Prevalence and antimicrobial susceptibility of virulent and avirulent multidrug-resistant Escherichia coli isolated from diarrheic neonatal calves.

OBJECTIVE: To determine the prevalence of selected virulence genes and the antimicrobial susceptibility of multidrug-resistant (MDR) Escherichia coli isolated from diarrheic neonatal calves. SAMPLE: 97 E coli isolates from diarrheic neonatal calves. PROCEDURES: E coli isolates were tested via PCR assay for 6 virulence genes and susceptibility to 17 drugs belonging to 9 classes. A 2-sample test of proportions was used to make comparisons between proportions of virulent and avirulent MDR isolates. RESULTS: 23 of 97 (23.7%) isolates were virulent, and 74 (76.3%) were avirulent. Of the 23 virulent isolates, 15 (65.2%) were positive for K99, 14 (60.9%) for F41, 12 (52.2%) for STa, 9 (39.1%) for Stx1, 6 (26.1%) for intimin, and 0 (0%) for Stx2. Twenty of 23 (87.0%) virulent isolates expressed ≥ 2 virulence genes, and 3 of 23 (13.0%) were positive for 1 virulence factor. Eight of 23 (34.8%) virulent isolates expressed STa, K99, and F41, whereas 1 of 23 (4.4%) was positive for STa, F41, intimin, and Stx1. The second most frequent gene pattern was Stx1 and intimin. Twenty of 23 (87.0%) virulent isolates were MDR; the highest prevalence of resistance was recorded for the macrolide-lincosides, followed by the tetracyclines and penicillins. Also, 17 of 23 (74.0%) virulent isolates were resistant to sulfadimethoxine, and 10 of 23 (43.5%) were resistant to trimethoprim-sulfamethoxazole. Additionally, 60 of 74 (81.0%) avirulent isolates were MDR. CONCLUSIONS AND CLINICAL RELEVANCE: The prevalence of multidrug resistance was comparable for virulent and avirulent E coli isolated from diarrheic neonatal calves. Cephalosporins and aminoglycosides had reasonable susceptibility.

A Multiplex PCR Assay to Characterize Potato virus Y Isolates and Identify Strain Mixtures.

Potato virus Y (PVY) has become a serious problem for the seed potato industry, with increased incidence and rejection of seed lots submitted for certification. New PVY strains and strain variants have emerged in recent decades in Europe and North America, including the PVYN strain that causes veinal necrosis in tobacco, and strain variants that represent one or three recombination events between the common strain (PVYO) and PVYN. Several reverse transcription-polymerase chain reaction (RT-PCR) assays have been described that characterize PVY isolates as to strain type, but they are limited in their ability to detect some combinations of mixed strain infections. We report here the development of a single multiplex RT-PCR assay that can assign PVY strain type and detect mixed infections with respect to the major strain types. Validation of this assay was achieved using 119 archived PVY isolates, which had been previously characterized by serology and bioassay and/or previously published RT-PCR assays. Results for single-strain isolates were comparable to previous results in most cases. Interestingly, 16 mixed infections were distinguished that had previously gone undetected. The new multiplex RT-PCR assay will be useful for researchers and seed production specialists interested in determining PVY infection type using a single assay.