Rapid Depletion of Free Vancomycin in Medium in the Presence of β-Lactam Antibiotics and Growth Restoration in Staphylococcus aureus Strains with β-Lactam-Induced Vancomycin Resistance

Abstract

Growth of the BIVR cells to an absorption level of ϳ0.3 at 578 nm required about 24 h in the presence of vancomycin alone at the MIC (4.0 g/ml). However, growth was achieved in only about 10 h when 1/1,000 to 1/2,000 the MIC of ␤-lactam antibiotic was added 2 h prior to the addition of vancomycin, suggesting that the ␤-lactams shortened the time to recovery from vancomycin-mediated growth inhibition. Free vancomycin in the culture medium decreased to 2.3 g/ml in the first 8 h in the culture containing vancomycin alone, yet cell growth was undetectable. When the vancomycin concentration dropped below ϳ1.5 g/ml at 24 h, the cells began to grow. In the culture supplemented with the ␤-lactam 2 h prior to the addition of vancomycin, the drug concentration continuously dropped from 4 to 0.5 g/ml in the first 8 h, and the cells began to grow at a vancomycin concentration of ϳ1.7 g/ml or at 4 h of incubation. The gene encoding the enzyme involved in D-Ala-D-lactate synthesis was undetectable. Based on these results, we concluded that BIVR is attributable mainly to a rapid depletion of vancomycin in the medium triggered or promoted by ␤-lactam antibiotics.

Low level β-lactamase production in methicillin-resistant staphylococcus aureus strains with β-lactam antibiotics-induced vancomycin resistance

“…The affected cells upregulate the peptidoglycan biosynthetic pathways and repair systems, producing large amounts of peptidoglycan precursors, such as lipid-intermediate II with free d -Ala- d -Ala terminals [12,13]. Vancomycin tightly binds with the d -Ala- d -Ala structure of peptidoglycan and its intermediate precursors [4,5].…”

Bacterial cell‐wall recycling

“…Two further observations more directly implicate peptidoglycan recovery (if not recycling) by S. aureus . A particular nosocomial methicillin‐resistant S. aureus (MRSA) strain found in Japan requires the presence of β‐lactam antibiotics to secure vancomycin resistance 158 . Although the origin of the strain is easily rationalized as a consequence of the extensive use combined β‐lactam‐vancomycin chemotherapy for MRSA infection, the requirement that one cell‐wall–targeting antibiotic be present—this MRSA strain suppresses β‐lactamase expression to this purpose 159 —to withstand a second cell‐wall–targeting antibiotic is seemingly paradoxical.…”

“…A particular nosocomial methicillin-resistant S. aureus (MRSA) strain found in Japan requires the presence of ␤-lactam antibiotics to secure vancomycin resistance. 158 Although the origin of the strain is easily rationalized as a consequence of the extensive use combined ␤-lactam-vancomycin chemotherapy for MRSA infection, the requirement that one cell-wall-targeting antibiotic be presentthis MRSA strain suppresses ␤-lactamase expression to this purpose 159 -to withstand a second cell-walltargeting antibiotic is seemingly paradoxical. Moreover, the role of the ␤-lactam is indirect: addition of a ␤-lactam antibiotic to a culture of this strain results in release of muropeptides into the medium.…”

Messenger Functions of the Bacterial Cell Wall-derived Muropeptides

“…18 A new variation on this second mechanism to attain vancomycin resistance is now described for a strain of methicillin-resistant S. aureus (MRSA). 19 MRSA has high-level resistance to the β-lactam class of antibiotics (this class includes the extensively clinically used penicillins, cephalosporins and carbapenems). β-Lactam antibiotics act as ... d -Ala- d -Ala mimetics to achieve irreversible inactivation of the transpeptidase domain of the bifunctional penicillin-binding protein (PBP) enzymes of peptidoglycan biosynthesis.…”