Analysis of bacteria growth curves The rifampicin resistant strains grew normally and showed the same colony appearance as the rifampicin susceptible isolate, on GC agar plates with the naked eye or with a light microscope (data not shown). As shown in figure 2, after GC broth inoculation, there were differences in growth between the susceptible and resistant strains from the starting point of the inoculation (T0) to the stationary phase. In particular,

the growth of the resistant strains showed primarily a delay in the onset of the logarithmic phase compared with the susceptible strain with different maximal OD600 = 0.82 of 1958, OD600 = 0.7 of 901, OD600 = 0.65 of 870 (figure Adriamycin in vitro 2). Figure 2 Growth curves in GC broth of rifampicin resistant and susceptible strains. Error bars represent the standard deviation buy MK-2206 of three culture replicates. Discussion As a transformable bacterium Neisseria meningitidis is incline to acquire exogenous bacterial DNAs, but it has been relatively

slow to acquire resistance. However, since it is a severe disease it is very important to monitor changes in the level of antibiotic susceptibility among clinical isolates. Resistance to rifampicin is only occasionally observed but the isolation of a resistant strain poses serious problems in managing the prophylaxis of close contacts. At present, it is unknown how changes in resistant phenotype correspond to different protein expression profiles. Some studies reveal that the molecular mechanism of resistance is correlated to different amino acid changes in a short central region of the rpoB gene encoding the β-subunit

of the RNA polymerase [3, 17]. Moreover, a scarce virulence of rifampicin resistant N. meningitidis find more isolates has been proved in an in vivo model [2]. It is interesting to focus on adaptation mechanisms under antibiotic challenge which have a cost in terms of fitness [18]. The results described in this paper permit to hypothesize that compensation for the rifampicin resistance phenotype may be responsible for the different protein expression in meningococcus. The phenomenon is not so rare among bacterial pathogens and the proteomic approach facilitates the comprehensive analysis of protein content. Most of the proteins recovered in the 2-DE maps belong to the cytosolic fraction. The latter permits to analyse differences in those proteins involved in metabolic pathways including the RNA polymerase, as the molecular target of rifampicin resistance. On the basis of the catalogue of proteins of the reference N. meningitidis strain MC58 [13], protein expression in two rifampicin resistant and one susceptible meningococci was analysed.