Incompatibility group A/C (IncA/C) plasmids have received recent attention for their broad host range and ability to confer resistance to multiple antimicrobial agents. Due to the potential spread of multidrug resistance (MDR) phenotypes from foodborne pathogens to human pathogens, the dissemination of these plasmids represents a public health risk. In this study, four animal-source IncA/C plasmids isolated from Escherichia coli were sequenced and analyzed, including isolates from commercial dairy cows, pigs and turkeys in the U.S. and Chile. These plasmids were initially selected because they either contained the floR and tetA genes encoding for florfenicol and tetracycline resistance, respectively, and/or the blaCMY-2 gene encoding for extended spectrum β-lactamase resistance. Overall, sequence analysis revealed that each of the four plasmids retained a remarkably stable and conserved backbone sequence, with differences observed primarily within their accessory regions, which presumably have evolved via horizontal gene transfer events involving multiple modules. Comparison of these plasmids with other available IncA/C plasmid sequences further defined the core and accessory elements of these plasmids in E. coli and Salmonella. Our results suggest that the bla CMY-2 plasmid lineage appears to have derived from an ancestral IncA/C plasmid type harboring floR-tetAR-strAB and Tn21-like accessory modules. Evidence is mounting that IncA/C plasmids are widespread among enteric bacteria of production animals and these emergent plasmids have flexibility in their acquisition of MDR-encoding modules, necessitating further study to understand the evolutionary mechanisms involved in their dissemination and stability in bacterial populations.

Florfenicol is an important antibiotic in veterinary medicine that is used extensively in aquaculture, including salmon farming in Chile. We analysed a set of 119 florfenicol-resistant Gram-negative bacilli from seven freshwater Chilean salmon farms for the molecular determinants involved in the florfenicol resistance. Ninety-seven of these strains were glucose non-fermenting bacilli, mainly belonging to the Pseudomonas genus, whereas 22 strains were glucose-fermenters. The floR gene was detected in 26 strains (21.8%) that had been isolated from three of the seven salmon farms. Most of the floR-carrying strains were glucose fermenters (21 strains), and most of the floR-carrying strains were also resistant to streptomycin, chloramphenicol and oxytetracycline. The minimum inhibitory concentrations against florfenicol were assessed in the presence and absence of the efflux pump inhibitor Phe-Arg-beta-naphthylamide (MC-207,110). There was evidence that in the majority of non-fermenting bacteria (82 strains), florfenicol resistance was at least partially mediated by non-specific efflux pump systems. Given the diversity of antibiotic resistance patterns observed in this study in the floR-positive isolates, a single antibiotic has the potential to co-select for a diversity of resistances. For this reason, human health as well as animal health can potentially be impacted by the use of antibiotics in aquaculture. To assess this potential risk, future studies should focus on the ability of different antibiotics used in aquatic environments to co-select for multiple resistances, the molecular basis of this diversity of resistance, and whether the genes conferring resistance can be transferred to other bacteria, including those of human health concern.

Cytomegalovirus (CMV) subunit vaccine candidates include glycoprotein B (gB), and phosphoprotein ppUL83 (pp65). Using a guinea pig cytomegalovirus (GPCMV) model, this study compared immunogenicity, pregnancy outcome, and congenital viral infection following pre-pregnancy immunization with a three-dose series of modified vaccinia virus Ankara (MVA)- vectored vaccines consisting either of gB administered alone, or simultaneously with a pp65 homolog (GP83)-expressing vaccine. Vaccinated and control dams were challenged at midgestation with salivary gland-adapted GPCMV. Comparisons included ELISA and neutralizing antibody responses, maternal viral load, pup mortality, and congenital infection rates. Strikingly, ELISA and neutralization titers were significantly lower in the gB/GP83 combined vaccine group than in the gB group. However, both vaccines protected against pup mortality (60.5% in controls vs. 11.4% and 8.3% in gB and gB/GP83 combination groups, respectively; p<0.0001). Reductions in pup viral load were noted for both groups compared to control, but preconception vaccine resulted in a significant reduction in GPCMV transmission in the monovalent gB group only (26/44, 59 % v. 27/34, 79 % in controls; p<0.05). We conclude that, in the MVA platform, adding GP83 to a gB subunit vaccine interferes with antibody responses and diminishes protection against congenital GPCMV infection, but does not decrease protection against pup mortality.

Guinea pig cytomegalovirus (GPCMV) provides a valuable model for congenital cytomegalovirus transmission. Salivary gland (SG)-passaged stocks of GPCMV are pathogenic, while tissue culture (TC) passage in fibroblasts results in attenuation. Nonpathogenic TC-derived virus N13R10 (cloned as a bacterial artificial chromosome [BAC]) has a 4-bp deletion that disruptsGP129, which encodes a subunit of the GPCMV pentameric complex (PC) believed to govern viral entry into select cell types, and GP130, an overlapping open reading frame (ORF) of unknown function. To determine if this deletion contributes to attenuation of N13R10, markerless gene transfer in Escherichia coli was used to construct virus r129, a variant of N13R10 in which the 4-bp deletion is repaired. Virions from r129 were found to contain GP129 as well as two other PC subunit proteins, GP131 and GP133, whereas these three PC subunits were absent from N13R10 virions. Replication of r129 in fibroblasts appeared unaltered compared to that of N13R10. However, following experimental challenge of immunocompromised guinea pigs, r129 induced significant weight loss, longer duration of viremia, and dramatically higher (up to 1.5 ؋ 10 6 -fold) viral loads in blood and end organs compared to N13R10. In pregnant guinea pigs, challenge with doses of r129 virus of >5 ؋ 10 6 PFU resulted in levels of maternal viremia, congenital transmission, pup viral loads, intrauterine growth restriction, and pup mortality comparable to that induced by pathogenic SG virus, although higher doses of r129 were required. These results suggest that the GP129-GP130 mutation is a significant contributor to attenuation of N13R10, likely by abrogating expression of a functional PC. IMPORTANCETissue culture adaptation of cytomegaloviruses rapidly selects for mutations, deletions, and rearrangements in the genome, particularly for viruses passaged in fibroblast cells. Some of these mutations are focused in the region of the genome encoding components of the pentameric complex (PC), in particular homologs of human cytomegalovirus (HCMV) proteins UL128, UL130, and UL131A. These mutations can attenuate the course of infection when the virus is reintroduced into animals for vaccine and pathogenesis studies. This study demonstrates that a deletion that arose during the process of tissue culture passage can be repaired, with subsequent restoration of pathogenicity, using BAC-based mutagenesis. Restoration of pathogenicity by repair of a frameshift mutation in GPCMV gene GP129 using this approach provides a valuable genetic platform for future studies using the guinea pig model of congenital CMV infection. Infection with human cytomegalovirus (HCMV) is a leading cause of disability in newborns, and development of an effective vaccine is a major public health priority (1, 2). Preclinical modeling of vaccines against congenital infection must rely on the study of species-specific CMVs, since HCMV will not infect nonhuman cells (3, 4). The study of guinea pig cytomegalovirus (GPCMV) is particularl...

Primary Zika virus (ZIKV) infections that occur during pregnancy can cause spontaneous abortion and profoundly disrupt fetal development. While the full range of developmental abnormalities associated with congenital Zika syndrome is not yet known, severe cases of the syndrome can present with microcephaly, extensive neurologic and ocular damage, and pronounced joint malformations. Animal models that accurately recapitulate congenital Zika syndrome are urgently needed for vaccine development and for the study of ZIKV pathogenesis. As guinea pigs have successfully been used to model transplacental infections by cytomegalovirus, syphilis, and Listeria monocytogenes, we sought to test whether ZIKV could productively infect guinea pigs and whether viral transmission with attendant fetal pathology would occur after a mid-gestation viral challenge. We found that guinea pig cells supported ZIKV replication in vitro. Experimental infection of non-pregnant animals did not result in overt disease but low-level, detectable viremia was observed. When pregnant guinea pigs were challenged with ZIKV at between 18 and 21 days gestational age, ZIKV was not detected in maternal or pup blood, plasma, or tissues and no significant differences in maternal weight gain or pup size were observed following challenge. Nonetheless, a robust antibody response against ZIKV was detected in both the pups and dams. These results suggest that, while guinea pigs can model aspects of the immune response to ZIKV infection during pregnancy, naturally circulating ZIKV strains are not pathogenic during the pregnancy of immunocompetent guinea pigs and do not interfere with normal pup development.