The Effect of Dietary Fish Oil on Survival After Infection with Klebsiella pneumoniae or Streptococcus pneumoniae VALTY ´ R STEFA ´ NSSON THORS 1 , AUÐUR ÞO ´ RISDO ´ TTIR 1 , HELGA ERLENDSDO ´ TTIR 2 , INGO ´ LFUR EINARSSON 3 , SIGURÐUR GUÐMUNDSSON 4 , EGGERT GUNNARSSON 5 and A ´ SGEIR HARALDSSON 1,3 From the 1 Department of Medicine, University of Iceland, 2 Department of Microbiology, Landspitali-University Hospital, Iceland, 3 Children’s Hospital Iceland, Landspı ´tali-University Hospital, Iceland, 4 Director of Health, Iceland, and 5 Institute of Experimental Pathology, University of Iceland, Iceland Dietary fish oil is believed to have a beneficial effect in various infections and in autoimmune disorders. This effect may correspond to an altered immune response. In order to discover whether the effect of dietary fish oil is different in various infections, we studied the survival of mice fed fish oil or corn oil supplemented diets and infected in the lungs with either Klebsiella pneumoniae or Streptococcus pneumoniae. 120 NMRI mice were divided into 4 groups, of which 2 groups were fed a fish oil supplemented diet and 2 a corn oil supplemented diet. After 6 weeks the mice were infected in the lungs with Klebsiella pneumoniae (fish oil groups and corn oil groups) or with Streptococcus pneumoniae serotype 3 (both groups). The survival rate was monitored. The experiment was performed twice. The survival of the mice fed fish oil enriched diet and infected with Klebsiella pneumoniae was significantly better compared with the mice fed corn oil enriched diet (p / 0.0001 and p / 0.0013). No difference was found between the mice fed corn oil enriched diet or fish oil enriched diet and infected with Streptococcus pneumoniae serotype 3 (p / 0.74 and p /0.15). Our results indicate that dietary fish oil has a beneficial effect on survival of mice after experimental pneumoniae when infected with Klebsiella pneumoniae, but not after infection with Streptococcus pneumoniae serotype 3. A ´ . Haraldsson, Children’s Hospital Iceland, Landspı´tali-University Hospital, 101 Reykjavı´k, Iceland (Tel. 543 1000, e-mail: asgeir@landspitali.is) INTRODUCTION The effects of dietary fish oil on the immune system have been extensively studied in recent years. The results indicate that dietary fish oil has a beneficial effect in various diseases and conditions, including infectious diseases as well as inflammatory and autoimmune disorders (1 /5). Fish oil is rich in omega-3 fatty acids, and dietary fish oil increases omega-3 fatty acids in cell membranes. Consequently, this may result in an increased production of inflammatory mediators, derived from omega-3 fatty acids but relatively less from omega-6 derived inflammatory agents, such as arachedonic acid. Earlier results from our group and others have shown the beneficial effect of dietary fish oil on survival after infections with Klebsiella pneumoniae (6, 7). In our studies we used corn oil, rich in omega-6 fatty acids or olive oil, rich in omega-9 fatty acids as control groups. In all these studies, fish oil clearly improved survival after infections with Klebsiella pneumoniae compared to the other additives, both when infected intramuscularly or in the lungs (6, 8). Most studies on the survival of mice fed fish oil have been carried out with Klebsiella pneumoniae, although other infective agents have been used. (7, 9  /13). Studies using Gram-positive bacteria are, however, scarce (14 /16). Streptococcus pneumoniae is a very common infectious agent in children and adults. It is thought that more than 150 million individuals are infected annually (17). Streptococcus pneumoniae is also the most frequent cause of bacterial meningitis, otitis and pneumonia (17). In order to discover any differences in the beneficial effect of dietary fish oil on various infectious agents, the current study was conducted in which survival was monitored in mice fed dietary fish oil or corn oil and infected with either Streptococcus pneumoniae serotype 3 or Klebsiella pneu- moniae. MATERIAL AND METHODS Experimental animals and diets The study was carried out at the Institute of Experimental Pathology at the University of Iceland. 120 female mice were divided into 4 equal groups. The mice had free access to food andwater during the experiment. For 6 weeks the mice were given standard rodent feed (Special Diets Services, Witham, Essex, UK). The mice were then divided into 4 groups; 2 groups were fed fish oil enriched diet (Ly ´si Ltd, Grandavegi, Reykjavı ´k, Iceland) and 2 groups were fed corn oil enriched diet (Wesson, Hunt-Wesson Inc., Fullerton, USA). The fish oil and corn oil were 10% w/w of the diet, and the fatty acid and calorie contents of the diets were comparable. The difference in fish oil and corn oil lies primarily in the high omega-3 fatty acid content of the fish oil. Infectious agents and infections The experiment was carried out twice. Streptococcus pneumoniae serotype 3 (Icelandic clinical strain) was provided by the Depart- ment of Microbiology, Landspı ´tali-University Hospital, Iceland. In Scand J Infect Dis 36: 102  /105, 2004 # 2004 Taylor & Francis. ISSN 0036-5548 DOI: 10.1080/00365540310018914 Scand J Infect Dis Downloaded from informahealthcare.com by University of Bristol on 09/24/13 For personal use only.