Identification of the most abundant lactobacillus species in the crop of 1- and 5-week-old broiler chickens

Abstract

Bacteria from crops of 1- and 5-week-old broiler chickens fed with two brands (diets A and B) of wheat-based diets were isolated on Lactobacillus-selective medium and identified (n = 300) based on partial 16S rRNA gene sequence. The most abundant Lactobacillus species were L. reuteri (33%), L. crispatus (18.7%), and L. salivarius (13.3%). Regardless of farm and feed, L. reuteri was the most abundant species (P < 0.005) in the crops of the younger chickens. However, the amount of L. reuteri was significantly reduced in the crops of the 5-week-old chickens regardless of the feed (P = 0.016). The diversity of L. reuteri isolates was studied by fatty acid analysis, and the 94 L. reuteri isolates could be arranged into several clusters. The nisin sensitivities of the L. reuteri isolates were determined because nisin is a candidate coccidiostat. Sensitive isolates were found more frequently in younger chickens (77%) than in 5-week-old chickens (23%), whereas chickens fed with commercial feed B had a higher proportion of nisin-resistant isolates (73%) than did chickens fed with feed A (45%). Nisin-resistant strains are potential candidates for adjunct cultures for maintaining L. reuteri in its natural niche in the crop and are potential targets for genetic engineering with nisin-selectable food-grade vectors. The diversity of the L. reuteri population suggested that one should consider including several strains representing different clusters and nisin resistance phenotypes in candidate probiotic feed supplements for chickens.

FIG. 1.

Number of isolates belonging to the three dominant Lactobacillus spp. identified from the crops of 1- and 5-week-old chickens from four different farms. Identification of species was based on partial 16S rRNA gene sequencing and comparison of the sequences obtained against the National Center for Biotechnology Information genome BLAST library. Homology of >97% was used as the criterion for species identification. Isolates from the vicinity of the crop epithelium are also included.

FIG. 2.

Number of the most dominant Lactobacillus species isolates identified from the cultures originating from the epithelium of crops and crop contents of the chicken from F4. Identification of species was based on partial 16S rRNA gene sequencing and comparison of sequences obtained against the National Center for Biotechnology Information genome BLAST library. Homology of >97% was used as the criterion for species identification.

FIG. 3.

Gas chromatography fatty acid profiles of the 94 L. reuteri strains from the four farms F1, F2, F3, and F4 and two ages, 1- and 5-week-old chickens, marked as 1 and 5, respectively. Fatty acid data, with ED referring to the same species when the ED was <25 and the same strain when the ED was <10, are shown. L. reuteri isolates inhibited by nisin concentrations of ≤50 IU ml⁻¹ are in lightface type, and those between 50 to 500 IU ml⁻¹ are in italic type, whereas those resistant to >500 IU ml⁻¹ are in boldface type.