Association of dry cow therapy with the antimicrobial susceptibility of fecal coliform bacteria in dairy cows.

The prophylactic use of intramammary antimicrobial drugs at the end of lactation in dairy cows, known as dry cow therapy (DCT), is widely practiced in US dairy herds. This extremely common use of high-dose, slow-release antimicrobials may influence the ecology of bacterial flora on dairy farms. We investigated the association between the antimicrobial used for intramammary DCT and the relative number of fecal coliform bacteria with reduced susceptibility to three antimicrobial drugs in dairy cattle. Most probable number (MPN) data were estimated from 463 individual fecal samples collected from lactating cows in 15 dairy herds in Ohio, USA. These data were used to calculate the relative number of fecal coliform bacteria with reduced susceptibility to cephalothin, streptomycin, and tetracycline for individual cow samples. The farms included in this project were classified based on DCT, with 8 farms using a cephalosporin-based product and the remaining 7 using a penicillin/streptomycin therapy. Results of a linear mixed model indicate that herds using a cephalosporin DCT had higher (P<0.01) relative numbers of fecal coliform bacteria with reduced susceptibility to cephalothin and streptomycin compared to those using a penicillin/streptomycin intramammary therapy. Relative numbers of fecal coliform bacteria with reduced susceptibility to tetracycline was not associated with DCT. These results suggest that high-dose slow-release antimicrobials applied locally in the udder to populations of dairy cows might influence the antimicrobial susceptibility of the enteric flora. However, the potential animal and public health implications of this result are not clear.

Prevalence of Yersinia enterocolitica in different phases of production on swine farms.

Swine have been identified as the primary reservoir of pathogenic Yersinia enterocolitica (YE), but little research has focused on the epidemiology of YE at the farm level. The objective of this study was to describe the prevalence of YE in different production phases on swine farms. In this cross-sectional study, individual pigs on eight swine operations were sampled for the presence of YE. On each farm, both feces and oral-pharyngeal swabs were collected from pigs in five different production phases: gestating, farrowing, suckling, nursery, and finishing. A pig was considered positive if either sample tested positive. Samples were cultured with cold enrichment followed by isolation on selective media plates. Presumptive isolates were confirmed as YE and assayed for the presence of ail with a multiplex PCR. Of the 2,349 pigs sampled, 120 (5.1%) tested positive, and of those, 51 were ail positive (42.5% of YE isolates). On all farms, there was a trend of increasing prevalence as pigs mature. Less than 1% of suckling piglets tested positive for YE. Only 1.4% (44.4% of which were ail positive) of nursery pigs tested positive, but 10.7% (48.1% of which were ail positive) of finishing pigs harbored YE. Interestingly, gestating sows had the second highest prevalence of YE at 9.1% (26.7% of which were ail positive), yet YE was never detected from the farrowing sows. These results represent the first on-farm description of YE in U.S. herds and provide the initial step for designing future studies of YE.

Identification and characterization of a regulatory domain on the carboxyl terminus of the measles virus nucleocapsid protein.

The paramyxovirus template for transcription and genome replication consists of the RNA genome encapsidated by the nucleocapsid protein (N protein). The activity of the complex, consisting of viral polymerase plus template, can be measured with minireplicons in which the genomic coding sequence is replaced by chloramphenical acetyltransferase (CAT) antisense RNA. Using this approach, we showed that the C-terminal 24 amino acids of the measles virus N protein are dispensable for transcription and replication, based upon the truncation of N proteins used to support minireplicon reporter gene expression. Truncation at the C-terminal or penultimate amino acid 524 resulted in no change in CAT expression, whereas larger truncations spanning residues 523 to 502 were accompanied by an approximately twofold increase in basal activity. Reporter gene expression was enhanced by supplementation with the major inducible 70-kDa heat shock protein (Hsp72) for minireplicons with the N protein or the N protein truncated at position 525 or 524 but not in systems with a truncation at position 523 or 522. Naturally occurring sequence variants of the N protein with variations at positions 522 and 523 were also shown to lack Hsp72 responsiveness independent of changes in basal activity. Since these residues lie within a linear sequence predicting a direct Hsp72 interaction, N protein-Hsp72 binding reactions were analyzed by using surface plasmon resonance technology. Truncation of the C-terminal portion of the N protein by protease digestion resulted in a reduced binding affinity between Hsp72 and the N protein. Furthermore, with synthetic peptides, we established a correlation between the functional responsiveness and the binding affinity for Hsp72 of C-terminal N protein sequences. Collectively, these results show that the C-terminal 24 amino acids of the N protein represent a regulatory domain containing a functional motif that mediates a direct interaction with Hsp72.