Abstract
Lactobacillus reuteri is a natural inhabitant of selected animal and human gastrointestinal tract (GIT). Certain strains have the capacity to transform glycerol to 3-hydroxypropionaldehyde (3-HPA), further excreted to form reuterin, a potent antimicrobial system. Reuterin-producing strains may be applied as a natural antimicrobial in feed to prevent pathogen colonization of animals, such as in chicken, and replace added antimicrobials. To date, only seven L. reuteri strains isolated from chicken have been characterized which limits phylogenetic studies and host-microbes interactions characterization. This study aimed to isolate L. reuteri strains from chicken GIT and to characterize their reuterin production and antimicrobial resistance (AMR) profiles using phenotypic and genetic methods. Seventy strains were isolated from faces, crops and ceca of six chicken from poultry farms and samples from slaughterhouse. Twenty-five strains were selected for further characterization. Draft genomes were generated for the new 25 isolates and integrated into a phylogenetic tree of 40 strains from different hosts. Phylogenetic analysis based on gene content as well as on core genomes showed grouping of the selected 25 L. reuteri chicken isolates within the poultry/human lineage VI. Strains harboring pdu-cob-cbi-hem genes (23/25) produced between 156 mM ± 11 and 330 mM ± 14 3-HPA, from 600 mM of glycerol, in the conditions of the test. All 25 chicken strains were sensitive to cefotaxime (MIC between 0.016 and 1 μg/mL) and penicillin (MIC between 0.02 and 4 μg/mL). Akin to the reference strains DSM20016 and SD2112, the novel isolates were resistant to penicillin, possibly associated with identified point mutations in ponA, pbpX, pbpF and pbpB. All strains resistant to erythromycin (4/27) carried the ermB gene, and it was only present in chicken strains. All strains resistant to tetracycline (5/27) harbored tetW gene. This study confirms the evolutionary history of poultry/human lineage VI and identifies pdu-cob-cbi-hem as a frequent trait but not always present in this lineage. L. reuteri chicken strains producing high 3-HPA yield may have potential to prevent enteropathogen colonization of chicken.
Highlights
Lactobacillus reuteri inhabits the gastrointestinal tract (GIT) of selected animals where it forms biofilms on the non-glandular, squamous epithelium lining the upper GIT
By applying a reuterin selective colourimetric method on the plate, a total of 70 L. reuteri strains were isolated from feces and cecum of 6 chicken and from the crops of chicken obtained from the abattoir
This result indicated the high frequency of reuterin-producing L. reuteri strains in the chicken GIT, compared to the absence of reuterin production phenotype for isolated rodent strains (Walter et al, 2011)
Summary
Lactobacillus reuteri inhabits the gastrointestinal tract (GIT) of selected animals where it forms biofilms on the non-glandular, squamous epithelium lining the upper GIT. L. reuteri is the most abundant Lactobacillus species in the GIT, mainly found in the crop and the cecum (Wang et al, 2014). The evolutionary adaptation differentiates the species in host-adapted phylogenetic lineages comprised of isolates from rodents (lineages I and III), humans (lineage II), pigs (lineages IV and V) and poultry/human (lineage VI) (Oh et al, 2010; Spinler et al, 2014). Identified herbivore strains isolated from goat, sheep, cow, and horse have not yet been assigned to phylogenetic lineages (Yu et al, 2018). Host adaption has been linked to the occurrence of specific functional traits, e.g., rodent L. reuteri isolates possess the genes responsible for the synthesis of urease, as the strains are exposed continuously to urea in the forestomach of mice (Walter et al, 2011). In case of herbivore isolates, specific genes involved in porphyrin and chlorophyll metabolism and biosynthesis of amino acids have been identified, indicating possible hostadaptation mechanisms involving amino acids biosynthesis in herbivores (Yu et al, 2018)
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