A patient with Salmonella Typhi bacteraemia requires susceptibility testing. The isolate shows reduced susceptibility to ciprofloxacin (MIC 0.125 mg/L; breakpoint for susceptibility ≤0.06 mg/L) but full sensitivity to ceftriaxone and azithromycin. This pattern is best described as:

• A Multidrug-resistant (MDR) typhoid — resistant to ampicillin, chloramphenicol, and co-trimoxazole
• B Non-susceptible to fluoroquinolones (NSFQ) typhoid — treatment with ceftriaxone or azithromycin preferred ✓
• C Extensively drug-resistant (XDR) typhoid — resistant to fluoroquinolones and third-generation cephalosporins
• D Fully susceptible; MIC 0.125 is within the susceptible range for Salmonella

Explanation

An S. Typhi isolate with a ciprofloxacin MIC of 0.125 mg/L exceeds the susceptibility breakpoint (≤0.06 mg/L by EUCAST/CLSI) but falls below the resistance breakpoint; it is classified as intermediate or non-susceptible to fluoroquinolones (NSFQ). NSFQ typhoid is often caused by plasmid-mediated quinolone resistance genes (qnr) or gyrA Ser83Phe mutation. Clinical failure with fluoroquinolones is expected even at intermediate MICs. Ceftriaxone IV or azithromycin oral are the preferred alternatives. XDR typhoid (as seen in Pakistan) adds resistance to third-generation cephalosporins.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.