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. 2018 Apr 26;62(5):e02206-17. doi: 10.1128/AAC.02206-17

Evaluation of the In Vitro Activity of Eravacycline against a Broad Spectrum of Recent Clinical Anaerobic Isolates

David R Snydman a,✉, Laura A McDermott a, Nilda V Jacobus a, Kathryn Kerstein b, Trudy H Grossman b,*, Joyce A Sutcliffe b,*
PMCID: PMC5923129  PMID: 29483114

ABSTRACT

The novel fluorocycline antibiotic eravacycline is in development for use in the treatment of serious infections caused by susceptible and multidrug-resistant (MDR) aerobic and anaerobic Gram-negative and Gram-positive pathogens. Eravacycline and 11 comparator antibiotics were tested against recent anaerobic clinical isolates, including MDR Bacteroides spp. and Clostridium difficile. Eravacycline was potent in vitro against all the isolates tested, including strains with tetracycline-specific resistance determinants and MDR anaerobic pathogens resistant to carbapenems and/or β-lactam–β-lactamase inhibitor combinations.

KEYWORDS: eravacycline, anaerobes, Bacteroides, antimicrobial resistance

TEXT

Increased resistance of anaerobic bacteria to standard antibiotics requires the development of new antibiotics for use in mixed aerobic-anaerobic organism infections (1–3). Eravacycline is a novel fluorocycline antibiotic in phase 3 clinical development for the treatment of serious infections due to Gram-negative and Gram-positive aerobic and anaerobic pathogens (4, 5). Eravacycline retains activity against commonly described tetracycline resistance mechanisms, such as tetracycline efflux pumps and ribosomal protection (6, 7), and is active in vitro against Gram-negative aerobic pathogens resistant to other classes of antibiotics, including Acinetobacter baumannii and Enterobacteriaceae expressing extended-spectrum β-lactamases, carbapenemases, and colistin/polymyxin resistance (8–14). The spectrum of eravacycline also includes potency against Gram-positive pathogens, such as methicillin-susceptible and -resistant staphylococci, vancomycin-susceptible and -resistant enterococci, and penicillin-susceptible and -resistant Streptococcus pneumoniae (10, 15). Eravacycline, however, has reduced activity against Pseudomonas aeruginosa and Burkholderia cenocepacia (10).

(These data were presented at the 55th Interscience Conference on Antimicrobial Agents and Chemotherapy, poster C-547, 17 to 21 September 2015, San Diego, CA [16].)

Earlier evaluations showed that eravacycline was potent against a wide variety of anaerobic pathogens in vitro (10, 17); however, the number of isolates in each species was limited and not as representative of antibiotic resistance as is currently seen. To expand and define the in vitro spectrum of eravacycline against anaerobic pathogens, particularly Bacteroides fragilis and Clostridium difficile, eravacycline and comparator antibiotics (tigecycline, minocycline, imipenem, meropenem, piperacillin-tazobactam, ampicillin-sulbactam, moxifloxacin, metronidazole, linezolid, clindamycin, and vancomycin [with Gram-positive isolates only]) were tested against 540 recent anaerobic clinical isolates, including MDR isolates, collected in the United States from 2012 to 2015 at Tufts Medical Center from hospitalized patient cultures and medical centers participating in B. fragilis and C. difficile surveillance studies (1, 3). Prior to testing, identification of the isolates was confirmed using API 20A methodology (bioMérieux, Inc., Durham, NC) and methods outlined in the Wadsworth-KTL anaerobic bacteriology manual (18), including plating on selective media and susceptibility to special potency antimicrobial disks. MIC assays were performed by an agar dilution method according to Clinical and Laboratory Standards Institute (CLSI) recommendations (19) using American Type Culture Collection strains Bacteroides fragilis ATCC 25285, Bacteroides thetaiotaomicron ATCC 29741, Eggerthella lenta ATCC 43055, and Clostridium difficile ATCC 700057 as controls. Percent resistance was calculated using applicable CLSI breakpoints (20), except for tigecycline, for which FDA breakpoints (21) were used, or EUCAST cutoff values (ECOFF) (22), which were used for C. difficile.

The activities of eravacycline and comparators against Gram-negative anaerobic isolates are illustrated in Table 1. Versus comparator antibiotics, eravacycline showed the lowest MIC values against isolates of the B. fragilis group, including those resistant to tigecycline, minocycline, meropenem, piperacillin-tazobactam, ampicillin-sulbactam, moxifloxacin, and clindamycin. All isolates within the B. fragilis group (n = 286) were inhibited by ≤4 μg/ml eravacycline. The MIC values that inhibited 90% of the isolates (MIC90) in a panel for eravacycline (MIC90, 1 μg/ml) were 8- and 16-fold lower than those of tigecycline (MIC90, 8 μg/ml) and minocycline (MIC90, 16 μg/ml), respectively. Eravacycline was potent against Prevotella spp. (n = 29) and Fusobacterium spp. (n = 20); all isolates were inhibited by ≤0.5 μg/ml eravacycline.

TABLE 1.

In vitro activities of eravacycline and comparator antibiotics against 335 Gram-negative anaerobic clinical isolates

Organism (n) Antimicrobial agent MIC (μg/ml)
 % resistant by guidelinea
Range MIC50 MIC90 CLSI/FDA EUCAST
Bacteroides fragilis group (286) Eravacycline 0.03 to 4 0.25 1 NA NA
Tigecycline 0.12 to 16 1 8 3.1 NA
Minocycline ≤0.25 to 64 8 16 NA NA
Imipenem ≤0.12 to 4 0.25 1 0 0
Meropenem ≤0.12 to 16 0.25 2 1.0 1.0
Piperacillin-tazobactam ≤0.5 to 256 4 32 0.7 10.8
Ampicillin-sulbactam ≤0.5 to >128 2 16 4.9 22.7
Moxifloxacin ≤0.5 to 64 2 32 38.8 NA
Linezolid ≤1 to >16 2 4 NA NA
Clindamycin ≤0.5 to >128 4 >128 43.7 43.7
Metronidazole ≤1 to 2 ≤1 2 0 0
Bacteroides fragilis (110) Eravacycline 0.03 to 4 0.25 1 NA NA
Tigecycline 0.12 to 16 1 8 4.5 NA
Minocycline ≤0.25 to 64 8 16 NA NA
Imipenem ≤0.12 to 4 0.25 1 0 0
Meropenem ≤0.12 to 16 0.25 2 1.8 1.8
Piperacillin-tazobactam ≤0.5 to 128 1 8 0.9 1.8
Ampicillin-sulbactam 1 to 32 2 16 1.8 17.3
Moxifloxacin ≤0.5 to 32 2 16 36.4 NA
Linezolid 2 to >16 2 4 NA NA
Clindamycin ≤0.5 to >128 1 >128 30.0 30.0
Metronidazole ≤1 to 2 ≤1 2 0 0
Non-B. fragilis (176) Eravacycline 0.06 to 4 0.25 1 NA NA
Tigecycline 0.12 to 16 1 8 2.3 NA
Minocycline ≤0.25 to 32 4 16 NA NA
Imipenem ≤0.12 to 4 0.5 1 0 0
Meropenem ≤0.12 to 16 0.25 2 0.6 0.6
Piperacillin-tazobactam ≤0.5 to 256 8 32 0.6 16.5
Ampicillin-sulbactam ≤0.5 to >128 4 16 6.8 26.1
Moxifloxacin ≤0.5 to 64 4 32 40.3 NA
Linezolid ≤1 to >16 2 4 NA NA
Clindamycin ≤0.5 to >128 8 >128 52.3 52.3
Metronidazole ≤1 to 2 ≤1 2 0 0
Bacteroides caccae (10) Eravacycline 0.12 to 0.5 0.5 0.5 NA NA
Tigecycline 0.5 to 4 1 4 0 NA
Minocycline 4 to 16 8 16 NA NA
Imipenem ≤0.12 to 1 0.25 0.5 0 0
Meropenem ≤0.12 to 4 0.25 1 0 0
Piperacillin-tazobactam ≤0.5 to 4 2 4 0 0
Ampicillin-sulbactam 1 to 8 2 8 0 0
Moxifloxacin ≤0.5 to 64 4 32 50.0 NA
Linezolid All 2 2 2 NA NA
Clindamycin 4 to >128 >128 >128 90.0 90.0
Metronidazole ≤1 to 2 ≤1 2 0 0
Bacteroides ovatus (30) Eravacycline 0.06 to 1 0.25 1 NA NA
Tigecycline 0.25 to 8 1 8 0 NA
Minocycline ≤0.25 to 16 4 8 NA NA
Imipenem ≤0.12 to 2 0.25 0.5 0 0
Meropenem ≤0.12 to 8 0.25 2 0 0
Piperacillin-tazobactam ≤0.5 to 32 4 32 0 13.3
Ampicillin-sulbactam ≤0.5 to 32 2 16 3.3 20.0
Moxifloxacin ≤0.5 to 32 4 8 20.0 NA
Linezolid ≤1 to 8 2 4 NA NA
Clindamycin ≤0.5 to >128 8 >128 53.3 53.3
Metronidazole ≤1 to 2 ≤1 2 0 0
Bacteroides thetaiotaomicron (70) Eravacycline 0.06 to 4 0.25 1 NA NA
Tigecycline 0.12 to 16 1 8 4.3 NA
Minocycline ≤0.25 to 16 4 8 NA NA
Imipenem ≤0.12 to 1 0.5 1 0 0
Meropenem ≤0.12 to 2 0.25 1 0 0
Piperacillin-tazobactam 1 to 64 16 32 0 20.0
Ampicillin-sulbactam 1 to 64 2 16 4.3 18.6
Moxifloxacin ≤0.5 to 64 2 32 35.7 NA
Linezolid 2 to 4 4 4 NA NA
Clindamycin ≤0.5 to >128 8 >128 51.4 51.4
Metronidazole ≤1 to 2 ≤1 2 0 0
Parabacteroides distasonis (26) Eravacycline 0.12 to 4 0.25 1 NA NA
Tigecycline 0.5 to 16 1 8 3.8 NA
Minocycline ≤0.25 to 32 4 16 NA NA
Imipenem 0.25 to 2 0.5 2 0 0
Meropenem ≤0.12 to 4 0.5 4 0 0
Piperacillin-tazobactam 1 to 64 8 32 0 26.9
Ampicillin-sulbactam 2 to 64 8 32 15.4 38.5
Moxifloxacin ≤0.5 to 64 2 32 46.2 NA
Linezolid 2 to 4 2 4 NA NA
Clindamycin ≤0.5 to >128 4 >128 38.5 38.5
Metronidazole ≤1 to 2 ≤1 2 0 0
Bacteroides uniformis (15) Eravacycline 0.06 to 1 0.25 1 NA NA
Tigecycline 0.25 to 8 1 4 0 NA
Minocycline ≤0.25 to 32 8 16 NA NA
Imipenem ≤0.12 to 2 0.25 1 0 0
Meropenem ≤0.12 to 4 0.25 2 0 0
Piperacillin-tazobactam ≤0.5 to 32 4 32 0 13.3
Ampicillin-sulbactam ≤0.5 to 16 2 16 0 20.0
Moxifloxacin ≤0.5 to 64 8 32 53.3 NA
Linezolid 2 to 4 2 4 NA NA
Clindamycin ≤0.5 to >128 >128 >128 60.0 60.0
Metronidazole ≤1 to 2 ≤1 2 0 0
Bacteroides vulgatus (18) Eravacycline 0.06 to 0.5 0.12 0.5 NA NA
Tigecycline 0.12 to 8 0.5 8 0 NA
Minocycline ≤0.25 to 16 8 16 NA NA
Imipenem 0.25 to 4 0.5 2 0 0
Meropenem 0.25 to 16 0.5 4 5.6 5.6
Piperacillin-tazobactam 2 to 256 4 32 5.6 11.1
Ampicillin-sulbactam 2 to 64 16 64 16.7 61.1
Moxifloxacin 1 to 64 32 64 72.2 NA
Linezolid 2 to >16 2 4 NA NA
Clindamycin ≤0.5 to >128 >128 >128 55.6 55.6
Metronidazole ≤1 to 2 ≤1 ≤1 0 0
Other Parabacteroides/Bacteroides spp. (7)b Eravacycline 0.06 to 1
Tigecycline 0.5 to 8
Minocycline ≤0.25 to 32
Imipenem ≤0.12 to 1
Meropenem 0.25 to 1
Piperacillin-tazobactam ≤0.5 to 16
Ampicillin-sulbactam 2 to >128
Moxifloxacin ≤0.5 to 8
Linezolid 2 to 4
Clindamycin ≤0.5 to >128
Metronidazole ≤1 to 2
Prevotella spp. (29) Eravacycline ≤0.015 to 0.5 0.25 0.5 NA NA
Tigecycline ≤0.06 to 1 0.5 1 0 NA
Minocycline ≤0.25 to 32 4 32 NA NA
Imipenem ≤0.12 to 2 ≤0.12 2 0 0
Meropenem ≤0.12 to 8 ≤0.12 2 0 0
Piperacillin-tazobactam ≤0.5 to 128 ≤0.5 8 3.4 3.4
Ampicillin-sulbactam ≤0.5 to 32 1 4 3.4 3.4
Moxifloxacin ≤0.5 to >64 1 16 10.3 NA
Linezolid ≤1 to 4 2 4 NA NA
Clindamycin ≤0.5 to >128 ≤0.5 >128 27.6 27.6
Metronidazole ≤1 to >16 ≤1 2 3.4 3.4
Fusobacterium spp. (20) Eravacycline ≤0.015 to 0.5 0.03 0.12 NA NA
Tigecycline ≤0.06 to 1 0.12 0.5 0 NA
Minocycline ≤0.25 to 0.5 ≤0.25 0.5 NA NA
Imipenem ≤0.12 to 0.5 ≤0.12 0.5 0 0
Meropenem ≤0.12 to 0.5 0.25 0.25 0 0
Piperacillin-tazobactam ≤0.5 to 2 1 2 0 0
Ampicillin-sulbactam ≤0.5 to 2 1 2 0 0
Moxifloxacin ≤0.5 to 2 ≤0.5 1 0 NA
Linezolid ≤1 to 2 ≤1 ≤1 NA NA
Clindamycin All ≤0.5 ≤0.5 ≤0.5 0 0
Metronidazole All ≤1 ≤1 ≤1 0 0
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a

The FDA breakpoint applicable only to tigecycline. EUCAST epidemiological cutoff (ECOFF) breakpoints were used for C. difficile. NA, not applicable.

b

Only the MIC range is indicated when the total number of isolates was <10.

The susceptibilities of the Gram-positive anaerobic isolates to eravacycline and comparator antibiotics are shown in Table 2. Eravacycline was potent against all isolates at concentrations of ≤1 μg/ml, including C. difficile strains resistant to moxifloxacin and clindamycin and with elevated MICs (4 μg/ml) to vancomycin and metronidazole. The eravacycline MIC90 values against Clostridium perfringens (n = 15), C. difficile (n = 76), other Clostridium spp. (n = 22), Peptostreptococcus spp. (n = 53), Propionibacterium species (including P. acnes, which was recently reclassified as Cutibacterium acnes spp.) (n = 13), and Bifidobacterium spp. (n = 15) were 1 μg/ml, 0.12 μg/ml, 0.12 μg/ml, 0.25 μg/ml, 0.25 μg/ml, and 0.5 μg/ml, respectively. The MIC ranges for E. lenta (n = 6) and Lactobacillus spp. (n = 5) were 0.03 to 0.12 μg/ml and 0.06 to 0.5 μg/ml, respectively.

TABLE 2.

In vitro activities of eravacycline and comparator antibiotics against 205 Gram-positive anaerobic clinical isolates

Species (n) Antimicrobial agent MIC (μg/ml)
 % resistant by guidelinea
Range MIC50 MIC90 CLSI/FDA EUCAST
Clostridium perfringens (15) Eravacycline 0.03 to 1 0.12 1 NA NA
Tigecycline 0.12 to 2 0.5 2 0 NA
Minocycline ≤0.25 to 8 0.5 8 NA NA
Imipenem ≤0.12 to 1 0.25 0.5 0 0
Meropenem ≤0.12 to 1 ≤0.12 0.25 0 0
Piperacillin-tazobactam ≤0.5 to 1 ≤0.5 1 0 0
Ampicillin-sulbactam ≤0.5 to 2 ≤0.5 1 0 0
Moxifloxacin ≤0.5 to 4 1 4 0 NA
Linezolid ≤1 to 2 2 2 NA NA
Clindamycin ≤0.5 to 128 1 64 13.3 13.3
Metronidazole ≤1 to 2 ≤1 2 0 0
Vancomycin 0.5 to 64 1 32 NA 20.0
Clostridium difficile (76) Eravacycline ≤0.015 to 0.25 0.06 0.12 NA NA
Tigecycline ≤0.06 to 1 0.12 0.25 0 6.6
Minocycline ≤0.25 to 16 ≤0.25 4 NA NA
Imipenem ≤0.12 to 16 4 8 6.6 NA
Meropenem ≤0.12 to 8 2 4 0 NA
Piperacillin-tazobactam ≤0.5 to 64 8 16 0 NA
Ampicillin-sulbactam ≤0.5 to 16 2 4 0 NA
Moxifloxacin ≤0.5 to 32 2 16 18.4 18.4
Linezolid ≤1 to 8 2 2 NA NA
Clindamycin ≤0.5 to >128 4 128 28.9 NA
Metronidazole ≤1 to 4 ≤1 ≤1 0 1.3
Vancomycin ≤0.5 to 4 1 2 NA 2.6
Other Clostridium spp. (22) Eravacycline ≤0.015 to 0.5 0.03 0.12 NA NA
Tigecycline ≤0.06 to 1 0.12 0.5 0 NA
Minocycline ≤0.25 to 16 ≤0.25 4 NA NA
Imipenem ≤0.12 to 4 1 4 0 0
Meropenem ≤0.12 to 2 1 2 0 0
Piperacillin-tazobactam ≤0.5 to 32 2 16 0 9.1
Ampicillin-sulbactam ≤0.5 to 2 ≤0.5 2 0 0
Moxifloxacin ≤0.5 to >64 2 4 9.1 NA
Linezolid ≤1 to 8 2 4 NA NA
Clindamycin ≤0.5 to >128 4 128 40.9 40.9
Metronidazole ≤1 to >16 ≤1 ≤1 4.5 4.5
Vancomycin ≤0.25 to 16 2 16 NA 31.8
Peptostreptococcus spp. (53) Eravacycline 0.03 to 0.25 0.12 0.25 NA NA
Tigecycline ≤0.06 to 1 0.25 0.25 0 NA
Minocycline ≤0.25 to 16 0.5 8 NA NA
Imipenem ≤0.12 to 0.5 ≤0.12 ≤0.12 0 0
Meropenem ≤0.12 to 0.5 ≤0.12 ≤0.12 0 0
Piperacillin-tazobactam ≤0.5 to 4 ≤0.5 ≤0.5 0 0
Ampicillin-sulbactam ≤0.5 to 2 ≤0.5 1 0 0
Moxifloxacin ≤0.5 to 16 ≤0.5 4 9.4 NA
Linezolid ≤1 to 2 ≤1 2 NA NA
Clindamycin ≤0.5 to >128 ≤0.5 64 11.3 11.3
Metronidazole ≤1 to >16 ≤1 ≤1 5.7 5.7
Vancomycin ≤0.25 to 4 0.5 1 NA 5.7
Propionibacterium spp./Cutibacterium acnes (13) Eravacycline ≤0.015 to 1 0.06 0.25 NA NA
Tigecycline 0.12 to 2 0.12 0.5 0 NA
Minocycline ≤0.25 to 8 0.5 2 NA NA
Imipenem ≤0.12 to 0.5 ≤0.12 ≤0.12 0 0
Meropenem ≤0.12 to 0.25 ≤0.12 0.25 0 0
Piperacillin-tazobactam ≤0.5 to 1 ≤0.5 ≤0.5 0 0
Ampicillin-sulbactam ≤0.5 to 4 ≤0.5 1 0 0
Moxifloxacin ≤0.5 to 4 ≤0.5 1 0 NA
Linezolid ≤1 to 2 ≤1 ≤1 NA NA
Clindamycin ≤0.5 to 64 1 64 23.1 23.1
Metronidazole ≤1 to >16 >16 >16 92.3 92.3
Vancomycin 0.5 to 32 1 8 NA 23.1
Bifidobacterium spp. (15) Eravacycline 0.12 to 0.5 0.25 0.5 NA NA
Tigecycline 0.12 to 1 0.5 1 0 NA
Minocycline 0.5 to 64 1 32 NA NA
Imipenem ≤0.12 to 2 0.5 2 0 0
Meropenem ≤0.12 to 8 0.5 4 0 0
Piperacillin-tazobactam 1 to 16 2 8 0 0
Ampicillin-sulbactam 1 to 16 1 2 0 6.7
Moxifloxacin 1 to 64 1 32 13.3 NA
Linezolid ≤1 to 2 ≤1 2 NA NA
Clindamycin ≤0.5 to >128 ≤0.5 >128 13.3 13.3
Metronidazole 4 to >16 >16 >16 93.3 93.3
Vancomycin 0.5 to 32 1 4 NA 13.3
Eggerthella lenta (6)b Eravacycline 0.03 to 0.12
Tigecycline ≤0.06 to 0.5
Minocycline 1 to 32
Imipenem ≤0.12 to 0.5
Meropenem ≤0.12 to 0.5
Piperacillin-tazobactam ≤0.5 to 64
Ampicillin-sulbactam ≤0.5 to 8
Moxifloxacin ≤0.5 to >64
Linezolid ≤1 to 4
Clindamycin ≤0.5 to 16
Metronidazole All ≤1
Vancomycin 1 to 4
Lactobacillus spp. (5)b Eravacycline 0.06 to 0.5
Tigecycline 0.25 to 1
Minocycline ≤0.25 to 4
Imipenem ≤0.12 to 2
Meropenem ≤0.12 to 8
Piperacillin-tazobactam ≤0.5 to 4
Ampicillin-sulbactam ≤0.5 to 2
Moxifloxacin ≤0.5 to 2
Linezolid ≤1 to 4
Clindamycin All ≤0.5
Metronidazole All >16
Vancomycin 0.5 to >64
Open in a new tab
a

The FDA breakpoint is applicable only to tigecycline. EUCAST epidemiological cutoff (ECOFF) breakpoints used for C. difficile. NA, not applicable.

b

Only the MIC range is indicated when the total number of isolates is <10.

The presence of the following tetracycline resistance genes previously reported in B. fragilis (http://faculty.washington.edu/marilynr/) was detected by standard PCR methodology for a set of 27 B. fragilis isolates covering the full range of minocycline MIC values (≤0.25 to 32 μg/ml): tet(Q) and tet(M), encoding ribosomal protection mechanisms (23); and tet(X), tet(X1), and tet(X2), encoding tetracycline-modifying flavin-dependent monooxygenases (24). The following primer sets were used in PCRs: for tet(Q), forward 5′-GTGCGTTTCGACAATGCATCTATTGTAG and reverse 5′-TGATGACATTGATTTTTGGAACATG primers (derived from GenBank accession no. Z21523) or forward 5′-ATCGGTATCAATGAGTTGTT and reverse 5′-GACTGATTCTGGAGGAAGTA primers (25); for tet(X), tet(X1), and tet(X2), forward 5′-CAGGAAGCAATGAAAAAAGCGG and reverse 5′-TAGCTTTTCTAAAGGAAATATCCG primers (derived from GenBank accession no. M37699); for tet(X) and tet(X2) only, forward 5′-TTAGCCTTACCAATGGGTGT and reverse 5′-CAAATCTGCTGTTTCACTCG primers (25); for tet(X1) only, forward 5′-TCAGGACAAGAAGCAATGAA and reverse 5′-TATTTCGGGGTTGTCAAACT primers (25); and for tet(M), forward 5′-AACTCGAACAAGAGGAAAGC and reverse 5′-ATGGAAGCCCAGAAAGGAT primers (26). Plasmids carrying the tet(X), tet(Q), or tet(M) gene were used as positive PCR control templates, and sequencing reactions were performed by Genewiz (Cambridge, MA) to verify tet(X) alleles as well as to determine the tet(Q) sequences of two isolates with the lowest minocycline MIC values (≤2 μg/ml).

As shown in Table 3, 23 of 27 isolates were positive for tet(Q), with minocycline, tigecycline, and eravacycline MIC values ranging from 0.5 to 32 μg/ml, 0.25 to 16 μg/ml, and 0.06 to 4 μg/ml, respectively, while the 4 isolates negative for tet(Q) had minocycline, tigecycline, and eravacycline MIC values ranging from ≤0.25 μg/ml, 0.5 to 2 μg/ml, and 0.12 to 0.5 μg/ml, respectively. The tet(Q) genes from two positive isolates with relatively lower minocycline MIC values of 0.5 and 2 μg/ml were sequenced; each encoded amino acid sequences with 100% identity to 74 Tet(Q) proteins in the UniProtKB database (http://www.uniprot.org/help/uniprotkb, released 15 March 2017), indicating that the Tet(Q) protein in these two isolates was a common variant. In addition to being positive for tet(Q), two isolates were positive for tet(X), and three isolates were positive for both tet(X1) and tet(X2); this set of isolates showed eravacycline, tigecycline, and minocycline MIC values ranging from 0.25 to 1 μg/ml, 2 to 8 μg/ml, and 2 to 32 μg/ml, respectively. No isolates were positive for tet(M).

TABLE 3.

In vitro activities of eravacycline and comparator tetracyclines against 27 Bacteroides fragilis clinical isolates characterized for tetracycline resistance determinants

No. of strains Presence of tetracycline resistance determinanta
 MIC range (μg/ml)b
tet(Q) tet(X)2 tet(X2)2 tet(X1)3 tet(M) ERV TIG MIN
4 − − − − − 0.12–0.5 0.5–2 ≤0.25
18 +4 − − − − 0.06–4 0.25–16 0.5–32
3 +4 − + + − 0.25–1 2–8 2–16
2 + + − − − 0.5–1 2–8 4–32
Open in a new tab
a

tet(X) was distinguished from tet(X2) by generating PCR products with universal tet(X) primers, sequencing with primers specific to both tet(X) and tet(X2), and identifying sequences specific to either tet(X) or tet(X2). tet(X1) was identified by generating PCR products with primers specific to tet(X1) and sequencing with the same primer set to verify tet(X1)-specific sequences. The tet(Q) gene in special studies laboratory strain numbers 28441 and 27741, with MIN MICs of 0.5 and 2 μg/ml, respectively, were sequenced and shown to encode amino acid sequences identical to each other and to 74 Tet(Q) proteins in the UniProtKB database (http://www.uniprot.org/help/uniprotkb, released on 15 March 2017), indicating that the genes encoded a common variant of Tet(Q).

b

MIC determined by agar dilution method; ERV, eravacycline; TIG, tigecycline; MIN, minocycline.

In conclusion, this evaluation showed that eravacycline exhibited potent activity in vitro against MDR B. fragilis and other Gram-negative species, as well as Gram-positive anaerobic species, including isolates containing tetracycline-specific resistance determinants and isolates resistant to commonly used antibiotics, including carbapenems, fluoroquinolones, clindamycin, and β-lactam–β-lactamase inhibitor combinations. Based on its activity in vitro, eravacycline shows promise for the treatment of mixed aerobic-anaerobic infections, such as intra-abdominal infections.

ACKNOWLEDGMENTS

We thank Barbara Rapino and Carolina Baez Giangreco for technical assistant and Roselia Martinez for aid in the editing and graphical presentation of the manuscript.

Financial support for this study was provided by Tetraphase Pharmaceuticals, Inc.

At the time of the study, Kathryn Kerstein, Trudy H. Grossman, and Joyce A. Sutcliffe were employees of Tetraphase Pharmaceuticals, Inc.

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