Roles of the carboxy-terminal half of Pseudomonas aeruginosa major outer membrane protein OprF in cell shape, growth in low-osmolarity medium, and peptidoglycan association

OprF, the major outer membrane protein of Pseudomonas aeruginosa, is multifunctional in that it can act as a nonspecific porin, plays a role in the maintenance of cell shape, and is required for growth in a low-osmolarity environment. The latter two structural roles of OprF, and OprF's association with the peptidoglycan, have been proposed to be localized in the carboxy terminus of the protein, based on this region's similarity to members of the OmpA family of proteins. To determine if this is correct, we constructed a series of C-terminally truncated OprF derivatives and examined their effects on P. aeruginosa cell length and growth in low-osmolarity medium. While the C terminus of OprF was required for wild-type cell length and growth in low-osmolarity medium, expression of the N terminus (first 163 amino acids [aa]) also influenced these phenotypes (compared with OprF deficiency). The first 154 to 164 aa of OprF seemed required for stable protein expression, consistent with the existence of a beta-barrel domain in the N terminus of OprF. Greater than 215 aa of the protein were required for strong peptidoglycan association, confirming that residues in the C-terminal end of OprF are required for peptidoglycan binding. OprF deficiency did not affect the in vivo growth of an OprF-deficient strain in a mouse chamber model. Collectively, these data suggest that the C terminus of OprF plays a role in cell length, growth of P. aeruginosa in low-osmolarity media (but not in vivo), and peptidoglycan association, while the N terminus has an influence on the first two characteristics and is additionally important for stable protein expression.

Epitope mapping of the Pseudomonas aeruginosa major outer membrane porin protein OprF

The Pseudomonas aeruginosa major outer membrane protein OprF has been proposed for use as a vaccine and as a target for immunotherapeutic and diagnostic monoclonal antibodies. The well-conserved epitopes for 10 surface-reactive, OprF-specific monoclonal antibodies were localized by both overlapping peptide analysis and immunodetection of OprF peptides generated by cyanogen bromide and the protease papain. Three of the monoclonal antibodies bound to specific overlapping octapeptides, which had been synthesized on 160 pins to cover the entire 326 amino acids of OprF. The highest reactivities were as follows: MA7-1 to the pin with attached peptide GTYETGNK (amino acids 55 to 62), MA7-2 to NLADFMKQ (amino acids 237 to 244), and MA5-8 to TAEGRAIN (amino acids 307 to 314). The other monoclonal antibodies showed no reactivity, indicating that they do not recognize linear epitopes. Two polyclonal sera were also tested and demonstrated weak reactivity with discrete regions of OprF, suggesting that the majority of antibodies produced might recognize conformational epitopes. Utilizing defined peptides generated with cyanogen bromide and papain, the conformational epitopes recognized by the seven monoclonal antibodies were localized to regions that were 42 to 90 amino acids long. These regions were located on two adjacent loops in the middle of an amended structural model of OprF.

Conservation of surface epitopes in Pseudomonas aeruginosa outer membrane porin protein OprF

The outer membrane proteins of several prominent bacterial pathogens demonstrate substantial variation in their surface antigenic epitopes. To determine if this was also true for Pseudomonas aeruginosa outer membrane protein OprF, gene sequencing of a serotype 5 isolate was performed to permit comparison with the published serotype 12 oprF gene sequence. Only 16 nucleotide substitutions in the 1053 nucleotide coding region were observed; none of these changed the amino acid sequence. A panel of 10 monoclonal antibodies (mAbs) reacted with each of 46 P. aeruginosa strains representing all 17 serotype strains, 12 clinical isolates, 15 environmental isolates and 2 laboratory isolates. Between two and eight of these mAbs also reacted with proteins from representatives of the rRNA homology group I of the Pseudomonadaceae. Nine of the ten mAbs recognized surface antigenic epitopes as determined by indirect immunofluorescence techniques and their ability to opsonize P. aeruginosa for phagocytosis. These epitopes were partially masked by lipopolysaccharide side chains as revealed using a side chain-deficient mutant. It is concluded that OprF is a highly conserved protein with several conserved surface antigenic epitopes.

Determinants of the efficacy of tobramycin therapy against isogenic nonmucoid and mucoid derivatives of Pseudomonas aeruginosa PAO1 growing in peritoneal chambers in mice

Mice which were supporting the growth of Pseudomonas aeruginosa in chambers implanted in their peritoneums were given two intramuscular injections of tobramycin (15 mg/kg of body weight each) at an interval of 8 h. Three hours later, chambers were removed and their contents were assessed for viable counts. Controls revealed that tobramycin levels in the chambers were 3.8 micrograms/ml 15 min after injection of 15 mg of tobramycin per kg and remained above the in vitro MICs (0.5 to 1 microgram/ml) for the tested strains for 8 h. It was demonstrated that tobramycin therapy was less effective with higher inocula and with longer delay before administration. Thus, in vivo, the concentration of bacteria in the chambers at the time of the first tobramycin injection had a profound effect on the bactericidal efficacy of tobramycin therapy. No such concentration dependence was observed in mock in vitro therapy experiments. A phage-selected mucoid derivative of P. aeruginosa PAO1 showed only a marginal increase in in vitro aminoglycoside susceptibility and no major alteration in in vivo susceptibility compared with its isogenic nonmucoid parent strain.

Filariasis of the breast

Filariasis of the breast is usually seen in endemic areas. Involvement may, however, present years after leaving an endemic area and be associated with circulating microfilariae. We describe the findings in a woman who developed a breast mass three years after a visit to her native India.

Sir Astley Paston Cooper, 1768-1841: "the prince of surgery"

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