Journal of Infectious Diseases and Treatment Open Access

Keywords

Oxazolidinone; Pneumonia; Gram-positive

Introduction

Bacterial pneumonia is a leading cause of morbidity and mortality in the United States (US) and Europe and results in substantial antibiotic usage [1-8]. It is now apparent that delaying pathogen-appropriate antimicrobial therapy to patients with either community-acquired (CAP) or hospitalacquired (HAP; nosocomial including ventilator-associated pneumonia [VAP]) pneumonia results in excess mortality [2,3,6,7,9,10].

Given the lack of timely, sensitive, and specific means of diagnosing bacterial pneumonia [2,6,11,12], initial antibiotic selection remains empiric for most patients while considering the suspected etiology, pathogen-directed therapy changes, and antibiotic resistance [1-3,6,10,11]. Although the causes of bacterial pneumonia may vary according to the onset of infection [2,6,12,13], Streptococcus pneumoniae and Staphylococcus aureus are predominant pathogens in CAP and HAP, respectively [1,2,4,6,8,10-13].

A HAP subset that includes patients with substantial exposure to the healthcare setting, so-called healthcareassociated pneumonia (HCAP), was designed to identify patients with pneumonia who may be at greater risk to be infected with resistant organisms [6,9,12,13]. Patients with HCAP generally have greater co-morbidities than other patients with CAP and, in some settings, may be more likely to become infected with organisms such as methicillin-resistant S. aureus (MRSA) in addition to CAP-associated organisms, such as S. pneumoniae [1,9-13]. As such, empiric treatments must adequately cover these key target pathogens, including multidrug-resistant organisms, resulting in the use of 2 or 3-drug regimens to cover >90% of the contemporary pathogens [3,5,7,12].

Tedizolid is an oxazolidinone derivative that exhibits greater potency and spectrum than linezolid when tested against a broad array of gram-positive cocci (GPC) that includes multidrug-resistant phenotypes, such as MRSA, vancomycinresistant enterococci (VRE), and linezolid-resistant phenotypes [14,15]. Importantly, tedizolid demonstrates activity against linezolid-resistant bacterial strains harboring the horizontally transmissible cfr gene in the absence of certain ribosomal mutations conferring reduced oxazolidinone susceptibility [15]. Tedizolid was approved in the US, Europe, and other regions to treat acute bacterial skin and skin structure infections (ABSSSI) and is undergoing Phase 3 clinical trials for treating HAP and VAP [15].

The vast majority of tedizolid in vitro studies confirm the activity and spectrum of this agent against pathogens associated with ABSSSI, but similar data is lacking for the GPC isolated from patients hospitalized with pneumonia [15-18]. In the present study, we employed the CLSI M07-A10 reference broth microdilution (BMD) method to determine the activity of tedizolid and comparator agents when tested against 6,095 GPC collected in US and European medical centers from January 2014 through December 2016 [19]. Antimicrobial susceptibilities of isolates from CAP/HCAP patients were compared to those from HAP patients.

Materials and Methods

Bacterial isolates

A total of 6,019 gram-positive pathogens were analyzed. The organisms were consecutively collected between January 2014 and December 2016 from 63 medical centers located in the US (3,723 isolates, 30 medical centers) and Europe (2,296 isolates, 33 medical centers in 14 countries). Within this collection, a total of 4,198 isolates were from patients hospitalized with pneumonia (CAP/HCAP), and a subset of 1,821 isolates were from patients with documented HAP. All organisms were isolated from documented infections and only 1 organism per patient infection episode was included in the survey. The isolates were all collected from respiratory tract specimens obtained from patients who were hospitalized with pneumonia. Those isolates cultured from clinical specimens obtained within 48 hours of hospital admission were classified as CAP/HCAP and those recovered from specimens obtained after 48 hours of admission were classified as HAP [2,6].

Isolates were identified locally and forwarded to a central monitoring laboratory (JMI Laboratories, North Liberty, Iowa USA) for confirmation of species identification, if necessary (using Vitek2, matrix-assisted laser desorption ionization-time of flight mass spectrometry or manual methods).

Antimicrobial susceptibility testing

Susceptibility testing was performed by BMD following the guidelines of the CLSI [20]. Quality control (QC) and interpretation of MIC results obtained against QC strains were performed according to CLSI M100-S26 [20]. MIC results for tested agents obtained against clinical isolates were interpreted using CLSI M100-S26 and EUCAST v6.0 breakpoint criteria, where published [20,21]. US FDA product package insert criteria were used as an alternative breakpoint source as necessary (e.g., tigecycline).

Results

The frequency of the different organisms isolated from patients with CAP/HCAP and HAP in US and European medical centers is shown in Table 1. The most common organisms from both regions were S. pneumoniae and S. aureus. MRSA accounted for 44.5% of S. aureus isolates from the US and 27.6% from Europe. S. pneumoniae was the predominant organism isolated from patients with CAP/HCAP in both the US (52.0% of all CAP/HCAP isolates) and Europe (90.4%), whereas S. aureus was the predominant organism isolated from HAP patients, accounting for 84.2% of isolates in the US (40.5% MRSA) and 68.2% (20.2% MRSA) in Europe

Table 1: Frequency of gram-positive cocci causing pneumonia in US and European hospitals (2014–2016). Note: US, United States; CAP, community-acquired pneumonia; HCAP, healthcare-associated pneumonia; HAP, hospital-acquired pneumonia; CoNS, coagulase-negative staphylococci; BHS, β-hemolytic streptococci; VGS, viridans group streptococci.

The in vitro activity of tedizolid against GPC isolated from patients hospitalized with pneumonia showed consistent potency over the 3-year study period: the majority of isolates were inhibited at MIC values of ≤ 0.25 mg/L and all isolates of staphylococci, streptococci, and enterococci were inhibited at ≤ 0.5 mg/L (Tables 2 and 3).

Table 2: Activity of tedizolid and comparator antimicrobial agents when tested against isolates causing HAP in US and European hospitals (2014–2016). Note: MSSA, methicillin-susceptible S. aureus; MRSA, methicillin-resistant S. aureus; CoNS, coagulasenegative staphylococci; TMP-SMX, trimethoprim-sulfamethoxazole ^aCriteria as published by CLSI and EUCAST. ^bBreakpoints from FDA Package Insert revised 12/2014. ^cUsing non-meningitis breakpoints. ^dUsing meningitis breakpoints. ^eUsing oral breakpoints.fUsing parenteral, meningitis breakpoints. gUsing parenteral, non-meningitis breakpoints.

Table 2: Antibiotics resistance pattern of organisms isolated.

Table 3: Activity of tedizolid and comparator antimicrobial agents when tested against isolates causing CAP/HCAP in US and European hospitals (2014–2016). Note: MSSA, methicillin-susceptible S. aureus; MRSA, methicillin-resistant S. aureus; CoNS, coagulase-negative staphylococci; TMP-SMX, trimethoprim-sulfamethoxazole. aCriteria as published by CLSI and EUCAST. bBreakpoints from FDA Package Insert revised 12/2014. cUsing non-meningitis breakpoints. dUsing meningitis breakpoints. eUsing oral breakpoints. fUsing parenteral, meningitis breakpoints. gUsing parenteral, non-meningitis breakpoints.

Activity of tedizolid and comparators against HAP isolates

Overall, tedizolid showed MIC50/90 results of 0.12/0.12 mg/L when tested against S. aureus, regardless of the geographic origin, year of isolation, or methicillin susceptibility phenotype (100.0% of isolates inhibited at ≤ 0.5 mg/L) (Table 2). Tedizolid (100.0/100.0% susceptible [US/Europe]) and comparator agents such as linezolid (100.0/100.0% susceptible), vancomycin (100.0/100.0% susceptible), teicoplanin (100.0/100.0% susceptible [US/EU] using CLSI criteria and 99.5/98.9% susceptible using EUCAST criteria), trimethoprim/ sulfamethoxazole (93.6/98.9% susceptible [US/EU]), tetracycline (92.3/91.1% susceptible [US/EU] using CLSI criteria and 88.9/90.6% susceptible using EUCAST criteria), tigecycline (100.0/100.0% susceptible [US/EU]), and ceftaroline (91.8/74.4% susceptible [US/EU]) demonstrated good antimicrobial coverage when tested against MRSA isolates from both regions (Table 2). Comparative analyses showed that tedizolid MIC results (MIC₅₀/MIC₉₀, 0.12/0.12 mg/L [US and EU]) were at least 8-fold lower than these agents, with the exception of tigecycline and trimethoprim/sulfamethoxazole, against US or EU isolates (Table 2).

Although an infrequent cause of HAP, coagulase-negative staphylococcal (CoNS) isolates from the US demonstrated MIC₅₀ values for tedizolid (MIC₅₀, 0.12 mg/L) that were identical to the MIC50 values for isolates from European countries (Table 2). A total of 62.5% and 87.2% of CoNS from the US and Europe, respectively, were methicillin-resistant (MR-CoNS) (Table 1). Overall, tedizolid, vancomycin, tigecycline, teicoplanin, and linezolid demonstrated activity in vitro against CoNS, while other comparators had limited coverage (12.9–80.6% susceptible).

Tedizolid showed comparable activity against S. pneumoniae causing HAP (MIC50/90, 0.12/0.25 mg/L) from both regions, and 100.0% of all isolates were inhibited by ≤ 0.5 mg/L (Table 2). A total of 6.2% and 10.3% of S. pneumoniae from the US and Europe, respectively, were nonsusceptible (MIC, ≥ 2 mg/L) to ceftriaxone and 55.0/51.9% (US/Europe) were nonsusceptible to penicillin (MIC, ≥ 0.12 mg/L). Overall, more than 90% of S. pneumoniae isolates were susceptible to linezolid, amoxicillinclavulanic acid (Europe only), ceftaroline, levofloxacin, and vancomycin. Erythromycin (41.9/61.4% susceptible [US/ Europe]), tetracycline (72.1/63.5% susceptible [US/Europe]), and trimethoprim-sulfamethoxazole (62.8/63.9% susceptible [US/Europe] using CLSI criteria and 64.3/75.5% susceptible using EUCAST criteria) were not active against this S. pneumoniae collection.

Tedizolid exhibited MIC₅₀ results of 0.12 mg/L when tested against β-hemolytic streptococci (BHS) and VGS isolates, respectively, regardless of geographical region (Table 2). Other agents, such as penicillin, vancomycin, teicoplanin, amoxicillinclavulanic acid, ceftaroline, ceftriaxone, linezolid, and levofloxacin demonstrated antimicrobial coverage (100.0% susceptible) against BHS (Table 2). When tested against VGS, tedizolid, linezolid, ceftaroline, ceftriaxone, vancomycin, and levofloxacin were all highly active (Table 2). VGS isolates from Europe were less susceptible to most comparators than US isolates.

Tedizolid (MIC₅₀, 0.12/0.25 mg/L[US/Europe]) was equally active when tested against Enterococcus faecalis from Europe and the US, inhibiting 100.0% of strains at the CLSI breakpoint for susceptibility (≤ 0.5 mg/L) (Table 2). E. faecalis isolates from both regions were all (100.0%) susceptible to ampicillin, vancomycin, teicoplanin, and linezolid (Table 2). These comparator agents had MIC₅₀ results (all MIC₅₀ of ≤ 2 mg/L) that were 4 to 8-fold higher than those obtained for tedizolid, regardless of geographic region. All Enterococcus faecium isolates (90.0/12.5% VRE [US/Europe]) were inhibited by tedizolid at ≤ 0.25 mg/L. Only linezolid showed clinically useful activity against E. faecium among comparators, including VRE isolates (100.0/100.0% susceptible [US/Europe]; Table 2).

Activity of tedizolid and comparators against CAP/HCAP isolates

The activity of tedizolid and comparators against isolates causing CAP/HCAP in US and European hospital patients is shown in Table 3. In contrast to HAP findings, isolates from patients with CAP were predominantly S. pneumoniae (51.9/89.6% of all CAP isolates [US/Europe]) followed by S. aureus (44.1/36.6% of all CAP isolates [US/Europe]) (Tables 1 and 3). Tedizolid was active against all CAP pathogens with 100.0% inhibited by ≤ 0.5 mg/L (Table 3). As with the HAP isolates, linezolid, ceftaroline, teicoplanin, tigecycline (staphylococci), and vancomycin all were active against these GPC.

Discussion

Adequate antimicrobial treatment is key to improving the unacceptably high rates of morbidity and mortality encountered in patients hospitalized with pneumonia [2,3,6,7,9]. Since causative pathogens commonly include MDR GPC, such as MRSA, effective treatments should demonstrate potency against clinically relevant gram-positive pneumonia isolates [12]. Although a clinical trial to evaluate tedizolid for treating ventilator-assisted adult patients with bacterial pneumonia is ongoing, surveillance data can be used to monitor real-world tedizolid activity in patients hospitalized with pneumonia.

This study evaluated the activity in vitro of tedizolid and comparators against a 3-year collection of gram-positive clinical isolates implicated in pneumonia, including MRSA. Overall, tedizolid activity was unchanged over three years and was comparable for isolates from both Europe and the US (data not shown). The in vitro potency of tedizolid was greater than the in vitro potency of the tested comparators, including linezolid. Tedizolid inhibited 100.0% of MRSA isolates at the CLSI and EUCAST approved breakpoint (≤ 0.5 mg/L). Equivalent potency results were observed for tedizolid when tested against isolates from Europe and the US.

In conclusion, tedizolid showed excellent activity against S. aureus (including MRSA), CoNS, S. pneumoniae, BHS, VGS, and enterococci isolated in 2014 through 2016 from patients hospitalized with pneumonia in the US and Europe.

Acknowledgements

The authors wish to thank the following staff members at JMI Laboratories: Castanheira M, Deshpande L, Duncan L, Flanigan L, Janechek M, Huband M, Oberholser J, Rhomberg P, Schuchert J, Streit J, and Woosley L for technical support.

Funding

This study was performed by JMI Laboratories and supported by Merck and Co., Inc., Kenilworth, NJ, USA, which included funding for services related to preparing this manuscript.

Transparency declaration

JMI Laboratories contracted to perform services in 2016 for Achaogen, Actelion, Allecra Therapeutics, Allergan, AmpliPhi Biosciences, API, Astellas Pharma, AstraZeneca, Basilea Pharmaceutica, Bayer AG, BD, Biomodels, Cardeas Pharma Corp., CEM-102 Pharma, Cempra, Cidara Therapeutics, Inc., CorMedix, CSA Biotech, Cutanea Life Sciences, Inc., Debiopharm Group, Dipexium Pharmaceuticals, Inc., Duke, Entasis Therapeutics, Inc., Fortress Biotech, Fox Chase Chemical Diversity Center, Inc., Geom Therapeutics, Inc., GSK, Laboratory Specialists, Inc., Medpace, Melinta Therapeutics, Inc., Merck and Co., Inc., Micromyx, MicuRx Pharmaceuticals, Inc., Motif Bio, N8 Medical, Inc., Nabriva Therapeutics, Inc., Nexcida Therapeutics, Inc., Novartis, Paratek Pharmaceuticals, Inc., Pfizer, Polyphor, Rempex, Scynexis, Shionogi, Spero Therapeutics, Symbal Therapeutics, Synlogic, TenNor Therapeutics, TGV Therapeutics, The Medicines Company, Theravance Biopharma, ThermoFisher Scientific, VenatoRx Pharmaceuticals, Inc., Wockhardt, Zavante Therapeutics, Inc. There are no speakers’ bureaus or stock options to declare.

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