Colostrum traits and newborn body weight and growth: comparison between single and twin underfed sheep pregnancies.

Maternal nutrition during gestation plays an important role in colostrum production, postnatal growth, and survival of newborn lambs, especially in twin gestations. This research aimed to investigate the effects of chronic natural undernutrition on colostrum traits and early lamb's postnatal growth born from single and twin sheep pregnancies developed in a restrictive prairie, representative of southern Patagonia. Single- and twin-bearing ewes (n = 20 per group) were maintained grazing in a natural pasture. At 140 days of gestation, ewes were placed in individual pens for lambing control. Colostrum was collected immediately after delivery and at 12, 24, and 36 h postpartum, for determination of yield and composition. Maternal blood was obtained at 140 days of gestation and at lambing for plasma glucose, progesterone, 17ß-estradiol, and IgG determination. Newborn lamb blood for determining glycaemia and IgG was collected at birth and at 12, 24, 36, and 120 h after birth. Lamb mortality and growth was assessed from birth until 30 days of life. No differences were observed in progesterone and 17ß-estradiol. There were no differences in colostrum yields and fat components, however single- had higher values of protein and lactose than twin-bearing ewes (p < 0.05 for both). Singletons had higher glycaemia than twins at 12 h postpartum (102.2 ± 32.8 vs. 73.4 ± 29.9 mg/dL, p < 0.05). Colostrum IgG content was similar at delivery but higher in single ewes at 12 and 24 h, reaching a similar values at 36 h (4.7 ± 9.7 and 5.8 ± 7.7 mg/mL in single and twin pregnancies, respectively). Newborn IgG was higher in singletons compared to twins at least until 48 h of life. Lams body weight was always superior in singleton than twins from birth until 30 days of life. Mortality did not differ during the first week of life, but it increased significantly only in twins until day 30 of life. Undernourishment in pregnant ewes affected colostrum quantity and quality, resulting in a lower postnatal growth and a higher mortality in twins. Alternative managements favoring fetal growth, birth weight and neonatal viability in twin sheep pregnancies are needed, when flocks are breed under harsh environments.

Host-pathogen interaction involving cytoskeleton changes as well as non-coding regulation as primary mechanisms for SRS resistance in Atlantic salmon.

The salmonid rickettsial syndrome (SRS) is a systemic bacterial infection caused by Piscirickettsia salmonis that generates significant economic losses in Atlantic salmon (Salmo salar) aquaculture. Despite this disease's relevance, the mechanisms involved in resistance against P. salmonis infection are not entirely understood. Thus, we aimed at studying the pathways explaining SRS resistance using different approaches. First, we determined the heritability using pedigree data from a challenge test. Secondly, a genome-wide association analysis was performed following a complete transcriptomic profile of fish from genetically susceptible and resistant families within the challenge infection with P. salmonis. We found differentially expressed transcripts related to immune response, pathogen recognition, and several new pathways related to extracellular matrix remodelling and intracellular invasion. The resistant background showed a constrained inflammatory response, mediated by the Arp2/3 complex actin cytoskeleton remodelling polymerization pathway, probably leading to bacterial clearance. A series of biomarkers of SRS resistance, such as the beta-enolase (ENO-ß), Tubulin G1 (TUBG1), Plasmin (PLG) and ARP2/3 Complex Subunit 4 (ARPC4) genes showed consistent overexpression in resistant individuals, showing promise as biomarkers for SRS resistance. All these results together with the differential expression of several long non-coding RNAs show the complexity of the host-pathogen interaction of S. salar and P. salmonis. These results provide valuable information on new models describing host-pathogen interaction and its role in SRS resistance.

Effects of Strategic Supplementation with Lupinus angustifolius and Avena sativa Grains on Colostrum Quality and Passive Immunological Transfer to Newborn Lambs.

The aim of the present study was to evaluate the effect of two types of nutritional supplementation during late gestation on the chemical composition, energy value, and IgG concentration in the colostrum and the IgG concentration in the blood serum of lambs. Pregnant Merino Precoz ewes (n = 36) carrying single fetuses were used. Animals were kept grazing on the Mediterranean annual grassland. From day ~90 of pregnancy, animals were allocated into three groups: daily supplementation with oat grain or lupine grain and a control group without supplementation. Immediately after parturition, colostrum was collected from each ewe, and a blood sample was taken from the lambs 24 h after birth. For the evaluation of the chemical composition of the colostrum, an EKOMILK® milk analyzer was used. The energy value of the colostrum was calorimetrically evaluated. IgG concentrations were measured by simple radial immunodiffusion. Data were analyzed by analysis of variance. Colostrum content of protein and non-fat solids was higher in the group supplemented with oat grain than in the lupine grain supplemented and control groups (p ≤ 0.05). In contrast, ewes supplemented with lupine grain had the highest concentration of fat in their colostrum (p ≤ 0.05). Oat grain supplementation resulted in higher concentrations of IgG, both in sheep colostrum and in the blood serum of their lambs (p ≤ 0.05), being higher than those observed in the lupine grain and control groups. Ewes that gave birth to male lambs had significantly higher concentrations of IgG in their colostrum compared to ewes that gave birth to females (p ≤ 0.05). The colostral IgG concentration positively correlated with the serum IgG concentration of the lambs (r = 0.32; p ≤ 0.05). The results indicate that the quality of colostrum and the immunological status of the newborn lambs can be improved by supplementation with oat grain.

SEROSURVEY FOR SELECTED PARASITIC AND BACTERIAL PATHOGENS IN DARWIN'S FOX (LYCALOPEX FULVIPES): NOT ONLY DOG DISEASES ARE A THREAT.

The Darwin's fox (Lycalopex fulvipes) is one of the most endangered carnivores worldwide, with the risk of disease spillover from domestic dogs being a major conservation threat. However, lack of epidemiologic information about generalist, non-dog-transmission-dependent protozoal and bacterial pathogens may be a barrier for disease prevention and management. To determine the exposure of some of these agents in Darwin's fox populations, 54 serum samples were collected from 47 Darwin's foxes in Southern Chile during 2013-18 and assessed for the presence of antibodies against Brucella abortus, Brucella canis, Coxiella burnetii, pathogenic Leptospira (serovars Grippotyphosa, Pomona, Canicola, Hardjo, and Copehageni), Toxoplasma gondii, and Neospora caninum. The highest seroprevalence was detected for T. gondii (78%), followed by pathogenic Leptospira (14%). All the studied Leptospira serovars were confirmed in at least one animal. Two foxes seroconverted to Leptospira and one to T. gondii during the study period. No seroconversions were observed for the other pathogens. No risk factors, either intrinsic (sex, age) or extrinsic (season, year, and degree of landscape anthropization), were associated with the probability of being exposed to T. gondii. Our results indicate that T. gondii exposure is widespread in the Darwin's fox population, including in areas with minimal anthropization, and that T. gondii and pathogenic Leptospira might be neglected threats to the species. Further studies identifying the causes of morbidity and mortality in Darwin's fox are needed to determine if these or other pathogens are having individual or population-wide effects in this species.

Genomic features and antimicrobial resistance patterns of Shiga toxin-producing Escherichia coli strains isolated from food in Chile.

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen that causes severe illness in humans, often associated with foodborne outbreaks. Antimicrobial resistance among foodborne E. coli has increased over the last decades becoming a public health issue. In this study, the presence and features of STEC were investigated in samples of meat, seafood, vegetables and ready-to-eat street-vended food collected in Chile, using a genomic and microbiological approach. Phenotypic and genotypic antimicrobial resistance profiles were determined, and serotype, phylogroup, sequence type (ST) and phylogenomics were predicted using bioinformatic tools. Three thousand three hundred samples collected in 2019 were screened, of which 18 were positive for STEC strains (0.5%), with stx2a (61.1%) being the predominant stx subtype. The presence of the virulence genes lpfA (100%), iha and ehaA (94.4%), and ehxA, hlyA and saa (83.3%) was confirmed among the STEC strains; the Locus of adhesion and autoaggregation (LAA) was predicted in 14 (77.8%) strains. Strains displayed resistance to colistin (100%), and intermediate resistance to enrofloxacin (11.1%) and chloramphenicol (5.6%). In this regard, mutations in the two-component regulatory system genes pmrA (S29G), pmrB (D283G) and phoP (I44L), and the presence of the qnrB19 gene were confirmed. STEC strains belonged to ST11231 (38.9%), ST297 and ST58 (16.7% each), and ST1635, ST11232, ST446, ST442 and ST54 (5.6% each), and the most frequently detected serotypes were O113:H21 (44.4%), O130:H11 and O116:H21 (16.7% each), and O174:H21 (11.1%). Strains belonging to the international ST58 showed genomic relatedness with worldwide strains from human and non-human sources. Our study reports for the first time the genomic profile of STEC strains isolated from food in Chile, highlighting the presence of international clones and sequence types commonly associated with human infections in different geographical regions, as well as the convergence of virulence and resistance in STEC lineages circulating in this country.

First genome sequence of Chilean Brucella canis SCL strain provides insights on the epidemiology and virulence factors, explaining differences between geographical origins

BACKGROUND: Brucella canis is the etiological agent of canine brucellosis, a worldwide neglected zoonosis that constitutes one of the major infectious causes of infertility and reproductive failure in dogs. Although genomic information available for this pathogen has increased in recent years, here we report the first genome sequencing of a B. canis strain in Chile, and the differences in virulence genes with other B. canis strains. RESULTS: Genome assembly produced a total length of 3,289,216 bp, N50 of 95,163 and GC% of 57.27, organized in 54 contigs in chromosome I, and 21 contigs in chromosome II. The genome annotation identified a total of 1981 CDS, 3 rRNA and 36 tRNA in chromosome I, and 1113 CDS and 10 tRNA in chromosome II. There is little variation between the different strains and the SCL isolate. Phylogenetic analysis showed that the Chilean SCL strain is closely related to B. canis and B. suis strains. Small differences were found when compared to the Serbian isolate, but all strains shared the same recent common ancestor. Finally, changes in the sequence of some virulence factors showed that the SCL strain is similar to other South American B. canis strains. CONCLUSIONS: This work sequenced and characterized the complete genome of B. canis strain SCL, evidencing the complete presence of all the genes of the virB operon, and minor changes in outer membrane proteins and in the urease operon. Our data suggest that B. canis was introduced from North America and then spread throughout the South American continent.

Prevalence and Genomic Characterization of Brucella canis Strains Isolated from Kennels, Household, and Stray Dogs in Chile.

Canine brucellosis caused by Brucella canis is a zoonotic disease that causes reproductive alterations in dogs, such as infertility, abortion, and epididymitis. This pathogen is especially prevalent in South America, and due to the lack of official control programs and the growing trend of adopting dogs it constitutes a public health risk that must be addressed. The aim of this study was to determine the prevalence of B. canis infection in kennel, shelter, and household dogs and to characterize the genomic properties of circulating strains, including ure and virB operons and omp25/31 genes. Samples from 771 dogs were obtained, and the infection was detected by blood culture and/or serology in 7.0% of the animals. The complete ure and virB operons and the omp25/31 genes were detected. Interestingly, we found different single-nucleotide polymorphisms (SNPs) in some of the analyzed genes, which could mean a change in the fitness or virulence of these strains. This study provides further evidence about dogs as a source of B. canis strains that can infect people. This also highlights the need to implement official control programs, including the mandatory testing of dogs, especially stray dogs, before adoption.

Phenotypic and Genotypic Antimicrobial Resistance in Non-O157 Shiga Toxin-Producing Escherichia coli Isolated From Cattle and Swine in Chile.

Non-O157 Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen that causes bloody diarrhea and hemolytic-uremic syndrome in humans, and a major cause of foodborne disease. Despite antibiotic treatment of STEC infections in humans is not recommended, the presence of antimicrobial-resistant bacteria in animals and food constitutes a risk to public health, as the pool of genes from which pathogenic bacteria can acquire antibiotic resistance has increased. Additionally, in Chile there is no information on the antimicrobial resistance of this pathogen in livestock. Thus, the aim of this study was to characterize the phenotypic and genotypic antimicrobial resistance of STEC strains isolated from cattle and swine in the Metropolitan region, Chile, to contribute relevant data to antimicrobial resistance surveillance programs at national and international level. We assessed the minimal inhibitory concentration of 18 antimicrobials, and the distribution of 12 antimicrobial resistance genes and class 1 and 2 integrons in 54 STEC strains. All strains were phenotypically resistant to at least one antimicrobial drug, with a 100% of resistance to cefalexin, followed by colistin (81.5%), chloramphenicol (14.8%), ampicillin and enrofloxacin (5.6% each), doxycycline (3.7%), and cefovecin (1.9%). Most detected antibiotic resistance genes were dfrA1 and tetA (100%), followed by tetB (94.4%), bla TEM-1 (90.7%), aac(6)-Ib (88.9%), bla AmpC (81.5%), cat1 (61.1%), and aac(3)-IIa (11.1%). Integrons were detected only in strains of swine origin. Therefore, this study provides further evidence that non-O157 STEC strains present in livestock in the Metropolitan region of Chile exhibit phenotypic and genotypic resistance against antimicrobials that are critical for human and veterinary medicine, representing a major threat for public health. Additionally, these strains could have a competitive advantage in the presence of antimicrobial selective pressure, leading to an increase in food contamination. This study highlights the need for coordinated local and global actions regarding the use of antimicrobials in animal food production.

Virulence Genes, Shiga Toxin Subtypes, Serogroups, and Clonal Relationship of Shiga Toxin-Producing Escherichia Coli Strains Isolated from Livestock and Companion Animals.

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen that causes severe illness in humans and is an important cause of foodborne disease. In Chile, there is limited information on the virulence characteristics of this pathogen in livestock, and none in companion animals. The aim of this study was to characterize STEC strains isolated from cattle, swine, dogs, and cats, in Chile, in terms of the presence of Shiga toxin types and subtypes, virulence genes, serogroups, and clonality. One-thousand two-hundred samples were collected, isolating 54 strains (4.5%), where stx1a (68.5%) and ehxA (74.1%) were the most frequently detected virulence genes. Only one strain belonging to the most clinically relevant serogroups was identified. Pulsed field gel electrophoresis analysis showed high clonal diversity among strains isolated from cattle, while those from swine showed the same pattern. This study provides further evidence regarding cattle and swine in Chile as a potential source of a wide variety of STEC strains that could potentially cause severe illness in humans, and that companion animals do not seem to represent a relevant reservoir. It also argues that preventive and control strategies should not be focused on detecting serogroups, but instead, on detecting their determinants of virulence.

Brucella canis induces canine CD4+ T cells multi-cytokine Th1/Th17 production via dendritic cell activation.

Brucella canis is a small intracellular Gram-negative bacterium that frequently leads to chronic infections highly resistant to antibiotic therapy in dogs. Also, it causes mild human brucellosis compared to other zoonotic Brucella spp. Herein we characterize the cellular immune response elicited by B. canis by analysing human and canine CD4+ T cells after stimulation with autologous monocyte-derived dendritic cells (MoDCs). Human and canine B. canis-primed MoDCs stimulated autologous CD4+ T cells; however, a Th1 response was triggered by human MoDCs, whereas canine MoDCs induced Th1/Th17 responses, with increased CD4+ T cells producing IFN-γ and IL-17A simultaneously. Each pattern of cellular response may contribute to host susceptibility, helping to understand the differences in B. canis virulence between these two hosts. In addition, other aspects of canine immunology are unveiled by highlighting the participation of IL-17A-producing canine MoDCs and CD4+ T cells producing IFN-γ and IL-17A.

Serologic Survey of Brucella canis and Leptospira spp. in Free-Ranging Wild and Domestic Canids from Tierra del Fuego, Chile.

We investigated exposure to Brucella canis and Leptospira spp. in sera from 56 canids sampled between 2008 and 2012 in Tierra del Fuego, Chile. No seropositives to B. canis were found. We detected antibodies against Leptospira spp. in Fuegian culpeo fox (Pseudalopex culpaeus lycoides; 20%), chilla foxes (Pseudalopex griseus; 8%), and dogs (Canis lupus familiaris; 3%).

Variability in the response of canine and human dendritic cells stimulated with Brucella canis.

Brucella canis is a small intracellular Gram-negative bacterium whose primary host is the dog, but it also can cause mild human brucellosis. One of the main causes of an inefficient immune response against other species of Brucella is their interaction with dendritic cells (DCs), which affects antigen presentation and impairs the development of an effective Th1 immune response. This study analysed the cytokine pattern production, by RT-qPCR and ELISA, in human and canine DCs against whole B. canis or its purified LPS. Human and canine DCs produced different patterns of cytokines after stimulation with B. canis. In particular, while human DCs produced a Th1-pattern of cytokines (IL-1ß, IL-12, and TNF-α), canine cells produced both Th1 and Th17-related cytokines (IL-6, IL-12, IL-17, and IFN-γ). Thus, differences in susceptibility and pathogenicity between these two hosts could be explained, at least partly, by the distinct cytokine patterns observed in this study, where we propose that human DCs induce an effective Th1 immune response to control the infection, while canine DCs lead to a less effective immune response, with the activation of Th17-related response ineffective to control the B. canis infection.

El desafío de controlar las enfermedades transmitidas por alimentos: bacteriófagos como una nueva herramienta biotecnológica / The challenge of controlling foodborne diseases: bacteriophages as a new biotechnological tool

Foodborne diseases are an increasing public health issue, in which bacterial pathogens have a transcendental role. To face this situation, the food industry has implemented several control strategies, using in the last decade some biotechnological tools, such as direct application of bacteriophages on food, to effectively control bacterial pathogens. Their bactericidal and safe properties to humans and animals have been widely described in the literature, being nowadays some bacteriophage-based products commercially available. Despite this, there are so many factors that can interfere in their biocontrol effectiveness on food, therefore is essential to consider these factors before their application. Thus, the optimal bacterial reduction will be achieved, which would produce a safer food. This review discusses some factors to consider in the use of bacteriophages as biocontrol agents of foodborne pathogens, including historical background, taxonomy and biological description of bacteriophages, and also advantages, disadvantages, and considerations of food applications.

Las enfermedades transmitidas por alimentos son un creciente problema de salud pública, donde los agentes patógenos bacterianos juegan un rol trascendental. La industria alimentaria ha implementado diversas medidas de control para enfrentar esta situación, utilizando en la última década algunas herramientas biotecnológicas, como es la aplicación de bacteriófagos directamente en los alimentos. Sus propiedades exclusivamente bactericidas e inocuas para el hombre y los animales han sido descritas ampliamente en la literatura científica, existiendo a la fecha algunos productos comerciales disponibles en el mercado internacional. A pesar de esto, diversos son los factores que pueden influir en su efectividad bio-controladora en alimentos, por lo que conocer dichos factores resulta fundamental antes de considerar su aplicación. De esta manera, se logrará obtener la máxima actividad reductora de la carga bacteriana, generando así un alimento más seguro. Esta revisión aborda ciertos factores a considerar para el uso de bacteriófagos como agentes bio-controladores de patógenos alimentarios, incluyendo antecedentes históricos, taxonomía y descripción biológica de bacteriófagos, así como ventajas, desventajas y consideraciones de su aplicación en alimentos.

[The challenge of controlling foodborne diseases: bacteriophages as a new biotechnological tool]. / El desafío de controlar las enfermedades transmitidas por alimentos: bacteriófagos como una nueva herramienta biotecnológica.

Foodborne diseases are an increasing public health issue, in which bacterial pathogens have a transcendental role. To face this situation, the food industry has implemented several control strategies, using in the last decade some biotechnological tools, such as direct application of bacteriophages on food, to effectively control bacterial pathogens. Their bactericidal and safe properties to humans and animals have been widely described in the literature, being nowadays some bacteriophage-based products commercially available. Despite this, there are so many factors that can interfere in their biocontrol effectiveness on food, therefore is essential to consider these factors before their application. Thus, the optimal bacterial reduction will be achieved, which would produce a safer food. This review discusses some factors to consider in the use of bacteriophages as biocontrol agents of foodborne pathogens, including historical background, taxonomy and biological description of bacteriophages, and also advantages, disadvantages, and considerations of food applications.

Una mezcla de bacteriófagos reduce los recuentos de Salmonella enterica serovar. Enteritis en tejidos de salmón fresco y ahumado / Bacteriophage cocktail reduces Salmonella enterica serovar. Enteritis counts in raw and somoked salmon tissues

El uso de bacteriófagos en el biocontrol de patógenos está adquiriendo cada vez más aceptación. En este estudio se evaluó la efectividad de bacteriófagos en la reducción de los recuentos de Salmonella Enteritidis en salmón fresco y ahumado. Para ello, 25 muestras por grupo fueron contaminadas con S. Enteritidis, tratadas con una mezcla de bacteriófagos e incubadas durante 10 días a 18 °C o a 4 °C. A los días 3, 6 y 10 se obtuvo una reducción signifi cativa de los recuentos de S. Enteritidis en las muestras de salmón fresco incubadas a ambas temperaturas: la reducción fue de entre 0,75 y 3,19 log10 UFC/g a 18 °C y de entre 2,82 y 3,12 log10 UFC/g a 4 °C. En salmón ahumado las reducciones fueron menores (entre 1,02 y 1,96 log10 UFC/g a 18 °C y entre 0,50 y 1,16 log10 UFC/g a 4 °C). Los resultados indican que estos bacteriófagos constituyen una potencial herramienta de biocontrol de S. Enteritidis en tejidos de salmón fresco y ahumado. © 2014 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L. Todos los derechos reservados

The use of bacteriophages for the biocontrol of food-borne pathogens is increasingly gaining acceptance. In this study, the effectiveness of bacteriophages to reduce Salmonella Enteritidis counts was evaluated in raw and smoked salmon tissues. Groups of 25 samples each were contaminated with S. Enteritidis, treated with a phage mix and then incubated for ten days at 18 °C and 4 °C. A signifi cant bacterial reduction was obtained on days 3, 6 and 10 in raw salmon samples incubated at 18 °C (from 0.75 to 3.19 log10 CFU/g) and at 4 °C (from 2.82 to 3.12 log10 CFU/g), whereas in smoked salmon lower reductions were achieved (from 1.02 to 1.96 log10 CFU/g at 18°C and from 0.50 to 1.16 log10 CFU/g at 4 °C). These results show the potential effectiveness of this bacteriophage cocktail as a biocontrol agent against S. Enteritidis in raw and smoked salmon tissues

Bacteriophage cocktail reduces Salmonella enterica serovar Enteritidis counts in raw and smoked salmon tissues.

The use of bacteriophages for the biocontrol of food-borne pathogens is increasingly gaining acceptance. In this study, the effectiveness of bacteriophages to reduce Salmonella Enteritidis counts was evaluated in raw and smoked salmon tissues. Groups of 25 samples each were contaminated with S. Enteritidis, treated with a phage mix and then incubated for ten days at 18 °C and 4 °C. A significant bacterial reduction was obtained on days 3, 6 and 10 in raw salmon samples incubated at 18 °C (from 0.75 to 3.19 log10 CFU/g) and at 4 °C (from 2.82 to 3.12 log10 CFU/g), whereas in smoked salmon lower reductions were achieved (from 1.02 to 1.96 log10 CFU/g at 18 °C and from 0.50 to 1.16 log10 CFU/g at 4 °C). These results show the potential effectiveness of this bacteriophage cocktail as a biocontrol agent against S. Enteritidis in raw and smoked salmon tissues.

Stability inside hen eggs of a salmonella enterica serovar enteritidis bacteriophage

Background: Bacteriophages are viruses that infect bacteria and therefore are widespread in nature. Those that lyse the pathogen Salmonella enterica serovar Enteritidis (SE) should be expected in niches in which this bacterium thrives, among others the avian egg. Furthermore, bacteriophages could remain viable in this milieu. Results: Upon artificially infecting hen eggs with the SE bacteriophage f18 we found that the bacteriophage titer remains stable at least for up to 144 hrs post-infection , both in yolk and albumen at 25ºC. Conclusion: Bacteriophage f18 withstands the physico-chemical conditions of the egg inner milieu and could be considered for SE-controlling measures in the poultry industry.

Host associated polymorphisms in the Corynebacterium pseudotuberculosis rpoB gene sequence.

Corynebacterium pseudotuberculosis is a widespread facultative intracellular pathogen that causes caseous lymphadenitis disease in sheep and goats, and generates cutaneous abscesses and granulomas in horses and cattle. Although some genes have been studied for diagnostic and phylogenetic analysis within the genus Corynebacterium, at subspecies level the pathogen has been poorly analyzed. The aim of this study was to characterize C. pseudotuberculosis strains isolated from domestic animals, through the sequencing of a hypervariable rpoB gene segment. As result, there were identified host associated rpoB polymorphisms in strains infecting sheep, goats and horses from Chile. These differences suggest the existence of bacterial genotypes, in which the nucleotide similarity values were ranging from 98.8 to 99.8%. In conclusion, the analysis of polymorphisms in the partial rpoB sequence can be used as a diagnostic tool that differentiates C. pseudotuberculosis strains at subspecies level.

Comparison of integron-linked antibiotic resistance genes in strains of Salmonella spp. isolated from swine in Chile in 2005 and 2008.

Salmonella spp. isolates obtained from healthy swine in 2008 were analyzed for antibiotic resistance phenotypes and genotypes. The resistance profiles of the 2008 isolates were compared with those of a Salmonella collection isolated from the same geographical area in 2005. The 2008 isolates consisted of strains that were 97% oxytetracycline resistant, 33.3% amoxicillin resistant, 31.8% amoxicillin- plus clavulanic acid resistant, 27.5% trimethoprim-sulfamethoxazole resistant, 17.3% streptomycin resistant, and 7.2% enrofloxacin-ciprofloxacin resistant. The presence of integrons and resistance genes and their topological association in resistant strains was assessed by PCR. The prevalence of class 1 integrons was the highest, at 46.2%, while class 2 integrons were present in 17.9% of the isolates. In strains that harboured class 1 integrons, we identified 3 different gene cassette arrangements; a single class 2 integron arrangement of dfrA1-sat1-aadA1 was found. Comparison of these results with data obtained from the 2005 isolates showed that Salmonella strains resistant to amoxicillin and amoxicillin plus clavulanic acid had clearly emerged over the span of 3 years, along with an increase in the prevalence of class 1 integrons and the acquisition of new gene cassette arrangements. These findings highlight the need for continual monitoring of regional isolates to establish more efficient vigilance programs that can address variations in resistance over short periods of time within the same geographical area.