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Widespread, local E. coli strains found in Mexico
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Researchers studying enterotoxigenic Escherichia coli in Mexico found a small number of strains that could be endemic to all of Mexico, and several strains that are specific to two cities, according to a study.
“While most strains of enterotoxigenic E. coli (ETEC) produce small outbreaks, a small number show widespread disease transmission over the entire country of Mexico — possibly in a common source that is distributed widely,” Herbert DuPont, MD, who was a researcher involved in the study, said in an interview.
The researchers examined samples of travelers’ diarrhea acquired from 213 American students in Guadalajara and Cuernavaca between 2004 and 2007. The two cities are 300 miles apart and have little interaction, which allowed the researchers to differentiate between sporadic and epidemic disease in their samples.
The organisms in all samples were presumed to be E. coli because of their phenotypic characteristics. However, biochemical testing revealed that only 85% were E. coli. Half of the remaining strains were Citrobacter freundii, and 9% were Klebsiella pneumoniae, according to the results.
“Non-E. coli produce toxins identical to ETEC and should be pursued as important new undescribed pathogens,” DuPont said. “We believe that non-E. coli, including organisms like toxigenic Citrobacter and Klebsiella, will be shown to be important pathogens.”
The researchers are the first to use random amplified polymorphic DNA assays to describe ETEC samples. Results indicated 24 clonal groups with two or more isolates each. Most groups (63%) contained only two isolates. Only 41% of the samples belonged to a clonal group, with the rest representing a single independent strain. Eight clonal groups (33%) spanned both cities, and 15 groups (63%) spanned different years.
“This seems to indicate that travelers to Mexico are exposed to many unrelated ETEC strains, as well as large, persistent widespread pools of ETEC,” the researchers wrote. “Further study identifying potential sources of this reservoir and the potential stability of specific strains of ETEC may aid in identifying potential targets of prevention.”
Ouyang-Latimer J. J Infect Dis. 2010;201:1831-1838.