Tetracycline Resistance Mechanisms Research Articles

A novel member of drug/metabolite transporter (DMT) family efflux pump, SA00565, contributes to tetracycline antibiotics resistance in Staphylococcus aureus USA300.

Drug efflux systems have recently been recognized as a significant mechanism responsible for multidrug resistance in bacteria. In this study, we described the identification and characterization of a new chromosomally encoded efflux pump (SA00565) in Staphylococcus aureus. SA00565, which belongs to the drug/metabolite transporter (DMT) superfamily, was predicted to be a 10-transmembrane segment transporter. To evaluate the role of sa00565 in resistance, we generated sa00565 gene deletion mutant (Δsa00565) and assessed its susceptibility to 35 different antibiotic treatments. Our results demonstrated that the Δsa00565 mutant exhibited reduced resistance to tetracycline and doxycycline, with 64-fold and 12-fold decreased MICs, respectively. The mechanism of SA00565-mediated tetracycline resistance was demonstrated that SA00565 possesses the capability to efficiently extrud intracellular tetracycline into the environment. The efflux activity of SA00565 was further validated using EtBr accumulation and efflux assays. In summary, our study uncovered a previously unknown function of a DMT family transporter, which serves as a tetracycline efflux pump, thereby contributing to tetracycline resistance in S. aureus.IMPORTANCEIn this study, we addressed the significance of drug efflux systems in multidrug resistance of Staphylococcus aureus, focusing on the unexplored efflux pump SA00565 in the drug/metabolite transporter (DMT) superfamily. Through phylogenetic analysis, gene knockout, and overexpression experiments, we identified the role of SA00565 in antibiotic resistance. The Δsa00565 mutant showed increased susceptibility to tetracycline and doxycycline in disk diffusion assays, with significantly lower MICs compared to the WT. Remarkably, intracellular tetracycline concentration in the mutant was two- to threefold higher, indicating SA00565 actively eliminates intracellular tetracycline. Our findings emphasize the pivotal contribution of SA00565 to tetracycline antibiotic resistance in S. aureus, shedding light on its functional attributes within the DMT superfamily and providing valuable insights for combating multidrug resistance.

Elevated proton motive force is a tetracycline resistance mechanism that leads to the sensitivity to gentamicin in Edwardsiella tarda.

Tetracycline is a commonly used human and veterinary antibiotic that is mostly discharged into environment and thereby tetracycline-resistant bacteria are widely isolated. To combat these resistant bacteria, further understanding for tetracycline resistance mechanisms is needed. Here, GC-MS based untargeted metabolomics with biochemistry and molecular biology techniques was used to explore tetracycline resistance mechanisms of Edwardsiella tarda. Tetracycline-resistant E. tarda (LTB4-RTET ) exhibited a globally repressed metabolism against elevated proton motive force (PMF) as the most characteristic feature. The elevated PMF contributed to the resistance, which was supported by the three results: (i) viability was decreased with increasing PMF inhibitor carbonylcyanide-3-chlorophenylhydrazone; (ii) survival is related to PMF regulated by pH; (iii) LTB4-RTET were sensitive to gentamicin, an antibiotic that is dependent upon PMF to kill bacteria. Meanwhile, gentamicin-resistant E. tarda with low PMF are sensitive to tetracycline is also demonstrated. These results together indicate that the combination of tetracycline with gentamycin will effectively kill both gentamycin and tetracycline resistant bacteria. Therefore, the present study reveals a PMF-enhanced tetracycline resistance mechanism in LTB4-RTET and provides an effective approach to combat resistant bacteria.

A Review of Omadacycline for Potential Utility in the Military Health System for the Treatment of Wound Infections

ABSTRACT Introduction Combat-related wound infections complicate the recovery of wounded military personnel, contributing to overall morbidity and mortality. Wound infections in combat settings present unique challenges because of the size and depth of the wounds, the need to administer emergency care in the field, and the need for subsequent treatment in military facilities. Given the increase in multidrug-resistant pathogens, a novel, broad-spectrum antibiotic is desired across this continuum of care when the standard of care fails. Omadacycline was FDA-approved in 2018 for treatment of adults with acute bacterial skin and skin structure infections (ABSSSI), as well as community-acquired bacterial pneumonia (CABP). It is a broad-spectrum antibiotic with activity against gram-positive, gram-negative, and atypical bacterial pathogens, including multidrug-resistant species. Omadacycline can overcome commonly reported tetracycline resistance mechanisms, ribosomal protection proteins, and efflux pumps, and is available in once-daily intravenous or oral formulations. In this review, we discuss the potential role of omadacycline, which is included in the Department of Defense Formulary, in the context of combat wound infections. Materials and Methods A literature review was undertaken for manuscripts published before July 21, 2023. This included a series of publications found via PubMed and a bibliography made publicly available on the Paratek Pharmaceuticals, Inc. website. Publications presenting primary data published in English on omadacycline in relation to ESKAPEE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter species) pathogens and Clostridioides difficile, including in vitro, in vivo, and clinical data were included. Results Of 260 identified records, 66 were included for evidence review. Omadacycline has in vitro activity against almost all the ESKAPEE pathogens, apart from P. aeruginosa. Importantly, it has activity against the four most prevalent bacterial pathogens that cause wound infections in the military healthcare system: S. aureus, including methicillin-resistant S. aureus, A. baumannii, K. pneumoniae, and E. coli. In vivo studies in rats have shown that omadacycline is rapidly distributed in most tissues, with the highest tissue-to-blood concentration ratios in bone mineral. The clinical efficacy of omadacycline has been assessed in three separate Phase 3 studies in patients with ABSSSI (OASIS-1 and OASIS-2) and with CABP (OPTIC). Overall, omadacycline has an established safety profile in the treatment of both ABSSSI and CABP. Conclusions Omadacycline has broad-spectrum activity, the option to be orally administered and an established safety profile, making it a potentially attractive replacement for moxifloxacin in the military individual first aid kit, especially when accounting for the increasing resistance to fluoroquinolones. Further studies and clinical evaluation are warranted to support broader use of omadacycline to treat combat wound infections in the military healthcare system.

Antimicrobial Susceptibility to 27 Drugs and the Molecular Mechanisms of Macrolide, Tetracycline, and Quinolone Resistance in Gemella sp.

Gemella is a catalase-negative, facultative anaerobic, Gram-positive coccus that is commensal in humans but can become opportunistic and cause severe infectious diseases, such as infective endocarditis. Few studies have tested the antimicrobial susceptibility of Gemella. We tested its antimicrobial susceptibility to 27 drugs and defined the resistant genes using PCR in 58 Gemella strains, including 52 clinical isolates and six type strains. The type strains and clinical isolates included 22 G. morbillorum, 18 G. haemolysans (GH) group (genetically indistinguishable from G. haemolysans and G. parahaemolysans), 13 G. taiwanensis, three G. sanguinis, and two G. bergeri. No strain was resistant to beta-lactams and vancomycin. In total, 6/22 (27.3%) G. morbillorum strains were erythromycin- and clindamycin-resistant ermB-positive, whereas 4/18 (22.2%) in the GH group, 7/13 (53.8%) G. taiwanensis, and 1/3 (33.3%) of the G. sanguinis strains were erythromycin-non-susceptible mefE- or mefA-positive and clindamycin-susceptible. The MIC90 of minocycline and the ratios of tetM-positive strains varied across the different species-G. morbillorum: 2 µg/mL and 27.3% (6/22); GH group: 8 µg/mL and 27.8% (5/18); G. taiwanensis: 8 µg/mL and 46.2% (6/13), respectively. Levofloxacin resistance was significantly higher in G. taiwanensis (9/13 69.2%) than in G. morbillorum (2/22 9.1%). Levofloxacin resistance was associated with a substitution at serine 83 for leucine, phenylalanine, or tyrosine in GyrA. The mechanisms of resistance to erythromycin and clindamycin differed across Gemella species. In addition, the rate of susceptibility to levofloxacin differed across Gemella sp., and the quinolone resistance mechanism was caused by mutations in GyrA alone.

Transcriptome analysis reveals the mechanism underlying the tetracycline resistance of Lactiplantibacillusplantarum FZJTZ19M1 and FZJTZ29M8

Lactiplantibacillusplantarum is a species of lactic acid bacteria (LAB) commonly used in food. However, before it is used in food, the safety evaluation of antibiotic resistance must be carried out. Our study found that L.plantarum FZJTZ19M1 and FZJTZ29M8 had a high tetracycline resistance phenotype, but they did not contain any known tetracycline resistance genes. To investigate the tetracycline resistance mechanism of these two strains, we used transcriptome technology to explore the differentially expressed genes (DEG) produced by these two strains after tetracycline induction. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, and protein-protein interaction (PPI) network analysis were used to reveal the important functional genes. Transcriptome results showed that 234 and 176 DEG were identified in L.plantarum FZJTZ19M1 and FZJTZ29M8, respectively. The results of GO, KEGG enrichment analysis, and PPI network analysis suggested that the resistance of L.plantarum FZJTZ19M1 to tetracycline might be caused by regulating amino acid metabolism and reducing the metabolism of fatty acids, biotin, and other substances. L.plantarum FZJTZ29M8 may increase resistance to tetracycline mainly by using (ATP-binding cassette) ABC transporters to excrete tetracycline from the body and reducing its cellular metabolism. This study revealed the tetracycline resistance mechanism of two L.plantarum strains at the transcriptional level and provided the theoretical reference for the safe application of this kind of LAB in food.

Tetracycline Resistance on Protein Synthesis

Tetracycline is an antibiotic with powerful antibacterial activities against a wide variety if microorganisms. It is a potent antibacterial antibiotic that inhibits protein synthesis to work and it is also a good medication because of its low toxicity and adverse reaction, oral absorption, and effectiveness against disease-causing germs. Its major mechanism of action is based on inhibition of protein synthesis. The relatively low toxicity & allergic reaction, effective oral absorption, and wide range of effectiveness against disease causing microorganisms are reasons why tetracycline is regarded as a good medication. Tetracycline mechanism of action is mainly its inhibitory ability of protein synthesis. It inhibits aminoacyl-tRNA from binding to the ribosome's A site and thus prevent any further amino acid addition to the developing polypeptide chain. It inhibits protein synthesis at once and disrupt several enzymatic activities essential to propagation and survival. This inhibitory ability is less apparent in surrounding human/animal cells during treatment, which is due to inability of such cell to pump tetracycline into their cytoplasm against concentration gradient unlike bacteria cells. In addition, its ability to disrupt cellular membrane causes organelles o leak from the cell and thus impedes propagation or multiplication. However, tetracycline resistance was observed over time. Tetracycline resistance has been observed to be caused by the action of intrinsic enzymes synthesized to inactivates or degrade it. Also, the excretion and efflux of tetracycline from the cytoplasm, thus reducing cytoplasmic concentration and ultimately, its efficacy. Such microorganism possesses membrane proteins or transporters that can export tetracycline at a rate equal to or greater than its influx rate. The transporters could be tetracycline specific or a multidrug transporter. Another mechanism of tetracycline resistance is known as ribosome's protection. Although the mechanism is not well known, ribosome protective resistance protein (TetM) binds to the ribosome's binding site. This molecule has similarities to elongation factor, and it allows the elongation of polypeptide chain while reducing the affinity of the binding site to tetracycline. This ultimately makes tetracycline ineffective against the microorganisms. This mechanism can also be used in conjunction with efflux mechanism of tetracycline resistance.

Tigecycline Immunodetection Using Developed Group-Specific and Selective Antibodies for Drug Monitoring Purposes.

Tigecycline (TGC), a third-generation tetracycline, is characterized by a more potent and broad antibacterial activity, and the ability to overcome different mechanisms of tetracycline resistance. TGC has proven to be of value in treatment of multidrug-resistant infections, but therapy can be complicated by multiple dangerous side effects, including direct drug toxicity. Given that, a TGC immunodetection method has been developed for therapeutic drug monitoring to improve the safety and efficacy of therapy. The developed indirect competitive ELISA utilized TGC selective antibodies and group-specific antibodies interacting with selected coating TGC conjugates. Both assay systems showed high sensitivity (IC50) of 0.23 and 1.59 ng/mL, and LOD of 0.02 and 0.05 ng/mL, respectively. Satisfactory TGC recovery from the spiked blood serum of healthy volunteers was obtained in both assays and laid in the range of 81-102%. TGC concentrations measured in sera from COVID-19 patients with secondary bacterial infections were mutually confirmed by ELISA based on the other antibody-antigen interaction and showed good agreement (R2 = 0.966). A TGC pharmacokinetic (PK) study conducted in three critically ill patients proved the suitability of the test to analyze the therapeutic concentrations of TGC. Significant inter-individual PK variability revealed in this limited group supports therapeutic monitoring of TGC in individual patients and application of the test for population pharmacokinetic modelling.

In vitro activity of a novel aminomethylcycline antibacterial (KBP-7072), a third-generation tetracycline, against clinical isolates with molecularly characterized tetracycline resistance mechanisms

ObjectivesThis study evaluated the in vitro activity of KBP-7072 against 413 contemporary surveillance isolates, including subsets with known tetracycline resistance genes.MaterialsIn total, 105 Klebsiella pneumoniae (51 tetracycline resistant), 103 Escherichia coli (52 tetracycline resistant), 103 Staphylococcus aureus (51 tetracycline resistant) and 102 Streptococcus pneumoniae (51 tetracycline resistant) isolates were included. These isolates were tested by broth microdilution using fresh media. CLSI/EUCAST breakpoints were applied, except for tigecycline and omadacycline, which used FDA criteria.ResultsKBP-7072 (MIC50, 0.06 mg/L), tigecycline (MIC50, 0.12 and 0.25 mg/L) and omadacycline (MIC50, 0.12 and 0.5 mg/L) showed similar MIC50s for tetracycline-susceptible and -resistant S. aureus. Other tetracycline comparators had their MIC50 increased 64- to 256-fold by tet. For S. pneumoniae, KBP-7072 (MIC50/90, ≤0.015/0.03 mg/L) showed the lowest MICs, which remained unchanged for tetracycline-susceptible or -resistant isolates [mostly tet(M)]. Similar MICs were observed for omadacycline (MIC50/90, 0.03–0.06/0.06 mg/L) and tigecycline (MIC50/90, 0.03/0.03 mg/L) in the S. pneumoniae population. Tetracycline-susceptible and -resistant E. coli [94.2% tet(A)/tet(B)], KBP-7072 (MIC90, 0.25 and 1 mg/L, respectively) and tigecycline (MIC90, 0.25 and 0.5 mg/L) showed similar MIC90s. KBP-7072 (MIC50/90, 0.25/0.5 mg/L) and tigecycline (MIC50/90, 0.5/0.5 mg/L) had the lowest MIC for tetracycline-susceptible K. pneumoniae. The MIC for KBP-7072 (MIC50/90, 1/4 mg/L) and tigecycline (MIC50/90, 1/2 mg/L) increased 2- to 8-fold for tetracycline-resistant K. pneumoniae, which mostly produced Tet(A).ConclusionsKBP-7072 activity was minimally affected by the presence of acquired tetracycline genes.

A novel plasmid from Aerococcus urinaeequi of porcine origin co-harboring the tetracycline resistance genes tet(58) and tet(61)

Tetracyclines are the broad-spectrum agents used in veterinary medicine and food animal production. Known mechanisms of tetracycline resistance include ribosome protection, active efflux and enzymatic inactivation. However, the presence of two different tet genes conferring different resistance mechanisms on the same plasmid has rarely been reported. In this study, we identified the tandem tetracycline resistance genes tet(61)-tet(58) on the novel plasmid pT4303. These tet genes were identified for the first time in Aerococcus urinaeequi. Reduced susceptibility to doxycycline was observed in S. aureus RN4220 harboring tet(61) when an extra tet(58) was expressed. Plasmid pT4303 was electrotransformed into S. aureus RN4220, E. faecalis JH2−2, S. suis BAA and E. coli DH5α and conferred tetracycline resistance (MIC ≥ 16) in both Gram-positive and Gram-negative bacteria, assuming that it might serve as a vehicle for the dissemination of the tetracycline resistance genes tet(61) and tet(58).

1253. In Vitro Activity of Omadacycline against 7000 Bacterial Pathogens from the United States Stratified by Infection Type (2019)

BackgroundOmadacycline (OMC) is a new aminomethylcycline antibacterial drug belonging to the tetracycline class, for intravenous or oral administration. It is well tolerated and has proven effective in the treatment of a variety of bacterial infections. OMC is active against bacterial strains expressing the most common clinically relevant tetracycline resistance mechanisms, namely efflux and ribosomal protection.Methods7,000 clinical isolates were collected during 2019 in the SENTRY Surveillance Program from 31 medical centers in the United States (US). Isolates were obtained from bloodstream infection (23.8%), skin and skin structure infection (21.6%), pneumonia in hospitalized patients (22.7%), urinary tract infection (14.5%), intraabdominal infection (6.2%), community acquired respiratory tract infection (10.3%) and other infection types (0.9%). Identifications were confirmed by MALDI-TOF. One isolate/patient/infection episode was tested. Broth microdilution susceptibility testing was conducted according to CLSI M07 (2018) and M100 (2020) guidelines. Results were interpreted using US FDA and CLSI breakpoint criteria.ResultsOMC demonstrated potent in vitro activity against Staphylococcus aureus isolates representing multiple infection types (MIC90, 0.12-0.25 mg/L; 94.7%-99.0% susceptible [S]) including MRSA (MIC90, 0.25 mg/L; 96.5% S) (Table). All S. lugdunensis (MIC90, 0.06 mg/L), Enterococcus faecalis (MIC90, 0.12-0.25 mg/L), and Haemophilus influenzae (MIC90, 1 mg/L) isolates were S to OMC. OMC was active against Streptococcus pyogenes isolates from SSSI (MIC90, 0.12 mg/L; 93.3%-98.5%S) including macrolide-resistant (R) strains. Similarly, S. pneumoniae isolates from RTI were S to OMC (MIC90, 0.06-0.12 mg/L; 98.8%-100%S) regardless of resistance to tetracycline or penicillin. Overall, 90.2%-93.6% of Enterobacter cloacae (MIC90, 4 mg/L) and 89.7%-94.7% of Klebsiella pneumoniae (MIC90, 4-8 mg/L) isolates from multiple infection types were S to OMC.ConclusionOMC demonstrated potent in vitro activity against Gram-positive and -negative bacterial pathogens from multiple infection types including SSSI and RTI and isolates displaying resistance to tetracycline, macrolides, and penicillin.Table 1 DisclosuresMichael A. Pfaller, MD, Amplyx Pharmaceuticals (Research Grant or Support)Basilea Pharmaceutica International, Ltd (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Department of Health and Human Services (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support) Jennifer M. Streit, BS, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support) Helio S. Sader, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support) Mariana Castanheira, PhD, 1928 Diagnostics (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Amplyx Pharmaceuticals (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support)

Amidochelocardin Overcomes Resistance Mechanisms Exerted on Tetracyclines and Natural Chelocardin.

The reassessment of known but neglected natural compounds is a vital strategy for providing novel lead structures urgently needed to overcome antimicrobial resistance. Scaffolds with resistance-breaking properties represent the most promising candidates for a successful translation into future therapeutics. Our study focuses on chelocardin, a member of the atypical tetracyclines, and its bioengineered derivative amidochelocardin, both showing broad-spectrum antibacterial activity within the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) panel. Further lead development of chelocardins requires extensive biological and chemical profiling to achieve favorable pharmaceutical properties and efficacy. This study shows that both molecules possess resistance-breaking properties enabling the escape from most common tetracycline resistance mechanisms. Further, we show that these compounds are potent candidates for treatment of urinary tract infections due to their in vitro activity against a large panel of multidrug-resistant uropathogenic clinical isolates. In addition, the mechanism of resistance to natural chelocardin was identified as relying on efflux processes, both in the chelocardin producer Amycolatopsis sulphurea and in the pathogen Klebsiella pneumoniae. Resistance development in Klebsiella led primarily to mutations in ramR, causing increased expression of the acrAB-tolC efflux pump. Most importantly, amidochelocardin overcomes this resistance mechanism, revealing not only the improved activity profile but also superior resistance-breaking properties of this novel antibacterial compound.

Omadacycline: a therapeutic review of use in community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections.

Omadacycline is a novel aminomethylcycline antimicrobial, US FDA approved for the treatment of community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections. It is not susceptible to common tetracyclineresistance mechanisms, and has demonstrated efficacy against a broad spectrum of pathogens including resistant isolates, which are increasing in prevalence and complexity. It is available in both intravenous and oral formats, and can be administered in single, once daily doses or multiple doses, with no dosing adjustments required for sex, age, hepatic or renal impairment. It can be a good option for patients with low treatment adherence, and oral therapy may be used to reduce length of hospitalization for iv. treatment. This article reviews the in vitro and in vivo activity, PK/PD profile, integrated data from clinical trials including clinical efficacy and safety profile, and looks to future application of omadacycline.

Genetic Determinants for Metal Tolerance and Antimicrobial Resistance Detected in Bacteria Isolated from Soils of Olive Tree Farms.

Copper-derived compounds are often used in olive tree farms. In a previous study, a collection of bacterial strains isolated from olive tree farms were identified and tested for phenotypic antimicrobial resistance and heavy metal tolerance. The aim of this work was to study the genetic determinants of resistance and to evaluate the co-occurrence of metal tolerance and antibiotic resistance genes. Both metal tolerance and antibiotic resistance genes (including beta-lactamase genes) were detected in the bacterial strains from Cu-treated soils. A high percentage of the strains positive for metal tolerance genes also carried antibiotic resistance genes, especially for genes involved in resistances to beta-lactams and tetracycline. Significant associations were detected between genes involved in copper tolerance and genes coding for beta-lactamases or tetracycline resistance mechanisms. A significant association was also detected between zntA (coding for a Zn(II)-translocating P-type ATPase) and tetC genes. In conclusion, bacteria from soils of Cu-treated olive farms may carry both metal tolerance and antibiotic resistance genes. The positive associations detected between metal tolerance genes and antibiotic resistance genes suggests co-selection of such genetic traits by exposure to metals.

Omadacycline invitro activity against a molecularly characterized collection of clinical isolates with known acquired tetracycline resistance mechanisms

Omadacycline and tigecycline MIC90 values were 2 μg/mL and 0.25 μg/mL, respectively, against Staphylococcus aureus carrying tet(M), whereas the minocycline, tetracycline, and doxycycline values were > 8 μg/mL. Similarly, omadacycline and tigecycline remained active against Enterococcus faecalis and Streptococcus pneumoniae harboring tet(L)and/or tet(M)(MIC90, 0.06–0.25 μg/mL), whereas other tetracyclines were inactive (MIC90, >8 μg/mL). Omadacycline and tigecycline remained more potent than minocycline, tetracycline, and doxycycline against Enterobacteriaceae carrying tet. This study demonstrates the effectiveness of modern tetracyclines, omadacycline, and tigecycline against isolates with tetracycline resistance genes.

Omadacycline: A Novel Oral and Intravenous Aminomethylcycline Antibiotic Agent

Omadacycline is a novel aminomethylcycline antibiotic developed as a once-daily, intravenous and oral treatment for acute bacterial skin and skin structure infection (ABSSSI) and community-acquired bacterial pneumonia (CABP). Omadacycline, a derivative of minocycline, has a chemical structure similar to tigecycline with an alkylaminomethyl group replacing the glycylamido group at the C-9 position of the D-ring of the tetracycline core. Similar to other tetracyclines, omadacycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. Omadacycline possesses broad-spectrum antibacterial activity against Gram-positive and Gram-negative aerobic, anaerobic, and atypical bacteria. Omadacycline remains active against bacterial isolates possessing common tetracycline resistance mechanisms such as efflux pumps (e.g., TetK) and ribosomal protection proteins (e.g., TetM) as well as in the presence of resistance mechanisms to other antibiotic classes. The pharmacokinetics of omadacycline are best described by a linear, three-compartment model following a zero-order intravenous infusion or first-order oral administration with transit compartments to account for delayed absorption. Omadacycline has a volume of distribution (Vd) ranging from 190 to 204L, a terminal elimination half-life (t½) of 13.5-17.1h, total clearance (CLT) of 8.8-10.6L/h, and protein binding of 21.3% in healthy subjects. Oral bioavailability of omadacycline is estimated to be 34.5%. A single oral dose of 300mg (bioequivalent to 100mg IV) of omadacycline administered to fasted subjects achieved a maximum plasma concentration (Cmax) of 0.5-0.6mg/L and an area under the plasma concentration-time curve from 0 to infinity (AUC0-∞) of 9.6-11.9mgh/L. The free plasma area under concentration-time curve divided by the minimum inhibitory concentration (i.e., fAUC24h/MIC), has been established as the pharmacodynamic parameter predictive of omadacycline antibacterial efficacy. Several animal models including neutropenic murine lung infection, thigh infection, and intraperitoneal challenge model have documented the in vivo antibacterial efficacy of omadacycline. A phase II clinical trial on complicated skin and skin structure infection (cSSSI) and three phase III clinical trials on ABSSSI and CABP demonstrated the safety and efficacy of omadacycline. The phase III trials, OASIS-1 (ABSSSI), OASIS-2 (ABSSSI), and OPTIC (CABP), established non-inferiority of omadacycline to linezolid (OASIS-1, OASIS-2) and moxifloxacin (OPTIC), respectively. Omadacycline is currently approved by the FDA for use in treatment of ABSSSI and CABP. Phase II clinical trials involving patients with acute cystitis and acute pyelonephritis are in progress. Mild, transient gastrointestinal events are the predominant adverse effects associated with use of omadacycline. Based on clinical trial data to date, the adverse effect profile of omadacycline is similar to studied comparators, linezolid and moxifloxacin. Unlike tigecycline and eravacycline, omadacycline has an oral formulation that allows for step-down therapy from the intravenous formulation, potentially facilitating earlier hospital discharge, outpatient therapy, and cost savings. Omadacycline has a potential role as part of an antimicrobial stewardship program in the treatment of patients with infections caused by antibiotic-resistant and multidrug-resistant Gram-positive [including methicillin-resistant Staphylococcus aureus (MRSA)] and Gram-negative pathogens.

An Improved Protocol for the Expression and Purification of Tetracycline Monooxgenase: An Enzyme Involved in Antibiotic Resistance

Tetracyclines are an important group of antibiotics used in agricultural and clinical settings. They function by binding to the 30S subunit of the prokaryotic ribosome to effectively halt translation. The emergence of tetracycline resistant strains of pathogenic bacteria has threatened the continued use of the drug. One mechanism of tetracycline resistance is the degradation of the drug by the flavin dependent enzyme tetracycline monooxygenase (TetX). Only a limited number of studies of the enzyme have been conducted to date due to the limited amounts of pure protein that can be obtained from current protocols (~6 mg/L of cell culture). The current report describes the development of optimized expression and purification protocols to obtain larger amounts of pure, soluble enzyme suitable for detailed kinetic studies to deduce its chemical mechanism. During the initial phase of this work the pET22a+ plasmid with the gene encoding for TetX was used to transform either DH5α or Rosetta (DE3) pLysS Escherichia coli cells. Expression trials of these cell lines in which both the temperature and times of incubation with isopropyl β-D-1-thiogalactopyrandoside were then carried out. Of the conditions tested, optimal expression of TetX was found with a 20 h induction period at 30 °C using E. coli DH5α cells. Ammonium sulfate precipitation trials were then conducted where it was concluded that a 20 fold purification of the enzyme is achieved through treatment with 40% saturation of salt and collection of the supernatant after centrifugation. A nickel affinity chromatographic protocol was also developed, which purified the enzyme to high levels as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis and the specific activity of the purified sample. The expression and purification protocol developed here resulted in ~36 mg/L of cell culture, which is a 6-fold improvement over published protocols.

Tigecycline is the First Clinically-Available Drug in a new class of Antibiotics called the Glycylcyclines: A Review

Tigecycline is a glycylcycline antibiotic developed and marketed by Wyeth under the brand name Tygacil. It was developed in response to the growing prevalence of antibiotic resistance in bacteria such as Staphylococcus aureus. It was granted fast-track approval by the U.S. Food and Drug Administration (FDA) on June 17, 2005. Tigecycline is the first clinically-available drug in a new class of antibiotics called the glycylcyclines. Glycylcyclines are a new class of antibiotics derived from tetracycline. These tetracycline analogues are specifically designed to overcome two common mechanisms of tetracycline resistance, namely resistance mediated by acquired efflux pumps and/or ribosomal protection. Glycylcycline antibiotics have a similar mechanism of action as tetracycline antibiotics. Both classes of antibiotics bind to the 30S ribosomal subunit to prevent the amino-acyl tRNA from binding to the A site of the ribosome. However, the glycylcyclines appear to bind more effectively than the tetracyclines.

Omadacycline: A Review of the Clinical Pharmacokinetics and Pharmacodynamics.

Omadacycline is a novel aminomethylcycline antibiotic (antibacterial). Omadacycline has had chemical structure modifications at the C9 and C7 positions of the core tetracycline rings that allow stability in the efflux pump and ribosomal protection protein mechanisms of tetracycline resistance. The systemic exposure (i.e., maximum plasma concentrations [Cmax] and area under the plasma concentration-time curve [AUC]) after intravenous (IV) administration were linear and predictable over the dose range of 25 and 600mg in healthy subjects. The oral bioavailability of omadacycline was 34.5% under fasted conditions (no food intake 6h before and 4h after dosing). Both AUC and Cmax values significantly decreased (41-61%) when a high-fat meal, with and without dairy, were administered 2h before oral dosing of omadacycline. Similar to other tetracyclines, it is advisable to avoid concurrent administration of divalent- or trivalent cation-containing products (e.g., antacids and iron-containing preparations) for at least 4h after oral administration of omadacycline. Omadacycline has a large volume of distribution (190L) and low plasma protein binding (21.3%) that was concentration independent. Systemic exposure of omadacycline in epithelial lining fluid (ELF) and alveolar macrophages was greater than in plasma in healthy adult subjects. Omadacycline is excreted unchanged in the feces (81.1%) and urine (14.4%), and has a low potential for drug-drug interactions since it was not a substrate, inhibitor, or inducer of major cytochrome-metabolizing enzymes or organic anion transporters (OATs). No clinically significant differences in the pharmacokinetics of omadacycline have been observed for age, sex, and renal or hepatic impairment. Pharmacokinetic-pharmacodynamic studies have confirmed that the AUC from time zero to 24h (AUC24)/minimum inhibitory concentration (MIC) ratio was the best index for correlating unbound plasma and total-drug ELF concentrations with the efficacy of omadacycline. A population pharmacokinetic model was developed with data from healthy subjects and infected patients and used to establish interpretive criteria for in vitro susceptibility testing and dosing regimens of omadacycline for treating acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia.

665. In vitro Activity of Omadacycline Against Recent (2018) Bacterial Pathogens from the United States and Europe Obtained from Skin and Skin Structure, Respiratory, and Urinary Tract Infections

BackgroundOmadacycline (OMC) was FDA approved to treat acute bacterial skin and skin structure infection (ABSSSI) and community-acquired bacterial pneumonia (CABP) for indicated organisms in 2018. Phase 2 OMC clinical trials for uncomplicated urinary tract infection (uUTI; NCT03425396) and acute pyelonephritis (NCT03757234) are ongoing. OMC is active against bacterial isolates expressing common tetracycline, penicillin, fluoroquinolone, and macrolide resistance mechanisms.MethodsIsolates (14,000) were collected in 2018 from 31 medical centers located in the United States and 38 medical centers in Europe, including 3,458 staphylococci, 1,551 streptococci, 746 enterococci, 574 Haemophilus spp., and 5,690 Enterobacterales isolates. One isolate per patient infection episode was tested. Identifications were confirmed by MALDI-TOF MS and susceptibility testing was performed using CLSI broth microdilution methods.ResultsOMC (MIC50/90, 0.12/0.25 mg/L) was highly active against S. aureus isolates from skin and skin structure infection (SSSI; 99.3% susceptible [S]) including MRSA (97.7%S) and MSSA (99.9%S) (table). Similarly, OMC demonstrated potent activity against S. aureus isolates from respiratory tract infection (RTI; MIC50/90, 0.12/0.25 mg/L) including MSSA (98.2%S). All S. lugdunensis isolates from SSSI were S (100.0%) to OMC. All Streptococcus anginosus group (100.0%) and 97.6% of S. pyogenes isolates from SSSI were S to OMC as were 98.0% of S. pneumoniae from RTI. No streptococci were resistant (R) to OMC. OMC (MIC50/90 0.12/0.25 mg/L) had potent activity against E. faecalis isolates from SSSI (99.0%S). OMC S against E. cloacae and K. pneumoniae isolates from SSSI was 92.1% S and 89.4% S, respectively. Similarly, 86.2% of K. pneumoniae isolates from RTI were S to OMC. Susceptibility of H. influenzae isolates from RTI to OMC was 99.8%S (no isolates were R). ≥90.0% of E. coli (MIC50/90, 1/2 mg/L) and K. pneumoniae (MIC50/90, 2/4 mg/L) UTI isolates were inhibited by ≤4 mg/L of OMC.ConclusionOMC was highly active against bacterial pathogens associated with ABSSSI, CABP, and UTI including staphylococci (97.7%-100.0%S), streptococci (97.6%-100.0%S), E. faecalis (99.0%S). E. cloacae (92.1%S), K. pneumoniae (86.2%-89.4%S), and E. coli. Disclosures All authors: No reported disclosures.

Omadacycline in community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections: a profile of its use

Omadacycline (Nuzyra™) is an orally bioavailable, first-in-class, semisynthetic aminomethylcycline antibacterial. A derivative of minocycline, omadacycline has a novel structure that overcomes common mechanisms of tetracycline resistance. In vitro, omadacycline had broad-spectrum activity against Gram-positive, Gram-negative, and atypical bacteria that can cause community-acquired bacterial pneumonia (CABP), and acute bacterial skin and skin structure infections (ABSSSI). In clinical trials, omadacycline was noninferior to moxifloxacin and linezolid in terms of early clinical response rates in patients with CABP and ABSSSI, respectively. Omadacycline was generally well tolerated, with most treatment-emergent adverse events being mild to moderate in severity.