Inhibition of bovine pathogen Escherichia coli by vaginal Lactobacillus acidophilus

OTERO, CLAUDIA; RUIZ HOLGADO, AÍDA PESCE; NADER-MACÍAS, MARIA ELENA

Roma, Italia

Congreso; Probiotics, prebiotics and new foods; 2001

Università Urbaniana. The Italian Digestive Disease Foundation.

Inhibition of bovine pathogen Escherichia coli by vaginal Lactobacillus acidophilus The objective of our research group is the selection of Lactobacillus strains for probiotic application in the bovine female reproductive tract, both as a barrier to pathogen income and as an alternative to use in the therapeutic of endometritis and metritis of pospartum cows. According to that, the capability to produce organic acids in 80 Lactobacillus strains isolated  from the bovine reproductive tract was screened. Lactobacillus acidophilus (strain 2014) was selected to further study the kinetic of lactic acid production and the inhibitory effect against b-hemolytic E. coli (strain 99/14)  isolated from exudates of cows with metritis. The plate diffusion technique was used to study the inhibitory effect of the supernatants fluids from the 80 Lactobacillus strains on E. coli growth according to standard method. The supernatants were added into 4 mm-holes punched on E. coli plates (106-107 CFU ml-1 on LAPTg agar). Aliquots of the samples were neutralized with NaOH (1 mol l-1). To study the kinetics of Lactic Acid  production, samples were taken at different times during growth of lactobacillus in LAPTg broth (37°C). The D and L-lactic acid isomers produced during the growth were quantified by the Enzymatic Bio Analysis method (Boehringer Mannheim)in the supernatants. The number of viable cells was determined by the plate dilution method. Associated cultures of lactobacillus and E. coli were performed in LAPTg broth at 37°C by using different inoculum levels. The growth of the different genus was determined by the plate dilution method.  All the Lactobacillus strains tested inhibited the E. coli growth in the plate diffusion method assayed. This effect can be attributed to the acid produced, because the inhibition disappeared after the neutralization of the supernatants. Only in 2.5% of the total number of strains tested, E. coli growth was not affected after neutralization. The levels of L-lactic acid increased simultaneously with the growth of the microorganisms. The highest concentration was reached at the early stationary growth phase with  2.5 g/l. The amounts of D-lactic acid increased in the late exponential phase, the highest concentration reached at the stationary growth phase with  6.3 g/l. In associated cultures, the growth of E. coli was inhibited by L. acidophilus. When  the difference between the initial inoculum of L. acidophilus and E. coli was 102  UFC/ml, a complete inhibition was observed after 24 h. However, when this difference was 104  UFC/ml, E. coli was inhibited after 10 h. At this point the concentration of D-lactic acid was highest. The L. acidophilus 2014 strain can be potentially used for probiotic purposes by the capability of inhibiting a bovine pathogen. This strain could be combined with other lactobacillus strains with different properties to be suggested as a probiotic to be used in the restoration of the vaginal microflora of cows.