Influence of avilamycin administration and its subsequent withdrawal on emergence and disappearance of antimicrobial resistance in enterococci in the intestine of broiler chickens

AIMS: To investigate the influence of avilamycin (AVM) administration and its subsequent withdrawal on the emergence and disappearance of AVM-resistant enterococci in the intestine of broiler chickens. METHODS AND RESULTS: Five chicks each of C, L and H groups were given the basal diet, the basal diet supplemented with 5 g AVM/ton and the basal diet supplemented with 50 g AVM/ton, respectively. The AVM-resistant Enterococcus faecalis population did not emerge during 30 days of the AVM administration period, whereas the AVM-resistant Enterococcus faecium with a minimum inhibitory concentration of >512 microg ml(-1) in the faeces of chicks of the L and H groups emerged on 3 and 1 days after the AVM administration, respectively. Thereafter, the AVM-resistant Ent. faecium population density in both L and H groups maintained high levels during the AVM administration period. Twenty days after the AVM withdrawal, the AVM-resistant Ent. faecium population disappeared from the intestines of both four of five chicks of L group and three of five chicks of H group. The AVM-resistant Ent. faecium population density in one chick from each of the groups, L and H, did not change before and after the AVM removal. CONCLUSIONS: The AVM-resistant Ent. faecium emerged during the AVM administration, and disappeared from the intestine of most chicks after the AVM withdrawal. However, the AVM-resistant Ent. faecium persisted in some chicks 20 days after AVM withdrawal. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results suggest that introducing an AVM withdrawal period could minimize the risk of AVM-resistant Ent. faecium becoming carcass contaminants, and that prudent antibiotic use alone is not sufficient to stem emergence of the AVM-resistant Ent. faecium.     

Fate of GFP-expressing Escherichia coli in the midgut and response to ingestion in a tick, Ornithodoros moubata (Acari: Argasidae)

Ticks are well-known vectors of various pathogens but migration of the pathogens in the tick midgut is not fully understood. In the present study, the fate of microbes in the midgut of Ornithodoros moubata was observed using green fluorescent protein (GFP)-expressing Escherichia coli. Fluctuations in the percentage of hemocytes in the hemolymph (Hc) and expression of an antimicrobial peptide, defensin, in the midgut was also investigated. Most E. coli gradually disappeared in the midgut after ingestion fluctuations in Hc coincided with the changes. Expression of defensin was also confirmed and slightly up-regulated after E. coli ingestion. Moreover, it was demonstrated that E. coli can not pass through the tick midgut epithelium after ingestion by the hemolymph cultures. It is known that various pathogens and host immunoglobulins ingested with a blood meal can enter into the hemocoel, which suggests the presence of unique and complex passage mechanisms for each molecule and organism. The results obtained here help to clarify that digestion enzymes is an important function of the tick midgut to protect against invading molecules and organisms.     

Mother–young distance in Japanese Black cattle at pasture

Distance between dam and offspring (1–121 days old) in a herd of Japanese Black cattle (Bos taurus) grazing a tropical grass (Paspalum notatum) pasture (1.5 ha) was investigated during 7-h grazing periods over grazing seasons from May (spring) to October (autumn). The mother–young distance was not constant throughout the grazing period, repeatedly increasing and decreasing. Although significant periodicity was always detected in the mother–young distance, there was no consistent dominant cycle, indicating the complexity of the within-day pattern of mother–young distance. The mean mother–young distance over the grazing period increased as a calf aged, reaching a plateau at an age of about 33 days. The mean distance of a calf from its mother was usually shorter than that from a non-mother cow, with the difference between the mean distances decreasing sharply until a calf became about 35 days old. The results and literature show that mutual independence of mother and young rapidly develops in the first 30–50 days after parturition. Electronic Publication     

Functional analysis of protein disulfide isomerases in blood feeding, viability and oocyte development in Haemaphysalis longicornis ticks

Three protein disulfide isomerases from Haemaphysalis longicornis ticks (designated as HlPDI-1, HlPDI-2, and HlPDI-3) were previously identified. In order to further analyze their biological functions, the dsRNA of each HlPDI gene and one dsRNA combination of HlPDI-1/HlPDI-3 were separately injected into female ticks. Reduction of gene and protein expression of HlPDIs by RNA interference (RNAi) was demonstrated by real-time PCR, RT-PCR and Western blot analysis. In single dsRNA-injected groups, HlPDI-1 RNAi impacted tick blood feeding and oviposition, HlPDI-2 RNAi impacted tick viability and HlPDI-3 RNAi had no significant impact by itself. However, the injection of a combination of HlPDI-1/HlPDI-3 dsRNA had synergistic effects on tick viability. Furthermore, the midgut and cuticle were severely damaged in HlPDI-2 dsRNA-injected ticks and HlPDI-1/HlPDI-3 dsRNA-injected ticks, respectively, and disruption of HlPDI genes led to a significant reduction of disulfide bond-containing vitellogenin (Vg) expression in ticks. These results indicate that PDIs from H. longicornis are involved in blood feeding, viability and oocyte development, probably by mediating the formation of disulfide bond-containing proteins of the ticks and the formation of basement membrane and cuticle components such as extracellular matrix (ECM). This is the first report on the functional analysis of PDI family molecules as well as the interactions of PDI and other molecules in blood-feeding arthropods.     

Involvement of an essential gene, mviN, in murein synthesis in Escherichia coli

We isolated a temperature-sensitive mutant with a mutation in mviN, an essential gene in Escherichia coli. At the nonpermissive temperature, mviN mutant cells swelled and burst. An intermediate in murein synthesis, polyprenyl diphosphate-N-acetylmuramic acid-(pentapeptide)-N-acetyl-glucosamine, accumulated in mutant cells. These results indicated that MviN is involved in murein synthesis.     

Parasiticidal activity of human α-defensin-5 against <Emphasis Type="Italic">Toxoplasma gondii</Emphasis>

Human defensins play a fundamental role in the initiation of innate immune responses to some microbial pathogens. In this paper, we show that human α-defensin-5 displays a parasiticidal role against Toxoplasma gondii, the causative agent of toxoplasmosis. Exposure of the tachyzoite form of T. gondii to defensin induced aggregation and significantly reduced parasite viability in a concentration-dependent peptide. Pre-incubation of tachyzoites with human α-defensin-5 followed by exposure to a mouse embryonal cell line (NIH/3T3) significantly reduced T. gondii infection in these cells. Thus, human α-defensin-5 is an innate immune molecule that causes severe toxocity to T. gondii and plays an important role in reducing cellular infection. This is the first report showing that human α-defensin-5 causes aggregation, leading to Toxoplasma destruction.     

Association of Mre11p with double-strand break sites during yeast meiosis

The repair of DNA double-strand breaks (DSBs) requires the activity of the Mre11/Rad50/Xrs2(Nbs1) complex. In Saccharomyces cerevisiae, this complex is required for both the initiation of meiotic recombination by Spo11p-catalyzed programmed DSBs and for break end resection, which is necessary for repair by homologous recombination. We report that Mre11p transiently associates with the chromatin of Spo11-dependent DSB regions throughout the genome. Mutant analyses show that Mre11p binding requires the function of all genes required for DSB formation, with the exception of RAD50. However, Mre11p binding does not require DSB formation itself, since Mre11p transiently associates with DSB regions in the catalysis-negative mutant spo11-Y135F. Mre11p release from chromatin is blocked in mutants that accumulate unresected DSBs. We propose that Mre11p is a component of a pre-DSB complex that assembles on the DSB sites, thus ensuring a tight coupling between DSB formation by Spo11p and the processing of break ends.