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

BACKGROUND: Lactobacilli are known as a valuable sourceof antimicrobial compounds and have a high potential of use infood biopreservation against food related microorganisms.OBJECTIVES: Antimicrobial potency of 63 dairy lactobacilliisolates against four highly important food-related microorganismswere evaluated. In addition, a new way in data organization wasintroduced, which led to a more informative and rationalcomparison of indicator microorganisms' susceptibilities to a setof compounds. Correlation of pH and antimicrobial propertieswas investigated. METHODS: Microbroth dilution assay wasused to evaluate indicator microorganisms' susceptibility tolactobacilli CFCS (cell free culture supernatant). Results wereorganized by both the conventional way - demonstrating theminimum inhibitory and lethal concentrations of CFCS - and anew suggested method, representing comparative effectivenessof each CFCS specimen against indicator microorganisms ofcomparison interest. RESULTS: Susceptibilities of tested strainswere in the following order: Escherichia coliO157:H7 > Listeriamonocytogenes > Aspergillus parasiticus> Candida parapsilosis.Despite the high susceptibility of L. monocytogenes, it showedthe highest resistance to death among the tested microorganisms.Eefficiency of Lactobacilli CFCS in killing the tested strainsshowed the following susceptibility order: E. coli O157:H7 > A.parasiticus> C. parapsilosis> L. monocytogenes. Antimicrobialproperty was in correlation with the pH value of CFCS. PH hada pronounced impact on susceptibilities of C. parapsilosisand E.coli in pH values of concentrated CFCS lower than 4 and 4.5,respectively. CONCLUSIONS: Potency of lactobacilli isolates ingrowth inhibition of the indicator microorganisms was foundpromising, and the suggested data organization method providedadditional information, leading to more precise comparison ofindicator microorganisms.