meropenem and lipoteichoic-acid

A major determinant of β-lactam resistance in methicillin-resistant Staphylococcus aureus (MRSA) is the drug insensitive transpeptidase, PBP2a, encoded by mecA. Full expression of the resistance phenotype requires auxiliary factors. Two such factors, auxiliary factor A (auxA, SAUSA300_0980) and B (auxB, SAUSA300_1003), were identified in a screen against mutants with increased susceptibility to β-lactams in the MRSA strain, JE2. auxA and auxB encode transmembrane proteins, with AuxA predicted to be a transporter. Inactivation of auxA or auxB enhanced β-lactam susceptibility in community-, hospital- and livestock-associated MRSA strains without affecting PBP2a expression, peptidoglycan cross-linking or wall teichoic acid synthesis. Both mutants displayed increased susceptibility to inhibitors of lipoteichoic acid (LTA) synthesis and alanylation pathways and released LTA even in the absence of β-lactams. The β-lactam susceptibility of the aux mutants was suppressed by mutations inactivating gdpP, which was previously found to allow growth of mutants lacking the lipoteichoic synthase enzyme, LtaS. Using the Galleria mellonella infection model, enhanced survival of larvae inoculated with either auxA or auxB mutants was observed compared with the wild-type strain following treatment with amoxicillin. These results indicate that AuxA and AuxB are central for LTA stability and potential inhibitors can be tools to re-sensitize MRSA strains to β-lactams and combat MRSA infections.

Topics: Amoxicillin; Animals; Anti-Bacterial Agents; Bacterial Proteins; beta-Lactam Resistance; beta-Lactams; Cefoxitin; Cell Wall; DNA, Bacterial; Drug Resistance, Bacterial; Humans; Larva; Lipopolysaccharides; Membrane Proteins; Meropenem; Methicillin-Resistant Staphylococcus aureus; Microbial Sensitivity Tests; Models, Animal; Moths; Mutation; Octoxynol; Oxacillin; Penicillin-Binding Proteins; Peptidoglycan; Phenotype; Staphylococcal Infections; Teichoic Acids; Virulence

There are marked differences in the amount of immunoreactive components such as lipoteichoic acid (LTA) released from Gram-positive bacteria following exposure to different antibiotics. Little is known about the kinetics and amount of release of such components in relation to bacterial killing.. Bacterial killing and LTA release from Streptococcus pneumoniae type 3 during exposure to ceftriaxone, meropenem, rifampicin, rifabutin, quinupristin/dalfopristin, and trovafloxacin in tryptic soy broth were quantified microbiologically and by ELISA, respectively. We applied a mathematical model to characterize quantitatively the amount of lipoteichoic acid released and the statistical moments of this release.. The model approach revealed that (i) the lag time to release of LTA was very similar for individually killed bacterial cells (approximately 120 min), whatever the killing mechanism effected by the antibiotic, and (ii) the amount of LTA released per killed bacterial cell, a value that we regard as an indicator of the relation between antibacterial efficacy and possible adverse immunostimulatory effects due to release of cell wall components, differs markedly between antibiotics, even at antibiotic concentrations inducing equal killing. Rifamycins were most effective in killing S. pneumoniae while causing the least LTA release per killed bacterial cell; the amount released was about one-half that by quinupristin-dalfopristin and trovafloxacin, and one-quarter that by ceftriaxone and meropenem.. In the evaluation of antibacterial drugs, the present model provides useful information on the whole process of bacterial killing and release of immunoreactive components from the bacterial cell wall.

Topics: Anti-Bacterial Agents; Ceftriaxone; Lipopolysaccharides; Meropenem; Rifabutin; Rifampin; Streptococcus pneumoniae; Teichoic Acids; Thienamycins; Virginiamycin