Analysis of Staphylococcus aureus clinical isolates with reduced susceptibility to ceftaroline: an epidemiological and structural perspective

Antibiotic Resistance to Molecules Commonly Prescribed for the Treatment of Antibiotic-Resistant Gram-Positive Pathogens: What Is Relevant for the Clinician?

Antibiotic resistance in Gram-positive pathogens is a relevant concern, particularly in the hospital setting. Several antibiotics are now available to treat these drug-resistant pathogens, such as daptomycin, dalbavancin, linezolid, tedizolid, ceftaroline, ceftobiprole, and fosfomycin. However, antibiotic resistance can also affect these newer molecules. Overall, this is not a frequent phenomenon, but it is a growing concern in some settings and can compromise the effectiveness of these molecules, leaving few therapeutic options. We reviewed the available evidence about the epidemiology of antibiotic resistance to these antibiotics and the main molecular mechanisms of resistance, particularly methicillin-resistant Sthaphylococcus aureus, methicillin-resistant coagulase-negative staphylococci, vancomycin-resistant Enterococcus faecium, and penicillin-resistant Streptococcus pneumoniae. We discussed the interpretation of susceptibility tests when minimum inhibitory concentrations are not available. We focused on the risk of the emergence of resistance during treatment, particularly for daptomycin and fosfomycin, and we discussed the strategies that can be implemented to reduce this phenomenon, which can lead to clinical failure despite appropriate antibiotic treatment. The judicious use of antibiotics, epidemiological surveillance, and infection control measures is essential to preserving the efficacy of these drugs.

Unraveling the mechanisms of Cefoxitin resistance in methicillin-resistant Staphylococcus aureus (MRSA): structural and molecular simulation-based insights

Methicillin-resistant Staphylococcus aureus (MRSA) severely affects human health, including the skin glands, nasal cavity, wound infections, bone infections, and pneumonia. Among the most effective MRSA drugs, Cefoxitin also develops resistance due to mutations in the mecA gene. Four mutations at positions E229K, E239R, G246K, and E447K are classified as high-level resistance mutations. However, the resistance mechanism of MRSA towards Cefoxitin caused by these mutations is still unclear, as there is less information available regarding the structural and functional effects of the mutations against Cefoxitin. Therefore, our present study was designed to explore the mechanisms of binding interactions between wild-type and mutated PBP2a against Cefoxitin using molecular docking and MD simulations. Subsequently, we identified that the mutant form of PBP2a affects the activity of Cefoxitin. Interestingly, the binding of Cefoxitin with G246K and E239R mutants demonstrates unstable behavior compared to E447K-Cefoxitin and E229K-Cefoxitin. In this study, we propose the resistance mechanism of Cefoxitin at the atomic level. The proposed drug-resistance mechanism will provide valuable guidance for the design of MRSA drugs. This research might provide a new framework for designing new agents against the mutated form of PBP2a.Communicated by Ramaswamy H. Sarma.

Ceftaroline: Systematic Review of Clinical Uses and Emerging Drug Resistance

OBJECTIVE

To assess the success rates of off-label uses of ceftaroline for infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and evaluate emerging ceftaroline resistance.

DATA SOURCES

We queried PubMed/MEDLINE, with the search term "Ceftaroline." Articles were restricted to the English language and year of publication (January 1, 2009-January 31, 2022).

STUDY SELECTION AND DATA EXTRACTION

Clinical trials, observational studies, and case reports that reported efficacy, safety, pharmacokinetics, use in MRSA infections other than acute bacterial skin infection and community-acquired pneumonia, and ceftaroline resistance were selected.

DATA SYNTHESIS

The search pooled 103 publications and all abstracts were reviewed. Forty-six articles that reported efficacy, safety, pharmacokinetics, or off-label use in multiple patients and 7 articles on ceftaroline resistance are used in this review. Ceftaroline has been approved for treatment of acute skin/soft tissue infection and community-acquired pneumonia. Ceftaroline's efficacy in off-label infections ranged from 66.7% to 87.3% depending on the types of infection. There were 14 documented cases of ceftaroline resistance associated with PBP2a changes.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Case series and observational studies have documented success with ceftaroline alone or in combination with vancomycin or daptomycin for treatment of MRSA bone and joint, endovascular, diabetic foot infections, and bacteremia from other causes.

CONCLUSION

Despite the lack of randomized controlled trials, ceftaroline is used as salvage therapy for different MRSA infections. The data from case series and observational studies are promising but ceftaroline should be used judiciously as ceftaroline-resistant MRSA begin to emerge.

Reduced Ceftaroline Susceptibility among Invasive MRSA Infections in Children: a Clinical and Genomic Investigation

Ceftaroline represents an attractive therapy option for methicillin-resistant Staphylococcus aureus (MRSA). Little data is available, however, regarding the frequency of reduced susceptibility (RS) to ceftaroline among pediatric MRSA infections. We screened invasive MRSA isolates at a tertiary children's hospital for ceftaroline RS. Ceftaroline RS occurred in 2.9% of isolates and only among health care associated infections. Ceftaroline RS isolates were more often clindamycin-resistant. Sequencing data indicated the predominance of the CC5 lineage among ceftaroline RS isolates.

Evaluation of the synergistic effect of ceftaroline against methicillin-resistant Staphylococcus aureus

OBJECTIVES

We aimed to determine the synergistic effects of ceftaroline (CPT) in combination with daptomycin (DAP), vancomycin (VAN), or linezolid (LNZ) against various methicillin-resistant Staphylococcus aureus (MRSA) strains.

METHODS

MRSA strains randomly selected from 2014 to 2018 were studied. Checkerboard titration and in vitro time-kill analyses were used to determine the synergistic activities of the antibiotic combinations.

RESULTS

A total of 10 genetically distinct MRSA strains were included in this study. The checkerboard titration analysis revealed that the CPT-DAP, CPT-VAN, and CPT-LNZ combinations had a synergistic effect against 30%, 10%, and 10% of the selected MRSA strains, respectively. Using time-kill analysis, we showed that CPT-DAP exhibited a significant synergistic and sustained bactericidal effect against both DAP-susceptible (Δ colony-forming units/ml, -5.79; P = 0.0495) and DAP-resistant (Δ colony-forming units/ml, -6.40; P = 0.0463) MRSA strains at a concentration of 0.5 × the minimum inhibitory concentration of CPT plus 0.5 × the minimum inhibitory concentration of DAP. No synergistic bactericidal effects were observed for the CPT-VAN and CPT-LNZ combinations against the selected strains.

CONCLUSION

The CPT-DAP combination showed better synergistic activity than the CPT-VAN and CPT-LNZ combinations against the enrolled MRSA strains. DAP, rather than VAN or LNZ, might be a better choice for CPT combination in the treatment of MRSA infections.

Nano-enabled strategies to combat methicillin-resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) has become a threat to global health because of limited treatments. MRSA infections are difficult to treat due to increasingly developing resistance in combination with protective biofilms of Staphylococcus aureus (S. aureus). Nanotechnology-based research revealed that effective MRSA treatments could be achieved through targeted nanoparticles (NPs) that withstand biological films and drug resistance. Thus, the principal aim towards improving MRSA treatment is to advance drug delivery tools, which successfully address the delivery-related problems. These potential delivery tools would also carry drugs to the desired sites of therapeutic action to overcome the adverse effects. This review focused on different types of nano-engineered carriers system for antimicrobial agents with improved therapeutic efficacy of entrapped drugs. The structural characteristics that play an essential role in the effectiveness of delivery systems have also been addressed with a description of recent scientific advances in antimicrobial treatment, emphasizing challenges in MRSA treatments. Consequently, existing gaps in the literature are highlighted, and reported contradictions are identified, allowing for the development of roadmaps for future research.

Characterization and Clonal Diffusion of Ceftaroline Non-Susceptible MRSA in Two Hospitals in Central Italy

Background: Ceftaroline represents a novel fifth-generation cephalosporin to treat infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Methods: Ceftaroline susceptibility of 239 MRSA isolates was assessed by disk diffusion and a MIC test strip following both EUCAST and CLSI guidelines. Non-susceptible isolates were epidemiologically characterized by pulsed-field gel electrophoresis, spa typing, and multilocus sequence typing, and further investigated by PCR and whole genome sequencing to detect penicillin-binding protein (PBP) mutations as well as antibiotic resistance and virulence genes. Results: Fourteen isolates out of two hundred and thirty-nine (5.8%) were non-susceptible to ceftaroline (MIC > 1 mg/L), with differences between the EUCAST and CLSI interpretations. The characterized isolates belonged to seven different pulsotypes and three different clones (ST228/CC5-t041-SCCmecI, ST22/CC22-t18014-SCCmecIV, and ST22/CC22-t022-SCCmecIV), confirming a clonal diffusion of ceftaroline non-susceptible strains. Mutations in PBPs involved PBP2a for ST228-t041-SCCmecI strains and all the other PBPs for ST22-t18014-SCCmecIV and ST22-t022-SCCmecIV clones. All isolates harbored antibiotic resistance and virulence genes with a clonal distribution. Conclusion: Our study demonstrated that ceftaroline non-susceptibile isolates belonged not only to ST228 strains (the most widespread clone in Italy) but also to ST22, confirming the increasing role of these clones in hospital infections.

In vitro susceptibility of ceftaroline against clinically important Gram-positive cocci, Haemophilus species and Klebsiella pneumoniae in Taiwan: Results from the Antimicrobial Testing Leadership and Surveillance (ATLAS) in 2012-2018

BACKGROUND/PURPOSE

Ceftaroline, with a unique activity against methicillin-resistant Staphylococcus aureus (MRSA), was not launched in Taiwan before 2019. The in vitro susceptibility data of ceftaroline against important Taiwanese pathogens are lacking.

METHODS

The in vitro susceptibility of ceftaroline against important pathogens collected from 2012 through 2018 were extracted from the Antimicrobial Testing Leadership and Surveillance program. Broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) to ceftaroline against all isolates.

RESULTS

During the study period, the in vitro data regarding isolates of S. aureus (n = 2049), Staphylococcus epidermidis (n = 185), Streptococcus pneumoniae (n = 334), Streptococcus pyogenes (n = 170), Haemophilus influenzae (n = 75), Haemophilus parainfluenzae (n = 10) and Klebsiella pneumoniae (n = 680) regardless of hospital sites of collection were analyzed. Among the S. aureus isolates studied, 19.4% showed MICs of 1 mg/L to ceftaroline, and 4.4% showed in vitro susceptible-dose dependent to ceftaroline (all MICs, 2 mg/L). Most of other Gram-positive cocci, all H. influenzae and H. parainfluenzae isolates were susceptible to ceftaroline. By contrast, about one-third (35.9%) of K. pneumoniae isolates, irrespective of infection sources, exhibited non-susceptibility to ceftaroline (MIC range, 0.015-256 mg/L; MIC50 and MIC90 values, 0.12 and 256 mg/L, respectively).

CONCLUSIONS

From the pharmacodynamic perspectives, the ceftaroline dosage of 600 mg as a 2-h intravenous infusion every 8 h is effective against all S. aureus and other Gram-positive isolates regardless of acquisition sites in Taiwan. Before ceftaroline is prescribed in treatment of the patient with Gram-negative infection, a cautious evaluation about patient's healthcare-associated factor is warranted.

What's new in mechanisms of antibiotic resistance in bacteria of clinical origin?

The discovery, commercialization and administration of antibiotics revolutionized the world of medicine in the middle of the last century, generating a significant change in the therapeutic paradigm of the infectious diseases. Nevertheless, this great breakthrough was soon threatened due to the enormous adaptive ability that bacteria have, through which they are able to develop or acquire different mechanisms that allow them to survive the exposure to antibiotics. We are faced with a complex, multifactorial and inevitable but potentially manageable threat. To fight against it, a global and multidisciplinary approach is necessary, based on the support, guidance and training of the next generation of professionals. Nevertheless, the information published regarding the resistance mechanisms to antibiotics are abundant, varied and, unfortunately, not always well structured. The objective of this review is to structure the, in our opinion, most relevant and novel information regarding the mechanisms of resistance to antibiotics that has been published from January 2014 to September 2019, analysing their possible clinical and epidemiological impact.

Mutation-Based Antibiotic Resistance Mechanism in Methicillin-Resistant Staphylococcus aureus Clinical Isolates

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 mutation in the allosteric site of PBP2a induces conformational changes in the active site and, thus, hinders its interaction with cefoxitin. Therefore, the present report indicates that mutation in the allosteric site of PBP2a provides a more closed active site conformation than wide-type PBP2a and then causes the high-level resistance to cefoxitin.

Emerging resistance mechanisms for 4 types of common anti-MRSA antibiotics in Staphylococcus aureus: A comprehensive review

Staphylococcus aureus is one of the leading hospital-associated and community-associated pathogens, which has caused a global public health concern. The emergence of methicillin-resistant S. aureus (MRSA) along with the widespread use of different classes of antibiotics has become a significant therapeutic challenge. Antibiotic resistance is a disturbing problem that poses a threat to humans. Treatment options for S. aureus resistant to β-lactam antibiotics include glycopeptide antibiotic, cyclic lipopeptide antibiotic, cephalosporins and oxazolidinone antibiotic. The most representative types of these antibiotics are vancomycin, daptomycin, ceftaroline and linezolid. The frequent use of the first-line drug vancomycin for MRSA treatment has increased the number of resistant strains, namely vancomycin intermediate resistant S. aureus (VISA) and vancomycin resistant S. aureus (VRSA). A systematic literature review of relevant published studies in PubMed before 2020 was conducted. In recent years, there have been some reports on the relevant resistant mechanisms of vancomycin, daptomycin, ceftaroline and linezolid. In this review, we have summarized the antibiotic molecular modes of action and different gene mutants at the whole-genome level, which will aid in further development on new drugs for effective MRSA treatment based on describing different resistance mechanisms of classic antibiotics.

Population structure-guided profiling of antibiotic resistance patterns in clinical Listeria monocytogenes isolates from Germany identifies pbpB3 alleles associated with low levels of cephalosporin resistance

Numbers of listeriosis illnesses have been increasing in Germany and the European Union during the last decade. In addition, reports on the occurrence of antibiotic resistance in Listeria monocytogenes in clinical and environmental isolates are accumulating. The susceptibility towards 14 antibiotics was tested in a selection of clinical L. monocytogenes isolates to get a more precise picture of the development and manifestation of antibiotic resistance in the L. monocytogenes population. Based on the population structure determined by core genome multi locus sequence typing (cgMLST) 544 out of 1220 sequenced strains collected in Germany between 2009 and 2019 were selected to cover the phylogenetic diversity observed in the clinical L. monocytogenes population. All isolates tested were susceptible towards ampicillin, penicillin and co-trimoxazole – the most relevant antibiotics in the treatment of listeriosis. Resistance to daptomycin and ciprofloxacin was observed in 493 (91%) and in 71 (13%) of 544 isolates, respectively. While all tested strains showed resistance towards ceftriaxone, their resistance levels varied widely between 4 mg/L and >128 mg/L. An allelic variation of the penicillin binding protein gene pbpB3 was identified as the cause of this difference in ceftriaxone resistance levels. This study is the first population structure-guided analysis of antimicrobial resistance in recent clinical isolates and confirms the importance of penicillin binding protein B3 (PBP B3) for the high level of intrinsic cephalosporin resistance of L. monocytogenes on a population-wide scale.

In vitro activity of ceftaroline against bacterial pathogens isolated from patients with skin and soft tissue and respiratory tract infections in the Middle East and Africa: AWARE global surveillance programme 2015-2018

OBJECTIVES

To report antimicrobial susceptibility testing surveillance data for ceftaroline and comparative agents from the AWARE global surveillance programme for bacterial pathogens causing skin and soft tissue infections (SSTIs) and lower respiratory infections (RTIs) in Middle East and African countries from 2015 to 2018.

METHODS

Pathogens were identified by MALDI-TOF/MS. Antimicrobial susceptibility testing was performed using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method. MICs were interpreted by both CLSI (M100, 2020) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) (v 10.0, 2020) breakpoints.

RESULTS

All MSSA (n = 1125) and 93.9% of MRSA (n = 1235) were susceptible to ceftaroline (MIC ≤ 1 μg/mL, CLSI and EUCAST). The maximum ceftaroline MIC observed for MRSA was 2 μg/mL; no ceftaroline-resistant MRSA were identified among SSTI (CLSI and EUCAST) and RTI (CLSI) isolates. All isolates of β-haemolytic Streptococcus (n = 324), and penicillin-susceptible (PSSP) and -intermediate Streptococcus pneumoniae (PISP; n = 369) were susceptible to ceftaroline. Rates of susceptibility to ceftaroline for penicillin-resistant S. pneumoniae (penicillin MIC ≥ 2 μg/mL; n = 175), and β-lactamase-negative (BLNHI; n = 224) and β-lactamase-positive Haemophilus influenzae (n = 49) were 99.4%, 98.7%, and 98.0% (CLSI) and 92.6%, 98.2%, and 83.7% (EUCAST), respectively. Rates of susceptibility to ceftaroline for ESBL-negative Escherichia coli (n = 442), Klebsiella pneumoniae (n = 381), and Klebsiella oxytoca (n = 103) were 92.1%, 93.2%, and 96.1%, respectively.

CONCLUSION

Ceftaroline-resistant isolates of MRSA causing SSTIs were not identified in Middle East and African countries in 2015-2018 using recently revised CLSI (in 2019) or EUCAST (in 2018) breakpoint criteria. Common bacterial pathogens causing SSTIs (Staphylococcus aureus, β-haemolytic Streptococcus) and lower RTIs (PSSP, PISP, BLNHI) demonstrated no resistance or low levels of resistance (0-1.8%) to ceftaroline.

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.

Comprehensive Genomic Investigation of Adaptive Mutations Driving the Low-Level Oxacillin Resistance Phenotype in Staphylococcus aureus

Antistaphylococcal penicillins such as oxacillin are the key antibiotics in the treatment of invasive methicillin-susceptible Staphylococcus aureus (MSSA) infections; however, mec gene-independent resistance adaptation can cause treatment failure. Despite its clinical relevance, the basis of this phenomenon remains poorly understood. Here, we investigated the genomic adaptation to oxacillin at an unprecedented scale using a large collection of 503 clinical mec-negative isolates and 30 in vitro-adapted isolates from independent oxacillin exposures. By combining comparative genomics, evolutionary convergence, and genome-wide association analysis, we found 21 genetic loci associated with low-level oxacillin resistance, underscoring the polygenic nature of this phenotype. Evidence of adaptation was particularly strong for the c-di-AMP signal transduction pathways (gdpP and dacA) and in the clpXP chaperone-protease complex. The role of mutations in gdpP in conferring low-level oxacillin resistance was confirmed by allele-swapping experiments. We found that resistance to oxacillin emerges at high frequency in vitro (median, 2.9 × 10^-6; interquartile range [IQR], 1.9 × 10^-6 to 3.9 × 10^-6), which is consistent with a recurrent minimum inhibitory concentration (MIC) increase across the global phylogeny of clinical isolates. Nevertheless, adaptation in clinical isolates appears sporadically, with no stably adapted lineages, suggesting a high fitness cost of resistance, confirmed by growth assessment of mutants in rich media. Our data provide a broader understanding of the emergence and dynamics of oxacillin resistance adaptation in S. aureus and a framework for future surveillance of this clinically important phenomenon.IMPORTANCE The majority of Staphylococcus aureus strains causing human disease are methicillin-susceptible (MSSA) and can be treated with antistaphylococcal penicillins (such as oxacillin). While acquisition of the mec gene represents the main resistance mechanism to oxacillin, S. aureus can acquire low-level resistance through adaptive mutations in other genes. In this study, we used genomic approaches to understand the basis of S. aureus adaption to oxacillin and its dynamic at the population level. By combining a genome analysis of clinical isolates from persistent MSSA infections, in vitro selection of oxacillin resistance, and genome-wide association analysis on a large collection of isolates, we identified 21 genes linked to secondary oxacillin resistance. Adaptive mutations in these genes were easy to select when S. aureus was exposed to oxacillin, but they also came at a substantial cost in terms of bacterial fitness, suggesting that this phenotype emerges preferentially in the setting of sustained antibiotic exposure.

Tentative clinical breakpoints and epidemiological cut-off values of nemonoxacin for Streptococcus pneumoniae and Staphylococcus aureus isolates associated with community-acquired pneumonia

OBJECTIVES

To determine the minimum inhibitory concentration (MIC) distribution, epidemiological cut-off (ECOFF) values and clinical breakpoints (CBPs) of nemonoxacin, a non-fluorinated quinolone, for community-acquired pneumonia (CAP)-related Streptococcus pneumoniae and Staphylococcus aureus.

METHODS

We pooled the susceptibility and clinical data of CAP patients enrolled in five clinical trials conducted in three countries from 2006 to 2017. Published pharmacokinetic (PK) profiles of oral (500 mg) and intravenous (IV) (500, 650 and 750 mg) nemonoxacin formulations and pharmacodynamic (PD) parameters of the two aforementioned CAP-related Gram-positive cocci (GPC) were used to determine plausible CBPs. Moreover, nemonoxacin MIC distributions of CAP-relatedS. pneumoniae (n = 1800) and S. aureus (n = 2000) isolates were obtained to evaluate ECOFF values using a visual estimation approach and ECOFFinder.

RESULTS

More than 92% of patients with CAP caused byS. pneumoniae or S. aureus with nemonoxacin MICs ≤ 0.25 mg/L presented positive clinical and microbiological outcomes. The ECOFF, MIC₉₀ and MIC₉₉ values of nemonoxacin were, respectively, 0.06, 0.125 and 1 mg/L for S. pneumoniae and 0.125, 1 and 8 mg/L for S. aureus. Based on differences in the PK profiles of oral and IV formulations, PD parameters of nemonoxacin for these CAP-GPC and clinical in vivo efficacy data, tentative CBPs of 0.5, 0.5 and 1 mg/L, respectively, were established for the 500 mg oral and 500 mg and 750 mg IV nemonoxacin formulations for S. pneumoniae, and 0.25, 0.5 and 1 mg/L for S. aureus.

CONCLUSION

This study provides plausible nemonoxacin CBPs for two important CAP-GPC.

Carbapenems drive the collateral resistance to ceftaroline in cystic fibrosis patients with MRSA

Chronic airways infection with methicillin-resistant Staphylococcus aureus (MRSA) is associated with worse respiratory disease cystic fibrosis (CF) patients. Ceftaroline is a cephalosporin that inhibits the penicillin-binding protein (PBP2a) uniquely produced by MRSA. We analyzed 335 S. aureus isolates from CF sputum samples collected at three US centers between 2015-2018. Molecular relationships demonstrated that high-level resistance of preceding isolates to carbapenems were associated with subsequent isolation of ceftaroline resistant CF MRSA. In vitro evolution experiments showed that pre-exposure of CF MRSA to meropenem with further selection with ceftaroline implied mutations in mecA and additional mutations in pbp1 and pbp2, targets of carbapenems; no effects were achieved by other β-lactams. An in vivo pneumonia mouse model showed the potential therapeutic efficacy of ceftaroline/meropenem combination against ceftaroline-resistant CF MRSA infections. Thus, the present findings highlight risk factors and potential therapeutic strategies offering an opportunity to both prevent and address antibiotic resistance in this patient population.

Narrow-Spectrum Antibacterial Agents-Benefits and Challenges

The number of antibacterial agents in clinical and preclinical development possessing activity against a narrow spectrum of bacterial pathogens is increasing, with many of them being nontraditional products. The key value proposition hinges on sparing antibiotic use and curtailing the emergence of resistance, as well as preventing the destruction of a beneficial microbiome, versus the immediate need for effective treatment of an active infection with a high risk of mortality. The clinical use of a targeted spectrum agent, most likely in combination with a rapid and robust diagnostic test, is a commendable goal with significant healthcare benefits if executed correctly. However, the path to achieving this will come with several challenges, and many scientific and clinical development disciplines will need to align their efforts to successfully change the treatment paradigm.

Susceptibility of clinical isolates of meticillin-resistant Staphylococcus aureus and phenotypic non-extended-spectrum β-lactamase-producing Klebsiella pneumoniae to ceftaroline in Taiwan: Results from Antimicrobial Testing Leadership and Surveillance (ATLAS) in 2012-2018 and Surveillance of Multicentre Antimicrobial Resistance in Taiwan (SMART) in 2018-2019

Data on ceftaroline (CPT) susceptibility amongst clinical isolates of meticillin-resistant Staphylococcus aureus (MRSA, n=1284) and phenotypic non-extended-spectrum β-lactamase-producing (non-ESBL-P) Klebsiella pneumoniae (n=466), obtained from the Antimicrobial Testing Leadership and Surveillance (ATLAS) programme from 2012 to 2018, and selected MRSA isolates from patients with bloodstream infections (BSIs) (n=95) from the Surveillance of Multicentre Antimicrobial Resistance in Taiwan (SMART) programme from 2018 to 2019 were analysed. The minimum inhibitory concentrations (MICs) of ATLAS isolates were determined using the broth microdilution method, whereas the MICs of SMART BSI-MRSA isolates were determined using the Etest and MicroScan system. The pharmacokinetic profiles and pharmacodynamic parameters of CPT were applied to explore the optimal dosage against infections caused by Taiwanese MRSA and K. pneumoniae isolates. Approximately 7.1% of ATLAS MRSA isolates were susceptible-dose dependent (S-DD) to CPT, and 19.7% of the non-ESBL-P K. pneumoniae isolates were not susceptible to CPT. Amongst the ATLAS MRSA isolates, the S-DD rates to CPT amongst isolates causing lower respiratory tract infections were 11.9% and 8.5% for isolates from intensive care units (ICUs) and general wards (GWs), and those causing skin and soft tissue infections (SSTIs) were 20% and 5.3% for isolates from ICUs and GWs, respectively (P=0.015). Of the SSTI MRSA isolates from GWs, 22.7% displayed vancomycin MICs >1 mg/L. Amongst 95 SMART BSI MRSA isolates, 28 (46.7%) isolates exhibited lower CPT MICs by the Etest compared with 60 isolates with CPT MICs of 1-2 mg/L by the MicroScan system. CPT 600 mg as a 2-h intravenous infusion every 8 h is suggested for treatment of infections caused by MRSA and phenotypic non-ESBL-P K. pneumoniae in Taiwan.

What's new in mechanisms of antibiotic resistance in bacteria of clinical origin?

The discovery, commercialization and administration of antibiotics revolutionized the world of medicine in the middle of the last century, generating a significant change in the therapeutic paradigm of the infectious diseases. Nevertheless, this great breakthrough was soon threatened due to the enormous adaptive ability that bacteria have, through which they are able to develop or acquire different mechanisms that allow them to survive the exposure to antibiotics. We are faced with a complex, multifactorial and inevitable but potentially manageable threat. To fight against it, a global and multidisciplinary approach is necessary, based on the support, guidance and training of the next generation of professionals. Nevertheless, the information published regarding the resistance mechanisms to antibiotics are abundant, varied and, unfortunately, not always well structured. The objective of this review is to structure the, in our opinion, most relevant and novel information regarding the mechanisms of resistance to antibiotics that has been published from January 2014 to September 2019, analysing their possible clinical and epidemiological impact.

Evaluation of the Presence and Characterization of Vancomycin-Intermediate and Heterogeneous Vancomycin-Intermediate Level Resistance Among Bloodstream Isolates of Methicillin-Resistant Staphylococcus aureus

Aims: Heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) could be misinterpreted as "susceptible" with routine susceptibility testing procedures, and the subpopulations with reduced susceptibility to glycopeptides can lead to therapeutic failure. The aim of this study was to evaluate the presence of VISA and hVISA strains among stocked bloodstream methicillin-resistant S. aureus (MRSA) isolates of 14 years. Materials and Methods: A total of 127 nonduplicate MRSA strains isolated from blood cultures between 2001 and 2014 were investigated. Glycopeptide minimum inhibitory concentration values were detected by microbroth dilution method. Susceptibilities to other antimicrobials were determined by the disk diffusion method and interpreted according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. Macrogradient test (MGT) and modified population analysis profile-area under the curve (modified PAP-AUC) methods were used to detect VISA and hVISA. Staphylococcal Cassette Chromosome mec (SCCmec), agr, and toxin gene typing were done by polymerase chain reaction. Genetic relatedness of the strains were evaluated by pulsed-field gel electrophoresis (PFGE). Results: All isolates were susceptible to glycopeptides, linezolid, and quinupristin-dalfopristin. All were resistant to tetracycline, 96% were resistant to aminoglycosides, fluoroquinolones, and rifampin. Only 58.3% of the isolates were susceptible to ceftaroline. Six isolates were suspected as hVISA by the MGT, but none could be confirmed by the modified PAP-AUC analysis. All isolates carried type-III SCCmec, sea was the most prevalent (96.9%) enterotoxin gene and agr group I locus was predominant (93.7%). PFGE analysis revealed four main and four unique patterns. Conclusion: No hVISA or VISA were detected. The resistance rate to ceftaroline seems remarkable due to its recent entry into the market in Turkey.

Clinical, Epidemiologic, and Laboratory Aspects of Methicillin-Resistant Staphylococcus aureus Infections

Oxacillin-resistant Staphylococcus aureus (abbreviated MRSA for historical reasons) is a major pathogen responsible for both hospital- and community-onset disease. Resistance to oxacillin in most clinical isolates of S. aureus is mediated by PBP2a, a penicillin-binding protein with low affinity to beta-lactams, encoded primarily by the mecA gene. Rapid and accurate methods of susceptibility testing of S. aureus isolates to identify MRSA infections are important tools to limit the spread of this organism. This review focuses on the clinical significance of MRSA infections and new approaches for the laboratory diagnosis and epidemiologic typing of MRSA strains.

Phylogeographical Analysis Reveals the Historic Origin, Emergence, and Evolutionary Dynamics of Methicillin-Resistant Staphylococcus aureus ST228

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a common healthcare-associated pathogen that remains a major public health concern. Sequence type 228 (ST228) was first described in Germany and spread to become a successful MRSA clone in several European countries. In 2000, ST228 emerged in Lausanne and has subsequently caused several large outbreaks. Here, we describe the evolutionary history of this clone and identify the genetic changes underlying its expansion in Switzerland.

MATERIALS AND METHODS

We aimed to understand the phylogeographic and demographic dynamics of MRSA ST228/ST111 by sequencing 530 representative isolates of this clone that were collected from 14 European countries between 1997 and 2012.

RESULTS

The phylogenetic analysis revealed distinct lineages of ST228 isolates associated with specific geographic origins. In contrast, isolates of ST111, which is a single locus variant of ST228 sharing the same spa type t041, formed a monophyletic cluster associated with multiple countries. The evidence points to a German origin of the sampled population, with the basal German lineage being characterized by spa type t001. The highly successful Swiss ST228 lineage diverged from this progenitor clone through the loss of the aminoglycoside-streptothricin resistance gene cluster and the gain of mupirocin resistance. This lineage was introduced first in Geneva and was subsequently introduced into Lausanne.

CONCLUSION

Our results reveal the radiation of distinct lineages of MRSA ST228 from a German progenitor, as the clone spread into different European countries. In Switzerland, ST228 was introduced first in Geneva and was subsequently introduced into Lausanne.

Using genomics to understand meticillin- and vancomycin-resistant Staphylococcus aureus infections

Resistance to meticillin and vancomycin in Staphylococcus aureus significantly complicates the management of severe infections like bacteraemia, endocarditis or osteomyelitis. Here, we review the molecular mechanisms and genomic epidemiology of resistance to these agents, with a focus on how genomics has provided insights into the emergence and evolution of major meticillin-resistant S. aureus clones. We also provide insights on the use of bacterial whole-genome sequencing to inform management of S. aureus infections and for control of transmission at the hospital and in the community.

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.

Adjunctive ceftaroline in combination with daptomycin or vancomycin for complicated methicillin-resistant Staphylococcus aureus bacteremia after monotherapy failure

Background:

Methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B) may fail to improve with standard monotherapy, particularly in patients with multifocal infection, incomplete source control, or persistent bacteremia. Synergy observed in vitro between ceftaroline (CPT) and daptomycin (DAP) or vancomycin (VAN) may translate into clinical benefit. Here, we describe our experience with DAP/CPT and VAN/CPT for complicated MRSA-B after monotherapy failure.

Methods:

Single-center, retrospective review of consecutive patients treated with DAP/CPT or VAN/CPT for MRSA-B after monotherapy failure from 1 January 2016 to 30 November 2018.

Results:

We identified 11 instances of combination therapy in 10 patients (DAP/CPT = 6, VAN/CPT = 5) with 1 patient receiving VAN/CPT followed by DAP/CPT. Rates of multifocal infection, incomplete source control, persistent bacteremia, and infective endocarditis were high (100%, 80%, 60%, and 60%, respectively). Combination therapy was initiated most commonly for persistent bacteremia (60%). When patients were persistently bacteremic, median preceding duration was 13 days and median time to clearance was 3 days. Total microbiologic cure rate was 100%. There were zero instances of bacteremia relapse at 30 days (30D) or 60 days (60D). All-cause 30D and 60D mortality rates were 11.1% and 33.3%, respectively.

Conclusions:

Combination therapy demonstrated success in diverse cases of refractory MRSA-B, including instances of persistent bacteremia paired with incomplete source control. Optimal timing and therapeutic cadence for combination therapy remain unclear. Our findings suggest that DAP/CPT and VAN/CPT can be considered for complicated MRSA bacteremia when other treatment options fail or are unavailable. We propose persistent bacteremia with incomplete source control to be a clinical niche particularly worthy of further investigation.

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.

Activity of ceftaroline against pathogens associated with community-acquired pneumonia collected as part of the AWARE surveillance program, 2015-2016

We report Assessing Worldwide Antimicrobial Resistance Evaluation (AWARE) program data for ceftaroline and comparators against isolates collected from identified lower respiratory tract sources in 2015 and 2016. MICs and susceptibility were determined using CLSI broth microdilution methodology and EUCAST breakpoints. Ceftaroline susceptibility among penicillin-resistant Streptococcus pneumoniae (MIC≥4 mg/L [nonmeningitis breakpoint]) ranged from 77.4% (Asia, 72/93) to 100% (Oceania, 16/16; Latin America, 15/15). Among MRSA, ceftaroline susceptibility ranged from 72.3% (Asia, 553/765) to 100% (Oceania, 39/39). Among β-lactamase-positive Haemophilus influenzae, ceftaroline susceptibility ranged from 69.2% (Asia, 36/52) to 100% (Oceania, 19/19). Susceptibility to ceftaroline against non-ESBL-producing Klebsiella pneumoniae was between 91.4% (Europe, 659/721) and 100% (Oceania, 55/55) and for Escherichia coli between 85.7% (Africa/Middle East, 42/49) and 92.1% (Oceania, 35/38). Ceftaroline is not active against ESBL producers. In this study, susceptibility to ceftaroline was high among the S. pneumoniae, Staphylococcus aureus, β-lactamase-negative H. influenzae, and ESBL-negative K. pneumoniae and E. coli collected.

Impact of EUCAST ceftaroline breakpoint change on the susceptibility of methicillin-resistant Staphylococcus aureus isolates collected from patients with complicated skin and soft-tissue infections

OBJECTIVES

In 2018, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) introduced an intermediate breakpoint for ceftaroline against Staphylococcus aureus. The objective of this study was to compare data on resistance to ceftaroline among methicillin-resistant S. aureus (MRSA) isolates using versions 7.1 (March 2017) and 8.0 (January 2018) of the EUCAST breakpoints.

METHODS

Participating centers were located in Africa, Asia, Europe, Oceania and South America. Isolates were collected from patients with complicated skin and soft-tissue infections and were cultured from integumentary sources. Methicillin resistance among S. aureus was confirmed locally using the oxacillin method. The CLSI broth microdilution method was used to measure ceftaroline MICs at the central laboratory. Versions 7.1 and 8.0 of the EUCAST breakpoints were used to interpret MIC data.

RESULTS

Between 2015 and 2016, 9559 isolates of S. aureus were collected, of which 5566 (58.2%) isolates were MRSA. Overall, the lowest rate of MRSA was in Asia (56.5%; 705/1247) and the highest rate was in Oceania (62.7%; 299/477). Using version 7.1 of the EUCAST breakpoints, 4.5% (250/5566) of all MRSA isolates were resistant to ceftaroline and when version 8.0 of the breakpoints was applied, 4.2% (235/5566) of MRSA were in the intermediate category and 0.3% (15/5566) of all isolates were considered resistant.

CONCLUSIONS

By applying version 8.0 of the EUCAST breakpoints, the majority of MRSA isolates that were resistant are now in the intermediate category for ceftaroline. Ceftaroline resistance among MRSA now appears rare.

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.

A Multicenter Study To Evaluate Ceftaroline Breakpoints: Performance in an Area with High Prevalence of Methicillin-Resistant Staphylococcus aureus Sequence Type 5 Lineage

Ceftaroline (CPT) is a broad-spectrum agent with potent activity against methicillin-resistant Staphylococcus aureus (MRSA). The sequence type 5 (ST5) Chilean-Cordobés clone, associated with CPT nonsusceptibility, is dominant in Chile, a region with high rates of MRSA infections. Here, we assessed the in vitro activity of CPT against a collection of MRSA isolates collected between 1999 and 2018 from nine hospitals (n = 320) and community settings (n = 41) in Santiago, Chile, and evaluated performance across testing methodologies. We found that our hospital-associated isolates exhibited higher CPT MIC distributions (MIC50 and MIC90 of 2 mg/liter) than the community isolates (MIC50 and MIC90 of 0.5 mg/liter), a finding that was consistent across time and independent of the culture source. High proportions (64%) of isolates were CPT nonsusceptible despite the absence of CPT use in Chile. Across methodologies, the Etest underestimated the MIC relative to the gold standard broth microdilution (BMD) test (MIC50 and MIC90 of 1 and 1.5 mg/liter, respectively). There was low (∼51%) categorical agreement (CA) between Etest and BMD results across CLSI and EUCAST breakpoints. The recent revision of CLSI guidelines abolished "very major error" (VME) from the previous guidelines (81%), which perform similarly to the EUCAST guidelines. The level of concordance between CLSI and EUCAST for BMD testing and Etest was >95%. Disk diffusion performed poorly relative to BMD under CLSI (CA, 55%) and EUCAST (CA, 36%) guidelines. Comparison of EUCAST to CLSI for disk diffusion (with EUCAST used as the reference) showed low agreement (CA, 25%; VME, 70%). In summary, CPT-nonsusceptible MRSA are dominant in clinical settings in Chile. Our results provide data to support the reevaluation of CPT breakpoints and to improve agreement across methodologies and agencies.

Summary of the safety and tolerability of two treatment regimens of ceftaroline fosamil: 600 mg every 8 h versus 600 mg every 12 h

BACKGROUND

The recommended adult dose of ceftaroline fosamil is 600 mg q12h by 1 h intravenous (iv) infusion for 5-14 days in complicated skin and soft tissue infection (cSSTI) and 5-7 days in community-acquired pneumonia (CAP). A dosage of 600 mg q8h by 2 h iv infusion is approved in some regions for cSSTI patients with Staphylococcus aureus infection where the ceftaroline MIC is 2 or 4 mg/L. This analysis compares the safety profiles of the q8h and q12h regimens.

METHODS

Safety data from six Phase III, randomized, double-blind clinical trials were collated into the q8h cSSTI pool (ceftaroline fosamil n = 506; NCT01499277) and the q12h pool {ceftaroline fosamil n = 1686; comprising five studies [two cSSTI (NCT00424190 and NCT00423657) and three CAP (NCT01371838, NCT00621504 and NCT00509106)]}.

RESULTS

The pattern and incidence of adverse events were similar between the q8h and q12h ceftaroline fosamil pools. Most were gastrointestinal and of mild or moderate intensity. Overall, rash intensity was similar between the q8h pool and the q12h pool. For the q8h regimen, there was a higher frequency of rash in some Asian study sites, associated with longer duration of therapy (≥7 days); most cases were mild and resolved following treatment discontinuation. No dose-related vital sign or ECG abnormalities were detected with either regimen.

CONCLUSIONS

The q8h regimen in cSSTI was generally well tolerated; the observed safety profile was consistent with the known safety profile of ceftaroline fosamil, reflective of the cephalosporin class and qualitatively consistent with the q12h regimen.

Evaluation of the Revised Ceftaroline Disk Diffusion Breakpoints When Testing a Challenge Collection of Methicillin-Resistant Staphylococcus aureus Isolates

We assessed ceftaroline disk diffusion breakpoints for Staphylococcus aureus when applying revised Clinical and Laboratory Standards Institute (CLSI) ceftaroline MIC breakpoints. Disk-MIC correlation was evaluated by testing a challenge collection (n = 158) of methicillin-resistant S. aureus (MRSA) isolates composed of 106 randomly selected isolates plus 52 isolates with decreased susceptibility to ceftaroline (MIC, 1 to 16 μg/ml). Disk diffusion was performed with 30-μg disks and Mueller-Hinton agar from 2 manufacturers each. Revised CLSI susceptible (S)/susceptible dose-dependent (SDD)/resistant (R) MIC breakpoints of ≤1/2 to 4/≥8 μg/ml were applied. The disk breakpoints that provided the lowest error rates were CLSI S/R breakpoints of ≥25 mm/≤19 mm, with no very major (VM) or major (Ma) errors and with minor (Mi) error rates of 0.0% for ≥2 doubling dilutions above the I or SDD (≥I + 2), 22.1% for I or SDD plus or minus 1 doubling dilution (I ± 1), and 2.3% for ≤2 doubling dilutions below the I or SDD ≤I - 2 (overall Mi error rate, 16.5%). No mutation in the penicillin-binding protein 2a (PBP2a) was observed in 5 of 15 isolates with a ceftaroline MIC of 2 μg/ml; 3 of 11 isolates with a ceftaroline MIC of 1 μg/ml exhibited mutations in the penicillin-binding domain (PBD; 1 isolate) or in the non-PBD (2 isolates). All isolates except 1, with a ceftaroline MIC of ≥4 μg/ml, showed ≥1 mutation in the PBD and/or non-PBD. In summary, results from the disk diffusion method showed a good correlation with those from the reference broth microdilution method. Our results also showed that the ceftaroline MIC distribution of isolates with no mutations in the PBP2a goes up to 4 μg/ml, and reference broth microdilution and disk diffusion methods do not properly separate wild-type from non-wild-type isolates.

Methicillin-resistant Staphylococcus aureus: livestock-associated, antimicrobial, and heavy metal resistance

Staphylococcus aureus is an opportunistic pathogen of human and other mammals that is of increasing clinical and veterinary importance due to its ability to rapidly develop antimicrobial resistance. The injudicious use of antibiotics has given rise to the emergence of antibiotic resistant S. aureus strains, most importantly methicillin-resistant Staphylococcus aureus (MRSA). The emergence of livestock-associated MRSA (LA-MRSA) has highlighted the importance of directed research toward its prevention, as well as the need for the discovery and development of more efficient treatment than is currently available. Furthermore, the treatment of MRSA is complicated by the co-selection of heavy metal and antibiotic resistance genes by microorganisms. Livestock and livestock production systems are large reservoirs of heavy metals due to their use in feed as well as environmental contaminant, which has allowed for the selection of LA-MRSA isolates with heavy metal resistance. The World Health Organization reported that Africa has the largest gaps in data on the prevalence of antimicrobial resistance, with no reports on rates for LA-MRSA harboring heavy metal resistance in South Africa. This review aimed to report the emergence of LA-MRSA in South Africa, specifically the most frequent sequence type ST398, globally. Furthermore, we aimed to highlight the importance of LA-MRSA in clinical and food security, as well as this research gap in South Africa. This review sheds light on the prevalence of heavy metals in livestock farms and abattoirs, and focuses on the phenomenon of the co-selection of heavy metal and antibiotic resistance genes in MRSA, emphasizing the importance of a focused direction for research in humans, animals as well as environment using one-health approach.

Reservoirs and Transmission Pathways of Resistant Indicator Bacteria in the Biotope Pig Stable and along the Food Chain: A Review from a One Health Perspective

The holistic approach of “One Health” includes the consideration of possible links between animals, humans, and the environment. In this review, an effort was made to highlight knowledge gaps and various factors that contribute to the transmission of antibiotic-resistant bacteria between these three reservoirs. Due to the broad scope of this topic, we focused on pig production and selected “indicator bacteria”. In this context, the role of the bacteria livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) and extended spectrum beta-lactamases carrying Escherichia coli (ESBL-E) along the pig production was particularly addressed. Hotspots of their prevalence and transmission are, for example, pig stable air for MRSA, or wastewater and manure for ESBL-E, or even humans as vectors in close contact to pigs (farmers and veterinarians). Thus, this review focuses on the biotope “stable environment” where humans and animals are both affected, but also where the end of the food chain is not neglected. We provide basic background information about antibiotics in livestock, MRSA, and ESBL-bacteria. We further present studies (predominantly European studies) in tabular form regarding the risk potentials for the transmission of resistant bacteria for humans, animals, and meat differentiated according to biotopes. However, we cannot guarantee completeness as this was only intended to give a broad superficial overview. We point out sustainable biotope approaches to try to contribute to policy management as critical assessment points in pig housing conditions, environmental care, animal health, and food product safety and quality as well as consumer acceptance have already been defined.

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.

Streptomyces as a Prominent Resource of Future Anti-MRSA Drugs

Methicillin-resistant Staphylococcus aureus (MRSA) pose a significant health threat as they tend to cause severe infections in vulnerable populations and are difficult to treat due to a limited range of effective antibiotics and also their ability to form biofilm. These organisms were once limited to hospital acquired infections but are now widely present in the community and even in animals. Furthermore, these organisms are constantly evolving to develop resistance to more antibiotics. This results in a need for new clinically useful antibiotics and one potential source are the Streptomyces which have already been the source of several anti-MRSA drugs including vancomycin. There remain large numbers of Streptomyces potentially undiscovered in underexplored regions such as mangrove, deserts, marine, and freshwater environments as well as endophytes. Organisms from these regions also face significant challenges to survival which often result in the production of novel bioactive compounds, several of which have already shown promise in drug development. We review the various mechanisms of antibiotic resistance in MRSA and all the known compounds isolated from Streptomyces with anti-MRSA activity with a focus on those from underexplored regions. The isolation of the full array of compounds Streptomyces are potentially capable of producing in the laboratory has proven a challenge, we also review techniques that have been used to overcome this obstacle including genetic cluster analysis. Additionally, we review the in vivo work done thus far with promising compounds of Streptomyces origin as well as the animal models that could be used for this work.

Ceftaroline Resistance by Clone-Specific Polymorphism in Penicillin-Binding Protein 2a of Methicillin-Resistant Staphylococcus aureus

A total of 281 nonduplicated Staphylococcus aureus blood isolates were collected from January to May 2017 from eight hospitals in South Korea to investigate the epidemiological traits of ceftaroline resistance in methicillin-resistant S. aureus (MRSA). Cefoxitin-disk diffusion tests and the mecA gene PCR revealed that 56.6% (159/281) of the S. aureus isolates were MRSA, and most belonged to ST5 (50.3%, 80/281) and ST72 (41.5%, 66/281). Of the MRSA isolates, 44.0% (70/159) were nonsusceptible to ceftaroline (MIC ≥ 2 mg/liter), whereas all of the methicillin-susceptible S. aureus isolates were susceptible to the drug. Eight amino acid substitutions in penicillin-binding protein 2a (PBP2a), including four (L357I, E447K, I563T, and S649A) in the penicillin-binding domain (PBD) and four (N104K, V117I, N146K, and A228V) in the non-PBD (nPBD) of PBP2a, were associated with ceftaroline resistance. The accumulation of substitutions in PBP2a resulted in the elevation of ceftaroline MICs: one substitution at 1 to 2 mg/liter, two or three substitutions at 2 to 4 mg/liter, and five substitutions at 4 or 16 mg/liter. Ceftaroline resistance in MRSA might be the result of clone-specific PBP2a polymorphism, along with substitutions both in PBD and nPBD, and the elevated ceftaroline MICs were associated with the substitution sites and accumulation of substitutions.

DISC: Describing Infections of the Spine treated with Ceftaroline

OBJECTIVES

Infections of the spine lead to considerable morbidity and a high cost to the global healthcare system. Currently, evidence for using ceftaroline, an advanced-generation cephalosporin active against methicillin-resistant Staphylococcus aureus (MRSA), in spine infections is limited.

METHODS

Describing Infections of the Spine treated with Ceftaroline (DISC) is a multicentre, retrospective, cohort study that evaluated ceftaroline for treating spine infections. Patients were included if they were aged ≥18 years, diagnosed with a spine infection and treated with ceftaroline for ≥28 days. A control group was identified with the same inclusion criteria as the study population except they were treated with a comparator antibiotic for ≥28 days.

RESULTS

Thirty-seven patients were included each in the ceftaroline and control groups. MRSA was the most commonly identified pathogen. With no differences between groups in age, sex, race or co-morbidities (with the exception of chronic kidney disease), treatment with ceftaroline led to similar clinical success compared with the control group. Multivariate regression analysis did not show a significant difference between the two groups in terms of clinical success after controlling for other covariates (adjusted odds ratio=1.49; P=0.711). More patients who received ceftaroline were discharged to an extended-care or rehabilitation facility than home compared with controls (81% vs. 54%, respectively; P=0.024). Side effects and toxicities were rare, including one case of eosinophilic pneumonia in the ceftaroline group.

CONCLUSIONS

Ceftaroline appears to be a safe and effective therapy for infections of the spine, including from MRSA.

Mechanisms of antimicrobial resistance among hospital-associated pathogens

INTRODUCTION

The introduction of antibiotics revolutionized medicine in the 20th-century permitting the treatment of once incurable infections. Widespread use of antibiotics, however, has led to the development of resistant organisms, particularly in the healthcare setting. Today, the clinician is often faced with pathogens carrying a cadre of resistance determinants that severely limit therapeutic options. The genetic plasticity of microbes allows them to adapt to stressors via genetic mutations, acquisition or sharing of genetic material and modulation of genetic expression leading to resistance to virtually any antimicrobial used in clinical practice. Areas covered: This is a comprehensive review that outlines major mechanisms of resistance in the most common hospital-associated pathogens including bacteria and fungi. Expert commentary: Understanding the genetic and biochemical mechanisms of such antimicrobial adaptation is crucial to tackling the rapid spread of resistance, can expose unconventional therapeutic targets to combat multidrug resistant pathogens and lead to more accurate prediction of antimicrobial susceptibility using rapid molecular diagnostics. Clinicians making treatment decisions based on the molecular basis of resistance may design therapeutic strategies that include de-escalation of broad spectrum antimicrobial usage, more focused therapies or combination therapies. These strategies are likely to improve patient outcomes and decrease the risk of resistance in hospital settings.

Ceftaroline efficacy against high-MIC clinical Staphylococcus aureus isolates in an in vitro hollow-fibre infection model

Objectives

The current CLSI and EUCAST clinical susceptible breakpoint for 600 mg q12h dosing of ceftaroline (active metabolite of ceftaroline fosamil) for Staphylococcus aureus is ≤1 mg/L. Efficacy data for S. aureus infections with ceftaroline MIC ≥2 mg/L are limited. This study was designed to generate in-depth pharmacokinetic/pharmacodynamics (PK/PD) understanding of S. aureus isolates inhibited by ≥ 2 mg/L ceftaroline using an in vitro hollow-fibre infection model (HFIM).

Methods

The PK/PD target of ceftaroline was investigated against 12 diverse characterized clinical MRSA isolates with ceftaroline MICs of 2 or 4 mg/L using q8h dosing for 24 h. These isolates carried substitutions in the penicillin-binding domain (PBD) and/or the non-PBD. Additionally, PD responses of mutants with ceftaroline MICs ranging from 2 to 32 mg/L were evaluated against the mean 600 mg q8h human-simulated dose over 72 h.

Results

The mean stasis, 1 log10-kill and 2 log10-kill PK/PD targets were 29%, 32% and 35% f T>MIC, respectively. In addition, these data suggest that the PK/PD target for MRSA is not impacted by the presence of substitutions in the non-PBD commonly found in isolates with ceftaroline MIC values of ≤ 2 mg/L. HFIM studies with 600 mg q8h dosing demonstrated a sustained long-term bacterial suppression for isolates with ceftaroline MICs of 2 and 4 mg/L.

Conclusions

Overall, efficacy was demonstrated against a diverse collection of clinical isolates using HFIM indicating the utility of 600 mg ceftaroline fosamil for S. aureus isolates with MIC ≤4 mg/L using q8h dosing.

Ceftaroline for Severe Methicillin-Resistant Staphylococcus aureus Infections: A Systematic Review

Ceftaroline is approved by the Food and Drug Administration for acute bacterial skin and skin-structure infections and community-acquired bacterial pneumonia, including cases with concurrent bacteremia. Use for serious methicillin-resistant Staphylococcus aureus (MRSA) infections has risen for a multitude of reasons. The aim of this article is to review the literature evaluating clinical outcomes and safety of ceftaroline prescribed for serious MRSA infections. We conducted a literature search in Ovid (Medline) and PubMed for reputable case reports, clinical trials, and reviews focusing on the use of ceftaroline for treatment of MRSA infections. Twenty-two manuscripts published between 2010 and 2016 met inclusion criteria. Mean clinical cure was 74% across 379 patients treated with ceftaroline for severe MRSA infections. Toxicities were infrequent. Ceftaroline treatment resulted in clinical and microbiologic cure for severe MRSA infections. Close monitoring of hematological parameters is necessary with prolonged courses of ceftaroline.

A combination of ceftaroline and daptomycin has synergistic and bactericidal activity in vitro against daptomycin nonsusceptible methicillin-resistant Staphylococcus aureus (MRSA)

There is an urgent need to optimize therapeutic options in patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia who have failed conventional therapy. Two clinical isolates were obtained from a 68-year-old male with persistent MRSA bacteremia before and after the development of daptomycin nonsusceptibility. The pharmacodynamic activity of monotherapies and combinations of ceftaroline, daptomycin, cefoxitin, nafcillin and vancomycin were evaluated in time-kill experiments versus 108 CFU/mL of the pre- and post-daptomycin nonsusceptible MRSA isolates. Cefoxitin, nafcillin and vancomycin alone or in combination with ceftaroline failed to generate prolonged bactericidal activity against the post-daptomycin nonsusceptible isolate whereas a ceftaroline-daptomycin combination resulted in 6, 24 and 48 h log10(CFU/mL) reductions of 3.90, 4.40 and 6.32. Population analysis profiles revealed a daptomycin heteroresistant subpopulation of the pre-daptomycin nonsusceptible MRSA isolate that expanded by >10,000× on daptomycin agar containing 2-16 mg/L in the post-daptomycin nonsusceptible isolate. Daptomycin and ceftaroline combinations may be promising against persistent MRSA bacteremia.

Ceftaroline-Resistant, Daptomycin-Tolerant, and Heterogeneous Vancomycin-Intermediate Methicillin-Resistant Staphylococcus aureus Causing Infective Endocarditis

We report a case of infective endocarditis (IE) caused by ceftaroline-resistant, daptomycin-tolerant, and heterogeneous vancomycin-intermediate methicillin-resistant S. aureus (MRSA). Resistance to ceftaroline emerged in the absence of drug exposure, and the E447K substitution in the active site of PBP2a previously associated with ceftaroline resistance was identified. Additionally, we present evidence of patient-to-patient transmission of the strain within the same unit. This case illustrates the difficulties in treating MRSA IE in the setting of a multidrug-resistant phenotype.

Antimicrobial activity of ceftaroline against methicillin-resistant Staphylococcus aureus (MRSA) isolates collected in 2013-2014 at the Geneva University Hospitals

Ceftaroline is a broad-spectrum antibiotic with activity against methicillin-resistant Staphylococcus aureus (MRSA) strains. Ceftaroline susceptibility of an MRSA set archived between 1994 and 2003 in the Geneva University Hospitals detected a high percentage (66 %) of ceftaroline resistance in clonotypes ST228 and ST247 and correlated with mutations in PBP2a. The ceftaroline mechanism of action is based on the inhibition of PBP2a; thus, the identification of PBP2a mutations of recently circulating clonotypes in our institution was investigated. We analyzed ceftaroline susceptibility in MRSA isolates (2013 and 2014) and established that resistant strains correlated with PBP2a mutations and specific clonotypes. Ninety-six MRSA strains were analyzed from independent patients and were isolated from blood cultures (23 %), deep infections (38.5 %), and superficial (skin or wound) infections (38.5 %). This sample showed a ceftaroline minimum inhibitory concentration (MIC) range between 0.25 and 2 μg/ml and disk diameters ranging from 10 to 30 mm, with a majority of strains showing diameters ≥20 mm. Based on the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints, 76 % (73/96) of isolates showed susceptibility to ceftaroline. Nevertheless, we still observed 24 % (23/96) of resistant isolates (MIC = 2 μg/ml). All resistant isolates were assigned to clonotype ST228 and carried the N146K mutation in PBP2a. Only two ST228 isolates showed ceftaroline susceptibility. The decreasing percentage of ceftaroline-resistant isolates in our hospital can be explained by the decline of ST228 clonotype circulating in our hospital since 2008. We present evidence that ceftaroline is active against recent MRSA strains from our hospital; however, the presence of PBP2a variants in particular clonotypes may affect ceftaroline efficacy.