Contamination of domestic groundwater systems by verotoxigenic escherichia coli (VTEC), 2003-2019: A global scoping review.

Verocytotoxin-producing E. coli (VTEC) are important agents of diarrhoeal disease in humans globally. As a noted waterborne disease, emphasis has been given to the study VTEC in surface waters, readily susceptible to microbial contamination. Conversely, the status of VTEC in potable groundwater sources, generally regarded as a "safe" drinking-water supply remains largely understudied. As such, this investigation presents the first scoping review seeking to determine the global prevalence of VTEC in groundwater supply sources intended for human consumption. Twenty-three peer-reviewed studies were identified and included for data extraction. Groundwater sample and supply detection rates (estimated 0.6 and 1.3%, respectively) indicate VTEC is infrequently present in domestic groundwater sources. However, where generic (fecal indicator) E. coli are present, the VTEC to E. coli ratio was found to be 9.9%, representing a latent health concern for groundwater consumers. Geographically, extracted data indicates higher VTEC detection rates in urban (5.4%) and peri­urban (4.9%) environments than in rural areas (0.9%); however, this finding is confounded by the predominance of research studies in lower income regions. Climate trends indicate local environments classified as 'temperate' (14/554; 2.5%) and 'cold' (8/392; 2%) accounted for a majority of supply sources with VTEC present, with similar detection rates encountered among supplies sampled during periods typically characterized by 'high' precipitation (15/649; 2.3%). Proposed prevalence figures may find application in preventive risk-based catchment and groundwater quality management including development of Quantitative Microbial Risk Assessments (QMRA). Notwithstanding, to an extent, a large geographical disparity in available investigations, lack of standardized reporting, and bias in source selection, restrict the transferability of research findings. Overall, the mechanisms responsible for VTEC transport and ingress into groundwater supplies remain ambiguous, representing a critical knowledge gap, and denoting a distinctive lack of integration between hydrogeological and public health research. Key recommendations and guidelines are provided for prospective studies directed at increasingly integrative and multi-disciplinary research.

Molecular modeling of RNA polymerase II mutations onto DNA polymerase I.

Genetic and molecular analysis in Drosophila melanogaster identifies eight suppressor mutations in the second largest subunit of RNA polymerase II. The suppressor mutations fall into two classes: five are strong, result from the same serine to cysteine amino acid residue substitution and rescue one conditional lethal allele in the largest subunit of RNA polymerase II; three are mild, result from a change in the same methionine residue to either isoleucine or valine, are located seven amino acid residues away from the strong suppressors and rescue two conditional lethal alleles in the largest subunit. Sequence analysis of the three regions around these mutations demonstrates that they are located within highly conserved domains but fails to explain the observed genetic interactions. One of the conditional lethal alleles maps within a region previously reported to share sequence similarity to Escherichia coli DNA polymerase I. As the gross structure of RNA polymerase II and DNA polymerase I is similar, even though their primary sequence is not, we predict that more similarities exist but may be too highly divergent to be detected by normal homology searches. We identify the most similar regions between each of the three conserved domains of RNA polymerase II, identified as functionally important because of the mutations we isolated, and DNA polymerase I. Molecular modeling these regions of RNA polymerase II onto the tertiary structure of DNA polymerase I predicts that all lie adjacent to the DNA binding cleft in positions such that they could interact with the phosphate backbone of DNA. This juxtaposition of mutations in the two largest subunits of RNA polymerase II suggest a mechanism for their genetic interactions.

Use of the laser in neurosurgery.

The laser has become the neurosurgical tool of the 1980s. In neurosurgery, the most important attribute of the laser is its ability to precisely vaporize tissue with minimal mechanical and thermal damage to the surrounding sensitive structures. Although the Nd:YAG laser has use in this medical specialty, the CO2 laser, with its immediate absorption in water, with resultant minimization of scatter and spread to surrounding and deeper tissue, is the most useful laser in neurosurgery and the focus of this article.

Multiple brain abscesses.

A young woman with 12 separate brain abscesses was treated medically after aspiration of one abscess for diagnostic bacteriological examination. She made an excellent recovery with only minimal residual neurological dysfunction. Surgical aspiration for detailed bacteriological studies followed by appropriate antimicrobial therapy is an effective way of treating multiple brain abscesses in the neurologically stable patient.

Nitroprusside.

Sodium nitroprusside has proved to be the most effective and best-tolerated vasodilator drug available for the management of acute hypertension, heart failure, and other vasoconstricted states as well as for the induction of controlled hypotension during surgery. It dilates both arteries and veins, has a rapid onset and offset of action, and is almost uniformly effective in achieving the desired degree of dilation by careful dosage titration. The need for close monitoring of its intravenous administration and the potential toxicity of prolonged infusions limit its general use from periods of hours to a few days, but its unique and usually well-maintained vascular actions make it an ideal agent for short-term therapy and a potentially useful model for development of new, orally effective vasodilator drugs.

Transcriptional competition and homeosis in Drosophila.

Interference between different classes of RNA polymerase II alleles causes a mutant phenotype called the "Ubx effect" that resembles one seen in flies haploinsufficient for the transcription factor, Ultrabithorax (Ubx). Flies carrying the mutation in the largest subunit of Drosophila RNA polymerase II, RpII215(4), display the Ubx effect when heterozygous as in RpII215(4)/+ but not when homozygous mutant or wild type. In this report we demonstrate that the interaction between alleles in different classes of polymerase occurs even in the absence of transcription by the wild-type polymerase. We utilized the resistance to the transcriptional inhibitor alpha-amanitin conferred by RpII215(4) to show that RpII215(4)/+ flies raised on alpha-amanitin-containing food still show the Ubx effect and are indistinguishable from flies raised on normal food. We demonstrate using HPLC that the intracellular concentration of alpha-amanitin in the developing larvae is sufficient to inhibit transcription by alpha-amanitin-sensitive polymerase. Furthermore, fluorescein-labeled alpha-amanitin accumulates in imaginal discs, which are the precursor cells for the tissue showing the homeotic transformation in adults. We conclude that the interaction between different classes of RNA polymerase II alleles resulting in the Ubx effect occurs prior to the block in transcription caused by alpha-amanitin.

Hydroxyurea increases fetal hemoglobin in cultured erythroid cells derived from normal individuals and patients with sickle cell anemia or beta-thalassemia.

Hydroxyurea (HU), an inhibitor of DNA synthesis, has been shown to increase fetal hemoglobin (HbF) levels in patients with sickle cell anemia and in some patients with beta-thalassemia. However, until now there have not been good in vitro model systems that simulate this effect for study of the molecular and cellular mechanism(s) involved in perturbing the normal ontogeny of the globin genes. We analyzed the cellular effects of HU using a two-phase liquid culture procedure (Fibach et al: Blood 73:100, 1989) in which human peripheral blood-derived progenitor cells undergo proliferation and differentiation. HU was found to have multiple effects on these cultured cells: (1) an increase in the proportion of HbF produced; (2) a decrease in cell number due to inhibition of cell proliferation; (3) an increase in hemoglobin content per cell (mean corpuscular hemoglobin [MCH]); and (4) an increase in cell size (mean corpuscular volume). The extent of these effects was related to the HU dose and time of addition. When added to cell cultures from normal individuals, 4 days following their exposure to erythropoietin (EPO), 100 mumol/L HU caused a 1.3- to 3.5-fold increase in the proportion of HbF, from 0.4% to 5.2% (mean 1.6) in untreated to 1.5% to 8.2% (mean 3.1) in HU-treated cultures and a 45% +/- 10% increase in MCH but only a 25% +/- 7% decrease in cell number on day 13. Cultures of cells derived from five patients with sickle cell anemia have shown a twofold to fivefold increase in the percentage of Hb F following addition of HU while four patients with beta-thalassemia showed a 1.3- to 6.2-fold increase. We believe that this primary cell culture procedure should prove useful in studying the cellular and molecular mechanisms of pharmacologic induction of HbF and might provide a valuable predictive assay system for evaluation of the response of individual patients with hemoglobinopathies to HU and similar agents.

Learning fibreoptic skills in ear, nose and throat clinics.

We have compared the progress of anaesthetists taught fibreoptic techniques on awake patients in ear, nose and throat clinics with that of anaesthetists taught by traditional methods. Twelve anaesthetists participated in the study and were randomly allocated to the ear, nose and throat group or to the traditional training group. Each individual in the ear, nose and throat group attended the outpatient clinic and performed ten nasendoscopies on awake patient, whose upper airway had been anaesthetised with cocaine, under the supervision of an ear, nose and throat surgeon. Each individual in the traditional roup performed ten nasendoscopies on anaesthetised oral surgery inpatients under the supervision of an anaesthetist. To assess the effectiveness of the two training methods, each anaesthetist in each group then attempted ten fibreoptic nasotracheal intubations on anaesthetised oral surgery patients. There was no significant difference between either the success rates or mean successful tracheoscopy times between the two groups. Nasendoscopy training in the ear, nose and throat clinic appears to be good way of learning fibreoptic skills, which can then be readily applied to fibreoptic tracheal intubation in anaesthetic practice.

Novel approach to investigate a source of microbial contamination of central venous catheters.

The potential route of contamination by skin microorganisms onto the distal tip of central venous catheters during insertion was investigated. Thirty patients undergoing cardiac surgery who required a central venous catheter (CVC) as part of their clinical management were studied. Following catheter placement, the device insertion equipment and the skin at the insertion site were sampled for microorganisms. The distal tips of the CVCs were also sampled in situ within 90 min post insertion. Bacteria were isolated from 20 of 30 (66%) CVC skin insertion sites, from 15 of 30 (50%) guidewires, and from five of 30 (16%) catheter distal tips in situ. These findings suggest that despite rigorous skin disinfection and strict aseptic technique, viable microorganisms are impacted during insertion onto the distal tip of the CVC, which may act as a subsequent nidus of infection.