Daniel Fernández

Fishes of southern South America: a story driven by temperature.

The latitudinal extension of southern South America imposes a thermal gradient that affects the structure of marine and freshwater fish assemblages and the biology of the species through direct exposure to the temperature gradients or by means of a web of historical and ecological relationships. We have reviewed biological and ecological data of marine and freshwater fishes from the southern Neotropics, including Patagonia, and report several examples of dependence on temperature, from glacial times to today’s climate change. We were able to identify historic and present effects on the diversity of fish assemblages, isolation, southern limits for the distribution of species, and morphological variation among populations. There is a wide range of characteristics that exemplify an adaptation to low temperatures, including biochemical peculiarities, physiological adjustments, and alternative life history patterns, and these appear in both freshwater and marine, and native and exotic fishes. The consequences of stable temperature regimes in both the ocean and thermal streams deserve special mention as these shape specialists under conditions of low selective pressure. At present, habitat use and interactions among species are being subject to changes as consequences of water temperature, and some of these are already evident in the northern and southern hemispheres.

Short communication: characterization of Shiga toxin-producing Escherichia coli isolated from newborn, milk-fed, and growing calves in Argentina.

Shiga toxin-producing Escherichia coli (STEC) cause foodborne pathogenic disease that is shed in the feces of cattle. The aim of this study was to evaluate how early young calves are colonized by STEC strains, potentially pathogenic for humans, and the prevalence in different calf categories. From 808 rectal swabs analyzed by PCR, 38% were stx positive. The prevalence in newborn (<24 h from birth), milk-fed (<2-mo-old), and growing calves (2-8 mo old) were 25, 43, and 58%, respectively. Forty different STEC serotypes were found among isolates from newborn, milk-fed, and growing calves that shed STEC strains potentially pathogenic for humans. The STEC strains could be acquired early from mothers, enabling the infection of other animal categories and confirming the risk to public health.

Genetic characterization of Shiga toxin-producing Escherichia coli O26:H11 strains isolated from animal, food, and clinical samples

The Shiga-toxin producing Escherichia coli (STEC) may cause serious illness in human. Here we analyze O26:H11 strains known to be among the most reported STEC strains causing human infections. Genetic characterization of strains isolated from animal, food, and clinical specimens in Argentina showed that most carried either stx1a or stx2a subtypes. Interestingly, stx2a-positive O26:H11 rarely isolated from cattle in other countries showed to be an important proportion of O26:H11 strains circulating in cattle and food in our region. Seventeen percent of the isolates harbored more than one gene associated with antimicrobial resistance. In addition to stx, all strains contained the virulence genes eae-β, tir, efa, iha, espB, cif, espA, espF, espJ, nleA, nleB, nleC, and iss; and all except one contained ehxA, espP, and cba genes. On the other hand, toxB and espI genes were exclusively observed in stx2-positive isolates, whereas katP was only found in stx1a-positive isolates. Our results show that O26:H11 STEC strains circulating in Argentina, including those isolated from humans, cattle, and meat products, present a high pathogenic potential, and evidence that cattle can be a reservoir of O26:H11 strains harboring stx2a.

Characterization of Shiga toxin-producing Escherichia coli O130:H11 and O178:H19 isolated from dairy cows.

Shiga toxin-producing E. coli (STEC) are isolated from human patients with bloody diarrhea, hemorrhagic colitis (HC), and hemolytic uremic syndrome (HUS). In the last years, the infections with non-O157 serotypes are increasing their frequency of association with human disease. STEC produce Shiga toxin (Stx) and other virulence factors that could contribute to human pathogenesis. Cattle are the main reservoir and the transmission to humans is through the consumption of undercooked meat, non-pasteurized dairy products, and vegetables or water contaminated with feces. We have previously determined that O130:H11 and O178:H19 serotypes were the most prevalent in dairy cows from Argentina. In the present study, 37 and 25 STEC isolates from dairy cows belonging to O130:H11 and O178:H19 serotypes, respectively, were characterized regarding to their cytotoxicity on Vero cells, stx subtypes, presence of sab and typing by multiple-locus variable-number tandem repeat analysis (MLVA). All strains demonstrated a cytotoxic effect, and in O130:H11 isolates, stx2EDL933 was the predominant subtype. In O178:H19 isolates the main stx2 subtype was stx2vha. The sab gene was detected in 65 and 24% of the isolates belonging to O130:H11 and O178:H19, respectively. Only one MLVA profile was identified among the O130:H11 isolates meanwhile 10 MLVA profiles were detected among the O178:H19 isolates which were grouped in two main clusters. In conclusion, our data show that O130:H11 and O178:H19 STEC isolates encode virulence factors associated with severe human disease and both serotypes should be considered for routinely testing. Our subtyping experiments showed that isolates could be distinguished based on the stx2 subtype and the presence/absence of sab gene, and for isolates belonging to O178:H19, also when the MLVA type was considered. However, MLVA subtyping of O130:H11 isolates will require the development of more specific markers.

Thermal ecology of Galaxias platei (Pisces, Galaxiidae) in South Patagonia: perspectives under a climate change scenario

The native freshwater fish Galaxias platei shows a wide latitudinal distribution in Patagonia, being found on both sides of the Andes. Currently, climate change poses one of the main threats to native fish, and its effects are appearing faster in high southern latitudes. The aim of this work was to analyse the possible effects of climate change in G. platei through its thermal responses. We hypothesized that juveniles of this species would be affected by indirect rather than by direct consequences of climate change. We determined the thermal tolerance polygon using Critical Thermal Methodology and preferred temperatures using a thermal gradient. Additionally, we evaluated routine metabolic rate using stop-flow respirometry. Results showed an intermediate to large polygon, with a non-negligible portion acquired through acclimation. Preferred temperatures and routine metabolic rates were positively related to acclimation temperature. Results suggest that G. platei thermal tolerance is dependent on its prior thermal history, have a eurythermal nature but maintain high levels of cold tolerance. Moreover, G. platei would be better suited at maintaining homeostasis at highest temperatures where more energy could be available for growth. This is the first time that thermal ecology data are registered for this species at its southernmost distribution.

Spatial patterns of summer demersal fish assemblages around the Antarctic Peninsula and South Shetland Islands

Abstract During the research programme conducted on the OV Puerto Deseado in the summers of 2011 and 2013, 36 stations were sampled using a demersal net at depths between 53–590 m in the Antarctic Peninsula and South Shetland Islands. A total 3378 fish specimens belonging to 36 species were recorded. Notothenidae was the best-represented family in species number, with Lepidonotothen nudifrons, L. larseni and Trematomus scotti being the most numerous species. Of the fish assemblages, 20% of the species were considered as dominant, 10% as common, 13% as occasional and 57% as rare. Six groups (and two sub-groups) were obtained by the ordination diagram based on geographical location: group 1=Gerlache Strait, group 2=Deception Islands, group 3=Biscoe Island, group 4=between Elephant and King George islands, group 5=northern Antarctic Peninsula, and group 6=South Shetland Islands, with sub-groups 6a shallower South Shetland Islands and 6b deeper South Shetland Islands. Sampling depth and water temperature significantly explained the spatial pattern. A latitudinal pattern of decreasing abundance from north-east to south-west was found in L. larseni and the opposite in T. scotti. The predictability of fish composition in the assemblages’ areas could be a useful tool for ecosystem-based management.

Multidrug resistance in Escherichia coli carrying integrons isolated from a pig farm with moderate antibiotic use

Fil: de la Torre, Eulalia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tandil. Centro de Investigacion Veterinaria de Tandil. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigacion Veterinaria de Tandil. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Centro de Investigacion Veterinaria de Tandil; Argentina

Variation in the Distribution of Putative Virulence and Colonization Factors in Shiga Toxin-Producing Escherichia coli Isolated from Different Categories of Cattle

Shiga toxin-producing Escherichia coli (STEC) are pathogens of significant public health concern. Several studies have confirmed that cattle are the main reservoir of STEC in Argentina and other countries. Although Shiga toxins represent the primary virulence factors of STEC, the adherence and colonization of the gut are also important in the pathogenesis of the bacteria. The aim of this study was to analyze and to compare the presence of putative virulence factors codified in plasmid -katP, espP, subA, stcE- and adhesins involved in colonization of cattle -efa1, iha- in 255 native STEC strains isolated from different categories of cattle from different production systems. The most prevalent gene in all strains was espP, and the less prevalent was stcE. katP was highly detected in strains isolated from young and rearing calves (33.3%), while subA was predominant in those isolated from adults (71.21%). Strains from young calves showed the highest percentage of efa1 (72.46%), while iha showed a high distribution in strains from rearing calves and adults (87.04 and 98.48% respectively). It was observed that espP and iha were widely distributed throughout all strains, whereas katP, stcE, and efa1 were more associated with the presence of eae and subA with the eae-negative strains. A great proportion of eae-negative strains were isolated from adults -dairy and grazing farms- and from rearing calves -dairy and feedlot-, while mostly of the eae-positive strains were isolated from dairy young calves. Data exposed indicate a correlation between the category of the animal and the production systems with the presence or absence of several genes implicated in adherence and virulence of STEC.

Virulence genes and genetic diversity assessment of Shiga toxin-producing Escherichia coli O91 strains from cattle, beef and poultry products

Shiga toxin-producing Escherichia coli (STEC) O91 has ranked in the top five of the non-O157 serogroups most frequently associated with human cases. In order to gain insight into the genetic diversity of O91 Latin American STEC strains, we analyzed their virulence properties and carried out a subtyping assay. A panel of 21 virulence genetic markers associated with human and animal infections was evaluated and the relatedness among strains was determined by a multiple-locus variable-number tandem repeats analysis (MLVA) comprising 9 VNTR loci. Twenty-two STEC O91 isolated from cattle and meat food and belonging to 5 serotypes (O91:H21, O91:H8, O91:H14, O91:H28, O91:H40) were studied. Eight virulence profiles were obtained for the O91 STEC strains: 4 for O91:H21 plus one for O91:H8, O91:H14, O91:H28 and O91:H40. All strains contained ehxA and lpfA0113 genes and only both stx1-positive strains lacked saa, which encodes the STEC autoagglutinating adhesin. Other genes involved in adhesion were detected: ehaA (91%), elfA and espP (86%), ecpA (82%) and, hcpA (77%). The gene encoding the cytolethal distending toxin type-V (CDT-V) was found only in O91:H8 and O91:H21, being present in the majority (89%) of strains of this last serotype. MLVA typing divided the total number of strains into 12 genotypes, and 9 of them were unique to a single strain. No association was observed between the virulence profiles and the source of the strains. Although they lack the eae gene, most of the strains have the genetic potential to adhere to host cells through other structures and possess cdt-V, which has been found in STEC strains involved in serious diseases. The MLVA showed clonal relatedness among strains isolated from cattle belonged to a same dairy farm and suggested that the same clone remains circulating throughout the year and, on the other hand, the need to increase the number of VNTR loci which could allow a higher discrimination among O91:H21 isolates.

Thermal responses of three native fishes from estuarine areas of the Beagle Channel, and their implications for climate change

The aim of this work was to analyze the thermal responses of Odontesthes nigricans, Eleginops maclovinus and diadromous Galaxias maculatus, key species in estuarine areas of the Beagle Channel (Tierra del Fuego, Argentina), under a climate change scenario. We hypothesized that in the southernmost limit of the species’ distribution, individuals are more likely to be affected by indirect consequences of climate change rather than direct temperature mortality. Their thermal tolerance limits were assessed using the Critical Thermal Methodology and their preferred temperatures, using a thermal gradient. Additionally, the Fulton’s condition factor and the energy density of individuals were analyzed as a proxy of the condition of fishes acclimated to different temperatures. Results showed that species analyzed have the ability to acclimate to the different temperatures, intermediate to large tolerance polygons and positive relationships between preferred and acclimation temperatures, indicating their eurythermic nature. Thus, O. nigricans, E. maclovinus and diadromous G. maculatus populations from Tierra del Fuego could experience enhanced performances because of moderate warming being and, as it was hypothesized, be influenced by indirect consequences of climate change (habitat degradation or changes in trophic structure) since they are living in environments that are widely cooler than their maximum tolerance.