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.

A Structure-Based Classification of Class A β-Lactamases, a Broadly Diverse Family of Enzymes

“…Additional singleamino-acid deletions have recently been reported (27). Another mechanism of acquired resistance involves the overexpression of the chromosomal ␤-lactamase of B. pseudomallei or the loss of a penicillin-binding protein or (PBP) and also porin (164,(166)(167)(168). Two chromosomally encoded ␤-lactamases (LUT-1 and MIN-1) have also been identified in this cluster (cluster 5) ( Table 1 and Fig.…”

“…Twelve positions displaying single-amino-acid substitutions are located in the active-site pocket, such as Cys69Phe and Cys69Tyr, or in the ⍀-loop (positions 162,164,166,169,170,171,172,174,176, and 179 but not position 167). Interestingly, a single-amino-acid deletion (Glu168del) may expand the in vitro spectrum of inactivation to ceftazidime in B. thailandensis (165).…”

One ring to rule them all: Current trends in combating bacterial resistance to the β‐lactams

“…78 Recently, antimicrobial resistance to ceftazidime in Burkholderia pseudomallei has been correlated with a deletion of PBP3, which is the primary target of ceftazidime in other Gram-negative bacilli including P. aeruginosa and E. coli. 79 Furthermore, the growing identification of microbes harboring both b-lactamases and low affinity PBPs presents a double resistance threat that is particularly worrisome.…”

Rapid Antimicrobial Susceptibility Testing of Bacillus anthracis, Yersinia pestis, and Burkholderia pseudomallei by Use of Laser Light Scattering Technology

“…The target of CAZ is penicillin-binding protein 3 (PBP3). The inhibition of PBP3 activity prevents the separation of B. pseudomallei daughter cells, resulting in the formation of filamentous cells (21). The presence of filamentous cells of the CAZ-susceptible strain after 7 h of exposure to CAZ is likely responsible for the variation in CFU per milliliter data in a manner similar to that seen with B. anthracis after chains of cells formed and started to settle to the bottom of the cuvette.…”