Antimicrobial agents for treatment of serious infections caused by resistant Staphylococcus aureus and enterococci

Antimicrobial resistance prevalence of Escherichia coli and Staphylococcus aureus amongst bacteremic patients in Africa: a systematic review

OBJECTIVES

Antimicrobial resistance (AMR) is a global concern among infectious diseases. Bloodstream infections can potentially become life-threatening if they become untreatable with conventional antimicrobials. This review aims to provide an understanding of the AMR prevalence and trends of common bacteremic pathogens, namely Escherichia coli and Staphylococcus aureus in the World Health Organization (WHO) Africa region.

METHODS

PubMed and Google Scholar were searched using relevant keywords for published human studies (excluding case reports and reviews) reporting bacteremic AMR data on the pathogens of interest between 2008 and 2019. Two reviewers independently screened the articles against a pre-defined eligibility criterion. Data extraction and analysis were achieved with different platforms: Covidence, Excel, R version 3.6.3, and QGIS v3.4.5. The pooled prevalence, 95% confidence intervals, and I² index (a measure of heterogeneity) were calculated for the various pathogen-antibiotic combinations.

RESULTS

Five hundred sixty-two papers were retrieved, with 27 papers included in the final analysis. Only 23.4% (11/47) of member states of the WHO African region had reports on AMR in bacteremia. The Clinical and Laboratory Standards Institute (CLSI) (78.5%) was the most common standard used in the region. For E. coli, the pooled resistance was: cefotaxime (42%), imipenem (4%), meropenem (0%), and colistin (0%). For S. aureus, the calculated pooled resistance was cloxacillin (34%), oxacillin (12%), and vancomycin (0%). There was a high degree of variation across studies (I² > 90%).

CONCLUSION

The pooled resistance rates indicate a concerning degree of methicillin-resistant and Extended Spectrum-ß-lactamase-producing pathogens. The paucity of AMR data also presents challenges for a comprehensive understanding of the situation in the region. Continent-wide and standardized surveillance efforts therefore need strengthening.

Antibiotics and Carbohydrate-Containing Drugs Targeting Bacterial Cell Envelopes: An Overview

Certain bacteria constitute a threat to humans due to their ability to escape host defenses as they easily develop drug resistance. Bacteria are classified into gram-positive and gram-negative according to the composition of the cell membrane structure. Gram-negative bacteria have an additional outer membrane (OM) that is not present in their gram-positive counterpart; the latter instead hold a thicker peptidoglycan (PG) layer. This review covers the main structural and functional properties of cell wall polysaccharides (CWPs) and PG. Drugs targeting CWPs are discussed, both noncarbohydrate-related (β-lactams, fosfomycin, and lipopeptides) and carbohydrate-related (glycopeptides and lipoglycopeptides). Bacterial resistance to these drugs continues to evolve, which calls for novel antibacterial approaches to be developed. The use of carbohydrate-based vaccines as a valid strategy to prevent bacterial infections is also addressed.

Early Effects of Rhodomyrtone on Membrane Integrity in Methicillin-Resistant Staphylococcus aureus

Strong evidence of high potency of rhodomyrtone as a promising antibacterial agent against pathogenic gram-positive bacteria has been clearly demonstrated in our previous work. The aim of this study was to provide insight into early action of rhodomyrtone, an acylphloroglucinol, on membrane damage in multidrug-resistant methicillin-resistant Staphylococcus aureus (MRSA). Early effects of rhodomyrtone on the bacterial membrane integrity were detected in a time-course study. Flow cytometry revealed a reduction in green fluorescent emission and increase in uptake of propidium iodide in rhodomyrtone-treated bacterial cells in a concentration- and time-dependent manner. Disruption of cytoplasmic membrane was further monitored by measuring cellular adenosine triphosphate (ATP) and potassium ion (K⁺). Leakage of both ATP and K⁺ and significant decrease in intracellular ATP in MRSA were observed following treatment. Pronounced changes in the bacterial ultrastructure and morphology were confirmed by transmission electron microscopy and scanning electron microscopy. Bacterial cell disruption, holes in cell surface, and bulge formations were noted in rhodomyrtone-treated cells. In this study, we provided relevant data to clarify that rhodomyrtone is a bacterial cell membrane-damaging agent. A possible early effect of this novel compound involves bacterial membrane disruption.

Right-Sided Infective Endocarditis and Pulmonary Infiltrates: An Update

Sixty years after its initial description, right-sided infective endocarditis (RSIE) still poses a challenge to all medical practitioners. Epidemiological data reveal a rising incidence attributable to the global surge in the number of intravenous drug users and the increased use of central vascular catheters and implantable cardiac devices. RSIE differs from left-sided infective endocarditis in more than just the location of the involved cardiac valve. They have different clinical presentations, diagnostic findings, and prognoses; hence, they require different management strategies. Cardiac murmurs and systemic emboli are usually absent in RSIE, whereas pulmonary embolism and its related complications dominate the clinical picture. Diagnostic delay of RSIE is secondary to the similarity in its initial presentation to other entities. Complications may ensue as a result of this delay. Diagnosis can be initially confirmed by using transthoracic echocardiography, except in patients with implanted cardioverter defibrillator, where a transesophageal echocardiogram is necessary. Various factors may increase mortality and morbidity in RSIE such as tricuspid valve vegetation size, fungal etiology, and low CD4 cell count in HIV patients. Oxacillin and vancomycin had been the traditionally used agents for the treatment of methicillin-susceptible and methicillin-resistant Staphylococcus aureus, respectively. More recently, daptomycin has shown promising results, which has led to its Food and Drug Administration (FDA) approval for the treatment of S. aureus bacteremia and associated RSIE. The aim of this article is to provide a comprehensive update on RSIE including epidemiology, pathogenesis, microbiology, diagnosis, management, and prognosis.

Native valve right sided infective endocarditis

Right-sided infective endocarditis (RSIE) accounts for 5-10% of all cases of infective endocarditis (IE), and is predominantly encountered in the injecting drug user (IDU) population, where HIV and HCV coinfections often coexist. Staphylococcus aureus is the most common pathogen. The pathogenesis of RSIE is still not well understood. RSIE usually presents as a persistent fever with respiratory symptoms whilst signs of systemic embolisation as seen in left-sided IE are notably absent. The prompt diagnosis of RSIE thus requires a high index of suspicion. Transthoracic echocardiography (TTE) can detect the majority of RSIE, whilst transoesophageal echocardiography (TOE) can increase sensitivity. Virulence of the causative organism and vegetation size are the major determinants of prognosis. Most cases of RSIE resolve with appropriate antibiotic administration.

Clinical experience with daptomycin in Italy: results from a registry study of the treatment of Gram-positive infections between 2006 and 2009

The purpose of this study was to evaluate post-marketing efficacy and safety data for therapy with daptomycin (DAP) in Italy. Data from patients treated with DAP at 30 centres between January 2006 and July 2009 were analysed according to the protocol of the EU-CORE(SM). In 359 patients, DAP was most commonly prescribed for skin and skin-structure infections (55%), infective endocarditis (13%), and bacteraemia (12.5%). DAP was associated with rapid improvement, and clinical success rates ranging from 77 to 91%, despite almost half of the patient population being ≥65 years of age, 86% having significant underlying disease, and many being affected by drug-resistant pathogens. Staphylococcus aureus represented 35% of all pathogens isolated. Success rates for all staphylococcal and enterococcal infections were >80%, including methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). Clinical outcomes were similar for DAP whether used as first- or second-line therapy. DAP was well tolerated even with prolonged treatment.

Importance of two Enterococcus faecium loci encoding Gls-like proteins for in vitro bile salts stress response and virulence

General stress proteins, Gls24 and GlsB, were previously shown to be involved in bile salts resistance of Enterococcus faecalis and in virulence. Here, we identified 2 gene clusters in Enterococcus faecium each encoding a homolog of Gls24 (Gls33 and Gls20; designated on the basis of their predicted sizes) and of GlsB (GlsB and GlsB1). The sequences of the gls33 and gls20 gene clusters from available genomes indicate distinct lineages, with those of hospital-associated CC17 isolates differing from non-CC17 by ∼7% and ∼3.5%, respectively. Deletion of an individual locus did not have a significant effect on virulence in a mouse peritonitis model, whereas a double-deletion mutant was highly attenuated (P<.004) versus wild-type. However, mutants lacking either gls33-glsB, gls20-glsB1, or both all exhibited increased sensitivity to bile salts. These results suggest that gls-encoded loci may be important for adaptation to the intestinal environment, in addition to being important for virulence functions.

Solution-phase parallel synthesis of novel membrane-targeted antibiotics

The increase in the incidence of antibiotic-resistant infections is a major concern to healthcare workers and requires the development of novel antibacterial agents. Recently, we described a series of benzophenone-containing antibiotics which displayed activity against antibiotic-resistant bacteria. We have shown that these agents function by disrupting the bacterial membrane. To further explore these compounds, a practical and efficient solution-phase parallel synthesis method was developed which allowed us to prepare combinatorial libraries of these agents. Using this method, we prepared 218 compounds in 58 reactions. All of the compounds were characterized by HPLC and MALDI-TOF mass spectrometry. Analysis of this library for antibacterial activity identified six compounds which displayed MIC values of 2.0 mg/L against Staphylococcus aureus. Examination of the structure-function relationships of these agents revealed that cationic groups were required and that cyclic, aliphatic amines were crucial for activity. Using the information generated here, we speculate on how the various structural features of the molecule are necessary for the interaction with the bacterial membrane.

New therapeutic choices for infections caused by methicillin-resistant Staphylococcus aureus

In recent years, a marked increase in the incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries. This review addresses the effectiveness and limitations of drugs classically used for the treatment of MRSA, e.g. vancomycin, and also newer anti-MRSA antimicrobials, e.g. second-generation glycolipopeptides, tigecycline, and beta-lactams.

Prevalence, species distribution and antimicrobial resistance of enterococci isolated from dogs and cats in the United States

AIMS

The contribution of dogs and cats as reservoirs of antimicrobial resistant enterococci remains largely undefined. This is increasingly important considering the possibility of transfer of bacteria from companion animals to the human host. In this study, dogs and cats from veterinary clinics were screened for the presence of enterococci.

METHODS AND RESULTS

A total of 420 enterococci were isolated from nasal, teeth, rectal, belly and hindquarters sites of 155 dogs and 121 cats from three clinics in Athens, GA. Eighty per cent (124 out of 155) of the dogs and 60% (72 out of 121) of the cats were positive for enterococci. From the total number of dog samples (n = 275), 32% (n = 87) were from hindquarter, 31% (n = 86) were rectal, and 29% (n = 79) were from the belly area. The majority of isolates originated from rectal samples (53 out of 145; 37%) from cats. The predominant species identified was Enterococcus faecalis (105 out of 155; 68%) from dogs and E. hirae (63 out of 121; 52%) from cats. Significantly more E. faecalis were isolated from rectal samples than any other enterococcal species (P < 0.05) for both dogs and cats suggesting site specific colonization of enterococcal species. The highest levels of resistance were to ciprofloxacin in E. faecium (9 out of 10; 90%), chloramphenicol resistance in E. faecalis (17 out of 20; 85%) and gentamicin resistance in E. faecalis (19 out of 24; 79%) from dog samples and nitrofurantoin resistance in E. faecium (15 out of 19; 79%) from cats. Multi-drug resistance (MDR) (resistance > or =2 antimicrobials) was observed to as few as two and as many as eight antimicrobials regardless of class.

CONCLUSION

This study demonstrated that dogs and cats are commonly colonized with antimicrobial resistant enterococci.

SIGNIFICANCE AND IMPACT OF THE STUDY

Dogs and cats may act as reservoirs of antimicrobial resistance genes that can be transferred from pets to people.

Identification of inhibitors of N5-carboxyaminoimidazole ribonucleotide synthetase by high-throughput screening

The increasing risk of drug-resistant bacterial infections indicates that there is a growing need for new and effective antimicrobial agents. One promising, but unexplored area in antimicrobial drug design is de novo purine biosynthesis. Recent research has shown that de novo purine biosynthesis in microbes is different from that in humans. The differences in the pathways are centered around the synthesis of 4-carboxyaminoimidazole ribonucleotide (CAIR) which requires the enzyme N(5)-carboxyaminoimidazole ribonucleotide (N(5)-CAIR) synthetase. Humans do not require and have no homologs of this enzyme. Unfortunately, no studies aimed at identifying small-molecule inhibitors of N(5)-CAIR synthetase have been published. To remedy this problem, we have conducted high-throughput screening (HTS) against Escherichia coliN(5)-CAIR synthetase using a highly reproducible phosphate assay. HTS of 48,000 compounds identified 14 compounds that inhibited the enzyme. The hits identified could be classified into three classes based on chemical structure. Class I contains compounds with an indenedione core. Class II contains an indolinedione group, and Class III contains compounds that are structurally unrelated to other inhibitors in the group. We determined the Michaelis-Menten kinetics for five compounds representing each of the classes. Examination of compounds belonging to Class I indicates that these compounds do not follow normal Michaelis-Menten kinetics. Instead, these compounds inhibit N(5)-CAIR synthetase by reacting with the substrate AIR. Kinetic analysis indicates that the Class II family of compounds are non-competitive with both AIR and ATP. One compound in Class III is competitive with AIR but uncompetitive with ATP, whereas the other is non-competitive with both substrates. Finally, these compounds display no inhibition of human AIR carboxylase:SAICAR synthetase indicating that these agents are selective inhibitors of N(5)-CAIR synthetase.

Susceptible, intermediate, and resistant - the intensity of antibiotic action

INTRODUCTION

To date, the resistance of infectious agents has been assessed by widely varying criteria in different countries. Therefore, published data on resistance often cannot be meaningfully compared. In Germany, different laboratories can potentially report different results for identical microorganisms, since there is no uniform system for categorization. This situation is unsatisfactory.

METHODS

Selective literature review and evaluation of committee reports.

RESULTS

The new ISO standard 20776 for determination of the resistance of infectious agents and the harmonized evaluation system of the European Society for Clinical Microbiology and Infectious Diseases provide a new basis for susceptibility testing. The categorization of infectious agents as "susceptible," "intermediate," or "resistant" to particular antibiotics will become more reliable and will be consistent throughout Europe.

DISCUSSION

For a number of antibiotics, the criteria for evaluation of infectious agents as "susceptible," "intermediate", or "resistant" will change. Comparability with earlier resistance data will be compromised. However, the new evaluation criteria reflect current knowledge on the pharmacokinetics and pharmacodynamics of antimicrobial substances.

[Staphylococcus aureus bacteremia and endocarditis]

The prevalence of Stapylococcus bacteriaemia is increasing worldwide, because of the increasing use of invasive procedures leading to nosocomial infections, but also of a changing way of life (increasing fashion for tattoos or piercing, use of intravenous drugs). Infective endocarditis develops in 10-30% of the cases of staphylococcus bacteriaemia. Staphylococcus aureus endocarditis must be suspected when it develops in the year following heart surgery or implantation of permanent devices. In drug users, it usually involves the tricuspid valve. According to the resistance of the germ to meticillin, antibiotic therapy uses a combination of intravenous penicillin or glycopeptide and an aminoside. Other antibiotics such as fosfomycin, rifampicin, fusidic acid, or clindamycin can be used when aminosides are contra-indicated. The role of newer antibiotic agents, such as daptomycin or linezolide, remains to be established.

Antimicrobial treatment for intra-abdominal infections

Treatment of patients with complicated intra-abdominal infections involves antimicrobial therapy, generally in conjunction with an interventional procedure to control the source of the infection. Antimicrobial regimens effective against common gram-negative and anaerobic enteric pathogens are the mainstay of therapy. For patients with community-acquired intra-abdominal infections, efficacy is comparable among the various single-agent or combination regimens recommended for therapy. Narrower-spectrum antimicrobial agents with a low potential for iatrogenic complications are appropriate for these patients. Patients with nosocomially-acquired, intra-abdominal infections are more likely to harbor resistant pathogens. Inadequate empiric antimicrobial therapy is associated with treatment failure and death. Therefore, broader spectrum antimicrobial regimens are recommended for these patients. In addition to coverage of more resistant gram-negative bacilli and anaerobes, use of agents effective against enterococci, resistant staphylococci and Candida should be considered. De-escalation of an initially broad antimicrobial regimen should be undertaken once definitive culture results are available.

Pulmonary versus systemic delivery of antibiotics: comparison of vancomycin dispositions in the isolated rat lung

Vancomycin dispositions in the respiratory system were compared after systemic and inhalatory administration under two respiratory conditions using the isolated-lung model. Inhalatory delivery led to much higher drug levels in pulmonary tissue and fluids. The respiratory pattern affects vancomycin disposition in the pulmonary system regardless of the administration route.

Estudio comparativo de pacientes con bacteriemia por Staphylococcus aureus sensible a la meticilina frente a S. aureus resistente a la meticilina: epidemiología y factores pronósticos

BACKGROUND AND OBJECTIVE

The influence of methicillin resistance in Staphylococcus aureus bacteremia (SAB) continues to be controversial. The aim of this study was to evaluate risk factors and mortality predictors in patients with SAB and the influence of methicillin resistance in mortality (SAMSB vs SAMRB).

PATIENTS AND METHOD

Prospective study including 213 in-patients with SAB.

RESULTS

Of 213 episodes of SAB, 131 (61.5%) were due to SAMS and 82 (38.5%) to SAMR. Risk factors associated with SAMRB were: nosocomial infection, presence of an ultimately or rapidly fatal underlying disease, diabetes mellitus, intravenous catheters, previous ICU hospitalization and therapy with broad-spectrum antibiotics. Severity and complications were more frequent in patients with SAMRB. Mortality was 42.6% in SAMRB cases vs 16% in SAMSB cases (p < 0.05). Multivariate analysis showed as independent predictors of mortality in patients with SAB: presence of an ultimately or rapidly fatal underlying disease, acute severity of illness at onset and inappropriate empirical therapy; methicillin resistance was not an independent predictor of mortality.

CONCLUSIONS

Methicillin resistance was not an independent predictor of mortality in patients with SAB. Presence of a fatal underlying disease, acute severity of illness at onset and inappropriate therapy were the main prognosis factors in patients with SAB.

Evaluation of the AdvanDx VRE EVIGENE assay for detection of vanA in vancomycin-resistant Staphylococcus aureus

AdvanDx VRE EVIGENE, a commercial vanA/vanB DNA hybridization assay to identify vancomycin-resistant enterococci (VRE), was evaluated for the detection of vanA in Staphylococcus aureus. Performance was assessed using S. aureus, VRE, and vancomycin-intermediate and -susceptible isolates. The assay demonstrated 100% sensitivity and specificity when analyzed visually and by optical density.

New agents for Staphylococcus aureus endocarditis

PURPOSE OF REVIEW

The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) as well as newly discovered S. aureus strains with reduced susceptibility to vancomycin mandates development of new antistaphylococcal agents. This review summarizes currently available and forthcoming antimicrobials for treatment of S. aureus endocarditis.

RECENT FINDINGS

No new antimicrobial has been proven superior to antistaphylococcal penicillins for treatment of methicillin-sensitive S. aureus (MSSA) endocarditis. Vancomycin has become standard treatment for MRSA but poor outcomes have been reported, both with susceptible and intermediately resistant S. aureus strains (VISA). Linezolid has successfully treated individual cases of MRSA endocarditis, but limitations include long-term safety. Daptomycin has recently been proven effective and well tolerated for MSSA and MRSA bacteremia, including right-sided endocarditis. New glycopeptides, including dalbavancin and telavancin, as well as the new cephalosporin ceftobiprole, have not yet been studied for treatment of endocarditis but appear active against MRSA and potentially VISA.

SUMMARY

Antistaphylococcal penicillins remain the treatment of choice for MSSA. Of the currently available newer agents, daptomycin appears to have the most rapid bactericidal activity and provides a much-needed alternative to vancomycin for treatment of MRSA or MSSA bacteremia and right-sided endocarditis.

Antimicrobial therapy of multidrug-resistant Streptococcus pneumoniae, vancomycin-resistant enterococci, and methicillin-resistant Staphylococcus aureus

Antibiotic resistance among pneumococci, enterococci, and staphylococci has become increasingly important in recent decades. Clinicians should be familiar with the nuances of antibiotic susceptibility testing and interpretation in selecting antibiotics for these infections. The clinical significance of penicillin-resistant Streptococcus pneumoniae, macrolide-resistant S pneumoniae, and multidrug-resistant S pneumoniae is discussed. The clinical spectrum and therapeutic approach to Enterococcus faecalis (i.e., vancomycin-sensitive enterococci) and E faecium (i.e., vancomycin-resistant enterococci) are discussed. Differences in therapeutic approach between methicillin-sensitive Staphylococcus aureus and methicillin-resistant S aureus (MRSA) infections are reviewed. Differences between in vitro susceptibility testing and in vivo effectiveness of antibiotics for hospital-acquired MRSA (HA-MRSA) are described. Finally, the clinical features of infection and therapy of HA-MRSA and community-acquired MRSA (CA-MRSA) infections are compared.

Restricted use of glycopeptides in paediatric cancer patients with fever and neutropenia

Until now, studies confirming the safety of glycopeptide restriction in the empirical treatment of prolonged fever and neutropenia included only nine children. In an open-label observational study, the use of teicoplanin in paediatric oncology patients was investigated. A period of unrestricted use (2001-2003) was compared with a second period (2004) following implementation of a restrictive treatment guideline. Empirical first-line treatment consisted of piperacillin/tazobactam; in 2004, fosfomycin was added after 72 h as the second-line combination instead of teicoplanin. In total, 213 episodes (n=163 in 2001-2003; n=50 in 2004) managed with teicoplanin or fosfomycin (only 2004) were eligible. Empirical treatment of fever of unknown origin with teicoplanin was reduced by 97%. In 2004, the mean length of stay was 0.4 days shorter, no infection-related death occurred and no vancomycin-resistant enterococci were detected. Restriction of empirical glycopeptides is safe in paediatric cancer patients after first-line treatment with piperacillin/tazobactam. Fosfomycin appears to offer a feasible and cost-saving alternative in second-line combination therapy.

Antimicrobial susceptibility of Gram-positive bacteria isolated from European medical centres: results of the Daptomycin Surveillance Programme (2002–2004)

The antimicrobial susceptibility patterns of 9322 contemporary (2002-2004) gram-positive bacterial isolates collected from 31 medical centres in 14 countries in Europe were evaluated by broth microdilution methods according to CLSI guidelines. The isolates collected comprised Staphylococcus aureus (4842 isolates), coagulase-negative staphylococci (CoNS; 1942 isolates), Enterococcus faecalis (1147 isolates), Enterococcus faecium (391 isolates), beta-haemolytic streptococci (660 isolates) and viridans group streptococci (340 isolates). The organisms were tested against daptomycin and more than 20 comparator agents in Mueller-Hinton broth, supplemented with calcium to 50 mg/L when testing daptomycin. Overall, methicillin (oxacillin) resistance rates were 26.7% and 77.0% for S. aureus (MRSA) and CoNS, respectively, and the vancomycin resistance rate among enterococci was 6.1%. MRSA rates varied from 0.6% in Sweden to 40.2-43.0% in Belgium, Greece, Ireland, the UK and Israel, and VRE rates varied from 0% in Switzerland to 21.2% in Ireland. More than 99.9% of isolates tested were considered susceptible to daptomycin according to breakpoints established by the United States Food and Drug Administration and the CLSI. Daptomycin was active against all gram-positive species, with the highest MIC being 2, 8, 0.5 and 2 mg/L for staphylococci, enterococci, beta-haemolytic streptococci and viridans group streptococci, respectively. Daptomycin activity was not influenced adversely by resistance to other agents among staphylococci or enterococci. This novel lipopeptide (daptomycin) appears to be an excellent alternative therapeutic option for serious infections caused by multidrug-resistant gram-positive organisms isolated in Europe.