobial usage w/ potential for adverse events & selective pressure

• Unnecessary additional pt care measures (diagnostic studies, imaging procedures, medications)

What is infection caused by?

• Normal flora in presence of impaired host defenses, translocation (trauma)

• Pathogen transfer:

  • Pt to pt

  • Vector to pt (animals, insects)

  • Environment to pt (hospital)

What are common markers of infection?

• Laboratory:

  • Increased WBC count (>12,000 cells/mm³)

  • >5-10% bands (left shift)

  • Inflammatory markers: erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), procalcitoninin

• Abnormal vital signs: HR, RR, BP, fever

• Erythema, pus, pain

• Radiographic imaging

• Microbiologic culture data

What are the types of granulocytes?

Polymorphonuclear granulocytes (PMNs)

• Neutrophils

• Eosinophils

• Basophils

What are the agranulocytes?

• Lymphocytes

• Monocytes

What is empiric coverage implemented w/ consideration of?

• Common disease state etiology

• Local susceptibility pattern (antibiogram)

What is definitive coverage guided by?

Culture & susceptibility results

What are the antibiotic selection factors?

Suspected/confirmed infection:

• Organism/pathogen identification

• Guideline/primary literature guidance

• Consideration of host factors

• Consideration of drug factors

What are host factors to antibiotic selection?

• Drug allergy

• Pregnancy/lactation

• Renal & hepatic function

• Concomitant drugs & diseases

• Prosthetic material

What are drug factors to antibiotic selection?

• Pharmacokinetics/pharmacodynamics

• Route of administration

• Tissue penetration

• Adverse effect profile

• Cost

• Specific factors:

  • Bactericidal vs. bacteriostatic

  • Combination vs. monotherapy

What is bacteriostatic?

• Inhibition of bacterial growth

• Kill < 3 log (99.9)% of inoculated bacteria w/in 18-24 hour period

What is bactericidal?

• Kills bacteria

• Kill > 3 log (99.9)% of inoculated bacteria w/in 18-24 hour period

What is combination therapy?

Evidence-based reasons for combination antibiotic therapy:

• Enhance coverage for empiric therapy (Pseudomonas aeruginosa)

• Polymicrobial infections

• Synergy: 1+1:3

  • Antimicrobial combination greater than sum of each antimicrobial by itself

What is antimicrobial stewardship?

General principles is appropriate & optimal:

• Drug

• Dose

• Route

• Interval

• Duration

• Monitoring

What are IDSA guidelines?

• Multidisciplinary AMSC team collaboration

• Formulary restriction or pre-authorization

• Prospective audit w/ intervention & feedback

What are key interventions w/ antimicrobial stewardship?

Antibiotic de-escalation, dose optimization, IV to PO, clinical guideline use

What do antibiogram results presented as?

Percent susceptible for organism & antibiotic