Infections, antibiotic treatment and the mircrobiome in relation to schizophrenia

Schizophrenia is a heterogeneous disorder with several potential pathophysiological mechanisms, including immune activation. Infections have been identified as a significant contributing risk factor for schizophrenia; this association is reviewed together with the potential impact of antibiotic treatment and alterations of the intestinal microbiota. Both infections and the treatment with antibiotics may alter the composition of the gut microbiota, causing dysbiosis, which in animal studies has been associated with alterations of behavior. Of the few studies that have been conducted on humans, some have suggested alterations in the microbial composition of individuals with schizophrenia compared to healthy controls, albeit with conflicting results. Recently, increased attention has emerged regarding potential adverse effects from antibiotics, as a number of these have been associated with an increased risk of psychotic episodes. Particularly, the fluoroquinolones have been associated with neurotoxic adverse events. The association between schizophrenia and infections, antibiotic treatment and dysbiosis, may be an epiphenomenon, which could be explained by other confounding factors. However, these associations could be causal and could therefore be important risk factors in a subgroup of patients. Large-scale well-matched longitudinal studies are needed with measurements of immune markers from multiple biological samples, ranging from material close to the brain, as cerebrospinal fluid and brain-scans targeting neuroinflammation, to analysis of blood and intestinal microbiota. This would help to obtain more definite results on the association between infections, immune components and microbiota alterations in relation to schizophrenia.