Determination of azithromycin heteroresistant in traveler's diarrhea.

is the most common cause of traveler's diarrhea (TD) and human bacterial gastroenteritis. A heteroresistant () isolate, identified by microbiological methods and characterized with molecular techniques, was obtained from a traveler in Nepal suffering TD. The presence of atypical colonies within the clear zone of inhibition was the first evidence of an atypical phenotype, leading to additional characterization of this heteroresistant strain. Antimicrobial susceptibility testing (AST) and population analysis profiling (PAP) demonstrated heteroresistance to azithromycin (AZM), a first-line antibiotic treatment for infections. Molecular analysis indicated a point mutation occurred on the 23S rRNA gene at the A2075G transitions, and the number of mutated gene copies was proportional to AZM resistance. Heteroresistant subpopulations from acute TD are likely underestimated, which may lead to treatment failures, as was the case for this patient. The presence of a heteroresistant strain in a high antibiotic environment may select for additional drug resistance and enable distribution into hospital and local communities.