When the DNA of Escherichia coli is damaged a set of events termed "SOS functions" occur to aid cellular survival. The recA and lexA proteins are involved in the regulation of these functions. To determine the role of the lexA protein, amber mutations, designated spr-55(amber), were isolated in the lexA-3 gene. The lack of the lexA-3 gene product abolished sensitivity to ultraviolet light and resulted in the constitutive synthesis of recA protein. Introduction of amber suppressor mutations restored the original lexA-3 phenotype. It was concluded that spr mutations inactivate lexA protein resulting in the constitutive expression of the SOS functions. These data provide evidence that the lexA protein is the repressor for the recA gene. The repair of phage lambda (λ⁺) by ultraviolet light was determined in the strains carrying alleles of the spr, uvrA, and recA genes. The survival of the phage was more in the spr-51 uvrA⁺ strain as compared to wild type. These results were not dependent on the recA genotype. Introduction of the uvrA-6 mutation into the spr-51 uvrA⁺ recA⁺ strains resulted in the same relative decrease of phage survival. These results suggest that lexA protein is involved in the regulation of uvrA-dependent excision repair and that inactivation of lexA leads to the constitutive expression of excision repair. New mutant forms of lexaA protein were isolated. The lexA⁺, lexA-3, lexA-10, and lexA-27 proteins displayed identical mobilities in the Weber and Osborn gel system. The lexA-10 and lexA-27 genes showed different phenotypes and encoded proteins of different mobilities in the Laemmli gel system. It was concluded that the differences in mobilities observed in the Laemmli gel system are due to alterations in charge or amino acid, not in size; furthermore; the molecular weight of lexA⁺ protein was determined to be 24 kilodaltons.

No description available.

No description available.

Shigatoxin-producing Escherichia coli (STEC) can cause infections in humans which can beserious and sometimes fatal. There is a great need for methods that are able to detect differentserogroups of STEC. In this project, conventional and real-time PCR assays for detection ofSTEC O104:H4 and O121, as recommended by the European Union Reference Laboratory(EU-RL) for STEC, were validated. The specificity, limit of detection, repeatability,efficiency and robustness were determined for three real-time PCR assays. The validationshowed that the real-time PCR reactions were specific and sensitive although some additionaltests are required.

Despite their beneficial effects, concerns have been raised about the role of antimicrobial growth promoters (AGP) in the emergence of antibiotic resistant bacteria. This study evaluated the effects of approved AGP on the emergence of antibiotic resistance in commensal E. coli and foodborne pathogen Salmonella. A survey of antibiotic resistance levels in commercial broiler chicken farms in the Fraser Valley (B.C.) and an experimental feeding trial were conducted from May 2004 to February 2005 and May to November 2005, respectively. The latter examined the effects of ten AGP formulations (bambermycin, penicillin, salinomycin, bacitracin, combination of salinomycin and bacitracin, chlortetracycline, virginiamycin 11ppm, virginiamycin 22ppm, monensin and narasin) on bird performance as well. Multiple antibiotic resistant commensal E. coli and Salmonella carrying virulence genes were found at commercial broiler chicken farms and therefore may serve as reservoirs for these genes. There was no significant difference between feed formulations on the phenotypic or genotypic characteristics of the isolates, except for tetracycline resistance gene tet(B). In the experimental feeding trial, broiler chickens were fed a diet including or excluding AGP. Birds were sampled prior to and weekly during feeding of the control and the AGPP containing diets. Although not detected on day 0, E. coli increased after day 7 to more than 9.9 log10 CFU/g in ceca. Multi-drug resistant E. coli were isolated from birds fed the ten AGP containing diets as well as the control diet. Except for penicillin, none of the AGP containing diets significantly improved bird performance compared to the control diet (P>0.05). Good management practices can significantly improve broiler chickens performance and decrease the mortality rate.

Información extraída del <a href="http://www.cindefi.org.ar/?page_id=61&language=es">sitio web del CINDEFI</a>

Se comprueba que en las enteritis de los cerdos de la Provincia de Buenos Aires actúan indistintamente microorganismos solos o asociados. De 172 muestras bacteriológicas de necropsias y casos clínicos de enteritis de cerdos se aislaron: Escherichia coli 139; Salmonella 15; Proteus 10; Klebsiella 21; Sighella 2; Serratia 1; Pseudomonas 1; Campylobacter 28; Treponema 29 y Clostridum perfrigens 2. De las 139 cepas de E.coli un alto porcentaje correspondieron a los tipos somáticos 0149,0141,0138, y 08. Con los tipos somáticos 09,0141 y 04-0123 se reproduce experimentalmente la enfermedad de los edemas. Se detecta una elevada resistencia a las drogas con las cepas de E. coli aisladas en diferentes desórdenes entéricos, especialmente con los antibióticos de uso común en terapéutica veterinaria de nuestro país. Los serotipos más frecuentes de Salmonellas aisladas corresponden a S.cholera suis y S.tiphymurium. Treponema sp. y Campylobacter son los agentes bacterianos más comunmente aislados en la Disentería porcina. Se aisla C.perfrigens en 2 casos de enteritis necrótica. / The present work proved that pig enteritis in de province of Buenos Aires are caused by several kinds of microorganism that can act alone or associated in the gut. In a survey of 172 bacteriological samples taken from necropsied pigs with clinical sing of diarrhoea the following bacterias were isolated: E. coli 139;Salmonella 15;Proteus 10;Klebsiella 21;Sighella 2;Serratia 1;Pseudomonas 1;Campylobacter 28;Treponema 29 y Clostridium perfrigens 2. From the 139 strains de E.coli a high rate belonged to the somatic types 0149,0141,0138 y 08. With the somatic types of E.coli 09,0141 y 04-0123 the experimental reproduction of the Odenema disease was done. The strains of E.coli isolated from enteric disease showed high resistence specialy to the antibiotics of common use in the veterinary practice in Argentina. Within the Salmonella group.S.cholera suis and S.tiphimurium were the serotype isolated more frecuently. From pigs with pathological diagnosis of Swine Disentery,Traeponema and Campylobacter sp were isolated and from two cases of Necrotic a Clostridium perfrigens was recovery.

A wastewater treatment and reuse system consisting of a tile drainage system, a constructed treatment wetland (CTW), a reservoir, and an irrigation system was established. The system supplied 780 mm of irrigation water for the 1.8 ha of drained land for the 2008 growing season. A hydraulic tracer study conducted in the CTW supported the use of a length to width ratio of 10:1. During 2008, annual nitrate-nitrogen (NO3--N) and Escherichia coli (E. coli) mass reductions were 67.6 and 63.3%, respectively. Elevated E. coli levels were observed in the reservoir during the warm season. Therefore, water may not be safe for irrigating crops consumed raw. The mean first-order areal uptake rate constants generated for NO3--N and E. coli were 8.0 and 6.4 m y-1, respectively, and are recommended for similar CTWs. A wetland area to drainage area ratio of 4.5% is recommended to achieve ? 70 % mass reduction of NO3--N and E. coli

In a series of field and watershed scale studies, the genetic diversity of Escherichia coli in secondary habitats (e.g. soils and sediments) of an agricultural watershed was assessed in order to examine the dynamics of E. coli inhabiting these matrices and to determine their contribution to waterborne populations. Using replicated field plots, persistent subpopulations of E. coli were observed to be significantly affected by hillslope position due to inherent differences in soil texture and moisture content. The dynamics of E. coli populating tile drainage effluent in a working cultivated field were monitored and it was observed that putatively naturalized E. coli dominated the effluent after approximately 55 days following manure amendments. The contribution of tile drainage effluents to the waterborne E. coli population in an adjacent stream was exponentially related to tile discharge rates, regardless of whether the effluent was populated by manure-associated or naturalized E. coli strains. Streambed E. coli populations differed according to stream geomorphological features, with strains responding to sediment texture and water velocity distributions among the features. In a temporal study of sediment E. coli, population turnover was observed to be affected by sediment redistribution in highenergy stream reaches and was stabilized by immigration from adjacent catchment sources in low-energy stream reaches. Reach-specific connectivity between sediment and waterborne E. coli populations was observed in this watershed. Reach- and catchmentscale hyporheic processes are speculated to be occurring, which may be in part influenced by strain-dependent attachment behaviour of E. coli strains in disjoint stream reaches influenced by different catchment sources of E. coli. The attachment of waterborne E. coli to suspended particles was observed to be associated with land use, water quality and suspended particle variables. The relationship of land use type to particle attachment reinforces the hypothesis that strain-specificity in attachment behaviour can affect the transport of E. coli in fluvial systems. This work provides evidence that putatively naturalized strains in cultivated fields can contribute a large part to waterborne E. coli, and that reach-specific hydrological factors need to be considered when relating sediment- to waterborne E. coli in fluvial systems.

No description available.