Mechanical damage to Gram-negative bacteria by surface plating with the Drigalski-spatula technique.

Colony counting by spreading bacterial suspensions on plating media by various techniques is of general concern. Comparative studies between hand plating (Drigalski-spatula technique) for different time intervals and spiral plating resulted in significant differences in colony counts. Lower counts of Gram-negative bacteria were obtained by using hand plating for more than 10s, compared with short time hand plating (5s) or spiral plating.