Comparison of restriction endonuclease analysis, ribotyping, and pulsed-field gel electrophoresis for molecular differentiation of Clostridium difficile strains

Low prevalence of nosocomial Clostridium difficile transmission, as determined by comparison of arbitrarily primed PCR and epidemiological data

An increased prevalence of patients with C. difficile-associated diarrhoea in a hospital setting suggested the possible existence of an endemic occurrence. A study was therefore designed to determine clonal relatedness among 173 isolates of C. difficile, collected consecutively during 1995 from 147 patients (89 inpatients and 58 outpatients) and to estimate the probability of nosocomial transmission. Arbitrarily primed PCR (AP-PCR) with three different primers, AP1, AP2 and CLD1, was used for fingerprinting and identified 21, 92 and 70 types, respectively. Overall DNA analysis of the combined AP-PCR data yielded 140 types, of which 130 were unique, whereas 10 types occurred repeatedly in 36 isolates from 33 patients; seven isolates were non-typeable by one of the primers. Epidemiological data confirmed that in eight of the 33 patients there was a high probability of nosocomial transmission. Despite a high prevalence of C. difficile among hospitalized patients, a low frequency of nosocomial transmission was suggested by high resolution molecular typing of bacterial isolates in conjunction with traditional epidemiological methods.

Clostridium difficile infection of a prosthetic joint presenting 12 months after antibiotic-associated diarrhoea

Clostridium difficile is a common cause of antibiotic-associated diarrhoea, but it rarely causes extra-colonic disease. An 83-year-old woman who developed culture-positive C. difficile-associated diarrhoea following pneumonia and a total hip replacement was treated successfully with oral metronidazole therapy. She was readmitted 12 months later for revision of the hip prosthesis because of increasing pain. At surgery an abscess associated with the prosthesis was discovered. Culture of the pus grew C. difficile. When the surgical isolate and the cryopreserved faecal isolates were compared using Pulsed Field Gel Electrophoresis (PFGE), an identical banding pattern was observed. This case extends the clinical spectrum of C. difficile infection by documenting a prolonged interval between the initial infection, and diagnosis of the prosthetic joint infection. The importance of molecular typing to show strain relatedness is demonstrated.

Subtyping of Haemophilus influenzae strains by pulsed-field gel electrophoresis

A total of 200 isolates of Haemophilus influenzae were analyzed by serotyping, biotyping, and pulsed-field gel electrophoresis (PFGE). A total of 178 epidemiologically unrelated strains of H. influenzae demonstrated a variety of genome patterns by PFGE, and 165 genotypes were thus obtained in this study. PFGE typing proved to have a much stronger discriminatory power than either serotyping or biotyping. Six serotype b strains were all classified into discrete genotypes. A PFGE analysis of 18 strains obtained from the nasopharynx, blood, and cerebrospinal fluid of patients with meningitis also supported the hypothesis that invasive H. influenzae disseminates from the nasopharynx to the bloodstream and then subsequently to other body sites. PFGE typing of 10 other strains isolated from household contacts of patients with H. influenzae infection revealed that the strain that caused the H. influenzae infection often colonized the nasopharynges of household contacts. Our findings suggest that PFGE analysis is useful for the epidemiological study of H. influenzae infection, even when the invasive disease is caused by serotype b strains.

Short protocol for pulsed field gel electrophoresis of a variety of Clostridia species

While pulsed field gel electrophoresis has become an important tool for genotyping of bacteria, one of its drawbacks is that standard methods are rather time-consuming. In order to overcome this problem, shortened procedures for DNA preparation have been developed for some bacterial species. The aim of this study was to examine if a short procedure used for pulsed field gel electrophoresis of Clostridium botulinum could be applied to other Clostridia species. For this, the protocol was modified and used to prepare the DNA of 34 strains of 25 different Clostridia species. In contrast to a standard procedure, which takes at least 5 days from DNA extraction to completion of the electrophoresis, this protocol yielded results within 2 days. In order to directly compare the results of the short protocol with those of the standard, long procedure, parallel DNA preparations were performed using both methods and the two DNA samples thus obtained per strain were then run on the same gel. Briefly, the procedure was as follows. After embedding the bacterial cells in agarose, the agarose blocks were incubated for 1 h in lysis solution containing lysozyme, mutanolysin, lysostaphin and RNase. This was followed by a 1-h proteinase K treatment. Then, slices were cut from the agarose blocks and washed for 15 min in TE buffer, these washes were repeated four times with fresh TE. After a 2-h restriction with SmaI, electrophoresis was carried out overnight.

Biodiversity of Clostridium botulinum type E strains isolated from fish and fishery products

The genetic biodiversity of Clostridium botulinum type E strains was studied by pulsed-field gel electrophoresis (PFGE) with two macrorestriction enzymes (SmaI-XmaI and XhoI) and by randomly amplified polymorphic DNA (RAPD) analysis with two primers (OPJ 6 and OPJ 13) to characterize 67 Finnish isolates from fresh fish and fishery products, 15 German isolates from farmed fish, and 10 isolates of North American or North Atlantic origin derived mainly from different types of seafood. The effects of fish species, processing, and geographical origin on the epidemiology of the isolates were evaluated. Cluster analysis based on macrorestriction profiles was performed to study the genetic relationships of the isolates. PFGE and RAPD analyses were combined and resulted in the identification of 62 different subtypes among the 92 type E isolates analyzed. High genetic biodiversity among the isolates was observed regardless of their source. Finnish and North American or North Atlantic isolates did not form distinctly discernible clusters, in contrast with the genetically homogeneous group of German isolates. On the other hand, indistinguishable or closely related genetic profiles among epidemiologically unrelated samples were detected. It was concluded that the high genetic variation was probably a result of a lack of strong selection factors that would influence the evolution of type E. The wide genetic biodiversity observed among type E isolates indicates the value of DNA-based typing methods as a tool in contamination studies in the food industry and in investigations of botulism outbreaks.

Ribotyping as an identification tool for Clostridium botulinum strains causing human botulism

Ribotyping was used for characterisation of 68 Clostridium botulinum strains and five related Clostridium species to determine the applicability of this method for identification of species causing human botulism. Thirteen restriction enzymes were initially tested for suitability for ribotyping of C. botulinum, of which EcoRI and HindIII were selected. Both enzymes clearly differentiated between proteolytic (group I) and a nonproteolytic (group II) strains of C. botulinum, and can be recommended for Group/species identification. Using a commercial software package (GelCompar), a numerical analysis of the discriminatory abilities of EcoRI and HindIII ribotyping within and between the two C. botulinum groups was performed. EcoRI had the higher discriminatory index (0.982), but the ribopatterns generated with group II strains were partly muddled and difficult to interpret. All HindIII ribopatterns were easy to analyse and the discriminatory index for all strains was almost equally high (0.954), whereas this enzyme did not discriminate well between group I isolates. The Clostridium strains diverged at 35+/-13% (mean+/-standard deviation) Dice similarity in dendrograms based on cluster analysis of the ribotyping results. These findings are in good agreement with taxonomical ribotyping studies with other bacterial genera, indicating that ribotyping is a highly suitable method for C. botulinum species identification.

Prevalence of Clostridium botulinum in Finnish trout farms: pulsed-field gel electrophoresis typing reveals extensive genetic diversity among type E isolates

The distribution of Clostridium botulinum serotypes A, B, E, and F in Finnish trout farms was examined. A total of 333 samples were tested with a neurotoxin-specific PCR assay. C. botulinum type E was found in 68% of the farm sediment samples, in 15% of the fish intestinal samples, and in 5% of the fish skin samples. No other serotypes were found. The spore counts determined by the most-probable-number method were considerably higher for the sediments than for the fish intestines and skin; the average values were 2,020, 166, and 310 C. botulinum type E spores kg-1, respectively. The contamination rates in traditional freshwater ponds and marine net cages were high, but in concrete ponds equipped with sediment suction devices the contamination rates were significantly lower. Pulsed-field gel electrophoresis (PFGE) typing of 42 isolates obtained in this survey and 12 North American reference strains generated 28 pulsotypes upon visual inspection, suggesting that there was extensive genetic diversity and that the discriminatory power of PFGE typing in C. botulinum type E was high. A numerical analysis of SmaI-XmaI macrorestriction profiles confirmed these findings, as it divided the 54 isolates into 15 clusters at a similarity level of 76%. For this material, this level of similarity corresponded to a three-band difference in the macrorestriction profiles, which indicated that there is no genotypic proof of a close epidemiological relationship among the clusters.

Comparison of restriction enzyme analysis, arbitrarily primed PCR, and protein profile analysis typing for epidemiologic investigation of an ongoing Clostridium difficile outbreak

During an outbreak of diarrhea in a general hospital in 1992, 166 Clostridium difficile isolates from 102 patients were typed by restriction enzyme analysis (REA), arbitrarily primed PCR (AP-PCR), and protein profile analysis (PP) techniques. A total of 18 types and 5 subtypes were identified by REA, 32 types were identified by AP-PCR, and 9 types were identified by PP. Analysis of the data indicated the presence of a predominant strain among 76, 75, and 84% of the isolates by REA, AP-PCR, and PP, respectively. Subsequently, 45 C. difficile isolates which had been collected in 1990 from 33 patients in the same hospital following a significant increase in the number of cases of diarrhea caused by C. difficile were studied by REA, AP-PCR, and PP typing techniques. Thirteen types and one subtype were identified by REA, 12 types were identified by AP-PCR, and 5 types were identified by PP. As with the isolates from 1992, a dominant strain was identified. This strain was represented by 53, 64, and 70% of the total number of isolates when the strains were typed by REA, AP-PCR, and PP, respectively. Every isolate (210 of 211) from both 1990 and 1992 that was available for typing was typeable by all three methods. Furthermore, the same dominant strain was identified in both 1990 and 1992 by each method. This study demonstrates that each of the three typing methods can be useful in epidemiologic investigations of C. difficile outbreaks and that one strain can be dominant in an institution over a number of years.

Genomic analysis of Clostridium botulinum group II by pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) was optimized for genomic analyses of Clostridium botulinum (non-proteolytic) group II. DNA degradation problems caused by extracellular DNases were overcome by fixation of cells with formaldehyde prior to isolation. A rapid (4-h) in situ DNA isolation method was also assessed and gave indistinguishable results. Genomic DNA from 21 strains of various geographical and temporal origins was digested with 15 rare-cutting restriction enzymes. Of these, ApaI, MluI, NruI, SmaI, and XhoI gave the most revealing PFGE patterns, enabling strain differentiation. Twenty strains yielded PFGE patterns containing 13 pulsotypes. From summation of MluI, SmaI, and XhoI restriction fragments, the genome size of C. botulinum group II was estimated to be 3.6 to 4.1 Mb (mean +/- standard deviation = 3,890 +/- 170 kb). The results substantiate that after problems due to DNases are overcome, PFGE analysis will be a reproducible and highly discriminating epidemiological method for studying C. botulinum group II at the molecular level.

Nosocomial outbreak of Clostridium difficile diarrhea in a pediatric service

An outbreak of nosocomial diarrhea that occurred in a pediatric orthopedic service between 1 December 1993 and 15 April 1994 is reported. A total of 37 patients (mean age, 9.6 years; range, 2 months-19.3 years) were involved in the outbreak, including six patients with bacteriologically documented Clostridium difficile infection. A multivariate analysis identified lincomycin treatment for at least three days as the only significant risk factor. Stool samples from four asymptomatic patients were also positive for Clostridium difficile and its cytotoxins. Isolates from all patients belonged to serogroup C, were highly resistant to lincomycin, and exhibited the same restriction pattern by pulsed-field gel electrophoresis. The outbreak ended after treatment with lincomycin was discontinued and hygiene control measures were implemented.

Molecular diagnostics of infectious diseases

Over the past several years, the development and application of molecular diagnostic techniques has initiated a revolution in the diagnosis and monitoring of infectious diseases. Microbial phenotypic characteristics, such as protein, bacteriophage, and chromatographic profiles, as well as biotyping and susceptibility testing, are used in most routine laboratories for identification and differentiation. Nucleic acid techniques, such as plasmid profiling, various methods for generating restriction fragment length polymorphisms, and the polymerase chain reaction (PCR), are making increasing inroads into clinical laboratories. PCR-based systems to detect the etiologic agents of disease directly from clinical samples, without the need for culture, have been useful in rapid detection of unculturable or fastidious microorganisms. Additionally, sequence analysis of amplified microbial DNA allows for identification and better characterization of the pathogen. Subspecies variation, identified by various techniques, has been shown to be important in the prognosis of certain diseases. Other important advances include the determination of viral load and the direct detection of genes or gene mutations responsible for drug resistance. Increased use of automation and user-friendly software makes these technologies more widely available. In all, the detection of infectious agents at the nucleic acid level represents a true synthesis of clinical chemistry and clinical microbiology techniques.

PCR ribotyping and arbitrarily primed PCR for the comparison of enterotoxigenic Bacteroides fragilis strains from two Polish university hospitals

OBJECTIVE: To study the clinical incidence and possible clonal relatedness of enterotoxigenic strains of Bacteroides fragilis among pediatric and adult patients in two Polish university hospitals. METHODS: Fecal samples from 201 adults and 131 infants (with or without diarrhea) and vaginal samples from 100 pregnant women nursed in two Polish university hospitals were analyzed with respect to carriage of enterotoxin-producing Bacteroides fragilis (ETBF). This putative pathogen was identified by cultivation and subsequent cytopathogenicity testing of culture supernatants on HT/29 C1 cells. RESULTS AND DISCUSSION: Two ETBF strains were isolated from childrens' feces; two additional strains were isolated from adults, and from the vaginal samples only a single strain was isolated. One strain (W2) was isolated from a child with diarrhea. These incidence figures, the fact that all ETBF isolates were shown to produce strongly differing amounts of the cytotoxin, and the genetic unrelatedness of the strains as demonstrated by two different PCR-mediated DNA typing procedures, indicates that clonal spread of ETBF is presently not a clinical problem in these hospitals. It was shown that PCR-mediated ribotyping and arbitrarily primed PCR can be applied with success to study the epidemiology of ETBF.

Arbitrary primed PCR rules out Clostridium difficile cross-infection among patients in a haematology unit

Eight out of 20 (40%) patients with haematological malignancies hospitalized in the same unit of our hospital from 24 January to 24 April 1995, suffered from diarrhoea due to Clostridium difficile. The C. difficile isolates were characterized by serotyping and by arbitrary primed polymerase chain reaction (AP-PCR) using three different 10-mer oligonucleotides. It was found by serotyping that five patients had non-typeable isolates and three had serogroup H isolates. The AP-PCR typed all the isolates and yielded various patterns suggesting that there had been no cross-transmission between the patients. Control faecal sample cultures showed that two patients were still carrying the same isolates after specific treatment with vancomycin or metronidazole, and that one patient had acquired an isolate with a new AP-PCR type. AP-PCR was found to be a rapid, effective discriminative method for the immediate epidemiological tracking of hospital-acquired infections due to C difficile.

Genotyping of outbreak-related and sporadic isolates of Clostridium difficile belonging to serogroup C

Serogroup C of Clostridium difficile is the serogroup most frequently related to outbreaks. Fifty-six toxigenic serogroup C isolates of C. difficile were genotyped by ribotyping PCR (ribo-PCR), random amplified polymorphic DNA (RAPD) assay, and pulsed-field gel electrophoresis (PFGE). Thirty-five of the 56 isolates were recovered from four unrelated outbreaks (Belgium, 1987, 1992, and 1995; France, 1992 to 1993) 7 derived from a spatiotemporal cluster in Cotonou, Benin (1992), and 14 were sporadic isolates. The serogroup C reference strain, also isolated during an outbreak (Belgium, 1983), was genotyped too. Ribo-PCR, the RAPD assay, and PFGE generated 2, 5, and 11 major genotypes, respectively. Combination of the three methods finally yielded 13 general types, although ribo-PCR did not play any role in enhancing resolution. Three general types were recovered from all the isolates from the five outbreaks and the cluster, with two types being predominant. The 14 sporadic serogroup C isolates were divided into 11 overall genotypes. These results indicate that genotyping methods, and more particularly the combination of the RAPD assay and PFGE, can resolve genetic diversity within toxigenic, serogroup C C. difficile strains. Also, this study suggests that outbreak-related serogroup C strains are limited to a few genetically stable and apparently very widely (internationally and intercontinentally) distributed genotypes.

Relapses or reinfections: analysis of a case of Clostridium difficile-associated colitis by two typing systems

Immunoblotting and pulsed-field gel electrophoresis of Clostridium difficile isolates were employed to differentiate reinfection by a newly acquired strain from relapse by an original strain in a 10-year-old patient with four episodes of C. difficile-associated colitis. Immunoblot typing demonstrated subserogroup K-1 of serogroup K for the first and second organisms, subserogroup A-1 of serogroup A for the third organism, and subserogroup G-4 of serogroup G for the fourth organism. PFGE analysis revealed consistent results with immunoblot analysis except that the strains from the fourth episode, whose DNA constantly degraded, were nontypable by this method. Five separate isolates of C. difficile from a specimen of each episode showed identical PFGE patterns, indicating that infections of multiple strains probably did not occur in this patient. These typing results suggested that the second episode after a 17-day course of vancomycin therapy represented a relapse by the strain causing the first episode, and that the third and fourth episodes after tapering vancomycin therapy were reinfections by other strains. Both immunoblot and PFGE typing systems are promising tools for analyzing recurrence of C. difficile infection.

Use of in-house studies of molecular epidemiology and full species identification for controlling spread of vancomycin-resistant Enterococcus faecalis isolates

Infection with multidrug-resistant (MDR) organisms is a major clinical challenge, and few, if any, therapeutic options remain available. Increasingly, infection control measures have taken on greater importance in preventing the nosocomial transmission of MDR organisms. During December 1994 and January 1995, we identified a cluster of vancomycin-resistant Enterococcus faecalis isolates involving 16 patients situated in different areas of our university-affiliated teaching hospital. Initial review of laboratory requisition forms for the patients' locations revealed no common association, suggesting that the occurrence was not due to horizontal spread. However, using genomic DNA extraction, restriction enzyme analysis, and gel electrophoresis, we found that 12 patients were infected with isolates originating from a single clone, 2 other patients were infected with isolates from a different clone, and the remaining 2 patients were infected with unique strains. Because the typing data suggested nosocomial spread, chart review was undertaken to determine a possible common exposure source. With three exceptions, clonal isolates were linked to patient movement between surgical floors, intensive care units, and a rehabilitation unit. A detailed review of patient records revealing the association would not have been performed without realization of clonality. Thus, the data demonstrate the utility of genomic typing for epidemiological purposes. In turn, targeted infection control measures that halted the spread of the potentially lethal MDR pathogen were instituted.

Enzyme electrophoresis combined with serogrouping for improved differentiation of Clostridium difficile strains

We used enzyme electrophoresis to study a set of epidemiologically related and unrelated isolates of Clostridium difficile. The 53 strains belonged to the most frequent serogroups (A1, C, G, H and K). Nine electrophoretic profiles were defined on the basis of five enzymes, and two were characteristic of a single strain. Each serogroup was resolved into two or three different enzyme patterns. By combining the two methods we were able to resolve the strains into 12 types. There was an excellent correlation between enzyme electrophoresis and serogrouping data. This method may be of use in investigating nosocomial transmission.

Comparison of PCR-based approaches to molecular epidemiologic analysis of Clostridium difficile

Representative isolates of the 10 serogroups of Clostridium difficile and 39 clinical isolates (30 toxigenic and 9 nontoxigenic), including 5 isolates from a confirmed nosocomial outbreak, were analyzed by using two previously described arbitrary-primer PCR (AP-PCR) molecular typing methodologies (AP-PG05 and AP-ARB11) and PCR ribotyping. The two AP-PCR methods investigated gave comparable results; AP-PG05 and AP-ARB11 identified 8 and 7 groups among the serogroup isolates and classified the clinical isolates into 21 and 20 distinct groups, respectively. PCR ribotyping also identified 8 unique groups among the serogroup isolates but classified the clinical isolates into 23 groups. In addition, when results obtained by the PCR methods were compared with typing data generated by pulsed-field gel electrophoresis (PFGE), PCR ribotyping and PFGE were found to be in agreement for 83% (29 of 35) of isolates typeable by both techniques while AP-PG05 was in agreement with PFGE for 60% (20 of 33) and AP-ARB11 was in agreement with PFGE for only 44% (17 of 36). These results indicate that PCR ribotyping is a more discriminatory approach than AP-PCR for typing C. difficile and, furthermore, that this technique generates results that are in higher concordance with those obtained by using an established method for differentiating isolates of this organism on a molecular level than are results generated by using AP-PCR.

Comparative usefulness of ribotyping, exotoxin A genotyping, and SalI restriction fragment length polymorphism analysis for Pseudomonas aeruginosa lineage assessment

Ribotyping, exotoxin A genotyping (EAGP), and restriction fragment length polymorphism (RFLP) analysis of total DNA with SalI (SalI RFLP) were compared for intraspecies discrimination of 93 Pseudomonas aeruginosa isolates. Type-ability of all methods was 100% and the results of typing with each method remained unchanged during laboratory manipulation. Clonal groups defined with each molecular method were largely coincident and, in those cases where inconsistencies were detected, isolates were analyzed by transverse alternating field gel electrophoresis (TAFE) and arbitrarily primed polymerase chain reaction (AP-PCR). SalI RFLP analysis was highly discriminative so as to distinguish unrelated isolates of close lineage. However, it was not a good method to identify isolates of unrelated lineage because SalI RFLP appeared to be subjected to convergent evolution. The index of discrimination suggested by Hunter and Gaston was determined to assess the discriminatory power of the molecular methods utilized either alone or in several combinations. Combined use of ribotyping and SalI RFLP analysis reached the highest index of discrimination (0.982) and proved to be a very valuable tool for epidemiological differentiation of P. aeruginosa isolates.

Clinical and molecular epidemiology of sporadic and clustered cases of nosocomial Clostridium difficile diarrhea

PURPOSE

A prospective clinical and molecular epidemiologic study was conducted to define the frequency of nosocomial Clostridium difficile patient-to-patient transmission in an urban tertiary referral hospital.

PATIENTS AND METHODS

Over a 6-month period, environmental cultures for C difficile were obtained from patients with new positive stool cytotoxin assay (index cases); stool samples were obtained from selected patient contacts (the roommate, occupants of adjacent rooms, and the patient occupying the index room after discharge of the index case); and hand cultures were obtained from personnel contacts. C difficile isolates were analyzed by pulse-field gel electrophoresis (PFGE) or, for isolates that were nontypeable by PFGE, by restriction enzyme analysis.

RESULTS

During the study period, we identified 98 index cases of C difficile toxin-associated diarrhea, including focal outbreaks on two wards totaling 26 cases within a 2-month interval. Environmental contamination was detected at > or = 1 sites in 58% of rooms and often involved wide dispersed areas. Among 99 prospectively identified patient contacts, C difficile was cultured from the stool of 31 (31%), including 12 with diarrhea and 19 who were asymptomatic. C difficile was cultured from the hands of 10 (14%) of 73 personnel. Molecular analysis resolved 31 typing profiles among the index isolates; the most common profile (designated strain D1) was represented by 30 isolates. Among the isolates from patient contacts, 5 of 12 from symptomatic contacts matched the corresponding index isolate, and only 1 of 19 from asymptomatically colonized contacts matched. Transmission to personnel or patient contacts of the strain cultured from the corresponding index case was correlated strongly with the intensity of environmental contamination. Strain D1 was frequently represented among isolates associated with heavy environmental contamination, with personnel carriage, and with development of symptomatic illness among prospectively identified contacts.

CONCLUSIONS

Intense environmental contamination and transmission to close personnel and patient contacts represented coordinated properties of an individual epidemic strain. For most epidemiologically linked contacts, positive cultures for C difficile did not result from transmission from the presumed index case.

Clostridium difficile infection

The spore-forming anaerobe Clostridium difficile has become a serious enteropathogen. Changes in the composition of natural intestinal flora, mainly due to antibiotic therapy, permit its colonization of, and multiplication in, the colon. The disease is caused by (entero)toxin A and (cyto)toxin B, and infection ranges from asymptomatic carrier state and mild diarrhea to pseudomembranous colitis. The clinical diagnosis is made by observing inflammatory, sometimes bloody, diarrhea and by the colonoscopic detection of epithelial necrosis, ulceration, and, in the advanced state, pseudomembrane formation. The laboratory supports the diagnosis by detecting toxin A and/or B by an enzyme-linked immunoassay with high specificity, but sometimes less sensitivity than with the cytotoxin assay in tissue culture cells. Fecal leukocytes or fecal lactoferrin may be found. Culture for the isolation and identification of toxigenic C. difficile is time consuming but necessary for epidemiological studies. Polymerase chain reaction (PCR) tests have been tested for detection of the toxin B gene directly in stool. Therapy consists of stopping all systemic antibiotic treatment and the use of oral metronidazole or vancomycin. There may be more relapses after vancomycin therapy, and the increasing vancomycin resistance of Enterococcus is worrisome. Prevention, especially of nosocomial spread, requires isolation and enforced handwashing. For epidemiological studies, the bacteria can be typed by molecular DNA analyses, including PCR, protein electrophoresis, and immunological tests.

Clostridium difficile-associated diarrhea and colitis

OBJECTIVES

To review and summarize the status of diagnosis, epidemiology, infection control, and treatment of Clostridium difficile-associated disease (CDAD).

DIAGNOSIS

A case definition of CDAD should include the presence of symptoms (usually diarrhea) and at least one of the following positive tests: endoscopy revealing pseudomembranes, stool cytotoxicity test for toxin B, stool enzyme immunoassay for toxin A or B, or stool culture for C difficile (preferably with confirmation of organism toxicity if a direct stool toxin test is negative or not done). Testing of asymptomatic patients, including those who are asymptomatic after treatment, is not recommended other than for epidemiologic purposes. Lower gastrointestinal endoscopy is the only diagnostic test for pseudomembranous colitis, but it is expensive, invasive, and insensitive (51% to 55%) for the diagnosis of CDAD. Stool culture is the most sensitive laboratory test currently in clinical use, but it is not as specific as the cell cytotoxicity assay.

EPIDEMIOLOGY

C difficile is the most frequently identified cause of nosocomial diarrhea. The majority of C difficile infections are acquired nosocomially, and most patients remain asymptomatic following acquisition. Antimicrobial exposure is the greatest risk factor for patients, especially clindamycin, cephalosporins, and penicillins, although virtually every antimicrobial has been implicated. Cases of CDAD unassociated with prior antimicrobial or antineoplastic use are very rare. Hands of personnel, as well as a variety of environmental sites within institutions, have been found to be contaminated with C difficile, which can persist as spores for many months. Contaminated commodes, bathing tubs, and electronic thermometers have been implicated as sources of C difficile. Symptomatic and asymptomatic infected patients are the major reservoirs and sources for environmental contamination. Both genotypic and phenotypic typing systems for C difficile are available and have enhanced epidemiologic investigation greatly.

INFECTION CONTROL

Successful infection control measures designed to prevent horizontal transmission include the use of gloves in handling body substances and replacement of electronic thermometers with disposable devices. Isolation, cohorting, handwashing, environmental disinfection, and treatment of asymptomatic carriers are recommended practices for which convincing data of efficacy are not available. The most successful control measure directed at reduction in symptomatic disease has been antimicrobial restriction.

TREATMENT

Treatment of symptomatic (but not asymptomatic) patients with metronidazole or vancomycin for 10 days is effective; metronidazole may be preferred to reduce risk of vancomycin resistance among other organisms in hospitals. Recurrence of symptoms occurs in 7% to 20% of patients and is due to both relapse and reinfection. Over 90% of first recurrences can be treated successfully in the same manner as initial cases. Combination treatment with vancomycin plus rifampin or the addition orally of the yeast Saccharomyces boulardii to vancomycin or metronidazole treatment has been shown to prevent subsequent diarrhea in patients with recurrent disease.

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.

PCR ribotyping and arbitrarily primed PCR for typing strains of Clostridium difficile from a Polish maternity hospital

Detection of the source of Clostridium difficile strains is of importance for the control of the nosocomial spread of this microorganism. For this purpose, vaginal and rectal swabs from 183 mothers, duplicate fecal samples (taken on days 1 and 4 after birth) from 183 neonates, and 94 environmental samples were cultured for C. difficile. The microorganism was never detected in the meconium obtained on day 1 after birth. On the other hand, an incidence of 17% C. difficile positivity was noted in the fecal samples obtained on day 4 after birth. Forty-two percent of the 31 colonized neonates had been delivered with complications. The bacteria were never encountered in the rectal swabs of the mothers, and C. difficile was identified in only one vaginal swab. In contrast, 13% of the environmental samples were positive for C. difficile. No major difference was encountered between patient and environmental isolates with respect to toxigenicity (58 to 65% toxigenic isolates). All strains were subsequently typed by PCR amplification of the 16S-23S ribosomal intergenic spacer regions and by arbitrarily primed PCR (AP-PCR) with different primers and combinations thereof. All environmental isolates and 11 of 31 neonatal strains were of a single type. The vaginal strain was unique, and among the maternity ward- and neonate-related isolates, only two additional AP-PCR types were identified. When a collection of C. difficile strains from patients hospitalized in other institutions and suffering from antibiotic-associated diarrhea or pseudomembranous colitis was analyzed in a similar manner, it appeared that the strain from the maternity ward was unique. The other strain commonly encountered among the neonates was also identified frequently among the isolates from patients with antibiotic-associated diarrhea or pseudomembranous colitis, indicating its general occurrence. On the basis of both epidemiological studies and PCR-mediated genotyping, it was shown that the environment and not the birth canal is the major source of C. difficile acquisition by neonates in this maternity hospital setting. Furthermore, AP-PCR appears to be a fast and useful method for epidemiologically relevant typing of C. difficile isolates.

Use of pulsed-field gel electrophoresis for epidemiological study of Escherichia coli O157:H7 during a food-borne outbreak

Food and patient isolates from an Escherichia coli O157:H7 outbreak associated with undercooked ground beef were characterized by pulsed-field gel electrophoresis and Shiga-like toxin genotype. Pulsed-field gel electrophoresis confirmed the epidemiologically implicated source of the two-state outbreak and differentiated between outbreak and sporadic strains.