| Přispěvatelé: |
Bugarski, Branko, Knežević-Jugović, Zorica, Vukašinović, Maja, Nedović, Viktor, Radulović, Zorica |
| Popis: |
Ponašanje preživele populacije ćelija soja Lb. plantarum 564 zasejane u MRS bujonu nakon dejstva pulsirajućih električnih polja (PEP) različitog intenziteta, praćeno je putem izotermalne kalorimetrije, merenjem optičke gustine i ukupnog broja ćelija. Ćelije bakterija su tretirane monopolarnim pulsevima pravugaonog oblika različite jačine i broja pulseva, što odgovara primenjenoj energiji od 1.3, 5.5, 12.2, 34.6, 65.8 and 658.1 J/cm3. Nakon PEP tretmana, bakterije su inokulisane u MRS bujon i inkubirane na 37°C u toku 24 sata. Rezultati istraživanja su pokazali da su PEP tretmani energije ispod 13 J/cm3 imali pozitivan efekat na rast i aktivnost ćelija, naročito tretmani niže energije (1.3-5.5 J/cm3). Prisustvo intracelulatnih jona i molekula u medijumu, koji pozitivno utiču na rast ćelija, bilo je posebno izraženo u mid-eksponencijalnoj fazi rasta, gde je generaciono vreme ćelija tretiranih pulsevima energije 5.5 J/cm3 bilo trostruko skraćeno. Stepen odavanja toplote oslobođene tokom rasta ćelija takođe je bio viši, što ukazuje na porast metaboličke aktivnosti PEP tretiranih ćelija, čija je acidifikaciona sposobnost takođe bila povećana. Pretpostavlja se da PEP tretmani nižeg intenziteta dovode do reverzibilne elektroporermeabilizacije ćelija, čija je vijabilnost ostala nepromenjena nakon izlaganja pulsevima energije 12.2 J/cm3, što znači da se ovi procesni parametri nalaze ispod kritične vrednosti potrebne za inaktivaciju ispitivanih laktobacila. Primena jačih PEP tretmana energije 34.6, 65.1 and 658.1 J/cm3 je dovela do inaktivacije ćelija za oko 1, 2 i 3 log redukcije, respektivno. U zavisnosti od jačine primenjenog tretmana, preživeli deo populacije Lb. plantarum 564 je nastavio da raste sa određenim zakašnjenjem, pri čemu je nova populacija formirala istu gustinu u MRS bujonu kao i populacija netretiranih ćelija. Tretirane ćelije su pokazale brži stepen rasta u kasnoj log-fazi, mada je trend rasta bio sličan kao kod netretiranih. Preživela subpopulacija ukazuje na prisustvo perzistera otpornih na dejstvo PEP tretmana... The behaviour of a surviving population of lactic acid bacteria strain Lactobacillus plantarum 564 growing in MRS broth after pulsed electric field (PEF) treatments of different intensities was monitored by isothermal calorimetry, optical density and plate counts. Bacterial cells were treated with monopolar square pulses at varying nominal electric field strengths and number of pulses, corresponding to applied energies of 1.33, 5.5, 12.2, 34.6, 65.8 and 658.1 J/cm3. After PEF treatments, samples were inoculated into MRS broth and incubated at 37°C for 24 hours. The presented results show that the PEF treatments with energy input below 13 J/cm3 had a positive effect on bacterial growth and cell activity, especially the treatments with the lower field intensities (1.3 – 5.5 J/cm3). The presence of intracellular ions and molecules in media that facilitates the growth of electroporated lactobacilli was particularly evident in mid-exponential growth phase, where the doubling time was reduced for more than 3 times after the exposure to electric pulses of 5.5 J/cm3. The heat production rate released during the growth of electroporated cells was also higher, indicating the enhanced metabollic activity of PEF treated cells. Also, the electroporated cells had better acidification ability than the untreated cells. It is assumed that the applied PEF treatments with an energy input of below 13 J/cm3 potentially induce reversible electroporation of the cell membrane, which has a positive impact on the cell growth. The viability of cells remained unaffected by pulse energy of 12.2 J/cm3, which means that such treatment conditions remained below the critical field strength for the inactivation of treated lactobacilli. The PEF treatments with higher energy of 34.6, 65.1 and 658.1 J/cm3 induced cell inactivation of approx. 1, 2 and 3 log reduction, respectively. After the application of pulses to a population of Lb. plantarum 564, the survived bacterial cells resume growth after a treatment-dependent delay. A new population density is obtained at the same final level as the original culture. Both the untreated and treated culture had similar growth rates, but the latter showed a higher growth rate during the late-growth phase. Evidence of bacterial persistence is shown on the survived population of bacteria subjected to PEF treatment... |
