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.
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