Moraxella catarrhalis uses a twin-arginine translocation system to secrete the β-lactamase BRO-2

Abstract

BackgroundMoraxella catarrhalis is a human-specific gram-negative bacterium readily isolated from the respiratory tract of healthy individuals. The organism also causes significant health problems, including 15-20% of otitis media cases in children and ~10% of respiratory infections in adults with chronic obstructive pulmonary disease. The lack of an efficacious vaccine, the rapid emergence of antibiotic resistance in clinical isolates, and high carriage rates reported in children are cause for concern. Virtually all Moraxella catarrhalis isolates are resistant to β-lactam antibiotics, which are generally the first antibiotics prescribed to treat otitis media in children. The enzymes responsible for this resistance, BRO-1 and BRO-2, are lipoproteins and the mechanism by which they are secreted to the periplasm of M. catarrhalis cells has not been described.ResultsComparative genomic analyses identified M. catarrhalis gene products resembling the TatA, TatB, and TatC proteins of the well-characterized Twin Arginine Translocation (TAT) secretory apparatus. Mutations in the M. catarrhalis tatA, tatB and tatC genes revealed that the proteins are necessary for optimal growth and resistance to β-lactams. Site-directed mutagenesis was used to replace highly-conserved twin arginine residues in the predicted signal sequence of M. catarrhalis strain O35E BRO-2, which abolished resistance to the β-lactam antibiotic carbanecillin.ConclusionsMoraxella catarrhalis possesses a TAT secretory apparatus, which plays a key role in growth of the organism and is necessary for secretion of BRO-2 into the periplasm where the enzyme can protect the peptidoglycan cell wall from the antimicrobial activity of β-lactam antibiotics.

Metallo-β-lactamases in the Age of Multidrug Resistance: From Structure and Mechanism to Evolution, Dissemination, and Inhibitor Design

“…This is a complex in which the SecYEG proteins form the translocon pore, while SecA acts as a cytoplasmic ATPase driving the export and transports proteins in their unfolded forms. , In contrast, the Tat system allows translocation of fully folded polypeptides . While certain SBLs are secreted via the Tat pathway, ,− at the moment there are no known MBLs undergoing this processing. As a result, folding and metal-ion acquisition by MBLs takes place in the periplasmic space in Gram-negative bacteria, following their translocation as unstructured polypeptides.…”

Residence ofStreptococcus pneumoniaeandMoraxella catarrhaliswithin polymicrobial biofilm promotes antibiotic resistance and bacterial persistencein vivo

“…Moraxella catarrhalis strain O35E is a well-characterized laboratory strain (Unhanand et al, 1992), and an isogenic beta-lactamase-deficient mutant in this background (hereafter referred to as 035E bro À ) has been recently described (Balder et al, 2013). Moraxella catarrhalis strains (O35E and O35E bro À ) were grown on brain heart infusion (BHI) agar containing vancomycin (3 lg mL À1 ).…”

The biogenesis of β-lactamase enzymes

“…Relatively few β-lactamases have been shown to use the Tat pathway for export. Those that have been described in pathogenic organism include L2 from S. maltophilia [177], BlaC from M. tuberculosis [179], BRO-2 from Moraxella catarrhalis [206], BlaA from Yersinia enterocolitica [207], and PenA from Burkholderia pseudomallei [180]. Interestingly, the normally Sec-dependent TEM-1 β-lactamase can be efficiently exported in an active form by the Tat pathway if it is provided with a twin arginine signal peptide, and has even been successfully used as a Tat reporter protein [177,208].…”

“…[145,[217][218][219][220]. Though less common, some Gram-negative species also carry membrane-anchored β-lactamases, including NDM-1 [176,221], PenA [180] and BRO-2 [206] (Fig. 5).…”