Gastrointestinal microbial population and impact of antibiotic treatment in early infants.

Introduction. The gastrointestinal microbial community is dynamic during the first years of life, before stabilizing to an adult-like state. However, little is known about the impact of antibiotic treatment on the developing human gut microbiome. Here we report a microbiological study on the gut composition of infants, approximately half of whom received multiple courses of antibiotics during the six months of life.Material and Methods. Fecal samples were collected from 56 infants about six months age, hospitalized at the Regina Margherita Children Hospital and affected by various diseases (bronchiolitis,urinary tract infections,pneumonia,etc).Specimens were processed at Public Health and Pediatrics Dept., Microbiology Section.Two groups were selected according to the antibiotic therapy (A=32) or not (B=24). Stool samples were collected from diaper and cultured on selective media to detect lactobacilli, bifidobacteria, enterococci, Enterobacteriaceae and yeasts. The qualitative analysis was performed using Gram staining and by biochemical methods (API System). Moreover, we considered the number of different taxa (species or strains) identified after antibiotic treatment (ceftriaxone, amoxicillin+clavulanate acid, clarithromyicin).Results. On average,the infants not treated with antibiotics had a richer microbial community compared to the infants who received antibiotics: Enterobacteriaceae (B=3.6x108 vs A=1.2x106 CFU/gr), aerobial total count (B=4.7x1010 vs A=2.5x108 CFU/gr), bifidobacteria (B=3.6x105 vs A=1.4x103CFU/gr).We observed that lactobacilli were detectable less frequently in the guts of infants treated with antibiotics than in the control group (B).The data obtained show that in A, breast or artificial feeding contribute to re-establish an intestinal bacterial balance similar to B group. Moreover, the investigation revealed that the gut microbiota of the clarithromyicin and ceftriaxone-treated infants had significantly higher proportions of enterococci than the controls (3x109, 1.2x109 vs 9.4 x108, respectively),while the Bifidobacterium genus was predominant in ceftriaxone and amoxicillin+clavulanate acid groups compared to untreated group (7.8x109,1.6x109vs 8.4x107). A larger percentage of subjects receiving antibiotics (12%) was colonized by Candida spp. than the controls (8%).Discussion and Conclusions. Our findings showed that antibiotics treatment in early infants affects all aspects of gastrointestinal microbial population, including species richness, diversity, community structure and the abundance of colonizing bacteria genera. However, the subsequent lactation with breast milk or artificial milk restore the altered population of lactobacilli and bifidobacteria to values comparable to those of children not treated with antibiotics