its hard to tell from the pictures but it looks more like a scratch on the outside. If its just a small scratch on the outside you shouldnt have to worry about it harboring bacteria. it could be a stress point that might lead to a crack, but I dont thinks its very likely. just be careful to not stress the carboy too much, try not to bump it, pour boiling water in it, or slide it on the floor (Ive scratched mine by sliding it on the floor when theres some dirt between it and the floor)