Zinc and Copper Reduce Conjugative Transfer of Resistance Plasmids from Extended-Spectrum Beta-Lactamase-Producing Escherichia coli.

The present work addresses the effect of excess levels of ZnCl2 and CuSO4 in the growth medium on the conjugative transfer of plasmids carrying the antibiotic resistance gene blaCMY-2 from extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. Norwegian poultry are not treated prophylactically with antibiotics, but still, ESBL-producing E. coli are found in the chicken populations. Chickens receive higher amounts of Zn and Cu than their biological need, and several metals have been shown to act as drivers of antimicrobial resistance. In the present study, ESBL-producing E. coli strains collected from retail chicken meat were mated in broth containing various concentrations of ZnCl2 and CuSO4. Manual counting of transconjugants showed that ZnCl2 and CuSO4 reduced the conjugation frequency between E. coli strains in a concentration-dependent manner. Quantitative real-time PCR analyses showed that the presence of ZnCl2 and CuSO4 in the growth media reduced expression of the conjugation genes traB and nikB. By propagating monocultures over several generations, it was found that the blaCMY-2 plasmids remained stable in the recipient strains. Together the results show that exposure of ESBL-producing E. coli to Zn and Cu reduce horizontal transfer of the blaCMY-2 resistance plasmid by reducing expression of genes involved in conjugation in the plasmid donor strain.

The winter ulcer bacterium Moritella viscosa demonstrates adhesion and cytotoxicity in a fish cell model.

Moritella viscosa is considered the main aetiological agent of 'winter ulcer' disease in farmed salmonid fish. To further understand the pathogenesis of this disease, M. viscosa interaction with fish cells was studied using a Chinook salmon embryo cell line (CHSE-214). As winter ulcer appears exclusively at temperatures below 7-8 degrees C, we attempted to identify if this connection is explained by temperature regulated bacterial virulence. Therefore, infection studies were performed at a temperature range from 4 to 15 degrees C. At all temperatures, M. viscosa caused CHSE cells to retract and round up, lose their attachment abilities and finally disintegrate. The bacterium adhered to CHSE cells and caused changes to the cytoskeleton, however, it did not invade the cells. Increased adherence was demonstrated at 4 degrees C compared to adherence at higher temperatures. Extracellular proteins exerted rapid pore formation and lysis of CHSE cells at a temperature range from 4 to 22 degrees C. Furthermore, only small differences were found comparing extracellular proteomes of M. viscosa from 4 and 15 degrees C. We propose that the pathogenic mechanisms exerted by M. viscosa on CHSE cells are disruption of the cytoskeleton which affects cell rigidity and structure, followed by pore formation and lysis caused by secreted products from the bacterium. These processes can also occur at temperatures above those experienced from winter ulcer outbreaks. However, the adhesion mechanisms appear to be temperature regulated and may contribute to temperature dependent disease outbreaks.

Adaptive response to environmental changes in the fish pathogen Moritella viscosa.

The marine psychrophilic bacterium Moritella viscosa is the causative agent of winter ulcer in farmed Atlantic salmon and cod. In this study, the growth requirements of the pathogen were established. The effects of changes in salinity and temperature on growth, surface features and proteomic regulation were also investigated. The genome of this bacterium has not yet been sequenced; therefore, comparative two-dimensional gel electrophoresis (2-DE) was used, coupled with high performance tandem mass spectrometry (MS/MS), to perform cross-species protein identification. Results from this study establish that M. viscosa is a true marine psychrophilic bacterium capable of surviving and proliferating in an oligotrophic and cold environment. Low temperature combined with 3-4% NaCl resulted in significantly higher cell yields and stability compared to high temperature and 1% NaCl. Nine cytoplasmic proteins were shown to be regulated by temperature and 12 by salinity. Several of the regulated proteins indicated a stressful situation at 15 degrees C compared to 4 degrees C, consistent with the growth characteristics observed. Furthermore, temperature and salinity were demonstrated to be important determinants of motility and viscosity of M. viscosa.

Antibiotic resistance in food-related bacteria--a result of interfering with the global web of bacterial genetics.

A series of antibiotic resistance genes have been sequenced and found to be identical or nearly identical in various ecological environments. Similarly, genetic vectors responsible for assembly and mobility of antibiotic resistance genes, such as transposons, integrons and R plasmids of similar or identical type are also widespread in various niches of the environment. Many zoonotic bacteria carry antibiotic resistance genes directly from different food-producing environments to the human being. These circumstances may have a major impact on the degree for success in treating infectious diseases in man. Several recent examples demonstrate that use of antibiotics in all parts of the food production chain contributes to the increasing level of antibiotic resistance among the food-borne pathogenic bacteria. Modern industrialized food production adds extra emphasis on lowering the use of antibiotics in all parts of agriculture, husbandry and fish farming because these food products are distributed to very large numbers of humans compared to more traditional smaller scale niche production.