Cytotoxicity of a novel lipid-like bacterial product

Negative and positive ion mode LC/MS/MS for simple, sensitive analysis of sorbic acid

Sorbic acid (SA: CH(3)-CH=CH-CH=CH-COOH) is one of the widely used food preservatives, although there have been some reports of its toxic activity, for example, on DNA and skin cells. In order to examine the effects of SA on mammalian tissues, we have developed a highly sensitive analytical method using LC/MS/MS with positive and negative ion mode electrospray ionization (ESI). In a previous study, we found that a nonacidic eluent offers better ionization efficiency than acids or their ammoniun salts. However, optimal results could not be obtained because the anion form of SA is poorly retained on a conventional reversed phase column. To resolve this problem, we chose a new type of column and used high-resolution mass spectrometry and positive ion mode analysis. There have only been a few reports using these methods in the positive mode, for example derivatized SA, because acid compounds such as SA are usually used in the negative ion mode. However, a new type of low-carbon-content and polar-endcapped C18 phase column was developed for better separation of SA from the matrix. High-resolution selected reaction monitoring (SRM) gave the best signal to noise ratio in normal-resolution SRM. In the positive ion mode, the CH(3)OH-0.05% HCOOH/0.1% CH(3)COOH eluent system yielded the best ionization efficiency. We propose a highly sensitive and simple analysis using a two-ion-mode ESI SRM method. Such systems should allow quantification of the amount of SA in or around the cells, without the need for pretreatment such as solid phase extraction.

Pore-forming bacterial protein hemolysins (cytolysins)

Protein toxins forming pores in biological membranes occur frequently in Gram-positive and Gram-negative bacteria. They kill either bacteria or eukaryotic cells (at most, a few seem to act on both groups of organisms). Most of the toxins affecting eukaryotes have clearly been shown to be related to the pathogenicity of the producing organisms. Toxin formation frequently involves a number of genes which encode the toxin polypeptide as well as proteins for toxin activation and secretion. Regulation of toxin production is usually coupled with that of the synthesis of a number of other virulence factors. Iron is the only known environmental factor that regulates transcription of a number of toxin genes by a Fur repressor-type mechanism, as has been originally described in Escherichia coli. Interestingly, the thiol-activated hemolysins (cytolysins) of Gram-positive bacteria contain a single cysteine which can be replaced by alanine without affecting the cytolytic activity. The Gram-negative hemolysins (cytolysins) are usually synthesized as precursor proteins, then covalently modified to yield an active hemolysin and secreted via specific export systems, which differ for various types of hemolysins.