Effect of NaOH (caustic wash) on the viability, surface characteristics and adhesion of spores of a Geobacillus sp. isolated from a milk powder production line

• Published in: Letters in applied microbiology Vol. 52; no. 2; pp. 104 - 108
• Main Authors: Brent Seale, R., Flint, S.H., James McQuillan, A., Bremer, P.J.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-02-2011; Blackwell
• Subjects: Animals; bacillus; Bacterial Adhesion - drug effects; bacterial spores; Biological and medical sciences; Caustics; dairy; Dairying; Fundamental and applied biological sciences. Psychology; Geobacillus; Geobacillus - drug effects; Geobacillus - isolation & purification; Geobacillus - ultrastructure; Microbial Viability; Microbiology; Milk - microbiology; Powders; Sodium Hydroxide - toxicity; Spores, Bacterial - drug effects; Spores, Bacterial - ultrastructure; Stainless Steel; Surface Properties; Bacillales; Applied microbiology; Bacillus; Dried milk; Production; Bacteria; Bacillaceae; bacterial spores; Adhesion; Viability; dairy; Spores
• ISSN: 0266-8254; 1472-765X
• DOI: 10.1111/j.1472-765X.2010.02970.x

Aim:  To investigate the viability, surface characteristics and ability of spores of a Geobacillus sp. isolated from a milk powder production line to adhere to stainless steel surfaces before and after a caustic (NaOH) wash used in clean‐in‐place regimes.
Methods and Results:  Exposing sessile spores to 1% NaOH at 65°C for 30 min decreased spore viability by two orders of magnitude. The zeta potential of the caustic treated spores decreased from −20 to −32 mV and they became more hydrophobic. Transmission electron microscopy revealed that caustic treated spores contained breaks in their spore coat. Under flow conditions, caustic treated spores suspended in 0·1 mol l−1 KCl were shown to attach to stainless steel in significantly greater numbers (4·6 log10 CFU cm−2) than untreated spores (3·6 log10 CFU cm−2).
Conclusions:  This research suggests that spores surviving a caustic wash will have a greater propensity to attach to stainless steel surfaces.
Significance of Study:  The practice of recycling caustic wash solutions may increase the risk of contaminating dairy processing surfaces with spores.