Plant-controlled supratidal anhydrite from Al-Khiran, Kuwait
We report here that in the supratidal zone of the Al-Khiran sabkha, diagenetic anhydrite occurs exclusively in association with the living halophyte Halocnemum strobilaceum (Pallas) M .B. This anhydrite has a hair cream-like consistency and the bulk of it has formed as pseudomorphs after gypsum crystals. On the death of the plant at the end of its life cycle, the anhydrite is hydrated back to gypsum. This two-way transformation results in a series of characteristic textures, whose preservation could be due to the comparative ‘youth’ of the sabkha, which is in the very earliest stages of evaporite diagenesis.
Anhydrite Diagenesis, Calcitization, and Organic Laminites, Winnipegosis Formation, Middle Devonian, Saskatchewan
ABSTRACT A laminite deposit consisting of calcareous, dolomitic, and anhydritic layers interleaved with black organic material floors interior parts of the Middle Devonian Winnipegosis salt basin of western Canada. Before compaction had affected it, part of the anhydritic laminite was diagenetically altered to coarsely crystalline calcite that enclosed the anhydrite and organic matter. This calcitized rock preserves features of the original sediment, and reveals that the laminar anhydrite had originally grown as anhydrite nodules in an organic substrate. In all essential respects, the crystal fabrics of the calcitized anhydrite nodules resemble those of Recent sabkha anhydrites, and the mode of growth was apparently identical. Enterolithic structure resulted from buckling of sheets of coalesced nodules, and was caused by continued growth of the nodules within confining laminae. Observed varieties of anhydrite fabric can be explained as products of compaction. The agency of pore-water pressure is important to the generation of flow fabrics. The range of anhydrite compaction-fabrics in general can be related to two matrix properties: compressibility and drainage. The original sediment, before invasion by anhydrite or calcitization, resembled blue-green algal mat. Volumetrically, the organic material comprised a large fraction of the sediment even after anhydrite-nodule growth, though later compaction reduced it to black partings where it was not calcitized. Stratigraphically, the presence of algal mat and nodular anhydrite on the basin floor implies nearly complete loss of water from the basin after Winnipegosis reef formation, and before halite accumulation supervened.
Coexistence of Virulence and Antibiotic Resistance Genes in Pasteurella multocida Isolated from Diseased Rabbits
Pasteurella multocida (P. multocida)is considered a predominant pathogenic bacterial agent causing respiratory manifestations (snuffles) in rabbits with considerable economic losses and unfavorable prognosis in Egypt. A few recent P. multocida strains exhibit resistance to the most commonly used antibiotics in the veterinary field. Therefore, the present study was carried out to investigate the prevalence of both virulence and antibiotic resistance genes among P. multocida isolated from diseased rabbits in Sharkia Governorate, Egypt. Only 10 out of 100 tested rabbits` nasal swabs were finally confirmed positive for P. multocida of serogroup A by polymerase chain reaction (PCR). Antibiotic susceptibility testing of the recovered isolates revealed that they were all multidrug resistant (MDR) with a predominance of resistance to amoxicillin, ampicillin, amoxicillin/clavulanic acid, neomycin and tetracycline (100% each), followed by kanamycin and streptomycin (90% each). All the recovered isolates were further subjected to PCR screening of some common virulence and antibiotic resistance genes of interest . With the exception of toxA gene, the other virulence associated genes (ptfA, Omp87 and nanB) were found among all the examined isolates. Totally, all MDR P. multocida isolates contained at least one antibiotic resistance gene with aphA1 being the most prevalent (100%), followed by ermX gene (40%). Antibiotic resistance genotyping demonstrated the presence of multiple antibiotic resistance genes among majority of the isolates (40%) with only one isolate harboring 4 genes encoding identical resistance phenotypes. Evidentially, all MDR P. multocida isolates possessed at least 3 virulence genes accompanied by the attendance of antibiotic resistance genes. These findings evidenced that rabbits are potential sources of pathogenic P. multocida strains harboring virulence and antibiotic resistance genes. Therefore, it is evident that there is an urgent need for the judicious use of antibiotics in rabbits` treatment systems to successfully mitigate the propagation of drug resistance across P. multocida species.