ABC transporters and the export of capsular polysaccharides from gram-negative bacteria.

In this review, we discuss the kps cluster of Escherichia coli as the paradigm for the ABC capsular polysaccharide exporter (CPSE) family. Components of the cluster form a multimeric protein complex consisting of both biosynthetic and export machinery. We compare the Kps exporter with capsule export systems from other members of the CPSE family.

NeuD plays a role in the synthesis of sialic acid in Escherichia coli K1.

The polysialic acid capsule of Escherichia coli K1 is an essential virulence determinant. The kps gene cluster, which encodes the proteins necessary for polymer synthesis and transport, is divided into three functional regions. In this report, we present evidence that the neuD gene from region 2 is involved in sialic acid synthesis. A non-polar chromosomal deletion in neuD was constructed. The defect was complemented by neuD in trans or by the addition of exogenous sialic acid. A NeuD homologue, Neu(III)D, from serotype III Streptococcus agalactiae (GBS) also restored capsule expression to the neuD deletion strain. These data confirm the role of neuD in E. coli sialic acid capsule synthesis and demonstrate that the neu(III)D homologue from GBS shares a similar enzymatic function.

Nucleotide sequence and genetic analysis of the neuD and neuB genes in region 2 of the polysialic acid gene cluster of Escherichia coli K1.

The K1 capsular polysaccharide, a polymer of sialic acid, is an important virulence determinant of extraintestinal pathogenic Escherichia coli. The genes responsible for the synthesis and expression of the polysialic acid capsule of E. coli K1 are located on the 17-kb kps gene cluster, which is functionally divided into three regions. Central region 2 encodes proteins necessary for the synthesis, activation, and polymerization of sialic acid, while flanking regions 1 and 3 are involved in polymer transport to the cell surface. In this study, we identified two genes at the proximal end of region 2, neuD and neuB, which encode proteins with predicted sizes of 22.7 and 38.7 kDa, respectively. Several observations suggest that the neuB gene encodes sialic acid synthase. EV24, a neuB chromosomal mutant that expresses a capsule when provided exogenous sialic acid, could be complemented in trans by the cloned neuB gene. In addition, NeuB has significant sequence similarity to the product of the cpsB gene of Neisseria meningitidis group B, which is postulated to encode sialic acid synthase. We also present data indicating that neuD has an essential role in K1 polymer production. Cells harboring pSR426, which contains all of region 2 but lacks region 1 and 3 genes, produce an intracellular polymer. In contrast, no polymer accumulated in cells carrying a derivative of pSR426 lacking a functional neuD gene. Unlike strains with mutations in neuB, however, neuD mutants are not complemented by exogenous sialic acid, suggesting that NeuD is not involved in sialic acid synthesis. Additionally, cells harboring a mutation in neuD accumulated sialic acid and CMP-sialic acid. We also found no significant differences between the endogenous and exogenous sialyltransferase activities of a neuD mutant and the wild-type organism. NeuD shows significant similarity to a family of bacterial acetyltransferases, leading to the theory that NeuD is an acetyltransferase which may exert its influences through modification of other region 2 proteins.

Identification of two genes, kpsM and kpsT, in region 3 of the polysialic acid gene cluster of Escherichia coli K1.

The polysialic acid capsule of Escherichia coli K1, a causative agent of neonatal septicemia and meningitis, is an essential virulence determinant. The 17-kb kps gene cluster, which is divided into three functionally distinct regions, encodes proteins necessary for polymer synthesis and expression at the cell surface. The central region, 2, encodes products required for synthesis, activation, and polymerization of sialic acid, while flanking regions, 1 and 3, are thought to be involved in polymer assembly and transport. In this study, we identified two genes in region 3, kpsM and kpsT, which encode proteins with predicted sizes of 29.6 and 24.9 kDa, respectively. The hydrophobicity profile of KpsM suggests that it is an integral membrane protein, while KpsT contains a consensus ATP-binding domain. KpsM and KpsT belong to a family of prokaryotic and eukaryotic proteins involved with a variety of biological processes, including membrane transport. A previously described kpsT chromosomal mutant that accumulates intracellular polysialic acid was characterized and could be complemented in trans. Results of site-directed mutagenesis of the putative ATP-binding domain of KpsT are consistent with the view that KpsT is a nucleotide-binding protein. KpsM and KpsT have significant similarity to BexB and BexA, two proteins that are essential for polysaccharide capsule expression in Haemophilus influenzae type b. We propose that KpsM and KpsT constitute a system for transport of polysialic acid across the cytoplasmic membrane.

Survival in patients with end-stage renal disease.

Based on age and medical condition at the time of treatment, 138 patients beginning dialysis for treatment of chronic renal failure between January 1, 1984 and December 31, 1988, were classified into low, average, and high risk of death. The survival in these three groups was shown to be significantly different after as little as 6 months. The classification scheme is simple, and can be performed at the bedside. Efforts to monitor quality assurance in the dialysis unit must account for the significant differences in expected survival that reflect the case-mix observed in a particular unit.

Parathyroid hormone and anaemia--an erythrocyte osmotic fragility study in primary and secondary hyperparathyroidism.

Parathyroid hormone (PTH) has been shown in vitro to enhance erythrocyte osmotic fragility (EOF) and has been incriminated as a factor in the anaemia seen in patients with primary hyperparathyroidism and in patients with renal disease and secondary hyperparathyroidism. Enhanced EOF has also been shown in patients with chronic renal failure but did not correlate with PTH levels. We studied a group of patients with primary hyperparathyroidism with and without anaemia, and patients with secondary hyperparathyroidism and anaemia. We found that EOF studies in these patients did not differ from normal control groups and that there was no relation between PTH, EOF, and haematocrit in either study group. We conclude that PTH over a range of concentrations seen in vivo does not affect erythrocyte osmotic fragility or cause anaemia.

Renovascular hypertension after combination chemotherapy for testicular cancer.

Chemotherapy with cis-platinum, vinblastine and bleomycin for germ cell tumors of the testis has been highly effective but it also has been associated with acute and chronic vascular damage. We report the development of hypertension in a 38-year-old man after chemotherapy that was shown to be owing to nonatherosclerotic partial occlusion of the major branches of the left renal artery. Vascular complications following combination chemotherapy for germ cell tumors are reviewed.

Renal injury associated with laxative abuse.

Surreptitious laxative abuse is a common cause of unexplained diarrhea, but has not been considered an important cause of irreversible electrolyte and renal functional abnormalities. We have described five patients with the laxative abuse syndrome associated with significant renal injury and electrolyte disorders. We conclude that laxative abuse, like analgesic abuse, is a cause of interstitial renal disease that is more common than generally recognized.

Systemic necrotizing vasculitis presenting as epididymitis.

Epididymitis is an uncommonly recognized complication of systemic necrotizing vasculitis. We report 2 cases in which epididymitis heralded the onset of more severe visceral organ involvement. Early biopsy of atypical epididymitis in patients with hypertension or constitutional symptoms is important if effective therapy is to be instituted before irreversible organ damage occurs.

Hypercalcemia-induced upper gastrointestinal bleeding after renal transplantation.

Hypercalcemia is common in patients after renal transplantation and may stimulate gastrin hypersecretion with associated peptic disease. We report on 2 patients with hypercalcemia and life-threatening gastrointestinal hemorrhage controlled by subtotal parathyroidectomy. Retrospective review of our last 10 patients with gastrointestinal hemorrhage revealed that all of those with normal renal function had elevated serum calcium levels. Because of the increased mortality associated with gastrointestinal hemorrhage in renal transplant patients (43%), patients prone to development of hypercalcemia may benefit from early subtotal parathyroidectomy.

Occult lead intoxication in patients with gout and kidney disease.

Ten patients with gout, hypertension, and mild to moderate renal insufficiency were studied for possible lead nephropathy by measuring stimulated urinary lead excretion. Seven had a history of lead exposure, 5 from illegal alcohol and 2 from industrial sources. Occult lead was assessed by 24 h urine collection measurements over a 72 h period after intramuscular administration of calcium disodium EDTA. Two patients with a history of lead exposure excreted 707 and 687 micrograms Pb/72 h, respectively, and a 3rd excreted 506 micrograms Pb/72 h. The remainder had a normal response, with mean urinary lead excretion of 251 +/- 42 micrograms Pb/72 h. Since we were unable to demonstrate that lead was important to the pathogenesis of the renal we were unable to demonstrate that lead was important to the pathogenesis of the renal failure in 7 patients despite a positive history of lead exposure in 2, we suggest that factors other than lead may be the cause of renal failure in most patients with gout and renal disease.

Thiazide-induced hyponatremia.

A 54-year-old woman had seizures and a focal neurologic deficit associated with hyponatremia induced by a thiazide diuretic. Prompt correction of hyponatremia by administration of hypertonic saline solution was followed by resolution of all neurologic defects. Metabolic balance studies and rechallenge with hydrochlorothiazide were undertaken to investigate the mechanism of the thiazide-induced hyponatremia. Abnormal vasopressin secretion was shown by a plasma vasopressin concentration of 0.5 microU/ml with a plasma osmolality of 268 mOsm/kg water after administration of a fluid challenge consisting of 45 ml/kg body weight. Rechallenge with chlorothiazide while on a sodium- and potassium-controlled balanced diet resulted in a decrease in serum sodium concentration (136 to 124 mEq/L) and plasma osmolality (283 to 261 mOsm/kg) within 18 hours. During this period, urine losses of monovalent cation were only 55 mEq and body weight was constant at 48.2 kg. A second challenge while the patient received all fluids and electrolytes intravenously again resulted in decreased serum sodium concentration (134 to 126 mEq/L) after urinary loss of only 69 mEq of cation. Thus this patient's hyponatremia cannot be accounted for solely by changes in external water and electrolyte balance; the rapidity with which changes were produced suggests that osmolar inactivation, probably intracellularly, may contribute to the severe hypotonicity seen in some patients.

High urine flow rate increase prostaglandin E excretion in the conscious dog.

Although previous studies from this and other laboratories have shown that urinary prostaglandin E excretion (UPGEV) can very independent of urine flow rate, recent studies during water diuresis in the conscious dog have suggested that high urine flow rate per se may increase UPGEV. To examine the effect of urine flow rate on UPGEV we administered either mannitol, chlorothiazide or Ringer's solution to mongrel dogs and measured UPGEV. During anesthesia neither mannitol or chlorothiazide increased UPGEV. There was, however, a consistent increase with all three agents in awake animals. This increase in UPGEV was independent of alterations in glomerular filtration rate. There was a consistent increase in urinary sodium excretion and decrease in urinary osmolality with all three agents. The changes in PGE, however, were similar to those found during water diuresis when no increase in sodium excretion was found. It is not presently clear whether these findings reflect a true increase in renal PGE synthesis due to some changes in flow or pressure within the renal medulla or rather represent unchanged PGE synthesis by renal tubular cells, the high tubule fluid flow rate causing increased entry into the tubular lumen in contrast to the renal interstitium.

The regulatory effects of growth rate and cyclic AMP levels on carbon catabolism and respiration in Escherichia coli K-12.

Cyclic AMP levels in glucose and succinate-limited and ammonia-limited glucose-containing continuous cultures of Escherichia coli were measured at different bacterial growth rates. Intracellular cyclic AMP concentrations were fairly constant (about 5 micrometer) at all dilution rates used when glucose was limiting. In ammonia-limited glucose cultures the cyclic AMP content was much lower (about 0.3 micrometer). In succinate-limited cultures cyclic AMP levels fell from 2.7 to 0.8 micrometer as dilution rate increased from 0.05 to 0.4 h-1. The effects of cyclic AMP on respiratory and carbon catabolic enzyme levels were studied. There was no indication of a direct cyclic AMP involvement in the regulation of these cellular functions. It seems more likely that the variations in enzyme levels observed resulted from variation of the specific growth rate of cultures.

Medical management of home hemodialysis patients.

Increased emphasis on home hemodialysis because of proposed changes in federal funding will result in dispersion of dialysis patients to areas geographically removed from a dialysis unit. Thus primary care of these patients will increasingly become the responsibility of physicians having little previous contact with dialysis. We review the diagnosis and treatment of common problems in the dialysis patient with emphasis on the major problem areas of vascular access and the cardiovascular, hematologic, and osseous complications of renal failure.