Current Microbiology

The antimicrobial resistance of 1,018 isolates of Enterobacteriaceae isolated from fecal specimens of the urban population of Riyadh, Saudi Arabia, was studied. Resistance to 1 or more of 10 antimicrobial agents was encountered in 50.2% of the isolates. Of the isolates tested,Escherichia coli (0.8%) andKlebsiella species (1.6%) were found resistant to seven antimicrobial agents simultaneously: ampicillin, chloramphenicol, kanamycin, colistin, streptomycin, tetracycline, and carbenicillin. Resistance to nalidixic acid was encountered in only 0.68% of theE. coli isolates. No isolate was found to be resistant to gentamicin. Eighty-six of the resistant strains were tested for their ability to transfer their resistance. Forty percent were able to do so withE. coli K-12.

Due to its high usage, mobility, and recalcitrant nature, atrazine is a common groundwater contaminant. Moreover, groundwaters that are contaminated with atrazine often contain nitrate as well. Nitrate interferes with the biological degradation of atrazine and makes it more difficult to use in situ biological methods to remediate atrazine contaminated groundwater. To solve this problem we used two reactors in sequence as models of in situ biobarriers; the first was a vegetable-oil-based denitrifying biobarrier and the second an aerobic reactor that oxygenated the denitrifying reactor’s effluent. The reactors were inoculated with an atrazine-degrading microbial consortium and supplied with water containing 5 mg l−1 nitrate–N and 3 mg l−1 atrazine. Our hypothesis was that the denitrifying barrier would remove nitrate from the flowing water and that the downstream reaction would remove atrazine. Our hypothesis proved correct; the two reactor system removed 99.9% of the atrazine during the final 30 weeks of the study. The denitrifying barrier removed ~98% of the nitrate and ~30% of the atrazine while the aerobic reactor removed ~70% of the initial atrazine. The system continued to work when the amount of nitrate–N in the influent water was increased to 50 mg l−1. A mercury poisoning study blocked the degradation of atrazine indicating that biological processes were involved. An in situ denitrifying barrier coupled with an air injection system or other oxygenation process might be used to remove both nitrate and atrazine from contaminated groundwater or to protect groundwater from an atrazine spill.

We have used the filamentous fungus, Neurospora crassa, as a model system to test the concept that antisense targeting of the cell-wall assembly enzyme, (1,3)β-glucan synthase [E.C. 2.4.1.34; UDP glucose: 1,3-β-D-glucan 3-β-D-glucosyltransferase], leads to a corresponding decrease in growth of the organism. Previously, our laboratory isolated a gene (glucan synthase-1, gs-1) that is required for (1,3)β-glucan synthase activity. Wild-type cells were transformed with DNA vectors encoding various RNAs complementary to the gs-1 messenger RNA (antisense RNA) cloned downstream from an inducible promoter (quinic acid-2 [qa-2p]). Stable transformants, expressing a partially inverted antisense message of gs-1 (pMYX107), exhibited dramatic reduction in growth compared with empty vector controls. Hyphal measurements of these transformants grown on race tubes indicated that all of the transformants showed various degrees of inhibition. Microscopic observations of transformants revealed shorter hyphal lengths when grown under conditions expressing antisense. Further characterization revealed that the specific activities of (1,3)β-glucan synthase were decreased by as much as 63% relative to empty vector controls. Together, these observations suggest that antisense against (1,3)β-glucan synthase led to a reduction in enzyme levels that resulted in altered cell-wall morphology and inhibition of growth. It is possible that antisense oligonucleotides against gs-1 may be useful antifungal agents.

Various pectinolytic strains ofClostridium, Erwinia, andPseudomonas species produced methanol as a major end product during growth on pectin but not on glucose or polygalacturonic acid. Pectin metabolism ofClostridium butyricum strain 4P1 correlated with a final product concentration of 16 mM at the end of growth, and a 1:1 stoichiometry for methanol production and percent initial substrate methoxylation. Growth on pectin was associated with high activity of pectin methylesterase and the absence of methanol consumption. The ecological significance of pectin metabolism and the establishment of microbial methylotrophic metabolism in nature is discussed.

The objective of the study was to determine the efficacy of ultrasound-treatment Saccharomyces cerevisiae and spray drying in preserving the viability of Lactiplantibacillus plantarum. The combination of ultrasound-treated S. cerevisiae and L. plantarum was evaluated. Next, the mixture was blended with maltodextrin and either Stevia rebaudiana-extracted fluid, prior to undergoing spray drying. The L. plantarum viability was assessed after the spray drying process, during storage, and in simulated digestive fluid (SDF) conditions. The results showed that the impact of ultrasound caused the crack and holes in the yeast cell wall. Besides, the moisture content values were not significantly different in all samples after spray drying. Although the amount of powder recovery in stevia-supplemented samples was not higher than that of the control sample, the L. plantarum viability was significantly improved after the spray drying process. The density of L. plantarum tended to be stable during the first 30 days of storage and decreased more rapidly after that. The results reveal that there was no statistically significant difference in the trend of the samples before and after storage. In the SDF test, the L. plantarum viability mixing with ultrasound-treated yeast cells in the spray drying samples was significantly improved. Besides, the presence of Stevia showed positive efficiency on the L. plantarum viability. The L. plantarum viability mixing with ultrasound-treated yeast cells and stevia-extracted fluid by spray drying process showed potential application due to making powder form which helped to improve the L. plantarum stability during the storage time.

In this paper we show the effect of oxygen and light on the expression of the photosynthetic apparatus of a mutant heterologously expressing the puc operon. This mutant was obtained by introducing in trans an expression plasmid, bearing the puc A, B, and C genes of Rhv. sulfidophilum, as well as its own promoter, in an LHII− mutant of Rb. capsulatus. The results showed that oxygen and light repressed LHII expression. Even low-light intensities lowered the LHII content to undetectable levels by spectrophotometry or by SDS-PAGE. In high-light grown cells, where the relative ratios of LHI and LHII complexes were significantly diminished, we were able to detect LHII complexes. Under the latter condition, the absorption spectrum showed that some pigment accumulated in the membrane even in the absence of cell division. These pigments were used in a later step to assemble LHII complexes, when the high-light grown cells were transferred to semiaerobiosis in the dark. Transition of high-light grown cells to low-light conditions allowed us to study the adaptability of these heterologous mutant cells. We observed that adaptation never occurred, in part probably owing to energy limitation.

The potential action of certain fatty acids has been studied since the early 1970s. Numerous effects on immune system functions have been related to dietary lipid administration; therefore, several of them have been applied in the treatment of inflammatory disorders. Nevertheless, n-3 polyunsaturated fatty acids may affect host resistance to infectious diseases. In addition, several studies have demonstrated that certain fatty acids are involved in apoptosis induction. Here, we have examined the action of different dietary lipids on the promotion of apoptosis in thymocytes from mice fed with dietary lipids and infected with Listeria monocytogenes. Thus, L. monocytogenes promoted an important cytotoxic effect in all of the groups, but it did not increase the percentage of DNA fragmentation. Similarly, an important increase of caspase-3 activity was demonstrated in OO and FO groups, but infection with L. monocytogenes exerted an inhibitory effect. Finally, L. monocytogenes did not modify proteasome activity among groups fed with dietary lipids. On the basis of this preliminary study, we can state that the infection of thymocytes from mice fed with dietary lipids does not promote a synergistic effect in the induction of apoptosis. Hence, these results may partially serve to elucidate the immune mechanisms involved in cells from mice fed with dietary lipids in an infectious process.

In this study, we investigated the incidence of Cronobacter spp. in seafood collected from retail fish markets of Mumbai, India. A total of 50 samples comprising fresh finfish (n = 32), shellfish (n = 6), dried fish (n = 9) and water (n = 3) were analyzed for Cronobacter spp. by selective enrichment, isolation and biochemical tests. Of 145 isolates presumptively identified as Cronobacter spp. by biochemical tests, 37 were confirmed as Cronobacter spp. by Polymerase Chain Reaction (PCR) specific to the internal transcribed spacer (ITS) regions. Based on the partial ITS gene sequence analysis, 35 isolates were identified as Cronobacter malonaticus and two as Cronobacter sakazakii. The highest incidence of Cronobacter spp. was in dried fish (55.6%), followed by shellfish (33.3%). The virulence gene ompA was detected in two Cronobacter sakazakii isolates. This is the first report of the incidence of Cronobacter spp. in fresh and dried seafood from India, which highlights the need to focus on this emerging pathogen in tropical seafood.

Bipolaris sorokiniana is a phytopathogenic fungus that causes diseases of cereal crops, such as leaf-spot disease, common root rot, and black point of grain. Because of its great morphological, physiological, and genetic variability, this fungus is difficult to control. The aim of this investigation was to study the variability of isolates of B. sorokiniana by means of vegetative incompatibility. Thirty-five isolates of B. sorokiniana from different geographical regions in Brazil and other countries were used. The vegetative incompatibility between the isolates and the influences of different culture media on these reactions were evaluated. The total protein profile of the isolates was analyzed when the isolates were cultured separately, and in cultures of compatibility and incompatibility reactions. Eighteen of 31 confrontations showed vegetative incompatibility. The results obtained with different culture media for the vegetative compatibility/incompatibility genotypes suggested that the type of substratum influences these reactions. No differences in protein profiles among the isolates were observed. This result suggests that there is no induction of expression of different proteins in vegetative incompatibility reactions.

Hybridoma cell lines were derived from the fusion of mouse myeloma cells with spleen cells from a mouse that had been immunized withAgrobacterium tumefaciens strain A759, a flagella-less mutant of strain C58 containing the Ti plasmid of strain B6. All of the 20 antibodies produced by the cloned hybridomas reacted with strain C58 and with other strains derived from C58. The antibodies did not react with 34 other strains ofA. tumefaciens, representing the three biovars, or with strains ofA. radiobacter, A. rubi, Rhizobium leguminosarum, R. meliloti, or other plant-associated bacteria such asErwinia herbicola andPseudomonas syringae. In addition to reacting with whole cells of strain A759, the antibodies reacted with phenol-water extracts of A759, indicating that they may recognize the lipopolysaccharide. These antibodies may be useful for ecological and epidemiological studies ofA. tumefaciens strain C58 in the agroecosystem.