Isolation of enteric pathogens from patients with travelers' diarrhea using fecal transport media

Characterization of Enterococcus spp. from human and animal feces using 16S rRNA sequences, the esp gene, and PFGE for microbial source tracking in Korea

Contamination from human and animal fecal waste is a primary cause of water pollution. Microbial source tracking (MST) may be a useful tool for high-quality environmental management and for assessing human health risks associated with water pollution. The goal of this study was to evaluate Enterococcus spp. as a target organism for MST. Thirty-four fecal samples were collected from five different sources (human, chicken, pig, cow, and goose) in South Korea. In total, 237 Enterococcus spp. were isolated from feces using membrane- Enterococcus indoxyl-beta-d-glucoside agar. The 16S rRNA gene and the whole genome were analyzed using nucleic acid sequencing and pulsed-field gel electrophoresis (PFGE), respectively. Both phylogenetic analysis and principal coordinate analysis using UniFrac were performed on the nucleic acid sequences of the 16S rRNA gene. According to P-tests from UniFrac, significant differences existed between Enterococcus spp. isolated from human feces and those from animal feces. In addition, we evaluated whether the esp gene of Enterococcus faecium could be a specific target for Enterococcus spp. isolated from human feces. Of 58 E. faecium isolates tested, only three were esp-positive. The specificity of the esp gene of E. faecium isolated from human feces was 100%, but the sensitivity was <10%. These results suggest that Enterococcus spp. have different molecular characteristics according to their fecal source and that these characteristics can be further identified by analyzing the esp gene and 16S rRNA sequences, whereas PFGE provides limited information on the fecal sources of Enterococcus spp.

Analysis of efficacy of CVD 103-HgR live oral cholera vaccine against all-cause travellers’ diarrhoea in a randomised, double-blind, placebo-controlled study

Enterotoxigenic Escherichia coli (ETEC), which produces heat labile toxin (LT) and/or heat stable toxin (ST), is considered to be the most common known cause of travellers' diarrhoea (TD). Owing to the antigenic similarity between cholera toxin and LT, immunization with inactivated oral B-subunit/whole-cell cholera vaccine (BS-WC) offers short term (3 months) but significant (>67%) protection against TD caused by LT-related ETEC. Since it expresses the cholera toxin B (CTB) subunit, the live attenuated oral cholera vaccine strain CVD 103-HgR, may induce similar protection. A trial was performed to determine if CVD 103-HgR live oral cholera vaccine would provide a protective efficacy of at least 50% against TD. In addition, the protective efficacy of the vaccine against TD specifically due to LT-ETEC and LT/ST-ETEC was determined. Volunteers (n=134) travelling to Indonesia, India, Thailand or West-Africa were randomised to receive either a placebo (n=65) or the vaccine (n=69). In the placebo group, 46% reported an episode of diarrhoea, compared to 52% in the vaccine group. No significant group differences were found with regard to incidence, duration or severity of all caused TD or ETEC-associated TD. However, ETEC-associated TD occurred earlier in the placebo group (median 5 days), compared to the vaccine group (median 15 days). In conclusion, CVD 103-HgR live oral cholera vaccine failed to provide a 50% protection against TD. This study does not exclude that the vaccine may offer a short-lived protection against ETEC-associated TD. However, the power of the study was limited by the unexpected low incidence of LT-ETEC-associated diarrhoea (9% of all TD) compared to ST-associated TD (24% of all TD).

Characterization of the Aeromonas hydrophila group isolated from retail foods of animal origin

During a recent survey of retail fresh foods of animal origin (fish and seafood, raw milk, poultry, and red meats) for organisms of the Aeromonas hydrophila group, we isolated representative strains from the various foods. In this study, we sought to characterize these isolates for biochemical properties and virulence-associated factors and to compare the food isolates with clinical isolates. We identified all food and clinical isolates as A. hydrophila and found that all isolates were typical in their biochemical reactions. Examination of the isolates for various virulence-associated factors indicated that most food and clinical isolates were serum resistant, beta-hemolytic, cytotoxin positive (against Y1 adrenal cells), hemagglutinin positive, Congo red positive, elastase positive, and staphylolysin positive. Mouse 50% lethal doses were log10 8 to 9 CFU for most isolates. All isolates had biotypes identical to those of enterotoxin-positive strains. The public health significance of these organisms in foods is not known at present, although their widespread occurrence and ability to grow competitively in foods kept at 5 degrees C represents a potential hazard.

A comparative study of furazolidone and placebo in addition to oral rehydration in the treatment of acute infantile diarrhea

Between July and October 1987 an outpatient study of 191 children with acute diarrhea was undertaken in two rural communities in Mexico. Through a double-blind randomization we compared the efficacy of a combination therapy of furazolidone, 7.5 mg/kg/day, plus standard oral rehydration therapy (ORT) (96 patients) versus a placebo plus ORT (95 patients), each given for 5 days. Diarrheal stool samples were collected from all patients before therapy. By means of a two-vial transport media system the samples were sent to a university laboratory and examined for viral, bacterial, and parasitic organisms. The most commonly isolated organisms were enterotoxigenic Escherichia coli (13%) and Giardia lamblia (13%). Patients who received furazolidone plus ORT showed a greater reduction in duration of diarrhea when compared with those receiving placebo plus ORT (63.4 h versus 71.44 h). There was also a trend toward shorter duration of diarrhea in patients with Giardia who were treated with furazolidone/ORT compared with Giardia patients in the placebo/ORT group. When fecal leukocytes were present in the stool, the furazolidone/ORT-treated patients had a significantly higher percentage of clinical cures (79% versus 54%, p = 0.03) and an overall shorter duration of diarrhea (62.0 h versus 80.6 h, p = 0.055) at the end of 5 days of therapy than did the placebo/ORT-treated group.

Clinical presentation as a guide to therapy for travelers' diarrhea

To better define the role of antimicrobial therapy among U.S. travelers in Mexico, clinical and nonculture laboratory parameters were compared for 56 patients with shigellosis and 204 others with diarrhea of other causes. The presence of fever, stool mucus and blood, and fecal leukocytes were significantly more common among patients with shigellosis (p less than 0.001) who also tended not to present with mild diarrhea (p less than 0.05). However, clinical and laboratory parameters were either too insensitive or too nonspecific to be useful in identifying most cases of shigellosis or in excluding the likelihood of its presence. Patients with mild clinical presentations, regardless of etiology, experienced resolution of disease sooner than those with moderate to severe presentations (p less than 0.01), but withholding therapy from patients with mild presentations resulted in 48% of these patients remaining ill at the end of 48 hours. Based on these findings, the authors advise empiric use of antimicrobial agents in travelers with diarrhea associated with fever, bloody stools, or fecal leukocytes, and for all travelers with moderate and severe diarrhea. If therapy is withheld from patients with initially mild presentations, a proportion might still require therapy, possibly an antimicrobial agent, for optimal control of symptoms.

Lack of correlation between known virulence properties of Aeromonas hydrophila and enteropathogenicity for humans

Five strains of Aeromonas hydrophila were selected for use in volunteer challenge trials. All five strains produced cytotoxin, hemolysin enterotoxin, lysine decarboxylase, acetylmethylcarbinol, and DNase. Two strains hydrolyzed esculin. All strains produced purulent hemorrhagic fluid accumulation in rabbit ileal loops, but failed to induce keratoconjunctivitis in guinea pigs. None of the strains produced mannose-resistant hemagglutinins. In challenge studies, diarrhea was demonstrated in only 2 of 57 human volunteers with doses ranging from 10(4) to 10(10) CFU. One person experienced mild diarrhea with 10(9) CFU of strain 6Y. A second person developed moderate diarrhea with 10(7) CFU of strain 3647. At higher doses, no diarrhea was seen in any of the volunteers. The other three strains (B158, SSU, 3284) failed to cause diarrhea and were not recovered from stools of volunteers. Additional virulence properties of A. hydrophila need to be sought before enteropathogenicity for humans can be established.

Evaluation of BW942C, a novel antidiarrheal agent, against enterotoxins of Escherichia coli and Vibrio cholerae

BW942C, an enkephalin-like pentapeptide with anti-diarrheal activity, was tested against crude toxins of Escherichia coli and Vibrio cholerae in the Y-1 adrenal cell assay, rabbit ileal loop assay, and suckling mouse assay. The effects of BW942C on in vitro ion transport were measured in rabbit ileum mounted in Ussing chambers. In vitro, BW942C decreased basal short-circuit current (2.26 and 3.15 mueq cm-2 h-1 in experimental samples and controls, respectively; n = 7, P less than 0.05) and increased basal net Cl absorption (1.59 and 0.50 mueq cm-2 h-1 in experimental samples and controls, respectively; P less than 0.025). Net Na absorption was also increased, but not significantly. BW942C did not block the secretory response to a maximal dose of purified heat-stable toxin. BW942C directly enhanced intestinal fluid absorption. In the Y-1 adrenal cell assay, 5 mg of BW942C per ml inhibited the cytopathic effect caused by cholera toxin or heat-labile enterotoxin of E. coli. In the rabbit ileal loop assay, E. coli heat-stable toxin, E. coli heat-labile enterotoxin, and cholera toxin were inhibited 35 to 70% by administration of BW942C. With the suckling mouse model, the fluid accumulation caused by E. coli heat-stable toxin was ablated by prior treatment with BW942C. The drug is currently being evaluated in patients with acute secretory diarrhea to determine its effect on clinical symptoms.