High prevalence of tetracycline resistance in Enterococcus isolates from broilers carrying the erm(B) gene.

A total of 73 isolates of Enterococcus spp. carrying the erm(B) gene were obtained from cloacal swabs of broiler chickens derived from 13 different farms in Belgium. The erm(B) gene encodes resistance to macrolides, lincosamides and streptogramin B antibiotics (MLS(B)). The isolates belonged to eight different species: Enterococcus avium (eight isolates), Enterococcus casseliflavus (11 isolates), Enterococcus cecorum (eight isolates), Enterococcus durans (seven isolates), Enterococcus faecalis (10 isolates), Enterococcus faecium (17 isolates), Enterococcus gallinarum (seven isolates) and Enterococcus hirae (five isolates). Acquired resistance to tetracycline was detected in 68 of the isolates, and in 62 of these it was associated with the presence of the resistance genes tet(L), tet(M), tet(O) or tet(S). In three E. faecium isolates that were phenotypically susceptible to tetracycline, tet(L) or tet(M) was present. The transposon integrase gene (int gene) of the Tn916/Tn1545 transposon family was detected in 18 of the 54 isolates that contained the tet(M) gene. It was concluded that acquired resistance to tetracycline antibiotics is often present in enterococci from poultry carrying the erm(B) gene. The use of tetracyclines in poultry may therefore co-select for resistance to MLS(B) antibiotics, which may be important as alternative therapy for enterococcal infections in humans.

Cloacal Lactobacillus isolates from broilers show high prevalence of resistance towards macrolide and lincosamide antibiotics.

Eighty-seven Lactobacillus strains isolated from cloacal swabs of broiler chickens derived from 20 different farms in Belgium were identified to species level and tested for susceptibility to macrolide and lincosamide antibiotics. Five different Lactobacillus species were identified as being predominantly present in the cloacae of broilers: Lactobacillus crispatus, Lactobacillus salivarius subsp. salivarius, Lactobacillus amylovorus, Lactobacillus gallinarum and Lactobacillu sreuteri. Acquired resistance prevalence to macrolides and lincosamides was very high in the investigated lactobacilli: 89% of the strains were resistant to either or both lincosamide and macrolide class antibiotics. The vast majority of these resistant strains (96%) displayed constitutive resistance. More than one-half of the macrolide and/or lincosamide resistant strains carried an erm(B), erm(C), mef(A), lnu(A) gene or a combination of these genes.

Cloacal Lactobacillus isolates from broilers often display resistance toward tetracycline antibiotics.

Lactobacillus crispatus, L. reuteri, L. amylovorus, L. gallinarum, and L. salivarius subsp. salivarius strains isolated from cloacal swabs of broiler chickens derived from 20 different farms in Belgium were tested for susceptibility to tetracycline and minocycline. Acquired resistance percentages to these antibiotics were extremely high for L. crispatus, L. reuteri, L. gallinarum, and L. salivarius subsp. salivarius (75%-100%). L. amylovorus on the contrary, displayed lower resistance percentages (25%) toward minocycline and tetracycline. In several strains, resistance against the tetracycline antibiotics was associated with the presence of the resistance genes tet(K), tet(L), tet(M), tet(W), and tet(Z). To our knowledge, this is the first report of tet(Z) in lactobacilli and tet(K), tet(L), and tet(W) in lactobacilli identified to species level. Our findings strengthen the evidence of intestinal Lactobacillus species acting as a pool of antimicrobial resistance genes urging the need for prudent use of tetracycline antibiotics in poultry production.

Susceptibility of Clostridium perfringens strains from broiler chickens to antibiotics and anticoccidials.

Clostridium perfringens strains isolated in 2002 from the intestines of broiler chickens from 31 different farms located in Belgium were tested for susceptibility to 12 antibiotics used for therapy, growth promotion or prevention of coccidiosis. All strains were uniformly sensitive to the ionophore antibiotics monensin, lasalocid, salinomycin, maduramycin and narasin. All were sensitive to avilamycin, tylosin and amoxicillin, while flavomycin (bambermycin) showed low or no activity. Chlortetracycline and oxytetracycline were active at very low concentrations, but low-level acquired resistance was detected in 66% of the strains investigated. Fifty percent of these strains carried the tetP(B) resistance gene, while the tet(Q) gene was detected in only one strain. One strain with high-level resistance against tetracyclines carried the tet(M) gene. Sixty-three percent of the strains showed low-level resistance to lincomycin. The lnu(A) and lnu(B) genes were each only found in one strain. Compared with a similar investigation carried out in 1980, an increase was seen in resistance percentages with lincomycin (63% against 49%) and a slight decrease with tetracycline (66% against 74%).

The effect of Ornithobacterium rhinotracheale vaccination of broiler breeder chickens on the performance of their progeny.

The effect of Ornithobacterium rhinotracheale vaccination of broiler breeders on antibody titres and performance of breeders and broilers was investigated. O. rhinotracheale antibody titres and performance data were recorded from 16 different broiler breeder flocks and from 79 of their broiler progeny flocks. Eight breeder flocks were vaccinated with an inactivated O. rhinotracheale vaccine while the other eight breeder flocks were left unvaccinated against this bacterium. Following vaccination, mean O. rhinotracheale antibody titres in the breeders rose to a 6.5 log(2) units higher value than in unvaccinated breeders, and remained at a mean titre of 15 log(2) units during the entire production period. This resulted in significantly higher maternal antibody titres against O. rhinotracheale in the broiler progeny of vaccinated breeder flocks compared with the offspring of unvaccinated flocks. Statistical analyses revealed no differences in performance between vaccinated and unvaccinated breeders. There was a significantly lower mean mortality rate and higher mean production index in the broilers derived from vaccinated breeders.