Pseudomonas Fluorescens in Sheep Milk Greek Yoghurt From Vlasina – A Biochemical Characterization

Abstract

Pseudomonas fluorescens is an aerobic, rod-shaped, non-sporulating gram-negative bacteria, mostlyfound in soil, decaying organic matter and feces. This species contaminates the milk mainly through animal feeddust, silage, utensils and polluted water. In addition to casein digestion, this psychotropic and lipolytic speciesgenerates butyric and caproic acids by fermentation of milk fat, which release a strong unpleasant odor and give arancid and bitter taste to dairy products. In this study we tested 48 hours old sheep's sour milk, produced in ahousehold in Vlasina, southeastern Serbia, using traditional method. Standard bacteriological protocols were usedfor isolation and identification Pseudomonas fluorescens strains. Biochemical identification was performed usingthe commercial API 32GN E system, and 60473057073 profile was obtained (Pseudomonas fluorescens, %Id=99.5and T=0.74). Positive biochemical tests were: N-acetyl-glukosamine (NAG), D-Ribose (RIB), Sodium malonate(MNT), Sodium acetate (ACE), Lactic acid (LAT), L-Alanine (ALA), D-Mannitol (MAN), D-Glucose (GLU), LArabinose(ARA), Capric acid (CAP), Valeric acid (VALT), Trisodium citrate (CIT), L-Histidine (HIS), Potasium2-ketogluconate (2KG), 3-Hydroxybutyric acid (3OBU), 4-Hydroxybenzoic acid (pOBE), L-Serine (SER), LProline(PRO) and Oxidase (OX). Negative biochemical tests were: L-Rhamnose (RHA), Inositol (INO), DSaccharose(SAC), D-Maltose (MAL), Itaconic acid (ITA), Suberic acid (SUB), Salicin (SAL), D-Melibose (MEL),L-Fucose (FUC), D-Sorbitol (SOR), Propionic acid (PROP), Potasium 5-ketogluconate (5KG), Glycogen (GLYG)and 3-hydroxybenzoic acid (mOBE). Based on the example of the strain Pseudomonas fluorescens, the API ID 32GN system proved to be precise and very efficient in the identification of this lipolytic type. Given thatpasteurization and cooling processes do not entirely inhibit the enzym activity and growth of this psychotrophicbacteria, informing individual milk and milk product manufacturers in the Vlasina region about good manufacturingpractices would limit contamination and bacteriological deterioration.