Introduction

Nowadays many attentions have been paid to in the other hand Pseudomonas aeruginosa as a top three opportunistic pathogen in hospitalized, immune compromised, and cystic fibrosis patients (1).

Infection caused by P. aeruginosa are often life_ threatening and difficult to treat because of its primary limited susceptibility to commonly use antimicrobial agents (2).

It is necessary to the utilization of alternative antibacterial therapies against Pseudomonas aeruginosa infections. Synergistic combinations of antibiotics and other antimicrobials maybe effective against infections where the development of resistance and/or subsequent failure to monotherapy is prevalent associate with prevention of emergence of bacterial resistance (3,4). One such preference is the possible therapeutic use of probiotics as an adjunct to chemotherapy (5). Probiotics are dietary supplements containing potentially useful yeasts or bacteria. According to the currently adopted description by FAO/WHO in 2001, probiotics are ‘live microorganisms, which when administered in requisite amounts confer a health benefit on the host’ (6, 4).supernatant  of Most lactobacillus bacteria(LAB) such L. plantarum contains several antimicrobials such as organic acids, hydrogen peroxide, aroma components, fatty acid  and low-molecular-mass compounds which kill pathogens(7).

LAB strains can produce organic acid through hetero-fermentative pathways, and these compounds may interact with cell membranes, induce intracellular acidification and diffuse passively across the membrane and protein denaturation (8). H2O2  by peroxidation of membrane lipids thus the  altering the cell membrane permeability and can act as a precursor of the production of bactericidal free radicals such as superoxide (O₂^ˉ ) and hydroxyl (OH^ˉ  ) radicals that can damage DNA (9).

Therapeutic role of probiotics in the P. aeruginosa (10,11,12), Staphylococcus aureus (13) and salmonella (6,14, 5) infections have been reported. Treatment with combination of probiotics and antibiotic have been reported to be successful in the management of Helicobacter pylori infection (15).

Combinatorial therapy by probiotic and antibiotic may provide higher antimicrobial activity and decrease the dose of antibiotic required in addition to replenishing the intestinal flora thereby providing benefit to the host and also decrease other antibiotics side effects (16). In the present study the possible effect of combinations between the cell-free lactobacillus supernatant (CFS) and Conventional Antibiotics such Amikacin or Gentamicin Ciprofloxacin and Azithromycin on their antibacterial potencies against Pseudomonas aeruginosa were evaluated.

 Materials and Methods

Bacterial strains and growth conditions

Pseudomonas aeruginosa  ATCC: 27853 and Lactobacillus plantarum ATCC:8014  was procured from Persian Type Culture Collection (PTCC).

aeruginosa sub cultured in nutrient broth (Merck, Germany) for 24 h at 37°C. L. plantarum were grown in De Mann Rogosa Sharpe (MRS) broth  (Merck, Germany) for 48 h at 37°C under anaerobic conditions in a Coy Laboratory anaerobic chamber. (17).

Antibiotic susceptibility tests

Qualitative antibacterial susceptibility of the P. aeruginosa were determined according to the standard disk diffusion (Kirby-Bauer) method (18) using paper disk  including (μg /disc): Azithromycin (15); Ceftriaxone (30); Imipenem (10); Amikacin (30); Chloramphenicol (30); Ceftazidim (30); Tobramycin (10); Gentamycin (10); Ciprofloxacin (5) purchased from Mast Co(Liverpool, UK)

Microbial suspension with 10⁶ colony forming units (CFU/ml) of P. aeruginosa have in NB were prepares specific on to Muller Hilton agar medium. The plates were incubated at 37°C for 24 h in aerobic condition and examined for the inhibition zones diameter appearing around each antibiotic disc. test were carried out thrice for each antibiotics  .Inhibitory zone diameters were compared with the standards provided by the National Committee for Clinical Laboratory Standards (NCCLS) (17).

Preparation of cell free supernatant (CFS) from Lactobacilli strains

CFS was prepared according to the method Ogunbanwo (19).Lactobacillus was grown in 1L deMan, Rogosa and Sharpe (MRS) broth (pH 5.7) for 48 h at 37°C in anaerobic condition. Cell free supernatant obtained by centrifuging the culture at 15000 rpm for 15 min at 4°C and then filtered through 0.45 μm filters (Millipore, Bedford,MA).

In-vitro inhibitory effect of CFS and Antibiotics

Well diffusion method

Antimicrobial activity of CFS was determined by the well diffusion method. In this method, bacterial inoculum colonies from overnight nutrient agar were used to make suspension of the test organisms to be equivalent to the 0.5 McFarland standard. Wells with 6 mm diameter were punched in the agar plates and they were filled with 100 µl of different concentrations of CFS including 10 µl/ml, 50 µl/ml and 100 µl/ml of CFS. The plates were then incubated at 37° C for 24 h and the diameter  zones of inhibition were assessed (20)

The experiments were repeated three times and the mean values of the diameter of inhibition zone with ± standard deviation were calculated.

Determination of minimum inhibitory concentrations (MICs)

The MICs were determined by broth micro dilution assay  according  to the procedures recommended by the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards 2006).

Dilutions of the antibiotics (Amikacin , Gentamicin, Ciprofloxacin and Azithromycin ), ranging from 0.125-256 µg/ml in Muller Hinton Broth were prepared by incorporating the antibiotic stock solution into Muller Hinton Broth. Dilutions of the CFS in the range of 0.12-250 µl/ml were also prepared by incorporation of the CFS into Muller Hinton Broth. Each plate includes positive and negative controls (17).

Briefly, a bacterial inoculum (100 μl), corresponding to 5  10⁵ CFU/ml, was added to 100 μl of serial twofold dilutions of the antibiotics in the wells of microtiter plates. The final volume of each well was 200 μl. The plates were incubated at 37°C for 24 h. The MIC was defined as “the lowest concentration of antibiotic which can inhibited visible growth of microorganism”.

100 μl of liquid from each well without visible growth on to MHA for determination of MBC was used and incubated at 37^ᴏC for 48-72 hrs.

Finally the lowest concentration of antimicrobial agent being able to reduced  99.9% of the bacteria was assessed as MBC (21). Experiments were done in triplicate.

Fractional inhibitory concentration (FIC) determination and interaction effect of two antimicrobial agents (antibiotics + CFS) on test bacteria

Drug interactions were assessed by using a checkerboard microdilution method, the concentrations of antimicrobial agent were typically ranged from four or five below the expected MIC to twice the anticipated MIC as in the 45 degree line in figure 1 (each square represents one plate), using two fold dilutions of each antimicrobial agent, also concentration of MIC point and dilution lower that it for each antimicrobial agent alone.

Inocula were prepared spectrophotometrically and further diluted in order to procure final concentrations ranging from 0.5  10⁶ CFU/ml. Each microdilution well included 100 μl of the diluted (two times) drug concentrations of both antimicrobials (antibiotics and CFS) was inoculated with 100 μl of the diluted (two times) inoculum suspension (final volume of each well, 200 μl). The trays were incubated at 37°C, and the results were read at 24 h visually with a ELISA reader system (statfax-2100, Awareness Technology Inc., USA).

The FIC index was then calculated by using the observing equation with summing the separate FICs for each drugs present in that well:

FIC_index = FIC_A+ FIC_B =  +

Where A is the concentration of drug A in well that is the lowest inhibitory concentration in its row, MIC _A is the MIC of the organism to drug A alone, and FIC _A  is the fractional inhibitory concentration of drug A. Also B is the concentration of drug B in a well that is the lowest inhibitory concentration in its column; MIC _B and FIC_B are defined in the same fashion for drug A.

According to this method, synergism has traditionally been defined as an FIC index of 0.5 or less and additivity as a FIC index of 1.0; antagonism has been defined as a FIC index of 2.0. Synergy was further sub-classified as marked (FIC ≤0.50) and weak (FIC index, between 0.50 and 1.0) (22,23).

Analysis of cell free supernatant (CFS) from L. plantarum for antimicrobial compounds

CFS of each strain of L. plantarum were prepared according to the method of Ogunbanwo(19). The supernatant was filtered using 0.45 µm Millipore filters and 2 aliquot were stored at –20°C until analysed for antimicrobial compounds contain lacticAacid,acetic acids and H2O2 (Sigma) by using reversed-phase fast performance liquid chromatography(RP-FPLC) (24).

Standard stock solutions of lactic acid pKa=3.086  (5.2 mg/mL), acetic acid (5.4  mg/mL) and Hydrogen peroxide (35%) were prepared in ultrapure water and stored at 4 °C (25) .

Standard solutions of organic acids and H2O2 were determined by RP-FPLC, using an AKTA Purifier system (GE Healthcare) equipped with YMC-Triart C18 (250 _˟ 4.6 mmI.D, S-5um, 12nm).

The degassed mobile phase of 0.009 M KH2PO4 adjusted by phosphoric acid to PH 2.06.filtered through a 0.45 µm membrane filter was used at a flow rate of 1ml/min. The wavelength of detection was optimized at 210 nm and the sample injection was 50 µL (24, 26) .CFS from Lactobacilli strains were analyzed by RP-HPLC under the same conditions (24, 27) .

Statistical analysis

The data were analyzed using Graph Pad Prism version 5 (Graphpad Software In, San Deigo, USA). All data were expressed as mean ± S.D. Statistical analyses were evaluated by one-way analysis of variance (ANOVA). Significant level for all tests was considered (p<0. 05)

Results

Antibiotic susceptibility pattern of P. aeruginosa were shown that was sensitive to Amikacin and Gentamicin, Ciprofloxacin while was resistance to Azithromycin (Table1).

The antimicrobial activities assayed against P. aeruginosa by agar well diffusion assay.

The antimicrobial activity of CFS from L.plantarum in different concentration were determined using the agar well diffusion method summarized in  Table 2. The activity was quantitatively assessed on the basis of the inhibition zone, and their activity index was also calculated along with the minimum inhibitory concentration (MIC), In Table 3, we shown the result of the and MIC and minimum bactericidal concentration (MBC) of the CFS and antibiotics were determined by microdilution method. Also, the FIC value for CFS and antibiotics were shown in Table 4. antimicrobial combination  between CFS and Gentamicin or Azithromycin demonstrated synergistic actions against P. aeruginosa. the combination of CFS and Ciprofloxacin or Amikacin demonstrated indifference action.

Table 1: Antibiotic susceptibility pattern of standard strain P.aeruginosa as determined by disc-diffusion technique

S-sensitive R-resistant

Table 2: Inhibition zone diameter of CFS from lactobacillus strains  against P.aeruginosa  PTCC:1430 ^a

zone of inhibition,including the diameter of the well(6mm);mean value of three independen experiments.

Table 3: Minnimum inhibitory concentration (MIC)and Minnimum bactericidal concentration (MBC)  of antimicrobial agents on  the  P.aeruginosa  PTCC:1430 ^a

^aAll determinations were done in  triplicate.

^bCFS dissolved in Cation Adjusted Muller Hinton Broth

antimicrobial compound in the CFS of lactobacillus were identified by comparison of retention times and the UV absorption spectra with those obtained from the corresponding standards.

Peaks  of standard solution  were  observed at (6.00±0.13) min for lactic acid, (6.02±0.06) min for acetic acid, and (3.06±0.0.6) min  for  H2O2, for an average of 5 injections. As a control, the antimicrobial compound profile of sterile MRS medium was analysed (Fig. 2A). Compared with this control chromatogram, the CFS of  L. plantarum (Fig. 2B) contained same peaks that corresponding  to acetic  acid(AA) (6. 23 min), lactic acid(LA) (5.73) and H2O2 (3.02 min).

Table  4: Effect of CFS from  lactobacillus  of  different antibiotics against P.aeruginosa

Table 5: Determination of antimicrobial compounds in CFS from Lactobacilli strains by using HPLC method

However, this  study  showed that  antimicrobial compound is already  present in sterile MRS medium,  but significantly change were abserved in the amount of compound  during growth of L. plantarum (p<0. 05) (Fig 2Aand 2B).

Figure 1: Simplified checher-board method (MIC A and B drugs is considered as 1 µg/ml.   Click here to View figure

Figure 2: HPLC profile of the cell free supernatant of sterile De Man-Rogosa Sharpe(MRS) medium(A), Lactobacillus  plantarum ATCC:8014 (B).   Click here to View figure

Discussion

aeruginosa infection is on of the most difficult or impossible to eradicate infections and therefore this bacterial infection needs new therapeutic protocol and strategy (10, 28).

Antimicrobial combinations has been utilized as an effective therapeutic strategy with the using of benefit various mechanisms of action (16).

A synergestic combination of aminoglycosides (Gentamicin, Tobramycin and Amikacin), fluoroquinolone (Ciprofloxacin) and Penicillins (Carbenicillin) has been used to treat Pseudomonas aeruginosa infections (29). Also, some P.aeruginosa strains have been reported to have resistance to many of  antibiotics (30, 31).

In the present study, the possible effect of CFS on the bactericidal activities of Conventional Antibiotics such  Amikacin or Gentamicin Ciprofloxacin and Azithromycin were evalute Consequently, the study of Conventional antibiotics in combination with probiotics might prove the benefit as to the using of combination the lower the dose of antibiotic alone.

In the present study, we put forward the hypothesis that whether treatment with combination of cell free supernatant from L.plantarum with Conventional antibiotics have higher antimicrobial activity against P. aeruginosa or not.

Keeping in view the combination of cell free supernatant from L.plantarum  and Conventional Antibiotics was further tested to evaluate the possible synergistic effect against P.aeruginosa.

Aminoglycosides and Azithromycin interfere and affect bacterial protein synthesis through binding to the 30s and 50s ribosomal subunits  of the bacterial cell respectively(32,33). The quinolones such ciprofloxacin exhibit their bactericidal action by blocking DNA replication through gyrase inhibition(34).

Previously, studies reported that aminoglicosids  caused increases  reactive oxygen species (ROS) levels in rats (35). In addition, an increase of reactive oxygen species in the bacterial cells in response to Ciprofloxacin has been shown (36).

In previous studies,  separation, purification and identification of antimicrobial agents produced by  LAB, were conducted by several techniques (15, 37, 38,39) and in this study presence of lactic acid ,acetic acid and H₂O₂ in CFS of L.plantarum  was confirmed by HPLC analysis.

The organic acids acts by collapsing the electrochemical proton gradient, and H2O2  by per oxidation of membrane lipids thus the  altering the cell membrane permeability which results in disruption of substrate transport systems (40, 41, 42).

Alakomi and colleagues (2000) also found that  lactic acid, in addition to its antimicrobial property  due to the lowering of the pH, also functions as a permeabilizer of the gram-negative bacterial outer membrane and may act as a potentiate of the effects of other antimicrobial substances (43).

In the present study a significant increase in antibiotics performance in the presence of CFS was observed in compared ,when P.aeruginosa is treated with antimicrobial agent for each of only.

These antibacterial mechanisms of H2O2  and Gentamicin to production of reactive oxygen species (ROS) might have act cooperatively with each other, leads to a higher bactericidal effect of the combination. in support of our finding , Hoffmann have also reported the sub-MICs of Azithromycin suppress the QS-controlled lasB expression  in parallel  with the  inhibition  of QS- controlled  virulence  factors, alginate and increased sensitivity to hydrogen peroxide in P. aeruginosa(44). Our results  showed that  the synergism abserved between CFS and   Azithromycin Can be made by the influence of Azithromycin increasing sensivity of  P. aeruginosa  on H2O2   produced by L.plantarum.

FIC index also further substantiated the synergism effect between the two compounds. We have previously demonstrated that CFS also reduced the MICs of Gentamicin and Azithromycin. This synergistic effect was also confirmed by checkerboard testing (Fig. 4). Gentamicin and Azithromycin had FIC indices of ˂0.5, indicating synergy between CFS and the antibiotic.

Reference

1. Davis. P, Drumm. B. M  and Konstan. M. W, Cystic fibrosis, Am. J Respir. Crit. Care Med,(1996), 154;1229–1256.
2. Vojtová. V, Kolár. M, Hricová. K, Uvízl. R, Neiser. J, Blahut. L, Urbánek. K, Antibiotic utilization and  Pseudomonas aeruginosa resistance in intensive care  units, New Microbiol, ,(2011), 34; 291-298
3. Hayssam Khalil, Tao Chen, Renée Riffon, Rutao Wang and Zhao Wang , Synergy between Polyethylenimine and Different Families of Antibiotics against a Resistant Clinical Isolate of Pseudomonas aeruginosa, Antimicrob. Agents Chemother,( 2008), 52(5);1635. DOI:10.1128/AAC.01071-07.
4. Ibezim  .E.C, Esimore.  C.O, Obodo. C.E, Nnamani  .P.O, Brown .S.A, Onyishi . I.V,  A study of the in-vitro interaction of co-trimoxazole and ampicillin using the checker board method, Afr J Biotechnol, (2006), 5(13);1284-1288.
5. Rishi .P, Preet.S, Kaur.P, Effect of L. plantarum cell-free extract andco-trimoxazole against Salmonella Typhimurium:a possible adjunct therapy,Annals of Clinical Microbiology and Antimicrobials, (2011), 10:9
6. Bergonzelli. G.E, Blum. S, Brussow. H, Theulaz. C, Probiotics as a treatment strategy for gastrointestinal diseases,Digestion,( 2005), 72;57-68.
7. Gibbs .P.A,Novel uses for lactic acid fermentation in food preservation,J Appl Bacteriol Symp Suppl ,(1987),63;51S-58S
8. Huang, L., Forsberg, C.W., and Gibbins, L.N.. Influence of external pH and fermentation products on Clostridium acetobutylicum intracellular pH and cellular distribution of fermented products, Appl. Environ. Microbiol,( 1986),51; 1230-1234.
9. Byczkowski. J, Gessner. T, Biological role of superoxide ion-radical, Int. J. Biochem, (1988),20; 569-580.
10. Jamalifar .H,Rahimi .H.R,Samadi. N,Shahverdi. A.R,Antimicrobial activity of different lactobacillus species against multi-drug resistant clinical isolates of Pseudomonas aeruginosa, Iran J Microbiol,2011,3(7);21_25.
11. Percival M, Choosing a Probiotic Supplement, Clinical Nutrition Insights,(1997),6(1);
12. Valdez .C , Peral M.C ,Interference of  Lactobacillus plantarum  with Pseudomonas aeruginosa in vitro and infected burns:the potential  use of  probiotics in wound treatment , ESCMID journal, (2005),11; 472-479
13. Gan .B.S, Kim .J, Reid. G, Cadieux. P, Howard .J.C, Lactoba-cillus fermentum RC-14 inhibits Staphylococcus aureus infection of surgical implants in rats, J Infect Dis,( 2002); 185; 1369_1372
14. Rishi. P, Kaur. S, Bhalla. M.P.S, Preet. S, Tiwari. R.P, Selection of probiotic Lactobacillus acidophilus and its prophylactic activity against murine Salmonellosis,  Int J Pro Pre ,(2008), 3(2);89-98.
15. Sgouras .D, Maragkoudakis. P ,K. Petraki, Martinez-Gonzalez. B,  Eriotou .E , In Vitro and In Vivo Inhibition of Helicobacter pylori by Lactobacillus casei Strain Shirota , Appl. Environ. Microbiol. (2004), 70 (1); 518-526
16. Rybak.J.M, Grath .M.J.B, Combination antimicrobial therapy for bacterial infections, Guidelines for the Clinician. Drugs,( 1996), 52(3);390-402
17.  Clinical  and Laboratory Standards Institute.  1993. Methods  for  dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Approved standard M7-A4. Clinical and Laboratory Standards Institute, Villanova, PA.
18. Bauer. A.W, Kirby. M.M, Sherris. J.C, Tuurck. M, Antimicrobial susceptibility testing by a standardised single disc method, Am J Clin Path, ( 1966), 45;493-496
19. Ogunbanwo. T. S, Sanni. I. A, Onilude. A. A, Characterization of bacteriocin produced by Lactobacillus plantarum F1 and Lactobacillus brevis OG1, Afr J Biotechnol, (2003), 2 (8); 219-227
20. Nitisinprasert. V, Nilphai. P, Bunyun. P, Sukyai. S.D.K, Screening and identification of effective thermotolerant Lactic Acid Bacteria producing antimicrobial activity against Escherchia coli and salmonella sp.Resistant to Antibiotic.,Kasetsart, (2000), 3 ; 387_400.
21. Murray P.R, (2005). Manual of Clinical Microbiology,Vol 1.8 th edition .ASM press.U.S.A. ISBN-10:1555813712.
22. Lorian .V,Antibiotics in laboratory medicine.5^thedition.Williams&wilkins,Philadelphia, ,(2005); 642-646 and 831-837.
23. Pillai.S.K, Moellering .C,Elipoulos. G.M,Antimicrobial combinations.In:Lorian V.editor.ANTIBIOTIC in laboratory medicine.Philadelphia:Williams &Wilkins,(2005);365-373.
24. Codaa. R, Cassonea. A, Rizzelloa. G, Nionellia. L, Cardinalib. G, Gobbettia. M, Antifungal activity of Wickerhamomyces anomalus and Lactobacillus plantarum during sourdough fermentation: identification of novel compounds and long-term effect during storage of wheat bread, Appl. Environ. Microbiol. doi:10.1128/AEM.02669-10
25. Sánchez-Machado. D.I, López-Cervantes. J, Martínez-Cruz. O, Quantification of Organic Acids in Fermented Shrimp Waste by HPLC,(2008), Food Technol. Biotechnol, 46 (4); 456–460
26. Abdallaha. M. O, Badaweyb. M. A, Derivative- Ratio Spectrophotometric, Chemometric and HPLC Validated methods for Simultaneous Determination of Amlodipine and Atorvastatin in Combined Dosage Form Int. J. Ind. Chem,( 2011), 2( 2) ; 78-85
27. Keersmaecker. S.C.J, Verhoeven.T.L.A, Desair. J, Marchal. M, Vanderleyden. J& Nagy.I,
28. Strong antimicrobial activity of Lactobacillus rhamnosus GG against Salmonella typhimurium is due to accumulation of lactic acid, FEMS Microbiol,2006, FEMS Microbiol Lett ,259 (2006) 89-96
29. Luzzaro .F, Mantengoli. E, Perilli. M et al, Dynamics of a  nosocomial outbreak of multidrug-resistant Pseudomonas aeruginosa producing the PER-1 extended-spectrum b-lac-  tamase, J Clin Microbiol ,(1999), 39; 1865-1870.
30. B.Edwin L.A,Patricia K.G,Susceptibility of Pseudomonas aeruginosa to Tobramycin or Gentamicin Alone and Combined with Carbenicillin, Antimicrob. Agents Chemother ,(1975),8(3);300-304.
31. Bryan. L.E, O’Hara. K, Wong. S, Lipopolysaccharide changes in impermeability-type aminoglycoside resistance in Pseudomonas aeruginosa, ,( 1984), 26;250-255.
32. Galbraith. L, Wilkinson. S. G, Legakis. N. J, Genimata. V, Katsorchis. T. A, Rietschel. E. T, Structural alterations in the envelope of a Gentamicin-resistant rough mutant of Pseudomonas aeruginosa, Ann. Microbiol (Paris) ,(1984).135;121-136
33. Flanders. S. A, Collard. H. R , Saint. S, Nosocomial pneumonia: state of the science, American Journal of Infection Control , (2006),34; 84-93.
34. Petropoulos. A.D, Kouvela. E.C, Starosta. A. L, Wilson. D.N, Dinos. G.P, Kalpaxis. D.L,
35. Time-Resolved Binding of Azithromycin to Escherichia coli Ribosomes, J. Mol. Biol.(2009), 38,1179–1192.
36. Hooper. D. C, Mode of action of fluoroquinolones, Drugs ,(1999), 58, 6-10.
37. Yazar. E, Elmas. M, Altunok. V, Sivrikaya. A, Oztekin. E, Birdane. Y.O, Effects of aminoglycoside antibiotics on renal antioxidants, malondialdehyde levels, and some serum biochemical parameters, The Canadian Journal of Veterinary Research,(2003), 67;239–240
38. Goswami. M, Mangoli. S. H, Jawali. N, Involvement  of Reactive  Oxygen Species in the Action of Ciprofloxacin against Escherichia coli, Antimicrob. Agents Chemother,(2006), 50(3); 949–954
39. Martine. M.C, Velreds. C, Inhibition of initinal adhesion of uropathogenic Entroccoccus faecalis to solid substrata by an adsorbed biosurfactant layer from Lactobacillus acidophilus ,Perliminary communication ,(1997),49 ; 790 – 794
40. Vodnar. D.C, Paucean. A, Dulf .F. A, Socaciu C, HPLC Characterization of Lactic Acid Formation and FTIR Fingerprint of Probiotic Bacteria during Fermentation Processes, Not. Bot. Hort. Agrobot. Cluj, (2010), 38 (1); 109-113
41. Yang.Z, (2000),ANtimicrobial compounds and extracellular polysaccharides produced by lactic acid bacteria: structures and properties, department of food technology, University of Helsinki, ISBN 951-45-9146-1 (PDF version) Helsingin yliopiston verkkojulkaisutHelsinki 2000
42.  Smulders. F.J.M, Barendsen. P, van Logtestijn. J.G, Mossel. D.A.A, van Der Marel G.M, Review: Lactic acid: considerations in favor of its acceptan ce as a meat decontaminant, J.Food Technol. 21, 419-436.
43. Earnshaw. R.G, The antimicrobial action of lactic acid bacteria: natural food preservation systems. In: The Lactic Acid Bacteria in Health and Disease. ed. Wood, B.J.B, (1992); 211-232, Elsevier Applied Science, London and New York.
44. Kong. S, Davison. A.J, 1980, The role of interactions between O2, H2, OH., e- and O2- in free radical damage to biological systems. Arch. Biochem. Biophys. 204; 13-29.
45. ALAKOMI. H -L, E. SKYTTA¨ , M. SAARELA, T. MATTILA-SANDHOLM, K. LATVA-KALA, AND I. M. HELANDER, Lactic Acid Permeabilizes Gram-Negative Bacteria  by Disrupting the Outer  Membrane, Appl Environ Microbiol ,(2000), 66 (5); 2001–2005
46. Hoffmann.N, Lee. B,  Hentzer. M, Rasmussen. T.B,  Azithromycin  Blocks Quorum  Sensing and Alginate Polymer Formation and Increases  the Sensitivity to Serum and Stationary-Growth-Phase Killing of Pseudomonas aeruginosa and Attenuates Chronic P. aeruginosa Lung Infection in Cftr /   Mice , Antimicrob. Agents Chemother, (2007),51(10); 3677–3687