ABSTRACT
We investigated the characteristics and persistence of Escherichia coli resistant to third-generation cephalosporins (3GCs) by early administration of ceftiofur or gentamicin and to analyze the impact of 3GC use in hatcheries. We studied 10 ceftiofur-treated flocks (CTFs) and 10 gentamicin-treated flocks (GTFs) of layers. Fecal samples were collected at 1, 2, 4, 8, 18, and 30 weeks of age for all flocks. Among the 446 E. coli isolates, 58 (29.0 %) of 200 isolates in CTFs were identified as 3GC-resistant E. coli and 28 (11.4 %) of 246 isolates in GTFs were identified as 3GC-resistant E. coli. The presence of 3GC-resistant E. coli isolates at 1, 2, and 4 weeks was significantly higher in CTFs than in GTFs (p < 0.05). Moreover, the rate of resistance to 3GCs gradually decreased from 83.3 % at 1 week of age to 4.4 % at 30 weeks of age in CTFs. Of the 86 3GC-resistant E. coli isolates, 32 isolates had ß-lactamase-encoding gene: blaCTX-M-14 (ten isolates), blaCTX-M-15 (three isolates), blaCMY-2 (five isolates), and blaTEM-1 (twenty-five isolates) genes. Plasmid replicon typing revealed that blaCTX-M-14, blaCTX-M-15, blaCMY-2, and blaTEM-1 were located on F, F and FIB, I1 and K, and I1 and FII, respectively. Furthermore, 18 isolates carried class 1 integrons, with four different gene cassettes. These results revealed that ceftiofur used in hatcheries can lead to an increase in the number of 3GC-resistant E. coli with many characteristics. A voluntary ban must be imposed on the use of 3GCs for 1-day-old chicks in poultry industry.