Differentially regulated proteins in Prevotella intermedia after oxidative stress analyzed by 2D electrophoresis and mass spectrometry.

Prevotella intermedia is a rod-shaped, Gram-negative anaerobic bacterium found in human indigenous microbiota that plays an important role in opportunistic infections. The successful colonization depends on the ability of anaerobes to respond to oxidative stress (OS) in oxygenated tissues as well as to resist oxidative events from the host immune system until anaerobic conditions are present at the infection site. As knowledge of the mechanisms of protection against OS in Prevotella is limited, studies are needed to clarify aspects of molecular biology, physiology and ecology of this bacterium. The aim of this study was to access the proteins differentially regulated in P. intermedia after exposure to molecular oxygen by using two-dimensional gel electrophoresis (2DE) associated with the approach of MALDI-TOF/TOF Tandem Mass Spectrometry. The identity of the protein was evaluated by database search for homologous genomic sequences of P. intermedia strain 17 (TIGR). Twenty five out of 72 proteins found were identified as up-regulated (17) or down-regulated (9). These proteins were related to a variety of metabolic process, some of which could be associated to antioxidant and redox regulatory roles. Our data indicate that OS may stimulate an adaptive response in P. intermedia whose effect on its biology may be evidenced by the increase in aerotolerance and changes in protein abundance in the oxygen adapted cells.

Enhanced pathogenicity of susceptible strains of the Bacteroides fragilis group subjected to low doses of metronidazole.

Different concentrations of metronidazole are used widely to treat protozoan and fungal infections. As an antibacterial drug, metronidazole is mainly used against anaerobes, of which the Bacteroides fragilis group is the most important in terms of the frequency of recovery and antimicrobial resistance patterns. The objective of this study was to investigate (1) in vivo metronidazole-induced modifications in the B. fragilis group reflected by altered virulence, and (2) the interference of metronidazole in cellular viability of these samples when subjected in vitro to human polymorphonuclear leukocytes (PMNs). Strains adapted to low metronidazole concentrations were observed to be more virulent, as demonstrated experimentally in mice by weight loss, quantitative evidence of tissue damage, hemorrhage and anatomopathology of spleen, liver and small intestine samples. A significant increase (P < 0.05) in mean bacterial viability rate of about 2.62-fold was observed for all the drug-adapted strains after contact with human PMNs. However, the level of this phenomenon was quite different among the tested species. These results draw attention to the risk that prolonged therapy, even with low concentrations of metronidazole, may affect the pathogenicity of Bacteroides strains, producing changes in host-bacteria relationships.