Annals of Occupational Hygiene Advance Access originally published online on July 27, 2004
Annals of Occupational Hygiene 2004 48(6):541-546; doi:10.1093/annhyg/meh043
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© 2004 British Occupational Hygiene Society Published by Oxford University Press;
Six Month Tracking of Microbial Growth in a Metalworking Fluid After System Cleaning and Recharging
1 Centre de Recherche, Hôpital Laval, Institut Universitaire de Cardiologie et de Pneumologie and Département de Biochimie et de Microbiologie de l'Université Laval, 2725 Chemin Ste-Foy, Québec, Ste-Foy, G1V 4G5, Canada; 2 Environmental Health Sciences Research Center, University of Iowa, Iowa City, IA, USA and 3 NYU Medical Center, Tuxedo, NY, USA
* Author to whom correspondence should be addressed. Fax: +1 418 656 4509; e-mail: caroline.duchaine{at}bcm.ulaval.ca
Received 3 July 2003; in final form 4 March 2004
Large volumes of metalworking fluids (MWFs) are used in manufacturing industries for cooling and lubrication of metal pieces and tools during machining. MWFs accumulate microbial growth through continuous recirculation and reuse. We studied the progression of microbial contamination for 6 months after dumping, cleaning and recharging (DCR) of a large semi-synthetic MWF system managed with several biocides. Fresh, uncontaminated fluid was added to the system after extensive cleaning. The following samples were collected and analyzed: pre-DCR fluid (before system cleaning); neat fluid diluted to 6% with water; in use MWF 12 h and 1, 3 and 6 months post-DCR. Samples were analyzed for total microorganism concentrations by direct counting using fluorescence microscopy and by plate counting on various media (R2A, BHI, Middlebrooks and rose bengal under aerobic conditions). In addition, PCR was performed for the detection of mycobacteria. There was a rapid progression in the total bacterial counts as determined by fluorescence microscopy: 5·7 x 107 cells/ml in the pre-DCR used fluid, no measurable bacteria in the neat fluid, 6·9 x 106 cells/ml after 12 h and 2·2 x 106, 3·6 x 108 and 6·1 x 108 cells/ml after 1, 3 and 6 months, respectively. On average, only 0·2% of the direct count organisms were quantified on R2A cultures. PCR showed the presence of mycobacteria in the used MWF at 3 and 6 months. Mycobacteria were also identified from cultures on Middlebrooks and R2A. This study demonstrates that standard methods for cleaning MWF systems are inadequate since residual bacteria in the system can rapidly repopulate the newly charged MWF.
Keywords: biocides • machining • metal working fluids • mycobacteria • PCR
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