Infectious diarrhea

Team-based, problem-solving exercises using studies of diarrhea and oral rehydration encourage students to integrate knowledge of systems physiology

We describe an inquiry activity that aims to develop students' ability to interpret findings that span whole body systems and so encourage the integration of knowledge. The scenario we choose was the physiological challenge posed by diarrhea and the physiological mechanisms that underpin oral rehydration therapy. Before the staff-facilitated inquiry activity, students engage with an online information resource and complete a formative, but mandatory, prelaboratory quiz. These tasks encourage students to develop some mastery of the relevant physiology before the timetabled inquiry activity. The 3-h inquiry activity is driven by a paper workbook containing data from published studies, mainly from veterinary physiology, of the various consequences of diarrhea. Figures from published data are arranged so that, initially, the impact of dehydration on a single system (the cardiovascular system) could be appreciated. Integration with other systems (respiratory and renal systems) is then introduced progressively through the activity. The exercise is designed as a team-based inquiry activity that emphasizes the value of discussion to identify appropriate features for interpretation of the data. Students are obliged to complete a postlaboratory quiz within 5 days of the inquiry activity, serving to consolidate the students' learning and provide staff with feedback on the attainment of intended learning outcomes. Marks from formative pre- and postlaboratory quizzes typically have a median mark in excess of 80% (pass mark is 50%), and qualitative feedback suggests that the majority of students recognized the value of the activity, despite simultaneously reporting that it was intellectually demanding.

Cholera toxin inhibits human hepatocarcinoma cell proliferation in vitro via suppressing ATX/LPA axis

AIM

To investigate the antitumor effect of cholera toxin (CT) in hepatocellular carcinoma (HCC) in vitro and the mechanisms underlying the effect.

METHODS

Human hepatocellular carcinoma cell lines Hep3B and Huh7, which expressed moderate and high level of autotaxin (ATX), respectively, were used. Cytokine level in the cells was evaluated using ELISA assay, and cell proliferation was investigated using MTT assay. ATX expression was determined using Western blot. ATX/lyso-PLD activity in the conditioned medium was measured using FS-3, a fluorescent lysophosphatidylcholine (LPC) analogue, as substrate.

RESULTS

Exposure to CT (7.5 and 10 ng/mL) significantly inhibited the cell growth, decreased secretion of proinflammatory cytokine TNF-α and promoted secretion of anti-inflammatory cytokines IL-4 and IL-10. CT at 10 ng/mL markedly suppressed ATX expression in Hep3B and Huh7 cells. Furthermore, ATX and lysophosphatidic acid (LPA) were found to be crucial for growth of the cancer cells. CT could inhibit TNF-α-induced expression and secretion of ATX that led to decreased activity of lysophospholipase D, thus decreasing the conversion of LPC to LPA.

CONCLUSION

CT inhibits hepatocellular carcinoma cell growth in vitro via regulating the ATX-LPA pathway.

What Have We Learnt from Bacterial Stool Culture Results? a Retrospective Study of Hospitalised Gastroenteritis Cases in a Regional Hospital in Hong Kong

Background

Stool culture is one of the common investigations done for patients with gastroenteritis, and fluoroquinolones have been used frequently for suspected bacterial gastroenteritis.

Objective

To study the yield of bacterial pathogens in stool culture in a local regional hospital for in-patients with gastroenteritis and the individual pathogens identified. Also, the value of stool culture and the prescription of fluoroquinolones as empirical antibiotics were reviewed.

Methods

This was a retrospective study. All in-patients with the principal diagnosis of “gastroenteritis” in the year 2007 were reviewed. We excluded pregnant patients and patients under 18 years of age. Patients were divided into two age groups and data were analysed including demographics, clinical findings, admission time and culture results. Antibiotics prescription behaviour was also analysed.

Results

A total of 837 adult patients fulfilled the criteria. Among them, 562 cases had their stool saved and sent for bacterial culture. Eighty-nine cases were found to have their stool cultures positive for bacteria. The identified pathogens were namely Vibrio parahaemolyticus (38.2%), Salmonella species (34.8%), Campylobacter species (11.2%), Plesiomonas species (10.1%) and Aeromonas species (3.4%) respectively. The yield of positive stool culture was 15.8%.

Conclusion

Vibrio parahaemolyticus and Salmonella species were still the most common pathogens for bacterial gastroenteritis among hospitalized patients in Hong Kong, especially in the young and middle aged. Their occurrence followed a seasonal pattern. Physicians had a tendency to prescribe fluoroquinolones for cases with fever and travel history. Also, the problem of antibiotic resistance did exist. It is important for practitioners to follow local guidelines before ordering microbiological investigations on stool and prescribing empirical antibiotic treatment.

Presumptive shigellosis: Clinical and laboratory characteristics of Bangladeshi patients

The aim of the study was to examine some selected clinical and laboratory parameters in distinguishing non-Shigella invasive diarrhoeas from culture-confirmed Shigella cases. We conducted a clinic-based, cross-sectional study at the Dhaka Hospital of ICDDR,B located in Bangladesh. In total, 389 patients of all age groups and of both genders, with a history of diarrhoea of less than 96 h and presence of visible blood and/or mucus in the stool were presumed to have shigellosis and enrolled in the study. Shigella was isolated from faecal cultures in 227 (58.4%) patients. The remaining 162 (41.6%) patients did not have Shigella isolated from their faecal cultures and constituted the comparison group. Another 238 randomly selected patients with non-Shigella diarrhoea from the Diarrhoeal Disease Surveillance System database of the Dhaka Hospital constituted another comparison group. Cases of culture-proven Shigella were similar to non-Shigella invasive diarrhoeal patients with presumptive shigellosis with regard to several biosocial variables. The nutritional status of children with shigellosis was significantly inferior to those with non-Shigella diarrhoea. The presence of macrophages more than 5/HPF in stool microscopic examination was significantly more frequent among patients infected with Shigella. Empirical antimicrobial therapy for shigellosis might be considered for malnourished diarrhoeal children presenting with history of visible blood and/or mucus in stool, and children older than 1 y of age. Further studies are needed in different geographical settings to identify clinical and laboratory parameters that could help identify patients with shigellosis.

Cholera toxin induces malignant glioma cell differentiation via the PKA/CREB pathway

Malignant gliomas are one of the leading causes of cancer deaths worldwide, but chemoprevention strategies for them are few and poorly investigated. Here, we show that cholera toxin, the traditional biotoxin and well known inducer of accumulation of cellular cAMP, is capable of inducing differentiation on malignant gliomas in vitro with rat C6 and primary cultured human glioma cells. Cholera toxin-induced differentiation was characterized by typical morphological changes, increased expression of glial fibrillary acid protein, decreased expression of Ki-67, inhibition of cellular proliferation, and accumulation of cells in the G(1) phase of the cell cycle. Cholera toxin also triggered a significant reduction in the G(1) cell-cycle regulatory proteins cyclin D1 and Cdk2 along with an overexpression of cell-cycle inhibitory proteins p21(Cip1) and p27(Kip1). Abrogation of cAMP-dependent protein kinase A activity by protein kinase A inhibitor or silencing of cAMP-responsive element binding proteins by RNA interference resulted in suppressed differentiation. These findings imply the attractiveness of cholera toxin as a drug candidate for further development of differentiation therapy. Furthermore, activation of the protein kinase A/cAMP-responsive element binding protein pathway may be a key and requisite factor in glioma differentiation.

Virulence of viable but nonculturable S. Typhimurium LT2 after peracetic acid treatment

S. Typhimurium LT2 cells suspended in sterilized sewage effluent water (SEW) and in distilled water microcosms were exposed to 0, 7, 15 and 20 mg/l peracetic acid, and tested for viability and virulence. After treatment for one hour, colony forming units decreased by at least 5 log units at peracetic acid concentration of 7 mg/l. In SEW, at peracetic acid concentration of 15 mg/l, the cells were nonculturable (VNC), but retained virulence as demonstrated by invasion assays of HeLa cells. Higher concentrations (greater than or equal to 20 mg/l) resulted in bacterial death, i.e. substrate non-responsive cells. Despite morphological alterations of the bacteria after peracetic acid treatment, visualized by transmission electronic microscopy, conservation of both adhesive and invasive capacities was confirmed by scanning electron microscopy after exposure to 0-15 mg/l peracetic acid. Public health professionals need to recognize that peracetic acid-treated Salmonella is capable of modifying its physiological characteristics, including entering and recovering from the viable but nonculturable state, and may remain virulent after a stay in SEW followed by peracetic acid treatment.

Lysophosphatidic acid inhibits cholera toxin-induced secretory diarrhea through CFTR-dependent protein interactions

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated chloride channel localized primarily at the apical or luminal surfaces of epithelial cells that line the airway, gut, and exocrine glands; it is well established that CFTR plays a pivotal role in cholera toxin (CTX)-induced secretory diarrhea. Lysophosphatidic acid (LPA), a naturally occurring phospholipid present in blood and foods, has been reported to play a vital role in a variety of conditions involving gastrointestinal wound repair, apoptosis, inflammatory bowel disease, and diarrhea. Here we show, for the first time, that type 2 LPA receptors (LPA₂) are expressed at the apical surface of intestinal epithelial cells, where they form a macromolecular complex with Na⁺/H⁺ exchanger regulatory factor–2 and CFTR through a PSD95/Dlg/ZO-1–based interaction. LPA inhibited CFTR-dependent iodide efflux through LPA₂-mediated G_i pathway, and LPA inhibited CFTR-mediated short-circuit currents in a compartmentalized fashion. CFTR-dependent intestinal fluid secretion induced by CTX in mice was reduced substantially by LPA administration; disruption of this complex using a cell-permeant LPA₂-specific peptide reversed LPA₂-mediated inhibition. Thus, LPA-rich foods may represent an alternative method of treating certain forms of diarrhea.

Diarrhea caused by enterotoxigenic Escherichia coli infection of humans is inhibited by dietary calcium

BACKGROUND & AIMS

In several rat infection experiments, we have shown that dietary calcium inhibits intestinal colonization and translocation of invasive salmonella. The aim of the present study was to find out whether calcium is also protective against enterotoxigenic Escherichia coli (ETEC) infection. This was first tested in our rat model and subsequently verified in a human infection study.

METHODS

Rats were fed a purified diet with either a low or a high amount of calcium phosphate and orally infected with ETEC. In addition, a parallel, double-blind, placebo-controlled intervention study of 3 weeks was performed with 32 healthy men. Subjects largely maintained their habitual diet and consumed either regular milk products (calcium supply, 1100 mg/day) or placebo milk products (calcium supply, 60 mg/day). On day 10, subjects ingested a live but attenuated ETEC strain (strain E1392/75-2A), able to induce mild although short-lived symptoms. Primary outcomes studied were infection-induced diarrhea (total fecal output and relative fecal dry weight) and fecal mucin excretion.

RESULTS

In humans, ETEC induced diarrhea in both groups, in that total fecal output doubled and mean relative fecal dry weight dropped from 25% to 20%. Additionally, fecal mucin excretion was increased in both groups. All these fecal parameters were completely normalized in the calcium group on the second infection day, in contrast to the placebo group, which recovered on the third infection day. Likewise, supplemental calcium inhibited ETEC colonization and diarrhea in rats.

CONCLUSIONS

Calcium in milk products improves human resistance to ETEC infection as it inhibits infectious diarrhea.

The role of antibiotics in the treatment of infectious diarrhea

Infectious diarrhea is a significant cause of morbidity and mortality and a common complaint in clinical practice. Routine empirical use of antibiotics for infectious diarrhea should be avoided because of the self-limited nature of most cases, the cost of antibiotics, and the potential to worsen the already significant problem of antibiotic resistance of enteric pathogens. For patients with severe invasive or prolonged diarrhea or who are at high risk of complications, such as the elderly, diabetics, cirrhotics, and immunocompromised patients, empirical treatment with a quinolone antibiotic for 3 to 5 days can be considered. Antibiotic treatment can be highly effective for Shigella, ETEC, and V. cholerae infections, and metronidazole is indicated for C. difficile colitis. The impact of antibiotics for other specific pathogens is modest, and antibiotic therapy should be reserved for the same group of patients who would be considered for empirical treatment. The most significant problem in the antibiotic treatment of infectious diarrhea is the progressive increase in resistance among enteric pathogens; only the prudent use of antimicrobials in all areas of daily practice can limit or delay the impact of this serious problem.

Laboratory approaches to infectious diarrhea

Future applications of advanced molecular diagnostics in clinical laboratories will enhance significantly capabilities to diagnose bacterial, parasitic, and viral agents in the early course of disease through enhanced assay sensitivities and specificities and improved turnaround times, theoretically leading to more timely and directed therapeutic intervention. Until such time, clinicians must continue to rely on clinical judgment and the diverse battery of traditional culture techniques, direct examination (including light microscopy and electron microscopy), and immunoassays that are available. Cost considerations and the ever-increasing array of infectious agents responsible for infectious gastroenteritis will continue to drive the development of practice guidelines to assist practitioners with reasoned and reasonable approaches to management of diarrheal illnesses.

Bacterial Infections of the Colon

The colon is a common site of infection for a heterogeneous group of bacterial pathogens. The presentation of disease in the colon is generally in the form of distinct syndromes, and it is important for physicians to recognize the causative organisms, because specific treatment is highly effective. The flouroquinolones have emerged as the treatment of choice for most food-borne bacterial pathogens. Resistance to these agents is not a major issue at present except in Campylobacter. Clostridium difficile remains sensitive to both metronidazole and oral vancomycin. The majority of patients will respond to metronidazole, but oral vancomycin should be limited to severe cases of pseudomembranous colitis or treatment failures with metronidazole. Vancomycin is expensive and has the potential for the propagation of vancomycin resistance in other bacteria, notably enterococci. Patients appearing with proctitis should be screened for sexually transmitted diseases.