The prevalence of multidrug resistance is higher among bovine than human Salmonella enterica serotype Newport, Typhimurium, and 4,5,12:i:- isolates in the United States but differs by serotype and geographic region.

Salmonella represents an important zoonotic pathogen worldwide, but the transmission dynamics between humans and animals as well as within animal populations are incompletely understood. We characterized Salmonella isolates from cattle and humans in two geographic regions of the United States, the Pacific Northwest and the Northeast, using three common subtyping methods (pulsed-field gel electrophoresis [PFGE], multilocus variable number of tandem repeat analysis [MLVA], and multilocus sequence typing [MLST]). In addition, we analyzed the distribution of antimicrobial resistance among human and cattle Salmonella isolates from the two study areas and characterized Salmonella persistence on individual dairy farms. For both Salmonella enterica subsp. enterica serotypes Newport and Typhimurium, we found multidrug resistance to be significantly associated with bovine origin of isolates, with the odds of multidrug resistance for Newport isolates from cattle approximately 18 times higher than for Newport isolates from humans. Isolates from the Northwest were significantly more likely to be multidrug resistant than those from the Northeast, and susceptible and resistant isolates appeared to represent distinct Salmonella subtypes. We detected evidence for strain diversification during Salmonella persistence on farms, which included changes in antimicrobial resistance as well as genetic changes manifested in PFGE and MLVA pattern shifts. While discriminatory power was serotype dependent, the combination of PFGE data with either MLVA or resistance typing data consistently allowed for improved subtype discrimination. Our results are consistent with the idea that cattle are an important reservoir of multidrug-resistant Salmonella infections in humans. In addition, the study provides evidence for the value of including antimicrobial resistance data in epidemiological investigations and highlights the benefits and potential problems of combining subtyping methods.

Metabolic control of recombinant protein N-glycan processing in NS0 and CHO cells.

Chinese hamster ovary and murine myeloma NS0 cells are currently favored host cell types for the production of therapeutic recombinant proteins. In this study, we compared N-glycan processing in GS-NS0 and GS-CHO cells producing the same model recombinant glycoprotein, tissue inhibitor of metalloproteinases 1. By manipulation of intracellular nucleotide-sugar content, we examined the feasibility of implementing metabolic control strategies aimed at reducing the occurrence of murine-specific glycan motifs on NS0-derived recombinant proteins, such as Galalpha1,3Galbeta1,4GlcNAc. Although both CHO and NS0-derived oligosaccharides were predominantly of the standard complex type with variable sialylation, 30% of N-glycan antennae associated with NS0-derived TIMP-1 terminated in alpha1,3-linked galactose residues. Furthermore, NS0 cells conferred a greater proportion of terminal N-glycolylneuraminic (sialic) acid residues as compared with the N-acetylneuraminic acid variant. Inclusion of the nucleotide-sugar precursors, glucosamine (10 mM, plus 2 mM uridine) and N-acetylmannosamine (20 mM), in culture media were shown to significantly increase the intracellular pools of UDP-N-acetylhexosamine and CMP-sialic acid, respectively, in both NS0 and CHO cells. The elevated UDP-N-acetylhexosamine content induced by the glucosamine/uridine treatment was associated with an increase in the antennarity of N-glycans associated with TIMP-1 produced in CHO cells but not N-glycans associated with TIMP-1 from NS0 cells. In addition, elevated UDP-N-acetylhexosamine content was associated with a slight decrease in sialylation in both cell lines. The elevated CMP-sialic acid content induced by N-acetylmannosamine had no effect on the overall level of sialylation of TIMP-1 produced by both CHO and NS0 cells, although the ratio of N-glycolylneuraminic acid:N-acetylneuraminic acid associated with NS0-derived TIMP-1 changed from 1:1 to 1:2. These data suggest that manipulation of nucleotide-sugar metabolism can promote changes in N-glycan processing that are either conserved between NS0 and CHO cells or specific to either NS0 cells or CHO cells.