How to Read This Antimicrobial Susceptibility Report
This report shows a bacterial isolate that is susceptible (S) to all tested antibiotics, with the numbers representing the minimum inhibitory concentrations (MICs) in mcg/mL—the lowest antibiotic concentration that inhibits bacterial growth.
Understanding the Report Format
Each line follows this pattern: ANTIBIOTIC NAME | S/I/R | MIC VALUE
- S = Susceptible: The organism will likely be killed by standard antibiotic doses
- I = Intermediate: Higher doses or specific body sites where drug concentrates may be needed
- R = Resistant: The antibiotic will not work effectively
The MIC number tells you how potent the antibiotic is against this specific organism—lower numbers indicate greater potency 1.
Your Specific Results
Your isolate shows universal susceptibility with excellent MIC values:
Beta-Lactam Antibiotics
- Amoxicillin/clavulanate: S at 8 mcg/mL
- Ampicillin/sulbactam: I at 16 mcg/mL (borderline—may need higher doses)
- Cefazolin: S at 2 mcg/mL (excellent first-generation cephalosporin activity) 2
- Cefepime: S at ≤0.12 mcg/mL (outstanding fourth-generation activity)
- Ceftazidime: S at ≤0.5 mcg/mL (excellent anti-Pseudomonal activity)
- Ceftriaxone: S at ≤0.25 mcg/mL (outstanding third-generation activity)
- Piperacillin/tazobactam: S at ≤4 mcg/mL (excellent broad-spectrum activity)
Carbapenems
- Imipenem: S at ≤0.25 mcg/mL (exceptional potency)
- Meropenem: S at ≤0.25 mcg/mL (exceptional potency)
Fluoroquinolones
- Ciprofloxacin: S at ≤0.06 mcg/mL (outstanding activity) 3
- Levofloxacin: S at ≤0.12 mcg/mL (outstanding activity)
Aminoglycosides
- Gentamicin: S at ≤1 mcg/mL (excellent activity) 4
Other Agents
- Nitrofurantoin: S at ≤16 mcg/mL (good for urinary tract infections)
- Trimethoprim/sulfamethoxazole: S at ≤20 mcg/mL (excellent activity)
Clinical Implications
This organism is NOT multidrug-resistant and has no extended-spectrum beta-lactamase (ESBL) or carbapenemase production 5. The exceptionally low MICs across all drug classes indicate a highly susceptible organism.
Treatment Selection Priority
For empiric or targeted therapy, choose based on infection site and severity 6:
For non-severe infections:
- First-line: Ceftriaxone, cefazolin (if appropriate site), or amoxicillin/clavulanate
- Alternative: Trimethoprim/sulfamethoxazole, ciprofloxacin (reserve for specific indications)
For severe infections:
- Piperacillin/tazobactam or cefepime
- Reserve carbapenems (meropenem/imipenem) for documented ESBL organisms or treatment failures 5
Critical caveat: The "I" result for ampicillin/sulbactam at 16 mcg/mL means this agent is borderline and should be avoided unless no alternatives exist, as clinical outcomes may be unpredictable 1.
Antimicrobial Stewardship Considerations
Avoid using broad-spectrum agents (carbapenems, fluoroquinolones) when narrower-spectrum options are susceptible 5. This organism's pan-susceptibility allows de-escalation to the narrowest effective agent based on infection type, which reduces collateral damage to normal flora and minimizes resistance selection pressure 7, 8.