Physico-chemical surface characterization of a bacterial population isolated from a milking machine

The hydrophobicity of 26 species of bacteria representative of the main genera isolated from a rubber short milk tube, which is a constituent of a cluster from a milking machine, was determined. The materials forming the cluster namely rubber, stainless steel (SS) 316, stainless steel (SS) 304, glass and polymethylmethacrylate (PMMA) were also assayed in terms of hydrophobicity. In relation with the hydrophobicity of bacteria, all the strains of Lactobacillus lactis lactis as well as of Enterococcus faecalis are hydrophobic. Concerning Pseudomonas aeruginosa and Staphylococcus sciuri, some are hydrophobic and others are hydrophilic. All the materials are hydrophobic, being rubber, SS 316 and SS 304 the most hydrophobic surfaces while glass is the less hydrophobic. The free energy of adhesion between the bacteria and the materials in aqueous medium was calculated and used to predict which material of the cluster has a higher ability for biofilm formation and by this way contribute for milk contamination due to the release of bacteria from the deposit. For all the situations studied, adhesion is thermodynamically favourable to SS 316, SS 304 and rubber and less favourable to PMMA and glass.