Variation in potency and spectrum of tigecycline activity against bacterial strains from U.S. medical centers since its approval for clinical use (2006 to 2012)

Prevalence of tigecycline resistance in methicillin-resistant Staphylococcus aureus: a systematic review and meta-analysis

Tigecycline (TG) is one of the newest antimicrobial drugs used in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. The TG Resistance Evaluation and Monitoring Test (T.E.S.T.) is a global surveillance study aimed at monitoring bacterial resistance to TG in MRSA. This study will provide comprehensive data on the activity of TG against MRSA strains across the world by 2022. An electronic search was conducted for articles published during 1997 to 2022 in Pubmed/Medline (n = 361), Scopus (n = 1735) and Web of science (n = 439) for the following keywords: ((Tygacil [Title/Abstract]) OR (Tigecycline [Title/Abstract])) AND (((Staphylococcus aureus [Title/Abstract]) OR (Methicillin resistant Staphylococcus aureus [Title/Abstract])) OR (MRSA [Title/Abstract])). The titles and abstracts of 2535 articles were screened and 48 publications that fulfilled the inclusion criteria were included. From all studies, 35 studies had a cross-sectional design, 11 studies were cohort and 2 studies were case control. Blood and respiratory tract were the main specimen source in MRSA. Meta-analysis showed the proportion of TG resistance is more than 0.004. The region (countries, continent), study type and detection method were examined as the contributing factors of heterogeneity among the studies. Microbial resistance to this antibiotic has been reported to be low, but this does not mean that it can be used widely and without supervision, but the resistance caused by it in MRSA and other pathogens should be carefully and regularly evaluated.

Combined effect of Polymyxin B and Tigecycline to overcome Heteroresistance in Carbapenem-Resistant Klebsiella pneumoniae

We assessed the prevalence of polymyxin B (PMB)- and tigecycline (TGC)-heteroresistant Klebsiella pneumoniae isolates and investigated the combined effect of PMB and TGC against dual-heteroresistant K. pneumoniae. Ninety-five nonduplicated carbapenem-resistant K. pneumoniae (CRKP) clinical isolates were collected from a tertiary-care teaching hospital in China. PCR was used to detect the resistant genes among the CRKP isolates. Population analysis profiling (PAP) was carried out to evaluate the existence of heteroresistance. A time-kill assay of PMB combined with TGC was conducted against heteroresistant K. pneumoniae strains. Real-time PCR was performed to determine the pmrA, phoP, and acrB expression levels. Among them, 74 isolates (77.9%) were susceptible to TGC, and 90 isolates (94.7%) were susceptible to PMB. In addition, of the TGC-susceptible isolates, 49 strains (66.2%) exhibited heteroresistant phenotypes. All of the PMB-susceptible isolates showed heteroresistant phenotypes. Forty-six isolates (48.4%) were heteroresistant to both TGC and PMB. All of the isolates carried the bla_KPC gene, and one strain carried both bla_KPC and bla_NDM genes. The time-kill assay revealed in four isolates that early bactericidal activity could be triggered by the combination of PMB and TGC, and there was no regrowth, even at a relatively lower concentration (0.125 mg/liter PMB with 1 mg/liter TGC). Upregulated expression of pmrA, phoP, and acrB indicated that heteroresistance could be related to two-component systems and the AcrAB-TolC efflux pump. The combination of PMB and TGC may be a treatment strategy for those infected with CRKP heteroresistant to PMB and/or TGC. IMPORTANCE Tigecycline and colistin are two of the last treatment options remaining for carbapenem-resistant Enterobacteriaceae. Unfortunately, tigecycline resistance and colistin heteroresistance are also increasing rapidly. In the current study, we identified a high prevalence of heteroresistance to both PMB and TGC among clinical isolates of carbapenem-resistant K. pneumoniae (CRKP). The resistant subpopulations could survive pressure from TGC or PMB but were killed by the combination at a relatively low dose. It is proposed that the combination of PMB and TGC may be a treatment strategy for patients who are infected with CRKP heteroresistant to PMB or TGC.

Successful treatment of pyogenic ventriculitis caused by extensively drug-resistant Acinetobacter baumannii with multi-route tigecycline: A case report

BACKGROUND

Pyogenic ventriculitis caused by extensively drug-resistant Acinetobacter baumannii (A. baumannii) is one of the most severe complications associated with craniotomy. However, limited therapeutic options exist for the treatment of A. baumannii ventriculitis due to the poor penetration rate of most antibiotics through the blood-brain barrier.

CASE SUMMARY

A 68-year-old male patient with severe traumatic brain injury developed pyogenic ventriculitis on postoperative day 24 caused by extensively drug-resistant A. baumannii susceptible to tigecycline only. Successful treatment was accomplished through multi-route administration of tigecycline, including intravenous combined with continuous ventricular irrigation plus intraventricular administration. The pus was cleared on the 3^rd day post-irrigation, and cerebrospinal fluid cultures were negative after 12 d.

CONCLUSION

Our findings suggest that multi-route administration of tigecycline can be a therapeutic option against pyogenic ventriculitis caused by extensively drug-resistant A. baumannii.

New Carbapenemase Inhibitors: Clearing the Way for the β-Lactams

Carbapenem resistance is a major global health problem that seriously compromises the treatment of infections caused by nosocomial pathogens. Resistance to carbapenems mainly occurs via the production of carbapenemases, such as VIM, IMP, NDM, KPC and OXA, among others. Preclinical and clinical trials are currently underway to test a new generation of promising inhibitors, together with the recently approved avibactam, relebactam and vaborbactam. This review summarizes the main, most promising carbapenemase inhibitors synthesized to date, as well as their spectrum of activity and current stage of development. We particularly focus on β-lactam/β-lactamase inhibitor combinations that could potentially be used to treat infections caused by carbapenemase-producer pathogens of critical priority. The emergence of these new combinations represents a step forward in the fight against antimicrobial resistance, especially in regard to metallo-β-lactamases and carbapenem-hydrolysing class D β-lactamases, not currently inhibited by any clinically approved inhibitor.

Acinetobacter baumannii Sequence Types Harboring Genes Encoding Aminoglycoside Modifying Enzymes and 16SrRNA Methylase; a Multicenter Study from Pakistan

Introduction

The aminoglycosides are widely used for the therapeutic management of infections caused by gram-negative bacteria, including the Acinetobacter baumannii strains. However, the resistance to the members of the aminoglycoside family, such as amikacin, gentamicin, and tobramycin, is increasingly being common among the clinical isolates.

Purpose

This study aimed to investigate the presence of 16SrRNA methylases and aminoglycoside modifying enzymes (AMEs) genes among aminoglycoside resistant A. baumannii isolates and to study the genetic diversity of the clinical population of A. baumannii in local hospitals.

Material and Methods

The 143 A. baumannii clinical strains were analyzed for antimicrobial susceptibility, genetic screening for enzymes conferring aminoglycosides resistance followed by the multilocus sequence typing.

Results

The 133/143 (93%) isolates were non-susceptible to at least one of the tested aminoglycosides, including amikacin, gentamicin, and tobramycin. The MIC distribution has shown that 87.486.7% strains were resistant to amikacin and gentamicin, respectively. The aphA6, aadB, aacC1, and aphA1 were found in 74.1%, 59.4%, 16.1%, and 11.2% isolates, respectively, whereas the armA was found in 28% of the strains having a higher MIC value (MIC; ≥256µg/mL). The MLST data have shown that the ST589 and ST2 were the most common STs and corresponded to 51 (35.7%) and 38 (26.6%) isolates, respectively, and few of the isolates corresponding to these STs were found to harbor the armA gene with a variable genotypic profile for AMEs.

Discussion

The study has reported the incidence of various enzymes conferring aminoglycoside resistance among the A. baumannii clones for the first time from Pakistan. The findings suggest the possibility of transmission of aminoglycoside resistance determinants through the lateral gene transfer as well as clonal dissemination.

Tigecycline Therapy for Infections Caused by Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae in Critically Ill Patients

: We aimed to evaluate tigecycline on the clinical effectiveness in treating complicated skin and soft tissue infections (cSSTI), complicated intra-abdominal infections (cIAI), and pneumonia, caused by extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae, as data are limited. From three medical centers in Taiwan, we retrospectively studied the cSSTI, cIAI, and/or pneumonia caused by ESBL-producing Enterobacteriaceae. Among the 71 patients, including 39 patients infected with Klebsiella pneumoniae, 30 infected with Escherichia coli and others, the clinical success rate of tigecycline-based therapy was 80%-90% for pneumonia and cSSTI caused by E. coli and 50%-60% for cIAI caused by K. pneumoniae and E. coli. Microbiological and clinical outcome of pneumonia caused by carbapenem-resistant K. pneumoniae was poor. Univariate Cox analysis showed that dyspnea, SOFA score, septic shock, thrombocytopenia, prolonged prothrombin time, and lesser microbiological eradication were significant factors associated with 30-day mortality after the end of therapy. Cox regression proportional hazards model revealed dyspnea and a SOFA score > 8 to be independently associated with time to death. For ESBL producers, tigecycline showed good effects for cSSTI and pneumonia by E. coli, ordinary for cIAI, but ineffective for pneumonia by K. pneumoniae. Dyspnea and a high SOFA score predict a poor outcome.

The global prevalence of Daptomycin, Tigecycline, Quinupristin/Dalfopristin, and Linezolid-resistant Staphylococcus aureus and coagulase-negative staphylococci strains: a systematic review and meta-analysis

Objective

Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) are among the main causes of nosocomial infections, which have caused major problems in recent years due to continuously increasing spread of various antibiotic resistance features. Apparently, vancomycin is still an effective antibiotic for treatment of infections caused by these bacteria but in recent years, additional resistance phenotypes have led to the accelerated introduction of newer agents such as linezolid, tigecycline, daptomycin, and quinupristin/dalfopristin (Q/D). Due to limited data availability on the global rate of resistance to these antibiotics, in the present study, the resistance rates of S. aureus, Methicillin-resistant S. aureus (MRSA), and CoNS to these antibiotics were collected.

Method

Several databases including web of science, EMBASE, and Medline (via PubMed), were searched (September 2018) to identify those studies that address MRSA, and CONS resistance to linezolid, tigecycline, daptomycin, and Q/D around the world.

Result

Most studies that reported resistant staphylococci were from the United States, Canada, and the European continent, while African and Asian countries reported the least resistance to these antibiotics. Our results showed that linezolid had the best inhibitory effect on S. aureus. Although resistances to this antibiotic have been reported from different countries, however, due to the high volume of the samples and the low number of resistance, in terms of statistical analyzes, the resistance to this antibiotic is zero. Moreover, linezolid, daptomycin and tigecycline effectively (99.9%) inhibit MRSA. Studies have shown that CoNS with 0.3% show the lowest resistance to linezolid and daptomycin, while analyzes introduced tigecycline with 1.6% resistance as the least effective antibiotic for these bacteria. Finally, MRSA and CoNS had a greater resistance to Q/D with 0.7 and 0.6%, respectively and due to its significant side effects and drug-drug interactions; it appears that its use is subject to limitations.

Conclusion

The present study shows that resistance to new agents is low in staphylococci and these antibiotics can still be used for treatment of staphylococcal infections in the world.

Antimicrobial susceptibility among Streptococcus pneumoniae and Haemophilus influenzae collected globally between 2015 and 2017 as part of the Tigecycline Evaluation and Surveillance Trial (TEST)

Purpose: In order to understand the prevalence of Streptococcus pneumoniae and Haemophilus influenzae globally and provide the basis for rational use of antimicrobials in clinical settings, in vitro activity of tigecycline and comparative agents was evaluated against 3929 S. pneumoniae and 4043 H. influenzae isolates obtained from 150 centers globally between 2015 and 2017 as a part of the Tigecycline Evaluation and Surveillance Trial (TEST). Methods: Broth microdilution methods were performed to determine the minimum inhibitory concentration (MIC) of the isolates according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI). The CLSI breakpoint was used to determine antimicrobial susceptibilities, except for that of tigecycline, for which the US Food and Drug Administration (FDA) breakpoints were used. Results: More than 99% of S. pneumoniae isolates were susceptible to vancomycin (100%), linezolid (100%), tigecycline (99.9%), and levofloxacin (99.1%). Macrolides (erythromycin, azithromycin, and clarithromycin, 67.1-69.4% susceptibility globally) and penicillin (61.7% in globally) were the drugs with more resisitance to S. pneumoniae. Penicillin-intermediate and -resistant isolates were found in 24.8% and 13.6% of S. pneumoniae isolates. H. influenzae was highly susceptible (>98.7%) to all antibiotics tested except for ampicillin, for which susceptibility was 76.1%. The number of drugs with the lowest susceptibility calculated in Asia were far more than other regions, with 61.5% (8 in 13 drugs) in S. pneumoniae and 70.0% (7 in 10 drugs) in H. influenzae, respectively. Conclusions: Vancomycin, linezolid, tigecycline, and levofloxacin can be used as the first choice in the empirical therapy of infection disease caused by S. pneumoniae. But macrolides and penicillin should be used prudently in treatment of the infection caused by S. pneumoniae, as well as ampicillin treat the infection caused by H. influenzae. Asia was the region with the most severe resistance in S. pneumoniae and H. influenzae.

Antibiotic Resistance and the MRSA Problem

Staphylococcus aureus is capable of becoming resistant to all classes of antibiotics clinically available and resistance can develop through de novo mutations in chromosomal genes or through acquisition of horizontally transferred resistance determinants. This review covers the most important antibiotics available for treatment of S. aureus infections and a special emphasis is dedicated to the current knowledge of the wide variety of resistance mechanisms that S. aureus employ to withstand antibiotics. Since resistance development has been inevitable for all currently available antibiotics, new therapies are continuously under development. Besides development of new small molecules affecting cell viability, alternative approaches including anti-virulence and bacteriophage therapeutics are being investigated and may become important tools to combat staphylococcal infections in the future.

Antimicrobial susceptibility among gram-positive and gram-negative blood-borne pathogens collected between 2012-2016 as part of the Tigecycline Evaluation and Surveillance Trial

Background

Antimicrobial activity of tigecycline and comparator agents was assessedin vitroagainst 27857 isolates source from blood samples collected between 2012 and 2016 as part of the Tigecycline Evaluation and Surveillance Trial (TEST).

Methods

The broth microdilution methods was used to determine  minimum inhibitory concentrations (MIC) of blood-borne isolates according to guildlines of the Clinical and Laboratory Standards Institute (CLSI). Antimicrobial susceptibility breakpoints from CLSI guidelines were used as standards to determine susceptibility against comparator agents, whereas tigecycline breakpoints were provided by the US Food and Drug Administration (FDA).

Results

More than 91% Enterobacteriaceae isolates, belonging to Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacaeandSerratia marcescens, were susceptible to amikacin, meropenem, and tigecycline. Meropenem resistance was observed in 8% ofK.pneumoniae isolates worldwide. Extended-spectrum β-lactamase (ESBL) was produced in 15.9 and 20.9%E.coli and K.pneumoniaeisolates, respectively. MIC₉₀ of tigecycline against Acinetobacter baumannii was 2 μg/ml.  The highest proportion of susceptible A.baumanniiisolates was 70.8% for minocycline. Among P.aeruginose  isolates worldwide, 71.1-94.9% were susceptible to six antibiotics. Almost all Staphylococcus aureusisolates were susceptible to linezolid(100%), vancomycin(100%), and tigecycline (99.9%). The proportion of methicillin-resistant S.aureus (MRSA) was 33.0% among S.aureusisolates worldwide; it was highest in Asia with 46.6%, followed by North America and Latin America with 37.7 and 34.2%, respectively. Vancomycin-resistant (VR) isolates represented 1.4% ofEnterococcus faecalis (VR.E.faecalis) and 27.6% of Enterococcus faecium(VR.E.faecium). Highest percentages of VR.E.faeciumwere found in North America and Latin America, with 61.6 and 58.1% of the isolates, respectively. Production of penicillin-resistant Streptococcus pneumoniae(PRSP) represented 9.0% of S. pneumoniae isolates worldwide; the PRSP proportion was 25.8% in Asia, 13.0% in Africa, and 11.8% in Latin America.

Conclusions

In our study, tigecycline was the only antibiotic that was active against over 90% of all major blood-borne pathogens. A global comparison revealed that antimicrobial resistance was higher in Africa, Asia and Latin America than in Europe and North America.

In vitro activity of tigecycline and comparators (2014-2016) among key WHO 'priority pathogens' and longitudinal assessment (2004-2016) of antimicrobial resistance: a report from the T.E.S.T. study

We report contemporary (2014-2016) Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) global data on activity of tigecycline and comparators against WHO 'priority pathogens', and global trends (2004-2016) in antimicrobial resistance. MICs were determined using CLSI broth microdilution methodology. Antimicrobial resistance was determined using CLSI breakpoints (FDA breakpoints for tigecycline). Data are reported for Africa, Asia, Europe, North America and South America. From 2014-2016, Africa, Asia and South America reported highest resistance rates among Acinetobacter baumannii; North America lowest (all antimicrobials tested). The tigecycline MIC₉₀ against A. baumannii was 2 mg/L in all regions except South America (1 mg/L). Among Enterobacteriaceae, meropenem resistance was low and tigecycline resistance was ≤1.3% in all regions (Escherichia coli, 0.0-0.3%; Klebsiella pneumoniae 0.0-1.3%; Enterobacter spp. 0.5-1.1%; Serratia marcescens 0.0-1.3%). Ceftriaxone resistance among E. coli ranged from 14.5% (North America) to 54.7% (Asia), and among K. pneumoniae from 9.1% (North America) to 54.0% (South America). North America reported highest rates of vancomycin-resistant Enterococcus faecium (64.6%); Europe lowest (17.7%). The tigecycline MIC₉₀ against methicillin-resistant Staphylococcus aureus (MRSA) ranged from 0.12 mg/L (Africa and North America) to 0.5 mg/L (Asia). From 2004-2016, carbapenem resistance increased among A. baumannii (all regions), reaching 92.3% in Africa and 85.7% in South America (2016). Rates of ceftriaxone-resistant E. coli increased in all regions except Asia. Ceftriaxone resistance in K. pneumoniae increased in Europe. Rates of vancomycin-resistant E. faecium and MRSA were highest in North America and South America (and Asia for MRSA); lowest in Europe.

Stenotrophomonas maltophilia colonization during allogeneic hematopoietic stem cell transplantation is associated with impaired survival

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) offers potential cure to acute myeloid leukemia (AML) patients. However, infections with commensal bacteria are an important cause for non-relapse mortality (NRM). We have previously described the impact of multidrug-resistant organism (MDRO) colonization on the survival of allo-HSCT patients. In the aforementioned publication, according to consensus, we there did not consider the opportunistic gram-negative bacterium Stenotrophomonas maltophilia (S. maltophilia) to be an MDRO. Since rate of S. maltophilia colonization is increasing, and it is not known whether this poses a risk for allo-HSCT patients, we here analyzed here its effect on the previously described and now extended patient cohort. We report on 291 AML patients undergoing allo-HSCT. Twenty of 291 patients (6.9%) were colonized with S. maltophilia. Colonized patients did not differ from non-colonized patients with respect to their age, remission status before allo-HSCT, donor type and HSCT-comorbidity index. S. maltophilia colonized patients had a worse overall survival (OS) from 6 months up to 60 months (85% vs. 88.1% and 24.7% vs. 59.7%; p = 0.007) due to a higher NRM after allo-HSCT (6 months: 15% vs. 4.8% and 60 months: 40.1% vs. 16.2% p = 0.003). The main cause of mortality in colonized patients was infection (46.2% of all deaths) and in non-colonized patients relapse (58.8% of all deaths). 5/20 colonized patients developed an invasive infection with S. maltophilia. The worse OS after allo-HSCT due to higher infection related mortality might implicate the screening of allo-HSCT patients for S. maltophilia and a closer observation of colonized patients as outpatients.

Surveillance of tigecycline activity tested against clinical isolates from a global (North America, Europe, Latin America and Asia-Pacific) collection (2016)

Tigecycline and comparators were tested by the reference broth microdilution method against 33 348 non-duplicate bacterial isolates collected prospectively in 2016 from medical centres in the Asia-Pacific (3443 isolates), Europe (13 530 isolates), Latin America (3327 isolates) and the USA (13 048 isolates). Among 7098 Staphylococcus aureus isolates tested, >99.9% were inhibited by ≤0.5 mg/L tigecycline (MIC_50/90, 0.06/0.12 mg/L), including >99.9% of methicillin-resistant S. aureus and 100.0% of methicillin-susceptible S. aureus. Tigecycline was slightly more active against Enterococcus faecium (MIC_50/90, 0.03/0.06 mg/L) compared with Enterococcus faecalis (MIC_50/90, 0.06/0.12 mg/L) and its activity was not adversely affected by vancomycin resistance when tested against these organisms. Tigecycline potency was comparable for Streptococcus pneumoniae (MIC_50/90, 0.03/0.06 mg/L), viridans group streptococci (MIC_50/90, 0.03/0.06 mg/L) and β-haemolytic streptococci (MIC_50/90, 0.06/0.06 mg/L) regardless of species and penicillin susceptibility. Tigecycline was active against Enterobacteriaceae (MIC_50/90, 0.25/1 mg/L; 97.8% inhibited at ≤2 mg/L) but was slightly less active against Enterobacteriaceae isolates expressing resistant phenotypes: carbapenem-resistant Enterobacteriaceae (MIC_50/90, 0.5/2 mg/L; 98.0% susceptible); multidrug-resistant (MIC_50/90, 0.5/2 mg/L; 93.1% susceptible); and extensively drug-resistant (MIC_50/90, 0.5/4 mg/L; 87.8% susceptible). Tigecycline inhibited 74.4% of 888 Acinetobacter baumannii isolates at ≤2 mg/L (MIC_50/90, 2/4 mg/L) and demonstrated good in vitro activity against Stenotrophomonas maltophilia (MIC_50/90, 1/2 mg/L; 90.6% inhibited at ≤2 mg/L) Tigecycline was active against Haemophilus influenzae (MIC_50/90, 0.12/0.25 mg/L) regardless of β-lactamase status. Tigecycline represents an important treatment option for resistant Gram-negative and Gram-positive bacterial infections.

The Surgical Infection Society Revised Guidelines on the Management of Intra-Abdominal Infection

BACKGROUND

Previous evidence-based guidelines on the management of intra-abdominal infection (IAI) were published by the Surgical Infection Society (SIS) in 1992, 2002, and 2010. At the time the most recent guideline was released, the plan was to update the guideline every five years to ensure the timeliness and appropriateness of the recommendations.

METHODS

Based on the previous guidelines, the task force outlined a number of topics related to the treatment of patients with IAI and then developed key questions on these various topics. All questions were approached using general and specific literature searches, focusing on articles and other information published since 2008. These publications and additional materials published before 2008 were reviewed by the task force as a whole or by individual subgroups as to relevance to individual questions. Recommendations were developed by a process of iterative consensus, with all task force members voting to accept or reject each recommendation. Grading was based on the GRADE (Grades of Recommendation Assessment, Development, and Evaluation) system; the quality of the evidence was graded as high, moderate, or weak, and the strength of the recommendation was graded as strong or weak. Review of the document was performed by members of the SIS who were not on the task force. After responses were made to all critiques, the document was approved as an official guideline of the SIS by the Executive Council.

RESULTS

This guideline summarizes the current recommendations developed by the task force on the treatment of patients who have IAI. Evidence-based recommendations have been made regarding risk assessment in individual patients; source control; the timing, selection, and duration of antimicrobial therapy; and suggested approaches to patients who fail initial therapy. Additional recommendations related to the treatment of pediatric patients with IAI have been included.

SUMMARY

The current recommendations of the SIS regarding the treatment of patients with IAI are provided in this guideline.

Emerging trends in antibiotic resistance: Implications for emergency medicine

BACKGROUND

Many bacteria are demonstrating increasing levels of resistance to commonly used antibiotics. While this has implications for the healthcare system as a whole, many patients infected with these resistant organisms will initially present to the emergency department (ED). The purpose of this review is to provide a summary of current trends in infections caused by the most clinically relevant resistant organisms encountered in emergency medicine.

METHODS

Bacteria were selected based on the Centers for Disease Control and Prevention's National Action Plan for Combating Antibiotic Resistant Bacteria, and PubMed database.

RESULTS

The following bacteria were included: methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococci, Escherichia coli, carbapenem-resistant Enterobacteriaceae, Neisseria gonorrhoeae, and Pseudomonas aeruginosa. All have shown increasing rates of resistance to one or more of the antibiotics commonly used to treat them. Increasing rates of antibiotic resistance are associated with worse clinical outcomes and greater healthcare costs.

CONCLUSIONS

Antibiotic resistance is increasing and poses significant a risk to both the patient and public health as a whole. Appropriate choice of initial antibiotic is important in improving clinical outcomes, which is often the role of the ED provider. On a broader level, the ED must also take part in institutional efforts such as Antibiotic Stewardship Programs, which have been shown to decrease costs and rates of infection with resistant organisms. Ultimately, a multifaceted approach will be required to curb the threat of antibiotic-resistant bacteria.

Surveillance of Dihydropteroate Synthase Genes in Stenotrophomonas maltophilia by LAMP: Implications for Infection Control and Initial Therapy

Stenotrophomonas maltophilia is a common nosocomial pathogen that causes high morbidity and mortality. Because of its inherent extended antibiotic resistance, therapeutic options for S. maltophilia are limited, and sulfamethoxazole/trimethoprim (SXT) is the only first-line antimicrobial recommended. However, with the spread of dihydropteroate synthase (sul1 and sul2) genes, global emergence of SXT resistance has been reported. There is an urgent need to develop a rapid and sensitive but cost-efficient method to monitor the dissemination of sul genes. In this study, we developed loop-mediated isothermal amplification (LAMP) assays for sul1 and sul2 using real-time turbidity and hydroxy naphthol blue coloration methods. The assays could quickly detect sul genes with high sensitivity and specificity. The LAMP detection limit was 0.74 pg/reaction of extracted genomic DNA for sul1 and 2.6 pg/reaction for sul2, which were both 10-fold more sensitive than the corresponding traditional PCR assays. Additionally, the LAMP assays could positively amplify DNA from sul1-producing strains, but not from the negative controls. We then used the LAMP assays to investigate the dissemination of sul genes among S. maltophilia isolates from patients in three hospitals in Beijing, China. Among 450 non-duplicated samples collected during 2012–2014, 56 (12.4%) strains were SXT-resistant. All these SXT-resistant strains were positive for sul genes, with 35 (62.5%) carrying sul1, 17 (30.4%) carrying sul2, and 4 (7.1%) carrying both sul1 and sul2, which indicated that sul genes were the predominant resistance mechanism. Of 394 SXT-susceptible strains, 16 were also sul-positive. To provide epidemiological data for the appropriate choice of antimicrobials for treatment of sul-positive S. maltophilia, we further tested the susceptibility to 18 antimicrobials. Among these, sul-positive strains showed the highest susceptibility to tetracycline derivatives, especially minocycline (MIC₅₀/MIC₉₀, 0.5/4; susceptibility rate, 95.4%). Ticarcillin-clavulanate and new fluoroquinolones (moxifloxacin and levofloxacin) also showed some in vitro activity. Apart from these three kinds of antimicrobials, other agents showed poor activity against sul-positive strains.

Update on ventilator-associated pneumonia

PURPOSE OF REVIEW

To highlight the importance of escalating pathogen resistance in ventilator-associated pneumonia (VAP) along with diagnostic and treatment implications.

RECENT FINDINGS

In a period of rising bacterial resistance, VAP remains an important infection occurring in critically ill patients. Risk factors for multidrug-resistant pathogens depend on both local epidemiology and host factors. New diagnostic techniques and antimicrobials can help with rapid bacterial identification and timely and appropriate treatment while avoiding emergence of bacterial resistance.

SUMMARY

Clinicians should be aware of risk factors for multidrug-resistant pathogens causing VAP and also of particularities of diagnosis and treatment of this important clinical entity.

Pathogen Prevalence and Antimicrobial Susceptibility Among Enterobacteriaceae Causing Hospital-associated Intra-abdominal Infections in Adults in the United States (2012-2013)

PURPOSE

Selection and prompt initiation of the appropriate empiric antimicrobial therapy are critical to decrease morbidity and mortality and shorten the length of hospitalization among patients with hospital-associated intra-abdominal infections (HA-IAIs). Therapeutic choices for the treatment of patients with HA-IAI require careful consideration. This study was conducted to evaluate the antimicrobial susceptibility of common pathogens collected from adult patients with HA-IAI in the United States.

METHODS

Gram-negative bacilli (N = 1285) were collected during 2012-2013 from SMART (Study for Monitoring Antimicrobial Resistance Trends). Isolates were tested at a central laboratory by using Clinical and Laboratory Standards Institute methods and interpretation of susceptibility to 12 antimicrobial agents.

FINDINGS

Most of the isolates (80.8%) were Enterobacteriaceae, and Escherichia coli was the most common species. Susceptibility to frequently used antimicrobial agents for treating IAI showed that ertapenem, imipenem, and amikacin were more active than other agents against Enterobacteriaceae, including multidrug-resistant isolates. More than 92% of E coli, including extended-spectrum β-lactamase (ESBL) producers, and Klebsiella pneumoniae isolates were susceptible to ertapenem, imipenem, and amikacin. Cefepime was the most active (>90% susceptibility) cephalosporin against all species except K pneumoniae (86.6%) but with much reduced activity against isolates with ESBLs. Piperacillin/tazobactam had reduced activity against Enterobacter species (70.4%-76.4% susceptible) and ESBL-producing K pneumoniae (22.5% susceptible). Fluoroquinolones exhibited poor activity against E coli (overall susceptibility <70%).

IMPLICATIONS

Proper empiric antimicrobial treatment, including combining appropriate agents, of HA-IAI requires detailed understanding of the epidemiology of common pathogens and antimicrobial resistance patterns. In light of rising rates of antimicrobial resistance, ongoing surveillance is critical for clinical decision-making.

Tetracycline Antibiotics and Resistance

Tetracyclines possess many properties considered ideal for antibiotic drugs, including activity against Gram-positive and -negative pathogens, proven clinical safety, acceptable tolerability, and the availability of intravenous (IV) and oral formulations for most members of the class. As with all antibiotic classes, the antimicrobial activities of tetracyclines are subject to both class-specific and intrinsic antibiotic-resistance mechanisms. Since the discovery of the first tetracyclines more than 60 years ago, ongoing optimization of the core scaffold has produced tetracyclines in clinical use and development that are capable of thwarting many of these resistance mechanisms. New chemistry approaches have enabled the creation of synthetic derivatives with improved in vitro potency and in vivo efficacy, ensuring that the full potential of the class can be explored for use against current and emerging multidrug-resistant (MDR) pathogens, including carbapenem-resistant Enterobacteriaceae, MDR Acinetobacter species, and Pseudomonas aeruginosa.

In vitro selection of Staphylococcus aureus mutants resistant to tigecycline with intermediate susceptibility to vancomycin

Background

Tigecycline (TIG) is an antibiotic belonging to the glycylcyclines class and appears to be a good choice to fight infections caused by Staphylococcus aureus. To date, TIG exhibits good activity against this microorganism. The aim of this work was to obtain in vitro mutants of S. aureus resistant to TIG and evaluate possible changes in their susceptibility patterns to other antibiotics.

Results

Two mutants of S. aureus resistant to TIG (MIC = 16 µg/mL) were selected in vitro from clinical isolates of methicillin-resistant S. aureus. In both mutants, corresponding to different lineage (ST5 and ST239), an increase of efflux activity against TIG was detected. One mutant also showed a reduced susceptibility to vancomycin, corresponding to the VISA phenotype (MIC = 4 µg/mL), with a loss of functionality of the agr locus. The emergence of the VISA phenotype was accompanied by an increase in oxacillin and cefoxitin MICs.

Conclusions

This study demonstrates that, under selective pressure, the increase of efflux activity in S. aureus is one of the mechanisms that may be involved in the emergence of tigecycline resistance. The emergence of this phenotype may eventually be associated to changes in susceptibility to other antibiotics such oxacillin and vancomycin.

Carbapenem resistance: overview of the problem and future perspectives

Carbapenem resistance, mainly among Gram-negative pathogens, is an ongoing public-health problem of global dimensions. This type of antimicrobial resistance, especially when mediated by transferable carbapenemase-encoding genes, is spreading rapidly causing serious outbreaks and dramatically limiting treatment options. In this article, important key points related to carbapenem resistance are reviewed and future perspectives are discussed.

Carbapenem-Resistant Enterobacteriaceae Infections in Children

Carbapenem-resistant Enterobacteriaceae (CRE) are an emerging global public health threat. Infections due to CRE are associated with significant morbidity and mortality. Few therapeutic options are available for treatment of these infections, and optimal antibiotic treatment regimens are unclear. Along with the rapidly increasing prevalence of CRE in the USA and worldwide, several studies have described the epidemiology of CRE in the adult population. While CRE are now also reported sporadically in children, there is a significant lack of data on the epidemiology, risk factors, treatment, and outcomes in this population. This article provides a comprehensive review of what is known to date about CRE, including clinical and molecular epidemiology, microbiologic diagnosis, antibiotic treatment options, and outcomes. In particular, this review will focus on the available data on CRE in the pediatric population.

Tigecycline resistance in clinical isolates of Enterococcus faecium is mediated by an upregulation of plasmid-encoded tetracycline determinants tet(L) and tet(M)

OBJECTIVES

Tigecycline represents one of the last-line therapeutics to combat multidrug-resistant bacterial pathogens, including VRE and MRSA. The German National Reference Centre for Staphylococci and Enterococci has received 73 tigecycline-resistant Enterococcus faecium and Enterococcus faecalis isolates in recent years. The precise mechanism of how enterococci become resistant to tigecycline remains undetermined. This study documents an analysis of the role of efflux pumps in tigecycline resistance in clinical isolates of Enterococcus spp.

METHODS

Various tigecycline MICs were found for the different isolates analysed. Tigecycline-resistant strains were analysed with respect to genome and transcriptome differences by means of WGS and RT-qPCR. Genes of interest were cloned and expressed in Listeria monocytogenes for verification of their functionality.

RESULTS

Detailed comparative whole-genome analyses of three isogenic strains, showing different levels of tigecycline resistance, revealed the major facilitator superfamily (MFS) efflux pump TetL and the ribosomal protection protein TetM as possible drug resistance proteins. Subsequent RT-qPCR confirmed up-regulation of the respective genes. A correlation of gene copy number and level of MIC was inferred from further qPCR analyses. Expression of both tet(L) and tet(M) in L. monocytogenes unequivocally demonstrated the potential to increase tigecycline MICs upon acquisition of either locus.

CONCLUSIONS

Our results indicate that increased expression of two tetracycline resistance determinants, a tet(L)-encoded MFS pump and a tet(M)-encoded ribosomal protection protein, is capable of conferring tigecycline resistance in enterococcal clinical isolates.

Update on infections caused by Stenotrophomonas maltophilia with particular attention to resistance mechanisms and therapeutic options

Stenotrophomonas maltophilia is a Gram-negative, biofilm-forming bacterium. Although generally regarded as an organism of low virulence, S. maltophilia is an emerging multi-drug resistant opportunistic pathogen in hospital and community settings, especially among immunocompromised hosts. Risk factors associated with S. maltophilia infection include underlying malignancy, cystic fibrosis, corticosteroid or immunosuppressant therapy, the presence of an indwelling central venous catheter and exposure to broad spectrum antibiotics. In this review, we provide a synthesis of information on current global trends in S. maltophilia pathogenicity as well as updated information on the molecular mechanisms contributing to its resistance to an array of antimicrobial agents. The prevalence of S. maltophilia infection in the general population increased from 0.8-1.4% during 1997-2003 to 1.3-1.68% during 2007-2012. The most important molecular mechanisms contributing to its resistance to antibiotics include β-lactamase production, the expression of Qnr genes, and the presence of class 1 integrons and efflux pumps. Trimethoprim/sulfamethoxazole (TMP/SMX) is the antimicrobial drug of choice. Although a few studies have reported increased resistance to TMP/SMX, the majority of studies worldwide show that S. maltophilia continues to be highly susceptible. Drugs with historically good susceptibility results include ceftazidime, ticarcillin-clavulanate, and fluoroquinolones; however, a number of studies show an alarming trend in resistance to those agents. Tetracyclines such as tigecycline, minocycline, and doxycycline are also effective agents and consistently display good activity against S. maltophilia in various geographic regions and across different time periods. Combination therapies, novel agents, and aerosolized forms of antimicrobial drugs are currently being tested for their ability to treat infections caused by this multi-drug resistant organism.

Global in vitro activity of tigecycline and comparator agents: Tigecycline Evaluation and Surveillance Trial 2004-2013

Background

The Tigecycline Evaluation and Surveillance Trial (TEST) is a global antimicrobial susceptibility surveillance study which has been ongoing since 2004. This report examines the in vitro activity of tigecycline and comparators against clinically important pathogens collected globally between 2004 and 2013.

Methods

Antimicrobial susceptibility was determined using guidelines published by the Clinical and Laboratory Standards Institute. The Cochran Armitage Trend Test was used to identify statistically significant changes in susceptibility between 2004 and 2013.

Results

Among the Enterobacteriaceae susceptibility was highest to the carbapenems [imipenem 97.1% (24,655/25,381), meropenem 97.0% (90,714/93,518)], tigecycline (97.0%, 115,361/118,899) and amikacin (96.9%, 115,200/118,899). Against Acinetobacter baumannii the highest rates of susceptibility were for minocycline (84.5%, 14,178/16,778) and imipenem (80.0%, 3,037/3,795). The MIC₉₀ for tigecycline was 2 mg/L. 40% (6,743/16,778) of A. baumannii isolates were multidrug-resistant. Enterococci were highly susceptible to tigecycline and linezolid (>99%); vancomycin resistance was observed among 2% of Enterococcus faecalis (325/14,615) and 35% of Enterococcus faecium (2,136/6,167) globally. 40% (14,647/36,448) of Staphylococcus aureus were methicillin-resistant while 15% (2,152/14,562) of Streptococcus pneumoniae were penicillin-resistant. Against S. aureus and S. pneumoniae susceptibility to linezolid, vancomycin, and tigecycline was ≥99.9%. Globally, 81% (331/410) of statistically significant susceptibility changes during the study period were decreases in susceptibility.

Conclusions

Amikacin, the carbapenems, and tigecycline were active against most gram-negative pathogens while linezolid, tigecycline, and vancomycin retained activity against most gram-positive pathogens collected in TEST during 2004–2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s12941-015-0085-1) contains supplementary material, which is available to authorized users.

Treatment Options for Carbapenem-Resistant Enterobacteriaceae Infections

This article provides a comprehensive review of currently available treatment options for infections due to carbapenem-resistant Enterobacteriaceae (CRE). Antimicrobial resistance in Gram-negative bacteria is an emerging and serious global public health threat. Carbapenems have been used as the "last-line" treatment for infections caused by resistant Enterobacteriaceae, including those producing extended spectrum ß-lactamases. However, Enterobacteriaceae that produce carbapenemases, which are enzymes that deactivate carbapenems and most other ß-lactam antibiotics, have emerged and are increasingly being reported worldwide. Despite this increasing burden, the most optimal treatment for CRE infections is largely unknown. For the few remaining available treatment options, there are limited efficacy data to support their role in therapy. Nevertheless, current treatment options include the use of older agents, such as polymyxins, fosfomycin, and aminoglycosides, which have been rarely used due to efficacy and/or toxicity concerns. Optimization of dosing regimens and combination therapy are additional treatment strategies being explored. Carbapenem-resistant Enterobacteriaceae infections are associated with poor outcomes and high mortality. Continued research is critically needed to determine the most appropriate treatment.

Description and validation of a spectrum score method to measure antimicrobial de-escalation in healthcare associated pneumonia from electronic medical records data

BACKGROUND

Comparison of antimicrobial de-escalation rates between healthcare settings is problematic. To objectively and electronically measure de-escalation a method based upon the spectrum of antimicrobial regimens administered (i.e., spectrum score) was developed.

METHODS

A Delphi process was used to develop applicable concepts. Spectrum scores were created for 27 antimicrobials based upon susceptibility for 19 organisms. National VA susceptibility data was used to estimate microbial spectrum. Susceptibility estimates were converted to ordinal scores, and values for organisms with multi-drug resistance potential were weighted more heavily. Organism scores were summed to create antibiotic-specific spectrum scores and extended mathematically to score multi-antimicrobial regimens. Vignettes were created from antimicrobial regimens administered to 300 patients hospitalized with pneumonia. Daily spectrum scores were calculated for each case. Hospitalization day 4 scores were subtracted from day 2 scores (i.e., spectrum score ∆). A positive spectrum score ∆ defined de-escalation. Experts ranked each pneumonia case on a 7-point Likert scale (Likert >4 indicated de-escalation). Spectrum score ∆s were compared to expert review. Findings were used to identify score deficiencies. Next, 40 pairs of cases were modified to include antimicrobial administration routes. Each pair contained almost similar regimens; however, one contained oral (PO) the other only intravenous (IV) antimicrobials on day 4 of therapy. Experts reviewed cases as described. Spectrum score ∆ credits to account for PO conversion were derived from the mean paired differences in Likert Score. De-escalation status was evaluated in 100 vignettes containing antimicrobial route by different experts and compared to the modified method.

RESULTS

Initial sensitivity and specificity of the spectrum score ∆ to detect expert classified de-escalation events was 86.3 and 96.0%, respectively. In paired cases, the mean (± SD) Likert score was 5.0 (1.5) and 4.6 (1.5) for PO and IV (P = 0.002), respectively. To improve de-escalation event detection, two credits were added to spectrum score ∆s based upon the percentage of antimicrobials administered PO on day 4. The final method, exhibited sensitivity and specificity to detect expert classified de-escalation events of 96.2 and 93.6%, respectively.

CONCLUSIONS

The final spectrum score method exhibited excellent agreement with expert judgments of de-escalation events in pneumonia.

Tigecycline : a critical safety review

INTRODUCTION

The emergence of multidrug-resistant (MDR) infections has been extensively observed worldwide and has become a priority issue over past decade. Tigecycline , a broad spectrum antibiotic covering against many MDR organisms, has been widely used. However, recent meta-analysis studies have raised a concern for its efficacy and safety. Reviewing tigecycline safety data would enhance the appropriate use of this medication.

AREAS COVERED

This article reviews the safety profile of tigecycline, including its side effects and drug interactions.

EXPERT OPINION

The increased mortality associated with tigecycline is not yet well understood. Based on current evidence, alternative options must be prioritized over tigecycline if available. When tigecycline use is warranted, vigilant observation to identify any breakthrough infections and careful monitoring of progression of the original infection are highly recommended. Considering a second agent (either for synergism or enhancing coverage) may be required.

Tigecycline therapy for carbapenem-resistant Klebsiella pneumoniae (CRKP) bacteriuria leads to tigecycline resistance

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is an increasing global threat. Here, we describe the prevalence and impact of tigecycline use in a cohort of patients with CRKP bacteriuria nested within a multicentre, prospective study. In the 21-month study period, 260 unique patients were included. Tigecycline was given to 80 (31%) patients. The use of tigecycline during the index hospitalization was significantly associated with the subsequent development of tigecycline resistance in the same patient (OR, 6.13; 95% CI, 1.15-48.65; p 0.03). In conclusion, the use of tigecycline with CRKP bacteriuria is common, and is associated with the subsequent development of tigecycline resistance.

Emerging novel and antimicrobial-resistant respiratory tract infections: new drug development and therapeutic options

The emergence and spread of antimicrobial-resistant bacterial, viral, and fungal pathogens for which diminishing treatment options are available is of major global concern. New viral respiratory tract infections with epidemic potential, such as severe acute respiratory syndrome, swine-origin influenza A H1N1, and Middle East respiratory syndrome coronavirus infection, require development of new antiviral agents. The substantial rise in the global numbers of patients with respiratory tract infections caused by pan-antibiotic-resistant Gram-positive and Gram-negative bacteria, multidrug-resistant Mycobacterium tuberculosis, and multiazole-resistant fungi has focused attention on investments into development of new drugs and treatment regimens. Successful treatment outcomes for patients with respiratory tract infections across all health-care settings will necessitate rapid, precise diagnosis and more effective and pathogen-specific therapies. This Series paper describes the development and use of new antimicrobial agents and immune-based and host-directed therapies for a range of conventional and emerging viral, bacterial, and fungal causes of respiratory tract infections.