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United States Department of Agriculture

Agricultural Research Service


item Zaidi, M
item Diaz, P
item Tollefson, L
item Cray, Paula
item Headrick, M

Submitted to: American Society for Microbiology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/20/2001
Publication Date: 5/20/2001
Citation: Zaidi, M., Diaz, P., Tollefson, L., Cray, P.J., Headrick, M. 2001. Increased recovery of fecal quinolone-resistant escherichia coli in children using a macconkey-nalidixic acid screening plate. American Society for Microbiology Meeting. Session. 153. Abstract. A-70. P. 17.

Interpretive Summary:

Technical Abstract: Background: Commensal bacteria may serve as reservoirs of antibiotic resistance genes. The possibility that these may be transferred to zoonotic pathogens is under study. Resistance to Quinolones is of particular interest because of their value in treating severe human infections. Methods: Plain MacConkey agar (Mac) was compared to MacConkey agar with 32 'g/ml nalidixic acid (MacNA) for isolation of quinolone-resistant E. coli from human fecal flora. Fecal samples were collected from children with diarrhea and asymptomatic children attending daycare centers and kindergartens. Feces was diluted with PBS, plated onto Mac and MacNA plates, and incubated for 24-48 hrs. E. coli growing on both Mac and MacNA plates were tested for antimicrobial susceptibility by disk diffusion. Results: Samples were collected from 172 children, of whom 27 had diarrhea (Gp.1), 135 were from five daycare centers/kindergartens (Gp.2), and 10 were from a follow-up cohort of children who were shedding Salmonella. One hundred and four E. coli isolates were recovered from MacNA. Of these 104 samples, 95 E. coli were also isolated from the Mac plate. Recovery of nalidixic acid and Ciprofloxacin-resistant E. coli from the 172 children was 61% and 30% using MacNA and 2% and 0.6%, respectively, using Mac. Isolation from groups 1-3 using MacNA is shown in the table. (Group 1 (n=27) had a Nalidixic acid-R. E. coli percentage of 63% and a Ciprofloxacin-R E coli percentage of 33%. Group 2 (n=135) had a Nalidixic acid-R. E. coli percentage of 58% and a Ciprofloxacin-R E coli percentage of 27%. Group 3 (n=10) had a Nalidixic acid-R. E. coli percentage of 100% and a Ciprofloxacin-R E coli percentage of 50%. ) When comparing resistance markers to tetracycline, streptomycin, and trimethoprim-sulphamethoxazole, 64% of MacNA E. coli presented all 3 markers, compared to 44% of Mac E. coli. Resistance to ceftriaxone was 2% for MacNA isolates compared to 0% in Mac isolates. Conclusions: Using a specific nalidixic acid screening plate, the recovery of quinolone-resistant E. coli in these children was much higher than previously reported. Selected strains were also more resistant to other antibiotics. Children with a history of Salmonella colonization appeared to have a higher prevalence of quinolone-resistant E. coli Future investigations is needed to determine the public health significance of these findings.

Last Modified: 10/17/2017
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