By Sean Henahan, Access Excellence

MEXICO CITY (7/1/96) Misuse of antibiotics in developing countries is creating a new pool of resistant bacteria- healthy young children- according to a new study. (Above: E.Coli on the move)

Mexican researchers studied 20 healthy children under the age of two years in San Pedro Martir, a suburb of Mexico City. Stools samples were taken from these children weekly for a 3-month period and tested for the presence of bacteria resistant to seven commonly used antibiotics: ampicillin, trimethoprim, tetracycline, chloramphenicol, gentamicin, nitrofurantoin and norfloxacin.

"All 20 children were colonized at some point by Escherichia. coli resistant to antibiotics. E. coli are common bacteria found in the intestinal tract of all humans. Data from this study confirm that in certain communities small children can be colonized by E.coli strains resistant to multiple commonly used antimicrobial agents. Furthermore, fecal shedding of these microorganisms persistently occurs for periods of at least a few months, which could represent an important route for the dissemination of antibiotic-resistant bacteria to other members of the community," said Dr. Juan J. Calva of the Instituto Nacional de la Nutricion "Salvador Zubiran" in Mexico City.

Of the 260 samples taken, only four (1.5%) contained strains of E. coli that were not resistant to at least one antibiotic. Nearly 90 percent of the samples contained isolates that were resistant to two or more antibiotics.

A few studies have already surveyed the frequency of antibiotic resistance and have shown a high frequency of naturally occurring fecal bacteria resistant to one or more antibiotics, notes Calva, but they have all been cross-sectional surveys and have not studied the problem over time.

"Despite the evidence of the high prevalence of potentially transferable antibiotic resistance in gut organisms of children, especially children in developing countries, to our knowledge there has been no assessment of the pattern of the intestinal carriage of drug-resistant coliforms, over time, among healthy children in a community," he says. "The longer the period of shedding of these microorganisms in feces, the greater the chances of interpersonal transmission and contamination of drinking water and food with these bacteria."

Over half the children in the study continuously shed antibiotic-resistant organisms in their feces over the entire 13-week period. Interestingly, in the cases of continuous shedding the bacteria were resistant to only ampicillin, trimethoprim, tretracycline or a combination of those three. Colonization by organisms resistant to the other antibiotics occurred only in a few children and was short lived.

The widely different patterns in resistance to specific antibiotics over time may be explained by the overuse and misuse of certain drugs in the management of common illnesses, says Calva. An earlier survey of antibiotic use in the same community found that approximately 5% of the population used at least one antibiotic in a 2-week period and the most commonly used antibiotics were ampicillin, trimethoprim and tetracycline, constituting one third of all reported drugs. Not surprisingly, the other four antibiotics constituted less than 2% of all antibiotics used.

"There seems to be an association between the common consumption of these three antibiotics and the continuous shedding of E.coli resistant to them in most of the studied children in this community," he says

The study appeared in the July 1996 issue of the journal Antimicrobial Agents and Chemotherapy.

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