Identification of penicillin-binding proteins (PBPs) in Inquilinus limosus

DI CONZA JOSÉ; PINO MARYLÚ; GUTKIND GABRIEL; AYALA JUAN

Congreso; FEMS 2013 - 5th Congress of European Microbiologists; 2013

Background Inquilinus limosus is a non-fermenting gram-negative bacillus increasingly isolated from cystic fibrosis patients. It shows a multiple resistance pattern exhibiting high-level resistance to β-lactams probably due to a combination of resistance mechanisms including PBPs affinity. Objective Our goal was to characterize the PBPs in a clinical isolate of I. limosus. Methods Using Bocillin we report the identification of eleven putative PBPs with apparent masses of 96, 89, 70, 67, 60, 58, 54, 52, 45, 42 and 39 kDa. In an attempt to identify the PBPs to which β-lactams preferentially binds, ampicillin, cefoxitin and ceftazidime were used in competition assays with Bocillin. It appeared that these antibiotic inhibited the binding of bocillin to the first and third of higher molecular weight PBP (IC50 < 4 µg/ml). Ampicillin and cefoxitin also inhibited an additional PBP (60 and 58 kDa respectively). Analysis of the partial genome sequence of I. limosus indicated that, in addition to mtgA, there are six putative proteins with sequence motifs that are strongly conserved in penicillin binding proteins (PBPs): four genes that code for high-molecular-weight (HMW)-PBPs (three classes A and one class B), and two genes encoding low-molecular-weight (LMW)-PBPs (two Classes C- type H). Conclusions The derived amino acid sequences of the putative PBPs maintained the three characteristic motifs found in orthologous known PBPs. Some HMW-PBPs are not inhibited for these β-lactams, and may be responsible of the resistance exhibited. These findings suggest that the PBPs of I. limosus are distinctive.