Bacteriocin Production, Antibiotic Susceptibility and Prevalence of Haemolytic and Gelatinase Activity in Faecal Lactic Acid Bacteria Isolated from Healthy Ethiopian Infants

Abstract

The objective of this study was to characterise lactic acid bacteria (LAB) isolated from faecal samples of healthy Ethiopian infants, with emphasis on bacteriocin production and antibiotic susceptibility. One hundred fifty LAB were obtained from 28 healthy Ethiopian infants. The isolates belonged to Lactobacillus (81/150), Enterococcus (54/150) and Streptococcus (15/150) genera. Lactobacillus species were more abundant in the breast-fed infants while Enterococcus dominated the mixed-fed population. Bacteriocin-producing LAB species were isolated from eight of the infants. Many different bacteriocins were identified, including one new bacteriocin from Streptococcus salivarius, avicin A (class IIa) from Enterococcus avium, one class IIa bacteriocin from Enterococcus faecalis strains, one unknown bacteriocin from E. faecalis and two unknown bacteriocins from Lactobacillus fermentum strains and the two-peptide gassericin T from Lactobacillus gasseri isolate. Susceptibility tests performed for nine antibiotics suggest that some lactobacilli might have acquired resistance to erythromycin (3 %) and tetracycline (4 %) only. The streptococci were generally antibiotic sensitive except for penicillin, to which they showed intermediate resistance. All enterococci were susceptible to ampicillin while 13 % showed penicillin resistance. Only one E. faecalis isolate was vancomycin-resistant. Tetracycline (51 %) and erythromycin (26 %) resistance was prevalent among the enterococci, but multidrug resistance was confined to E. faecalis (47 %) and Enterococcus faecium (33 %). Screening of enterococcal virulence traits revealed that 2 % were β-haemolytic. The structural genes of cytolysin were detected in 28 % of the isolates in five enterococcal species, the majority being E. faecalis and Enterococcus raffinosus. This study shows that bacteriocin production and antibiotic resistance is a common trait of faecal LAB of Ethiopian infants while virulence factors occur at low levels.

Antagonistic Activity, Antimicrobial Susceptibility and Potential Virulence Factors of Enterococcus faecalis

“…Hemolytic activity is not only related to the presence of cylA gene and other factors should be taken into consideration, such as the environment and the presence of other genes in the operon [28]. Hemolytic activity and the cylA gene were not observed in a study on E. faecium strains isolated from seafood [9], although Valenzuela et al [5] reported that in 17% of E. faecalis isolates from plants and animals that contained the cylA gene, there was no hemolytic activity.…”

“…The presence of a specific gene does not mean its phenotypic expression, as reported for E. faecalis isolates from several sources including water and foods [2,15,28,35,39]. Hemolytic activity serves as an indicator of pathogenicity potential in Enterococcus spp.…”

“…Enterococcus resistance to antimicrobials results from their need for survival and persistence in highly competitive environments [28]. Resistance to antimicrobial agents in aquatic microorganisms indicates ecosystem change by human action, especially when antibiotics are released into sewers through the urine, feces and eventually animal carcasses [29].…”

“…Birri et al [28] who studied the gelatinolytic profile in bacteria of the Enterococcus genus and reported greatest prevalence in the E. faecalis species. Cormelato et al [40] compared gelatinase activity in E. faecium and E. faecalis isolates and also observed a greater presence of the gelE gene in E. faecalis.…”

“…1). Cytolysin production is due to an operon consisting of H genes, principally the cylA gene, because without it the expression of cylL L/S structural gene does not occur [28]. The CylL L/S structural gene does not appear to be an exclusive characteristic in isolates from clinical samples because it can be detected in the most diverse samples studied, including soil, water and foodstuffs [6].…”