Antimicrobials Reporting

This section focuses on the selection of appropriate antimicrobials for reporting based on the bacterial species isolated and the clinical source of the specimen. This is a critical aspect of antimicrobial susceptibility testing, as it ensures that clinicians receive relevant and actionable information for guiding antibiotic therapy

General Principles

Relevance to Infection: The antimicrobials reported should be those likely to be used to treat infections caused by the isolated organism in the specific body site
CLSI Guidelines: Follow CLSI guidelines for the selection of antimicrobials to be tested and reported. CLSI provides recommendations based on the spectrum of activity of the antibiotics, the prevalence of resistance, and the clinical relevance of the organism
Body Site Considerations: The choice of antimicrobials should consider the ability of the antibiotic to reach effective concentrations at the site of infection. For example, some antibiotics do not penetrate the blood-brain barrier well, making them unsuitable for treating meningitis
Intrinsic Resistance: Report antimicrobials that are known to be active against the isolated organism. Do not report antimicrobials that the organism is intrinsically resistant to
Local Resistance Patterns: Consider local resistance patterns and antibiotic stewardship guidelines when selecting antimicrobials for reporting
Antimicrobial Stewardship: The selection of antimicrobials should support antimicrobial stewardship efforts, which aim to optimize antibiotic use and minimize the development of resistance

Antimicrobials for Reporting by Species and Body Site

Gram-Positive Cocci
- Staphylococcus aureus
  - Bloodstream Infections, Pneumonia, Skin and Soft Tissue Infections:
    - Report: Penicillin (if susceptible), oxacillin (or cefoxitin), vancomycin, linezolid, daptomycin, trimethoprim-sulfamethoxazole, clindamycin (with D-test)
    - Consider: Ceftaroline (if oxacillin-resistant and susceptible), telavancin, dalbavancin, oritavancin, tigecycline, ceftobiprole
  - MRSA:
    - Report: Vancomycin, linezolid, daptomycin, trimethoprim-sulfamethoxazole, clindamycin (with D-test)
    - Consider: Ceftaroline, telavancin, dalbavancin, oritavancin, tigecycline, ceftobiprole
  - Methicillin-Susceptible Staphylococcus aureus (MSSA):
    - Report: Penicillin, oxacillin, cefazolin, cephalexin, clindamycin (with D-test), trimethoprim-sulfamethoxazole
- Staphylococcus epidermidis and other Coagulase-Negative Staphylococci (CoNS)*
  - Bloodstream Infections, Infections associated with indwelling devices:
    - Report: Oxacillin (or cefoxitin), vancomycin, linezolid, daptomycin, trimethoprim-sulfamethoxazole
  - Consider: Gentamicin, rifampin (in combination)
- Streptococcus pneumoniae
  - Respiratory Tract Infections, Meningitis:
    - Report: Penicillin (if susceptible), ceftriaxone, cefotaxime, vancomycin, levofloxacin, moxifloxacin, linezolid
  - Consider: Telithromycin
- Streptococcus pyogenes (Group A Streptococcus)
  - Skin and Soft Tissue Infections, Pharyngitis:
    - Report: Penicillin, amoxicillin, cephalexin, clindamycin (with D-test), erythromycin, azithromycin
  - Consider: Ceftriaxone
Gram-Negative Bacilli
- Escherichia coli
  - Urinary Tract Infections, Bloodstream Infections:
    - Report: Ampicillin (if susceptible), amoxicillin-clavulanate, cefazolin, ceftriaxone, cefepime, piperacillin-tazobactam, gentamicin, amikacin, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin, nitrofurantoin (urine only), fosfomycin (urine only)
    - Consider: Carbapenems, tigecycline, ceftolozane-tazobactam, ceftazidime-avibactam, cefiderocol
  - ESBL-producing:
    - Report: Carbapenems, ceftolozane-tazobactam, ceftazidime-avibactam, cefiderocol, tigecycline, fosfomycin
- Klebsiella pneumoniae
  - Pneumonia, Bloodstream Infections, Urinary Tract Infections:
    - Report: Ampicillin (if susceptible), amoxicillin-clavulanate, cefazolin, ceftriaxone, cefepime, piperacillin-tazobactam, gentamicin, amikacin, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin
    - Consider: Carbapenems, tigecycline, ceftolozane-tazobactam, ceftazidime-avibactam, cefiderocol
  - Carbapenem-Resistant Enterobacteriaceae (CRE):
    - Report: Ceftazidime-avibactam, cefiderocol, tigecycline, fosfomycin, aminoglycosides (amikacin, gentamicin)
  - ESBL-producing:
    - Report: Carbapenems, ceftolozane-tazobactam, ceftazidime-avibactam, cefiderocol, tigecycline, fosfomycin
- Proteus mirabilis
  - Urinary Tract Infections:
    - Report: Ampicillin, amoxicillin-clavulanate, cefazolin, ceftriaxone, cefepime, piperacillin-tazobactam, gentamicin, amikacin, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin, nitrofurantoin (urine only)
- Pseudomonas aeruginosa
  - Pneumonia, Bloodstream Infections, Wound Infections:
    - Report: Piperacillin-tazobactam, ceftazidime, cefepime, ceftolozane-tazobactam, imipenem-cilastatin, meropenem, gentamicin, amikacin, ciprofloxacin, levofloxacin, colistin
    - Consider: Aztreonam, ceftazidime-avibactam, cefiderocol
- Acinetobacter baumannii
  - Pneumonia, Bloodstream Infections, Wound Infections:
    - Report: Carbapenems (if susceptible), ampicillin-sulbactam, colistin, tigecycline
    - Consider: Minocycline, cefiderocol
- Enterobacter species (e.g., E. cloacae, E. aerogenes)
  - Pneumonia, Bloodstream Infections, Urinary Tract Infections:
    - Report: Ampicillin (if susceptible), amoxicillin-clavulanate, cefazolin, ceftriaxone, cefepime, piperacillin-tazobactam, gentamicin, amikacin, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin
    - Consider: Carbapenems, tigecycline, ceftolozane-tazobactam, ceftazidime-avibactam, cefiderocol
  - ESBL-producing:
    - Report: Carbapenems, ceftolozane-tazobactam, ceftazidime-avibactam, cefiderocol, tigecycline, fosfomycin
  - Carbapenem-Resistant:
    - Report: Ceftazidime-avibactam, cefiderocol, tigecycline, fosfomycin, aminoglycosides (amikacin, gentamicin)
Anaerobes
- Bacteroides fragilis
  - Intra-abdominal Infections, Wound Infections:
    - Report: Metronidazole, carbapenems, piperacillin-tazobactam, cefoxitin, clindamycin (if susceptible)
    - Consider: Tigecycline, ceftolozane-tazobactam, ceftazidime-avibactam, cefiderocol
Other Important Species
- Haemophilus influenzae
  - Respiratory Tract Infections, Meningitis:
    - Report: Ampicillin (if susceptible), amoxicillin-clavulanate, ceftriaxone, cefotaxime, cefuroxime, azithromycin, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin
- Moraxella catarrhalis
  - Respiratory Tract Infections:
    - Report: Penicillin (if susceptible), amoxicillin-clavulanate, ceftriaxone, cefuroxime, azithromycin, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin
- Neisseria gonorrhoeae
  - Gonorrhea:
    - Report: Ceftriaxone, azithromycin
- Chlamydia trachomatis
  - Chlamydia:
    - Report: Azithromycin, doxycycline
- Mycoplasma pneumoniae
  - Pneumonia:
    - Report: Tetracyclines, macrolides, fluoroquinolones

Body Site-Specific Considerations

Central Nervous System (CNS)
- Antimicrobials must cross the blood-brain barrier
- Report: Ceftriaxone, cefotaxime, vancomycin, ampicillin, meropenem, piperacillin-tazobactam, linezolid (for Staphylococcus and Enterococcus), metronidazole (for anaerobes)
Lower Respiratory Tract
- Consider local resistance patterns and the severity of the infection
- Report: Beta-lactams, macrolides, fluoroquinolones, trimethoprim-sulfamethoxazole (for Pneumocystis jirovecii)
Urinary Tract
- Consider antimicrobials that achieve high concentrations in urine
- Report: Nitrofurantoin, fosfomycin, trimethoprim-sulfamethoxazole, fluoroquinolones, beta-lactams, aminoglycosides
Bloodstream
- Report: Broad-spectrum antimicrobials effective against the likely pathogens
- Consider: Vancomycin, linezolid, daptomycin, ceftaroline, ceftazidime-avibactam, cefiderocol, carbapenems, aminoglycosides
Skin and Soft Tissue
- Report: Antimicrobials effective against Staphylococcus and Streptococcus
- Consider: Beta-lactams, clindamycin, trimethoprim-sulfamethoxazole, tetracyclines, linezolid, daptomycin, ceftaroline

Reporting Practices

Susceptibility Categories: Report susceptibility categories (S, I, R) for each antimicrobial tested
MICs: Report MIC values for relevant antimicrobials, especially for serious infections and when guiding dosing decisions
Comments: Include comments when appropriate, such as:
- Presence of ESBL or carbapenemase
- Inducible clindamycin resistance
- Limitations of testing
- Recommendations for follow-up testing
Alerts: Flag critical results, such as resistance to carbapenems or vancomycin, for immediate reporting to the clinician
Electronic Reporting: Utilize electronic laboratory information systems (LIS) to facilitate rapid and accurate reporting of results

Key Terms

Antimicrobial Susceptibility Testing: Laboratory tests to determine the susceptibility of a bacterium to antibiotics
CLSI (Clinical and Laboratory Standards Institute): An organization that provides standardized methods and interpretive criteria for antimicrobial susceptibility testing
Susceptibility Category: A classification (S, I, R) that indicates whether an organism is likely to be inhibited by an antimicrobial
MIC (Minimum Inhibitory Concentration): The lowest concentration of an antimicrobial that inhibits bacterial growth
Empiric Therapy: Treatment initiated before the causative organism is identified and susceptibility results are available
Antimicrobial Stewardship: Efforts to optimize antibiotic use and minimize the development of resistance
ESBL (Extended-Spectrum Beta-Lactamase): A type of beta-lactamase that hydrolyzes extended-spectrum cephalosporins
CRE (Carbapenem-Resistant Enterobacteriaceae): Enterobacteriaceae that is resistant to carbapenems
MRSA (Methicillin-Resistant Staphylococcus aureus): Staphylococcus aureus that is resistant to methicillin and other beta-lactam antibiotics
VRE (Vancomycin-Resistant Enterococcus): Enterococcus species that is resistant to vancomycin
Intrinsic Resistance: Natural resistance of a bacterial species to an antibiotic

Intrinsic Resistance Patterns

MRSA/MSSA, VRE, ESBL/CRE