Rational evaluation of antimicrobial properties of lactobacilli isolates against some pathogenic microorganisms: a new method comparing the susceptibility of indicator microorganisms

Abstract

BACKGROUND: Lactobacilli are known as a valuable source<br />of antimicrobial compounds and have a high potential of use in<br />food biopreservation against food related microorganisms.<br />OBJECTIVES: Antimicrobial potency of 63 dairy lactobacilli<br />isolates against four highly important food-related microorganisms<br />were evaluated. In addition, a new way in data organization was<br />introduced, which led to a more informative and rational<br />comparison of indicator microorganisms' susceptibilities to a set<br />of compounds. Correlation of pH and antimicrobial properties<br />was investigated. METHODS: Microbroth dilution assay was<br />used to evaluate indicator microorganisms' susceptibility to<br />lactobacilli CFCS (cell free culture supernatant). Results were<br />organized by both the conventional way - demonstrating the<br />minimum inhibitory and lethal concentrations of CFCS - and a<br />new suggested method, representing comparative effectiveness<br />of each CFCS specimen against indicator microorganisms of<br />comparison interest. RESULTS: Susceptibilities of tested strains<br />were in the following order: Escherichia coliO157:H7 > Listeria<br />monocytogenes > Aspergillus parasiticus> Candida parapsilosis.<br />Despite the high susceptibility of L. monocytogenes, it showed<br />the highest resistance to death among the tested microorganisms.<br />Eefficiency of Lactobacilli CFCS in killing the tested strains<br />showed the following susceptibility order: E. coli O157:H7 > A.<br />parasiticus> C. parapsilosis> L. monocytogenes. Antimicrobial<br />property was in correlation with the pH value of CFCS. PH had<br />a pronounced impact on susceptibilities of C. parapsilosisand E.<br />coli in pH values of concentrated CFCS lower than 4 and 4.5,<br />respectively. CONCLUSIONS: Potency of lactobacilli isolates in<br />growth inhibition of the indicator microorganisms was found<br />promising, and the suggested data organization method provided<br />additional information, leading to more precise comparison of<br />indicator microorganisms.