β-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: 7.56). 04/2009; 5(3):e1000353. DOI: 10.1371/journal.ppat.1000353
Source: PubMed


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.

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Available from: Andreas Dötsch, Jul 09, 2014
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    • "P. aeruginosa is a highly adaptable microorganism and can develop resistance to different antibiotics. Multidrug-resistance (MDR) strains of P. aeruginosa use different mechanisms for developing resistance such as producing enzymes for inactivating β-lactams like ESBL (extended spectrum beta lactamase), MBL (metallo-β-lactamase) [10], [11], and biofilm formation can enhance ability of resistance in P. aeruginosa [12]. P. aeruginosa isolated from respiratory tract with typical non-mucoid phenotype, but in prolonged infection, can shift to mucoid form with producing large amounts of exopolysaccharide called alginate [13], [14]. "
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    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.
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    • "These observations suggest that AmpC is the major resistance determinant and MexAB pump by itself is not enough to confer b-lactam resistance. Resistance to b-lactams is also regulated by the CreBCD system (Moya et al., 2009; Zamorano et al., 2010). CreBC forms a two-component system that positively regulates expression of an inner membrane protein CreD (Avison et al., 2001); together, they regulate b-lactam resistance (Avison et al., 2004). "
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    • "The mexABoprM operon is constitutively expressed in wild-type cells under usual laboratory conditions, where the operon contributes to P. aeruginosa's intrinsic resistance to most β-lactams (except for imipenem) and many other antimicrobial agents, including quinolones, tetracycline, chloramphenicol, and macrolides (Morita et al., 2001). Blocking of dacB-encoded non-essential PBP4 determines a highly efficient and complex β-lactam resistance response, triggering the overproduction of AmpC and the specific activation of the CreAB (BlrAB) two-component regulator (Moya et al., 2009). Carbapenems are an important class of anti-pseudomonal βlactams . "
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