10 Fast detection of bacteria in samples presumed to be un-contaminated, such as blood, is of great 11 importance. Indeed, rapid diagnosis allows the setup of appropriate antibiotic treatment. Besides clinical 12 issues, there are many other domains, such as food processing or drug manufacturing, where the strict 13 absence of any bacteria has to be assessed. Because the bacterial load found in most contaminated 14 samples is often below the limit of detection for currently validated assays, a preliminary enrichment step 15 is required to allow bacterial multiplication before proceeding to the analysis step, whatever it might be-16 cultural, immunological or molecular methods. In this study, we describe the use of a biosensor for single-17 step bacteria detection. The whole analysis is performed in less than 20 hours, during the growth phase of 18 the microorganisms , using an array of antimicrobial peptides (AMPs) coupled with a surface plasmon 19 resonance imager (SPRI). A wide range of bacterial strains are assayed, showing differentiated affinity 20 patterns with the immobilized peptides, which are confirmed by multivariate analysis. This work 21 establishes the evidence that antimicrobial peptides, mostly used so far in the antibiotic drug industry, are 22 suited for the wide-spectrum detection of unknown bacteria in samples, even at very low initial loads. 23 Moreover, the small set of AMPs that were assayed provided a specific affinity profile for each pathogen, 24 as confirmed by multivariate analyses. Furthermore, this work opens up the possibility of applying this 25 method in more complex and relevant samples such as foodstuff, urine or blood. 26 27 28