Fotodinamička inaktivacija patogene bakterije Listeria monocytogenes u hrani

The aim of this study is to examine the possibility to inactivate food pathogen Listeria monocytogenes by nonthermal antimicrobial treatment – photosensitization. L. monocytogenes was incubated with 5-aminolevulinic acid (ALA) (7.5 mM) for 0–2 h to produce endogenous photosensitizers and then illuminated with visible light. The LED-based light source used for the illumination of L. monocytogenes emitted light at λ=400 nm with energy density of 20 mW/cm2. The illumination time varied from 0 to 20 min, and a total energy dose reached 0–24 J/cm2. The obtained results reveal that L. monocytogenes can effectively produce endogenous porphyrins after incubation with 7.5 mM ALA. Subsequent illumination of cells with visible light significantly decreased their viability in vitro (4 log). After adhesion of Listeria to the surface of packaging material and following photosensitization, the surface-attached bacterial population was inactivated by 3.7 log. In addition, most resistant Listeria biofilms are susceptible to this treatment. Their inactivation reached 3.1 log under certain experimental conditions. The cells and biofilms of Gram-positive bacteria L. monocytogenes ATCL3C 7644 could be effectively inactivated by ALA-based photosensitization in the solution as well as adhered onto the surface of packaging material in a nonthermal way.Svrha je ovoga rada bila istražiti mogućnost inaktivacije patogene bakterije Listeria monocytogenes u hrani fotosenzitivnom, tj. netermičkom antimikrobnom metodom. Nakon inkubacije sa 7,5 mM 5-aminolevulinske kiseline (ALA), tijekom 0-2 h, bakterija L. monocytogenes je proizvela endogene fotoaktivne tvari, nakon čega je osvijetljena vidljivom svjetlošću. Za to je upotrijebljena LED svjetiljka koja emitira svjetlost valne duljine λ=400 nm, s gustoćom energije od 20 mW/cm2. Vrijeme je osvjetljenja variralo od 0 do 20 min, a ukupna je doza svjetla bila 0–24 J/cm2. Dobiveni su rezultati pokazali da L. monocytogenes nakon inkubacije sa 7,5 mM ALA učinkovito proizvodi endogene porfirine. Osvjetljavanjem stanica bakterija vidljivom svjetlošću bitno se smanjila njihova sposobnost preživljavanja in vitro za 4 log. Nakon fotosensitizacije stanica bakterija pričvršćenih na površinu materijala za pakiranje, njihova je populacija smanjena za 3,7 log. Obradom je čak smanjen i broj stanica otpornog biofilma za 3,1 log. Utvrđeno je da se stanice i biofilmovi Gram-pozitivne bakterije L. monocytogenes ATCL3C 7644, u otopini ili pričvršćene na površinu materijala za pakiranje, mogu uspješno inaktivirati fotosensitizacijom pomoću ALA

Impact of High-Power Pulsed Light on Microbial Contamination, Health Promoting Components and Shelf Life of Strawberries

Svrha je ovoga rada bila procijeniti učinak pulsirajućeg svjetla velike snage na mikrobnu kontaminaciju i hranjiva svojstva jagoda. Ispitani su sljedeći parametri: broj mikroorganizama, produljenje vremena skladištenja, antioksidativni kapacitet, čvrstoća, udjel ukupnih fenola, antocijanina i vitamina C, te boja plodova tretiranih pulsirajućim svjetlom. Rezultati pokazuju da je dekontaminacija jagoda pomoću pulsirajućeg svjetla bila značajna u usporedbi s kontrolnim uzorkom. Mezofilne bakterije, prirodno prisutne na površini plodova jagode inaktivirane su za 2,2 log; inokulirane bakterije Bacillus cereus za 1,5 log i Listeria monocytogenes za 1,1 log. Kvasci tj. mikrofungi na površini plodova inaktivirani su za 1 log. Vrijeme skladištenja jagoda produljeno je za 2 dana. Tijekom postupka temperatura na površini plodova nije prelazila 42 °C. Nisu uočene bitne razlike u udjelu ukupnih fenola, antocijanina i vitamina C, te u antioksidativnom kapacitetu jagoda prije i nakon tretmana. Također nije došlo do promjene boje ili čvrstoće plodova. Stoga je zaključeno da je primjena pulsirajućeg svjetla velike snage brza, učinkovita, netermička i ekološki prihvatljiva metoda mikrobne dekontaminacije jagoda.The aim of this work is to evaluate the impact of high-power pulsed light (HPPL) on the microbial control and nutritional properties of strawberries. Berries were treated with HPPL and afterwards analyzed in terms of microbial contamination, shelf life extension, antioxidant capacity, firmness, total phenolic, total anthocyanin and ascorbic acid content, and colour. Results indicate that the decontamination of strawberries by HPPL was significant compared to control. Naturally distributed mesophilic bacteria on the surface of strawberries were inactivated by 2.2 log, and inoculated Bacillus cereus and Listeria monocytogenes were inactivated by 1.5 and 1.1 log, respectively. Yeasts/microfungi distributed on the surface of strawberries were inactivated by 1 log. The shelf life of treated strawberries was extended by 2 days. The increase of temperature on the surface of fruit never exceeded 42 °C. No significantly important differences were observed in total phenolic, total anthocyanin and ascorbic acid content, and antioxidant capacity of strawberry fruits before and after pulsed light treatment. Moreover, no impact on the strawberry colour or firmness was found after HPPL treatment. In conclusion, HPPL is fast, effective, non-thermal and environmentally friendly technique which can be applied for microbial control of strawberries

Inactivation of Opportunistic Pathogens Acinetobacter baumannii and Stenotrophomonas maltophilia by Antimicrobial Photodynamic Therapy

Acinetobacter baumannii and Stenotrophomonas maltophilia are opportunistic pathogens causing hospital infections with limited treatment options due to bacterial multidrug resistance. Here, we report that antimicrobial photodynamic therapy (aPDT) based on the natural photosensitizers riboflavin and chlorophyllin inactivates A. baumannii and S. maltophilia. The riboflavin and chlorophyllin photostability experiments assessed the photomodifications of photosensitizers under the conditions subsequently used to inactivate A. baumannii and S. maltophilia. A. baumannii planktonic cells were more sensitive to riboflavin-aPDT, while biofilm bacteria were more efficiently inactivated by chlorophyllin-aPDT. S. maltophilia planktonic and biofilm cells were more susceptible to chlorophyllin-aPDT compared to riboflavin-aPDT. The results suggest that riboflavin- and chlorophyllin-aPDT can be considered as a potential antimicrobial treatment for A. baumannii and S. maltophilia inactivation

Maisto patogenų inaktyvacija fotoaktyvuotu chlorofilinu: poveikio mechanizmas, optimizavimas ir pritaikymo galimybės

Despite tremendous progress in technology and biomedical science the number of reported food-borne infections continues to rise. Thus, development of innovative approaches for more effective inactivation of food pathogens seems an urgent task. One of the new nonthermal treatments is photosensitization. The main goal of the dissertation was to evaluate prospects of photosensitization as antimicrobial treatment and its possible applications in food industry. The main food pathogens (Salmonella enterica, Listeria monocytogenes, Bacillus cereus) can be effectively inactivated by aminolevulinic acid (ALA) based photosensitization in vitro and on the surface of packaging material. However, ALA is a rather expensive compound and it requires a longer time to produce porphyrins involved in photosensitization treatment. The experimental results indicate that cheaper photosensitizer chlorophyllin (Chl) is effective against food pathogens and gray mold Botrytis cinerea. In order to increase susceptibility of microorganisms to Chl-based photosensitization Chl and chitosan (Chl-CHS) conjugate were performed. It reduced the viability of strawberry surface–attached yeasts/molds significantly without any negative impact on visual quality of berries. Experimental data support the idea that photoactivated Chl–CHS conjugate can be a useful tool for the future development of edible photoactive antimicrobial coatings which can preserve strawberries and prolong their shelf-life

Photodynamic Inactivation of Food Pathogen Listeria monocytogenes

The aim of this study is to examine the possibility to inactivate food pathogen Listeria monocytogenes by nonthermal antimicrobial treatment – photosensitization. L. monocytogenes was incubated with 5-aminolevulinic acid (ALA) (7.5 mM) for 0–2 h to produce endogenous photosensitizers and then illuminated with visible light. The LED-based light source used for the illumination of L. monocytogenes emitted light at λ=400 nm with energy density of 20 mW/cm2. The illumination time varied from 0 to 20 min, and a total energy dose reached 0–24 J/cm2. The obtained results reveal that L. monocytogenes can effectively produce endogenous porphyrins after incubation with 7.5 mM ALA. Subsequent illumination of cells with visible light significantly decreased their viability in vitro (4 log). After adhesion of Listeria to the surface of packaging material and following photosensitization, the surface-attached bacterial population was inactivated by 3.7 log. In addition, most resistant Listeria biofilms are susceptible to this treatment. Their inactivation reached 3.1 log under certain experimental conditions. The cells and biofilms of Gram-positive bacteria L. monocytogenes ATCL3C 7644 could be effectively inactivated by ALA-based photosensitization in the solution as well as adhered onto the surface of packaging material in a nonthermal way

Impact of High-Power Pulsed Light on Microbial Contamination, Health Promoting Components and Shelf Life of Strawberries

The aim of this work is to evaluate the impact of high-power pulsed light (HPPL) on the microbial control and nutritional properties of strawberries. Berries were treated with HPPL and afterwards analyzed in terms of microbial contamination, shelf life extension, antioxidant capacity, firmness, total phenolic, total anthocyanin and ascorbic acid content, and colour. Results indicate that the decontamination of strawberries by HPPL was significant compared to control. Naturally distributed mesophilic bacteria on the surface of strawberries were inactivated by 2.2 log, and inoculated Bacillus cereus and Listeria monocytogenes were inactivated by 1.5 and 1.1 log, respectively. Yeasts/microfungi distributed on the surface of strawberries were inactivated by 1 log. The shelf life of treated strawberries was extended by 2 days. The increase of temperature on the surface of fruit never exceeded 42 °C. No significantly important differences were observed in total phenolic, total anthocyanin and ascorbic acid content, and antioxidant capacity of strawberry fruits before and after pulsed light treatment. Moreover, no impact on the strawberry colour or firmness was found after HPPL treatment. In conclusion, HPPL is fast, effective, non-thermal and environmentally friendly technique which can be applied for microbial control of strawberries

Inactivation of Opportunistic Pathogens <i>Acinetobacter baumannii</i> and <i>Stenotrophomonas maltophilia</i> by Antimicrobial Photodynamic Therapy

Acinetobacter baumannii and Stenotrophomonas maltophilia are opportunistic pathogens causing hospital infections with limited treatment options due to bacterial multidrug resistance. Here, we report that antimicrobial photodynamic therapy (aPDT) based on the natural photosensitizers riboflavin and chlorophyllin inactivates A. baumannii and S. maltophilia. The riboflavin and chlorophyllin photostability experiments assessed the photomodifications of photosensitizers under the conditions subsequently used to inactivate A. baumannii and S. maltophilia. A. baumannii planktonic cells were more sensitive to riboflavin-aPDT, while biofilm bacteria were more efficiently inactivated by chlorophyllin-aPDT. S. maltophilia planktonic and biofilm cells were more susceptible to chlorophyllin-aPDT compared to riboflavin-aPDT. The results suggest that riboflavin- and chlorophyllin-aPDT can be considered as a potential antimicrobial treatment for A. baumannii and S. maltophilia inactivation

Riboflavin- and chlorophyllin-based antimicrobial photoinactivation of Brevundimonas sp. ESA1 biofilms

Some Brevundimonas spp. are globally emerging opportunistic pathogens that can be dangerous to individuals with underlying medical conditions and for those who are immunocompromised. Gram-negative Brevundimonas spp. can form resilient sessile biofilms and are found not only in different confined terrestrial settings (e.g., hospitals) but are also frequently detected in spacecraft which is inhabited by astronauts that can have altered immunity. Therefore, Brevundimonas spp. pose a serious health hazard in different environments, especially in its biofilm form. Conventional antimicrobials applied to disrupt, inactivate, or prevent biofilm formation have limited efficiency and applicability in different closed-loop systems. Therefore, new, effective, and safe biofilm control technologies are in high demand. The present work aimed to investigate antimicrobial photoinactivation (API) of Brevundimonas sp. ESA1 monocultural biofilms mediated by non-toxic, natural photosensitizers such as riboflavin (RF) and chlorophyllin (Chl) with an emphasis of this technology as an example to be safely used in closed-loop systems such as spacecraft. The present study showed that Chl-based API had a bactericidal effect on Brevundimonas sp. ESA1 biofilms at twice the lower irradiation doses than was needed when applying RF-based API. Long-term API based on RF and Chl using 450 nm low irradiance plate has also been studied in this work as a more practically applicable API method. The ability of Brevundimonas sp. ESA1 biofilms to reduce alamarBlue™ and regrowth analysis have revealed that after the applied photoinactivation, bacteria can enter a viable but non-culturable state with no ability to resuscitate in some cases

Antimicrobial photoinactivation approach based on natural agents for control of bacteria biofilms in spacecraft

A spacecraft is a confined system that is inhabited by a changing microbial consortium, mostly originating from life-supporting devices, equipment collected in pre-flight conditions, and crewmembers. Continuous monitoring of the spacecraft’s bioburden employing culture-based and molecular methods has shown the prevalence of various taxa, with human skin-associated microorganisms making a substantial contribution to the spacecraft microbiome. Microorganisms in spacecraft can prosper not only in planktonic growth mode but can also form more resilient biofilms that pose a higher risk to crewmembers’ health and the material integrity of the spacecraft’s equipment. Moreover, bacterial biofilms in space conditions are characterized by faster formation and acquisition of resistance to chemical and physical e ects than under the same conditions on Earth, making most decontamination methods unsafe. There is currently no reported method available to combat biofilm formation in space e ectively and safely. However, antibacterial photodynamic inactivation based on natural photosensitizers, which is reviewed in this work, seems to be a promising method