Frequency and distribution of tetracycline resistance genes in genetically diverse, nonselected, and nonclinical Escherichia coli strains isolated from diverse human and animal sources

Abstract

Nonselected and natural populations of Escherichia coli from 12 animal sources and humans were examined for the presence and types of 14 tetracycline resistance determinants. Of 1,263 unique E. coli isolates from humans, pigs, chickens, turkeys, sheep, cows, goats, cats, dogs, horses, geese, ducks, and deer, 31% were highly resistant to tetracycline. More than 78, 47, and 41% of the E. coli isolates from pigs, chickens, and turkeys were resistant or highly resistant to tetracycline, respectively. Tetracycline MICs for 61, 29, and 29% of E. coli isolates from pig, chickens, and turkeys, respectively, were >/=233 micro g/ml. Muliplex PCR analyses indicated that 97% of these strains contained at least 1 of 14 tetracycline resistance genes [tetA, tetB, tetC, tetD, tetE, tetG, tetK, tetL, tetM, tetO, tetS, tetA(P), tetQ, and tetX] examined. While the most common genes found in these isolates were tetB (63%) and tetA (35%), tetC, tetD, and tetM were also found. E. coli isolates from pigs and chickens were the only strains to have tetM. To our knowledge, this represents the first report of tetM in E. coli.

FIG. 1.

Average MICs of tetracycline for E. coli isolates obtained from pigs, chickens, turkeys, sheep, cows, goats, cats, humans, dogs, horses, geese, ducks, and deer, as determined by the plate dilution method.

FIG. 2.

Representative agarose gel of PCR products from nonclinical E. coli isolates, using primer group I, containing primers for tetB, tetC, and tetD. Lanes: 1, no template control; 2, E. coli H25; 3, E. coli H45; 4, E. coli H77; 5, E. coli P282; 6, E. coli P284; 7, E. coli P285; 8, E. coli P286; 9, E. coli P289; 10, E. coli P290; 11, E. coli P291; 12, E. coli P293; 13, E. coli P294; 14, E. coli P295; 15, E. coli P296; 16, E. coli P297; 17, E. coli P298; 18, E. coli P300; 19, E. coli P304; 20, E. coli P307; 21, E. coli P308; 22, E. coli P309; 23, E. coli P310; and 24, E. coli P312. E. coli isolate numbers beginning with P and H were isolated from pigs and horses, respectively. Lane M, molecular weight markers (100 bp ladder). The sizes of the amplicons in base pairs are indicated on the left.

FIG. 3.

Frequency of tetM, tetA, tetD, tetC, and tetB in E. coli isolates obtained from pigs, chickens, turkeys, sheep, cows, goats, humans, cats,dogs, horses, geese, ducks, and deer, as determined by colony multiplex PCR. The tetracycline genes tetE, tetG, tetK, tetL, tetO, tetS, tetA(P), tetQ, and tetX were not found among any of the 325 E. coli isolates tested.

FIG. 4.

Percentages of E. coli isolates obtained from pigs, chickens, turkeys, sheep, cows, goats, humans, cats, dogs, horses, geese, ducks, and deer, containing multiple tetracycline resistance genes as determined by multiplex PCR using primers for tetA, tetB, tetC, tetD, tetE, tetG, tetK, tetL, tetM, tetO, tetS, tetA(P), tetQ, and tetX.