Properties of the penicillin-binding proteins of four species of the genus Bacteroides

Abstract

The peniciilin-binding proteins (PBPs) of four species of the genus Bacteroides were examined in cell envelope preparations from exponentially growing cultures and intact cells. Upon examination by sodium dodecyl sulfate-polyacrylamide electrophoresis, three major high-molecular-weight PBPs (molecular weight, 58,000 to 82,000) were resolved, and low-molecular-weight PBPs were seen in all strains except Bacteroidesfragilis. The sporadic appearance of PBP 4 in B. fragilis (molecular weight, approximately 45,000) was shown not to be influenced by the concentration of free iron available in the medium or by the stage of growth at which the batch culture was harvested. No PBP that was inhibited by an aerobic environment was demonstrated. The affinity of 35 ,B-lactam antibiotics for the PBPs from envelope preparations was examined and correlated with the morphological response. Most compounds bound initially to PBP 2 and then PBP 1, correlating with a primary response of filamentation and then spheroplasting and lysis. Compounds such as clavulanic acid bound to PBP 3 at concentrations causing round cells. Based on the data from this study, it is proposed that the three high-molecular-weight PBPs of Bacteroides fragilis, Bacteroides vulgatus, Bacteroides thetaiotaomicron, and Bacteroides ovatus correlate to the three high-molecular-weight PBPs of Escherichia coli and that the PBPs of Bacteroides species perform the same enzymic role in cell wall biosynthesis as their counterparts in E. coli. Therefore, the components of PBP 1 are involved in cell elongation, PBP 2 is involved in septum formation, and PBP 3 is involved in maintenance of cell shape (i.e., PBP 2 in Bacteroides spp. = PBP 3 in E. coli, and PBP 3 in Bacteroides spp. = PBP 2 in E. coli).Species of the genus Bacteroides are commonly encountered in infection, and certain of the species are the anaerobes most resistant to antimicrobial agents (8) and in particular the P-lactam class of antibiotics, owing to the presence of potent P-lactamases (17,18). The development of 3-lactamase-stable r-lactams has not led to greatly enhanced activity for Bacteroides species, and the recent emergence of resistance to cefoxitin, which is not attributable to classical P-lactamase activity (2, 6), has renewed interest in the mechanism of action of 1-lactams in Bacteroides species.

Relationship between penicillin-binding protein patterns and β-lactamases in clinical isolates of Bacteroides fragilis with different susceptibility to β-lactam antibiotics

“…Imipenem and meropenem bind initially to PBP3Bfr to produce round cells and then interact with PBP2Bfr. Imipenem also binds to PBP1Bfr at concentrations that correlate with the MIC (Piddock & Wise, 1986). In a competition assay, imipenem can displace benzylpenicillin from B. fragilis proteins that have a molecular mass of 60-100 kDa (Edwards & Greenwood, 1996).…”

“…The primary target in Bacteroides spp. for most â-lactam antibiotics is PBP2Bfr (78 kDa), which is involved in septation and corresponds to PBP3 of E. coli (PBP3Eco) (Georgopapadakou et al, 1983;Piddock & Wise, 1986). …”

Purification and characterization of a new beta-lactamase from Bacteroides uniformis

“…Since PBPs are the targets of beta-lactam antibiotics, changes in these proteins that decrease their affinity for a beta-lactam decrease the effectiveness of that beta-lactam agent against the isolate. The majority of beta-lactams bind initially to PBP 2 and then to the PBP 1 complex (22). A decreased affinity for one or both of these PBPs may affect the level of resistance.…”

Accumulation of Norfloxacin by Bacteroides fragilis

“…Bacterial growth was measured by two methods: the first by monitoring the viable cell count and the second by monitoring the optical density of the culture (22). When the viable cell count was determined anaerobically, at no time was the culture removed from the anaerobic cabinet.…”