Ceftobiprole- and ceftaroline-resistant methicillin-resistant Staphylococcus aureus

ESKAPE pathogens: antimicrobial resistance, epidemiology, clinical impact and therapeutics

The rise of antibiotic resistance and a dwindling antimicrobial pipeline have been recognized as emerging threats to public health. The ESKAPE pathogens - Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp. - were initially identified as critical multidrug-resistant bacteria for which effective therapies were rapidly needed. Now, entering the third decade of the twenty-first century, and despite the introduction of several new antibiotics and antibiotic adjuvants, such as novel β-lactamase inhibitors, these organisms continue to represent major therapeutic challenges. These bacteria share several key biological features, including adaptations for survival in the modern health-care setting, diverse methods for acquiring resistance determinants and the dissemination of successful high-risk clones around the world. With the advent of next-generation sequencing, novel tools to track and combat the spread of these organisms have rapidly evolved, as well as renewed interest in non-traditional antibiotic approaches. In this Review, we explore the current epidemiology and clinical impact of this important group of bacterial pathogens and discuss relevant mechanisms of resistance to recently introduced antibiotics that affect their use in clinical settings. Furthermore, we discuss emerging therapeutic strategies needed for effective patient care in the era of widespread antimicrobial resistance.

Altered PBP4 and GdpP functions synergistically mediate MRSA-like high-level, broad-spectrum β-lactam resistance in Staphylococcus aureus

Infections caused by Staphylococcus aureus are a leading cause of mortality worldwide. S. aureus infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are particularly difficult to treat due to their resistance to next-generation β-lactams (NGBs) such as methicillin, nafcillin, and oxacillin. Resistance to NGBs, which is alternatively known as broad-spectrum β-lactam resistance, is classically mediated by PBP2a, a penicillin-binding protein encoded by mecA (or mecC) in MRSA. Thus, presence of mec genes among S. aureus spp. serves as the predictor of resistance to NGBs and facilitates determination of the proper therapeutic strategy for a staphylococcal infection. Although far less appreciated, mecA-deficient S. aureus strains can also exhibit NGB resistance. These strains, which are collectively termed as methicillin-resistant lacking mec (MRLM), are currently being identified in increasing numbers among natural resistant isolates of S. aureus. The mechanism/s through which MRLMs produce resistance to NGBs remains unknown. In this study, we demonstrate that mutations that alter PBP4 and GdpP functions, which are often present among MRLMs, can synergistically mediate resistance to NGBs. Furthermore, our results unravel that this novel mechanism potentially enables MRLMs to produce resistance toward NGBs at levels comparable to those of MRSAs. Our study provides a fresh new perspective about alternative mechanisms of NGB resistance, challenging our current overall understanding of high-level, broad-spectrum β-lactam resistance in S. aureus. It thus suggests reconsideration of the current approach toward diagnosis and treatment of β-lactam-resistant S. aureus infections.

IMPORTANCE

In Staphylococcus aureus, high-level, broad-spectrum resistance to β-lactams such as methicillin, also referred to as methicillin resistance, is largely attributed to mecA. This study demonstrates that S. aureus strains that lack mecA but contain mutations that functionally alter PBP4 and GdpP can also mediate high-level, broad-spectrum resistance to β-lactams. Resistance brought about by the synergistic action of functionally altered PBP4 and GdpP was phenotypically comparable to that displayed by mecA, as seen by increased bacterial survival in the presence of β-lactams. An analysis of mutations detected in naturally isolated strains of S. aureus revealed that a significant proportion of them had similar pbp4 and GGDEF domain protein containing phosphodiesterase (gdpP) mutations, making this study clinically significant. This study not only identifies important players of non-classical mechanisms of β-lactam resistance but also indicates reconsideration of current clinical diagnosis and treatment protocols of S. aureus infections.

Altered PBP4 and GdpP functions synergistically mediate MRSA-like high-level, broad-spectrum β-lactam resistance in Staphylococcus aureus

Infections caused by Staphylococcus aureus are a leading cause of mortality worldwide. S. aureus infections caused by Methicillin-Resistant Staphylococcus aureus (MRSA) are particularly difficult to treat due to their resistance to Next Generation β-lactams (NGB) such as Methicillin, Nafcillin, Oxacillin etc. Resistance to NGBs, which is alternatively known as broad-spectrum β-lactam resistance is classically mediated by PBP2a, a Penicillin-Binding Protein encoded by mecA (or mecC) in MRSA. Thus, presence of mec genes among S. aureus serves as the predictor of resistance to NGBs and facilitates determination of the proper therapeutic strategy for a staphylococcal infection. Although far less appreciated, mecA deficient S. aureus strains can also exhibit NGB resistance. These strains, which are collectively termed as Methicillin-Resistant Lacking mec (MRLM) are currently being identified in increasing numbers among natural resistant isolates of S. aureus. The mechanism/s through which MRLMs produce resistance to NGBs remains unknown. In this study, we demonstrate that mutations that alter PBP4 and GdpP functions, which are often present among MRLMs can synergistically mediate resistance to NGBs. Furthermore, our results unravel that this novel mechanism potentially enables MRLMs to produce resistance towards NGBs at levels comparable to that of MRSAs. Our study, provides a fresh new perspective about alternative mechanisms of NGBs resistance, challenging our current overall understanding of high-level, broad-spectrum β-lactam resistance in S. aureus. It thus suggests reconsideration of the current approach towards diagnosis and treatment of β-lactam resistant S. aureus infections.

Molecular Determinants of β-Lactam Resistance in Methicillin-Resistant Staphylococcus aureus (MRSA): An Updated Review

The development of antibiotic resistance in Staphylococcus aureus, particularly in methicillin-resistant S. aureus (MRSA), has become a significant health concern worldwide. The acquired mecA gene encodes penicillin-binding protein 2a (PBP2a), which takes over the activities of endogenous PBPs and, due to its low affinity for β-lactam antibiotics, is the main determinant of MRSA. In addition to PBP2a, other genetic factors that regulate cell wall synthesis, cell signaling pathways, and metabolism are required to develop high-level β-lactam resistance in MRSA. Although several genetic factors that modulate β-lactam resistance have been identified, it remains unclear how they alter PBP2a expression and affect antibiotic resistance. This review describes the molecular determinants of β-lactam resistance in MRSA, with a focus on recent developments in our understanding of the role of mecA-encoded PBP2a and on other genetic factors that modulate the level of β-lactam resistance. Understanding the molecular determinants of β-lactam resistance can aid in developing novel strategies to combat MRSA.

Synergistic Combinations of FDA-Approved Drugs with Ceftobiprole against Methicillin-Resistant Staphylococcus aureus

New strategies are urgently needed to address the public health threat of antimicrobial resistance. Synergistic agent combinations provide one possible pathway toward addressing this need and are also of fundamental mechanistic interest. Effective methods for comprehensively identifying synergistic agent combinations are required for such efforts. In this study, an FDA-approved drug library was screened against methicillin-resistant Staphylococcus aureus (MRSA) (ATCC 43300) in the absence and presence of sub-MIC levels of ceftobiprole, a PBP2a-targeted anti-MRSA β-lactam. This screening identified numerous potential synergistic agent combinations, which were then confirmed and characterized for synergy using checkerboard analyses. The initial group of synergistic agents (sum of the minimum fractional inhibitory concentration ∑FIC_min ≤0.5) were all β-lactamase-resistant β-lactams (cloxacillin, dicloxacillin, flucloxacillin, oxacillin, nafcillin, and cefotaxime). Cloxacillin-the agent with the greatest synergy with ceftobiprole-is also highly synergistic with ceftaroline, another PBP2a-targeted β-lactam. Further follow-up studies revealed a range of ceftobiprole synergies with other β-lactams, including with imipenem, meropenem, piperacillin, tazobactam, and cefoxitin. Interestingly, given that essentially all other ceftobiprole-β-lactam combinations showed synergy, ceftaroline and ceftobiprole showed no synergy. Modest to no synergy (0.5 < ∑FIC_min ≤ 1.0) was observed for several non-β-lactam agents, including vancomycin, daptomycin, balofloxacin, and floxuridine. Mupirocin had antagonistic activity with ceftobiprole. Flucloxacillin appeared particularly promising, with both a low intrinsic MIC and good synergy with ceftobiprole. That so many β-lactam combinations with ceftobiprole show synergy suggests that β-lactam combinations can generally increase β-lactam effectiveness and may also be useful in reducing resistance emergence and spread in MRSA. IMPORTANCE Antimicrobial resistance represents a serious threat to public health. Antibacterial agent combinations provide a potential approach to combating this problem, and synergistic agent combinations-in which each agent enhances the antimicrobial activity of the other-are particularly valuable in this regard. Ceftobiprole is a late-generation β-lactam antibiotic developed for MRSA infections. Resistance has emerged to ceftobiprole, jeopardizing this agent's effectiveness. To identify synergistic agent combinations with ceftobiprole, an FDA-approved drug library was screened for potential synergistic combinations with ceftobiprole. This screening and follow-up studies identified numerous β-lactams with ceftobiprole synergy.

Structural basis of broad-spectrum β-lactam resistance in Staphylococcus aureus

Broad-spectrum β-lactam antibiotic resistance in Staphylococcus aureus is a global healthcare burden1,2. In clinical strains, resistance is largely controlled by BlaR13, a receptor that senses β-lactams through the acylation of its sensor domain, inducing transmembrane signalling and activation of the cytoplasmic-facing metalloprotease domain4. The metalloprotease domain has a role in BlaI derepression, inducing blaZ (β-lactamase PC1) and mecA (β-lactam-resistant cell-wall transpeptidase PBP2a) expression3-7. Here, overcoming hurdles in isolation, we show that BlaR1 cleaves BlaI directly, as necessary for inactivation, with no requirement for additional components as suggested previously8. Cryo-electron microscopy structures of BlaR1-the wild type and an autocleavage-deficient F284A mutant, with or without β-lactam-reveal a domain-swapped dimer that we suggest is critical to the stabilization of the signalling loops within. BlaR1 undergoes spontaneous autocleavage in cis between Ser283 and Phe284 and we describe the catalytic mechanism and specificity underlying the self and BlaI cleavage. The structures suggest that allosteric signalling emanates from β-lactam-induced exclusion of the prominent extracellular loop bound competitively in the sensor-domain active site, driving subsequent dynamic motions, including a shift in the sensor towards the membrane and accompanying changes in the zinc metalloprotease domain. We propose that this enhances the expulsion of autocleaved products from the active site, shifting the equilibrium to a state that is permissive of efficient BlaI cleavage. Collectively, this study provides a structure of a two-component signalling receptor that mediates action-in this case, antibiotic resistance-through the direct cleavage of a repressor.

A Comprehensive Review of Recent Advances in the Biological Activities of Quinazolines

Quinazoline heterocycles are critical in the development of medications. Quinazoline derivatives have been intensively researched, providing a wide range of compounds with diverse biological roles. The quinazoline nucleus has garnered a lot of attention in medical chemistry in recent years. It was assumed to be a pharmacophore component in the development of physiologically interesting drugs. This review is an attempt to increase the potential of quinazoline by highlighting a wide range of advancements demonstrated by numerous derivatives of the quinazoline moiety, as well as focusing on diverse pharmacological actions of the quinazoline moiety. This review compiles recent studies on the quinazoline moiety described in the literature by researchers.

Inhibition of the Quorum Sensing System, Elastase Production and Biofilm Formation in Pseudomonas aeruginosa by Psammaplin A and Bisaprasin

Natural products derived from marine sponges have exhibited bioactivity and, in some cases, serve as potent quorum sensing inhibitory agents that prevent biofilm formation and attenuate virulence factor expression by pathogenic microorganisms. In this study, the inhibitory activity of the psammaplin-type compounds, psammaplin A (1) and bisaprasin (2), isolated from the marine sponge, Aplysinellarhax, are evaluated in quorum sensing inhibitory assays based on the Pseudomonas aeruginosa PAO1 lasB-gfp(ASV) and rhlA-gfp(ASV) biosensor strains. The results indicate that psammaplin A (1) showed moderate inhibition on lasB-gfp expression, but significantly inhibited the QS-gene promoter, rhlA-gfp, with IC50 values at 14.02 μM and 4.99 μM, respectively. In contrast, bisaprasin (2) displayed significant florescence inhibition in both biosensors, PAO1 lasB-gfp and rhlA-gfp, with IC50 values at 3.53 μM and 2.41 μM, respectively. Preliminary analysis suggested the importance of the bromotyrosine and oxime functionalities for QSI activity in these molecules. In addition, psammaplin A and bisaprasin downregulated elastase expression as determined by the standard enzymatic elastase assay, although greater reduction in elastase production was observed with 1 at 50 μM and 100 μM. Furthermore, the study revealed that bisaprasin (2) reduced biofilm formation in P. aeruginosa.

Loss of GdpP function in Staphylococcus aureus leads to β-lactam tolerance and enhanced evolution of β-lactam resistance

Infections caused by Staphylococcus aureus are a leading cause of mortality. Treating infections caused by S. aureus is difficult due to resistance against most traditional antibiotics, including β-lactams. We previously reported the presence of mutations in gdpP among S. aureus strains that were obtained by serial passaging in β-lactam drugs. Similar mutations have recently been reported in natural S. aureus isolates that are either non-susceptible or resistant to β-lactam antibiotics. gdpP codes for a phosphodiesterase that cleaves cyclic-di-AMP (CDA), a newly discovered second messenger. In this study, we sought to identify the role of gdpP in β-lactam resistance in S. aureus. Our results showed that gdpP associated mutations caused loss of phosphodiesterase function, leading to increased CDA accumulation in the bacterial cytosol. Deletion of gdpP led to an enhanced ability of the bacteria to withstand a β-lactam challenge (two to three log increase in bacterial colony forming units) by promoting tolerance without enhancing MICs of β-lactam antibiotics. Our results demonstrated that increased drug tolerance due to loss of GdpP function can provide a selective advantage in acquisition of high-level β-lactam resistance. Loss of GdpP function thus increases tolerance to β-lactams that can lead to its therapy failure and can permit β-lactam resistance to occur more readily.

Evaluation of in vitro activity of ceftaroline on methicillin resistant Staphylococcus aureus blood isolates from Iran

Background and Objectives:

Ceftaroline (CPT) is a novel cephalosporin with potent activity against methicillin-resistant Staphylococcus aureus (MRSA). Despite its recent introduction, CPT resistance in MRSA has been described worldwide. We aimed in the current study to evaluate the in vitro activity of CPT against 91 clinical MRSA and 3 MSSA isolates.

Materials and Methods:

Susceptibility of isolates to CPT was tested using E-test and disk diffusion (DD) method. The nucleotide sequence of the mecA gene and molecular types of isolates with reduced susceptibility to CPT were further studied to identify resistance conferring mutations in PBP2a and the genetic relatedness of the isolates respectively.

Results:

Overall, 92.5% of isolates were found to be CPT susceptible (MICs≤1mg/l) and 7 MRSA isolates were characterized with MIC=2mg/l and categorized as susceptible dose dependent. Compared to E-test, DD revealed a categorical agreement rate of 93.6% and the obtained rates for minor, major /very major error were found to be 6.3% and 0% respectively. The MRSA isolates with increased CPT MICs (n=7), belonged to spa types t030 (n=6) and t13927 (n=1) and all carried N146K substitution in PBP2a allosteric domain, except for one isolate which harbored a wild-type PBP2a.

Conclusion:

While resistance to CPT was not detected we found increased CPT MICs in 7.69% of MRSA isolates. Reduced susceptibility to CPT in the absence of mecA mutations is indicative of contribution of secondary chromosomal mutations in resistance development.

Characterization of an osteomyelitis case caused by dalbavancin, ceftaroline, and vancomycin non-susceptible methicillin-resistant Staphylococcus aureus

We report a case of osteomyelitis due to methicillin-resistant Staphylococcus aureus (MRSA) that is also non-susceptible to vancomycin, dalbavancin, ceftaroline, and ceftobiprole, in the absence of exposure to the latter three antibiotics. It was isolated from a patient with a 26-year history of cranial surgeries and episodes of osteomyelitis. Whole-genome sequencing was performed. It was found to belong to ST247 and the mecA gene was detected within the SSCmec type I (1B) gene cassette that lacked the E447K mutation known to produce resistance to ceftobiprole and ceftaroline. However, mutations in other genes related to resistance to these antibiotics were found.

A Strong Synergy Between the Thiopeptide Bacteriocin Micrococcin P1 and Rifampicin Against MRSA in a Murine Skin Infection Model

Antibiotic-resistant bacterial pathogens have become a serious threat worldwide. One of these pathogens is methicillin-resistant Staphylococcus aureus (MRSA), a major cause of skin and soft tissue infections. In this study we identified a strain of Staphylococcus equorum producing a substance with high antimicrobial activity against many Gram-positive bacteria, including MRSA. By mass spectrometry and whole genome sequencing the antimicrobial substance was identified as the thiopeptide bacteriocin micrococcin P1 (MP1). Based on its properties we developed a one-step purification protocol resulting in high yield (15 mg/L) and high purity (98%) of MP1. For shorter incubation times (5-7 h) MP1 was very potent against MRSA but the inhibitory effect was overshadowed by resistance development during longer incubation time (24h or more). To overcome this problem a synergy study was performed with a number of commercially available antibiotics. Among the antibiotics tested, the combination of MP1 and rifampicin gave the best synergistic effect, with MIC values 25 and 60 times lower than for the individual drugs, respectively. To assess the therapeutic potential of the MP1-rifampicin combination, we used a murine skin infection model based on the use of the multidrug-resistant luciferase-tagged MRSA strain Xen31. As expected, neither of the single antimicrobials (MP1 or rifampicin) could eradicate Xen31 from the wounds. By contrary, the MP1-rifampicin combination was efficient not only to eradicate but also to prevent the recurrence of Xen31 infection. Furthermore, compared to fucidin cream, which is commonly used in skin infection treatments, MP1-rifampicin combination was superior in terms of preventing resistance development. Our results show that combining MP1, and probably other thiopeptides, with antibiotics can be a promising strategy to treat SSTIs caused by MRSA and likely many other Gram-positive bacteria.

Cell Membrane Adaptations Mediate β-Lactam-Induced Resensitization of Daptomycin-Resistant (DAP-R) Staphylococcus aureus In Vitro

The reversal of daptomycin resistance in MRSA to a daptomycin-susceptible phenotype following prolonged passage in selected β-lactams occurs coincident with the accumulation of multiple point mutations in the mprF gene. MprF regulates surface charge by modulating the content and translocation of the positively charged cell membrane phospholipid, lysyl-phosphatidylglycerol (LPG). The precise cell membrane adaptations accompanying such β-lactam-induced mprF perturbations are unknown. This study examined key cell membrane metrics relevant to antimicrobial resistance among three daptomycin-resistant MRSA clinical strains, which became daptomycin-susceptible following prolonged exposure to cloxacillin ('daptomycin-resensitized'). The causal role of such secondary mprF mutations in mediating daptomycin resensitization was confirmed through allelic exchange strategies. The daptomycin-resensitized strains derived either post-cloxacillin passage or via allelic exchange (vs. their respective daptomycin-resistant strains) showed the following cell membrane changes: (i) enhanced BODIPY-DAP binding; (ii) significant reductions in LPG content, accompanied by significant increases in phosphatidylglycerol content (p < 0.05); (iii) no significant changes in positive cell surface charge; (iv) decreased cell membrane fluidity (p < 0.05); (v) enhanced carotenoid content (p < 0.05); and (vi) lower branched chain fatty acid profiles (antiso- vs. iso-), resulting in increases in saturated fatty acid composition (p < 0.05). Overall, the cell membrane characteristics of the daptomycin-resensitized strains resembled those of parental daptomycin-susceptible strains. Daptomycin resensitization with selected β-lactams results in both definable genetic changes (i.e., mprF mutations) and a number of key cell membrane phenotype modifications, which likely facilitate daptomycin activity.

Exploring the possible targeting strategies of liposomes against methicillin-resistant Staphylococcus aureus (MRSA)

Multi antibiotic-resistant bacterial infections are on the rise due to the overuse of antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the pathogens listed under the category of serious threats where vancomycin remains the mainstay treatment despite the availability of various antibacterial agents. Recently, decreased susceptibility to vancomycin from clinical isolates of MRSA has been reported and has drawn worldwide attention as it is often difficult to overcome and leads to increased medical costs, mortality, and longer hospital stays. Development of antibiotic delivery systems is often necessary to improve bioavailability and biodistribution, in order to reduce antibiotic resistance and increase the lifespan of antibiotics. Liposome entrapment has been used as a method to allow higher drug dosing apart from reducing toxicity associated with drugs. The surface of the liposomes can also be designed and enhanced with drug-release properties, active targeting, and stealth effects to prevent recognition by the mononuclear phagocyte system, thus enhancing its circulation time. The present review aimed to highlight the possible targeting strategies of liposomes against MRSA bacteremia systemically while investigating the magnitude of this effect on the minimum inhibitory concentration level.

Cranberry-Derived Proanthocyanidins Potentiate β-Lactam Antibiotics against Resistant Bacteria

The emergence and spread of extended-spectrum β-lactamases (ESBLs), metallo-β-lactamases (MBLs), or variant low-affinity penicillin-binding proteins (PBPs) pose a major threat to our ability to treat bacterial infection using β-lactam antibiotics. Although combinations of β-lactamase inhibitors with β-lactam agents have been clinically successful, there are no MBL inhibitors in current therapeutic use. Furthermore, recent clinical use of new-generation cephalosporins targeting PBP2a, an altered PBP, has led to the emergence of resistance to these antimicrobial agents. Previous work shows that natural polyphenols such as cranberry-extracted proanthocyanidins (cPAC) can potentiate non-β-lactam antibiotics against Gram-negative bacteria. This study extends beyond previous work by investigating the in vitro effect of cPAC in overcoming ESBL-, MBL-, and PBP2a-mediated β-lactam resistance. The results show that cPAC exhibit variable potentiation of different β-lactams against β-lactam-resistant Enterobacteriaceae clinical isolates as well as ESBL- and MBL-producing E. coli We also discovered that cPAC have broad-spectrum inhibitory properties in vitro on the activity of different classes of β-lactamases, including CTX-M3 ESBL and IMP-1 MBL. Furthermore, we observe that cPAC selectively potentiate oxacillin and carbenicillin against methicillin-resistant but not methicillin-sensitive staphylococci, suggesting that cPAC also interfere with PBP2a-mediated resistance. This study motivates the need for future work to identify the most bioactive compounds in cPAC and to evaluate their antibiotic-potentiating efficacy in vivoIMPORTANCE The emergence of β-lactam-resistant Enterobacteriaceae and staphylococci compromises the effectiveness of β-lactam-based therapy. By acquisition of ESBLs, MBLs, or PBPs, it is highly likely that bacteria may become completely resistant to the most effective β-lactam agents in the near future. In this study, we described a natural extract rich in proanthocyanidins which exerts adjuvant properties by interfering with two different resistance mechanisms. By their broad-spectrum inhibitory ability, cranberry-extracted proanthocyanidins could have the potential to enhance the effectiveness of existing β-lactam agents.

Anandamide alters the membrane properties, halts the cell division and prevents drug efflux in multidrug resistant Staphylococcus aureus

Antibiotic resistance is a serious public health problem throughout the world. Overcoming methicillin and multidrug-resistant Staphylococcus aureus (MRSA/MDRSA) infections has become a challenge and there is an urgent need for new therapeutic approaches. We have previously demonstrated that the endocannabinoid Anandamide (AEA) can sensitize MRSA to antibiotics. Here we have studied the mechanism of action using a MDRSA clinical isolate that are sensitized by AEA to methicillin and norfloxacin. We found that AEA treatment halts the growth of both antibiotic-sensitive and antibiotic-resistant S. aureus. The AEA-treated bacteria become elongated and the membranes become ruffled with many protrusions. AEA treatment also leads to an increase in the percentage of bacteria having a complete septum, suggesting that the cell division is halted at this stage. The latter is supported by cell cycle analysis that shows an accumulation of bacteria in the G2/M phase after AEA treatment. We further observed that AEA causes a dose-dependent membrane depolarization that is partly relieved upon time. Nile red staining of the bacterial membranes indicates that AEA alters the membrane structures. Importantly, 4'-6-diamidino-2-phenylindole (DAPI) accumulation assay and ethidium bromide efflux (EtBr) assay unveiled that AEA leads to a dose-dependent drug accumulation by inhibiting drug efflux. In conclusion, our study demonstrates that AEA interferes with cell division, alters the membrane properties of MDRSA, and leads to increased intracellular drug retention, which can contribute to the sensitization of MDRSA to antibiotics.

Analysis of Multidrug Resistance in Staphylococcus aureus with a Machine Learning-Generated Antibiogram

Multidrug resistance (MDR) surveillance consists of reporting MDR prevalence and MDR phenotypes. Detailed knowledge of the specific associations underlying MDR patterns can allow antimicrobial stewardship programs to accurately identify clinically relevant resistance patterns. We applied machine learning and graphical networks to quantify and visualize associations between resistance traits in a set of 1,091 Staphylococcus aureus isolates collected from one New York hospital between 2008 and 2018. Antimicrobial susceptibility testing was performed using reference broth microdilution. The isolates were analyzed by year, methicillin susceptibility, and infection site. Association mining was used to identify resistance patterns that consisted of two or more individual antimicrobial resistance (AMR) traits and quantify the association among the individual resistance traits in each pattern. The resistance patterns captured the majority of the most common MDR phenotypes and reflected previously identified pairwise relationships between AMR traits in S. aureus Associations between β-lactams and other antimicrobial classes (macrolides, lincosamides, and fluoroquinolones) were common, although the strength of the association among these antimicrobial classes varied by infection site and by methicillin susceptibility. Association mining identified associations between clinically important AMR traits, which could be further investigated for evidence of resistance coselection. For example, in skin and skin structure infections, clindamycin and tetracycline resistance occurred together 1.5 times more often than would be expected if they were independent from one another. Association mining efficiently discovered and quantified associations among resistance traits, allowing these associations to be compared between relevant subsets of isolates to identify and track clinically relevant MDR.

Genome-Wide Association Studies for the Detection of Genetic Variants Associated With Daptomycin and Ceftaroline Resistance in Staphylococcus aureus

Background

As next generation sequencing (NGS) technologies have experienced a rapid development over the last decade, the investigation of the bacterial genetic architecture reveals a high potential to dissect causal loci of antibiotic resistance phenotypes. Although genome-wide association studies (GWAS) have been successfully applied for investigating the basis of resistance traits, complex resistance phenotypes have been omitted so far. For S. aureus this especially refers to antibiotics of last resort like daptomycin and ceftaroline. Therefore, we aimed to perform GWAS for the identification of genetic variants associated with DAP and CPT resistance in clinical S. aureus isolates.

Materials/methods

To conduct microbial GWAS, we selected cases and controls according to their clonal background, date of isolation, and geographical origin. Association testing was performed with PLINK and SEER analysis. By using in silico analysis, we also searched for rare genetic variants in candidate loci that have previously been described to be involved in the development of corresponding resistance phenotypes.

Results

GWAS revealed MprF P314L and L826F to be significantly associated with DAP resistance. These mutations were found to be homogenously distributed among clonal lineages suggesting convergent evolution. Additionally, rare and yet undescribed single nucleotide polymorphisms could be identified within mprF and putative candidate genes. Finally, we could show that each DAP resistant isolate exhibited at least one amino acid substitution within the open reading frame of mprF. Due to the presence of strong population stratification, no genetic variants could be associated with CPT resistance. However, the investigation of the staphylococcal cassette chromosome mec (SCCmec) revealed various mecA SNPs to be putatively linked with CPT resistance. Additionally, some CPT resistant isolates revealed no mecA mutations, supporting the hypothesis that further and still unknown resistance determinants are crucial for the development of CPT resistance in S. aureus.

Conclusion

We hereby confirmed the potential of GWAS to identify genetic variants that are associated with antibiotic resistance traits in S. aureus. However, precautions need to be taken to prevent the detection of spurious associations. In addition, the implementation of different approaches is still essential to detect multiple forms of variations and mutations that occur with a low frequency.

Malonyl-proteome profiles of Staphylococcus aureus reveal lysine malonylation modification in enzymes involved in energy metabolism

BACKGROUND

Protein lysine malonylation, a novel post-translational modification (PTM), has been recently linked with energy metabolism in bacteria. Staphylococcus aureus is the third most important foodborne pathogen worldwide. Nonetheless, substrates and biological roles of malonylation are still poorly understood in this pathogen.

RESULTS

Using anti-malonyl-lysine antibody enrichment and high-resolution LC-MS/MS analysis, 440 lysine-malonylated sites were identified in 281 proteins of S. aureus strain. The frequency of valine in position - 1 and alanine at + 2 and + 4 positions was high. KEGG pathway analysis showed that six categories were highly enriched, including ribosome, glycolysis/gluconeogenesis, pentose phosphate pathway (PPP), tricarboxylic acid cycle (TCA), valine, leucine, isoleucine degradation, and aminoacyl-tRNA biosynthesis. In total, 31 malonylated sites in S. aureus shared homology with lysine-malonylated sites previously identified in E. coli, indicating malonylated proteins are highly conserved among bacteria. Key rate-limiting enzymes in central carbon metabolic pathways were also found to be malonylated in S. aureus, namely pyruvate kinase (PYK), 6-phosphofructokinase, phosphoglycerate kinase, dihydrolipoyl dehydrogenase, and F1F0-ATP synthase. Notably, malonylation sites were found at or near protein active sites, including KH domain protein, thioredoxin, alanine dehydrogenase (ALD), dihydrolipoyl dehydrogenase (LpdA), pyruvate oxidase CidC, and catabolite control protein A (CcpA), thus suggesting that lysine malonylation may affect the activity of such enzymes.

CONCLUSIONS

Data presented herein expand the current knowledge on lysine malonylation in prokaryotes and indicate the potential roles of protein malonylation in bacterial physiology and metabolism.

Prevalence and molecular epidemiology of ceftaroline non-susceptible methicillin-resistant Staphylococcus aureus isolates, first clinical report from Iran

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major pathogens in Iran with a high prevalence and a high level of antibiotic resistance. Ceftaroline is a fifth generation cephalosporin binding and inhibiting penicillin binding protein (PBP2a).

METHODS

In the present study, 228 clinical MRSA isolates were collected from four cities of Iran and their susceptibility to ceftaroline was evaluated by E-test and the disk diffusion method.

RESULTS

Our results showed a high susceptibility rate (97.3%) to ceftaroline in MRSA strains from Iran. Six isolates were found to be ceftaroline non-susceptible (CPT-NS) with Minimum inhibitory concentration (MIC) ≥2 µg/mL. All CPT-NS isolates were isolated from blood and tracheal aspirate and belonged to SCCmec type III as well as agr type I and were all susceptible to vancomycin. Out of six isolates, three, two and one belonged to spa type t030, t4864, and t969, respectively. Vancomycin, quinupristin/dalfopristin, linezolid, chloramphenicol, and tigecycline were the most active agents against CPT-NS isolates.

CONCLUSION

Due to the broad-spectrum activity and low toxicity of ceftaroline as well as the increased rate of vancomycin resistance among MRSA strains in recent years, ceftaroline can be considered as a novel approach to treat MRSA-induced infections.

Successful Development of Bacteriocins into Therapeutic Formulation for Treatment of MRSA Skin Infection in a Murine Model

The emergence of antibiotic-resistant pathogens has caused a serious worldwide problem in infection treatment in recent years. One of the pathogens is methicillin-resistant Staphylococcus aureus (MRSA), which is a major cause of skin and soft tissue infections. Alternative strategies and novel sources of antimicrobials to solve antibiotic resistance problems are urgently needed. In this study, we explored the potential of two broad-spectrum bacteriocins, garvicin KS and micrococcin P1, in skin infection treatments.

The emergence of antibiotic-resistant pathogens has caused a serious worldwide problem in infection treatment in recent years. One of the pathogens is methicillin-resistant Staphylococcus aureus (MRSA), which is a major cause of skin and soft tissue infections. Alternative strategies and novel sources of antimicrobials to solve antibiotic resistance problems are urgently needed. In this study, we explored the potential of two broad-spectrum bacteriocins, garvicin KS and micrococcin P1, in skin infection treatments. The two bacteriocins acted synergistically with each other and with penicillin G in killing MRSA in vitro. The MICs of the antimicrobials in the three-component mixture were 40 ng/ml for micrococcin P1 and 2 μg/ml for garvicin KS and penicillin G, which were 62, 16, and at least 1,250 times lower than their MICs when assessed individually. To assess its therapeutic potential further, we challenged the three-component formulation in a murine skin infection model with the multidrug-resistant luciferase-tagged MRSA Xen31, a strain derived from the clinical isolate S. aureus ATCC 33591. Using the tagged-luciferase activity as a reporter for the presence of Xen31 in wounds, we demonstrated that the three-component formulation was efficient in eradicating the pathogen from treated wounds. Furthermore, compared to Fucidin cream, which is an antibiotic commonly used in skin infection treatments, our formulation was also superior in terms of preventing resistance development.

Penicillin binding protein 2a: An overview and a medicinal chemistry perspective

Antimicrobial resistance is an imminent threat worldwide. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the "superbug" family, manifesting resistance through the production of a penicillin binding protein, PBP2a, an enzyme that provides its transpeptidase activity to allow cell wall biosynthesis. PBP2a's low affinity to most β-lactams, confers resistance to MRSA against numerous members of this class of antibiotics. An Achilles' heel of MRSA, PBP2a represents a substantial target to design novel antibiotics to tackle MRSA threat via inhibition of the bacterial cell wall biosynthesis. In this review we bring into focus the PBP2a enzyme and examine the various aspects related to its role in conferring resistance to MRSA strains. Moreover, we discuss several antibiotics and antimicrobial agents designed to target PBP2a and their therapeutic potential to meet such a grave threat. In conclusion, we consider future perspectives for targeting MRSA infections.

A penicillin-binding protein that can promote advanced-generation cephalosporin resistance and genome adaptation in the opportunistic pathogen Pseudomonas aeruginosa

A previous soil metagenomics study recovered a novel cephalosporin resistance determinant, pbp^{TET A6}, for which the exact resistance mechanism was unclear. This study used a three-dimensional structure-guided mutagenesis approach to demonstrate that PBP^{TET A6} is likely to be a class A penicillin-binding protein (PBP), and that its ability to confer cephalosporin resistance is directly linked to the functional integrity of its transpeptidase (TP) catalytic core. Screening of a library of PBP^{TET A6} variants carrying randomly introduced point mutations revealed additional residue modifications that compromised resistance, all of which were proximal to the TP active site except one which was found in a 29-amino-acid-long superstructure (α6-α7 loop) absent in other class A PBP homologues. Based on the site-specific mutagenesis results, it is hypothesized that residue arginine-400 plays an important role in limiting the access of certain cephalosporin compounds to the enzymatic core of the TP domain of PBP^{TET A6}. Using a combination of adaptive evolution assays and whole-genome sequencing, the potential impact of PBP^{TET A6} on promoting the development of resistance in the clinically significant opportunistic pathogen Pseudomonas aeruginosa was investigated. Under the selective pressure of serial ceftazidime exposures, the pbp^{TET A6}-expressing P. aeruginosa population readily evolved by excluding a ~400-kbp chromosomal element to acquire additional resistance against cephalosporins, suggesting that PBP^{TET A6} has a catalytic effect on facilitating antibiotic-resistance-associated genome adaptation. Overall, the soil environment contains genes conferring resistance to critically important antibiotics by cryptic mechanisms. Understanding what impact anthropogenic activities might have on the abundance and evolution of these genes should be a priority.

Exploration of (3-benzyl-5-hydroxyphenyl)carbamates as new antibacterial agents against Gram-positive bacteria

A series of (3-benzyl-5-hydroxyphenyl)carbamates were evaluated as new antibacterial agents. Several compounds showed potent inhibitory activity against sensitive and drug-resistant Gram-positive bacteria. The compounds are ineffective against all tested Gram-negative bacteria. The structure of the ester group exerted a profound effect on antibacterial activity. 4,4-Dimethylcyclohexanyl carbamate 6h exhibited the most potent inhibitory activity against the standard and clinically isolated Staphylococcus aureus, Staphylococcus epidermidis, and Enterococcus faecalis (minimum inhibitory concentration = 4-8 µg/ml) strains. The preliminary experimental evidence indicated that these carbamates target the bacterial cell wall and share a similar mechanism of action with vancomycin.

An experiment-informed signal transduction model for the role of the Staphylococcus aureus MecR1 protein in β-lactam resistance

The treatment of hospital- and community-associated infections by methicillin-resistant Staphylococcus aureus (MRSA) is a perpetual challenge. This Gram-positive bacterium is resistant specifically to β-lactam antibiotics, and generally to many other antibacterial agents. Its resistance mechanisms to β-lactam antibiotics are activated only when the bacterium encounters a β-lactam. This activation is regulated by the transmembrane sensor/signal transducer proteins BlaR1 and MecR1. Neither the transmembrane/metalloprotease domain, nor the complete MecR1 and BlaR1 proteins, are isolatable for mechanistic study. Here we propose a model for full-length MecR1 based on homology modeling, residue coevolution data, a new extensive experimental mapping of transmembrane topology, partial structures, molecular simulations, and available NMR data. Our model defines the metalloprotease domain as a hydrophilic transmembrane chamber effectively sealed by the apo-sensor domain. It proposes that the amphipathic helices inserted into the gluzincin domain constitute the route for transmission of the β-lactam-binding event in the extracellular sensor domain, to the intracellular and membrane-embedded zinc-containing active site. From here, we discuss possible routes for subsequent activation of proteolytic action. This study provides the first coherent model of the structure of MecR1, opening routes for future functional investigations on how β-lactam binding culminates in the proteolytic degradation of MecI.

In Vitro Ceftaroline Resistance Selection of Methicillin-Resistant Staphylococcus aureus Involves Different Genetic Pathways

The pathways in the development of ceftaroline resistance of methicillin-resistant Staphylococcus aureus (MRSA) isolates belonging to the ST8, ST239, and ST228 were evaluated. Ceftaroline-resistant derivatives were isolated through selection during 40 passages. Ceftaroline MIC measurements and whole-genome sequencing were performed after 5, 20, and 40 passages. In two ST8 derivative isolates, ceftaroline MIC increased up to 128 mg/L. Mutations were acquired in gdpP and graS in one isolate after 20 passages and in gdpP in another after 40 passages. MIC for two ST239 derivatives increased to 128 mg/L. Substitutions in Pbp4 and polymorphisms in the upstream region of pbp4 were identified in both derivatives after 40 passages. In one isolate, additional mutation in gdpP and deletion in graR were detected. In an ST228 derivative, MIC increased to 32 mg/L with one mutation in penicillin-binding protein 2a (Y446N) detected after five passages and a second (E447K) after 20 passages. Three pathways in the development of ceftaroline resistance were identified. For ST8 and ST239 derivatives mutations were detected in gdpP and pbp4, respectively, whereas in ST228 - in mecA. Most derivatives harbored additional mutations whose potential role in the development of resistance has not been determined.

Staphylococcus aureus from hospital-acquired pneumonia from an Italian nationwide survey: activity of ceftobiprole and other anti-staphylococcal agents, and molecular epidemiology of methicillin-resistant isolates

OBJECTIVES

To determine the prevalence of Staphylococcus aureus from hospital-acquired pneumonia (HAP) in Italy and the susceptibility to ceftobiprole and comparators of MSSA and MRSA isolates. A secondary objective was to characterize the clonality and acquired resistance and virulence genes of MRSA.

METHODS

Consecutive non-replicate isolates from HAP were collected from 13 laboratories distributed across Italy, from January to May 2016. Antimicrobial susceptibility testing was performed by broth microdilution, and results were interpreted according to the EUCAST breakpoints. All MRSA isolates were subjected to WGS using an Illumina platform. Clonality and resistance and virulence gene content were investigated with bioinformatics tools.

RESULTS

Among 333 isolates from HAP, S. aureus was the third most common pathogen (18.6%). The proportion of MRSA was 40.3%. Susceptibility to ceftobiprole was 100% for MSSA and 95.5% for MRSA. Lower susceptibility rates of 78.4% and 94.6% in MSSA and 36.4% and 12.1% in MRSA isolates were observed for erythromycin and levofloxacin, respectively. The MRSA from HAP mostly belonged to clonal complex (CC) 22 (47.0%), CC5 (25.8%) and CC8 (15.2%), with a minority of other lineages (ST1, ST6, ST7, ST30, ST152 and ST398). Acquired resistance and virulence genes in most cases exhibited a clonal distribution. The three ceftobiprole-resistant isolates exhibited an MIC of 4 mg/L and belonged to ST228-MRSA-I of CC5.

CONCLUSIONS

S. aureus is an important cause of HAP in Italy. Ceftobiprole exhibited good in vitro activity against S. aureus isolated from HAP, including MRSA. A trend to replacement of ST228 with ST22 was noticed compared with previous studies.

Genotypic analysis of Italian MRSA strains exhibiting low-level ceftaroline and ceftobiprole resistance

The aim of this study was to address the involvement of PBP mutations in the bactericidal activity to novel cephalosporins, alone and in combination with daptomycin, in not-related multidrug-resistant methicillin-resistant Staphylococcus aureus strains isolated during a nationwide Italian survey. MICs determination and time-killing assays were performed and mecA, pbp1, pbp2, pbp3, pbp4, and gdpP genes were sequenced. Ten strains showed low-level resistance to ceftaroline and ceftobiprole. PBP2a sequence analysis identified four different mutations (N146K; N204K; T235I; E239K) uniquely present in the non-penicillin-binding domain (nPBD). Epidemiologically, this resistance was associated with the most widespread MDR Italian clone ST228-SCCmecI-t001/t041, confirming its proclivity to accumulate mutations, and it is also associated to substitutions in the GdpP signaling protein, involved in the maintenance of di-AMP balance, recently associated with resistance to beta-lactams. Despite these mutations, both drugs retained their potent in vitro bactericidal activity and showed a synergistic effect towards difficult-to-treat isolates.

Antimicrobial resistance in methicillin-resistant Staphylococcus aureus to newer antimicrobial agents

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) result in significant morbidity and mortality for patients in both community and health care settings. This is primarily due to the difficulty in treating MRSA, which is often resistant to multiple classes of antibiotics. Understanding the mechanisms of antimicrobial resistance (AMR) in MRSA provides insight into the optimal use of antimicrobial agents in clinical practice and also underpins critical aspects of antimicrobial stewardship programs. In this review we delineate the mechanisms, prevalence, and clinical importance of resistance to antibiotics licensed in the past 20 years that target MRSA, as well as new drugs in the pipeline which are likely to be licensed soon. Current gaps in scientific knowledge about MRSA resistance mechanisms are discussed, and topics in the epidemiology of AMR in S. aureus that require further investigation are highlighted.

Promising antibacterial agents against multidrug resistant Staphylococcus aureus

Rapid emergence of multidrug resistant Staphylococcus aureus infections has created a critical health menace universally. Resistance to all the available chemotherapeutics has been on rise which led to WHO to stratify Staphylococcus aureus as high tier priorty II pathogen. Hence, discovery and development of new antibacterial agents with new mode of action is crucial to address the multidrug resistant Staphylococcus aureus infections. The egressing understanding of new antibacterials on their biological target provides opportunities for new therapeutic agents. This review underlines on various aspects of drug design, structure activity relationships (SARs) and mechanism of action of various new antibacterial agents and also covers the recent reports on new antibacterial agents with potent activity against multidrug resistant Staphylococcus aureus. This review provides attention on in vitro and in vivo pharmacological activities of new antibacterial agents in the point of view of drug discovery and development.

The Continuing Threat of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus has been an exceptionally successful pathogen, which is still relevant in modern age-medicine due to its adaptability and tenacity. This bacterium may be a causative agent in a plethora of infections, owing to its abundance (in the environment and in the normal flora) and the variety of virulence factors that it possesses. Methicillin-resistant S. aureus (MRSA) strains—first described in 1961—are characterized by an altered penicillin-binding protein (PBP2a/c) and resistance to all penicillins, cephalosporins, and carbapenems, which makes the β-lactam armamentarium clinically ineffective. The acquisition of additional resistance determinants further complicates their eradication; therefore, MRSA can be considered as the first representative of multidrug-resistant bacteria. Based on 230 references, the aim of this review is to recap the history, the emergence, and clinical features of various MRSA infections (hospital-, community-, and livestock-associated), and to summarize the current advances regarding MRSA screening, typing, and therapeutic options (including lipoglycopeptides, oxazolidinones, anti-MRSA cephalosporins, novel pleuromutilin-, tetracycline- and quinolone-derivatives, daptomycin, fusidic acid, in addition to drug candidates in the development phase), both for an audience of clinical microbiologists and infectious disease specialists.

Synthesis and evaluation of new quinazolin-4(3H)-one derivatives as potent antibacterial agents against multidrug resistant Staphylococcus aureus and Mycobacterium tuberculosis

Staphylococcus aureus and Mycobacterium tuberculosis are major causative agents responsible for serious nosocomial and community-acquired infections impacting healthcare systems globally. Over several decades, these pathogens have developed resistance to multiple antibiotics significantly affecting morbidity and mortality. Thus, these recalcitrant pathogens are amongst the most formidable microbial pathogens for which international healthcare agencies have mandated active identification and development of new antibacterial agents for chemotherapeutic intervention. In our present work, a series of new quinazolin-4(3H)-one derivatives were designed, synthesized and evaluated for their antibacterial activity against ESKAP pathogens and pathogenic mycobacteria. The experiments revealed that 4'c, 4'e, 4'f and 4'h displayed selective and potent inhibitory activity against Staphylococcus aureus with MIC values ranging from 0.03-0.25 μg/mL. Furthermore, compounds 4'c and 4'e were found to be benign to Vero cells (CC₅₀ = >5 μg/mL) and displayed promising selectivity index (SI) > 167 and > 83.4 respectively. Additionally, 4'c and 4'e demonstrated equipotent MIC against multiple drug-resistant strains of S. aureus including VRSA, concentration dependent bactericidal activity against S. aureus and synergized with FDA approved drugs. Moreover, compound 4'c exhibited more potent activity in reducing the biofilm and exhibited a PAE of ∼2 h at 10X MIC which is comparable to levofloxacin and vancomycin. In vivo efficacy of 4'c in murine neutropenic thigh infection model revealed that 4'c caused a similar reduction in cfu as vancomycin. Gratifyingly, compounds 4d, 4e, 9a, 9b, 14a, 4'e and 4'f also exhibited anti-mycobacterial activity with MIC values in the range of 2-16 μg/mL. In addition, the compounds were found to be less toxic to Vero cells (CC₅₀ = 12.5->100 μg/mL), thus displaying a favourable selectivity index. The interesting results obtained here suggest the potential utilization of these new quinazolin-4(3H)-one derivatives as promising antibacterial agents for treating MDR-Staphylococcal and mycobacterial infections.

Emerging Strategies to Combat ESKAPE Pathogens in the Era of Antimicrobial Resistance: A Review

The acronym ESKAPE includes six nosocomial pathogens that exhibit multidrug resistance and virulence: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. Persistent use of antibiotics has provoked the emergence of multidrug resistant (MDR) and extensively drug resistant (XDR) bacteria, which render even the most effective drugs ineffective. Extended spectrum β-lactamase (ESBL) and carbapenemase producing Gram negative bacteria have emerged as an important therapeutic challenge. Development of novel therapeutics to treat drug resistant infections, especially those caused by ESKAPE pathogens is the need of the hour. Alternative therapies such as use of antibiotics in combination or with adjuvants, bacteriophages, antimicrobial peptides, nanoparticles, and photodynamic light therapy are widely reported. Many reviews published till date describe these therapies with respect to the various agents used, their dosage details and mechanism of action against MDR pathogens but very few have focused specifically on ESKAPE. The objective of this review is to describe the alternative therapies reported to treat ESKAPE infections, their advantages and limitations, potential application in vivo, and status in clinical trials. The review further highlights the importance of a combinatorial approach, wherein two or more therapies are used in combination in order to overcome their individual limitations, additional studies on which are warranted, before translating them into clinical practice. These advances could possibly give an alternate solution or extend the lifetime of current antimicrobials.

Evolution and Antibacterial Evaluation of 8-Hydroxy-cycloberberine Derivatives as a Novel Family of Antibacterial Agents Against MRSA

Twenty-five new derivatives of 8-hydroxycycloberberine (1) were synthesized and evaluated for their activities against Gram-positive bacteria, taking 1 as the lead. Part of them displayed satisfactory antibacterial activities against methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA), as well as vancomycin-intermediate Staphylococcus aureus (VISA). Especially, compound 15a displayed an excellent anti-MRSA activity with MICs (minimum inhibitory concentrations) of 0.25–0.5 μg/mL, better than that of 1. It also displayed high stability in liver microsomes and whole blood, and the LD₅₀ value of over 65.6 mg·kg⁻¹ in mice via intravenous route, suggesting a good druglike feature. The mode of action showed that 15a could effectively suppress topo IV-mediated decatenation activity at the concentration of 7.5 μg/mL, through binding a different active pocket of bacterial topo IV from quinolones. Taken together, the derivatives of 1 constituted a promising kind of anti-MRSA agents with a unique chemical scaffold and a specific biological mechanism, and compound 15a has been chosen for the next investigation.

4(3H)-Quinazolinone derivatives: Promising antibacterial drug leads

Emergence of drug resistance has created unmet medical need for the development of new classes of antibiotics. Discovery of new antibacterial agents with new mode of action remains a high priority universally. 4(3H)-quinazolinone, a fused nitrogen heterocyclic compound has emerged as a biologically privileged structure, possessing a wide range of biological properties viz. anticancer, antibacterial, antitubercular, antifungal, anti-HIV, anticonvulsant, anti-inflammatory and analgesic activities. Promising antibacterial properties of quinazolinones have enthused the medicinal chemists to explore and develop this fused heterocyclic system for new antibacterial agents. Utilization of quinazolinone core for the design and synthesis of new antibacterial agents has recently gained momentum. This review aims to provide an overview of the structures and antibacterial activity of various 4(3H)-quinazolinone derivatives covering various aspects of in vitro and in vivo pharmacological activities and structure activity relationships (SARs).

Plasmid-Encoded Transferable mecB-Mediated Methicillin Resistance in Staphylococcus aureus

During cefoxitin-based nasal screening, phenotypically categorized methicillin-resistant Staphylococcus aureus (MRSA) was isolated and tested negative for the presence of the mecA and mecC genes as well as for the SCCmec-orfX junction region. The isolate was found to carry a mecB gene previously described for Macrococcus caseolyticus but not for staphylococcal species. The gene is flanked by β-lactam regulatory genes similar to mecR, mecI, and blaZ and is part of an 84.6-kb multidrug-resistance plasmid that harbors genes encoding additional resistances to aminoglycosides (aacA-aphD, aphA, and aadK) as well as macrolides (ermB) and tetracyclines (tetS). This further plasmidborne β-lactam resistance mechanism harbors the putative risk of acceleration or reacceleration of MRSA spread, resulting in broad ineffectiveness of β-lactams as a main therapeutic application against staphylococcal infections.

Ceftobiprole Activity against Gram-Positive and -Negative Pathogens Collected from the United States in 2006 and 2016

Ceftobiprole is an advanced cephalosporin with potent activity against Gram-positive and Gram-negative bacteria that has been approved in many European and non-European countries to treat community- and hospital-acquired pneumonia (excluding ventilator-associated pneumonia). This study reports on the activity of ceftobiprole against a large set of clinical isolates obtained from hospitalized patients in the United States in 2016 that caused serious infections, including pneumonia, bacteremia, and skin and skin structure infections. To assess any potential temporal changes in ceftobiprole activity, the 2016 results were compared to corresponding MIC data from a 2006 U.S. survey that included key target pathogens. Ceftobiprole exhibited potent activity against Staphylococcus aureus (including methicillin-resistant S. aureus isolates, which were 99.3% susceptible), coagulase-negative staphylococci (100% susceptible), Enterococcus faecalis (100% susceptible), Streptococcus pneumoniae (99.7% susceptible), and other tested streptococci. Similarly, ceftobiprole was highly active against Enterobacteriaceae isolates that did not exhibit an extended-spectrum β-lactamase (ESBL) phenotype, including Escherichia coli (99.8% susceptible) and Klebsiella pneumoniae (99.6% susceptible). A total of 99.6% of all Haemophilus influenzae and Moraxella catarrhalis isolates were inhibited at ≤1 mg/liter ceftobiprole, and 72.7% of the Pseudomonas aeruginosa isolates were susceptible to ceftobiprole. With the exception of decreased cephalosporin susceptibility among Enterobacteriaceae isolates, which correlates with an increased prevalence of ESBL-producing isolates, ceftobiprole had similar activities against the isolate sets collected in 2006 and 2016. Therefore, ceftobiprole remains highly active when tested in vitro against a large number of current Gram-positive or Gram-negative pathogens that cause serious infections.

High Rate of Ceftobiprole Resistance among Clinical Methicillin-Resistant Staphylococcus aureus Isolates from a Hospital in Central Italy

Ceftobiprole is a fifth-generation cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA). One-year surveillance at the Regional Hospital of Ancona (Italy) disclosed a 12% ceftobiprole resistance rate (12/102 isolates; MIC, ≥4 mg/liter). Epidemiological characterization demonstrated that the resistant isolates all belonged to different clones. Penicillin-binding protein (PBP) analysis showed substitutions in all PBPs and a novel insertion in PBP2a. The mecB and mecC genes were not detected. Ceftobiprole susceptibility screening is essential to avoid therapeutic failure and the spread of ceftobiprole-resistant strains.

GW779439X and Its Pyrazolopyridazine Derivatives Inhibit the Serine/Threonine Kinase Stk1 and Act As Antibiotic Adjuvants against β-Lactam-Resistant Staphylococcus aureus

As antibiotic resistance rises, there is a need for strategies such as antibiotic adjuvants to conserve already-established antibiotics. A family of bacterial kinases known as the penicillin-binding-protein and serine/threonine kinase-associated (PASTA) kinases has attracted attention as targets for antibiotic adjuvants for β-lactams. Here, we report that the pyrazolopyridazine GW779439X sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to various β-lactams through inhibition of the PASTA kinase Stk1. GW779439X potentiates β-lactam activity against multiple MRSA and MSSA isolates, including the sensitization of a ceftaroline-resistant isolate to ceftaroline. In silico modeling was used to guide the synthesis of GW779439X derivatives. The presence and orientation of GW779439X's methylpiperazine moiety was crucial for robust biochemical and microbiologic activity. Taken together, our data provide a proof of concept for developing the pyrazolopyridazines as selective Stk1 inhibitors which act across S. aureus isolates.

Ceftobiprole medocaril for the treatment of community-acquired pneumonia

INTRODUCTION

Ceftobiprole is a novel broad-spectrum cephalosporin with excellent activity against a broad range of pathogens that are important in community-acquired pneumonia (CAP), including drug-resistant pneumococci, methicillin-resistant Staphylococcus aureus, and Pseudomonas aeruginosa. Areas covered: This article reviews the spectrum of activity, the main pharmacological and pharmacodynamic characteristics of ceftobiprole as well its clinical efficacy and safety in the treatment of CAP in adult patients. Expert opinion: Taking into account that the current treatment guidelines for CAP recommend the use of an adequate empirical therapy to improve its prognosis, ceftobiprole shows a profile of antimicrobial activity that would cover most etiological agents in patients with risk factors for infection caused by multidrug resistant organisms. The results of the pivotal clinical trial of patients hospitalized with CAP treated with ceftobiprole showed a high rate of clinical cure. The clinical tolerance of ceftobiprole in clinical trials was generally very good. These findings make ceftobiprole a good parenteral therapeutic alternative for the empirical treatment of CAP that requires hospitalization, especially in patients with risk factors for CAP caused by resistant microorganisms.

Susceptibility to ceftobiprole of respiratory-tract pathogens collected in the United Kingdom and Ireland during 2014-2015

Purpose

Lower respiratory tract infections (LRTIs) can cause significant morbidity and mortality and are becoming increasingly difficult to treat because of the growing prevalence of resistance to conventional antimicrobial agents. This study aimed to assess the current in vitro susceptibility of respiratory tract pathogens collected from the UK and Ireland to ceftobiprole, an advanced-generation cephalosporin, as compared with other antibiotics.

Methods

Pathogens isolated from patients with LRTIs were analyzed as part of the British Society for Antimicrobial Chemotherapy Antimicrobial Resistance Surveillance Programme during 2014–2015. Antibiotic susceptibility was evaluated using European Committee on Antimicrobial Susceptibility Testing breakpoints, including the ceftobiprole pharmacokinetic/pharmacodynamic non-species-specific breakpoint when species-specific breakpoints were not available.

Results

One thousand one hundred and sixty-eight isolates from community-onset LRTIs and 1,264 isolates from hospital-onset LRTIs were analyzed. The ceftobiprole susceptibility rate was 99.8% (428/429) for Streptococcus pneumoniae, 100% (502/502) for Haemophilus influenzae, and 99.6% (236/237) for Moraxella catarrhalis. All Staphylococcus aureus isolates, including methicillin-susceptible S. aureus (MSSA; N=181) and methicillin-resistant S. aureus (MRSA; N=35), were susceptible to ceftobiprole. Overall, ceftobiprole susceptibility was observed in 88.1% (215/244) of Escherichia coli isolates, 83.4% (156/187) of Klebsiella pneumoniae isolates and 86.7% (98/113) of Enterobacter spp. isolates.

Conclusion

Ceftobiprole had in vitro activity against all S. aureus (both MSSA and MRSA) isolates, and almost all S. pneumoniae isolates, as well as against Gram-negative bacteria associated with community-onset or hospital-onset LRTIs. Based on this analysis, ceftobiprole is a good treatment option when broad-spectrum antibiotic coverage is needed for LRTIs.

Synthesis of 1,2,3-triazole linked 4(3H)-Quinazolinones as potent antibacterial agents against multidrug-resistant Staphylococcus aureus

Methicillin and vancomycin resistant Staphylococcus aureus infections are an emerging global health concern leading to increasing morbidity and mortality. Continuous increase in drug resistance has underlined the need for discovery and development of new antibacterial agents acting via novel mechanisms to overcome this pressing issue. In this context, a number of 1,2,3-triazole linked 4(3H)-quinazolinone derivatives were designed and synthesized as potent antibacterial agents. When evaluated against ESKAP pathogen panel, compounds 7a, 7b, 7c, 7e, 7f, 7g, 7h, 7i, 9a, 9c, 9d and 9e exhibited significantly selective inhibitory activities towards Staphylococcus aureus (MIC = 0.5-4 μg/mL). To understand and confirm the specificity of these compounds, the compounds 7a and 9a were tested against E. coli and A. baumannii in combination with sub-lethal concentrations of Polymyxin B nonapeptide (PMBN) and were found to be inactive. This clearly indicated that these compounds possess specific and potent activity towards S. aureus and are inactive against gram-negative pathogens. Encouragingly, the compounds were also found to be non toxic to Vero cells and displayed favourable selectivity index (SI = 40 to 80). Furthermore, 7a and 9a were found to possess potent inhibitory activity when tested against multidrug resistant S. aureus including strains resistant to vancomycin (MIC values 0.5-32 μg/mL), indicating that the compounds are able to escape current drug-resistance mechanisms. With the potent anti-bacterial activity exhibited the new series of 1,2,3-triazole linked 4(3H)-quinazolinones have emerged as promising candidates for treating multidrug resistant Staphylococcus aureus infections.

Genetic Diversity among Staphylococcus aureus Isolates Showing Oxacillin and/or Cefoxitin Resistance Not Linked to the Presence of mec Genes

Methicillin-resistant Staphylococcus aureus isolates lacking mec genes (n = 32), collected from Belgian hospitals, were characterized for their β-lactamase production and the presence of mutations in pbp genes, the pbp4 promoter, and genes involved in penicillin-binding protein 4 overproduction (gdpP and yjbH). Twelve isolates were β-lactamase hyperproducers (BHPs), while 12 non-BHP isolates might produce an incomplete GdpP protein. Most isolates showed nucleotide missense mutations in pbp genes. A few isolates also showed mutations in the pbp4 promoter.

In vitro activity of novel anti-MRSA cephalosporins and comparator antimicrobial agents against staphylococci involved in prosthetic joint infections

OBJECTIVES

Ceftaroline and ceftobiprole are new parenteral cephalosporins with potent activity against methicillin-resistant (MR) staphylococci, which are the leading cause of prosthetic joint infections (PJIs). The aim of this study was to determine and compare the in vitro activities of both molecules against staphylococcal isolates recovered from clinically documented PJIs.

METHODS

A collection of 200 non-duplicate clinical isolates [100 Staphylococcus aureus and 100 coagulase-negative staphylococci (CoNS), including 19 and 27 MR isolates, respectively] was studied. Minimum inhibitory concentrations (MICs) of oxacillin, ceftaroline, ceftobiprole, vancomycin, teicoplanin, clindamycin, levofloxacin, linezolid and daptomycin were determined by the broth microdilution method. Bactericidal activity (at 4× MIC) of ceftaroline, ceftobiprole, vancomycin, teicoplanin, linezolid and daptomycin was assessed by time-kill assay.

RESULTS

Among the S. aureus isolates, 100% were susceptible to ceftaroline (MIC50/90, 0.25/0.5μg/mL) and 98% were susceptible to ceftobiprole (MIC50/90, 0.5/1μg/mL), regardless of their methicillin resistance. The two ceftobiprole-non-susceptible strains (including one MRSA) showed MICs at 4mg/L. Against CoNS isolates, ceftaroline and ceftobiprole exhibited in vitro potency with MIC50/90 values at 0.06/0.25μg/mL and 0.25/1μg/mL, respectively. At 4× MIC, ceftaroline and ceftobiprole showed rapid and marked bactericidal activity against both S. aureus and CoNS (after 24/12h and 12/6h of incubation, respectively), whilst none of the other molecules tested had a bactericidal effect by 24h.

CONCLUSIONS

This study showed that ceftaroline and ceftobiprole have excellent in vitro activity against clinical isolates of staphylococci involved in PJIs. These molecules may therefore represent promising alternatives for the treatment of such infections.

Antimicrobial activity of ceftobiprole and comparator agents when tested against contemporary Gram-positive and -negative organisms collected from Europe (2015)

Susceptibility testing of ceftobiprole and comparators against 12,240 isolates was performed following CLSI/EUCAST guidelines. The percentage of susceptible MRSA isolates was higher for ceftobiprole (96.5% susceptible) than for ceftaroline (86.2% susceptible). Both ceftobiprole (MIC_50/90, 0.5/2 mg/L) and ceftaroline (MIC_50/90, 0.25/1 mg/L) demonstrated potent activity against coagulase-negative staphylococci. Ceftobiprole demonstrated good potency against Enterococcus faecalis (MIC_50/90 values of 0.5/2 mg/L); ceftaroline (MIC_50/90, 2/8 mg/L) was 4-fold less active against these strains. Ceftobiprole activity was comparable to that of the other β-lactam agents tested against S. pneumoniae (MIC_90, 0.5 mg/L vs 0.12-2 mg/L [other β-lactams]), viridans-group streptococci (MIC₉₀,0.25 mg/L vs 0.006-1 mg/L [other β-lactams]), and β-hemolytic streptococci (MIC_90,0.03 mg/L vs 0.015-0.06 mg/L [other β-lactams]). Overall, 73.8% of Enterobacteriaceae isolates tested were susceptible to ceftobiprole. Ceftobiprole inhibited 70.4% of P. aeruginosa at ≤4 mg/L and all isolates of Haemophilus influenzae and Moraxella catarrhalis at ≤ 0.5 mg/L. Ceftobiprole was active in vitro against a broad range of clinically-relevant contemporary Gram-positive and Gram-negative bacterial isolates.

Peptidoglycan Cross-Linking Preferences of Staphylococcus aureus Penicillin-Binding Proteins Have Implications for Treating MRSA Infections

Methicillin-resistant Staphylococcus aureus (MRSA) infections are a global public health problem. MRSA strains have acquired a non-native penicillin-binding protein called PBP2a that cross-links peptidoglycan when the native S. aureus PBPs are inhibited by β-lactams. It has been proposed that the native S. aureus PBPs can use cell wall precursors having different glycine branch lengths (penta-, tri-, or monoglycine), while PBP2a can only cross-link peptidoglycan strands bearing a complete pentaglycine branch. This hypothesis has never been tested because the necessary substrates have not been available. Here, we compared the ability of PBP2a and two native S. aureus transpeptidases to cross-link peptidoglycan strands bearing different glycine branches. We show that purified PBP2a can cross-link glycan strands bearing penta- and triglycine, but not monoglycine, and experiments in cells provide support for these findings. Because PBP2a cannot cross-link peptidoglycan containing monoglycine, this study implicates the enzyme (FemA) that extends the monoglycine branch to triglycine on Lipid II as an ideal target for small molecules that restore sensitivity of MRSA to β-lactams.

Efficacy of Ceftaroline against Methicillin-Susceptible Staphylococcus aureus Exhibiting the Cefazolin High-Inoculum Effect in a Rat Model of Endocarditis

Certain Staphylococcus aureus strains exhibit an inoculum effect (InE) with cefazolin (CFZ) that has been associated with therapeutic failures in high-inoculum infections. We assessed the in vitro activities of ceftaroline (CPT), CFZ, and nafcillin (NAF) against 17 type A β-lactamase (βla)-producing, methicillin-susceptible S. aureus (MSSA) strains, including the previously reported TX0117, which exhibits the CFZ InE, and its βla-cured derivative, TX0117c. Additionally, we determined the pharmacokinetics of CPT in rats after single intramuscular doses of 20 and 40 mg/kg of body weight and evaluated the activities of CPT (40 mg/kg every 8 h [q8h]), CFZ, and NAF against TX0117 and TX0117c in a rat model of infective endocarditis. No InE was observed for CPT or NAF, whereas a marked InE was detected for CFZ (MIC, 8 to ≥128 μg/ml). CPT and NAF treatment against TX0117 resulted in mean bacterial counts of 2.3 and 2.1 log10 CFU/g in vegetations, respectively, compared to a mean of 5.9 log10 CFU/g in the CFZ-treated group (CPT and NAF versus CFZ, P = 0.001; CPT versus NAF, P = 0.9830). Both CFZ and CPT were efficacious against the βla-cured derivative, TX0117c, compared to time zero (t0) (P = <0.0001 and 0.0015, respectively). Our data reiterate the in vivo consequences of the CFZ InE and show that CPT is not affected by this phenomenon. CPT might be considered for high-inoculum infections caused by MSSA exhibiting the CFZ InE.