Combinations of antibacterial active substances, pharmaceutical compositions containing same and their use in the treatment of infections - Patents.com

Abstract

The object of the present invention is combinations of antibacterial active substances, pharmaceutical compositions containing them and their use in the prevention and treatment of infectious diseases in humans and animals.

Description

[Technical field]

[0001] The object of the present invention is combinations of antibacterial active substances, pharmaceutical compositions containing them and their use in the treatment of infectious diseases in humans and animals. [Background technology]

[0002] Resistance to antimicrobial agents, also referred to as "antimicrobial resistance", is an adaptive phenomenon whereby microorganisms acquire the ability to survive antimicrobial agents that were initially able to inhibit the growth of or kill said microorganisms.

[0003] The overuse and misuse of antimicrobial drugs in human and animal therapy and animal husbandry is one of the causes of the emergence and spread of resistant bacterial strains.

[0004] It is therefore clear that antimicrobial resistance is recognised as a global public health priority, as it has important implications not only from a clinical point of view but also from an economic point of view.

[0005] For this reason, the scientific community has long been searching for alternatives to antimicrobial therapy for the treatment of bacterial infections. Among the various alternatives, some organic acids (OAs), and / or natural or synthetic essential oils, and / or some plant-derived molecules (synthetically reproduced plant-derived molecules are also called "nature identical substances" (NICs)) show effective antibacterial activity and are therefore currently used not only in human and veterinary therapy, but also in livestock nutrition, among others.

[0006] Similar problems must be addressed with coccidiosis, an intestinal disease caused by a protozoan that is particularly prevalent and serious in poultry farms.

[0007] Hongbin Si et al.'s paper (XP-002687332) is about the antibacterial effect of oregano essential oil alone and in combination with antibiotics against extended-spectrum β-lactamase-producing Escherichia coli.

[0008] Oliva Alessandra et al.'s paper (XP-055973526) presents an extensive investigation of tea tree oil (TTO) against a number of multidrug-resistant (MDR) microorganisms, particularly gram-negative bacteria and methicillin-resistant Staphylococcus aureus.

[0009] WO 2021 / 114201A1 describes a composition comprising at least one essential oil or at least one essential oil extract having broad-spectrum antibacterial activity.

[0010] Giulia Giovagnoni et al. (XP-055973294) describes an in vivo study evaluating the antimicrobial efficacy of conventional antimicrobial agents and MCFAs (medium-chain fatty acids with antimicrobial activity) against Brachyspira hyodysenteriae against deposited strains (including ATCC 27164) isolated in northern Italy.

[0011] Bozkurt M. et al. (XP-055973593) describes oregano essential oil (OEO) as a potential candidate drug for the control of chicken coccidiosis. The objective of this study was to determine whether synergistic effects could occur when combining OEO with the approved coccidiostat monensin sodium (MON) at low doses as a feed supplement.

[0012] However, there is a continuing need to discover new treatments to conventional antimicrobial therapy that minimize the use of commonly used antimicrobial agents by limiting their dosage and / or frequency of administration, while at the same time exerting potent antimicrobial activity and preventing the development of antimicrobial resistance. Summary of the Invention

[0013] Objective of the invention The aim of the present invention is to provide a combination of active ingredients with strong antibacterial and anticoccidial activity, reducing the use of conventional drugs and limiting the risk of the development of antibacterial resistance.

[0014] Another object of the present invention is to provide pharmaceutical compositions comprising said combination and their use in the treatment of animals and humans. [Brief description of the drawings]

[0015] (Not stated in the original text)

[0016] Detailed Description of the Invention After extensive and intensive research and development activities, the applicant has surprisingly discovered that some specific molecules, including some Nature Identical Substances (NICs), can significantly amplify the activity of certain antibacterial agents and exert strong and synergistic antibacterial action against certain bacterial genera. In addition to Nature Identical Substances (NCIs), natural or synthetic essential oils such as garlic oil, thyme oil, oregano oil, rosemary oil, etc., are also of interest, including thymol, carvacrol, eugenol, etc.

[0017] Thus, according to one of its aspects, the object of the present invention is to provide a composition for use in the treatment of bacterial infections caused by Brachyspira spp., E. coli spp., Salmonella spp., Campylobacter spp. or Streptococcus spp., Vibrio spp., comprising: (i) at least one compound selected from the group consisting of: at least one organic acid or salt thereof selected from the group consisting of sorbic acid, citric acid, benzoic acid, hexanoic acid, lauric acid and mixtures thereof; at least one plant-derived terpene, preferably including thymol, carvacrol, eugenol and mixtures thereof or selected from the group consisting of: Monolaurin; Along with (ii) at least one antibacterial agent selected from the group consisting of colistin, amoxicillin, neomycin, tylosin, lincomycin, enrofloxacin, tetracycline, florfenicol, tiamulin, doxycycline, and pharmaceutically acceptable salts thereof; A synergistic pharmaceutical composition or combination comprising or consisting of:

[0018] Preferably, said compound (i) is selected from plant terpenes, even more preferably, said compound (i) is selected from eugenol and thymol and mixtures thereof; more preferably, said compound (i) is thymol.

[0019] Preferably, said compound (i) is chosen from natural or synthetic essential oils such as thyme oil, oregano oil, rosemary oil, among others, which also contain thymol, carvacrol, eugenol.

[0020] Preferably, said compound (i) is selected from natural or synthetic essential oils, such as garlic oil.

[0021] Preferably, said antibacterial agent (ii) is selected from the group comprising or consisting of colistin, tetracycline, and neomycin and mixtures thereof; more preferably, said (ii) is colistin.

[0022] According to a preferred embodiment, said compound (i) is selected from plant terpenes, preferably eugenol and thymol, and mixtures thereof, and said antibacterial agent (ii) is selected from the group comprising or consisting of colistin, tetracycline and neomycin, and mixtures thereof.

[0023] According to one embodiment, the present invention provides a method for the treatment of a bacterial infection caused by Brachyspira spp., Escherichia coli spp., Salmonella spp., Campylobacter spp. or Streptococcus spp., comprising administering to said patient: a. tetracycline or one of its pharma- ceutically acceptable salts and citric acid and / or its salts; b. tetracycline or one of its pharma- ceutically acceptable salts and sorbic acid and / or its salts; c. tetracycline or one of its pharma- ceutically acceptable salts and benzoic acid and / or its salts; d. tetracycline or one of its pharma- ceutically acceptable salts and thymol; e. tetracycline or one of its pharma- ceutically acceptable salts and eugenol; f. neomycin or one of its pharma- ceutically acceptable salts and sorbic acid and / or its salts; g. neomycin or one of its pharma- ceutically acceptable salts and benzoic acid and / or its salts; h. neomycin or one of its pharma- ceutically acceptable salts and thymol; i. neomycin or one of its pharma- ceutically acceptable salts and eugenol; j. colistin or one of its pharma- ceutically acceptable salts and sorbic acid and / or a salt thereof; k. colistin or one of its pharma- ceutically acceptable salts and benzoic acid and / or its salts; l. colistin or one of its pharma- ceutically acceptable salts and thymol; m. colistin or one of its pharma- ceutically acceptable salts and eugenol; n. colistin or one of its pharma- ceutically acceptable salts and hexanoic acid and / or its salts; The present invention relates to a synergistic pharmaceutical composition or combination comprising or consisting of at least one of the above.

[0024] According to one embodiment, an object of the present invention is a synergistically acting pharmaceutical composition or combination comprising or selected from the group consisting of combinations (a) to (n) as defined above for use in a method for the prevention and / or treatment of infections caused by Brachyspira spp., Escherichia coli spp., Salmonella spp., Campylobacter spp. or Streptococcus spp.

[0025] According to one embodiment, the subject of the invention is a synergistic combination comprising or alternatively consisting of thymol and colistin and / or at least one pharma- ceutically acceptable salt thereof.According to a further aspect of the invention, said synergistic combination consists of thymol and colistin and / or at least one pharma- ceutically acceptable salt thereof.

[0026] Compound (i) and antibacterial agent (ii) are known in the art.

[0027] For example, thymol, 2-isopropyl-5-methylphenol, a Nature Identical Substance (NIC) known for its antibacterial activity and lack of serious side effects; thymol occurs naturally in plants of the Thymus genus.

[0028] Colistin is a polymyxin antibacterial agent formed from a mixture of cyclic colistin A and B polypeptides. Although highly effective, colistin is not widely used due to the risk of potential nephrotoxicity. Therefore, the possibility of exploiting the potent antibacterial properties of colistin at low doses, made possible by the co-administration of thymol to enhance its efficacy, represents an important technological advance in the field of antibacterial therapy.

[0029] As mentioned above, colistin and the other antibacterial agents may be present in the combination of the invention in their native form or, where chemically possible, in the form of one of their pharma- ceutically acceptable salts, e.g., sodium salts, phosphate salts, sulfate salts, etc. Unless otherwise specified, the term "antibacterial agent" as used herein includes pharma- ceutically acceptable salts, where chemically possible.

[0030] In the present invention, not only Nature Identical Substances (NICs) but also natural or synthetic essential oils such as garlic oil, thyme oil, oregano oil and rosemary oil, including inter alia thymol, carvacrol, eugenol, etc., are considered for the purposes of the present invention.

[0031] In a preferred embodiment, the combination for use according to the invention is characterized in that said compound (i) is selected from natural or synthetic essential oils, preferably from garlic oil, thyme oil, oregano oil, rosemary oil, especially also containing thymol, carvacrol, eugenol, preferably from said essential oils, and (ii) in combination with at least one antibacterial agent comprising or selected from the group consisting of colistin, amoxicillin, neomycin, tylosin, lincomycin, enrofloxacin, tetracycline, florfenicol, tiamulin, doxycycline and one of its pharmaceutically acceptable salts, for use in the treatment of bacterial infections caused by Brachyspira spp., Escherichia coli spp., Salmonella spp., Campylobacter spp. or Streptococcus spp., Vibrio spp.

[0032] Studies carried out by the applicant on the combination of conventional antibacterial agents with the same natural compounds or other molecules, such as organic acids known for their antibacterial activity, have shown that certain combinations of the invention, such as, but not limited to, thymol and colistin, exert strong antibacterial activity. Indeed, similarly strong antibacterial activity was obtained when bacterial strains were treated in vitro with a mixture of the two active ingredients at concentrations significantly lower than their respective minimum inhibitory concentrations (MICs). Of particular relevance is the fact that component (i) allows the effective dose of antibiotic (ii) to be reduced by up to 50% while still achieving a comparable antibacterial effect, as shown in the experimental section below. As a result, by using the combination of the invention, a subject can be administered half the MIC dose of antibacterial agent (e.g. colistin), which on the one hand reduces side effects for the treated subject and on the other hand reduces the possibility of the development of antibacterial resistance.

[0033] According to another aspect of the invention, it is an object of the present invention to use one or more compounds (i), such as thymol, to enhance the antibacterial activity of one or more antibacterial compounds (ii), such as colistin.

[0034] According to another aspect, an object of the present invention is a pharmaceutical composition comprising a combination of the invention in all the above embodiments, together with one or more pharma- ceutically acceptable excipients and vehicles, for use in the prevention and / or treatment of bacterial infections caused by Brachyspira spp., Escherichia coli spp., Salmonella spp., Campylobacter spp. or Streptococcus spp., Vibrio spp.

[0035] According to the present invention, prevention and treatment are understood to be for humans or animals.

[0036] According to another aspect of the invention, the object of the invention is to provide a method for the treatment and / or prevention of infections caused by Eimeria coccidia, comprising: (iii) preferably, plant-derived terpene compounds selected from thymol, carvacrol and eugenol; more preferably, thymol; and (iv) an antibacterial agent selected from narasin, salinomycin, and monensin, and / or at least one pharma- ceutically acceptable salt thereof; It is a synergistic combination comprising:

[0037] Advantageously, the combinations and pharmaceutical compositions of the invention comprise or consist of thymol and colistin.

[0038] Advantageously, the combinations and pharmaceutical compositions of the present invention comprise or consist of thymol and colistin for use in a method for treating bacterial infections caused by Brachyspira spp., Escherichia spp., Salmonella spp., Campylobacter spp. or Streptococcus spp., Vibrio spp.

[0039] For example, the combinations and compositions of the present invention are particularly useful for the prevention and treatment of bacterial infections or coccidiosis in poultry and mammal farms, for example livestock such as sheep, cattle and pigs.

[0040] The composition of the present invention can be in unit dose form or multiple dose form according to intended use.In fact, for administration to humans or single animals, it is more useful to have a dosage unit, and for administration to many animals, such as in livestock farms, it is more advantageous to have multiple dose composition, for example, to divide and add to feed or water as necessary.

[0041] According to another aspect of the invention, the object of the invention is the combination and / or composition of the invention for use in the prevention and / or treatment of bacterial infections or coccidiosis, said use being characterized by the fact that the antibacterial agent (ii) or (iv), when combined with compound (i) or (ii), is administered in a "conventional" dose or in a dose lower than the MIC dose, expressed as the minimum inhibitory concentration. The antibacterial agent (ii) or (iv) is preferably administered in a dose ranging from 50% to 90%, more preferably from 50% to 70%, advantageously about 50% of the MIC dose.

[0042] By "MIC dose" herein is meant the minimum dose of an antibacterial agent that inhibits the growth or replication of a bacterial strain, based on which a threshold is defined to describe whether a microorganism is sensitive or resistant to the action of the antibacterial agent itself (https: / / www.eucast.org / ).

[0043] According to another aspect of the invention, the object of the invention is the combination and / or composition of the invention for use in the prevention and treatment of bacterial infections or coccidiosis, said use being characterized by the fact that both compound (i) or (iii) and antibacterial agent (ii) or (iv) are administered in dosages lower than the respective conventional dosages when such compounds are administered separately and not in combination with each other. According to a preferred embodiment of this aspect of the invention, antibacterial agent (ii) or (iv) is preferably administered in the range of 25% to 90%, more preferably 25% to 70%, advantageously 25% to 50% of the MIC dosage.

[0044] According to another aspect of the invention, an object of the invention is a method for preventing and treating bacterial infections, comprising administering to a subject in need of treatment an effective amount of a compound or composition of the invention as described herein.

[0045] The compositions according to the invention comprising the combination according to the invention together with pharma- ceutically acceptable excipients and / or vehicles may be obtained according to known methods.

[0046] By way of example, oral or parenteral compositions may be prepared, with oral compositions being preferred.

[0047] Among the oral compositions, liquid preparations such as solutions, suspensions, emulsions, syrups, etc.; solid preparations such as agglomerated powders, granules, pellets, capsules, tablets, etc.; and semi-solid preparations such as pastes, gels, etc. may be prepared.

[0048] The excipients and vehicles used in the preparation of the compositions of the invention may be selected from those conventionally used in the pharmaceutical technical field.

[0049] By way of example, water, aqueous alcohol solutions, glycerin, polyethylene glycol, propylene glycol, N,N-dimethylacetamide, etc., along with any stabilizers, thickeners, surfactants, buffers, and flavoring and / or sweetening agents, may be used as vehicles for the solutions. The solubility of the components may be increased by the selection of an appropriate pH and / or the addition of hydrophilic polymers such as cyclodextrins and polyvinylpyrrolidone, and the complexes thus formed may be lyophilized and redissolved in a suitable liquid.

[0050] Suspensions can be prepared using water and hydrophilic polymers such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and surfactants such as polysorbates.

[0051] Emulsions or microemulsions are two-phase systems and can be prepared by mixing two immiscible phases, such as oil-in-water, water-in-oil, or multiple emulsions (oil-in-water-in-oil or water-in-oil-in-water). Emulsions generally require the addition of a suitable surfactant, according to methods known to those skilled in the art.

[0052] A solid composition may be prepared from powders, granules, solid dispersions, or pellets / beads, the latter of which may be obtained from a microencapsulation process.

[0053] The main solid forms are in the form of sachets, capsules or tablets.

[0054] Sachets are powder or granular formulations which may be dissolvable in the oral cavity or which may be administered after dissolution or dispersion in a suitable liquid, usually water.

[0055] Tablets are generally obtained by compressing powders, granules or beads and are formulated with or without excipients, including diluents, binders, disintegrants, lubricants or ingredients capable of modifying absorption in the stomach or intestine. Tablets can be uncoated, coated, effervescent soluble, dispersible, orodispersible, modified release, gastroresistant or for use in the buccal cavity.

[0056] Capsules are manufactured with a hard or soft shell, usually made of gelatin, possibly film-coated. Capsules contain solids, liquids or pastes and are in the form of soft capsules, hard capsules, modified release capsules, gastro-resistant capsules or wafer-shaped capsules.

[0057] Other solid forms may be in the form of chewing gum.

[0058] Also included are lipid-based formulations, which can be classified according to their composition, size, chemical properties and basic lipid system into lipid solutions, lipid suspensions, emulsions, microemulsions, nanoemulsions, self-emulsifying and self-microemulsifying systems, solid lipid nanoparticles, solid lipid dispersions, niosomes and liposomes.As such, all these formulations are known to those skilled in the art and can include conventional excipients and vehicles such as surfactants, lipids, water, solvents, cosolvents, polysaccharides, etc.

[0059] Considering the hydrophobicity of some compounds (i) and (iii), e.g. thymol, and the resulting low aqueous solubility, nanosuspension type systems including casein using "pH-driven" techniques, nanoemulsions and oil-in-water (O / W) microemulsions, solid lipid particles, liposomes, cyclodextrins or encapsulation in natural polymers may be used for the preparation of the compositions of the invention.

[0060] The present invention will now be described with reference to the following examples, which are given for illustrative purposes only and are not intended to limit the invention in any way. EXAMPLES

[0061] Experimental Section Example 1 Evaluating the efficacy of antimicrobial and nature-identical substances / organic acids combinations The objective of this study was to evaluate whether nature identical substances (NICs) and organic acids (OAs) with known antimicrobial activity can synergistically increase the activity of known antimicrobial agents (ABs) against specific microorganisms. Specifically, the following was performed: - Single studies to evaluate the effect of the individual components of the combination (AB, NIC, OA) on the target microorganisms and establish effective / ineffective doses; -Combination studies combining an ineffective dose of AB with low doses of NIC or OA (which are only partially effective alone) to evaluate whether the efficacy of AB can be increased by combining it with NIC or OA.

[0062] material and method In this study, Streptococcus suis and Escherichia coli K88 were used.

[0063] Bacterial strains Strains were stored at -80°C in appropriate media containing glycerol, and were thawed and cultured according to conventional methods. The characteristics of the strains and the media are shown in Table 1 below. [Table 1]

[0064] Test compounds and stock solutions All ABs shown in Tables 2 and 3 below were obtained and tested from Aplha Aesar. The OAs used are shown in Tables 2 and 3 below and were all obtained from Merck. Stock solutions were prepared as appropriate using methods and media appropriate for the various strains and these may contain 3.5% ethanol to increase solubility.

[0065] Antibacterial Testing The tests were carried out using the microdilution method in 96-well plates with microtiter determinations in medium and culture conditions appropriate for the bacterial strain. 5 ~10 6 CFU / ml) were incubated with the compounds to be tested, and control strains were incubated in medium containing 3.5% ethanol where necessary to exclude the inhibitory effect of ethanol present in the stock solution. After incubation, the MIC was defined as the lowest concentration at which the absorbance at 630 nm was zero and recorded on a Varioskan® LUX multimode microplate reader (Thermo Fisher Scientific). For each test, the percentage of inhibition relative to the control was calculated.

[0066] Phase 1 - Individual Testing AB was tested in the range of 64-0.13 ppm, OA in the range of 100-78 mM, and NIC in the range of 7.5-0.06 nM.

[0067] Table 2 shows the screening of S. suis 701 and S. suis 702. [Table 2]

[0068] Table 3 shows the screening of E. coli 95 and E. coli 97. [Table 3]

[0069] Phase 2 – Combination Testing After stage 1, strains were tested in combination with subeffective doses of AB and OA or NIC in a 2 × 2 checkerboard model. Specifically, two subeffective doses of AB were combined with two subeffective doses (half and quarter of the MIC) of OA or NIC, as shown in Figure 1.

[0070] result Representative results are shown below, with % indicating percentage of inhibition (compounds alone and in combination). [Table 4]

[0071] Tables 4-7 show the % inhibition of the components of the combinations at the effective concentrations and sub-effective amounts (half and quarter of the MIC) shown in Tables 2 and 3, as well as the % inhibition of the combination.

[0072] As will be appreciated, certain combinations provide inhibition that is significantly greater than the individual components and well beyond the additive effect. [Table 5] [Table 6] [Table 7] [Table 8]

[0073] Example 2 Evaluation of the effect of combinations of antimicrobial agents and identical natural compounds against coccidiosis. Anticoccidial tests were performed using a model combining host cell lines and Eimeria species to determine the anticoccidial properties of a given compound, e.g., its ability to prevent Eimeria invasion into cells. More specifically, in this test, Madin-Darby bovine kidney (MDBK) cells and Eimeria tenella sporozoites were used as host cells and coccidia, respectively. MDBK cells were seeded in 24 wells and cultured for 48 h in basal medium containing Dulbecco's modified Eagle's medium, 10% fetal bovine serum, 1x penicillin-streptomycin, and 10 mM L-glutamine to reach confluence. The cells were incubated at 37°C with 5% CO2. Coccidial inocula were prepared according to the method of Shirley et al. in "Biotechnology Guidelines on techniques in coccidiosis research" with some modifications. Sporocysts obtained by mechanical disruption were cultured at a final concentration of 1x10 6 Sporocysts were resuspended at 1000μl / mL in esch medium (0.25% trypsin, 5mg / mL bile salts, 2mg / mL MgCl2). Sporocysts were fragmented for 90 minutes at 41°C. Released sporocysts were then filtered through a 5μm Pluristrainer®, washed by centrifugation (500×g, 10 minutes) and counted. Eimeria sporozoites were infected by overlaying with medium containing either alone (control) or the treatment of interest. Each well was filled with 5×10 4 After infection with sporozoites, cells were incubated for 24 hours at 37° C. and 5% CO2. The invasion rate was determined by the number of extracellular sporozoites and predicted by the following formula:

number

[0074] According to the scheme shown in Figure 2, the combinations of antimicrobial agents (iv) narasin (10 ppm), salinomycin (1 ppm) and monensin (1 ppm) with compounds (iii) thymol (7 ppm), carvacrol (7 ppm) and eugenol (14 ppm) were tested alone or in combination.

[0075] The results are shown in Figures 3 to 5. As can be seen from the figures, the combination showed a significantly higher effect than the effects of the components (iii) and (iv) alone.

Claims

1. A synergistic combination agent for use in the treatment of bacterial infections caused by Brachyspira species, E. coli species, Salmonella species, Campylobacter species, or Streptococcus species, or Vibrio species, (i) Compounds selected from the following: Organic acids selected from sorbic acid, citric acid, benzoic acid, hexanoic acid, and lauric acid; Plant-derived terpenes selected from thymol, carvacrol, and eugenol; and Monolaurin; and (ii) Antimicrobial agents selected from colistin, neomycin, tylosin, lincomycin, enrofloxacin, tetracycline, florfenicol, thiamrin, doxycycline and / or at least one of their pharmaceutically acceptable salts; A combination agent containing the above.

2. The combination agent according to claim 1, characterized in that the compound (i) is selected from eugenol and thymol, preferably thymol.

3. The combination agent according to claim 1, characterized in that the compound (i) is selected from natural or synthetic essential oils of garlic oil, thyme oil, oregano oil, and rosemary oil, which contain thymol, carvacrol, and eugenol.

4. The combination agent according to claim 1, wherein the antimicrobial agent (ii) is selected from colistin, tetracycline, and neomycin; preferably colistin.

5. One or more of the following: a. Tetracycline or one of its pharmaceutically acceptable salts and citrate; b. Tetracycline or one of its pharmaceutically acceptable salts and sorbic acid; c. Tetracycline or one of its pharmaceutically acceptable salts and benzoic acid; d. Tetracycline or one of its pharmaceutically acceptable salts and thymol; e. Tetracycline or one of its pharmaceutically acceptable salts and eugenol; f. Neomycin or one of its pharmaceutically acceptable salts and sorbic acid; g. Neomycin or one of its pharmaceutically acceptable salts and benzoic acid; h. Neomycin or one of its pharmaceutically acceptable salts and thymol; i. Neomycin or one of its pharmaceutically acceptable salts and eugenol; j. Colistin or one of its pharmaceutically acceptable salts and sorbic acid; k. colistin or one of its pharmaceutically acceptable salts and benzoic acid; l. colistin or one of its pharmaceutically acceptable salts and thymol; m. colistin or one of its pharmaceutically acceptable salts and eugenol; n. colistin or one of its pharmaceutically acceptable salts and hexanoic acid The combination agent according to claim 1, characterized in that it is selected from among.

6. The combination agent according to claim 5, characterized by being selected from colistin or one of its pharmaceutically acceptable salts and thymol.

7. A pharmaceutical composition comprising the combination agent according to any one of claims 1 to 6, one or more pharmaceutically acceptable excipients and vehicles, for use in the treatment of bacterial infections caused by Brachyspira species, Escherichia coli species, Salmonella species, Campylobacter species, or Streptococcus species, Vibrio species.

8. The pharmaceutical composition according to claim 7, wherein the infection is caused by a species of Escherichia coli or Streptococcus.

9. The pharmaceutical composition according to claim 7, characterized in that the antibacterial agent (ii) is administered in a dose less than the MIC dose, preferably in a dose in the range of 50% to 90% of the MIC dose, more preferably in a dose in the range of 50% to 70%, and even more preferably in a dose of 50% of the MIC dose.

10. The pharmaceutical composition according to claim 7, characterized in that the antibacterial agent (ii) is administered in an amount in the range of 25% to 90%, preferably 25% to 70%, and more preferably 25% to 50%, relative to the MIC dose.

11. A synergistic combination agent for use in the treatment and / or prevention of infections caused by Eimeria species, (iii) Plant-derived terpenes selected from thymol, carvacrol, and eugenol; and (iv) Antimicrobial agents selected from naracin, salinomycin and monensin and / or at least one pharmaceutically acceptable salt thereof; A combination agent containing the above.

12. A pharmaceutical composition comprising the combination agent according to claim 11 and one or more pharmaceutically acceptable excipients and vehicles for use in the treatment of infections caused by Eimeria species.

13. The pharmaceutical composition according to claim 7, characterized by being a formulation for oral administration.

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