A 54-year-old man has fever and chills on day 9 of a triple-lumen central venous catheter. The catheter is removed and the distal 5 cm segment is sent for culture using the semiquantitative roll-plate (Maki) technique. Colonies are counted after overnight incubation on blood agar. Which count supports catheter-related bloodstream infection?

• A More than 15 CFU per plate ✓
• B More than 1000 CFU per millilitre of broth from the segment
• C Growth of any colony-forming units at all
• D More than 100 CFU per plate

Explanation

In the Maki semiquantitative technique the catheter tip is rolled across blood agar and growth of more than 15 colony-forming units indicates significant colonisation consistent with catheter-related infection when paired with matching peripheral blood cultures. The 1000 CFU/mL cutoff belongs to quantitative vortex-sonication methods such as the Cleri technique, not the roll plate. Any-growth criteria reflect contamination, and 100 CFU is far above the validated threshold.

Reference: Mackie and McCartney Practical Medical Microbiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.