The aim of the present study was to investigate phenotype resistance profiles and some

genetic determinants in resident E. coli bacteria isolated from broilers whose ration was supplemented

with a probiotic formula containing a Bacillus licheniformis BL11 strain (Huvepharma, Belgium).

For bacteriological examination, cloacal swabs were collected at various intervals throughout the

study: from day-old, 14-day-old and 28-day-old chickens. A total of 300 swabs were collected for

bacteriological examination: 150 from control and 150 from probiotic-supplemented chickens. The

total number of E. coli strains isolated from control and experimental broilers was 214: 107 strains

from the control group and another 107 from birds that received a probiotic with the feed.

Among E. coli isolates from day-old broilers in the experimental group, the highest resistance

rate was observed against gentamicin (69.0%), followed by that against ampicillin and amoxicillin/

clavulanic acid (52.4%). Escherichia coli isolated from probiotic-supplemented broilers at 14 days

of age demonstrated statistically significantly higher rate of resistance (P ≤ 0.05) against cefotaxime

(51.6%) and ceftazidime (38.7%) compared with isolates from the control group (12.0%). Also, the

prevalence of E. coli strains resistant against amoxicillin/clavulanic acid in supplemented broilers

(35.5%) was insignificantly lower than the respective rate in control chickens (48.0%). At 28 days

of age, the resistance against ciprofloxacin in poultry E. coli isolates in probiotic-fed broilers was

significantly higher (P ≤ 0.01) than the resistance rate in non-supplemented birds (85.3% and 52.7%,

respectively). The resistance to ampicillin among the isolates from experimental broilers was statistically

significantly more common (P ≤ 0.01), i.e., 82.3%, as well as against third generation cephalosporins

(44.1%, 41.2%). The genetic analysis of resistance in commensal E. coli isolates revealed the presence

of bla CTX-M-1, tetA and QnrS genes. In conclusion, we should note that in our study related to the use of

Bacillus licheniformis BL 11 strain, a probiotic formula in broilers, no basic differences were observed

both in terms of the prevalence of resistance to chemotherapeutics and in terms of economic indicators

in the broilers in the control and experimental groups.