title: Antimicrobial resistance to ceftazidime involving loss of penicillin-binding protein 3 in Burkholderia pseudomallei.
abstract: Known mechanisms of resistance to β-lactam antibiotics include β-lactamase expression, altered drug target, decreased bacterial permeability, and increased drug efflux. Here, we describe a unique mechanism of β-lactam resistance in the biothreat organism Burkholderia pseudomallei (the cause of melioidosis), associated with treatment failure during prolonged ceftazidime therapy of natural infection. Detailed comparisons of the initial ceftazidime-susceptible infecting isolate and subsequent ceftazidime-resistant variants from six patients led us to identify a common, large-scale genomic loss involving a minimum of 49 genes in all six resistant strains. Mutational analysis of wild-type B. pseudomallei demonstrated that ceftazidime resistance was due to deletion of a gene encoding a penicillin-binding protein 3 (BPSS1219) present within the region of genomic loss. The clinical ceftazidime-resistant variants failed to grow using commonly used laboratory culture media, including commercial blood cultures, rendering the variants almost undetectable in the diagnostic laboratory. Melioidosis is notoriously difficult to cure and clinical treatment failure is common in patients treated with ceftazidime, the drug of first choice across most of Southeast Asia where the majority of cases are reported. The mechanism described here represents an explanation for ceftazidime treatment failure, and may be a frequent but undetected resistance event.
authors.affiliation: Department of Microbiology and Immunology, Faculty of Tropical Medicine,  Mahidol University, Bangkok 10400,  Thailand.
authors.forename: Narisara
authors.initials: N
authors.lastname: Chantratita
authors.forename: Drew A
authors.initials: DA
authors.lastname: Rholl
authors.forename: Bernice
authors.initials: B
authors.lastname: Sim
authors.forename: Vanaporn
authors.initials: V
authors.lastname: Wuthiekanun
authors.forename: Direk
authors.initials: D
authors.lastname: Limmathurotsakul
authors.forename: Premjit
authors.initials: P
authors.lastname: Amornchai
authors.forename: Aunchalee
authors.initials: A
authors.lastname: Thanwisai
authors.forename: Hui Hoon
authors.initials: HH
authors.lastname: Chua
authors.forename: Wen Fong
authors.initials: WF
authors.lastname: Ooi
authors.forename: Matthew T G
authors.initials: MT
authors.lastname: Holden
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Day
authors.forename: Patrick
authors.initials: P
authors.lastname: Tan
authors.forename: Herbert P
authors.initials: HP
authors.lastname: Schweizer
authors.forename: Sharon J
authors.initials: SJ
authors.lastname: Peacock
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001210:Asia, Southeastern; D001483:Base Sequence; D016957:Burkholderia pseudomallei / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002442:Ceftazidime / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics / Q000502:physiology; D017353:Gene Deletion; D005798:Genes, Bacterial; D006801:Humans; D008554:Melioidosis / Q000188:drug therapy / Q000382:microbiology; D046915:Penicillin-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017211:Treatment Failure
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D046915:Penicillin-Binding Proteins; D002442:Ceftazidime