Beta-lactam resistance response triggered by inactivation of a nonessential penicillin-binding protein.

Servicio de Microbiología and Unidad de Investigación, Hospital Son Dureta, Instituto Universitario de Investigación en Ciencias de la Salud Palma de Mallorca, Spain.
PLoS Pathogens (Impact Factor: 8.06). 04/2009; 5(3):e1000353. DOI: 10.1371/journal.ppat.1000353
Source: PubMed

ABSTRACT It has long been recognized that the modification of penicillin-binding proteins (PBPs) to reduce their affinity for beta-lactams is an important mechanism (target modification) by which Gram-positive cocci acquire antibiotic resistance. Among Gram-negative rods (GNR), however, this mechanism has been considered unusual, and restricted to clinically irrelevant laboratory mutants for most species. Using as a model Pseudomonas aeruginosa, high up on the list of pathogens causing life-threatening infections in hospitalized patients worldwide, we show that PBPs may also play a major role in beta-lactam resistance in GNR, but through a totally distinct mechanism. Through a detailed genetic investigation, including whole-genome analysis approaches, we demonstrate that high-level (clinical) beta-lactam resistance in vitro, in vivo, and in the clinical setting is driven by the inactivation of the dacB-encoded nonessential PBP4, which behaves as a trap target for beta-lactams. The inactivation of this PBP is shown to determine a highly efficient and complex beta-lactam resistance response, triggering overproduction of the chromosomal beta-lactamase AmpC and the specific activation of the CreBC (BlrAB) two-component regulator, which in turn plays a major role in resistance. These findings are a major step forward in our understanding of beta-lactam resistance biology, and, more importantly, they open up new perspectives on potential antibiotic targets for the treatment of infectious diseases.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Pseudomonas aeruginosa is one of the most important opportunistic bacteria, causing a wide variety of infections particularly in immunocompromised patients. The extracellular glycocalyx is produced in copious amounts by mucoid strains of P. aeruginosa. Mucoid and non-mucoid P. aeruginosa strains show some differences in their antimicrobial susceptibility pattern. The aim of this study was to investigate the frequency of mucoid and non-mucoid types and their antimicrobial susceptibility patterns isolated from Milad and Mostafa Khomeini Hospital in Tehran, Iran. One hundred P. aeruginosa isolates were collected which all were confirmed by conventional biochemical tests and PCR assay using specific primers for oprI and oprL lipoproteins. Mucoid and non-mucoid types of isolates were determined by culturing isolates on BHI agar containing Congo red and Muir mordant staining method. The susceptibility pattern of isolates against 23 different antibiotics was assessed using MIC sensititre susceptibility plates. Fifty of 100 of isolates were mucoid type, of which 14 isolates were from Mostafa Khomeini Hospital. Frequency of mucoid type of P. aeruginosa in Mostafa Khomeini hospital (70%) was higher than that seen in Milad hospital (45%). The statistical analysis of MICs results showed significant differences in antimicrobial resistance among mucoid and non-mucoid types (non mucoid strains showed more resistance against tested antibiotics). This may be due to the tendency of some antibiotics to attach to extracellular glycocalyx of mucoid strains.
    GMS hygiene and infection control. 01/2014; 9(2):Doc13.
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the Gram-negative enterobacterium Erwinia (Pectobacterium) and Serratia sp. ATCC 39006, intrinisic resistance to the carbapenem antibiotic 1-carbapen-2-em-3-carboxylic acid is mediated by the CarF and CarG proteins, by anunknown mechanism. Here, we report a high-resolution crystal structure for the Serratia sp. ATCC 39006 carbapenem resistance protein, CarG. This structure of CarG is the first in the carbapenem instrinsic resistance (CIR) family of resistance proteins from carbapenem-producing bacteria. The crystal structure shows the protein to form a homodimer, in agreement with results from analytical gel filtration. The structure of CarG does not show homology with any known antibiotic resistance proteins nor does it belong to any well characterised protein structural family. However, it is a close structural homologue of the bacterial inhibitor of invertebrate lysozyme, PliI-Ah, with some interesting structural variations, including the absence of the catalytic site responsible for lysozyme inhibition. Both proteins show a unique β sandwich fold with short terminal α helices. The core of the protein is formed by stacked anti-parallel sheets that are individually very similar in the two proteins but differ in their packing interface, causing the splaying of the two sheets in CarG. Furthermore, a conserved cation binding site identified in CarG is absent from the homologue.
    Journal of Molecular Biology 02/2014; · 3.91 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Production of beta-lactamases, the enzymes that degrade beta-lactam antibiotics, is the most widespread and threatening mechanism of antibiotic resistance. In the past, extensive research has focused on the structure, function, and ecology of beta-lactamases while limited efforts were placed on the regulatory mechanisms of beta-lactamases. Recently, increasing evidence demonstrate a direct link between beta-lactamase induction and cell wall metabolism in Gram-negative bacteria. Specifically, expression of beta-lactamase could be induced by the liberated murein fragments, such as muropeptides. This article summarizes current knowledge on cell wall metabolism, beta-lactam antibiotics, and beta-lactamases. In particular, we comprehensively reviewed recent studies on the beta-lactamase induction by muropeptides via two major molecular mechanisms (the AmpG-AmpR-AmpC pathway and BlrAB-like two-component regulatory system) in Gram-negative bacteria. The signaling pathways for beta-lactamase induction offer a broad array of promising targets for the discovery of new antibacterial drugs used for combination therapies. Therefore, to develop effective mitigation strategies against the widespread beta-lactam resistance, examination of the molecular basis of beta-lactamase induction by cell wall fragment is highly warranted.
    Frontiers in Microbiology 01/2013; 4:128. · 3.94 Impact Factor

Full-text (3 Sources)

Available from
Jul 9, 2014