"Although commensal bacteria are not the specific targets, they are continually exposed to antimicrobial therapy, and many have become potential reservoirs of resistant strains and resistance genes that can be transferred to pathogenic bacteria," Dr. Bartoloni said in a presentation on April 2^nd. Indeed, this concept has been used to estimate the spread of acquired microbial resistance.

The ANTRES study was designed to investigate faecal carriage of resistant E. coli in healthy children in 4 urban areas of Bolivia and Peru. The study population consisted of 800 healthy children age 6 to 72 month from each of the 4 urban areas.

The baseline ANTRES survey was carried out in 2002. Dr. Bartoloni reported on its combination with results from the second ANTRES survey in 2005.

Analysis of data from the 2002 and 2005 surveys showed various levels of antimicrobial resistance in commensal E. coli. High resistance rates to ampicillin (95% vs 96%, respectively), trimethoprim-sulphamethoxazole (SXT; 94% vs 94%), tetracycline (93% vs 93%) and chloramphenicol (69% vs 70%) were confirmed, along with the lower resistant rate to kanamycin (about 30%).

There was a significant increasing trend in resistance to streptomycin (82% vs 92%) and gentamicin (21% vs 27%), and large significant increases in resistance to the quinolones nalidixic acid (35% vs 57%) and ciprofloxacin (18% vs 33%), and to ceftriaxone (0.1% vs 1.7%).

"These results were consistently observed in the 4 surveyed urban areas," Dr. Bartoloni said, although the specific increases in each area varied. Thus, while all 4 sites showed similar low levels of ceftriaxone resistance in 2002 (about 0.1% each), by 2005 the 2 Peru sites each showed increases to 1.5%, with the 2 Bolivian sites increasing to 2.9% and 0.9%.

Similarly, across the Peruvian and Bolivian sites (respectively), the 2002 resistances to nalidixic acid (about 25%-45%) and ciprofloxacin (about 10%-25%) increased to about 40% to 70%, and to about 20% to almost 50%, with the greatest increases (20%-30%) seen for the 2 Peruvian sites in both cases.

Dr. Bartoloni also indicated that in a study in 1992 in the same Bolivian area of Camiri, the data showed a resistance rate of 4% to the quinolone nalidixic acid, and no resistance to the quinolone ciprofloxacin.

Thus, these increased resistance rates seen with the quinolones and expanded-spectrum cephalosporins in the child population are particularly alarming, he said, and make it necessary to understand how they have developed, particularly as the available data on household antibiotic consumption excluded previous use of these antibiotics in the children who participated in the survey.

At present, the researchers believe that this phenomenon most likely reflects increased exposure of these children to resistant E. coli within a contaminated household setting and/or via the food chain, Dr. Bartoloni said.

To understand this system better, however, further monitoring of the situation is needed in addition to a better understanding of the epidemiological relationship between these bacteria and those of the clinical isolates, he said.

Similarly, there is the need to know if these resistant strains are also carried by adults, and how they might correlate with the antibiotic consumption in the hospitals and the community, he said.


[Presentation title: Increasing Resistance to Quinolones and Expanded-Spectrum Cephalosporins in Commensal Escherichia Coli From Children Living in Urban Areas of Latin America: A Report From the ANTRES Research Project. Abstract O358]

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