We previously demonstrated that brief nonkilling neutrophil exposure diminishes the binding affinity of S. aureus penicillin-binding protein (PBP) 2. We sought to investigate further the role of the neutrophil in the ...We previously demonstrated that brief nonkilling neutrophil exposure diminishes the binding affinity of S. aureus penicillin-binding protein (PBP) 2. We sought to investigate further the role of the neutrophil in the alteration of antimicrobial activity and its interaction with PBP-2 by studying the activity of cefotaxime, which highly binds to PBP 2, and cephalexin, which minimally binds to PBP 2. Using S. aureus, cultured in vitro in sterile-filtered normal and neutrophil depleted abscess fluid, we sought to demonstrate an in vivo significance of the neutrophil effect upon the activity of antimicrobials that target PBP-2 by studying the same antimicrobials in an experimental S. aureus abscess. Rats were implanted with perforated tissue cages and infected with S. aureus;some rats were neutrophil depleted by mechlorethamine. Abscess fluids from normal and neutropenic abscesses were harvested, pooled, sterile-filtered and stored for the time-kill studies. Treatment studies were performed by administering either 300 μg/kg/d cefotaxime or cephalexin for 7 days in other rats with 24 hour-old tissue-cage S. aureus abscesses. In time-kill studies, cefotaxime was highly active against stationary phase S. aureus in MHB and in neutropenic abscess fluid, but less active in the non-neutropenic abscess fluid (p 10 kill, p = 0.029 vs. 0.81 ± 2.5, p = NS). These data suggest that neutrophil exposure, which diminishes S. aureus PBP-2 binding affinity [or total quantity], also adversely affects the antimicrobial activity of cefotaxime, which binds to PBP-2, as compared to cephalexin. Altered PBP targets from neutrophil exposure may be a mechanism of antimicrobial resistance within abscesses.展开更多
Objective To develop a rapid multi-residue assay for detecting 16 demanded by the European Union （EU）. Methods A recombinant penicillin-binding protein （PBP） 2x＊ from Streptococcus pneumoniae R6 was expressed in ...Objective To develop a rapid multi-residue assay for detecting 16 demanded by the European Union （EU）. Methods A recombinant penicillin-binding protein （PBP） 2x＊ from Streptococcus pneumoniae R6 was expressed in vitro and six β-1actams were conjugated to HRP by four methods. A rapid multi-residue assay for β-1actams was established with PBP2x＊ and HRP-conjugate. Results PBP2x＊ was expressed and purified successfully and the ideal HRP-conjugate was identified. The multi-residue assay was developed. After optimization, penicillin G, ampicillin, amoxicillin, cloxacillin, dicloxacillin, oxacillin, nafcillin, cephalexin, ceftiofur, cefalonium, cefquinome, cefazolin, cefoperazone, cephacetrile, and cephapirin can be detected at levels below MRL in milk with simple pretreatment. Conclusion This assay developed can detect all 16 β-1actams demanded by the European Union （EU）. The whole procedure takes only 45 min and can detect 42 samples and the standards with duplicate analysis.展开更多
文摘We previously demonstrated that brief nonkilling neutrophil exposure diminishes the binding affinity of S. aureus penicillin-binding protein (PBP) 2. We sought to investigate further the role of the neutrophil in the alteration of antimicrobial activity and its interaction with PBP-2 by studying the activity of cefotaxime, which highly binds to PBP 2, and cephalexin, which minimally binds to PBP 2. Using S. aureus, cultured in vitro in sterile-filtered normal and neutrophil depleted abscess fluid, we sought to demonstrate an in vivo significance of the neutrophil effect upon the activity of antimicrobials that target PBP-2 by studying the same antimicrobials in an experimental S. aureus abscess. Rats were implanted with perforated tissue cages and infected with S. aureus;some rats were neutrophil depleted by mechlorethamine. Abscess fluids from normal and neutropenic abscesses were harvested, pooled, sterile-filtered and stored for the time-kill studies. Treatment studies were performed by administering either 300 μg/kg/d cefotaxime or cephalexin for 7 days in other rats with 24 hour-old tissue-cage S. aureus abscesses. In time-kill studies, cefotaxime was highly active against stationary phase S. aureus in MHB and in neutropenic abscess fluid, but less active in the non-neutropenic abscess fluid (p 10 kill, p = 0.029 vs. 0.81 ± 2.5, p = NS). These data suggest that neutrophil exposure, which diminishes S. aureus PBP-2 binding affinity [or total quantity], also adversely affects the antimicrobial activity of cefotaxime, which binds to PBP-2, as compared to cephalexin. Altered PBP targets from neutrophil exposure may be a mechanism of antimicrobial resistance within abscesses.
文摘Objective To develop a rapid multi-residue assay for detecting 16 demanded by the European Union （EU）. Methods A recombinant penicillin-binding protein （PBP） 2x＊ from Streptococcus pneumoniae R6 was expressed in vitro and six β-1actams were conjugated to HRP by four methods. A rapid multi-residue assay for β-1actams was established with PBP2x＊ and HRP-conjugate. Results PBP2x＊ was expressed and purified successfully and the ideal HRP-conjugate was identified. The multi-residue assay was developed. After optimization, penicillin G, ampicillin, amoxicillin, cloxacillin, dicloxacillin, oxacillin, nafcillin, cephalexin, ceftiofur, cefalonium, cefquinome, cefazolin, cefoperazone, cephacetrile, and cephapirin can be detected at levels below MRL in milk with simple pretreatment. Conclusion This assay developed can detect all 16 β-1actams demanded by the European Union （EU）. The whole procedure takes only 45 min and can detect 42 samples and the standards with duplicate analysis.
