The post-antibiotic effect of manuka honey on gastrointestinal pathogens Sir, An increasing number of studies have shown that honey has substantial antimicrobial activity . This has mostly been demonstrated by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests in which microorganisms are exposed to a constant level of honey for a long period. However, the efficacy of honey taken orally would be greatly affected by dilution in large amounts of body fluids and water from food and drink as well as by a short period of contact with bacterial cells owing to rapid peristalsis in the gastrointestinal tract. We therefore investigated how long it would take manuka honey to eliminate microorganisms and whether or not honey has a post-antibiotic effect (PAE) similar to other common drugs.Manuka honey (SummerGlow Apiaries Ltd., Hamilton, New Zealand) used in this work had non-peroxide antibacterial activity equivalent to that of 16.5% (w/v) phenol when tested by the method described by Allen et al. [2]. Artificial honey [3] consisting of sugars and distilled water was included as a control. Escherichia coli ATCC 25922, Salmonella serotype Typhimurium Phage Type 104 (ESR, Christchurch, New Zealand), Pseudomonas aeruginosa, Enterobacter aerogenes, Enterobacter cloacae, Shigella flexneri, Shigella sonnei (Waikato Hospital, Hamilton, New Zealand), Salmonella serotype Enteritidis and Yersinia enterocolitica (Medlab, Hamilton, New Zealand) were tested using Mueller-Hinton broth (MHB) (BD, Sparks, MD). Before exposure to the honey solution, it