Minor Role In Resistance Research Articles

Mycobiota on Wild Oat (Avena fatua L.) Seed and Their Caryopsis Decay Potential

Wild oat is a serious weed in cereals that is difficult to control due to long-term survival in the weed seed bank. The mycobiota associated with dormant wild oat (Avena fatua L.) seeds buried for six months in a no-till wheat field were evaluated for their caryopsis decay potential. Of the 118 representative isolates tested, only 15% were found to have caryopsis decay potential. One isolate of Fusarium avenaceum and three isolates of Fusarium culmorum completely decayed wild oat caryopses within two weeks. Only a few isolates were susceptible to the antifungal activity from water or acetone extracts of wild oat hulls, suggesting that soluble chemicals from the hull play a minor role in resistance to decay. The procedures developed here can be used to isolate and screen individual organisms to determine their potential for seed decay and weed biocontrol. Accepted for publication 20 December 2010. Published 10 February 2011.

Role of antibody in immunity and control of chicken coccidiosis

Research has been carried out worldwide to try to elucidate the mechanism of protective immunity against coccidiosis. It was concluded from early studies that cellular immunity is the key to protection against Eimeria, whereas humoral immunity plays a very minor role in resistance against infection. By contrast, other studies have pointed towards the ability of antibody to block parasite invasion, development and transmission and to provide passive and maternal immunity against challenge infection. Herein, recent results demonstrate the ability of antibodies (raised by live immunization or against purified stage-specific Eimeria antigens) to inhibit parasite development in vitro and in vivo and readdress the question of the role of antibody in protection against coccidiosis.

Characterization of Pathways Dependent on the uvsE , uvrA1 , or uvrA2 Gene Product for UV Resistance in Deinococcus radiodurans

The genome of a radiation-resistant bacterium, Deinococcus radiodurans, contains one uvsE gene and two uvrA genes, uvrA1 and uvrA2. Using a series of mutants lacking these genes, we determined the biological significance of these components to UV resistance. The UV damage endonuclease (UvsE)-dependent excision repair (UVER) pathway and UvrA1-dependent pathway show some redundancy in their function to counteract the lethal effects of UV. Loss of these pathways does not cause increased sensitivity to UV mutagenesis, suggesting either that these pathways play no function in inducing mutations or that there are mechanisms to prevent mutation other than these excision repair pathways. UVER efficiently removes both cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) from genomic DNA. In contrast, the UvrA1 pathway does not significantly contribute to the repair of CPDs but eliminates 6-4PPs. Inactivation of uvrA2 does not result in a deleterious effect on survival, mutagenesis, or the repair kinetics of CPDs and 6-4PPs, indicating a minor role in resistance to UV. Loss of uvsE, uvrA1, and uvrA2 reduces but does not completely abolish the ability to eliminate CPDs and 6-4PPs from genomic DNA. The result indicates the existence of a system that removes UV damage yet to be identified.

Detection of mutations in quinolone resistance-determining regions in levofloxacin- and methicillin-resistant Staphylococcus aureus: effects of the mutations on fluoroquinolone MICs

The minimum inhibitory concentrations (MICs) of 18 antibiotics were determined for 66 clinical isolates of staphylococci. Genotypes, mutations in the quinolone resistance-determining regions (QRDRs), and effect of efflux were determined in the 18 levofloxacin-resistant isolates, for which the MICs of levofloxacin were high (≥8 μg/ml). The increased levofloxacin resistance mainly resulted from some combinations of mutations in the QRDRs, although NorA-mediated efflux may play a minor role in resistance. A combination of mutations in GrlA (Ser80Phe), GrlB (Pro451Ser), and GyrA (Ser84Leu) was found in 4 methicillin-resistant Staphylococcus aureus (MRSA) isolates that were unrelated genotypically. The mutations in grlA QRDR varied in the isolates classified as being in an identical pulsed-field gel electrophoresis (PFGE) group, although the grlB, gyrA, and gyrB QRDRs were the same. These results suggest that the patterns of amino acid mutations in the QRDRs can provide distinct epidemiologic information from PFGE genotypes in fluoroquinolone-resistant MRSA. A combination of at least three mutations in GrlA, GrlB, and/or GyrA is required to increase the MICs of fluoroquinolones, although all of the levofloxacin-resistant MRSA retained the MICs of sitafloxacin in the range of 1 to 2 μg/ml.

Disturbance of endothelial barrier function by bacterial toxins and atherogenic mediators: a role for Rho/Rho kinase.

Disturbance of endothelial barrier function by bacterial toxins and atherogenic mediators: a role for Rho/Rho kinase.

Monooxygenases play only a minor role in resistance to synthetic pyrethroids in the cattle tick, Boophilus microplus.

We investigated the role of monooxygenases in resistance to synthetic pyrethroids (SPs) in the cattle tick, Boophilus microplus. We found that monooxygenases play only a minor role in resistance to SPs in both resistant and susceptible strains of B. microplus. We blocked the monooxygenases with piperonyl butoxide (PBO) and simultaneously applied the SPs, flumethrin and cypermethrin to larval B. microplus. PBO increased the effect of flumethrin (synergism ratios 2.7-8.9) more than it increased the effect of cypermethrin (synergism ratios 1.9-3.1). Of the four strains tested, Parkhurst, which is resistant to SPs, was the least affected by the addition of PBO (synergism ratios after cypermethrin was applied 1.9; after flumethrin 2.7) whereas N.R.F.S., the strain susceptible to SPs, was the most affected by synergism between PBO and SPs (synergism ratio after cypermethrin was applied 3.1; after flumethrin 8.9). We hypothesize that B. microplus lacks monooxygenases capable of conferring resistance to SPs because it and its recent ancestors were blood-feeders rather than herbivores.

Resistance to organophosphorus and pyrethroid insecticides in Culex pipiens (Diptera: Culicidae) from Tunisia.

Resistance to the organophosphates temephos and chlorpyrifos, the carbamate propoxur, the pyrethroid permethrin, and the organochloride DDT was investigated in Tunisian populations of Culex pipiens pipiens (L.) collected between 1990 and 1996. Resistance to temephos was uniformly low, reaching 10-fold in the most resistant population. In contrast, resistance to chlorpyrifos was highly variable, reaching the highest level (> 10,000-fold) recorded worldwide. The chlorpyrifos-resistant populations also were highly resistant to propoxur. Some populations also showed high resistance to permethrin (up to 5,000-fold) and moderate resistance to DDT (approximately 20-fold). Bioassays conducted in the presence of synergists showed that increased detoxification had only a minor role in resistance, although several over-produced esterases known to be involved in organophosphate resistance were detected. To better understand the factors influencing the distribution of resistance in Tunisia, the polymorphism of genes involved in organophosphate resistance (i.e., over-produced esterases and insensitive acetylcholinesterase) was investigated in relation to the genetic structure of populations studied by analyzing the electrophoretic polymorphism of "neutral" genes. Over the area studied, and despite a high level of gene flow, resistance genes showed a patchy distribution. Results are discussed in relation to the selection pressure caused by insecticide treatments.

Interactions of Plasmodium berghei sporozoites and murine Kupffer cells in vitro.

Malaria sporozoites must leave the bloodstream and cross a layer of sinusoidal lining cells in order to infect hepatocytes and undergo exoerythrocytic schizogony. To determine whether Kupffer cells (KC) derived from this layer interact with sporozoites, murine KC were isolated from perfused livers of BALB/cJ mice and incubated in vitro with Plasmodium berghei sporozoites. Isolated KC had characteristic macrophage surface Ag and were phagocytic, ingesting both latex particles and Leishmania major amastigotes. In the absence of immune serum, sporozoites associated with fewer than 10% of these KC. By 30 min, 10% of the cell-associated sporozoites were completely ingested, 30% were in the process of being ingested, and 60% were attached to the surface of the cells. Opsonization of sporozoites with monoclonal or polyclonal antibodies directed against P. berghei circumsporozoite protein markedly enhanced sporozoite association with KC. Up to 40% of cells exposed to opsonized sporozoites had parasites inside or attached to their surfaces. Sporozoites attached to or ingested by KC were uniformly destroyed within 240 min in all cultures; there was no evidence of conversion of sporozoites to the exoerythrocytic stage within KC by light microscopy, and there was no evidence of residual sporozoites, either inside or outside of cells, by either light or electron microscopy. These data suggest that under nonimmune conditions, KC play a minor role in resistance to infection by malaria sporozoites. However, when sporozoites are opsonized by circumsporozoite antibodies, phagocytosis by KC may be an important immune mechanism that prevents parasitization of hepatocytes.

Susceptibility to dental caries

The role of the pulp and saliva in caries susceptibility and resistance was evaluated by a combination of endodontic treatment and desalivation. Evidence was presented that the pulp plays a major role in caries susceptibility. Pulpal activity is modified by a hormonal factor or factors of salivary gland origin. Saliva appears to play a minor role in resistance to caries.