The latter are proteins that lyse amongst others red blood cells, allowing for instance the bacterium to scavenge iron compounds. The assay described herein allows to rapidly and quantitatively measuring alpha toxin from staphylococcal cultures. This allows studying expression with regard to strain or CC affiliations, but also with regard to regulation under different growth conditions in the presence of antibiotics, etc. It could also be expanded by spotting additional antibodies for other exotoxins such as PVL on the same array,GSK621 facilitating simultaneous measurements of several virulence factors. The most surprising aspect in this work was that the in vitro production of alpha haemolysin normally strongly correlates with affiliation to clonal complexes. This can theoretically be explained at least by two different assumptions. One is a possible presence of allelic variants resulting in proteins that might less efficiently be recognised by the antibodies used. The second one could be that expression and/or regulation indeed vary,Cangrelor tetrasodium salt depending on the affiliation to phylogenetic lineages. The first possible explanation could be true in CC75/‘‘S. argenteus’’. As mentioned above, a genome sequence from this lineage shows several differences compared to other S. aureus sequences. Thus antibodies specific for other alpha toxin variants might false-negative results or give a false impression of low toxin levels. Raising monoclonal antibodies specifically for CC75/‘‘S. argenteus’’ alpha toxin might resolve this issue in future. For other lineages, allelic differences between hla sequences of different clonal complexes are rather small, even less when regarding protein rather than DNA sequences. Allelic variations are so not a likely cause for the different alpha toxin measurements for these lineages. It was observed that CC395 was usually alpha toxin positive while CC22, CC30, CC45 and CC398 are negative in the described test. However, a published CC395 sequence is identical to sequences from several CC45 strains and virtually identical to CC22, CC30 and CC398 sequences. The variations within major complexes for which many sequences are available appear to be larger than between complexes.