Prevalence, antimicrobial resistance profile and comparison of selective plating media for the isolation of Salmonella spp. in free-ranging waterfowl from Entre Rios, Argentina.

The present study was conducted to estimate the apparent prevalence of Salmonella spp. in free-ranging waterfowl that inhabitant Entre Ríos, Argentina, determine the antimicrobial resistance of the isolated, and compare the performance of two selective plating media used for Salmonella isolation. Five hundred ninety nine free-living waterfowl were sampled one time by cloacal swab from April 2014 to July 2016. Only 6 samples from waterfowl belonged to all counties sampled were positive to Salmonella spp., so the apparent prevalence was 1%. Four serovars were isolated (Salmonella ser. Typhimurium, S. ser. Schwarzengrund, S. enterica subsp. I [4,12: i: -], S. enterica subsp. IIIb [60: r: e, n, x, z15]), which were susceptible to 15 antibiotics tested and resistant to erythromycin. Furthermore, some strains showed an intermediate resistant to neomycin, ciprofloxacin and/or streptomycin. The multiple antibiotic resistances index was 0.05. For Hektoen enteric agar and Salmonella Shigella agar, the relative accuracy, sensitivity, specificity, positive predictive value, and negative predictive value did not show any difference between them. The agreement was good between these two plating-media and the difference between these plating-media was not statistically significant. The low prevalence of Salmonella spp. in waterfowl in Entre Rios should not be discounted, since Salmonella ser. Typhimurium was the most prevalent serovar and some free-ranging waterfowl species studied can migrate from/to different countries, increasing the possibility to cross-contaminated Salmonella to resident or other migrant birds.

Salmonella spp. contamination in commercial layer hen farms using different types of samples and detection methods.

The performance of detection methods (culture methods and polymerase chain reaction assay) and plating media used in the same type of samples were determined as well as the specificity of PCR primers to detected Salmonella spp. contamination in layer hen farms. Also, the association of farm characteristics with Salmonella presence was evaluated. Environmental samples (feces, feed, drinking water, air, boot-swabs) and eggs were taken from 40 layer hen houses. Salmonella spp. was most detected in boot-swabs taken around the houses (30% and 35% by isolation and PCR, respectively) follow by fecal samples (15.2% and 13.6% by isolation and PCR, respectively). Eggs, drinking water, and air samples were negative for Salmonella detection. Salmonella Schwarzengrund and S. Enteritidis were the most isolated serotypes. For plating media, relative specificity was 1, and the relative sensitivity was greater for EF-18 agar than XLDT agar in feed and fecal samples. However, relative sensitivity was greater in XLDT agar than EF-18 agar for boot-swab samples. Agreement was between fair to good depending on the sample, and it was good between isolation and PCR (feces and boot-swabs), without agreement for feed samples. Salmonella spp. PCR was positive for all strains, while S. Typhimurium PCR was negative. Salmonella Enteritidis PCR used was not specific. Based in the multiple logistic regression analyses, categorization by counties was significant for Salmonella spp. presence (P-value = 0.010). This study shows the importance of considering different types of samples, plating media and detection methods during a Salmonella spp. monitoring study. In addition, it is important to incorporate the sampling of floors around the layer hen houses to learn if biosecurity measures should be strengthened to minimize the entry and spread of Salmonella in the houses. Also, the performance of some PCR methods and S. Enteritidis PCR should be improved, and biosecurity measures in hen farms must be reinforced in the region of more concentrated layer hen houses to reduce the probability of Salmonella spp. presence.

Reproductive isolation due to the genetic incompatibilities between Thrichomys pachyurus and two subspecies of Thrichomys apereoides (Rodentia, Echimyidae).

We tested intrinsic reproductive isolation between 3 taxa of the South American caviomorph rodent Thrichomys (Rodentia, Echimyidae): T. pachyurus, T. apereoides subsp. apereoides and T. apereoides subsp. laurentius. They were mated in captivity and produced viable progeny. Some F1 hybrid females were fertile, whereas all F1 males were sterile. Histological examination revealed meiotic arrest at the primary spermatocyte stage. No sperm was detected in testes or epididymes. Electron microscopic analysis of surface spread synaptonemal complexes revealed a complete failure of chromosome pairing in F1 hybrids of T. pachyurus with T. apereoides subsp. laurentius and T. apereoides subsp. apereoides. In the male hybrids between T. apereoides subsp. apereoides and T. apereoides subsp. laurentius, meiosis did not proceed beyond diplotene, although all of the chromosomes, including heteromorphic ones, paired in an orderly fashion. Backcross males with homomorphic karyotypes showed segregation in meiosis progression. This indicates that male hybrid sterility is due to genetic, but not chromosomal, incompatibility of the parental taxa.