**1. Introduction**

Phenol‐soluble modulins (PSMs) are a family of multifunctional, amphipathic and α‐helical peptides produced by virtually all staphylococcal strains [1–3]. They have recently drawn much attention owing to the key contribution of some PSM peptides to staphylococcal viru‐ lence, in particular in highly virulent *Staphylococcus aureus* [4]. In addition, they have antibac‐ terial activity, likely to compete with other environmental rival bacteria such as streptococci [5, 6], as well as biofilm structuring and dissemination functions [7, 8]. *Staphylococcus aureus* is an important and versatile opportunistic human pathogen that can cause a wide range of acute and chronic diseases, which range from superficial infections to invasive and life‐threat‐ ening ones [9, 10].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PSMs were first identified in 1999 by the group of Seymour Klebanoff with the descrip‐ tion of a "pro‐inflammatory complex". They were isolated by hot phenol extraction from *S. epidermidis* culture filtrate [11]. The peptides were named PSMα, PSMβ and δ‐toxin. Afterwards, the PSM compositon of *S.aureus* was also analyzed more systematically, which include the shorter α‐type (four PSMα1‐PSMα4 peptides and δ‐toxin) and the longer β‐type (the PSMβ1 and PSMβ2 peptides). The PSMs are encoded at three different locations in the genome. Four PSMα1‐PSMα4 peptides are encoded in the PSMα operon. PSMβ1 and PSMβ2 are encoded in the PSMβ operon. δ‐toxin is encoded within the coding sequence for RNAIII [12, 13].

*S. aureus* are considered to be second to salmonella as important foodborne pathogens, which have been frequently reported as agents leading to outbreaks of diseases caused by entero‐ toxins in ready‐to‐eat food and food products. The pathogenic mechanisms of *S. aureus* have been examined extensively through different stages of infection. Various staphylococcal components contribute to virulence with an improved understanding of specific functions [14–16].Proteomics studies have revealed that the production of virulence factors by different isolates of *S. aureus* is diverse and only a few of these seem to be invariantly produced [17]. PSMs are the most commonly identified staphylococcal virulence factors, especially in the community‐associated (CA)‐MRSA lineages. Recently, it was found that many *in vitro* PSM phenotypes were strongly inhibited by serum lipoproteins, and can exert their contribution to pathogenesis by intracellular killing and participate in neutrophil killing after phagocytosis [18]. In addition, PSMs at low concentration can lead to immune cell chemotaxis and inflam‐ matory reaction. High concentration of PSMs may cause cytolysis, damaging neutrophils, immune cells, red blood cells and white blood cells [19, 20]. Thus, it is important to develop a rapid, specific and accurate method to detect PSMs in food products for the prevention of transmission.

At present, there are only a few methods for determination of PSMs, such as imaging mass spectrometry and liquid chromatography‐ion trap or quadrupole mass spectrom‐ etry [11, 21]. The sample pre‐treatment of the method using imaging mass spectrometry is quite cumbersome and time‐consuming. The resolution of the method by liquid chro‐ matography‐ion trap or quadrupole mass spectrometry is too low to separate interfering substances with similar charge‐to‐mass ratios. Here, we describe a simple and effective method with higher sensitivity and selectivity for PSM analysis in *S*. *aureus* by high‐per‐ formance liquid chromatography‐quadrupole time‐of‐flight mass spectrometry system (HPLC‐QTOF).
