Enterococci from breast-fed infants exert higher antibacterial effects than those from adults: A comparative study

Maryam Rahmani, Fereshteh Saffari, Omid Aboubakri, Shahla Mansouri
2020 Human Microbiome Journal  
Enterococci are members of human gut microbiota which their colonization has been demonstrated even before birth. This indicates their importance in infant health. As this population is dynamic and varies with age, this study was designed to assess and compare the antibacterial effects of enterococci from breast-fed infants and those from adults. Fecal isolates of enterococci were isolated from infants and healthy adults and were identified to the species level by phenotypic and genotypic
more » ... and genotypic methods. Further, they were evaluated for their potential to exert antibacterial effect against ten standard bacterial strains using bilayer spot test. Of a total of eighty-nine recovered enterococcal isolates, Enterococcus faecium and E. faecalis were the most common species (98%) and showed inhibitory effects at least against one indicator strain. Comparison between isolates from two studied groups showed that isolates from neonates introduced significantly higher growth inhibitory effects against six indicator strains (P < 0.05) and these effects were frequently attributable to E. faecium isolates. In addition, the highest growth inhibitory effect was observed against Listeria monocytogenes. Antimicrobial effects of enterococci in human microbiota change during time. The beneficial role of these organisms within the neonatal period suggests the potential of enterococci from breast-fed infants for probiotic application. Key words: Enterococci, infants, antibacterial effects, microbiota 1mm (±) and 0 mm (-), defined as high, moderate, weak, no clear and no inhibition, respectively [18]. 2.3. Statistical analysis. Manne Whitney test was used to determine the significance of differences between isolates, and the chi-square test was used for categorical variables. The statistical analyses were performed by using SPSS (version 22) software and a P < 0.05 was statistically considered significant. Results 3.1. Bacterial isolates. Totally, from 61 and 66 fecal specimens collected from neonates and adults, respectively, 62% and 73% of specimens contained enterococcus spp. As presented in Table 1 , 89 isolates were identified as Enterococcus spp. No significant difference was found for distribution of species between two groups (neonates and adults) ( Table 1) . 3.2. Antibacterial activity. Overall, all enterococci showed growth inhibition effect at least against one indicator strain. As shown in Table 2 , the best activity was detected against L. monocytogenes, so that 88.5 % (77 of 87) of tested enterococci showed inhibition zone > 2mm. Comparison between isolates from neonates and adults showed that inhibition effect against P. aeruginosa, K. pneumoniae, E. coli, EPEC, EHEC and S. aureus was exerted significantly higher by neonatal isolates than from adult's (P < 0.05) (Fig. 2) . These effects were frequently attributable to E. faecium isolates (6 indicator strain, P < 0.05) (Fig. 3 , Suppl. 1). Exceptionally, for L. monocytogenes, isolates from adults showed more antibacterial effects than those from neonates, but this difference was not statistically significant (Fig. 2) . Regardless of the source of enterococci (neonate or adult), comparison between the mean of inhibition zone diameter introduced by E. faecalis and E. faecium isolates, did not show any significant difference except against EPEC, EIEC and K. pneumoniae which were inhibited significantly higher by E. faecalis isolates (P < 0.05) (Suppl. 2).
doi:10.1016/j.humic.2020.100072 fatcat:2virsza7mzc5vhpbnr2oq5j7mi