Phase variation of the lpf operon is a mechanism to evade cross-immunity between Salmonella serotypes.

Conventional wisdom holds that phase variation is a mechanism for immune evasion. However, despite fimbrial phase variation, mice previously exposed to Salmonella typhimurium are protected against a subsequent challenge. We evaluated whether lpf phase variation instead may be a mechanism to evade cross-immunity between Salmonella serotypes. Mice were immunized orally with S. typhimurium aroA mutants either that expressed the lpf operon (phase-on variant) or in which the entire lpf operon had been removed by deletion. During a subsequent challenge with virulent Salmonella enteritidis a selection against lpf phase-on variants was observed in mice previously exposed to S. typhimurium long polar fimbriae. Vaccination with S. typhimurium did not confer protection against challenge with S. enteritidis, presumably because lpf phase-off variants were able to evade cross-immunity. We propose that lpf phase variation is a mechanism to evade cross-immunity between Salmonella serotypes, thereby allowing their coexistence in a host population.

Expression and transcriptional control of the Salmonella typhimurium Ipf fimbrial operon by phase variation.

The lpf operon mediates adhesion of Salmonella typhimurium to murine Peyer's patches. To investigate expression of this virulence factor, a transcriptional fusion between the lpf operon and the genes lacZYA of Escherichia coli was constructed and introduced into the S. typhimurium chromosome. The resulting strain yielded both Lac+ and Lac- colony phenotypes. Alternation between Lac+ (phase ON) and Lac- (phase OFF) phenotypes occurred by a heritable phase variation mechanism, as inoculation of broth cultures with bacteria picked from a Lac+ colony gave rise to a considerably higher proportion of Lac+ colonies than inoculation with bacteria picked from a Lac- colony. During growth in vitro, phase transition from ON to OFF and from OFF to ON occurred at rates 6.8 x 10(-3) and 2.4 x 10(-4) events per cell per generation respectively. In a murine intestinal organ culture model, selection for the ON expression state occurred when attached bacteria were recovered from Peyer's patches, suggesting that Lac phase variation correlated with expression of lpf mediated adherence. Selection for either the ON or the OFF expression state of the Ipf operon in vivo was studied in mice immunized with either GST or GST-LpfA fusion protein. A strong selection against phase ON cells occurred only in animals immunized with GST-LpfA. The ability of animals immunized with GST-LpfA to distinguish between phase ON and phase OFF bacteria provided evidence for the presence of LpfA fimbrial protein in phase ON cells and for its exposure to the immune system.

IroN, a novel outer membrane siderophore receptor characteristic of Salmonella enterica.

Speciation in enterobacteria involved horizontal gene transfer. Therefore, analysis of genes acquired by horizontal transfer that are present in one species but not its close relatives is expected to give insights into how new bacterial species were formed. In this study we characterize iroN, a gene located downstream of the iroBC operon in the iroA locus of Salmonella enterica serotype Typhi. Like iroBC, the iroN gene is present in all phylogenetic lineages of S. enterica but is absent from closely related species such as Salmonella bongori or Escherichia coli. Comparison of the deduced amino acid sequence of iroN with other proteins suggested that this gene encodes an outer membrane siderophore receptor protein. Mutational analysis in S. enterica and expression in E. coli identified a 78-kDa outer membrane protein as the iroN gene product. When introduced into an E. coli fepA cir fiu aroB mutant on a cosmid, iroN mediated utilization of structurally related catecholate siderophores, including N-(2,3-dihydroxybenzoyl)-L-serine, myxochelin A, benzaldehyde-2,3-dihydroxybenzhydrazone, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-L-lysine, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-L-lysine amide, and enterochelin. These results suggest that the iroA locus functions in iron acquisition in S. enterica.

Silica-ELISA method improves detection and quantitation of minor glycolipid components in lipid mixtures and of other antigens.

This paper describes a new type of ELISA plate in which the reaction wells have been coated with silica gel. ELISA using these prototype silica-ELISA plates is markedly more sensitive for glycolipid antigens in lipid mixtures than ELISA using polystyrene plates without silica. Silica-ELISA plates also improve the analysis of certain protein and carbohydrate antigens. This technology may be of considerable benefit in the analysis of minor lipids and other antigens from human brain, cerebrospinal fluid or blood.

Role of intragastric and intraoesophageal alkalinisation in the genesis of complications in Barrett's columnar lined lower oesophagus.

Patients with Barrett's columnar lined lower oesophagus have severe acid gastrooesophageal reflux and may develop complications, including ulceration, stricture, and carcinoma. The aim of this study was to establish if a relationship exists between the pH profile in the oesophagus and stomach and the development of complications in patients with Barrett's columnar lined lower oesophagus. Twenty four hour ambulatory oesophageal pH monitoring was performed in 26 patients with Barrett's columnar lined lower oesophagus and combined with 24 hour ambulatory gastric pH monitoring in 16. Ten of the 26 with Barrett's columnar lined lower oesophagus had complications including stricture (eight), deep ulceration (one), and carcinoma (one). Oesophageal acid exposure (% time < pH 4) was similar in patients with or without complications (19.2% v 19.3% p > 0.05). Oesophageal alkaline exposure (% time > pH 7) was greater in patients with complications (24.2% v 8.4% p > 0.05). Of the 16 patients who underwent gastric pH monitoring there was a clear relationship between gastric and oesophageal alkalinisation in 13. These results support the hypothesis that complications in Barrett's columnar lined lower oesophagus develop in association with increased exposure of the oesophagus to an alkaline environment which appears to be secondary to duodenogastric reflux. The routine use of 24 hour ambulatory gastric pH monitoring in conjunction with oesophageal pH monitoring can help identify those patients at risk.

Barrett's oesophagus: effect of antireflux surgery on symptom control and development of complications.

Forty-five patients with histologically proven Barrett's columnar-lined oesophagus (CLO) were treated in one unit over a 9-year period. Patients were studied prospectively as part of a surveillance programme; all initially received standard conservative treatment including high-dose H2-receptor antagonists. A satisfactory initial response was seen in 21 patients, but in 24 the symptoms were unchanged or progressed; 19 patients in the latter group were considered suitable for antireflux surgery and underwent fundoplication. Symptoms of heartburn or dysphagia persisted or recurred in 88 per cent of patients receiving medical treatment alone and complications developed in 38 per cent, including nine strictures and one adenocarcinoma. In patients undergoing antireflux surgery, symptoms persisted or recurred in 21 per cent and complications developed in 16 per cent (P < 0.01). Complete regression of Barrett's CLO occurred in two patients (11 per cent) after antireflux surgery. The results of this study suggest the superiority of antireflux surgery over pharmacological acid suppression in the control of symptoms and prevention of complications in patients with Barrett's CLO.

A more physiological alternative to total fundoplication for the surgical correction of resistant gastro-oesophageal reflux.

The incidence of mechanical complications associated with the Nissen fundoplication has prompted evaluation of an anti-reflux procedure designed to be simpler and more physiological, and encompassing a broader view of the many factors involved in the anti-reflux mechanism. Preliminary assessment of the first 100 patients with a mean follow-up of 3.5 years showed symptomatic improvement in 96 per cent and complete relief in 85 per cent. A further 100 patients were studied using formal symptom scoring, endoscopy, manometry and pH monitoring performed before operation and 3 months after operation. Similar clinical results were accompanied by improvement in endoscopic oesophagitis in 95 per cent, complete healing in 74 per cent and restoration of the pH profile to physiological levels in 84 per cent. Troublesome mechanical complications comprised a 2 per cent incidence of dysphagia, but there was no gas bloat or inability to belch or vomit, which may relate to the restoration of lower oesophageal sphincter characteristics close to those of 30 asymptomatic controls. The procedure is simpler to perform than total fundoplication, is well tolerated and is applicable to patients with reflux stricture and impaired oesophageal body motility. The results of this study support the hypotheses that effective reflux control can be achieved without total fundoplication by attention to several factors of known relevance to the anti-reflux mechanism, and that restoration of characteristics of the lower oesophageal sphincter close to physiological levels results in a lower incidence of mechanical complications.

Symptoms and endoscopic findings--can they predict abnormal nocturnal acid gastro-oesophageal reflux?

Nocturnal gastro-oesophageal reflux is known to be particularly damaging to the oesophageal mucosa, being associated with stricture formation and columnarisation. At present, this can only be detected by prolonged intra-oesophageal pH monitoring. A total of 50 patients with endoscopic oesophagitis were evaluated by ambulatory pH monitoring to detect the presence of nocturnal reflux. Whether certain symptoms in the presence of a hiatal hernia would identify those patients with reflux at night was investigated. Thirty-three patients had nocturnal reflux, two-thirds of whom had a hiatal hernia. Heartburn at night was of limited value (specificity = 65%) in detecting acid reflux whereas regurgitation and cough showed greater specificity (88% and 100% respectively) but lacked sensitivity (45% and 12% respectively). The combination of nocturnal symptoms and a hiatal hernia in patients with endoscopic oesophagitis correctly identified 58% of patients with nocturnal reflux and was highly specific (100%). This study has confirmed that symptoms and endoscopic findings can detect a significant proportion of 'at risk' patients, but the remainder will require pH monitoring to assess their pattern of acid exposure.

Gastro-oesophageal reflux associated with nifedipine.

A 57-year-old woman presented with a 3-week history of dysphagia for solids, 6 months after starting treatment with nifedipine. Endoscopy demonstrated oesophagitis and a benign oesophageal stricture. Twenty-four-hour ambulatory pH monitoring demonstrated decreased acid reflux 8 weeks after withdrawal of nifedipine, with coincidental symptomatic and endoscopic improvement. Nifedipine may induce, or aggravate, pre-existing, gastro-oesophageal reflux.