Substrate Inhibition of VanA byd-Alanine Reduces Vancomycin Resistance in a VanX-Dependent Manner

Abstract

Infectious diseases caused by multidrug-resistant (MDR) pathogens are spreading rapidly and are among the biggest threats to human health (1-4). A particular problem with drug discovery from microbial sources is the high frequency of rediscovery of known compounds, which necessitates new approaches to replenish the antimicrobial drug pipelines (5-7). To deal with the increasing antibiotic resistance, novel antibiotics are called for, or alternatively, the life spans of the current drugs must be prolonged by compounds counteracting resistance. Exemplary is amoxicillin-clavulanic acid (Augmentin), which is a combination of a ␤-lactam antibiotic (amoxicillin) and a ␤-lactamase inhibitor (clavulanic acid) (8).The cell wall and its biosynthetic machinery are a major target of the action of clinical antibiotics, including fosfomycin, bacitracin, cycloserine, ␤-lactam antibiotics (penicillins and cephalosporins), and glycopeptide antibiotics (vancomycin and teicoplanin) (9-11). Enterococci and many other Gram-positive pathogenic bacteria are resistant to a wide spectrum of antibiotics and can often be treated only with specific ␤-lactam antibiotics or with vancomycin (12-14). Vancomycin resistance was first discovered in the 1950s (15). Vancomycin resistance is exchanged between bacteria via movable elements such as transposon Tn1546, which is carried by many vancomycin-resistant enterococci (VRE) (16). The most common forms of transferable vancomycin resistance are the VanA-and VanB-type resistance, the expression of which is inducible by vancomycin. VanA-type strains are resistant to high levels of vancomycin as well as to another glycopeptide antibiotic, teicoplanin, while VanB-type strains show only inducible resistance to vancomycin but retain susceptibility to teicoplanin (17). While vancomycin resistance is most prevalent in enterococci (18), resistance has spread to methicillin-resistant Staphylococcus aureus (MRSA) (19). (15,23). The vancomycin resistance gene cluster provides resistance to both vancomycin and teicoplanin and is located on the genome of the vancomycin producer Amycolatopsis mediterranei (24,25) as well as that of other actinomycetes, including the model species Streptomyces coelicolor A3 (26, 27).Streptomycetes are Gram-positive soil bacteria with a complex multicellular life style (28-30). Streptomycetes are a major source of antibiotics and many other natural products of medical and biotechnological importance, such as anticancer, antifungal, or herbicidal compounds (31, 32). Due to the competitive environment of the soil, these microorganisms readily exchange genetic

ddcP, pstB, and excess D-lactate impact synergism between vancomycin and chlorhexidine against Enterococcus faecium 1,231,410

“…This result suggests that excess D-lactate presence contributes to synergism phenotype, possibly by resulting in peptidoglycan precursors ending in D-lactate. As expected based on the results of Aart et al [ 29 ], vancomycin MIC decreased in the presence of D-alanine, and we observed only a 2-fold additional MIC decrease in the presence of both D-alanine and H-CHG ( Table 2 ).…”

“…This increased the efficacy of vancomycin against Streptomyces and E . faecium [ 29 ]. Another study has reported the formation of modified cytoplasmic cell wall precursor termini in the presence of D-hydroxy acids, including D-lactate, and correlation of this with vancomycin resistance levels in Lactobacillus [ 30 ].…”

An Alternative and Conserved Cell Wall Enzyme That Can Substitute for the Lipid II Synthase MurG

“…For the cytoplasmic PG precursor isolation and identification, we used a modification of the method previously described ( 61 ). The alpha strain and the divIVA and dcw mutants were grown in LPB for 7 days, while the wild-type K. viridifaciens strain was grown for 3 days in a modified version of LPB lacking sucrose.…”

Inhibition of Campylobacter jejuni Biofilm Formation by D-Amino Acids

“…It is interesting to note that bacterial PG dipeptide D-Ala-D-Ala, which is generated by D-Ala-D-Ala ligase ( ddlA ), is the usual target for vancomycin, but in C. jejuni, PG contains D-Alanyl-D-Lactate (D-Ala-D-Lac) termini resulting in reduced efficacy of vancomycin by up to 1000-fold. Substitution by D -alanyl- D -serine (D-Ala-D-ser) termini reduces the efficacy of this antibiotic by up to 7-fold [ 4 , 55 , 56 , 57 , 58 ]. This further suggests that alr and not ddlA, is likely to be the primary target for D-ser and DCS in C. jejuni .…”