Cornelis Poppe

Acquisition of Resistance to Extended-Spectrum Cephalosporins by Salmonella enterica subsp. enterica Serovar Newport and Escherichia coli in the Turkey Poult Intestinal Tract

ABSTRACT Salmonella enterica subsp. enterica serovar Newport resistant to the extended-spectrum cephalosporins (ESCs) and other antimicrobials causes septicemic salmonellosis in humans and animals and is increasingly isolated from humans, animals, foods, and environmental sources. Mechanisms whereby serovar Newport bacteria become resistant to ESCs and other classes of antimicrobials while inhabiting the intestinal tract are not well understood. The present study shows that 25.3% of serovar Newport strains isolated from the turkey poult intestinal tract after the animals were dosed with Escherichia coli harboring a large conjugative plasmid encoding the CMY-2 β-lactamase and other drug resistance determinants acquired the plasmid and its associated drug resistance genes. The conjugative plasmid containing the cmy-2 gene was transferred not only from the donor E. coli to Salmonella serovar Newport but also to another E. coli serotype present in the intestinal tract. Laboratory studies showed that the plasmid could be readily transferred between serovar Newport and E. coli intestinal isolates. Administration of a single dose of ceftiofur, used to prevent septicemic colibacillosis, to 1-day-old turkeys did not result in the isolation of ceftiofur-resistant E. coli or Salmonella serovar Newport. There was a remarkable association between serotype, drug resistance, and plasmid profile among the E. coli strains isolated from the poults. This study shows that Salmonella serovar Newport can become resistant to ESCs and other antibiotics by acquiring a conjugative drug resistance plasmid from E. coli in the intestines.

Subinhibitory concentrations of tetracycline affect virulence gene expression in a multi-resistant Salmonella enterica subsp. enterica serovar Typhimurium DT104

Treatment of salmonellosis with antibiotics is controversial and may prolong carriage and shedding. Therefore, this study sought to investigate if exposure to antimicrobials influences the expression of factors involved in virulence and host colonization. The effect of subinhibitory tetracycline treatment (16 microg/ml, 30 min) on a multi-drug resistant Salmonella Typhimurium DT104 strain was investigated using a targeted microarray. Real-time reverse transcriptase PCR was used to confirm and further assess transcription of 10 selected genes. An in vitro cell invasion assay was performed to assess the invasiveness of the tetracycline-treated isolate. Out of 323 genes, 11 were significantly up-regulated and four were down-regulated in the microarray assays. The hilD and hilA genes, both regulators of Salmonella Pathogenicity Island 1, were up-regulated. Other up-regulated genes included the fliC, fliD, motA and motB genes, involved in motility, the fur gene, an important regulator of iron acquisition systems and of acid tolerance. The drug-exposed replicates showed a 2.5-fold increase in intracellular bacteria over the non-exposed control in cell cultures. These findings suggest a drug-induced expression profile consistent with the early stages of Salmonella infection and invasion concomitant with an increased ability to invade epithelial cells in vitro.

Characterization of blaCMY-2 Plasmids in Salmonella and Escherichia coli Isolates from Food Animals in Canada

ABSTRACT One hundred thirty-four bla CMY-2 plasmids from Salmonella and Escherichia coli strains from animals and food in Canada were characterized. Five plasmid groups were identified based on replicon type and restriction profiles. Three groups contained E. coli plasmids only. IncA/C plasmids included most multiresistant plasmids and all those of bovine origin.

A longitudinal study of the Salmonella status on Ontario swine farms within the time period 2001-2006.

In order to describe the farm-level Salmonella status, 113 Ontario swine farms were tested for Salmonella one to five times within the time period 2001-2006. During 422 visits, 6844 fecal samples were collected and cultured for Salmonella. Salmonella was recovered from 437 (6.38%) of the fecal samples, and 69 (61%) of the farms had at least one positive sample over the entire period of the study. Salmonella was not recovered on 11 farms of the 54 farms visited five times, nor from 7 of the 17 farms visited four times. On seven farms Salmonella was not recovered over the first four visits but were cultured on the fifth visit. The isolates belonged to 30 different serovars, and serogroup B and C1 were the most common serogroups. Salmonella Typhimurium (including var. Copenhagen) was the most common serovar recovered from 35.5% of the farms with DT104 as the most frequent phage type. Only 24% of the total random variance in prevalence of Salmonella was due to repeated measurement, while the variation in prevalence of Salmonella Typhimurium (including var. Copenhagen) and DT104 due to repeated measurement was 37% and 52% of total random variance, respectively. Although the observed trends may be partly attributed to the different culturing methods, different types of samples, and sampling strategies used in each year, it may also denote the dynamics of Salmonella as a bacterial population on swine farms. These findings indicate that monitoring over time may be useful to detect changes in Salmonella on swine farms.

Effect of plasmid pTENT2 on severity of porcine post-weaning diarrhoea induced by an O149 enterotoxigenic Escherichia coli

A particularly virulent O149:H10 enterotoxigenic Escherichia coli clone harbours a newly characterized plasmid pTENT2 carrying the tetracycline-resistance tetA and the virulence genes estA, paa, and sepA that were not present in less virulent clones. The objectives of this study were to assess whether the additional genes on pTENT2 played a role in the increased severity of post-weaning diarrhoea and if they provided any potential advantage for the emergence of the highly virulent clone. Groups of pigs were dosed orally with isogenic pTENT2-positive and pTENT2-negative ETEC strains, and the clinical and pathological changes were compared between the groups. Two additional groups were given the pTENT2-positive strains and maintained on feed with or without chlortetracycline to assess the effect of subtherapeutic levels of tetracycline on the short-term persistence of the ETEC O149:H10 clone. The severity of diarrhoea within the first few hours post-inoculation was significantly increased (p=0.0408) in animals receiving pTENT2-positive strains as compared to animals receiving pTENT2-negative strains. There were no consistent or significant histopathological differences between any of the groups and no significant difference in the persistence of ETEC between groups.

Epidemiology, Pathogenesis, Genoserotyping, Antimicrobial Resistance, and Prevention and Control of Non-Typhoidal Salmonella Serovars

Purpose of reviewNon-typhoidal Salmonella (NTS) are among the most commonly reported cause of bacterial foodborne zoonoses. In this review, we discuss the current status of non-typhoidal salmonellosis with respect to its epidemiology, pathogenesis, antimicrobial resistance, and prevention and control measures.Recent findingsAmong the NTS, a relatively small group, which includes S. Typhimurium and S. Enteritidis, is responsible for the majority of human salmonellosis. Multidrug-resistant NTS is an emerging threat in food-animal production. Whole genome sequencing is being rapidly adopted to provide the highest possible resolution of Salmonella for outbreak investigations and routine surveillance. New advances in the study of host–pathogen interactions during Salmonella infections highlight the role of Salmonella pathogenicity islands, type III secretion systems and effectors in pathogenesis.SummaryA good understanding of the epidemiology, pathogenesis, host–pathogen interactions and emergence of virulent types of NTS will aid in the development and implementation of vaccine and public health strategies to control Salmonella from farm to fork.