LEVELS OF BACTERIA, FUNGI AND ENDOTOXIN IN STORED TIMBER

Four series of wood samples were taken from the heartwood, sapwood and bark of six species of timber logs (American basswood, black cherry, black locust, red oak, soft maple and white poplar) in the summer fall, winter and spring. The samples were examined by dilution plating for total aerobic bacteria, gram-negative bacteria and fungi. The chromogenic modification of the Limulus amebocyte lysate test was also used for bacterial endotoxin. The numbers of the micro-organisms and endotoxin in the wood were significantly higher during warm periods (spring and summer) than during cold periods (fall and winter). They were highest in the wood of American basswood and black locust, exceeding the levels of 10(7) cfu g-1 and 10(5) endotoxin units g-1, respectively. Gram-negative bacteria and Corynbacterium spp. prevailed among aerobic bacteria recovered from heartwood and sapwood while Bacilli spp. were the most common in the bark. Enterobacter agglomerans (synonym: Erwinia herbicola), Agrobacterium radiobacter, Pseudomonas fluorescens, Pseudomonas maltophilia & Acinetobacter calcoaceticus were most common among gram-negative bacteria. Yeasts dominated the fungal flora of heartwood and sapwood, whereas filamentous fungi constituted a prevailing fraction in the bark. The results indicate that the microflora of the timber that apparently was undecayed may reach high levels and may contain allergenic and/or toxic species which pose a potential risk for sawmill workers.