Detection and prevalence of verotoxin-producing Escherichia coli O157 and non-O157 serotypes in a Canadian watershed.

Verotoxin-producing Escherichia coli (VTEC) strains are the cause of food-borne and waterborne illnesses around the world. Traditionally, surveillance of the human population as well as the environment has focused on the detection of E. coli O157:H7. Recently, increasing recognition of non-O157 VTEC strains as human pathogens and the German O104:H4 food-borne outbreak have illustrated the importance of considering the broader group of VTEC organisms from a public health perspective. This study presents the results of a comparison of three methods for the detection of VTEC in surface water, highlighting the efficacy of a direct VT immunoblotting method without broth enrichment for detection and isolation of O157 and non-O157 VTEC strains. The direct immunoblot method eliminates the need for an enrichment step or the use of immunomagnetic separation. This method was developed after 4 years of detecting low frequencies (1%) of E. coli O157:H7 in surface water in a Canadian watershed, situated within one of the FoodNet Canada integrated surveillance sites. By the direct immunoblot method, VTEC prevalence estimates ranged from 11 to 35% for this watershed, and E. coli O157:H7 prevalence increased to 4% (due to improved method sensitivity). This direct testing method provides an efficient means to enhance our understanding of the prevalence and types of VTEC in the environment. This study employed a rapid evidence assessment (REA) approach to frame the watershed findings with watershed E. coli O157:H7 prevalences reported in the literature since 1990 and the knowledge gap with respect to VTEC detection in surface waters.

Oral delivery systems for encapsulated bacteriophages targeted at Escherichia coli O157:H7 in feedlot cattle.

Bacteriophages are natural predators of bacteria and may mitigate Escherichia coli O157:H7 in cattle and their environment. As bacteriophages targeted to E. coli O157:H7 (phages) lose activity at low pH, protection from gastric acidity may enhance efficacy of orally administered phages. Polymer encapsulation of four phages, wV8, rV5, wV7, and wV11, and exposure to pH 3.0 for 20 min resulted in an average 13.6% recovery of phages after release from encapsulation at pH 7.2. In contrast, untreated phages under similar conditions had a complete loss of activity. Steers (n = 24) received 10(11) CFU of naladixic acid-resistant E. coli O157:H7 on day 0 and were housed in six pens of four steers. Two pens were control (naladixic acid-resistant E. coli O157:H7 only), and the remaining pens received polymer-encapsulated phages (Ephage) on days -1, 1, 3, 6, and 8. Two pens received Ephage orally in gelatin capsules (bolus; 10(10) PFU per steer per day), and the remaining two pens received Ephage top-dressed on their feed (feed; estimated 10(11) PFU per steer per day). Shedding of E. coli O157:H7 was monitored for 10 weeks by collecting fecal grab and hide swab samples. Acceptable activity of mixed phages at delivery to steers was found for bolus and feed, averaging 1.82 and 1.13 x 10(9) PFU/g, respectively. However, Ephage did not reduce shedding of naladixic acid-resistant E. coli O157:H7, although duration of shedding was reduced by 14 days (P < 0.1) in bolus-fed steers as compared with control steers. Two successful systems for delivery of Ephage were developed, but a better understanding of phage-E. coli O157:H7 ecology is required to make phage therapy a viable strategy for mitigation of this organism in feedlot cattle.

Salmonella contamination of hatching and table eggs: a comparison.

This study determined and compared Salmonella contamination rates of pools of surplus, early and culled hatching eggs from layer and broiler breeder flocks, and of pools of early and regular table eggs from layer flocks. Each pool contained 6 eggs. Five methods were used for the isolation of Salmonella. Nine of 126 pools of culled layer hatching eggs, 2 of 126 pools of surplus layer hatching eggs, and one of 126 pools of early layer hatching eggs were contaminated with Salmonella. All 126 pools of broiler breeder surplus, and early and culled hatching eggs tested negative for Salmonella. All 168 pools of regular table eggs tested negative for Salmonella, whilst one of 84 pools of early table eggs contained Salmonella agona. The pools of culled layer hatching eggs and surplus layer hatching eggs that contained S. typhimurium were derived from the same breeder operation. Similarly, the pools of culled and early layer hatching eggs that contained S. heidelberg were derived from one breeder operation. Pools of culled hatching eggs were more frequently contaminated with Salmonella than other hatching or table eggs. Pools containing eggs that were both cracked and dirty were more frequently contaminated with Salmonella than all other pools of eggs. The overall Salmonella contamination rate of the table eggs was 0.07 to 0.4%. Critical control points (macroscopic classification of the eggs as cracked and dirty) were validated microbiologically.

The effect of premise order in conditional reasoning: a test of the mental model theory.

The difference in difficulty between modus ponens (if p then q; p; therefore q) and modus tollens (if p then q; not-q; therefore not-p) arguments has been traditionally explained by assuming that the mind contains a rule for modus ponens, but not for modus tollens. According to the mental model theory, modus tollens is a more difficult deduction than modus ponens because people do not represent the case not-q in their initial model of the conditional. On the basis of this theory, we predicted that conditions in which reasoners are forced to represent the not-q case should improve correct performance on modus tollens. In particular, we predicted that the presentation of the minor premise (not-q) as the initial premise should produce facilitation. Experiment 1 showed that this is the case: whereas the inversion of the premise order did not affect modus ponens, it produced a significant increase of valid conclusions for modus tollens. Experiment 2 showed that this facilitation does not depend on the negative form (contrary vs. contradictory) of the minor premise. Experiments 3 and 4 (and/or some of their replications) demonstrated that facilitation also occurs when participants are asked to find the cases compatible with not-q or to evaluate a p conclusion. No premise order effect was found for sentences which make explicit the not-q case right from the start, i.e. p only if q conditionals and biconditionals (Experiments 5 and 6). Finally, Experiments 7 and 8 showed that the conditional fallacies are not significantly affected by the premise order.

Scanning electron microscopy of rabbit tubes at different intervals after anastomosis using fibrin glue.

Eighteen New Zealand White rabbits were submitted to tubal anastomosis using fibrin glue. The animals were then killed at different intervals (2-56 days) and the tubes were removed for analysis with the scanning electron microscope in order to study re-epithelialization and ciliogenesis. For the first 4 days after the operation the epithelium seemed to suffer considerable traumatic effects and was de-epithelialized. On the 6th day cells with microvilli appeared and towards the 10th day the first cilia were seen. Ciliogenesis was complete between 2 and 4 weeks after the operation, at which time the cilia re-acquired the ability to beat in coordination, as well as attaining normal quantity and length. The time required for recovery by the epithelium after anastomosis with fibrin glue would thus seem similar to that required when other suture materials are used. Fibrin glue thus combines the advantage of a considerable reduction in operating times with the ability to be rapidly reabsorbed, with complete restitutio ad integrum of the tissues.