Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Alberta, 2010. / Title from pdf file main screen (viewed on June 18, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Department of Chemistry, University of Alberta. Includes bibliographical references.

Thesis (M.Sc.)--University of Alberta, 2010. / Title from PDF file main screen (viewed on Apr. 30, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Food Science and Technology, Department of Agricultural, Food and Nutritional Science, University of Alberta. Includes bibliographical references.

Bacteriocins (BCNs) are ribosomally synthesized polypeptides or proteins with antimicrobial activity, produced by different groups of bacteria. Many lactic acid bacteria (LAB) produce BCNs with broad spectra of inhibition. The antimicrobial activity of BCNs against spoilage organisms (SPOs) has raised considerable interest in their application in juice preservation. The objectives of the study were to: (i) isolate, identify and screen BCN producing bacteria for antimicrobial activity against spoilage bacteria and fungi, (ii) optimize production of BCN from selected producers and (iii) investigate the industrial application of the BCN as a preservative in fruit juice. Eleven LAB strains of BCN producers were screened for antimicrobial activity. BCNs from Lactobacillus plantarum and Pediococcus pentosaceus 34 were the most effective against juice spoilage bacteria and fungi. The effect of medium components on bacteriocin production in L. plantarum and P. pentosaceus 34 was also determined. Clementine:Valencia (1:1) juice was used for the first time as the growth medium for L. plantarum and P. pentosaceus 34. The BCN from L. plantarum showed the highest activity and was, therefore, chosen for juice fermentation studies. The identification of L. plantarum was confirmed by biochemical tests, polymerase chain reaction (PCR) and sequencing of the recA gene. The highest BCN activity was observed for L. plantarum grown in De Man-Rogosa-Sharpe (MRS) and a combination of all supplements (i.e. peptone, MnSO4.H2O, Tween 80, glucose and whey), followed by MRS and Tween 80, peptone, MnSO4.H2O and MRS alone. MRS was a better medium for BCN production than juice [Clementine:Valencia (1:1)]. Size exclusion chromatography (SEC) was used to isolate the active L. plantarum BCN fraction which corresponded to an approximate molecular weight of 3.2 kDa and was proteinaceous in nature. Plantaricin structural genes (plnEF, plnJ, plnK, plnN) were detected in the L. plantarum strain by PCR and sequenced, and were chromosomally encoded as no plasmids could be detected. This implies that the BCN from L. plantarum is most likely a type of class IIa plantaricin which is responsible for the broad inhibitory activity observed. For the industrial application studies, L. plantarum BCN-containing cell free supernatant (BCNsup) added to “Ready to Drink” (RTD) Clementine:Valencia (1:1) juice at concentrations of 3 600 - 500 000 ppm decreased growth of SPOs, Lactobacillus acidophilus and Streptococcus thermophilus. At 250 000 ppm, the L. plantarum BCNsup achieved 5.3 and 6.8 log reductions of the L. acidophilus, after 24 and 48 h, respectively, which is larger than the USFDA (2001) requirement of a 5 log reduction in SPO activity, for preservation of fruit juices. However, there was a decrease in the activity when the BCNsup was applied to industrial (Valor) RTD juice (mango-orange) at decreasing concentrations of 100 000, 50 000 and 25 000 ppm. Organoleptic tests showed that the BCN did not alter flavor or taste of the juice and did not cause toxicity or allergic reactions. A food safety risk assessment was conducted in order to determine the Critical Control Point(s) [CCP(s)] at which the BCN could be applied to control identified microbiological hazards, and a Hazard Analysis and Critical Control Point (HACCP) plan was developed. This is the first report on the optimisation of L. plantarum BCN production in juice [Clementine:Valencia (1:1)], followed by inoculation into RTD juice (mango-orange), including a HACCP plan for the application of the BCN as a preservative in juice.

The sensitivity of Erwinia carotovora subsp. atroseptica to bacteriocins produced by strains in the common potato serogroups of E. carotovora was investigated. Bacteriocins produced by representative strains of the common serogroups had activity spectra containing strains from one to six sensitive serogroups. Similarly, indicator strains representing different serogroups showed variable sensitivity. One indicator strain was sensitive to bacteriocins produced by only one producing strain while others were sensitive to bacteriocins produced by strains in several different serogroups. Bacteriocin production in the serogroups tested was detected only from strains that were biochemically E.c. subsp. carotovora (Ecc). Strains in all four E.c. subsp. atroseptica (Eca) serogroups were bacteriocin sensitive and non-producers. Some Ecc strains were bacteriocin producers and sensitive to bacteriocins produced by strains in other serogroups. Production and sensitivity were not correlated with the frequency of distribution of the more common serogroups isolated in nature. Representative strains in the two most common serogroups (I and III) were sensitive to bacteriocins produced by representative strains in three and six serogroups respectively. Strains in some of the less common serogroups (IX, XI and XVI) were bacteriocin producers but were not sensitive to the bacteriocins produced by the representative strains tested. Thus, a role for bacteriocins in the survival of these strains in nature cannot be ruled out. Of the 44 serogroup XI strains tested by the agar overlay technique, 31 were "typical producers", 10 were "differential producers" and only three were "non-producers". However, bacteriocin production in the latter group could be detected after induction with Mitomycin C but not with UV light. In the five serogroups in which several strains were tested, bacteriocin production and sensitivity were serogroup rather than subspecies characteristics. In dual culture studies the starting ratio of "typical producer" to sensitive strains of 1:1000 prevented detectable growth of the sensitive strains. By comparison a starting ratio of 100:1 with a "non-producer" strain did not prevent growth of the sensitive strains. Similar results were obtained when potato tuber discs were inoculated with varying starting ratios and the population monitored after 48 h. Thus, bacteriocin producing strains have a selective advantage when grown together in vitro with the bacteriocin sensitive, non-producing strains. Bacteriocin titres were enhanced by Mitomycin C induction and partial purification. Following ammonium sulfate precipitation and ultracentrifugation (150 000 x g for 90 min), bacteriocin activity in the resuspended pellet was associated with particles which by transmission electron microscopy resembled contractile, bacteriophage tail-like particles. These particles (due to their molecular size) were associated with small (≈ 4 mm) clear zones of inhibition in the spot assay tests. "Bacteriocin-like" activity in the supernatant was resolved by gel filtration into three fractions with estimated molecular weights of 17 700, 29 500 and 224 000 D. The first two fractions showed large (up to 20 mm) diffuse zones of inhibition. The third fraction showed small (≈ 4 mm) clear zones of inhibition. All four fractions had similar activity spectra against representative indicator strains and were produced by all of the serogroup XI producer strains tested. Relative production differed depending on the strain. The threshold of sensitivity displayed by the indicator strains varied with the fractions. The resuspended pellets had the highest titres which suggested that those macromolecular bacteriocins were responsible for the antagonism in in vitro and possibly in nature. / Land and Food Systems, Faculty of / Graduate

Carnocyclin A (CclA) is a remarkably stable, potent bacteriocin produced by Carnobacterium maltaromaticum UAL307. Elucidation of the amino acid and genetic sequences revealed that CclA is a circular bacteriocin. Preliminary structural studies (dynamic light scattering, NMR, circular dichroism, stereochemical analysis) indicated that CclA is monomeric and alpha-helical in aqueous conditions and composed of L-residues. The 3D structure of [13C,15N]CclA was solved by NMR, revealing a compact arrangement of four helices. To examine the structure of the precursor peptide (pCclA) several fusion proteins were constructed and overexpressed; however, pCclA could not be isolated. To investigate the requirements for cyclization, several internally hexahistidine-tagged (His6) pCclA mutants were constructed. Expression conditions are underway. PisI was heterologously expressed and confirmed to impart protection against piscicolin 126 (PisA). Labeled and unlabeled PisA and PisI were purified following overexpression as maltose-binding protein fusions (MalE-fusions) and Factor Xa cleavage. NMR studies indicated that PisI and PisA do not physically interact. The 3D structure of PisI was solved by NMR, confirming that the four-helix bundle is a conserved motif for the immunity proteins of type IIa bacteriocins. The putative receptor proteins for these bacteriocins were cloned and overexpressed as His6-fusion proteins. Experiments are underway to optimize the expression and purification of these membrane proteins. The peptidase domain of the ABC-transporter protein (CbnTP) for carnobacteriocin B2 (CbnB2) was overexpressed as a His6-fusion protein. Active protease could not be purified from inclusion bodies, but was obtained as soluble protein following low-temperature overexpression. The CbnB2 precursor pCbnB2 (and a truncated derivative pCbnB2-RP) was purified following overexpression as a MalE-fusion and Factor Xa cleavage. pCbnB2 was incubated with CbnTP and MALDI-TOF and activity testing confirmed that CbnTP cleaved the leader peptide from pCbnB2. Five CysSer CbnTP mutants were constructed. Crystallographic studies of CbnTP are underway. Six bacteriocins (nisin, gallidermin, lacticin 3147, CclA, PisA, enterocin 710C) were tested against Gram-negative bacteria (E. coli DH5, Pseudomonas aeruginosa ATCC 14207, Salmonella typhimurium ATCC 23564) in the absence and presence of EDTA. PisA and lacticin 3147 exhibited minimal activity, whereas the other bacteriocins killed at least one strain, in the presence of EDTA.

No description available.

Thesis (M. S.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 109-127).

Orientador: Ana Lúcia Barretto Penna / Coorientador: Sabrina Neves Casarotti / Banca: Neuza Jorge / Banca: Aline Teodoro de Paula / Resumo: As bactérias acidoláticas (BAL) são bastante utilizadas em processos fermentativos na indústria de laticínios, porém algumas delas agem não somente como fermentadoras, com a produção de ácidos orgânicos a partir dos carboidratos presentes, mas também podem produzir substâncias que colaboram para a segurança microbiológica do produto fermentado ou compostos benéficos à saude. Em estudos in vitro anteriores, foi constatado que Leuconostoc mesenteroides subsp. mesenteroides SJRP55 apresenta potencial probiótico e ação bacteriostática sobre bactérias patogênicas, como Listeria monocytogenes e Escherichia coli. Neste trabalho foi avaliado o efeito de Leuconostoc mesenteroides subsp. mesenteroides SJRP55 em creme fermentado, em co-cultura com outras BAL, e estudar as características físico-químicas e microbiológicas do creme, além de avaliar a capacidade de bioconservação pela produção de bacteriocinas, ácidos orgânicos e propriedade funcional pela produção de ácido linoleico conjugado (CLA) e pela atividade antioxidante por inibição de radicais livres. Foi utilizado creme de leite UHT homogeneizado padronizado em 20% de gordura e fermentado conforme quatro tratamentos: T1 - cultura mista de Lactococcus lactis subsp. lactis e Lc. lactis subsp. cremoris; T2 - cultura mista de Lc. lactis subsp. lactis e Lc. lactis subsp. cremoris + Listeria monocytogenes ATCC 15313; T3 - Cultura mista de Lc. lactis subsp. lactis e Lc. lactis subsp. cremoris + Ln. mesenteroides subsp. mesenteroides... / Abstract: Lactic acid bacteria (LAB) are widely used in fermentation processes in the dairy industry, however some of them act not only as starters, with the production of organic acids from the carbohydrates, but they can also produce substances that contribute to the microbiological safety of the fermented product or produce health benefic compounds. In previous in vitro studies, it was found that Leuconostoc mesenteroides subsp. mesenteroides SJRP55 presents probiotic potential and bacteriostatic action on pathogenic bacteria, such as Listeria monocytogenes and Escherichia coli. In this study it was evaluated the effect of Leuconostoc mesenteroides subsp. mesenteroides SJRP55 in fermented cream, in co-cultivation with other BAL, and to study the physicochemical and microbiological characteristics of the cream, besides evaluating the capacity of bioconservation by the production of bacteriocins, organic acids and functional property by the production of conjugated linoleic acid (CLA) and antioxidant activity through the inhibition of free radicals. UHT milk cream standardized at 20% fat was fermented according to four treatments: T1 - Mixed culture of Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris, T2 - Mixed culture of Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris + Listeria monocytogenes ATCC 15313, T3 - Mixed culture of Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris + Ln. mesenteroides subsp. mesenteroides SJRP55, and T4 - Mixed ... / Mestre

Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Antimicrobial peptides continue to be one of the most important classes of food additives. The food industry is especially interested in the application of naturally occuring and biologically derived preservatives. Among the metabolites of industrial importance produced by propionibacteria are peptides called bacteriocins. Bacteriocins are ribosomally synthesized peptides with antagonistic activity against closely related microorganisms. Many microorganisms associated with food produce bacteriocins, which have stimulated interest in the use of these peptides as natural food preservatives. Numerous bacteriocins are produced by lactic acid bacteria, but only a few have been reported for propionibacteria. Since propionic acid bacteria have GRAS (generally regarded as safe) status, their metabolic compounds should be safe for human consumption. Propionibacterium thoenii 447, isolated from Emmentaler cheese, produces a bacteriocin-like peptide, named thoeniicin 447, with a narrow spectrum of activity. The peptide displays a bactericidal mode of action against Lactobacillus delbrueckii subsp. bulgaricus and a bacteriostatic action against Propionibacterium acnes. Optimal bacteriocin production was detected during the early stationary growth phase. The peptide is resistant to heat treatments of 60°C and 80°C for 15 and 30 min and to 100°C for 15 min, but loses 80% of its activity after autoclaving (10 min at 121°C). Thoeniicin 447 remains active after incubation in buffers with pH values ranging from 1-10. The peptide is inactivated by pepsin, pronase, a-chymotrypsin, trypsin and Proteinase K. Thoeniicin 447 was partially purified by ammonium sulfate precipitation, followed by SP-Sepharose cation exchange chromatography. The estimated size of thoeniicin 447, according to tricine-SDSPAGE, is approximately 6 kDa. Based on DNA sequencing, the mature peptide is 7130 Da in size and homologous to propionicin Tl produced by P. thoenii strain 419. Thoeniicin 447 is a relatively small, cationic and heat-stable peptide and can therefor be classified as a member of class II bacteriocins. These features are very similar to those of bacteriocins produced by lactic acid bacteria. However, no unique classification system has been proposed for bacteriocins of propionibacteria. As a member of the genus Propionibacterium, P. thoenii 447 is generally regarded as safe. This, together with the narrow spectrum of activity, particularly the action against P. acnes, heat tolerance of thoeniicin 447 and its activity over a wide pH range renders the peptide suitable for possible pharmaceutical applications. / AFRIKAANSE OPSOMMING: Antimikrobiese middels sal deurgaans beskou word as een van die belangrikste klasse van voedsel bymiddels. Die voedselindustrie is veral geïnteresseerd in die toepassing van preserveermiddels van 'n meer natuurlike en biologiese oorsprong. Onder die metaboliese produkte van industriële belang wat deur propionibakterieë geproduseer word is antimikrobiese peptiede (bakteriosiene). Bakteriosiene is ribosomaal-gesintetiseerde peptiede met 'n antagonistiese aktiwiteit teenoor naverwante bakterieë. Verskeie bakteriosiene word deur melksuurbakterieë geproduseer, terwyl slegs enkele vir propionibakterieë beskryf is. Baie van hierdie propionibakterieë word in die algemeen as veilig beskou en het GRAS status. Die metaboliete wat hulle produseer behoort dus veilig vir menslike gebruik te wees. Propionibacterium thoenii 447 is uit Emmentaler kaas geisoleer en produseer 'n bakteriosien-agtige peptied, naamlik thoeniicin 447 met 'n beperkte spektrum van aktiwiteit. Die peptied het 'n bakteriosidiese werking teenoor Lactobacillus delbrueckii subsp. bulgaricus en 'n bakteriostatiese werking teenoor Propionibacterium acnes. Optimum bakteriosien produksie is verkry tydens die vroeë stationêre groeifase. Die peptied is bestand teen hittebehandelings van 60°C en 80°C vir 15 en 30 min, asook 100°C vir 15 min, maar verloor 80% van sy aktiwiteit na outoklavering (lOmin by 121°C). Die peptied blyaktief na inkubasie in buffers van pH 1-10. Die peptied word deur pepsien, pronase, uchymotripsien, tripsien en Proteinase K geïnaktiveer. Thoeniicin 447 is met behulp van ammoniumsulfaat-presipitasie, gevolg deur SPSepharose katioon-uitruilchromatografie gedeeltelik gesuiwer. Skeiding op "n trisien-SDS poliakrielarnied-jel het 'n aktiewe band van ongeveer 6 kDa getoon. Volgens die DNA volgorde bepaling is thoeniicin 447, 7130 Da in grootte en homoloog aan Propionicin Tl, geisoleer vanaf P. thoenii stam 419. Thoeniicin 447 is 'n relatiewe klein, kationiese en hitte-bestande peptied en kan op grond hiervan as 'n lid van die klas II bakteriosiene geklassifiseer word. Hierdie eienskappe is soortgelyk aan die eienskappe van bakteriosiene geproduseer deur melksuurbakterieë. Tot op hede is geen klassifikasiesisteem vir die bakteriosiene van propionibakterieë voorgestel nie. As 'n lid van die genus Propionibacterium, word P. thoenii 447 in die algemeen as veilig beskou. Dit, tesame met die nou spektrum van aktiwiteit, veral teenoor P. acnes, die hittetoleransie van thoeniicin 447, asook die aktiwiteit oor 'n wye pH-grens, maak die peptied geskik vir moontlike farmaseutiese toepassings.