Enrofloxacin resistant bacteria will be susceptible to ciprofloxacin
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The extent to which antibiotic-resistant bacteria are excreted by humans who have not been exposed to antibiotics is not known. Children, who rarely receive fluoroquinolones, provide opportunities to assess the frequency of fecal excretion by fluoroquinolone-naïve hosts of fluoroquinolone-resistant gram-negative bacilli. Fresh nondiarrheal stools from children were processed by screening them on agar containing ciprofloxacin to recover ciprofloxacin-resistant gram-negative bacilli. Resistant isolates were identified, and ciprofloxacin MICs were determined. Resistant Escherichia coli isolates were also analyzed for urovirulence-associated loci. Thirteen (2.9%) of 455 stools yielded ciprofloxacin-resistant E. coli (seven children), Stenotrophomonas maltophilia (four children), and Achromobacter xylosoxidans and Enterobacter aerogenes (one child each). Neither the subjects themselves nor members of their households used fluoroquinolones in the 4 weeks preceding collection. Six of the seven resistant E. coli isolates belonged to phylogenetic groups B2 and D, in which extraintestinal pathogenic E. coli bacteria are frequently found. All resistant E. coli isolates contained at least three putative E. coli virulence loci. Most ciprofloxacin-resistant bacteria were resistant to additional antibiotics. Potentially pathogenic bacteria that are resistant to therapeutically important antimicrobial agents are excreted by some humans, despite these persons' lack of exposure to the particular drugs. The sources of these resistant organisms are unknown. This underrecognized reservoir of drug-resistant potential pathogens poses public health challenges.
Acquired antimicrobial resistance in bacteria poses major challenges for medical practice, public health, and the pharmaceutical industry. Organisms with reduced susceptibilities might proliferate and become more likely to disseminate when selective pressure is exerted by antimicrobial agents, as has been observed during prophylaxis of traveler's diarrhea with trimethoprim or trimethoprim-sulfamethoxazole (24). Human populations that have not been exposed to antibiotics provide opportunities to test the hypothesis that antibiotic-resistant microflora can be acquired in the community in the absence of selective pressure in a particular human host. If this hypothesis is correct, efforts to determine the origins of such resistant organisms may need to focus on determining the sources of their nonselective acquisition by human hosts, such as foods or other colonized humans.
Children are an easily defined population in which to determine if resistance to certain classes of antimicrobial agents can occur in unexposed individuals. Fluoroquinolones (e.g., ciprofloxacin), although extensively used in adults, are not approved for routine childhood administration because of concern about cartilage toxicity (10). Consequently, pediatric usage of fluoroquinolones, except for the treatment of selected illnesses, such as cystic fibrosis, is quite unusual in North America. Gram-negative bacilli, which are potential pathogens, are intrinsically susceptible to fluoroquinolones. Because children are rarely exposed to fluoroquinolones, gram-negative bacilli resistant to this class of antimicrobial agents in the fecal microflora of children probably emerged via selective pressure exerted in a different setting or host, before these individuals ingested the organisms. To attempt to determine if such resistant bacteria exist in the feces of children within the general population who have no history of relevant antimicrobial exposure, we conducted a prospective analysis of stools from children who had not been directly exposed to fluoroquinolones.