Antimicrobial Drug Resistance in Escherichia coli from Humans and Food Animals, United States, 1950–2002

We conducted a retrospective study of Escherichia coli isolates recovered from human and food animal samples during 1950-2002 to assess historical changes in antimicrobial drug resistance.A total of 1,729 E. coli isolates (983 from humans, 323 from cattle, 138 from chickens, and 285 from pigs) were tested for susceptibility to 15 antimicrobial drugs.A signifi cant upward trend in resistance was observed for ampicillin (p<0.001),sulfonamide (p<0.001), and tetracycline (p<0.001).Animal strains showed increased resistance to 11/15 antimicrobial agents, including ampicillin (p<0.001),sulfonamide (p<0.01), and gentamicin (p10 years (vancomycin) (2,3).Escherichia coli is usually a commensal bacterium of humans and animals.Pathogenic variants cause intestinal and extraintestinal infections, including gastroenteritis, urinary tract infection, meningitis, peritonitis, and septicemia (4,5).Therapeutic options vary depending on the type of infection.For example, for urinary tract infections, trimethoprim/sulfamethoxazole and fl uoroquinolones are treatments of choice (6), whereas for Shiga toxinproducing E. coli infections, antimicrobial drug therapy is not recommended ( 7).E. coli is sometimes used as a sentinel for monitoring antimicrobial drug resistance in fecal bacteria because it is found more frequently in a wide range of hosts, acquires resistance easily (8), and is a reliable indicator of resistance in salmonellae (9).Surveillance data show that resistance in E. coli is consistently highest for antimicrobial agents that have been in use the longest time in human and veterinary medicine (10).The past 2 decades have witnessed major increases in emergence and spread of multidrug-resistant bacteria and increasing resistance to newer compounds, such as fl uoroquinolones and certain cephalosporins (3).For example, a study of the susceptibility of E. coli isolates recovered from hospitals during a 12-year period (1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982) showed no major change in resistance to any of the antimicrobial drugs tested (11).In contrast, a retrospective analysis of E. coli from urine specimens collected from patients during 1997-2007 showed an increasing resistance trend for ciprofl oxacin, trimethoprim/sulfamethoxazole, and amoxicillin/clavulanic acid (12).Similarly a 30-year follow-up study on E. coli in Sweden showed Antimicrobial Drug Resistance in Escherichia coli from Humans and Food Animals, United States,