Role of platelet-activating factor in Chinese hamster ovary cell responses to cholera toxin.

Cholera toxin (CT)-induced intestinal secretion and Chinese hamster ovary cell (CHO) elongation involves cyclic adenosine monophosphate and protein synthesis-dependent prostaglandin formation. We previously reported inhibition of CT-induced intestinal secretion and CHO elongation by platelet-activating factor (PAF) receptor antagonists and secretion of PAF by human intestinal epithelial cells exposed to CT. Herein, we show that PAF is involved after cAMP and that PAF, like CT, mediates prostaglandin E2 synthesis in CHO cells. CT-induced CHO elongation was blocked by specific PAF receptor antagonists, BN52021 and SR27417. SR27417 blocked dibutyryl cAMP-induced CHO elongation, but did not alter CHO elongation caused by PGE2. Neither CT-stimulated cAMP accumulation nor PGE2 production was inhibited by SR27417. Both PGE2 and PAF caused significant CHO elongation, but the latter did not stimulate significant cAMP production. In addition, PAF, like CT and dibutyryl cAMP, stimulated significant PGE2 production. Finally, the protein synthesis inhibitor cycloheximide, which completely blocks the effect of CT on prostaglandin synthesis, also blocked that of PAF, suggesting that PAF also mediates protein synthesis-dependent prostaglandin formation. We conclude that PAF is involved in CHO cytoskeletal responses to CT after the accumulation of cAMP and, like CT, PAF stimulates protein synthesis-dependent prostaglandin accumulation.

Extracellular cGMP inhibits transepithelial sodium transport by LLC-PK1 renal tubular cells.

Both atrial natriuretic peptide (ANP) and sodium nitroprusside (SNP) inhibit tubular sodium reabsorption by generation of guanosine 3',5'-cyclic monophosphate (cGMP). To determine the role of extracellular cGMP in this response, monolayers of porcine renal tubular LLC-PK1 cells were incubated for 5 min with ANP, SNP, cGMP, or 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) (10 nM to 0.1 mM). Transepithelial sodium transport was measured as amiloride-inhibitable short-circuit current (Isc). Incubation of cell monolayers with 1 microM of ANP, cGMP, or 8-BrcGMP inhibited Isc by > 70%, as did SNP at 100 microM (P < 0.01). Adenosine 3',5'-cyclic monophosphate (0.1 mM) had no significant effect. Incubation of monolayers with 1 microM LY-83583 (an inhibitor of guanylyl cyclase), 10 microM probenecid (an organic anion transport inhibitor), or preincubation with 1 microgram/ml nocodazole (a microtubule disrupter) reduced extracellular accumulation of cGMP (P < 0.05) and abolished the SNP-mediated reduction of Isc. However, addition of these inhibitors did not affect reduction of Isc by exogenous cGMP. We conclude that SNP inhibits sodium transport by LLC-PK1 monolayers through generation of cGMP but that extrusion of cGMP out the cell is necessary for its effect.

Etiology and epidemiology of persistent diarrhea in northeastern Brazil: a hospital-based, prospective, case-control study.

With the improved therapy for acute diarrhea, persistent diarrhea (> 14 days) is emerging as a major problem in developing countries. However, the etiologies and pathogenesis of persistent diarrhea remain poorly understood. We conducted a prospective case-control study in children < 3 years old presenting to the hospital with persistent diarrhea in Fortaleza, Brazil. Over the study period (August 1988 to March 1991), 56 children seen with persistent diarrhea, 52 children seen with acute diarrhea, and 42 controls attending the same hospital/clinic for illnesses other than diarrhea were enrolled. A potential pathogen was found in 91% of children with persistent diarrhea and 90% of those with acute diarrhea versus 45% of controls (both p's < 0.01). Thirty-four percent of persistent (19/56) and 38% of acute (20/52) diarrhea cases versus 2% (1/42) of controls (both p's < 0.01) had multiple pathogens. Enteroaggregative Escherichia coli (EAggEC) were found in 68% (38/56) of children with persistent diarrhea versus 31% (13/42) of controls (p < 0.01) and in 46% (24/52) of those with acute diarrhea. Furthermore, when the EAggEC were subdivided into aggregative adherence (AA) gene probe positive (18/56; 32%) and negative (20/56; 36%), both subgroups were still significantly different from controls [6/42 (14%) and 7/42 (17%), respectively; both p's < 0.05].(ABSTRACT TRUNCATED AT 250 WORDS)

Prosthetic valve endocarditis: superiority of surgical valve replacement versus medical therapy only.

The objective of our study was to assess the long-term outcome of patients with prosthetic valve endocarditis. We used a multicenter, prospective, observational study design. Six university teaching hospitals with high volume cardiothoracic surgery participated. Seventy-four patients with prosthetic valve endocarditis as defined by explicit, objective criteria were selected for participation. All patients were followed up prospectively for 1 year. Thirty-one percent and 69% had development of endocarditis within 60 days of valve insertion ("early") and after 60 days ("late"), respectively. The most common causes were Staphylococcus epidermidis (40%), Staphylococcus aureus (20%), streptococcal species (18%), and aerobic gram-negative bacilli (11%). Physical signs of endocarditis (new or changing murmur, stigmata, emboli) were seen in 58%. At 6 months and 12 months, mortality was 46% and 47%, respectively. Surgical replacement of the infected valve led to significantly lower mortality (23%) as compared with medical therapy alone (56%), as assessed by both univariate and multivariate analyses (p < 0.05). Improved outcome was seen for the surgical group even when controlling for severity of illness at time of diagnosis. From these findings we conclude that accurate assessment of outcome in prosthetic valve endocarditis requires long-term follow-up of at least 6 months following diagnosis. Surgical therapy warrants greater scrutiny; evaluation in controlled clinical trials is appropriate.

Role of platelet activating factor in the intestinal epithelial secretory and Chinese hamster ovary cell cytoskeletal responses to cholera toxin.

With the recent heightened concern about cholera around the world come new questions about the mechanism by which cholera toxin causes diarrhea. Peterson and Ochoa have suggested that prostaglandin synthesis is key to both the intestinal epithelial secretory and the CHO cell responses to cholera toxin [Peterson, J. W. and Ochoa, G. (1989) Science 245, 857-859]. Because platelet activating factor (PAF) can be a potent stimulus for prostaglandin synthesis, we examined its role in the intestinal and tissue culture effects of cholera toxin. We report that the specific PAF receptor antagonists BN 52021 and SR 27417 inhibit the effects of cholera toxin on intestinal secretion in rabbit ileal loops in vivo and on the cytoskeleton of Chinese hamster ovary cells in vitro. We also show that PAF itself can cause net fluid secretion in the rabbit model and that PAF potentiates the effects of cholera toxin on intestinal secretion. Finally, we demonstrate that cholera toxin stimulates significant PAF production (2.6-fold) in isolated T-84 intestinal epithelial cells. We conclude that cholera toxin stimulates PAF production and that PAF is involved in both the secretory and cytoskeletal responses to cholera toxin. These findings further support the involvement of additional mediators of cholera toxin effects other than mucosal cell cyclic AMP and help explain the effects of cholera toxin on prostaglandin synthesis.

Cryptosporidiosis: Pathogenesis and immunology.

Cryptosporidium parvum is an increasingly recognized agent of intestinal infection in normal and immunocompromised humans, and in many other animals. The intraepithelial cell infection results in villous atrophy, mild submucosal inflammation, reduction of brush-border enzymes and a characteristic persistent watery diarrhea. The infection is self-limiting in immunocompetent hosts, probably because of specific acquired immunity; specific serum and secretory antibody responses develop that may be required for clearance and protection against reinfection. Passive milk antibody, especially i f in high titers, may be partially protective but severe, persistent infection in athymic rodents and humans with AIDS demonstrate that T cells are essential for controlling the infection. Specific anti-bodies and lymphocyte extracts have been tested in cases of cryptosporidiosis but the interpretation of the results remains controversial. Here, Shu-Xian Zu, Guo-Dong Fang, Ronald Foyer and Richard Guerrant emphasize that effective treatment and prevention remain dependent on advances in our understanding of the host cell-parasite relationship.

Use of ciprofloxacin versus use of aminoglycosides for therapy of complicated urinary tract infection: prospective, randomized clinical and pharmacokinetic study.

The efficacy of oral ciprofloxacin was compared with that of parenteral aminoglycoside for therapy of complicated urinary tract infection in a prospective randomized trial. The setting was a chronic-care Veterans Administration facility in which long-term bladder catheterization and resistant bacteria were common. Sixty-five consecutive patients were stratified for presence and type of bladder catheter, the presence of Providencia and Pseudomonas aeruginosa organisms versus other urinary pathogens, and renal dysfunction. A pharmacokinetic study of ciprofloxacin concentrations in serum and urine was performed with selected patients. Urinary catheters were present in 94%. All patients were symptomatic, and 58.5% had fever. Ciprofloxacin, 500 mg every 12 h orally, was compared with parenteral aminoglycoside for 7 to 10 days. Clinical response, defined by resolution of symptoms and fever at 5 to 9 days posttherapy (short-term) and 28 to 30 days posttherapy (long-term), was essentially identical for both treatment groups. Bacteriologic response, defined by sterile urine cultures, showed that ciprofloxacin was significantly more efficacious (P = 0.0005) than aminoglycoside at 5 to 9 days posttherapy. However, by 28 to 30 days, the response rate was essentially identical. Emergence of resistance to the study antibiotic was seen in 62 and 70% of those who did not show a bacteriological response and were receiving ciprofloxacin and aminoglycosides, respectively. Concentrations of ciprofloxacin and aminoglycoside in the urine substantially exceeded the MIC for the urinary pathogens isolated, although these concentrations did not correlate with short-term bacteriologic response for either antibiotic. Ciprofloxacin was efficacious in complicated urinary tract infection compared with the current standard of parenteral aminoglycoside among catheterized patients with relatively resistant bacteria.

Community-acquired pneumonia caused by Legionella dumoffii in a patient with hairy cell leukemia.

A case of community-acquired pneumonia caused by Legionella dumoffii in a patient with hairy cell leukemia is described. Diagnosis was confirmed by isolation by culture of sputum and broncho-alveolar lavage specimens, positive direct fluorescent antibody stains, and antibody seroconversion from 1:16 (acute) to 1:4096 (six months). The blue white autofluorescence of the L. dumoffii colonies when viewed under ultraviolet light was particularly useful in preliminary identification. The patient recovered from his pneumonia after administration of erythromycin and rifampin. Legionella have been shown to multiply in monocytes and cell-mediated immunity appears to be the primary mechanism of host defense in man. Hairy cell leukemia is characterized by monocyte dysfunction and such patients have a predilection for infection by microbes that are controlled by cell-mediated defenses. We review other cases of community-acquired L. dumoffii pneumonia as well as other cases of Legionella infection in patients with hairy cell leukemia.

New and emerging etiologies for community-acquired pneumonia with implications for therapy. A prospective multicenter study of 359 cases.

Three hundred fifty-nine consecutive patients with community-acquired pneumonia admitted to university, community, and VA hospitals underwent a standardized evaluation, including specialized tests for Legionella spp. and Chlamydia pneumoniae (TWAR). The most common underlying illnesses were immunosuppression (36.3%), chronic obstructive pulmonary disease (32.4%), and malignancy (28.4%). The most frequent etiologic agents were Streptococcus pneumoniae (15.3%) and Hemophilus influenzae (10.9%). Surprisingly, Legionella spp. and C. pneumoniae were the third and fourth most frequent etiologies at 6.7% and 6.1%, respectively. Aerobic gram-negative pneumonias were relatively uncommon causes of pneumonia despite the fact that empiric broad-spectrum combination antibiotic therapy is so often directed at this subgroup. In 32.9%, the etiology was undetermined. Antibiotic administration before admission was significantly associated with undetermined etiology (p = 0.0003). There were no distinctive clinical features found to be diagnostic for any etiologic agent, although high fever occurred more frequently in Legionnaires' disease. Clinical manifestations for C. pneumoniae were generally mild, although 38% of patients had mental status changes. Mortality was highest for Staphylococcus aureus (50%) and lowest for C. pneumoniae (4.5%) and Mycoplasma pneumoniae (0%). We document that specialized laboratory testing for C. pneumoniae and Legionella spp. should be more widely used rather than reserved for cases not responding to standard therapy. Furthermore, realization that C. pneumoniae and Legionella spp. are common etiologies for community-acquired pneumonia should affect empiric antibiotic prescription.

Prognosis of patients hospitalized with community-acquired pneumonia.

PURPOSE: Our purpose was to determine which clinical features predict short-term mortality in patients with community-acquired pneumonia. PATIENTS AND METHODS: We conducted a prospective multicenter study of 347 patients hospitalized in Pittsburgh (the derivation cohort) and 253 hospitalized and ambulatory patients in Boston (the validation cohort) with clinical and radiographic evidence of pneumonia. Patients in the derivation cohort underwent an extensive microbiologic evaluation including bacteriologic sputum culture, blood cultures, direct fluorescent antibody testing for Legionella species, and serologic testing for Mycoplasma pneumoniae, Legionella species, and Chlamydia TWAR. RESULTS: The overall mortality was 18% in the derivation cohort and 13.2% in the validation cohort. We identified five independent predictors of mortality in the derivation cohort: pleuritic chest pain (risk ratio, 0.4; 95% confidence interval [CI], 0.17 to 0.99), mental status changes (risk ratio, 2.6; 95% CI, 1.4 to 4.6), a severe vital sign abnormality (risk ratio, 2.1; 95% CI 1.2 to 3.6), neoplastic disease (risk ratio, 5.0; 95% CI, 2.7 to 9.1), and "high-risk" pneumonia etiology (risk ratio, 2.8; 95% CI, 1.6 to 5.0). A mortality index based on these factors accurately classified patients into five risk classes of increasing mortality. In the derivation cohort, the 6-week mortality rates were 0% in class I, 2.9% in class II, 13.1% in class III, 32.7% in class IV, and 89.5% in class V. There was little deterioration in the predictive accuracy of the model when tested in the validation cohort: mortality was 2.2% in class I, 0% in class II, 13.5% in class III, 33.3% in class IV, and 55.6% in class V. CONCLUSIONS: This prognostic classification may help direct triage decisions, assess appropriateness of care, and guide the design and analysis of therapeutic trials in patients with community-acquired pneumonia.

Disease due to the Legionellaceae (other than Legionella pneumophila). Historical, microbiological, clinical, and epidemiological review.

More than 20 species of the Legionellaceae family of bacteria have been discovered since the discovery of Legionella pneumophila. Thirteen have been implicated as causative agents of pneumonia including the Pittsburgh pneumonia agent (Tatlockia micdadei, Legionella micdadei). Although outbreaks of nosocomial pneumonia in immunosuppressed hosts have been well-described, most cases have occurred sporadically in the community. The spectrum of disease ranges from severe life-threatening pneumonia to a self-limiting febrile illness (Pontiac fever). Isolation from the natural aquatic environment has preceded its discovery as agents of human disease in 6 species, while environmental isolation has not yet been obtained for 3 species implicated in disease. The mode of transmission is uncertain, but cases of dual infection by L. pneumophila and the newer species suggests that the epidemiology of these new organisms will be similar to that of L. pneumophila. The antibiotic of choice appears to be erythromycin. The historical background, epidemiology, microbiology, and clinical manifestations of these newly-discovered organisms are reviewed in comparative fashion.

Community-acquired Legionnaires' disease.

Legionellae are ubiquitous aquatic organisms. They are unique among the agents commonly responsible for bacterial pneumonia in humans in that they are not part of the normal human flora but are acquired from environmental sources. Prospective studies have shown that legionellae consistently rank among the top three bacteria as etiologic agents of community-acquired pneumonia. The clinical presentation of Legionnaires' disease is not distinguishable from that of other bacterial pneumonias. Culture of respiratory secretions using selective media, combined with one or more rapid diagnostic methods (direct fluorescent antibody staining, radiolabelled DNA probe, or urinary antigen detection) provides a specific diagnosis in the vast majority of cases. Sporadic cases have been linked to legionella colonization of water systems in homes and the work setting. Antibiotics commonly used in the therapy of community-acquired pneumonias, such as beta-lactam agents, are ineffective. Specific therapy with erythromycin reduces mortality to less than 10%.

Infections caused by the Pittsburgh pneumonia agent.

Of the Legionellaceae family, Pittsburgh pneumonia agent (Tatlockia micdadei, Legionella micdadei) is second only to Legionella pneumophila in causing human pneumonia. In nosocomial infection, the patients tend to be immunosuppressed. The clinical presentation is nonspecific, although in immunosuppressed hosts the presentation may mimic that of pulmonary embolus (pleuritic chest pain, nonproductive cough, pleural-based densities on chest rontgenogram). The reservoir for the organism is water, and prevention of nosocomial infections can be accomplished by disinfection of the water supply. Diagnosis is best established by isolation of the organism from respiratory secretions by using selective, dye-containing buffered charcoal-yeast extract agar. The organisms can be acid-fast when clinical specimens are stained. Erythromycin is the antibiotic of choice, although tetracyclines, trimethoprim-sulfamethoxazole, and rifampin have also proved to be efficacious.

Legionella species as hospital-acquired respiratory pathogens.

Nosocomial pneumonia caused by legionella is an increasingly recognized entity. Legionella sp responsible for documented nosocomial disease include Legionella pneumophila, Tatlockia micdadei, Legionella bozemanii, Legionella dumoffi and Legionella oakridgensis. The clinical presentation is nonspecific although diarrhea occurs frequently. Hyponatremia occurs significantly more frequently in legionnaires' disease than pneumonias caused by other agents. Chest roentgenographic findings are nonspecific, although cavitation can be seen in immunosuppressed patients. Laboratory methods require the use of direct fluorescent antibody (DFA) stains, culture using selective media, serologic testing, and detection of antigen in urine. The DFA test is not sensitive; however, it does correlate with the severity of disease. Culture from sputa is now feasible. Bronchoalveolar lavage is a promising technique for obtaining specimens. The ideal specimen for culture is that obtained by transtracheal aspiration, which bypasses oropharyngeal contamination. Combination therapy of erythromycin and rifampin is recommended for selected patients. Because the source of the organism is the hospital water distribution system, we recommend routine environmental surveillance, especially in hospitals in which organ transplants are performed. The role of cooling towers as a vector for dissemination of the organism is disputed. Disinfection of the water supply can be accomplished by using heat eradication. Chlorination has generally proven unsatisfactory because of organism persistence as well as corrosive damage to the plumbing system from the chlorine. Both physician awareness and availability of specialized laboratory testing are necessary for the detection of cases.