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Escherichia coli has served as a model organism for studies in molecular genetics and physiology since the 1960s. Yet the function of 20% of the 4288 known and predicted proteins in E. coli is still not known. Almost two-thirds of these proteins have homologs in other microorganisms, but their function(s) is not known in any organism. One such protein is YciG. YciG was chosen as the focus of this study because, intriguingly, an ortholog of YciG is found in the genome of the fungus Neurospora crassa. The gene encoding YciG is predicted to be in an operon with two other genes, yciF and yciE. Genes in the same operon often encode proteins with related functions, so the study was extended to include YciF and YciE. To determine the function of these proteins, in-frame deletion alleles were constructed and strains lacking one or more of the three proteins were tested for mutant phenotypes. Expression of the yciGFE operon is induced by several stresses and is regulated by RpoS, which controls the general stress response in E. coli. Therefore, we tested the ability of the mutant strains to survive environmental stresses. Our results revealed that YciG was important for stationary-phase resistance to thermal stress, oxidative stress and, in particular, acid stress. Both RpoS-dependent and RpoS-independent acid resistance mechanisms are found in E. coli. YciG was shown to be required for RpoS-independent acid resistance, but further experiments are needed to determine whether YciG also is required for RpoS-dependent acid resistance. YciG was not required for normal exponential growth of E. coli, as mutants lacking YciG had the same growth rate as the wild-type parent. No mutant phenotypes have been found yet for mutants lacking YciF or YciE. yciE deletion mutants showed the same growth rate and the same level of acid resistance as wild-type cells. The acid resistance of yciF mutants has not yet been tested, and strains lacking YciE and/or YciF need to be assayed for their ability to survive stresses other than acid stress.

Escherichia coli has served as a model organism for studies in molecular genetics and physiology since the 1960s. Yet the function of 20% of the 4288 known and predicted proteins in E. coli is still not known. Almost two-thirds of these proteins have homologs in other microorganisms, but their function(s) is not known in any organism. One such protein is YciG. YciG was chosen as the focus of this study because, intriguingly, an ortholog of YciG is found in the genome of the fungus Neurospora crassa. The gene encoding YciG is predicted to be in an operon with two other genes, yciF and yciE. Genes in the same operon often encode proteins with related functions, so the study was extended to include YciF and YciE. To determine the function of these proteins, in-frame deletion alleles were constructed and strains lacking one or more of the three proteins were tested for mutant phenotypes. Expression of the yciGFE operon is induced by several stresses and is regulated by RpoS, which controls the general stress response in E. coli. Therefore, we tested the ability of the mutant strains to survive environmental stresses. Our results revealed that YciG was important for stationary-phase resistance to thermal stress, oxidative stress and, in particular, acid stress. Both RpoS-dependent and RpoS-independent acid resistance mechanisms are found in E. coli. YciG was shown to be required for RpoS-independent acid resistance, but further experiments are needed to determine whether YciG also is required for RpoS-dependent acid resistance. YciG was not required for normal exponential growth of E. coli, as mutants lacking YciG had the same growth rate as the wild-type parent. No mutant phenotypes have been found yet for mutants lacking YciF or YciE. yciE deletion mutants showed the same growth rate and the same level of acid resistance as wild-type cells. The acid resistance of yciF mutants has not yet been tested, and strains lacking YciE and/or YciF need to be assayed for their ability to survive stresses other than acid stress.

Microbiological detection of foodborne pathogens is ineffective for monitoring critical control points (CCP) within a slaughter/processing Hazard Analysis and Critical Control Point (HACCP) system. Pathogens are usually absent from carcass surfaces and their uneven distribution makes it difficult to obtain a representative sample. However, microbiological testing can be applied within a HACCP plan to validate and verify the effectiveness of decontamination procedures designed to control hazards. With proper data collection, the reduction of an indicator group at a point in processing can indicate that a specific pathogen is being effectively controlled, especially when pathogen levels are too low to allow confirmation of process control, as they typically are in beef slaughter processing. Since E. coli O157:H7 has been shown to have some acid resistance, the ability of typical indicator organisms to accurately predict the reduction of this pathogen by carcass decontamination procedures has been a concern. Obtaining potential indicator bacteria from the same environmental reservoir as E. coli O157:H7 may provide non-pathogenic indicators with similar heat- and acid-resistance characteristics suitable for use in processing plant environments for validation and verification of carcass decontamination treatments within HACCP plans. Potential indicator bacteria were isolated from hides of cattle at slaughter facilities in Arizona, Georgia, and Texas and compared with isolates of E. coli O157:H7 from the same locations to determine similarity in acid- and heat-resistance characteristics. After evaluation at 2 heating temperatures (55 and 65??C) and 3 pH levels (3.0, 4.0, and 5.0), it was determined that several potential indicator bacteria were slightly more resistant than E. coli O157:H7 to heating and acid treatment. The greatest reduction in numbers for E. coli O157:H7 and indicator bacteria occurred at pH 3.0 and temperature of 65??C. Counts of bacteria grown at pH 4.0 and 5.0 were not significantly different. Testing indicated that several of the isolates from cattle hides would make good process control indicators since the indicator bacteria were reduced by heating or acid conditions at similar or greater rates when compared to E. coli O157:H7, providing an increased level of security that pathogens have been reduced in processing.

No período de 1999 a 2002, uma linhagem de Salmonella Enteritidis esteve envolvida em mais de 90% das salmoneloses ocorridas no RS. Este trabalho teve por objetivo avaliar a cinética de crescimento, a resistência ácida e a resistência térmica dessa linhagem e compará-la com S. Typhimurium e S. Bredeney não envolvidas em surtos alimentares, porém isoladas na mesma região. Em uma primeira etapa, a cinética de crescimento foi avaliada semeando-se cada sorovar em caldo nutriente (CN) e em salada de batata com maionese caseira (SMC), os quais foram mantidos a 30°C e 9,5°C. Em CN, a cinética de crescimento a 30°C foi semelhante para todos os sorovares, porém, em SMC a S. Enteritidis apresentou maior quantidade de células nas primeiras 6 horas de crescimento, sendo que somente depois de 12 horas todos os sorovares atingiram quantidades semelhantes de células. Em CN e em SMC, na temperatura de 9,5°C, não foi detectado crescimento de nenhum dos sorovares de Salmonella durante as primeiras 24 horas, sugerindo que essa temperatura foi suficiente para controlar a multiplicação desses microrganismos. Em uma segunda etapa, avaliou-se a resistência ácida e térmica dos diferentes sorovares de Salmonella. Para tanto, os três sorovares foram inoculados separadamente em CN e CN enriquecido com 1% de glicose (CNG), este último utilizado para produção de culturas ácido-adaptadas. Em seguida, os microrganismos foram submetidos a diferentes pH (3,5; 4,0 e 4,5) e temperaturas (52, 56 e 60ºC). Os resultados demonstraram que a S. Bredeney apresentou maior resistência para os pH 3,5 e 4,0, porém a S. Enteritidis demonstrou maior capacidade de adaptação ácida do que S. Typhimurium e S. Bredeney. Em pH 4,5 todos os sorovares, tanto não adaptados quanto ácido-adaptados, mantiveram a mesma quantidade de células viáveis durante 300 minutos. Quando expostas a 52ºC, S. Bredeney apresentou maior resistência, entretanto somente a S. Enteritidis foi protegida com a adaptação ácida. Para 56 e 60ºC, a S. Enteritidis, não adaptada e ácido-adaptada, apresentou maior resistência. A análise por SDS-PAGE demonstrou diferenças no perfil protéico de células não adaptadas e ácidoadaptadas para todos os sorovares testados. Com base nestes resultados, a capacidade de multiplicação mais rápida nas primeiras horas de cultivo em SMC, a maior capacidade de adaptação ácida e a maior resistência térmica demonstradas pela S. Enteritidis podem estar relacionadas ao freqüente envolvimento desse sorovar nas salmoneloses do RS. / During the period of 1999 to 2002, a strain of Salmonella Enteritidis was involved in more than 90 % of foodborne salmonellosis occurred in Rio Grande do Sul (RS) State. This work aimed to evaluate the growth kinetics, and the acid and the thermal resistance of this strain, comparing with S. Typhimurium and S. Bredeney, which were not involved in foodborne outbreaks, but were isolated in the same region. In the first stage of this study, the growth kinetics was assessed. Each serovar was inoculated separately in nutrient broth (CN) and in potato salad prepared with homemade mayonnaise (SMC), and then incubated at 30 ºC and 9.5 ºC. In CN, at 30 ºC, similar growing characteristics were found for all serovars, however in SMC S. Enteritidis demonstrated higher counts at the first 6 hours. Only after 12 hours of incubation, all serovars reached similar counts. In CN and in SMC, at 9.5 ºC, during the first 24 hours, there was no detectable growth of any Salmonella serovar, suggesting that such temperature was adequate to control the multiplication of tested Salmonella serovars. In the second stage of the study, the acid and the thermal resistances of Salmonella serovars were evaluated. The three serovars were cultivated separately in Nutrient Broth and Nutrient Broth supplemented with 1 % glucose (NBG). The latter medium was used to induce acid-adapted cells. Then, the three serovars were exposed to different pH (3.5, 4.0, and 4.5) and temperatures (52, 56, and 60 ºC). Results indicated that S. Bredeney presented higher resistance to pH 3.5 and 4.0, but S. Enteritidis presented a better capacity of acid adaptation than S. Typhimurium and S. Bredeney. At pH 4.5, all serovars demonstrated a similar behavior, remaining at same levels of viable cells until 300 minutes. At 52 ºC, S. Bredeney presented greater survivor rates, however acid adaptation protected only S. Enteritidis. At 56 ºC and 60 ºC, non-adapted and acidadapted S. Enteritidis were more thermally resistant than other serovars tested. SDS-PAGE analysis demonstrated differences in protein profile of non-adapted and acid-adapted cells of all serovars. The capacity of rapid multiplication in the first hours of cultivation, the greater acid adaptation and thermal resistance presented by S. Enteritidis, may be related to the frequent involvement of this strain in salmonellosis cases in the RS.

No período de 1999 a 2002, uma linhagem de Salmonella Enteritidis esteve envolvida em mais de 90% das salmoneloses ocorridas no RS. Este trabalho teve por objetivo avaliar a cinética de crescimento, a resistência ácida e a resistência térmica dessa linhagem e compará-la com S. Typhimurium e S. Bredeney não envolvidas em surtos alimentares, porém isoladas na mesma região. Em uma primeira etapa, a cinética de crescimento foi avaliada semeando-se cada sorovar em caldo nutriente (CN) e em salada de batata com maionese caseira (SMC), os quais foram mantidos a 30°C e 9,5°C. Em CN, a cinética de crescimento a 30°C foi semelhante para todos os sorovares, porém, em SMC a S. Enteritidis apresentou maior quantidade de células nas primeiras 6 horas de crescimento, sendo que somente depois de 12 horas todos os sorovares atingiram quantidades semelhantes de células. Em CN e em SMC, na temperatura de 9,5°C, não foi detectado crescimento de nenhum dos sorovares de Salmonella durante as primeiras 24 horas, sugerindo que essa temperatura foi suficiente para controlar a multiplicação desses microrganismos. Em uma segunda etapa, avaliou-se a resistência ácida e térmica dos diferentes sorovares de Salmonella. Para tanto, os três sorovares foram inoculados separadamente em CN e CN enriquecido com 1% de glicose (CNG), este último utilizado para produção de culturas ácido-adaptadas. Em seguida, os microrganismos foram submetidos a diferentes pH (3,5; 4,0 e 4,5) e temperaturas (52, 56 e 60ºC). Os resultados demonstraram que a S. Bredeney apresentou maior resistência para os pH 3,5 e 4,0, porém a S. Enteritidis demonstrou maior capacidade de adaptação ácida do que S. Typhimurium e S. Bredeney. Em pH 4,5 todos os sorovares, tanto não adaptados quanto ácido-adaptados, mantiveram a mesma quantidade de células viáveis durante 300 minutos. Quando expostas a 52ºC, S. Bredeney apresentou maior resistência, entretanto somente a S. Enteritidis foi protegida com a adaptação ácida. Para 56 e 60ºC, a S. Enteritidis, não adaptada e ácido-adaptada, apresentou maior resistência. A análise por SDS-PAGE demonstrou diferenças no perfil protéico de células não adaptadas e ácidoadaptadas para todos os sorovares testados. Com base nestes resultados, a capacidade de multiplicação mais rápida nas primeiras horas de cultivo em SMC, a maior capacidade de adaptação ácida e a maior resistência térmica demonstradas pela S. Enteritidis podem estar relacionadas ao freqüente envolvimento desse sorovar nas salmoneloses do RS. / During the period of 1999 to 2002, a strain of Salmonella Enteritidis was involved in more than 90 % of foodborne salmonellosis occurred in Rio Grande do Sul (RS) State. This work aimed to evaluate the growth kinetics, and the acid and the thermal resistance of this strain, comparing with S. Typhimurium and S. Bredeney, which were not involved in foodborne outbreaks, but were isolated in the same region. In the first stage of this study, the growth kinetics was assessed. Each serovar was inoculated separately in nutrient broth (CN) and in potato salad prepared with homemade mayonnaise (SMC), and then incubated at 30 ºC and 9.5 ºC. In CN, at 30 ºC, similar growing characteristics were found for all serovars, however in SMC S. Enteritidis demonstrated higher counts at the first 6 hours. Only after 12 hours of incubation, all serovars reached similar counts. In CN and in SMC, at 9.5 ºC, during the first 24 hours, there was no detectable growth of any Salmonella serovar, suggesting that such temperature was adequate to control the multiplication of tested Salmonella serovars. In the second stage of the study, the acid and the thermal resistances of Salmonella serovars were evaluated. The three serovars were cultivated separately in Nutrient Broth and Nutrient Broth supplemented with 1 % glucose (NBG). The latter medium was used to induce acid-adapted cells. Then, the three serovars were exposed to different pH (3.5, 4.0, and 4.5) and temperatures (52, 56, and 60 ºC). Results indicated that S. Bredeney presented higher resistance to pH 3.5 and 4.0, but S. Enteritidis presented a better capacity of acid adaptation than S. Typhimurium and S. Bredeney. At pH 4.5, all serovars demonstrated a similar behavior, remaining at same levels of viable cells until 300 minutes. At 52 ºC, S. Bredeney presented greater survivor rates, however acid adaptation protected only S. Enteritidis. At 56 ºC and 60 ºC, non-adapted and acidadapted S. Enteritidis were more thermally resistant than other serovars tested. SDS-PAGE analysis demonstrated differences in protein profile of non-adapted and acid-adapted cells of all serovars. The capacity of rapid multiplication in the first hours of cultivation, the greater acid adaptation and thermal resistance presented by S. Enteritidis, may be related to the frequent involvement of this strain in salmonellosis cases in the RS.

No período de 1999 a 2002, uma linhagem de Salmonella Enteritidis esteve envolvida em mais de 90% das salmoneloses ocorridas no RS. Este trabalho teve por objetivo avaliar a cinética de crescimento, a resistência ácida e a resistência térmica dessa linhagem e compará-la com S. Typhimurium e S. Bredeney não envolvidas em surtos alimentares, porém isoladas na mesma região. Em uma primeira etapa, a cinética de crescimento foi avaliada semeando-se cada sorovar em caldo nutriente (CN) e em salada de batata com maionese caseira (SMC), os quais foram mantidos a 30°C e 9,5°C. Em CN, a cinética de crescimento a 30°C foi semelhante para todos os sorovares, porém, em SMC a S. Enteritidis apresentou maior quantidade de células nas primeiras 6 horas de crescimento, sendo que somente depois de 12 horas todos os sorovares atingiram quantidades semelhantes de células. Em CN e em SMC, na temperatura de 9,5°C, não foi detectado crescimento de nenhum dos sorovares de Salmonella durante as primeiras 24 horas, sugerindo que essa temperatura foi suficiente para controlar a multiplicação desses microrganismos. Em uma segunda etapa, avaliou-se a resistência ácida e térmica dos diferentes sorovares de Salmonella. Para tanto, os três sorovares foram inoculados separadamente em CN e CN enriquecido com 1% de glicose (CNG), este último utilizado para produção de culturas ácido-adaptadas. Em seguida, os microrganismos foram submetidos a diferentes pH (3,5; 4,0 e 4,5) e temperaturas (52, 56 e 60ºC). Os resultados demonstraram que a S. Bredeney apresentou maior resistência para os pH 3,5 e 4,0, porém a S. Enteritidis demonstrou maior capacidade de adaptação ácida do que S. Typhimurium e S. Bredeney. Em pH 4,5 todos os sorovares, tanto não adaptados quanto ácido-adaptados, mantiveram a mesma quantidade de células viáveis durante 300 minutos. Quando expostas a 52ºC, S. Bredeney apresentou maior resistência, entretanto somente a S. Enteritidis foi protegida com a adaptação ácida. Para 56 e 60ºC, a S. Enteritidis, não adaptada e ácido-adaptada, apresentou maior resistência. A análise por SDS-PAGE demonstrou diferenças no perfil protéico de células não adaptadas e ácidoadaptadas para todos os sorovares testados. Com base nestes resultados, a capacidade de multiplicação mais rápida nas primeiras horas de cultivo em SMC, a maior capacidade de adaptação ácida e a maior resistência térmica demonstradas pela S. Enteritidis podem estar relacionadas ao freqüente envolvimento desse sorovar nas salmoneloses do RS. / During the period of 1999 to 2002, a strain of Salmonella Enteritidis was involved in more than 90 % of foodborne salmonellosis occurred in Rio Grande do Sul (RS) State. This work aimed to evaluate the growth kinetics, and the acid and the thermal resistance of this strain, comparing with S. Typhimurium and S. Bredeney, which were not involved in foodborne outbreaks, but were isolated in the same region. In the first stage of this study, the growth kinetics was assessed. Each serovar was inoculated separately in nutrient broth (CN) and in potato salad prepared with homemade mayonnaise (SMC), and then incubated at 30 ºC and 9.5 ºC. In CN, at 30 ºC, similar growing characteristics were found for all serovars, however in SMC S. Enteritidis demonstrated higher counts at the first 6 hours. Only after 12 hours of incubation, all serovars reached similar counts. In CN and in SMC, at 9.5 ºC, during the first 24 hours, there was no detectable growth of any Salmonella serovar, suggesting that such temperature was adequate to control the multiplication of tested Salmonella serovars. In the second stage of the study, the acid and the thermal resistances of Salmonella serovars were evaluated. The three serovars were cultivated separately in Nutrient Broth and Nutrient Broth supplemented with 1 % glucose (NBG). The latter medium was used to induce acid-adapted cells. Then, the three serovars were exposed to different pH (3.5, 4.0, and 4.5) and temperatures (52, 56, and 60 ºC). Results indicated that S. Bredeney presented higher resistance to pH 3.5 and 4.0, but S. Enteritidis presented a better capacity of acid adaptation than S. Typhimurium and S. Bredeney. At pH 4.5, all serovars demonstrated a similar behavior, remaining at same levels of viable cells until 300 minutes. At 52 ºC, S. Bredeney presented greater survivor rates, however acid adaptation protected only S. Enteritidis. At 56 ºC and 60 ºC, non-adapted and acidadapted S. Enteritidis were more thermally resistant than other serovars tested. SDS-PAGE analysis demonstrated differences in protein profile of non-adapted and acid-adapted cells of all serovars. The capacity of rapid multiplication in the first hours of cultivation, the greater acid adaptation and thermal resistance presented by S. Enteritidis, may be related to the frequent involvement of this strain in salmonellosis cases in the RS.

Brucella est l'agent causal de la brucellose, une zoonose bactérienne répandue à l'échelle mondiale. Durant les dernières années, de nouvelles souches et espèces de Brucella (dont Brucella microti) ont été isolées de l’environnement et d’animaux sauvages. Ces souches, phylogénétiquement anciennes, sont plus acido-résistantes que les espèces classiques, plus récentes et inféodées aux animaux domestiques et à l’homme. Chez Escherichia coli, le système glutamate décarboxylase (GAD) et le système glutaminase (AR2_Q), basés respectivement sur la décarboxylation du glutamate et la déamination de la glutamine, sont les systèmes d’acido-résistance (AR) les plus efficaces. Notre équipe a démontré que le système GAD (GadB et GadC) est fonctionnel seulement dans les nouvelles souches et espèces de Brucella, et participe à la réussite de l’infection des souris par voie orale. Dans cette thèse, le rôle de nouveaux facteurs et les mécanismes moléculaires impliqués dans l’acido-résistance ont été explorés. Premièrement, nous avons montré que GlsA et GadC sont les deux protéines structurales du système AR2_Q qui, avec le système GAD, joue un rôle essentiel dans l’AR de ces nouvelles souches. De plus, chez ces mêmes souches, le système uréase intervient également dans la survie en milieu acide.Nos résultats suggèrent que les systèmes GAD, AR2_Q et uréase, en fonction de la disponibilité des substrats, pourraient contribuer à améliorer l’adaptation des nouvelles espèces dans les environnements acides naturels et/ou dans le tractus gastro-intestinal de leurs hôtes. / Brucella is the etiological agent of brucellosis, a worldwide bacterial zoonosis. In the last ten years, new and atypical strains of Brucella (among which Brucella microti) were isolated from the environment and wild hosts. These strains, of ancient origin, are considered more environmental and acid resistant than classical Brucella species, which are mostly pathogenic for livestock and humans. In Escherichia coli, the glutamate decarboxylase (GAD)-dependent system and the glutaminase (AR2_Q) system, based on the decarboxylation of glutamate and on the deamination of glutamine, respectively, are most efficient in conferring acid resistance (AR). Our team has previously demonstrated that in Brucella the GAD system (GadB and GadC) is functional only in new/atypical strains and contributes to murine infection by oral route. In this thesis, novel molecular mechanisms and factors involved in specific AR of new/atypical Brucella species were explored. Firstly, we have shown that in these strains, GlsA and GadC are the two structural proteins of the AR2_Q system, which, in concert with the GAD system, plays an essential role in AR. In addition, the functionality and role of the urease system in AR was also demonstrated in these strains.Our results suggest that the GAD, AR2_Q and urease systems may participate in a better adaptation of new Brucella species to certain natural acidic habitats and/or to the gastrointestinal tract of their hosts, depending on substrate availability.

worse than degradation at the crown of the sewer pipe. Furthermore, results from this study show that high resistance under the static acid corrosion exposure condition cannot be extended to mean high resistance under the erosion-corrosion exposure condition for some concrete mixes. In this study, the static HCl test and the dynamic HCl test were used to measure the resistance of concrete mixes under the static corrosion exposure condition and erosion-corrosion exposure condition respectively. However, concretes that exhibited high resistance to the erosion-corrosion exposure condition were consistent in exhibiting high resistance to the static corrosion exposure condition. This finding is consistent with the sequence of corrosion processes in MIC, wherein dissolution of the concrete components occurs before the precipitation of corrosion products. Therefore, it expected that high resistance in the dynamic acid test (i.e. resistance to dissolution) implies high resistance in the static test, which measures the combined resistance of dissolution and resistance emanating from corrosion products. Both static and dynamic acid corrosion tests revealed that the geopolymer concretes tested in this study outperformed PC and CAC concretes. Results from the static HCl test showed that GP-ferro-quartz concrete, the most durable concrete specimen, provided a 69-fold improvement in resistance when compared to PC-dolomite mixes (control #1) and a 4.72-fold improvement in resistance when compared to CAC-dolomite mixes (control #2). Results from the dynamic HCl test show that the GP-ferro-quartz mix provided a 180-fold increase in resistance when compared to the PC-dolomite mix and a 275-fold increase when compared to CAC-dolomite mix. The CACdolomite mix was found to have the lowest resistance to the erosive-corrosive exposure conditions of the dynamic HCl test. Thus, in terms of the concrete MIC resistance properties identified in this study, it is suggested that the CAC-dolomite mix had poor kinetic resistance to dissolution. However, under the static acid test (static corrosion exposure condition), the CAC-dolomite mix performed better than the PC-dolomite mix and GP-dolomite mix. CAC-dolomite concrete performed inferiorly only to the set of GP-siliceous-aggregate mixes in the static HCl test. The difference in the performance of CAC-dolomite concrete performance between the static and dynamic test is largely attributed to the formation of alumina gel, an acid corrosion product of CAC hardened paste, which envelopes the concrete specimen and reduces the rate of surface corrosion in the static HCl test. However, under v the dynamic HCl test, the gel layer is brushed off the surface of the concrete specimen rendering it ineffective in protecting the concrete specimen from corrosion. Previous research on the acid attack of concrete posits that the chemical make-up of concrete materials has a strong bearing on corrosion behaviour. To this end, various measures have been suggested such as the ratio of calcium to silicon (Ca/Si) in concrete. The approach utilised in this study was to calculate the “basicity value” which provides the ratio of major basic to acidic oxides found in the concrete. XRF analysis of the hardened cement pastes and the 5 aggregate types used in the experiments enabled the calculation of basicity values. The combined basicity value for concrete specimens was determined by proportionally summing (according to mass) the basicity values of the aggregate and hardened cement paste parts. A strongly correlated linear relationship between the basicity value of concrete and the corrosion rate from the dynamic HCl test was established. This empirical relationship warrants further investigation and verification, as it would, in principle provide a means to estimate the dissolution rate of concrete by calculating its basicity instead of undertaking laboratory acid tests. Basicity was also found to be useful in determining the corrosion compatibility of binder type and aggregate types. It was found that the difference between the basicity value of hardened cement paste and the basicity value of the aggregate was useful in determining the type and extent of preferential corrosion of a concrete specimen tested under the dynamic HCl test. For ease of reading, this difference was called the “basicity differential”. By visually assessing corroded concrete specimens from the dynamic HCl test, it is was possible to determine whether the hardened cement paste or aggregate component was preferentially corroded, and to gauge the extent of preferential corrosion visually. GP-ferro-quartz and GP-granite concretes had the lowest levels of preferential corrosion which corresponded to their low basicity differential values. In contrast, CAC-dolomite concrete had the highest basicity discrepancy which corresponded visually to a high preferential corrosion of the hardened cement paste. Mineralogical analysis via XRD, found that the hardened cement pastes of the three binder types consisted mainly of amorphous phases (>70%). The crystalline phase of the geopolymer hardened cement paste was mostly constituted by insoluble minerals such as mullite. This partially explains the higher corrosion resistance of geopolymer concretes. However, a more comprehensive explanation needs to include analysis of the amorphous phases, which fell outside the scope of this study. SEM analysis of HCl corroded geopolymer hardened cement paste found that fly ash spheres embedded within the geopolymer matrix were preferentially corroded. This indicates that fly ash content negatively affected the rate of corrosion of the geopolymer hardened cement paste. Furthermore, SEM analysis showed that the geopolymer matrix surrounding the fly ash spheres was relatively intact.

C. jejuni, a pathogenic gram-negative bacterium infecting the human gastrointestinal tract has lately been shown to cause bacteraemia to a wider extent than previously known. In some genotypes, this is thought to be related to GDP-Mannose 4,6 dehydratase encoded by the gene wcbK in the capsule polysaccharide operon and its potential phase variated regulated nature mediated by a homopolymeric guanine tract. This potential regulatory tract has been reported to be controlling the survival in serum by switching expression of wcbK “ON” or “OFF”. This master thesis report evaluates C. jejuni’s ability to survive human serum and low pH, as proxies for the conditions that bacteria meet in human blood or the stomach, respectively. By next generation sequencing, I evaluated the correlation between survival in human serum and the wcbK gene’s “ON” or “OFF” state. Furthermore, the temporal stability of the serum resistant phenotype was assessed over multiple generations. I found that a serum resistant fraction of the C. jejuni population could be enriched by selection in normal human serum. The serum resistant part of the population did not decrease during repeated subculture for 10 generations in bacterial culture medium. However, there was no correlation between the extent of serum resistance in the population and the “ON” or “OFF” state of the wcbK gene.