ORIGINAL ARTICLE Survey of bacterial populations present in US-produced linerboard with high recycle content K. Namjoshi, S. Johnson, P. Montello and G. S. Pullman Institute of Paper Science and Technology, Georgia Institute of Technology, Atlanta, GA, USA Introduction In 1993, the American Forest and Paper Association reported 16Æ7 million tonnes of old corrugated material, 62% of all containerboard used, was recovered in the United States for recycling. Fifty-eight percentage of the recovered containerboard was recycled into new container- board. By 2007, recovery of old corrugated containers reached 78Æ3% (AF&PA, 2007). With the high use of recy- cled fibre, bacterial contamination could become a prob- lem depending on the exposure history of paperboard to bacterial sources and end-product use. Specifically, there is a need to identify the type and amount of bacteria present in recycled containerboard and to determine whether the micro-organisms found are of potential health concern. If bacteria of concern persist, it is likely that recycled materials will see increased regula- tion. In addition, the consumer will turn elsewhere for substitute products or to companies with microbial qual- ity control programmes. If significant populations of bac- teria are found, a future question would focus on bacterial populations after repeated recycling. At the time, this research began there were only a few published reports on the microbiological content of paperboard and no reports on paperboard with recycle content (Bendt 1985; Vaisanen et al. 1989, 1991, 1994; Kneifel and Kaser 1994). The goals for our work were as follows: (i) adopt or develop methods to detect and quantify aerobic micro- organisms present on recycled fibre with a focus on Keywords Bacillus, paperboard, paper microbiology, recycled fibre, thermal death. Correspondence Gerald S. Pullman, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th Street NW, Atlanta, GA 30332-0620, USA. E-mail: Jerry.Pullman@ipst.gatech.edu Present address P. Montello, Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602, USA. 2009 ⁄ 0421: received 5 March 2009, revised 20 April 2009 and accepted 30 May 2009 doi:10.1111/j.1365-2672.2009.04437.x Abstract Aims: To survey paperboard products from 17 US mills for bacterial populations and for bacteria potentially harmful to human health. Methods and Results: Culturable aerobic bacteria were isolated from paper- board products using selective and nonselective medium. Resulting colonies from samples from three regions of the United States were identified using fatty acid methyl ester analysis. Percentages of bacteria species found were Bacillus megaterium (47), Bacillus licheniformis (15), Bacillus pumilus (12), Paenibacillus macerans (5), Paenibacillus pabuli (3), Bacillus subtilis (2), Bacillus cereus (2), Bacillus coagulans (1), Bacillus circulans (1), Bacillus brevis (1), Bacillus thuringiensis (1), Paenibacillus polymyxa (1), Cellulomonas turbata (1), Cellulomonas flavigena (1), unidentified Bacillus sp. (3) and unidentified bacteria (1). Conclusions: Recycled paperboard contained high populations of bacteria, and a positive correlation was found between recycle content and bacterial popula- tions. Escherichia coli, Salmonella, Shigella or confirmed coliform bacteria were not found in any product. Significance and Impact of the Study: Populations of bacteria did not differ significantly from original counts over a 4-month period of dry storage, indicating that bacteria persist in paperboard over long periods and may re- enter the recycling process. The predominance of heat-tolerant endospore- forming bacteria explains the high bacteria counts found in paperboard made from recycled materials. Journal of Applied Microbiology ISSN 1364-5072 416 Journal compilation ª 2009 The Society for Applied Microbiology, Journal of Applied Microbiology 108 (2010) 416–427 ª 2009 The Authors