Novel mutations in penicillin-binding protein genes in clinical Staphylococcus aureus isolates that are methicillin resistant on susceptibility testing, but lack the mec gene (original) (raw)
Related papers
mBio, 2014
We identified mutated genes in highly resistant subpopulations of methicillin-resistant Staphylococcus aureus (MRSA) that are most likely responsible for the historic failure of the β-lactam family of antibiotics as therapeutic agents against these important pathogens. Such subpopulations are produced during growth of most clinical MRSA strains, including the four historically early MRSA isolates studied here. Chromosomal DNA was prepared from the highly resistant cells along with DNA from the majority of cells (poorly resistant cells) followed by full genome sequencing. In the highly resistant cells, mutations were identified in 3 intergenic sequences and 27 genes representing a wide range of functional categories. A common feature of these mutations appears to be their capacity to induce high-level β-lactam resistance and increased amounts of the resistance protein PBP2A in the bacteria. The observations fit a recently described model in which the ultimate controlling factor of the phenotypic expression of β-lactam resistance in MRSA is a RelA-mediated stringent response. IMPORTANCE It has been well established that the level of antibiotic resistance (i.e., minimum concentration of a β-lactam antibiotic needed to inhibit growth) of a methicillin-resistant Staphylococcus aureus (MRSA) strain depends on the transcription and translation of the resistance protein PBP2A. Here we describe mutated loci in an additional novel set of genetic determinants that appear to be essential for the unusually high resistance levels typical of subpopulations of staphylococci that are produced with unique low frequency in most MRSA clinical isolates. We propose that mutations in these determinants can trigger induction of the stringent stress response which was recently shown to cause increased transcription/translation of the resistance protein PBP2A in parallel with the increased level of resistance.
Aim: This study was conducted to detect the mecA gene polymorphism in ovine wounds and its possible association with the structure and function of penicillin binding protein A2 (PBP2A). Methods: One genetic locus of 1,967 bp that covered the majority of the coding regions of the mecA gene within methicillin-resistant Staphylococcus aureus (MRSA) DNA sequences was designed. Results: In addition to standard microbiological tests, PCR-sequencing reactions and phylogenetic analyses confirmed the identity of the targeted MRSA bacteria. Seven novel missense SNPs, including N57T, N115Y, D120N, D139N, G152V, E189K, and F211V, were observed in the mecA amplicons. Multiple state-of-the-art in silico tools were utilized to assess the consequences of each observed SNP in terms of its effect on the corresponding PBP2A protein structure and function. It was shown that some MRSA isolates exhibited a highly PBP2A-damaging SNP, G152V, which showed an entirely deleterious effect on the PBP2A. Furthermore, G152V induced an alteration in the PBP2A interaction with its receptor, which presumably reduced its affinity to bind with the beta-lactams. Conclusion: The present report indicated a possible role for the observed deleterious G152V SNP in the reduction of PBP2A binding with beta-lactams, which has led to a remarkable increase in MRSA’s resistance to antibiotics. Keywords: Infection, In silico, MecA, Missense, Variations.
Pharmaceuticals, 2021
β-Lactam antibiotics target penicillin-binding proteins and inhibit the synthesis of peptidoglycan, a crucial step in cell wall biosynthesis. Staphylococcus aureus acquires resistance against β-lactam antibiotics by producing a penicillin-binding protein 2a (PBP2a), encoded by the mecA gene. PBP2a participates in peptidoglycan biosynthesis and exhibits a poor affinity towards β-lactam antibiotics. The current study was performed to determine the diversity and the role of missense mutations of PBP2a in the antibiotic resistance mechanism. The methicillin-resistant Staphylococcus aureus (MRSA) isolates from clinical samples were identified using phenotypic and genotypic techniques. The highest frequency (60%, 18 out of 30) of MRSA was observed in wound specimens. Sequence variation analysis of the mecA gene showed four amino acid substitutions (i.e., E239K, E239R, G246E, and E447K). The E239R mutation was found to be novel. The protein-ligand docking results showed that the E239R muta...
International Journal of Antimicrobial Agents, 2012
Meticillin-resistant Staphylococcus aureus (MRSA) remains one of the principal multiply resistant bacterial pathogens causing serious healthcare-associated and community-onset infections. This paper reviews recent studies that have elucidated the virulence strategies employed by MRSA, key clinical trials of agents used to treat serious MRSA infections, and accumulating data regarding the implications of antibacterial resistance in MRSA for clinical success during therapy. Recent pre-clinical data support a species-specific role for Panton-Valentine leukocidin in the development of acute severe S. aureus infections and have elucidated other virulence mechanisms, including novel modes of internalisation, varying post-invasion strategies (featuring both upregulation and downregulation of virulence factors) and phenotypic switching. Recent double-blind, randomised, phase III/IV clinical trials have demonstrated the efficacy of linezolid and telavancin in hospital-acquired pneumonia (HAP) and complicated skin and skin-structure infections (cSSSIs) caused by MRSA. Tigecycline was non-inferior to imipenem/cilastatin in non-ventilator-associated HAP but was inferior in ventilator-associated pneumonia and has shown a higher rate of death than comparators on meta-analysis. Ceftaroline was clinically and microbiologically non-inferior to vancomycin/aztreonam in the treatment of MRSA cSSSI. Key resistance issues include a rise in vancomycin minimum inhibitory concentrations in MRSA, reports of clonal isolates with linezolid resistance mediated by acquisition of the chloramphenicol/florfenicol resistance gene, and case reports of daptomycin resistance resulting in clinical failure. Novel antimicrobial targets must be identified with some regularity or we will face the risk of untreatable S. aureus infections.
Progression of β-Lactam Resistance in Staphylococcus aureus
Staphylococcus aureus [Working Title], 2021
Staphylococcus aureus is a notorious human pathogen that causes superficial and invasive infections both in nosocomial and community-acquired settings. The prevalence of staphylococcal infections became more challenging after emerging resistance against topical antibiotics. S. aureus evolved resistance to β-lactam antibiotics due to modification and expression of penicillin-binding proteins (PBP), inactivation of drug by β-lactamase synthesis, limiting uptake of drug by biofilm formation, and reducing uptake by expression of efflux pump. The wave of resistance was first observed in penicillin by β-lactamase production and PBPs modification. The second wave of resistance emerged to methicillin by appearing methicillin-resistant S. aureus (MRSA) strains. Cephalosporin has long been used as the last resort for preventing MRSA infections, but resistant strains appeared during treatment. In progression to control MRSA or related infections, carbapenems have been used but strains develope...
Clinical laboratory science: journal of the American Society for Medical Technology
Awareness of the threat of MRSA is growing. Scientists have put a lot of effort into trying to divide and classify MRSA strains into groups to better understand it. This led to the discovery that the resistance gene, mecA, and surrounding DNA could be grouped into several types. It was also discovered that the MRSA strains that caused hospital-acquired (nosocomial) infections were different strains than those seen in the communities. Several studies led to the realization that the number of MRSA infections is increasing, that more Staphylococcus aureus infections are caused by MRSA strains, and that the community strains are now showing up in the hospital. There have been government initiatives to try to decrease MRSA infections, with the most perplexing issue being that of whether or not to perform surveillance cultures on as many people as possible to eradicate MRSA from the community, as well as the hospital.
Molecular genetics of methicillin-resistant Staphylococcus aureus
A large and growing proportion of Staphylococcus aureus clinical isolates are methicillin resistant, and are resistant to practically all beta-lactam antibiotics. Methicillin-resistant S. aureus (MRSA) strains harbor mecA, which is carried by a unique mobile genetic element, staphylococcal cassette chromosome mec (SCCmec) integrated into the S. aureus chromosome. The mecA gene encodes a methicillin-insensitive transpeptidase, the production of which confers resistance to otherwise inhibitory concentrations of beta-lactam antibiotics. Several distinct clones have been identified among MRSA that apparently have been generated by integration of distinct types of SCCmec. While MRSA are primarily nosocomial pathogens, recent observations indicate that other MRSA clones are colonizing a significant proportion of healthy individuals in the community as well. Community-acquired MRSA (C-MRSA), may become a new threat to humans, and international cooperation of researchers and clinicians will be of cardinal importance in addressing this problem.
Antimicrobial agents and chemotherapy, 2014
In staphylococci, methicillin resistance is mediated by mecA-encoded penicillin-binding protein 2a (PBP2a), which has a low affinity for beta-lactams. Recently, a novel PBP2a homolog was described as being encoded by mecC, which shares only 70% similarity to mecA. To prove that mecC is the genetic determinant that confers methicillin resistance in Staphylococcus aureus, a mecC knockout strain was generated. The S. aureus ΔmecC strain showed considerably reduced oxacillin and cefoxitin MICs (0.25 and 4 μg/ml, respectively) compared to those of the corresponding wild-type methicillin-resistant S. aureus (MRSA) strain (8 and 16 μg/ml, respectively). Complementing the mutant in trans with wild-type mecC restored the resistance to oxacillin and cefoxitin. By expressing mecC and mecA in different S. aureus clonal lineages, we found that mecC mediates resistance irrespective of the genetic strain background, yielding oxacillin and cefoxitin MIC values comparable to those with mecA. In addi...
Methicillin-Resistant Staphylococcus Aureus (Mrsa) Remains a Major Threat to Public Health
Methicillin-resistant Staphylococcus aureus (MRSA) represents a major public health challenge due to its antibiotic resistance and potential for severe infections in both humans and animals. This review examines the current state of MRSA as a global health threat, emphasizing its virulence factors, transmission mechanisms, and impact on public health. MRSA's resistance to methicillin and other antibiotics confounds treatment and control efforts primarily due to the encoding of penicillin-binding protein 2a (PBP2a) by the mecA gene which has a low affinity for β-lactams, resulting in resistance to the entire class of antibiotics. The ability of the bacterium to cause a spectrum of infections, from mild skin conditions to life-threatening diseases like toxic shock syndrome, pneumonia, endocarditis, bacteremia and osteomyelitis, highlights its clinical significance. MRSA's spread is facilitated by its presence in healthcare settings, community environments, and livestock, with significant implications for food safety and public health. The review underscores the urgent need for enhanced surveillance, novel treatment strategies, and effective infection control measures to combat MRSA's growing threat.