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In the last 10 years, Salmonella Heidelberg has been extensively isolated from poultry in several countries. In this context, molecular characterization is essential to understand whether the strains have entered the farms from a single or several sources. Thus, the aim of this study was to determine the genetic relationship and antimicrobial susceptibility of S. Heidelberg strains isolated between 2011 and 2012 from broiler farms belonging to three integrated poultry companies located in Argentina. The genetic relatedness of the S. Heidelberg isolates was determined by pulsed-field gel electrophoresis (PFGE), and resistance to 21 antimicrobials was determined by the disc diffusion method. The isolates were assigned to four PFGE patterns. Most of the strains showed 100% similarity and belonged to the same integrated poultry company. This PFGE pattern was also prevalent in S. Heidelberg strains isolated from humans in several provinces of Argentina, which suggests an epidemiological association between human and poultry strains. All the isolates were classified as multidrug-resistant (MDR), and no clear relationship was observed between PFGE and resistance patterns. S. Heidelberg strains may circulate among farms from the same integrated company due to common sources of contamination. To guarantee the safety of the poultry product for the consumers, holistic approaches including surveillance of Salmonella throughout the production chain together with control measures are crucial., (© 2021 Wiley-VCH GmbH.)

E. coli O157:H7 is a foodborne pathogen responsible for bloody diarrhea, hemorrhagic colitis and hemolytic uremic syndrome (HUS). The objective of the present work was to evaluate the ability of colostral IgG obtained from Stx2-immunized cows to prevent against E. coli O157:H7 infection and Stx2 cytotoxicity. Hyperimmune colostrum (HC) was obtained from cows intramuscularly immunized with inactivated Stx2 or vehicle for controls. Colostral IgG was purified by affinity chromatography. Specific IgG antibodies against Stx2 and bovine lactoferrin (bLF) levels in HC and the corresponding IgG (HC-IgG/bLF) were determined by ELISA. The protective effects of HC-IgG/bLF against Stx2 cytotoxicity and adhesion of E. coli O157:H7 and its Stx2-negative mutant were analyzed in HCT-8 cells. HC-IgG/bLF prevention against E. coli O157:H7 was studied in human colon and rat colon loops. Protection against a lethal dose of E. coli O157:H7 was evaluated in a weaned mice model. HC-IgG/bLF showed high anti-Stx2 titers and high bLF levels that were able to neutralize the cytotoxic effects of Stx2 in vitro and in vivo. Furthermore, HC-IgG/bLF avoided the inhibition of water absorption induced by E. coli O157:H7 in human colon and also the pathogenicity of E. coli O157:H7 and E. coli O157:H7Δstx2 in rat colon loops. Finally, HC-IgG/bLF prevented in a 100% the lethality caused by E. coli O157:H7 in a weaned mice model. Our study suggests that HC-IgG/bLF have protective effects against E. coli O157:H7 infection. These beneficial effects may be due to specific anti-Stx2 neutralizing antibodies in combination with high bLF levels. These results allow us to consider HC-IgG/bLF as a nutraceutical tool which could be used in combination with balanced supportive diets to prevent HUS. However further studies are required before recommendations can be made for therapeutic and clinical applications., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Problem Addressed: Shiga toxin-producing Escherichia coli (STEC) are a group of bacteria responsible for food-associated diseases. Clinical features include a wide range of symptoms such as diarrhea, hemorrhagic colitis and the hemolytic uremic syndrome (HUS), a life-threatening condition., Objective: Our group has observed that animals naturally colonized with STEC strains of unknown serotype were not efficiently colonized with E. coli O157:H7 after experimental infection. In order to assess the basis of the interference, three STEC strains were isolated from STEC persistently-colonized healthy cattle from a dairy farm in Buenos Aires, Argentina., Methods and Results: The three isolated strains are E. coli O22:H8 and carry the stx1 and stx2d genes. The activatable activity of Stx2d was demonstrated in vitro. The three strains carry the adhesins iha, ehaA and lpf O113 . E. coli O22:H8 formed stronger biofilms in abiotic surface than E. coli O157:H7 (eae+, stx2+) and displayed a more adherent phenotype in vitro towards HeLa cells. Furthermore, when both serotypes were cultured together O22:H8 could reduce O157:H7 adherence in vitro. When calves were intragastrically pre-challenged with 10 8 CFU of a mixture of the three STEC strains and two days later challenged with the same dose of the strain E. coli O157:H7 438/99, the shedding of the pathogen was significantly reduced., Conclusions: These results suggest that E. coli O22:H8, a serotype rarely associated with human illness, might compete with O157:H7 at the bovine recto-anal junction, making non-O157 carrying-calves less susceptible to O157:H7 colonization and shedding of the bacteria to the environment., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Ruminants are the primary reservoir of Shiga-toxin producing Escherichia coli (STEC) O157:H7 and the main source of infection for humans. The aim of this study was to assess the immunogenic properties of a candidate vaccine consisting on the recombinant proteins of E. coli O157:H7 IntiminC280, the carboxy-terminal fraction of Intimin γ, EspB and the fusion protein between the B subunit of Stx2 and Brucella Lumazine Synthase (BLS)(BLS-Stx2B), in Holstein Fresian calves.To accomplish this goal we vaccinated calves with two doses of different vaccine formulations: 2 antigens (IntiminC280, EspB), 3 antigens (IntiminC280, EspB, BLS-Stx2B), BLS-Stx2B alone and a control non-vaccinated group. All antigens were expressed as recombinant proteins in E. coli. Specific IgG titres increased in vaccinated calves and the inclusion of BLS-Stx2B in the formulation seems to have a stimulatory effect on the humoral response to IntiminC280 and EspB after the booster. The neutralizing activity of antibodies against these two antigens was assessed in Red Blood Cell lysis assays and adherence to Hep-2 cells as a correlate of T3SS activity. Both sera from animals vaccinated with 2 or 3 antigens inhibited both virulence properties. Serological response to Stx2 was observed in animals vaccinated only with BLS-Stx2B and with 3 antigens and neutralization of Stx2 cytotoxicity was also observed in both groups. In conclusion, immunization of calves with BLS-Stx2B, IntiminC280 and EspB elicited a potent humoral response able to neutralize Shiga toxin 2 cytotoxity and the T3SS virulence properties in vitro. These results suggest that this formulation is a good candidate vaccine to reduce STEC shedding in cattle and needs to be further assessed in vivo., Competing Interests: The authors have declared that no competing interests exist.

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is responsible for intestinal disease and hemolytic uremic syndrome (HUS), a serious systemic complication which particularly affects children. In this study, we evaluated whether passive immunization protects from EHEC O157:H7 colonization and renal damage, by using a weaned BALB/c mouse model of infection. Recombinant proteins EspB and the carboxyl-terminal fragment of 280 amino acids of γ-intimin (γ-IntC280) were used in combination with a macrophage-activating lipopeptide-2 (MALP) adjuvant to immunize pregnant mice by the intranasal route. Neonatal mice were allowed to suckle vaccinated or sham-vaccinated dams until weaning when they were challenged by the oral route with a suspension of an E. coli O157:H7 Stx2+ strain. The excretion of the inoculated strain was followed for 72h. All vaccinated dams exhibited elevated serum IgG response against both γ-Int C280 and EspB. Passive immunization of newborn mice resulted in a significant increase in serum IgG titers against γ-Int C280 and a slight increase in EspB-specific antibodies. The neonates from vaccinated dams showed a significant reduction in EHEC O157:H7 colonization 48h post challenge. In addition, the level of plasma urea concentration, a marker of renal failure, was significantly higher in offsprings of sham-vaccinated mice. In conclusion, vaccination of pregnant dams with γ-Int C280 and EspB could reduce colonization and systemic toxicity of EHEC O157:H7 in their suckling offsprings., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Escherichia coli O157:H7 is the main causative agent of haemolytic uremic syndrome. Cattle are the main reservoir of these bacteria, and have been shown to develop immune response to colonization. Our aim was to investigate the faecal shedding pattern of E. coli O157:H7 in calves challenged intragastrically with either 10(8) or 10(10) CFU, as well as the ability of specific preexisting antibodies to reduce shedding of the pathogen. Shedding was analysed by direct counting as well as enrichment of rectoanal mucosal swabs. Statistical analysis was performed using a linear model for repeated measures with and without the inclusion of preexisting antibodies against the carboxy-terminal fraction of intimin-γ (γ-intimin C280) as a covariable. Results suggest that there is a statistical difference in the area under the shedding curves between both doses for 14 as well as 28 days after challenge (p = 0.0069 and 0.0209, resp.). This difference is increased when the prechallenge antibodies are taken into account (p = 0.0056 and 0.0185). We concluded that the bacterial dose influences shedding on calves experimentally challenged and that preexisting antibodies against E. coli O157:H7 γ-intimin C280 could partially reduce faecal excretion.

Escherichia coli O157:H7 is responsible for severe intestinal disease and hemolytic uremic syndrome (HUS), a serious systemic complication which particularly affects children. Cattle are the primary reservoir for E. coli O157:H7 and the main source of infection for humans. In this study, we evaluated the ability of transferred maternal colostral antibodies against γ-Intimin C280 and EspB, to protect young weaned calves from E. coli O157:H7 infection. Hyperimmune colostra were obtained by immunization of pregnant cows with a mix of the mentioned antigens. All vaccinated cows mounted a significant IgG response against γ-Intimin C280, and EspB in sera and colostra. Colostrum-fed calves also exhibited high serum IgG titers against γ-Intimin C280 and EspB along with a rise in mucosal γ-Intimin C280-specific IgG antibodies at recto-anal junction and ileum. Additionally, 70 day-old calves received a challenge with E. coli O157:H7 but no reduction in total bacterial shedding or frequency of E. coli O157:H7 excretion from these calves was observed. Most tissue samples showed granulocyte focal infiltrations of the lamina propria and enterocyte erosion. In conclusion, up to the 70th day, the passively acquired γ-Intimin-C280 and EspB-IgG antibodies present in sera and recto-anal mucosa reached a titer insufficient to reduce EHEC O157 shedding and damages of experimentally inoculated young calves., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Many animal and human pathogenic Gram-negative bacteria such as Salmonella, Yersinia, enterohemorrhagic Escherichia coli (EHEC), and enteropathogenic Escherichia coli (EPEC) possess a type III secretion system (TTSS) that is used to deliver virulence proteins directly into the host cell. Recent evidence has suggested that CoilA and CoilB, two synthetic peptides corresponding to coiled-coil domains of the translocator protein EspA, are effective in inhibiting the action of TTSS from EPEC. In the current study, the action of these coiled-coil peptides on the TTSS of EHEC O157:H7 and Citrobacter rodentium was examined. CoilA and CoilB showed to be effective in reducing the red blood cell lysis mediated by EHEC O157:H7 and the in vitro secretion of translocator proteins EspB and EspD by EHEC O157:H7 and EspD by C. rodentium. Treatment of mice with CoilA and CoilB peptides prevented colon damage when the animals were inoculated with C. rodentium. Colon samples of the non-treated group showed areas with loss of superficial epithelium, damaged cells, and endoluminal mononuclear inflammatory infiltrate, consistent with histological lesions induced by C. rodentium, whereas mice treated with the synthetic peptides displayed normal surface epithelium showing a similar structure as the uninfected control group. These encouraging results prompt us to test coiled-coil peptides as treatment or vaccines in other models of bacterial infections in future work., (Copyright © 2012 Elsevier GmbH. All rights reserved.)

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a major cause of intestinal disease and hemolytic uremic syndrome, a serious systemic complication that particularly affects children. Cattle are primary reservoirs for EHEC O157:H7 and the main source of infection for humans. Vaccination of cattle with different combinations of bacterial virulence factors has shown efficacy in decreasing EHEC O157:H7 shedding. It is, therefore, important to demonstrate whether vaccination of pregnant cows with EHEC O157:H7 induces high titers of transferable antibodies to avoid early colonization of calves by the bacteria. In this study we evaluated the ability of EspA, EspB, the C-terminal fragment of 280 amino acids of γ-intimin (γ-intimin C₂₈₀) and inactivated Shiga toxin (Stx) 2 proteins to induce specific antibodies in colostrum and their passive transference to colostrum-fed calves. Friesian pregnant cows immunized by the intramuscular route mounted significantly high serum and colostrum IgG responses against EspB and γ-intimin C₂₈₀ that were efficiently transferred to their calves. Antibodies to EspB and γ-intimin C₂₈₀ were detected in milk samples of vaccinated cows at d 40 postparturition. Significant Stx2-neutralizing titers were also observed in colostrum from Stx2-vaccinated cows and sera from colostrum-fed calves. The results presented showed that bovine colostrum with increased levels of antibodies against EHEC O157:H7 may be obtained by systemic immunization of pregnant cows, and that these specific antibodies are efficiently transferred to newborn calves by feeding colostrum. Hyperimmune colostrum and milk may be an alternative to protect calves from early colonization by EHEC O157:H7 and a possible key source of antibodies to block colonization and toxic activity of this bacterium., (Copyright © 2012 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Pets can be reservoirs of Shiga toxin-producing Escherichia coli (STEC) strains. The aim of this study was to examine nine strains belonging to several serotypes (O91:H21, O91:H16, O178:H19, O8:H19, O22:H8, O22:HNT, ONT:H8), previously recovered from cats or dogs. To this end, we assessed a set of additional virulence genes (stx(2) subtype, subAB, ehxA, eae and saa), cytotoxic activity, and genetic relationships with strains isolated from cattle, meat and humans using pulsed-field gel electrophoresis (PFGE). Most of the isolates carried the stx(2) and/or stx(2vh-b) sequences, while only the O91:H21 isolate presented the mucus-activatable stx(2d) variant, as confirmed by sequencing the genes of subunits A and B. All the strains showed cytotoxic activity in cultured cells. One of the two O178:H19, selected for its high level of cytotoxicity in Vero cells, showed the ability to cause functional alterations in the human colon mucosa in vitro. None of the strains possessed the subAB, eae or saa genes and only the strains belonging to serotype O8:H19 carried the ehxA gene. The isolates shared 90-100% similarity by PFGE to epidemiologically unrelated strains of the corresponding serotypes recovered from cattle, meat or humans. Our results demonstrate that dogs and cats may have a role in the infection of humans by STEC, probably serving as a vehicle for bovine strains in the cycle of human infection, and thus emphasize the health risks for owners and their families., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Cattle are the main reservoir of enterohemorrhagic Escherichia coli O157:H7, a bacterium that, in humans, causes hemorrhagic colitis and hemolytic uremic syndrome (HUS), a life-threatening disease, especially in children and older people. Therefore, the development of vaccines preventing colonization of cattle by E. coli O157:H7 could be a main tool for an HUS control program. In the present study, we evaluated bacterial ghosts (BGs) of E. coli O157:H7 as an experimental vaccine against this pathogen. BGs are empty envelopes of Gram-negative bacteria, which retain the morphological surface make-up of their living counterparts and are produced by controlled expression of the cloned protein E, which causes loss of all the cytoplasm content. In this work, E. coli O157:H7 BGs were used for subcutaneous immunization of calves. The vaccinated animals elicited significant levels of BG-specific IgG but not IgA antibodies in serum. Low levels of IgA and IgG antibodies against BGs were detected in saliva from vaccinated animals. Following oral challenge with E. coli O157:H7, a significant reduction in both the duration and total bacterial shedding was observed in vaccinated calves compared to the nonimmunized group. We demonstrated that systemic vaccination with E. coli O157 BGs provides protection in a bovine experimental model. Further research is needed to reach a higher mucosal immune response leading to an optimal vaccine., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is the most prevalent EHEC serotype that has been recovered from patients with haemolytic uremic syndrome (HUS) worldwide. Vaccination of cattle, the main reservoir of EHEC O157:H7, could be a logical strategy to fight infection in humans. This study evaluated a vaccine based on the carboxyl-terminal fragment of 280 amino acids of γ-intimin (γ-intimin C₂₈₀) and EspB, two key colonization factors of E. coli O157:H7. Intramuscular immunization elicited significantly high levels of serum IgG antibodies against both proteins. Antigen-specific IgA and IgG were also induced in saliva, but only the IgA response was significant. Following experimental challenge with E. coli O157:H7, a significant reduction in bacterial shedding was observed in vaccinated calves, compared to control group. These promising results suggest that systemic immunization of cattle with intimin and EspB could be a feasible strategy to reduce EHEC O157:H7 faecal shedding in cattle., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Non-enterotoxin (CPE)-producing Clostridium perfringens type A has been associated with enteritis in calves. Recent evidence has suggested that a novel toxin, named beta2 (CPB2), is implicated in the pathogenesis of this disease, although there is little evidence supporting this. In the current study, the role of C. perfringens type A in an outbreak of enteritis in calves was studied. Two 20-day-old dairy calves exhibiting apathy and reluctance to eat, with paresis of the anterior limbs, were euthanized for postmortem examination. Gross and histological changes compatible with acute enteritis, rumenitis, meningitis, and pneumonia were seen in both calves. Clostridium perfringens type A non-CPE, non-CPB2 was isolated from the abomasum and the small intestine. Escherichia coli ONTH8 (with cdtBIII and f17 virulence genes detected by polymerase chain reaction) was also isolated from the brain, abomasum, and intestine from both calves. All the samples were negative for Salmonella spp. When the C. perfringens strain was inoculated into bovine ligated small and large intestinal loops, cell detachment, erosion, and hemorrhage of the lamina propria were observed, predominantly in the small intestine. The results suggest that non-CPE, non-CPB2 C. perfringens type A is able to induce pathologic changes in the intestine of calves, probably enhanced by other pathogens, such as some pathogenic E. coli strains.

Vegetable tannins are water-soluble polyphenolic compounds of varying molecular weights that occur abundantly in nature. The diet of many free-ranging wild animals contains significant amounts of tannins. Also, commercial tannins are used in animal industry as food additives to improve animal performance. In order to further determine the capacity of tannins to inhibit the development of intestinal diseases produced by Clostridium pefringens, we evaluated here the effect of tannins from quebracho, chestnut or combinations of both on C. perfringens and their toxins. The C. perfringens (types A, B, C, D and E) growth obtained from the intestine of healthy and diseased animals was reduced in a dose-dependent manner in the presence of quebracho tannins, chestnut tannins, combinations of both or a commercial formula based in these tannins. Although the minimal inhibitory concentration of both tannins varied between isolates, no statistically significant differences were observed between isolates from healthy or sick animals. Comparative analysis showed that the concentrations of quebracho tannin inhibiting the growth of C. perfringens were higher than chestnut tannin. In fact, antibacterial effect of quebracho tannin was increased up to 20 times with the addition of 25% of chestnut tannin and 85 times with 75% of chestnut tannin. Antibacterial activity of the commercial product was up to ~50 times higher than quebracho tannin alone. Quebracho tannin showed partial bactericidal activity, whereas chestnut tannin activity was stronger. Both tannins were able to reduce the alpha toxin lecithinase activity and epsilon toxin cytotoxicity in MDCK cells. These results suggest that tannin-supplemented diet could be useful to prevent some clostridial diseases., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Background: Enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC) are two categories of E. coli strains associated with human disease. A major virulence factor of both pathotypes is the expression of a type three secretion system (TTSS), responsible for their ability to adhere to gut mucosa causing a characteristic attaching and effacing lesion (A/E). The TTSS translocates effector proteins directly into the host cell that subvert mammalian cell biochemistry., Methods/principal Findings: We examined synthetic peptides designed to inhibit the TTSS. CoilA and CoilB peptides, both representing coiled-coil regions of the translocator protein EspA, and CoilD peptide, corresponding to a coiled-coil region of the needle protein EscF, were effective in inhibiting the TTSS dependent hemolysis of red blood cells by the EPEC E2348/69 strain. CoilA and CoilB peptides also reduced the formation of actin pedestals by the same strain in HEp-2 cells and impaired the TTSS-mediated protein translocation into the epithelial cell. Interestingly, CoilA and CoilB were able to block EspA assembly, destabilizing the TTSS and thereby Tir translocation. This blockage of EspA polymerization by CoilA or CoilB peptides, also inhibited the correct delivery of EspB and EspD as detected by immunoblotting. Interestingly, electron microscopy of bacteria incubated with the CoilA peptide showed a reduction of the length of EspA filaments., Conclusions: Our data indicate that coiled-coil peptides can prevent the assembly and thus the functionality of the TTSS apparatus and suggest that these peptides could provide an attractive tool to block EPEC and EHEC pathogenesis.

Shiga toxin-negative Escherichia coli O157 strains of various H types have been associated with diarrhea in children and are considered potentially pathogenic for humans. In this study, we describe non-Shiga toxin-producing E. coli O157 E. coli strains previously obtained from dogs in Argentina. Different E. coli phylogenetic lineages corresponding to flagellar types H16, H29 and H45 were identified. E. coli serotypes O157:H16 and O157:H45 contained intimin subtypes epsilon and alpha 1, respectively. Serotype O157:H45 carried the bfp gene encoding the bundle-forming pilus. Localized adherence-like patterns to HEp-2 cells were observed in O157:H16 strains, while O157:H45 adhered in a typical localized pattern. A total of eight different XbaI-pulse field electrophoresis patterns with more than 74 % similarity were identified among the nine E. coli O157:H16 strains. Our data emphasized the fact that dogs may harbor human pathogenic E. coli O157 which do not correspond to Shiga toxin-producing strains and whose potential human health hazard should not be underestimated.

Mucosal vaccine formulations based on purified recombinant C280 gamma-Intimin and EspB (Escherichia coli secreted protein B) from enterohaemorragic E. coli co-administered with a pegylated derivative of the TLR2/6 agonist MALP-2 (macrophage-activating lipopeptide) as adjuvant were evaluated in BALB/c mice. After intranasal vaccination, strong humoral and cellular immune responses were observed against C280 gamma-Intimin and EspB. Sera of immunized mice inhibit bacterial haemolytic activity in vitro. Antigen-specific T-cell proliferation, IL-4, IL-2 and IFN-gamma producing cells, and secretory IgA were mostly detected in animals receiving MALP-2 as adjuvant. These results suggest that C280 gamma-Intimin and EspB are good candidate antigens to be incorporated into mucosal vaccines against this important pathogen.

Enterohemorrhagic Escherichia coli (EHEC) is the main cause of hemolytic-uremic syndrome, an endemic disease in Argentina which had an incidence in 2005 of 13.9 cases per 100,000 children younger than 5 years old. Cattle appear to be a major reservoir of EHEC, and a serological response to EHEC antigens has been demonstrated in natural and experimental infections. In the current study, antibodies against proteins implicated in EHEC's ability to form attaching and effacing lesions, some of which are exported to the host cell via a type three secretion system (TTSS), were identified in bovine colostrum by Western blot analysis. Twenty-seven (77.0%) of the 35 samples examined contained immunoglobulin G (IgG) antibodies against the three proteins assayed in this study: EspA, EspB, and the carboxy-terminal 280 amino acids of gamma-intimin, an intimin subtype associated mainly with O157:H7 and O145:H- serotypes. Every colostrum sample was able to inhibit, in a range between 45.9 and 96.7%, the TTSS-mediated hemolytic activity of attaching and effacing E. coli. The inhibitory effect was partially mediated by IgG and lactoferrin. In conclusion, we found that early colostrum from cows contains antibodies, lactoferrin, and other unidentified substances that impair TTSS function in attaching and effacing E. coli strains. Bovine colostrum might act by reducing EHEC colonization in newborn calves and could be used as a prophylactic measure to protect non-breast-fed children against EHEC infection in an area of endemicity.

Cattle are recognized as the major reservoir of STEC and the source of infection for human beings. Until recently, intervention strategies to decrease the contamination of meat products have been focused on the slaughter plant with the application of practices to reduce the contamination and proliferation of STEC. This has now changed following the development of intervention strategies in the farm. This could be one of the most important points of intervention to lower the incidence of human infection. Vaccines, probiotics, bacteriophages, and changes in production practices may be useful as strategies to control EHEC in the cattle. The application of such intervention measures could be difficult due to the fact that this zoonotic agent rarely causes disease in bovines. The HUS is endemic in Argentina, and the factors leading to this epidemiological situation remain unknown. However, intervention strategies undoubtedly will contribute to reduce the incidence of this zoonosis.

Shiga toxin-producing E. coli (STEC) is one of the most important emergent pathogen in foods, being its main reservoir bovine cattle. STEC can cause diarrhea, hemorrhagic colitis and hemolytic-uremic syndrome. The present work have studied the cytotoxic action in human colon of cultures of two STEC strains isolated from faeces of calves with bloody diarrhea. Colonic mucosa was mounted as a diaphragm in a Ussing chamber and incubated with the cultures of pathogenic strains. Net water flow (Jw) decreased and the short-circuit current (Isc) increased significantly (p < 0.01) compared to negative control. Tissues showed an erosion of the mucose, epithelial exfoliation, and presence of pseudo-membranes in the lumen. Mild circulatory lesions were observed in the lamina propia. A moderate neutrophils infiltration was observed in the lumen and into the epithelial cells. Colonic crypts were not disrupted. Both experimental strains caused a similar lesion on colon tissues. This is the first study that shows that cultures of STEC strains isolated from bovine cattle produce cytotoxic effects in vitro in human colon.

Shiga toxin-producing Escherichia coli belonging to serotype O26:H11 was isolated from a 2-month-old guanaco with severe watery diarrhea. E. coli colonies carried the stx1 and eae genes, showed localized adherence to HEp-2 cells, and produced enterohemolysin. A serological response to lipopolysaccharide O26 was observed at the onset of diarrhea.

Faecal samples from 76 diarrhoeic calves belonging to 36 farms located in the Pampas plain, Argentina, were examined for Shiga toxin-producing Escherichia coli (STEC). A total of 15 STEC strains were isolated from 12 (15.8%) calves which came from six different farms. All stx positive strains assayed by PCR were also positives in the Vero cell cytotoxicity test. The majority (60.0%) of the STEC strains carried the stx(1) gene. Twelve (80.0%) of the STEC isolates which belonged to serotypes O5:H- (n = 4), O26:H11 (n = 4), O26:H- (n = 1), O111:H- (n = 2), and O123:H38 (n = 1) were also enterohaemolysin (EHly) positive and carried the gene encoding for intimin (eae). All the stx positive strains were negative for the bfpA gene. Localized adherence to HEp-2 cells were observed in 83.3% of the eae+ STEC strains. STEC belonging to serotype O5:H- showed atypical biochemical properties, including urease production. Urease was also produced by two strains belonging to serotypes O153:H? and non-typeable, respectively. Resistance to three or more antibiotics was observed in 12 (80.0%) of the STEC isolates. Most of the serotypes of STEC recovered in this survey carried virulence traits that are associated with increased human and bovine pathogenicity. The present study shows that highly virulent STEC strains are being shed by diarrhoeic calves from farms located in a high incidence area of human STEC infections.

CS31A is a K88-related non-fimbrial adhesin first described on Escherichia coli strains isolated from diarrhoeic and septicaemic calves. In this report, CS31A antigen was screened by immunological methods and confirmed by PCR among bovine E. coli isolates. In addition, CS31A-producing strains were characterized with respect to different fimbrial antigens, O-serogroup and other properties related to virulence. Faecal or tissue specimens of 100 diarrhoeic or septicaemic calves and 27 older cattle with different pathologies from 71 outbreaks or individual cases that occurred in Buenos Aires province, Argentina, were examined. CS31A + E. coli strains were isolated from 21 (21.0%) calves from 16 outbreaks or individual cases. No CS31A + E. coli was detected in samples from cattle more than 1 year old. Fimbriae F5, F41, F17a and F17b were not detected among the CS31A-producing strains. Three (14.3%) of the CS31A+ E. coli strains expressed the F17c fimbria. All of the 21 isolates exhibited at least one property of septicaemic strains (resistance to serum, production of aerobactin or colicins) but none of them demonstrated heat-stable enterotoxigenic activity. CS31A + E. coli isolates belonged to 10 serogroups, more commonly O8, O7, O17 and O21. The results obtained here confirm the worldwide distribution of CS31A antigen in bovine E. coli strains. However, CS31A + or CS31A + /F17c + E. coli were less frequently isolated than they were in North hemisphere countries.

Thirty-five samples of eviscerated poultry from processing plants in greater Buenos Aires were examined for the presence of Salmonella. Eighteen samples (51.2%) were found to be contaminated with salmonellae on testing with the non-destructive rinse method. Out of 7 plants investigated, 6 exhibited the presence of Salmonella in the product. A total of 6 confirmed species were found, S. infantis being the most frequently isolated. Rappaport-Vassiliadis and Tetrathionate-Brilliant Green broths were used as enrichment media, combined with Bismuth Sulphite or Brilliant Green-Phenol Red-Lactose-Sucrose-Deoxycholate agars as isolations media. The combination Rappaport-Vassiliadis broth and Bismuth Sulphite agar, was the only one that allowed the detection of all positive samples, including the six confirmed Salmonella species. Taking in to account the percentage of presumed colonies that were later confirmed, the Rappaport-Vassiliadis broth/Bismuth Sulphite agar proved the most specific.

The isolation of Yersinia enterocolitica from a child's feces with an acute diarrhea is reported for the first time in Argentina. The strain was classified as belonging to the biotype 4 of Wauters, serotype O:3, phage type VIII. The virulence-associated test of autoagglutination, calcium dependency and production of heat-stable enterotoxin were positive, whereas neither lethality for the adult mouse by oral route, nor invasiveness by using the Serény test in the mouse, were demonstrated. A plasmid of approximately 40 Mdal was detected. The suckling mouse LD50 was 4.1 x 10(6) cells. These characteristics are in agreement with those reported for most of the Yersinia enterocolitica strains belonging to the same serotype.

A total of 23 lots of dehydrated and instant products for babies and children were analyzed. Neither Salmonella, C. perfringens, B. cereus, St. aureus, Group A beta-hemolytic streptococci, fecal coliforms, E. coli nor aflatoxins could be detected in the 115 samples studied. With the exception of the cereals, results obtained for the Aerobic Plate Count (RAP), the Moulds and Yeast Count (RHL) and the Total Coliforms Count (RCT) were, respectively, 91% equal of lower then 3 per gram, and 92% lower than 100 per gram. The results obtained justify the proposition of consultants of FAO/WHO, to limit determination to RAP, RCT, and investigation of Salmonella. According to specifications of FAO/WHO, 10,5% of the lots examined would be considered non acceptable. With regard to the cereals, the lower sensitivity of the used techniques, due to the physical sample characteristics, makes it advisable to adopt RHL here, too.

Eighteen lots of processed cheese and processed cheese spread were analyzed. Results obtained for the yeasts and molds count (RHL) and the total coliforms count (RCT) were 88.9% inferior to 100 per gram, in the 90 subsamples studied. The fecal coliforms count (RCF) and the S. aureus count were, respectively, 96.6% and 94.4% inferior to 10 per gram, for the same subsamples. Taking into account the format presented by the International Commission on Microbiological Specifications for Foods and the results of our survey, a three class plan is proposed for the following microbiological tests: RHL (n = 5, c = 2, m = 100, M = 1000); RCT (n = 5, c = 2, m = 100, M = 1000); RCF (n = 5, c = 2, m = 10, M = 100); and S. aureus count (n = 5, c = 1, m = 100, M = 1000). Therefore, applying these microbiological specifications, 4 lots (22.2%) would be rejected.