Changes during travel in the composition and antibiotic resistance pattern of the intestinal Enterobacteriaceae flora: results from a study of mecillinam prophylaxis against travellers' diarrhoea.

A randomized double-blind study was carried out in a group of Danish students visiting Mexico for 2 weeks to investigate the efficacy of mecillinam when given orally in preventing travellers' diarrhoea. The subjects took either 200 mg mecillinam daily as a single dose or placebo for 14 days. Nine (56%) out of 16 taking placebo and 3 (19%) out of 16 taking mecillinam developed travellers' diarrhoea (p less than 0.05). The pathogenic aetiology was not ascertained. A complete change in the Enterobacteriaceae flora took place during travel. A highly antibiotic-resistant Enterobacteriaceae flora was acquired in Mexico in subjects on mecillinam prophylaxis as well as on placebo. Selection of mecillinam-resistant bacteria was minimal.