Reivindicaciones
1. A method for evaluating the integrity of the cell wall of a bacterium in a pure culture in the presence of an antibiotic acting on the bacterial cell wall which comprises: i) adding to said pure culture of said bacterium an antibiotic acting on the bacterial cell wall, and ii) determining the presence of extracellular DNA fragments in the culture medium, wherein the presence of extracellular DNA fragments in the culture medium is indicative that the integrity of the cell wall of the bacterium has been damaged. 2. The method according to claim 1, wherein the method comprises between steps (i) and (ii), immobilizing a sample from the culture of step (i) on a slide. 3. A method for evaluating the integrity of the cell wall of the bacteria present in a culture in the presence of an antibiotic acting on the bacterial cell wall which comprises: i) adding to said culture an antibiotic acting on the bacterial cell wall, ii) adding lysis solution to the culture resulting from step i), wherein said lysis solution is a lysis solution specific for those bacteria the cell wall of which has been damaged by the antibiotic acting on the bacterial cell wall, and comprises a buffer with a pH comprised between 3 and 11.5, and iii) determining the presence of bacterial nucleoid, wherein the presence of bacterial nucleoid in the medium is indicative that the integrity of the cell wall of the bacteria has been damaged. 4. The method according to claim 3, wherein the bacteria present in the culture belong to the same species or to different species. 5. The method according to claim 3 or 4, wherein the lysis solution further comprises up to 3% of an ionic detergent or a non-ionic detergent. 6. The method according to claim 5, wherein the ionic detergent is a detergent selected from the group consisting of sodium dodecylsulfate, alkylbenzene sulfonate, laurylsarcosine, glycocholic acid salt hydrate, and the mixtures thereof. 7. The method according to claim 5, wherein the non-ionic detergent is selected from the group consisting of t-octylphenoxypolyethoxyethanol, N,N-Bis(3-D-gluconamidopropyl)cholamide, tricosaethylene glycol dodecylether, N-decanoyl-N-methylglutamine, digitonin, dodecanoyl-N-methylglucamide, heptanoyl-N-methylglutamide, branched octylphenoxypoly(ethyleneoxy)ethanol, N-nonanoyl-N-methylglucamine, octylphenoxypolyethoxyethanol, N-octanoyl-N-methylglutamine, Span 20 solution and polysorbate 20. 8. The method according to any of claims 3 to 7, wherein the lysis solution further comprises up to 3 M concentration of a salt. 9. The method according to claim 3 or 4, wherein the lysis solution comprises 0.2 M (hydroxymethyl)-1,3-propanediol, 0.025% sodium dodecylsulfate, 0.5 M or 0.05 M sodium chloride, and pH 10. 10. The method according to claim 3 or 4, wherein the lysis solution comprises 0.2 M (hydroxymethyl)-1,3-propanediol, 5% Triton X-100, 1 M sodium chloride, and pH 10. 11. The method according to claim 3 or 4, wherein the lysis solution comprises 0.3 M dibasic sodium phosphate, 2% sodium dodecylsulfate, 0.05 M ethylenediamine-tetraacetic acid and pH 11.45. 12. The method according to any of claims 3 to 11, wherein the method further comprises before or after step (ii), immobilizing a sample from the culture on a support. 13. The method according to any of claims 1 to 12, wherein the observation of the presence of extracellular DNA fragments or of the bacterial nucleoid in the culture medium is carried out by means of staining. 14. The method according to claim 13, wherein the staining is carried out by means of using one or more fluorochromes. 15. The method according to claim 14, wherein said fluorochromes are selected from the group consisting of Hoechst 33342, Hoechst 33258, DAPI, chromomycin A3, mithramycin, ethidium bromide, acridine orange, thiazole orange, 7-AAD, cyanine derivatives, and the variants of fluorochromes TOTO, YOYO, BOBO, POPO, JOJO, LOLO, SYTOX, PO-PRO, BO-PRO, YO-PRO, TO-PRO, JO-PRO, PO-PRO and LO-PRO. 16. The method according to any of claims 1 to 15, wherein the antibiotic acting on the bacterial cell wall is selected from the group consisting of a β-lactam antibiotic, an isoniazid, an ethionamide, an ethambutol, a cycloserine and a glycopeptide antibiotic. 17. The method according to claim 16, wherein the β-lactam antibiotic is selected from the group consisting of penicillins, cephalosporins, cephamycins, carbacephem, carbapenems, monobactams and β-lactamase inhibitors. 18. The method according to claim 17, wherein the β-lactamase inhibitors are selected from the group consisting of clavulanic acid, sulbactam and tazobactam. 19. The method according to claim 16, wherein the glycopeptide antibiotic is vancomycin or teicoplanin. 20. A method for determining the sensitivity of a bacterium to an antibiotic acting on the bacterial cell wall which comprises evaluating the integrity of the cell wall of said bacterium by means of a method according to any of claims 1 to 19, wherein if the integrity of the cell wall of the bacterium has been damaged, then the bacterium is sensitive to the antibiotic. 21. A method for designing an antibiotic therapy customized for an individual suffering a bacterial disease which comprises i) isolating the bacterium causing the bacterial disease from a sample originating from said individual, and ii) evaluating the integrity of the cell wall of said bacterium by means of a method according to any of claims 1 to 19, wherein if the integrity of the cell wall of said bacterium has been damaged, then said individual can receive a therapy based on an antibiotic acting on the cell wall. 22. A method for identifying a compound acting on the bacterial cell wall which comprises: i) contacting a culture containing a bacterium sensitive to an antibiotic acting on the bacterial cell wall in the presence of the candidate compound, and ii) evaluating the integrity of the cell wall of said bacterium by means of a method according to any of claims 1 to 19, wherein if the integrity of the cell wall of said bacterium has been damaged, then the candidate compound is a compound acting on the bacterial cell wall. 23. A method for identifying a persister bacterium or a bacterium tolerant to an antibiotic acting on the bacterial cell wall in a culture containing sensitive bacteria, which comprises evaluating the integrity of the cell wall of the bacteria present in said culture by means of a method according to any of claims 3 to 19, wherein the bacterium the cell wall integrity of which has not been damaged is identified as a persister or tolerant bacterium. 24. A lysis solutioncharacterized in that it only affects the bacteria having the bacterial wall damaged by the action of an antibiotic, comprising a buffer and a pH between 3 and 11.5. 25. The lysis solution according to claim 24, wherein said lysis solution further comprises up to 3% of an ionic detergent or a non-ionic detergent 26. The lysis solution according to claim 25, wherein the ionic detergent is a detergent selected from the group consisting of sodium dodecylsulfate, alkylbenzene sulfonate, laurylsarcosine, glycocholic acid salt hydrate, and the mixtures thereof. 27. The lysis solution according to any of claims 25, wherein the non-ionic detergent is selected from the group consisting of t-octylphenoxypolyethoxyethanol, N,N-Bis(3-D-gluconamidopropyl)cholamide, Brij(r) 35 P, N-decanoyl-N-methylglutamine, digitonin, dodecanoyl-N-methylglutamide, heptanoyl-N-methylglutamide, branched octylphenoxypoly(ethyleneoxy)ethanol, N-nonanoyl-N-methylglutamine, Nonidet P 40, N-octanoyl-N-methylglutamine, Span 20 solution and polysorbate 20. 28. The lysis solution according to any of claims 24 to 27, wherein the lysis solution further comprises up to 3 M concentration of a salt. 29. The lysis solution according to claim 24, wherein the lysis solution comprises 0.2 M (hydroxymethyl)-1,3-propanediol, 0.025% sodium dodecylsulfate, 0.5 M or 0.05 M sodium chloride, and pH 10. 30. The lysis solution according to claim 24, wherein the lysis solution comprises 0.2 M (hydroxymethyl)-1,3-propanediol, 5% Triton X-100, 1 M sodium chloride, and pH 10. 31. The lysis solution according to claim 24, wherein the lysis solution comprises 0.3 M dibasic sodium phosphate, 2% sodium dodecylsulfate, 0.05 M ethylenediamine-tetraacetic acid, and pH 11.45. 32. Use of a lysis solution according to any of claims 24 to 31 for evaluating bacterial cell wall integrity. 33. A kit comprising a lysis solution according to any of claims 24 to 31.
