The examined bacteria, MSSA-B and/or MRSA-B cells (sonicated and vortexed), were separated on the original FS capillary modified by GOTMS in the preliminary experiments. However, only a broad peak of unresolved MSSA-B and MRSA-B cells was detected instead of a narrow peak like in Ref. [21]. This was probably caused by a change in the surface properties of the cells after their incubation in whole blood which corresponds to the earlier findings [44].
S. aureus possesses a number of adhesins, such as polysaccharide intercellular adhesin, which enables the adhesion of staphylococcal cells to each other and by this way facilitates the formation of staphylococcal aggregates [48]. Moreover, S. aureus belongs to the plasma-coagulase positive staphylococci that produce virulence factors such as coagulase [49] and clumping factor A [15,50,51] which also support the staphylococcal cells aggregation in blood environment due to conversion of fibrinogen to fibrin. This property also causes a rapid agglomeration of the purified cells of S. aureus, MSSA-B and MRSA-B. Therefore, rigorous sonication and vortexing of the sample suspension prior to the separation by CE is necessary. Fig. 1A shows the record of the CZE separation of carefully sonicated and vortexed MSSA-B and MRSA-B cells (5 107 cell mL1 each) on SCW-etched FS capillary modified with GOTMS at the optimized conditions.