Biochemical Characterization of the Subclass B3 Metallo-β-Lactamase PJM-1 from Pseudoxanthomonas japonensis

Biochemical characterization of the L1-like metallo-β-lactamase from Stenotrophomonas lactitubi

L1-like metallo-β-lactamases (MBLs) exhibit diversity and are highly conserved. Although the presence of the blaL1-like gene is known, the biochemical characteristics are unclear. This study aimed to characterize an L1-like MBL from Stenotrophomonas lactitubi. It showed 70.9-99.7% similarity to 50 L1-like amino acid sequences. The characteristic kinetic parameter was its high hydrolyzing efficiency for ampicillin and nitrocefin. Furthermore, L1-like from S. lactitubi was distinctly more susceptible to inhibition by EDTA than that to inhibition by 2,6-pyridinedicarboxylic acid.

Three novel Luteimonas species from a root and rhizosphere soil of Kalidium cuspidatum: Luteimonas endophytica sp. nov., Luteimonas rhizosphaericola sp. nov. and Luteimonas kalidii sp. nov

Three Gram-stain-negative, aerobic and rod-shaped bacterial strains, designated RD2P54T, M1R5S18T and M1R5S59T, were isolated from a root and rhizosphere soil of Kalidium cuspidatum, in Baotou, PR China. The three strains showed 94.1–98.7 % 16S rRNA gene sequence similarities to Luteimonas strains, indicating they belonged to the genus Luteimonas . The phylogenomic tree based on core genomes showed that strain RD2P54T tightly clustered with Luteimonas salinisoli SJ-92T, while strains M1R5S18T and M1R5S59T clustered with each other and with Luteimonas viscosa XBU10T and Luteimonas saliphila SJ-9T. Though strains M1R5S18T and M1R5S59T showed high 16S rRNA similarity (99.4 %) to each other, the low average nucleotide identity based on blast (ANIb; 88.6 %) and digital DNA–DNA hybridization (dDDH; 31.6 %) values between them indicated that they belonged to two different species. The ANIb and dDDH values of strains RD2P54T, M1R5S18T and M1R5S59T with their closely neighbours are well below the delineation threshold values for identifying strains as representing different species. All three strains take iso-C15 : 0 and summed feature 9 (C16 : 0 10-methyl and/or iso-C17 : 1  ω9c) as major fatty acids, and ubiquinone-8 as the sole respiratory quinone. The major polar lipids of all three strains are diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. Based on phenotypic and phylogenetic data, these three strains should be considered to represent three novel species of the genus Luteimonas , for which the names Luteimonas endophytica sp. nov. (type strain RD2P54T=CGMCC 1.61535T =KCTC 92470T), Luteimonas rhizosphaericola sp. nov. (type strain M1R5S18T=CGMCC 1.61537T =KCTC 92469T) and Luteimonas kalidii sp. nov. (type strain M1R5S59T=CGMCC 1.61536T =KCTC 92471T) are proposed.

Strategies to Name Metallo-β-Lactamases and Number Their Amino Acid Residues

Metallo-β-lactamases (MBLs), also known as class B β-lactamases (BBLs), are Zn(II)-containing enzymes able to inactivate a broad range of β-lactams, the most commonly used antibiotics, including life-saving carbapenems. They have been known for about six decades, yet they have only gained much attention as a clinical problem for about three decades. The naming conventions of these enzymes have changed over time and followed various strategies, sometimes leading to confusion. We are summarizing the naming strategies of the currently known MBLs. These enzymes are quite diverse on the amino acid sequence level but structurally similar. Problems trying to describe conserved residues, such as Zn(II) ligands and other catalytically important residues, which have different numbers in different sequences, have led to the establishment of a standard numbering scheme for BBLs. While well intended, the standard numbering scheme is not trivial and has not been applied consistently. We revisit this standard numbering scheme and suggest some strategies for how its implementation could be made more accessible to researchers. Standard numbering facilitates the comparison of different enzymes as well as their interaction with novel antibiotics and BBL inhibitors.

Metallo-β-lactamase-mediated antimicrobial resistance and progress in inhibitor discovery

Resistance to β-lactam antibiotics is rapidly growing, substantially due to the spread of serine-β-lactamases (SBLs) and metallo-β-lactamases (MBLs), which efficiently catalyse β-lactam hydrolysis. Combinations of a β-lactam antibiotic with an SBL inhibitor have been clinically successful; however, no MBL inhibitors have been developed for clinical use. MBLs are a worrying resistance vector because they catalyse hydrolysis of all β-lactam antibiotic classes, except the monobactams, and they are being disseminated across many bacterial species worldwide. Here we review the classification, structures, substrate profiles, and inhibition mechanisms of MBLs, highlighting current clinical problems due to MBL-mediated resistance and progress in understanding and combating MBL-mediated resistance.