Comparison of muscle proteome profiles in pure breeds of Norwegian Landrace and Duroc at three different ages.

We have used proteomics as a tool to unravel the changes in protein composition between two pure pig breeds and three age groups. Forty two female pigs of Norwegian Landrace and Duroc breed slaughtered at 6, 9 and 12 months age were included in the study. Each of the breeds was raised in separate farms and was slaughtered at the same day in a commercial abattoir. A sample from the adductor muscle was collected approximately 45min postmortem. Proteome analyses of the water soluble proteins using 2D electrophoresis showed that of the 1125 analyzed protein spots, 94 and 41 proteins are changed in abundance according to breed and age, respectively. A total of 63 changed proteins were identified by mass spectrometry. The identified proteins were classified as structural proteins, metabolic proteins, stress/defense proteins and other proteins. This demonstrates a difference in metabolism and muscle composition between breeds and age groups and shows that proteomics is a useful tool to uncover the molecular basis for physiological differences in muscles between pig breeds and age groups.

Persistence of multidrug-resistant Staphylococcus haemolyticus in an animal veterinary teaching hospital clinic.

In the recent decades, coagulase-negative staphylococci (CNS) have emerged as important nosocomial pathogens with the ability to develop resistance to antibiotics and disinfectants. Multidrug-resistant CNS are currently a common finding in hospital settings and hospitalized patients. Little is known about the occurrence and persistence of multidrug-resistant CNS in animal clinics. A survey of the environmental bacterial flora in a small animal clinic showed a predominance of bacterial species commonly isolated from skin and feces of warm-blooded animals and the environment. At samplings separated by 3 years, multidrug-resistant Staphylococcus haemolyticus was isolated from the floor of four separate animal cages and from a cat's postoperative wound infection. Pulsed-field electrophoresis, multilocus enzyme typing, susceptibility testing, and genotypic characterization suggested that the multidrug-resistant S. haemolyticus isolates belonged to an epidemiological clone. All isolates harbored a chromosomal copy of the mecA gene, a 45-kb plasmid harboring the blaZ and qacA/B determinants, and all except one isolate carried multiple plasmids in the size range 1-22 kb, of which those <5 kb encoded resistance to tetracycline (tetK), macrolides (ermB), and chloramphenicol (cat). One isolate carried a chromosomal copy of the bifunctional gene aacA-aphD conferring resistance to gentamicin. The isolate that was deficient of small plasmids had reverted to a macrolide and chloramphenicol-susceptible phenotype, but had retained its tetracycline resistance due to IS257-mediated integration of the tetK plasmid into the mec region of the chromosome. This finding illustrates bacterial intracellular mobility of resistance genes in natural environments, and highlights the role of insertion sequences in the evolution of multidrug resistance islands on the bacterial chromosome.

Frequency of disinfectant resistance genes and genetic linkage with beta-lactamase transposon Tn552 among clinical staphylococci.

A total of 61 strains of Staphylococcus aureus and 177 coagulase-negative staphylococcal strains were isolated from the blood of patients with bloodstream infections and from the skin of both children under cancer treatment and human immunodeficiency virus-positive patients. The MIC analyses revealed that 118 isolates (50%) were resistant to quaternary ammonium compound-based disinfectant benzalkonium chloride (BC). The frequencies of resistance to a range of antibiotics were significantly higher among BC-resistant staphylococci than among BC-sensitive staphylococci. Of 78 BC-resistant staphylococcal isolates, plasmid DNA from 65 (83%), 2 (3%), 43 (55%), and 15 (19%) isolates hybridized to qacA or -B (qacA/B), qacC, blaZ, and tetK probes, respectively. The qacA/B and blaZ probes hybridized to the same plasmid in 19 (24%) staphylococcal strains. The plasmids harboring both qacA/B and blaZ genes varied from approximately 20 to 40 kb. The Staphylococcus epidermidis Fol62 isolate, harboring multiresistance plasmid pMS62, contained qacA/B and blaZ together with tetK. Molecular and genetic studies indicated different structural arrangements of blaZ and qacA/B, including variable intergenic distances and transcriptional directions of the two genes on the same plasmid within the strains. The different organizations may be due to the presence of various genetic elements involved in cointegration, recombination, and rearrangements. These results indicate that qac resistance genes are common and that linkage between resistance to disinfectants and penicillin resistance occurs frequently in clinical isolates in Norway. Moreover, the higher frequency of antibiotic resistance among BC-resistant strains indicates that the presence of either resistance determinant selects for the other during antimicrobial therapy and disinfection in hospitals.

Resistance to quaternary ammonium compounds in food-related bacteria.

Microbial resistance to antimicrobial agents continues to be a major problem. The frequent use and misuse of disinfectants based on quaternary ammonium compounds (QACs) in food-processing industries have imposed a selective pressure and may contribute to the emergence of disinfectant-resistant microorganisms. A total number of 1,325 Gram-negative isolates (Escherichia coli, other coliforms Vibrio spp., and Aeromonas spp.) and 500 Enterococcus spp. from food and food-processing industries and fish farming were screened for natural resistance to the QAC-based disinfectant benzalkonium chloride (BC). Of the 1,825 isolates, 16 strains, mainly from meat retail shops, showed low-level resistance to BC. None of the Enterococcus spp. from broiler, cattle, and pigs, the antibiotic-resistant E. coli from pig intestine and fish pathogens Vibrio spp. and Aeromonas spp. from the Norwegian fish farming industry were resistant to BC. The BC-resistant strains were examined for susceptibility to 15 different antibiotics, disinfectants, and dyes. No systematic cross-resistance between BC and any of the other antimicrobial agents tested was detected. Stable enhanced resistance in Enterobacter cloacae isolates was demonstrated by step-wise adaptation in increasing concentrations of BC. In conclusion, BC resistance among food-associated Gram-negative bacteria and Enterococcus spp. is not frequent, but resistance may develop to user concentrations after exposure to sublethal concentrations of BC.