title: Bacteremia due to Staphylococcus aureus with reduced susceptibility to vancomycin.
abstract: Four cases of bacteremia caused by Staphylococcus aureus with heteroresistance to vancomycin (hetero-VRSA) were described. In at least two of these four mortalities, the cause of death was temporally related to the hetero-VRSA bacteremia. The vancomycin and teicoplanin MICs of the resistant subpopulations of these four hetero-VRSA were 8 and 24 microg/ml, respectively. All isolates were producers of beta-lactamase, produced penicillin-binding protein PBP2a, and possessed the mecA gene accounting for methicillin resistance. Thickening of the peptidoglycan cell wall was observed by electron microscopy. When ampicillin was combined with vancomycin, in vitro synergism was detected using the checkerboard titration method (epsilonFIC = 0.13). The use of vancomycin plus ampicillin-sulbactam could be a viable option in treating severe hetero-VRSA infection in view of the higher affinity of ampicillin toward PBP2a.
authors.affiliation: Division of Infectious Diseases, Department of Microbiology, The University of Hong Kong, Queen Mary Hospital, University Pathology Building, Pokfulam Road, Hong Kong.
authors.forename: S S
authors.initials: SS
authors.lastname: Wong
authors.forename: T K
authors.initials: TK
authors.lastname: Ng
authors.forename: W C
authors.initials: WC
authors.lastname: Yam
authors.forename: D N
authors.initials: DN
authors.lastname: Tsang
authors.forename: P C
authors.initials: PC
authors.lastname: Woo
authors.forename: S K
authors.initials: SK
authors.lastname: Fung
authors.forename: K Y
authors.initials: KY
authors.lastname: Yuen
mesh_terms: D000368:Aged; D000667:Ampicillin / Q000627:therapeutic use; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D016470:Bacteremia / Q000188:drug therapy* / Q000382:microbiology; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000032:analysis; D004269:DNA, Bacterial / Q000032:analysis; D016521:Electrophoresis, Gel, Pulsed-Field; D017809:Fatal Outcome; D005260:Female; D006602:Hexosyltransferases; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D008854:Microscopy, Electron; D008875:Middle Aged; D002267:Muramoylpentapeptide Carboxypeptidase / Q000032:analysis; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000627:therapeutic use; D010458:Peptidyl Transferases; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification / Q000648:ultrastructure; D017334:Teicoplanin / Q000627:therapeutic use*; D014640:Vancomycin / Q000627:therapeutic use*; D020713:Vancomycin Resistance; D001618:beta-Lactamases / Q000032:analysis
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D017334:Teicoplanin; D014640:Vancomycin; D000667:Ampicillin; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D001618:beta-Lactamases