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Biomedical subjects

Y J Tang

Publications and source records attributed to Y J Tang.

At least 37 records · Page 2Linked to original sources
PubMed1999

Clostridium difficile: a survey of fecal carriage in cats in a veterinary medical teaching hospital.

Fecal samples collected from 245 cats over a 6-month period were analyzed for the presence of Clostridium difficile. After culture on selective media, isolates were identified by a latex agglutination test, and the presence of toxin A and toxin B gene sequences was determined by polymerase chain reaction. Clostridium difficile was isolated from 23 (9.4%) of the cats, and 34.8% of that group were colonized with toxigenic strains. All of the cats colonized with toxigenic C. difficile had > or = 1 of the risk factors (antibiotic use, antineoplastic therapy, immunosuppressive virus infection) associated with C. difficile infection in humans. Clostridium difficile was not found in any of the cats from a clinically healthy outpatient group of cats examined from the same hospital nor in cats from a specific-pathogen-free research colony on the same campus tested during the same time period. The data obtained in this study confirm the presence of C. difficile in cats at a veterinary teaching hospital. DNA fingerprinting analysis of these isolates allowed separation of the strains into 5 groups. Type 4 strain found in 7 cats was also recovered from the floor drain in the same hospital, suggesting a possible source of infection. Whether the organism is of clinical significance in diarrheal diseases of cats remains to be determined.

Animals↗
PubMed1998

Isolation of a toxin B-deficient mutant strain of Clostridium difficile in a case of recurrent C. difficile-associated diarrhea.

Clostridium difficile-associated diarrhea (CDAD) recurs in approximately 15%-20% of patients after discontinuation of metronidazole or vancomycin therapy. Most recurrences are believed to be endogenous relapses due to the persistence of spores. However, there is evidence that reinfection with a different strain is a cause of recurrence. We report the case of a patient with a history of multiple episodes of C. difficile colitis. The patient, a 56-year-old female, has had 5 years of repeated recurrences, each shortly after discontinuing vancomycin therapy. During the course of these episodes, three isolates were cultured from her stools at different times. These isolates were analyzed for the presence of toxin A and B gene sequences and genotyped by means of arbitrarily primed polymerase chain reaction (AP-PCR). The original two isolates contained the toxin A and B genes, as determined by PCR, and were of the same AP-PCR type. During her last relapse, a C. difficile strain lacking at least a portion of the toxin B gene was isolated. AP-PCR analysis of this isolate showed a different DNA banding pattern from that of the previous isolates. A vancomycin susceptibility assay revealed a slight decrease in vancomycin activity as compared with that against the prior isolate. This case demonstrates two unique features: (1) recurrent infections can be due to reinfections and (2) toxin B mutants can possibly cause CDAD. This study also raises concerns about long-term vancomycin use and the development of resistance of C. difficile to vancomycin.

Bacterial Proteins↗
PubMed1998

Detection of Bacteroides fragilis enterotoxin gene by PCR.

Bacteroides fragilis constitutes about 1% of the bacterial flora in intestines of normal humans. Enterotoxigenic strains of B. fragilis have been associated with diarrheal diseases in humans and animals. The enterotoxin produced by these isolates induces fluid changes in ligated intestinal loops and an in vitro cytotoxic response in HT-29 cells. We developed a nested PCR to detect the enterotoxin gene of B. fragilis in stool specimens. After DNA extraction, a 367-bp fragment was amplified with two outer primers. The amplicon from this reaction was subjected to a second round of amplification with a set of internal primers. With these inner primers, a 290-bp DNA fragment was obtained which was confirmed as part of the B. fragilis enterotoxin gene by Southern blotting with a nonradioactive internal probe and a chemiluminescence system. By this approach, B. fragilis enterotoxin gene sequences were detected in eight known enterotoxigenic human isolates and nine enterotoxigenic horse isolates. No amplification products were obtained from DNA extracted from 28 nonenterotoxigenic B. fragilis isolates or B. distasonis, B. thetaiotaomicron, B. uniformis, B. ovatus, Escherichia coli, or Clostridium difficile. The sensitivity of this assay allowed us to detect as little as 1 pg of enterotoxin DNA sequences or 100 to 1,000 cells of enterotoxigenic B. fragilis/g of stool. Enterotoxin production of all isolates was confirmed in vitro in HT-29 cells. A 100% correlation was obtained between enterotoxin detection by cytotoxin assay and the nested PCR assay. This rapid and sensitive assay can be used to identify enterotoxigenic B. fragilis and may be used clinically to determine the role of B. fragilis in diarrheal diseases.

Animals↗
PubMed1997

Isolation of various genotypes of Clostridium difficile from patients and the environment in an oncology ward.

The epidemiology of Clostridium difficile-associated diarrhea (CDAD) is not well defined in nonepidemic situations because precise biotyping techniques have only recently become available. Arbitrarily primed polymerase chain reaction (AP-PCR) was used to determine strain identity of C. difficile isolates recovered on our oncology ward, at an incidence rate of 0.84%. Twenty-one strains of C. difficile, which were grouped into 18 different AP-PCR types, were isolated from patients' specimens. Forty-two C. difficile isolates recovered from the environment (33 toxigenic and 9 nontoxigenic) represented 9 different AP-PCR types. The most commonly found type, a toxigenic strain accounting for 29% of the environmental isolates, was widespread throughout the ward. None of the environmental types were found among the isolates from patients. Three patients' isolates were of the same AP-PCR type, and two of these patients had occupied neighboring rooms at the same time. The diversity of C. difficile isotypes suggests that endemic nosocomial CDAD is not necessarily clonally spread.

California↗
PubMed1996

Detection of Cryptosporidium parvum DNA in human feces by nested PCR.

Cryptosporidium parvum is a coccidian protozoan that causes diarrhea in humans, often chronic and severe in patients with AIDS. Conventionally, diagnosis is made by concentration of stools followed by acid-fast staining (AF) or immunofluorescent staining. The threshold of detection in human stool specimens by these methods may require the presence of 50,000 (immunofluorescent staining) to 500,000 (AF) oocysts per g of stool. In this study, a nested PCR assay was developed to detect C. parvum DNA directly from stool specimens. After extraction of DNA from formalinized stool, a 400-bp fragment of C. parvum DNA was amplified with two 26-mer outer primers. The amplicon from this reaction was amplified with a second primer pair. With these nested primers, a 194-bp DNA fragment was amplified and confirmed as C. parvum DNA by internal probing with an enzyme-linked chemiluminescence system. This PCR-based test allowed the detection of 500 oocysts per g of stool or 100 ng of C. parvum DNA. Studies indicate that the primers utilized are specific for the DNA of C. parvum. DNA sequences were also detected in stool specimens from 4 of 28 patients previously reported negative by AF. In summary, a rapid, sensitive, and specific assay for the detection of C. parvum directly from stool specimens has been developed. This test has the potential for detecting asymptomatic infection, monitoring the response to therapy, and detecting the organism in environmental sources.

AIDS-Related Opportunistic Infections↗
PubMed1995

Comparison of arbitrarily primed PCR with restriction endonuclease and immunoblot analyses for typing Clostridium difficile isolates.

Arbitrarily primed PCR (AP-PCR) was used to genotype 26 clinical isolates of Clostridium difficile previously analyzed by immunoblotting (IB) and 20 isolates typed by restriction endonuclease analysis (REA) with HindIII. Two levels of differentiation were achieved with the AP-PCR approach by use of two different arbitrary primers. With the 19-mer arbitrary primer T-7 (first level of differentiation), a good correlation was found between IB and AP-PCR typing. Twenty isolates grouped into six IB types were separated into seven major AP-PCR types. These seven AP-PCR groups were further discriminated into 12 subtypes after genotyping with the arbitrary primer PG-05 (second level of differentiation). The remaining six isolates, all of different IB types, showed a unique and distinct DNA banding pattern with both of the arbitrary primers, T-7 and PG-05. Twenty isolates representing 20 REA types from 15 REA groups were resolved into 13 AP-PCR DNA profiles with the arbitrary primer T-7. A good correlation was found at this level of differentiation between the major REA groups, Y and M, and AP-PCR typing. While AP-PCR with this primer failed to differentiate isolates in REA groups J, G, R, and B, AP-PCR with PG-05 resolved these four isolates into four distinct AP-PCR types. In addition, one of three M strains and one of four Y strains displayed a slightly different DNA banding pattern by AP-PCR (with PG-05) from that of the other strains in the group. We conclude that AP-PCR is a rapid and sensitive method which not only complements other typing schemes but also may be a substitute and prove to be especially suited for immediate epidemiological tracking of nosocomial infections due to C. difficile.

Bacterial Typing Techniques↗
PubMed1995

Genomic fingerprinting of epidemic and endemic strains of Stenotrophomonas maltophilia (formerly Xanthomonas maltophilia) by arbitrarily primed PCR.

Arbitrarily primed PCR (AP-PCR) was used to type 64 clinical isolates of Stenotrophomonas maltophilia from 60 patients and the hands of one nurse. Forty-seven different patterns were observed, most patients having isolates with unique genomic fingerprints. A single pattern, however, was obtained from six of eight patients involved in an intensive care nursery outbreak, confirming the suspected nosocomial transmission of this microorganism. This strain was also found in four other patients hospitalized at the same time but in different units. AP-PCR typing results had a good correlation with the 49 patterns obtained when the isolates were typed by contour-clamped homogeneous electric field gel electrophoresis. Although AP-PCR is slightly less discriminatory than contour-clamped homogeneous electric field gel electrophoresis, it offers several advantages and should be considered as a practical option for molecular typing during investigations of outbreaks.

Bacterial Typing Techniques↗
PubMed1995

Apparent outbreaks of Clostridium difficile-associated diarrhea in horses in a veterinary medical teaching hospital.

Intestinal colonization with toxigenic strains of Clostridium difficile was documented in 9 of 10 horses with acute onset diarrhea in a veterinary medical teaching hospital, whereas a similar isolate was detected in only 1 of 23 other horses without diarrhea in the hospital. One horse with diarrhea was infected simultaneously with both C. difficile and Salmonella krefeld. Clostridium difficile was detected by fecal culture on selective medium, confirmed with a latex particle agglutination test, and identified as toxigenic by polymerase chain reaction amplification of toxin A and toxin B gene sequences. Using an arbitrarily-primed polymerase chain reaction, 6 distinct C. difficile isolates were detected in the feces of the 9 affected horses at the time of the outbreak of diarrhea.

Animals↗
PubMed1995

[Seasonal variation in the ultrastructure and calcium uptake rate of cardiac sarcoplasmic reticulum in ground sqirrel].

The ultrastructure and calcium uptake rate of the cardiac sarcoplasmic reticulum (SR) was quantatively compared between the ground squirrels (Citellus dauricus) in hibernating and non-hibernating season. (1) In our ultrastructural investigation, OsFeCN post-fixation method was used to enhance the staining of SR, which made the SR structure more recognizable. (2) The results of morphometrical analysis demonstrated that the volume density of SR and lipid droplet in the cardio-myocyte was significantly higher (P < 0.01) in the hibernating animal than in the summer active one, and the subcompartment of SR with this difference was non-junctional SR. (3) The cardiac SR from hibernating ground squirrels had a higher (P < 0.01) calcium uptake rate as measured by the absorbence of arsenazo-III Ca2+ indicator, than that from autumn active ones. Altogether, our results suggested that the function of SR in the uptake of cytosolic calcium was enhanced in hibernating season, which may play an important role in the cold tolerance of myocardium of a hibernator.

Animals↗
PubMed1994

Specific detection of Clostridium difficile toxin A gene sequences in clinical isolates.

The polymerase chain reaction (PCR) was used to specifically detect toxin A gene sequences of Clostridium difficile in DNA isolated from human faeces. A set of oligonucleotide primers derived from the non-repetitive region of the toxin A gene was developed to amplify a 634-bp DNA fragment. All 28 cytotoxic strains of C. difficile, previously characterized by a toxin B-PCR assay, were positive for the presence of toxin A gene sequences. No amplification products were obtained from DNAs extracted from non-toxigenic strains, strains of C. sordellii, or C. bifermentans. In addition, amplification of DNA extracted from C. difficile 8864, a strain which does not produce toxin A, resulted in multiple bands which probed negative for toxin A gene sequences. DNAs extracted from nine stool specimens which were positive for toxin B by the cytotoxicity assay and by the toxin B-PCR assay were also positive in this assay. Toxin A gene sequences were detected in DNAs obtained from 4/11 stool specimens which were negative by the toxin B cytotoxicity assay. These four specimens were from patients who had a history of relapses due to C. difficile-associated colitis, and whose stools had previously been found to be positive by the toxin B-PCR test despite no detectable toxin B in the specimens. These data indicate a comparable degree of clinical sensitivity between these two toxin-gene PCR-based assays. This rapid, sensitive and specific assay may be useful not only in the diagnosis of C. difficile infections, but also in molecular studies of the toxin A gene in C. difficile strains.

Bacterial Proteins↗
PubMed1994

Genotyping of Clostridium difficile isolates.

Arbitrarily primed polymerase chain reaction (AP-PCR) was used to genotype Clostridium difficile isolates from various sources. Four major molecular types were identified among strains from the American Type Culture Collection previously typed by serogroup and from isolates from patients at the University of California, Davis Medical Center, from a patient at a Utah institution, and from the environment. These groups contained subgroups that displayed, in addition to the common group bands, at least one unique band. Two strains isolated from patients at our institution had the same DNA banding patterns. These patients were hospitalized during the same period, raising the possibility of cross-infection through hospital contact or another common source. These results suggest that this AP-PCR approach will be useful in epidemiologic studies of C. difficile infections.

Base Sequence↗
PubMed1994

Fecal shedding of Clostridium difficile in dogs: a period prevalence survey in a veterinary medical teaching hospital.

The goal of this study was to determine the fecal prevalence of Clostridium difficile in dogs who were patients at a veterinary medical teaching hospital. Stool specimens collected from 152 dogs (in- and outpatients) were analyzed for the presence of C. difficile. An additional 42 stool specimens were collected and examined from dogs recently housed at local animal shelters. Following culture on selective medium, C. difficile was identified by a latex agglutination test, and the presence of the toxin A and B genes was determined individually by polymerase chain reaction. Clostridium difficile was isolated from the feces of 28 of the veterinary hospital patients (18.4%); isolates from 14 of these patients (50.0%) were toxigenic. Diarrhea was a clinical finding in 5 (35.7%) of the dogs carrying toxigenic isolates of C. difficile, whereas diarrhea was noted in only 2 of 14 dogs (14.3%) shedding nontoxigenic isolates. Three of 14 dogs (21.4%) shedding toxigenic isolates of C. difficile were receiving antibiotics at the time of stool collection, whereas 5 of 14 dogs (37.5%) shedding nontoxigenic strains of C. difficile were receiving antibiotics. The carriage rate of C. difficile was significantly higher for animals categorized as inpatients of the veterinary hospital. The carriage rate also provided evidence for an increased risk for fecal shedding with increasing age. Clostridium difficile was not isolated from any of the 42 dogs recently housed at local animal shelters. This study confirms the presence of toxigenic C. difficile in dogs at a veterinary teaching hospital.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1993

Diagnosis and monitoring of Clostridium difficile infections with the polymerase chain reaction.

Toxigenic Clostridium difficile is the etiologic agent of pseudomembranous colitis. We have developed an assay system for the rapid direct detection of toxigenic C. difficile in human stool samples. After DNA extraction, polymerase chain reaction (PCR) amplification is undertaken with primers targeting specific sequences in the C. difficile 16S rRNA gene. Next, toxigenic strains of C. difficile are distinguished from nontoxigenic strains by PCR amplification of toxin A and/or B gene sequences. This study included 12 patients with C. difficile colitis, seven of whom had clinical relapses after discontinuation of vancomycin therapy. We detected toxigenic C. difficile in stools from four (57%) of these seven patients before relapse--at a time when no toxin B was detectable in stools and results of anaerobic culture were negative. The PCR assay is 100-fold more sensitive than anaerobic culture methods. The course of the infection in one patient (both during and after therapy) was monitored by the PCR technique. The multigene analysis approach permitted the detection of colonization with a nontoxigenic strain when this patient's relapses had cleared. This clinically applicable assay allows earlier detection of infection with toxigenic C. difficile. The result is more timely therapeutic intervention.

Aged↗
PubMed1993

Specific detection of toxigenic strains of Clostridium difficile in stool specimens.

Clostridium difficile is the infectious agent responsible for antibiotic-associated colitis. We report the use of the polymerase chain reaction technique to identify toxigenic strains of C. difficile in human stool specimens. A set of primers based on the nucleotide sequence of the toxin B gene, which amplified a 399-bp fragment from isolates producing toxin B, was designed. We examined 28 known toxigenic strains, which were all positive by this assay. DNAs from the nontoxigenic strains examined and from strains of Clostridium sordellii and C. bifermentans were not amplified with these primers. The sensitivity of this assay allowed us to identify as little as 10% toxigenic C. difficile cells in the presence of 90% nontoxigenic cells and to detect the toxin B gene in 1 pg of DNA from a toxigenic strain. DNAs extracted from 18 clinical stool specimens that were positive for toxin B by the tissue culture cytotoxicity assay were also positive by this assay. In addition, we detected toxin B sequences in DNA from 2 of 18 stool specimens that were negative for toxin B by the cytotoxicity assay. These two stool specimens were from patients who had a clinical pattern of colitis that was compatible with C. difficile causation. This rapid, sensitive assay will be useful for specific identification of toxigenic C. difficile and for revealing cases that are undetected by analysis of fecal samples for toxin B alone.

Bacterial Proteins↗
PubMed1990

Study on sperm function in men long after cessation of gossypol treatment.

Sperm function was assessed in 19 men 3-10 years after cessation of gossypol treatment and 2-9 years after recovery of normal sperm density. Nineteen normal fertile men of similar age served as the controls. The zona-free hamster egg-sperm penetration assay (SPA) revealed a highly significant difference (P less than 0.01) in the penetration rates between the treated and the control groups. Hormone assays indicated that there were no significant differences in circulating levels of luteinizing hormone (LH) and testosterone (T) between the two groups, but the follicle stimulating hormone (FSH) level of the treated group was significantly higher than that of the controls (P less than 0.05). The results showed that sperm function in the treated group was lower than that in the control, which may be a result of persistent gossypol-mediated damage to the testes.

Adult↗
PubMed1990

[Experimental study on anti-acute leukemia with Chinese traditional drugs].

This paper deals with the experimental study on L7212 leukemic model of mice with Chinese medicine Liushenwan, Zhijinding and Xihuangwan for the treatment. This study proved that these drugs possessed the effect of inhibiting and killing L7212 leukemic cells of the experimental leukemic mice (P less than 0.05-0.001). They affected the S stage of the cell multiplication cycle time mainly (P less than 0.01). They could relieve the infiltration of leukemic cells in the liver and spleen of L7212 mice (P less than 0.001) and obviously prolong the survival time of the mice (P less than 0.01-0.001).

Animals↗
PubMed1989

A NosA-specific bacteriophage can be used to select denitrification-defective mutants of Pseudomonas stutzeri.

phi PS5, a double-stranded DNA bacteriophage of Pseudomonas stutzeri JM604 that adsorbs specifically to the outer-membrane protein NosA, was isolated from stagnant irrigation ditch water. Mutant strains that do not produce NosA are resistant to phi PS5 and cannot grow anaerobically with N2O as the sole electron acceptor. phi PS5 did not adsorb to nosA mutants and adsorption to the wild-type strain was reduced when cells were grown with a high concentration of copper, a condition that represses the synthesis of NosA. The isolation of spontaneous phi PS5-resistant mutants yielded strains that were clearly defective in growth on N2O at about a 10% incidence. About half of these strains could respire N2O when supplied with a high concentration of exogenous copper.

Adsorption↗