Amdinocillin: interaction with other beta-lactam antibiotics for gram-negative bacteria

Interactions of OP0595, a Novel Triple-Action Diazabicyclooctane, with β-Lactams against OP0595-Resistant Enterobacteriaceae Mutants

OP0595 is a novel diazabicyclooctane which, like avibactam, inhibits class A and C β-lactamases. In addition, unlike avibactam, it has antibacterial activity, with MICs of 0.5 to 4 μg/ml for most members of the family Enterobacteriaceae, owing to inhibition of PBP2; moreover, it acts synergistically with PBP3-active β-lactams independently of β-lactamase inhibition, via an "enhancer effect." Enterobacteriaceae mutants stably resistant to 16 μg/ml OP0595 were selected on agar at frequencies of approximately 10(-7). Unsurprisingly, OP0595 continued to potentiate substrate β-lactams against mutants derived from Enterobacteriaceae with OP0595-inhibited class A and C β-lactamases. Weaker potentiation of partners, especially aztreonam, cefepime, and piperacillin--less so meropenem--remained frequent for OP0595-resistant Enterobacteriaceae mutants lacking β-lactamases or with OP0595-resistant metallo-β-lactamases (MBLs), indicating that the enhancer effect is substantially retained even when antibiotic activity is lost.

OP0595, a new diazabicyclooctane: mode of action as a serine β-lactamase inhibitor, antibiotic and β-lactam 'enhancer'

OBJECTIVES

The production of a growing diversity of β-lactamases by Gram-negative bacteria challenges antimicrobial chemotherapy. OP0595, discovered separately by each of Meiji Seika Pharma and Fedora Pharmaceuticals, is a new diazabicyclooctane serine β-lactamase inhibitor that also acts as an antibiotic and as a β-lactamase-independent β-lactam 'enhancer'.

METHODS

Inhibitory activity against serine β-lactamases and affinity for PBPs were determined using nitrocefin and Bocillin FL, respectively. MICs alone and in combination with β-lactam agents were measured according to CLSI recommendations. Morphological changes in Escherichia coli were examined by phase-contrast microscopy.

RESULTS

IC50s of OP0595 for class A and C β-lactamases were <1000 nM, with covalent binding demonstrated to the active-site serine of CTX-M-44 and AmpC enzymes. OP0595 also had direct antibiotic activity against many Enterobacteriaceae, associated with inhibition of PBP2 and conversion of the bacteria into spherical forms. Synergy between OP0595 and β-lactam agents was seen against strains producing class A and C β-lactamases vulnerable to inhibition. Lastly, OP0595 lowered the MICs of PBP3-targeted partner β-lactam agents for a non-β-lactamase-producing E. coli mutant that was resistant to OP0595 itself, indicating β-lactamase-independent 'enhancer'-based synergy.

CONCLUSIONS

OP0595 acts in three ways: (i) as an inhibitor of class A and C β-lactamases, covalently binding at their active sites; (ii) as an antibacterial, by inhibiting PBP2 of several Enterobacteriaceae; and (iii) as an 'enhancer' of β-lactam agents that bind to other PBPs besides PBP2 for several Enterobacteriaceae. OP0595 has considerable potential to overcome resistance when it is combined with various β-lactam agents.

Function of penicillin-binding protein 2 in viability and morphology of Pseudomonas aeruginosa

OBJECTIVES

To investigate the function of penicillin-binding protein 2 (PBP 2) in Pseudomonas aeruginosa PAO1.

METHODS

The growth and morphology of P. aeruginosa cultured in the absence and presence of mecillinam was assessed. The gene encoding PBP 2, pbpA, was identified in the genome of P. aeruginosa PAO1 and both its full-length and an engineered truncated form were cloned and expressed in Escherichia coli. Site-directed mutagenesis was used to confirm Ser-327 as the catalytic nucleophile of its transpeptidase domain. Allelic exchange was used to construct a chromosomal mutant of pbpA in strain PAO1.

RESULTS

PAO1 grew with a spherical morphology in the presence of mecillinam at concentrations as high as 2000 mg/L. Both wild-type and truncated, soluble forms of PBP 2 were shown to bind penicillins and a competition assay demonstrated their specificity for mecillinam. The PAO1 DeltapbpA insertional mutant also grew as spheres, and complementation with a plasmid encoding active pbpA, but not with an inactive Ser-327 --> Ala derivative, restored rod-shape morphology. MIC values of a variety of beta-lactams were significantly lower for the insertional mutant compared with wild-type PAO1. The muropeptide profile of peptidoglycan from PAO1 DeltapbpA analysed by HPLC/MALDI TOF MS indicated wild-type levels of cross-linking despite the loss of PBP 2 transpeptidase activity.

CONCLUSIONS

PBP 2 in P. aeruginosa is responsible for the rod-shape morphology of the cells and contributes significantly to beta-lactam resistance. The viability of cells lacking an active PBP 2 suggests that the organization of the peptidoglycan biosynthetic machinery is different in this pathogen compared with E. coli.