Molecular epidemiologic analysis of Vibrio cholerae O1 isolates by pulsed-field gel electrophoresis

Vibrio cholerae O1 El Tor strains linked to global cholera show region-specific patterns by pulsed-field gel electrophoresis

Vibrio cholerae O1 El Tor, causative agent of the ongoing seventh cholera pandemic, is native to the aquatic environment of the Ganges Delta, Bay of Bengal (GDBB). Recent studies traced pandemic strains to the GDBB and proposed global spread of cholera had occurred via intercontinental transmission. In the research presented here, NotI-digested genomic DNA extracted from V. cholerae O1 clinical and environmental strains isolated in Bangladesh during 20042014 was analyzed by pulsed-field gel electrophoresis (PFGE). Results of cluster analysis showed 94.67% of the V. cholerae strains belonged to clade A and included the majority of clinical strains of spatio-temporal origin and representing different cholera endemic foci. The rest of the strains were estuarine, all environmental strains from Mathbaria, Bangladesh, and occurred as singletons, clustered in clades B and C, or in the small clades D and E. Cluster analysis of the Bangladeshi strains and including 157 El Tor strains from thirteen countries in Asia, Africa, and the Americas revealed 85% of the total set of strains belonged to clade A, indicating all were related, yet did not form an homogeneous cluster. Overall, 15% of the global strains comprised multiple small clades or segregated as singletons. Three sub-clades could be discerned within the major clade A, reflecting distinct lineages of V. cholerae O1 El Tor associated with cholera in Asia, Africa, and the Americas. The presence in Asia and the Americas of non-pandemic V. cholerae O1 El Tor populations differing by PFGE and from strains associated with cholera globally suggests different ecotypes are resident in distant geographies.

Vibrio cholerae embraces two major evolutionary traits as revealed by targeted gene sequencing

Vibrio cholerae inhabits aquatic environments worldwide and has over 200 recognized serogroups classified by O-polysaccharide specificity. Here, we report that V. cholerae selects either of two genetic traits during their evolution. Sequencing of the specific gene locus MS6_A0927 revealed that 339 of 341 strains of V. cholerae and closely related Vibrio species originating from 34 countries over a century carried either metY (M) (~1,269 bp) or luxR-hchA (LH) (~1,600 bp) genes, and consequently those vibrios were separated into two clusters, M (45.4%) and LH (54.6%). Only two strains contained both M and LH in the same locus. Moreover, extensive polymorphisms in those genes were detected in M and LH with 79 and 46 sequence variations, respectively. V. cholerae O1 strains isolated from cholera outbreaks worldwide, and some non-O1 strains evolving from O1 via exchange of genes encoding cell surface polysaccharides possessed LH alleles. Analysis of polymorphisms in the gene locus implicated a high degree of genetic diversity and identical subpopulations among the V. cholerae species.

Antibiotic resistance and plasmid profiling of Vibrio spp. in tropical waters of Peninsular Malaysia

Vibrio species isolated from four different sampling stations in the west coast of Peninsular Malaysia were screened for their antimicrobial resistance and plasmid profiles. A total of 138 isolates belonging to 15 different species were identified. Vibrio campbellii, V. parahaemolyticus, V. harveyi, and V. tubiashii were found to predominance species at all stations. High incidence of erythromycin, ampicillin, and mecillinam resistance was observed among the Vibrio isolates. In contrast, resistance against aztreonam, cefepime, streptomycin, sulfamethoxazole, and sulfonamides was low. All the Vibrio isolates in this study were found to be susceptible to imipenem, norfloxacin, ofloxacin, chloramphenicol, trimethoprim/sulfamethoxazole, and oxytetracycline. Ninety-five percent of the Vibrio isolates were resistant to one or more different classes of antibiotic, and 20 different resistance antibiograms were identified. Thirty-two distinct plasmid profiles with molecular weight ranging from 2.2 to 24.8 kb were detected among the resistance isolates. This study showed that multidrug-resistant Vibrio spp. were common in the aquatic environments of west coast of Peninsular Malaysia.

Molecular tools in understanding the evolution of Vibrio cholerae

Vibrio cholerae, the etiological agent of cholera, has been a scourge for centuries. Cholera remains a serious health threat for developing countries and has been responsible for millions of deaths globally over the past 200 years. Identification of V. cholerae has been accomplished using a variety of methods, ranging from phenotypic strategies to DNA based molecular typing and currently whole genomic approaches. This array of methods has been adopted in epidemiological investigations, either singly or in the aggregate, and more recently for evolutionary analyses of V. cholerae. Because the new technologies have been developed at an ever increasing pace, this review of the range of fingerprinting strategies, their relative advantages and limitations, and cholera case studies was undertaken. The task was challenging, considering the vast amount of the information available. To assist the study, key references representative of several areas of research are provided with the intent to provide readers with a comprehensive view of recent advances in the molecular epidemiology of V. cholerae. Suggestions for ways to obviate many of the current limitations of typing techniques are also provided. In summary, a comparative report has been prepared that includes the range from traditional typing to whole genomic strategies.

Survivability and molecular variation in Vibrio cholerae from epidemic sites in China

The survival behaviour of Vibrio cholerae in cholera epidemics, together with its attributes of virulence-associated genes and molecular fingerprints, are significant for managing cholera epidemics. Here, we selected five strains representative of V. cholerae O1 and O139 involved in cholera events, examined their survival capacity in large volumes of water sampled from epidemic sites of a 2005 cholera outbreak, and determined virulence-associated genes and molecular subtype changes of the surviving isolates recovered. The five strains exhibited different survival capacities varying from 17 to 38 days. The virulence-associated genes of the surviving isolates remained unchanged, while their pulsotypes underwent slight variation. In particular, one waterway-isolated strain maintained virulence-associated genes and evolved to share the same pulsotype as patient strains, highlighting its role in the cholera outbreak. The strong survival capacity and molecular attributes of V. cholerae might account for its persistence in environmental waters and the long duration of the cholera outbreak, allowing effective control measures.

Genotypic characterization of Vibrio cholerae isolates using several DNA fingerprint techniques

Serious pandemics of cholera have occurred throughout the known history of mankind, especially in India, which is a motherland for cholera disease. For the last 20 years several DNA-based typing methods have been employed to study the clonal relatedness between Vibrio cholerae isolates irrespective of their geographical locations. Traditional typing methods, such as biochemical tests, phage typing, serotyping, biotyping and antimicrobial susceptibility tests, have produced reliable and informative data regarding V. cholerae for a long time. Gradually molecular typing techniques have taken the place of traditional typing methods because they produce the same results upon repeat testing of V. cholerae strain. In this article we focus on the discriminatory power of different DNA fingerprint techniques that are generally used to know the homogeneity and heterogeneity among different V. cholerae isolates.

Genotypic Characterization of Vibrio vulnificus Clinical Isolates in Korea

Objectives

Vibrio vunificus is known to cause septicemia and severe wound infections in patients with chronic liver diseases or an immuno-compromised condition. We carried out the molecular characterization of V. vulnificus isolates from human Vibrio septicemia cases based on pulsed-field gel electrophoresis (PFGE) using NotI and SfiI.

Methods and Results

PFGE was used to characterize a total of 78 strains from clinical cases after NotI or SfiI digestion. The geographical distribution of PFGE patterns for the strains from the southern part of Korea, a high-risk region for Vibrio septicemia, indicated that the isolates from southeastern Korea showed a comparatively higher degree of homology than those from southwestern Korea.

Conclusions

We report the genetic distribution of V. vulnficus isolated from Vibrio septicemia cases during 2000–2004 in Korea. This method has potential use as a subspecies-typing tool for V. vulnificus strains isolated from distant geographic regions.

Molecular evidence of cholera outbreak caused by a toxigenic Vibrio cholerae O1 El tor variant strain in Kelantan, Malaysia

A total of 20 Vibrio cholerae isolates were recovered for investigation from a cholera outbreak in Kelantan, Malaysia, that occurred between November and December 2009. All isolates were biochemically characterized as V. cholerae serogroup O1 Ogawa of the El Tor biotype. They were found to be resistant to multiple antibiotics, including tetracycline, erythromycin, sulfamethoxazole-trimethoprim, streptomycin, penicillin G, and polymyxin B, with 35% of the isolates being resistant to ampicillin. All isolates were sensitive to ciprofloxacin, norfloxacin, chloramphenicol, gentamicin, and kanamycin. Multiplex PCR analysis confirmed the biochemical identification and revealed the presence of virulence genes, viz., ace, zot, and ctxA, in all of the isolates. Interestingly, the sequencing of the ctxB gene showed that the outbreak strain harbored the classical cholera toxin gene and therefore belongs to the newly assigned El Tor variant biotype. Clonal analysis by pulsed-field gel electrophoresis demonstrated that a single clone of a V. cholerae strain was responsible for this outbreak. Thus, we present the first molecular evidence that the toxigenic V. cholerae O1 El Tor variant has invaded Malaysia, highlighting the need for continuous monitoring to facilitate early interventions against any potential epidemic by this biotype.

Comparison of different electrophoretic parameters of Pulse-Field Gel Electrophoresis for Vibrio cholerae subtyping

Molecular subtyping is used to distinguish pathogenic bacterial strains during epidemiological surveys of infectious diseases and the discovery of novel pathogens. There is a need to standardize protocols involving Pulse-Field Gel Electrophoresis (PFGE), a crucial method in molecular subtyping, to make inter-laboratory results comparable and information exchange possible. The PFGE pattern varies with electrophoretic parameters (EPs), so it is important to select the parameter that can distinguish the patterns better. To optimize EPs of PFGE for Vibrio cholerae, we analyzed 24 isolates of V. cholerae O1 biotype El Tor and 26 isolates of O139 by PFGE with Not|. We used four different EPs and compared the similarity coefficients from the four groups by Friedman test. Based on the principle that the electrophoretic parameter producing smaller similarity in the PFGE patterns has higher level of discriminatory power, the one producing the smallest similarity coefficients is considered to be optimal. This method could be applied to determine the optimal molecular subtyping protocol for other bacteria.

Vibrio cholerae strain typing and phylogeny study based on simple sequence repeats

Vibrio cholerae is the etiological agent of cholera. Its natural reservoir is the aquatic environment. To date, practical typing of V. cholerae is mainly serological and requires about 200 antisera. Simple sequence repeats (SSR), also termed VNTR (for variable number of tandem repeats), provide a source of high genomic polymorphism used in bacterial typing. Here we describe an SSR-based typing method that combines the variation in highly mutable SSR loci, with that of shorter, relatively more stable mononucleotide repeat (MNR) loci, for accurate and rapid typing of V. cholerae. In silico screening of the V. cholerae genome revealed thousands of perfect SSR tracts with an average frequency of one SSR every 152 bp. A panel of 32 V. cholerae strains, representing both clinical and environmental isolates, was tested for polymorphism in SSR loci. Two strategies were applied to identify SSR variation: polymorphism of SSR tracts longer than 12 bp (L-SSR) assessed by capillary fragment-size analysis and MNR polymorphism assessed by sequencing. The nine L-SSR loci tested were all polymorphic, displaying 2 to 13 alleles per locus. Sequence analysis of eight MNR-containing loci (MNR-multilocus sequence typing [MLST]) provided information on both variations in the MNR tract itself, and single nucleotide polymorphism (SNP) in their flanking sequences. Phylogenetic analysis of the combined SSR data showed a clear discrimination between the clinical strains belonging to O1 and O139 serogroups, and the environmental isolates. Furthermore, discrimination between 27 strains of the 32 strains was achieved. SSR-based typing methods combining L-SSR and MNR-MLST were found to be efficient for V. cholerae typing.

Molecular analysis of vibrio cholerae strains isolated in Malaysia: public health implications

The genetic diversity or clonality among Vibrio cholerae O1, O139 and non-O1/ non-O139 of clinical and environmental origin using ribotyping and PFGE was performed in order to ascertain the public health implications of the different genotypes circulating within the Malaysian environment. Using an in-house typing scheme, of the 214 strains included, 202 strains were isolated locally between 1992 and 1998, seven were obtained from Bangladesh and five were reference strains. Amongst the 176 El Tor O1 strains, 152 clinical strains demonstrated five ribotypes--E1a, E1b, E2a, E3 and E1c. E1b was the most predominant ribotype demonstrated by 84% of the El Tor O1 strains and was present in all years demonstrating that this strain was intrinsic to Malaysia. PFGE analysis of these strains demonstrated minimal variation amongst the 15 PFGE profiles obtained. Ribotpye E2a amongst five clinical and two environmental O1 strains, were from one location and had previously been reported in Indonesia and the Philippines, thus demonstrating strong evidence that these strains may have been imported into Malaysia. Among Vibrio cholerae O139 strains, 91.7% were of ribotype A1a similar to the original O139, while two others were of ribotype A1b and one of A1e, corresponding to ribotypes 1, 2 and 3 of Dalsgaard and colleagues' scheme for O139 strains. PFGE analysis demonstrated that 89% of ribotype A1a could be differentiated into three PFGE genotypes which were very closely related. The eight non-O1/non-O139 serogroup strains were heterogeneous in both ribotype and PFGE patterns.

DNA fingerprinting ofVibrio cholerae andAeromonas species by pulsed-field minigel electrophoresis

DNA molecules of Vibrio cholerae and Aeromonas species were prepared by incubating immobilized cells for 4 and 2 h, respectively, with a nonenzymatic solution that contains chemical reagents only (NDSUPlus). This method gave results as reproducible as the enzymatic one that uses proteinase K, and rendered DNA molecules suitable for fingerprinting by mini-CHEF electrophoresis. As rapid DNA separations at high electric field are achieved in mini-CHEF chamber with low heat evolution, DNA restriction fragments were separated in 5 h at 10 V/cm in a single resolution window. Then, fragment separations in three resolution windows were done in 15 h. This time is shorter than the one needed by the large CHEF chamber for resolving fragments in a single resolution window. Three windows permitted to include larger numbers of restriction fragments in the calculation of isolate similarities. Both sample preparation and mini-CHEF electrophoresis may represent an alternative for performing massive epidemiological studies of V. cholerae and Aeromonas species.

Molecular epidemiology and origin of cholera reemergence in Italy and Albania in the 1990s

In 1994 a cholera epidemic occurred in Italy and Albania after more than a decade of case absence. To investigate genotypic characteristics and the origin of the epidemic strains, 110 Vibrio cholerae O1 El Tor isolates from Italy and Albania were studied by randomly amplified polymorphic DNA analysis (RAPD), BglI ribotyping, and pulsed-field gel electrophoresis (PFGE) of genomic DNA. The Italian and Albanian strains were all ribotype 6 and their RAPD and PFGE patterns were identical as well. These findings indicated that the 1994 isolates belonged to the same clone and that the clone was part of the larger global spread of epidemic ribotype 6 strains, which started in southern Asia in 1990.

Establishment of a universal size standard strain for use with the PulseNet standardized pulsed-field gel electrophoresis protocols: converting the national databases to the new size standard

The PulseNet National Database, established by the Centers for Disease Control and Prevention in 1996, consists of pulsed-field gel electrophoresis (PFGE) patterns obtained from isolates of food-borne pathogens (currently Escherichia coli O157:H7, Salmonella, Shigella, and Listeria) and textual information about the isolates. Electronic images and accompanying text are submitted from over 60 U.S. public health and food regulatory agency laboratories. The PFGE patterns are generated according to highly standardized PFGE protocols. Normalization and accurate comparison of gel images require the use of a well-characterized size standard in at least three lanes of each gel. Originally, a well-characterized strain of each organism was chosen as the reference standard for that particular database. The increasing number of databases, difficulty in identifying an organism-specific standard for each database, the increased range of band sizes generated by the use of additional restriction endonucleases, and the maintenance of many different organism-specific strains encouraged us to search for a more versatile and universal DNA size marker. A Salmonella serotype Braenderup strain (H9812) was chosen as the universal size standard. This strain was subjected to rigorous testing in our laboratories to ensure that it met the desired criteria, including coverage of a wide range of DNA fragment sizes, even distribution of bands, and stability of the PFGE pattern. The strategy used to convert and compare data generated by the new and old reference standards is described.

Pulsed-field gel electrophoresis analysis of Vibrio vulnificus strains isolated from Taiwan and the United States

Vibrio vulnificus is a marine bacterium that causes human wound infections and septicemia with a high mortality rate. V. vulnificus strains from different clinical and environmental sources or geographic regions have been successfully characterized by ribotyping and several other methods. Pulsed-field gel electrophoresis (PFGE) is a highly discriminative method, but previous studies suggested that it was not suitable for examining the correlation of V. vulnificus strains from different origins. We employed PFGE to determine its efficacy for characterizing V. vulnificus strains from different geographic regions, characterizing a total of 153 strains from clinical and environmental origins from the United States and Taiwan after SfiI or NotI digestion. V. vulnificus strains showed a high intraspecific diversity by PFGE after SfiI or NotI digestion, and about 12% of the strains could not be typed by the use of either of these enzymes. For PFGE with SfiI digestion, most of the clinical and environmental strains from the United States were grouped into cluster A, while the strains from Taiwan were grouped into other clusters. Clinical strains from the United States showed a higher level of genetic homogeneity than clinical strains from Taiwan, and environmental strains from both regions showed a similarly high level of heterogeneity. PFGE with NotI digestion was useful for studying the correlation of clinical strains from the United States and Taiwan, but it was not suitable for analyzing environmental strains. The results showed that PFGE with SfiI digestion may be used to characterize V. vulnificus strains from distant geographic regions, with NotI being a recommended alternative enzyme.

Phenotypic and genotypic characteristics and epidemiological significance of ctx+ strains of Vibrio cholerae isolated from seafood in Malaysia

Of 97 strains of Vibrio cholerae isolated from various seafoods in Malaysia in 1998 and 1999, 20 strains carried the ctx gene and produced cholera toxin. Fourteen, one, and five of these toxigenic strains belonged to the O139, O1 Ogawa, and rough serotypes, respectively. The rough strains had the rfb gene of the O1 serotype. The toxigenic strains varied in their biochemical characteristics, the amount of cholera toxin produced, their antibiograms, and the presence or absence of the pTLC plasmid sequence. DNA fingerprinting analysis by arbitrarily primed PCR, ribotyping, and a pulsed-field gel electrophoresis method classified the toxigenic strains into 3, 7, and 10 types, respectively. The relatedness of these toxigenic strains to clinical strains isolated in other countries and from international travelers was examined by using a dendrogram constructed from the pulsed-field gel electrophoresis profiles. The results of the examination of the antibiogram and the possession of the toxin-linked cryptic plasmid were consistent with the dendrogram-based relatedness: the O139 strains isolated from Malaysian seafoods could be separated into two groups that appear to have been introduced from the Bengal area independently. The rough strains of Malaysian seafood origin formed one group and belonged to a cluster unique to the Thailand-Malaysia-Laos region, and this group may have persisted in this area for a long period. The single O1 Ogawa strain detected in Malaysian seafood appears to have an origin and route of introduction different from those of the O139 and the rough strains.

Molecular subtyping of Vibrio cholerae O1 and O139 by pulsed-field gel electrophoresis in Hong Kong: correlation with epidemiological events from 1994 to 2002

Two hundred twenty isolates of Vibrio cholerae O1 and O139 collected from 1994 to 2002 in Hong Kong were analyzed by pulsed-field gel electrophoresis (PFGE). Chromosomal DNAs from all V. cholerae isolates in agarose plugs were digested with the restriction enzyme NotI, resulting in 20 to 27 bands. Sixty distinctive PFGE patterns in the range of 10 to 300 kb were noted among 213 isolates typeable by PFGE. By comparing the common PFGE patterns obtained from four well-defined outbreaks of V. cholerae O1 and O139 with those obtained from other, epidemiologically unrelated isolates during the study period, indistinguishable and similar PFGE patterns were identified, indicating their close relatedness, in agreement with the results of epidemiological investigations. Heterogeneous PFGE patterns (with four to six banding differences), however, were identified among strains that were imported from other parts of Asia, including Indonesia, India, and Pakistan. Correlations with epidemiological information further support the usefulness of PFGE as an epidemiological tool in laboratory investigations of suspected outbreaks. Standardization of PFGE methodology will allow international comparison of fingerprint patterns and will form the basis of a laboratory network for tracking V. cholerae.

Genetic diversity of Vibrio cholerae O1 in Argentina and emergence of a new variant

The genetic diversity of Vibrio cholerae O1 strains from Argentina was estimated by random amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE). Twenty-nine isolates carrying the virulence genes ctxA, zot, ace, and tcpA appeared to represent a single clone by both typing methods; while 11 strains lacking these virulence genes exhibited several heterogeneous RAPD and PFGE patterns. Among the last group, a set of isolates from the province Tucumán showed a single RAPD pattern and four closely related PFGE profiles. These strains, isolated from patients with diarrhea, did not produce the major V. cholerae O1 virulence determinants, yet cell supernatants of these isolates caused a heat-labile cytotoxic effect on Vero and Y-1 cells and elicited significant variations on the water flux and short-circuit current in human small intestine mounted in an Ussing chamber. All these effects were completely abolished by incubation with a specific antiserum against El Tor hemolysin, suggesting that this virulence factor was responsible for the toxic activity on both the epithelial cells and the small intestine specimens and may hence be involved in the development of diarrhea. We propose "Tucumán variant" as the designation for this new cluster of cholera toxin-negative V. cholerae O1 strains.

Molecular characterization of Vibrio cholerae O1 strains isolated in Romania

A collection of 89 Vibrio cholerae O1 strains, isolated in Romania between 1977 and 1994, and 6 strains from the Republic of Moldavia, was characterized by ribotyping, toxin gene restriction pattern (toxinogenotype) and distribution of cholera toxin gene (ctx), accessory toxin gene (ace) and zonula occludens toxin gene (zot). After Bg/I endonuclease restriction of chromosomal DNA, a total of 18 ribotypes and 21 toxinogenotypes were distinguished. Deletions in the core region of the toxin gene cassette were found in 20% of strains; however, with the exception of one strain, all the isolates contained the ctx gene. Used in association, the three methods of molecular typing provided an accurate characterization of V. cholerae O1 isolates.

Molecular epidemiology of Vibrio cholerae O1 isolated from sporadic cholera cases in Okinawa, Japan

In July 1994, 6 cholera cases due to Vibrio cholerae O1 El Tor Ogawa sporadically appeared in Okinawa. All 6 patients had no history of traveling abroad. In the period of this cholera outbreak, a strain of V. cholerae O1 El Tor Ogawa was detected from an imported fish at the Naha port quarantine station. The isolates were characterized to clarify whether or not, they belonged to a common clone. Phenotypes were identical except that one strain revealed cured Celebes and the others were original Celebes in kappa phage typing. The restriction fragment patterns of DNA of the isolates hybridized with an enzyme-labeled oligonucleotide probe for cholera toxin gene (ctx) were identical. Randomly amplified polymorphic DNA of the isolates were identical when a primer was used, but 2 patterns were seen when another primer was used. Pulsed-field gel electrophoresis of the chromosomal DNA digested with NotI restriction enzyme showed 3 patterns. The DNA fragment pattern of the strain isolated from the imported fish was different from the clinical isolates. These results suggested that there was no epidemiological relation among the strains of V. cholerae O1 isolated during this period.

Phenotypic and genotypic biotyping of environmental strains of Vibrio cholerae non-O1 isolated in Italy

The purpose of this study was to characterize strains of Vibrio cholerae non-O1 isolated in Italy from different sources by biochemical and serological assays, antibiotic susceptibility testing, and molecular biotyping. Serotyping and genomic analysis by pulsed-field gel electrophoresis proved to be useful in discriminating the isolates. The data obtained show a wide heterogeneity at the genomic level, and in keeping with this, the serogrouping classification provided evidence of a high variability of the investigated strains. In addition, none of the strains tested produced cholera-like toxins.

Cryptic appearance of a new clone of Vibrio cholerae serogroup 01 biotype El Tor in Calcutta, India

In this study, pulsed-field gel electrophoresis (PFGE) was applied to determine if the Vibrio cholerae 01 strains which reappeared after being temporarily displaced in Calcutta by the 0139 serogroup were different from those isolated before the advent of the 0139 serogroup. NotI digestion generated a total of 11 different patterns among the 24 strains of V. cholerae randomly selected to represent different time frames. Among the V. cholerae 01 strains isolated after July 1993, 4 PFGE banding designated as H through K were observed with pattern H dominating. Pattern H was distinctly different from all other patterns encountered in this study including patterns A, B and C of V. cholerae 01 E1 Tor, which dominated before November 1992, and pattern F, which was the dominant V. cholerae 0139 pattern. Further, pattern H was also different from the NotI banding patterns of the representative strains of the 4 toxigenic clonal groups of V. cholerae 01 E1 Tor currently prevailing in different parts of the world. NotI fragments of the new clone of V. cholerae 01 did not hybridize with an 0139 specific DNA probe, indicating that there was no 0139 genetic material in the new clone of V. cholerae 01. Hybridization data with an 01-specific DNA probe again differentiated between the clones of V. cholerae 01 existing before the genesis of the 0139 serogroup and the 01 strains currently prevalent.

Analysis of gram negative recolonization of the neuropathic bladder among patients with spinal cord injuries

Over a 4 year period, 119 acute spinal cord injury (SCI) patients were enrolled in this study. The 101 males and 18 females had a mean age of 35.9 years (range 16-87). Sixty-two patients were tetraplegic and 57 were paraplegic. All patients had a urine specimen taken for culture, colony count and sensitivity once weekly while they were receiving intermittent catheterization. Of these, 22 patients (18.5%), none of whom had underlying genito-urinary (GU) pathology, developed recolonization by an organism of the same species and genus previously cultured. All 22 reached sterile-urine between colonizations after being treated with antibiotics for at least 7 days. The 16 males and six females had a mean age of 35.1 years (range 17-79). Sixteen were tetraplegic and six were paraplegic. Plasmid analysis (PA) was used to determine whether these recolonizations were from the same or from a different strain. In those instances where the bacteria harbored no plasmids or where the results of plasmid analysis were otherwise inconclusive, bacteria were also compared using restriction fragment length polymorphism (RFLP) analysis. Recolonization was caused primarily by E. coli and K. pneumoniae. While there was no significant difference between the two organisms with respect to the number of days when sterile urine occurred to the time when recolonization was observed, there were significant differences seen in both organisms with regard to the time lapse from one colonization to the next: the average number of days to recolonization with an identical organism was 10.3 days, whereas with a different strain it was 15.9 days (P < 0.04). When a different organism was cultured between the recolonizations, the mean recolonization interval was 17.9 days. When no intervening organism occurred, the interval was 9.5 days (P < 0.005). Both intervals measured the days from the first sterile urine after the first colonization to the next colonization. These data indicate the proclivity for two common Gram negative normal bowel inhabitants to recolonize the neuropathic bladder of spinal cord injured patients even after adequate treatment. PA and RFLP provide a means of discriminating between relapses by the same organism versus recurrences by a different organism of the same species and genus. Those with the same identity tend to recur sooner than those of different identities and may be suspected when relapse occurs within two weeks of cessation of 7 day course of antibiotics. While an intervening organism may delay the relapse (or recurrence), it does not prevent it and identical organisms can reappear even after adequate therapeutic regimens. Since none of the patients in this study had GU pathology, recolonization by an identical strain (relapse) does not necessarily warrant an extensive investigation for disease within the GU tract.

Use of molecular typing methods to trace the dissemination of Listeria monocytogenes in a shrimp processing plant

Molecular typing of bacteria has been widely used in epidemiological studies but not as extensively for tracing the transmission of pathogenic bacteria in food plants. This study was conducted to examine the potential use of two molecular typing methods, random amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE), to trace Listeria monocytogenes contamination in a shrimp processing plant. Ribotyping and phase typing were also performed on a select number of strains. One hundred fifteen strains of L. monocytogenes collected in different areas of a shrimp processing plant were first serotyped and then subtyped by molecular typing. RAPD and PFGE showed great promise for typing L. monocytogenes isolates since distinguishable and reproducible DNA polymorphisms were obtained. When the composite profile from both (RAPD and PFGE) methods was generated, there was an increase in the discriminatory power to discern differences between strains of L. monocytogenes. The results indicated that environmental strains all fell into composite profile groupings unique to the environment, while strains from both water and utensils shared another composite profile group. L. monocytogenes fresh shrimp isolates belonging to one profile group were found in different areas of the processing line. This same profile group was also present in food handlers from the processing and packaging areas of the plant.

Comparison of macrorestriction analysis of genomic DNA by pulsed-field gel electrophoresis and ribotyping with conventional methods for differentiation of Escherichia coli 0124 isolates

OBJECTIVE: To evaluate the usefulness of different phenotypic and genotypic markers for epidemiological typing of enteroinvasive Escherichia coli 0124 (EIEC 0124). METHODS: Seven sporadic EIEC 0124 isolates and 22 isolates from two different outbreaks were characterized. Chromosomal deoxyribonucleic acid (DNA) macrorestriction analysis with XbaI resolved by pulsed-field gel electrophoresis (PFGE) and ribotyping with each of the three restriction endonucleases BglII EcoRI, and ClaI were compared with biotyping, antimicrobial susceptibility patterns and plasmid profiles. RESULTS: Biotypes and antimicrobial resistance profiles of the outbreak-associated strains showed considerable variation, thereby limiting the usefulness of such phenotypic markers. Only 57% of the sporadic isolates harbored plasmids. Three different ribotypes based on 5 to 7 bands were recorded among sporadic isolates whereas all outbreak-associated strains showed the same ribotype. BglII appeared to give the best discrimination whereas EcoRI and ClaI provided no additional information. Sporadic EIEC 0124 isolates showed a marked diversity of macrorestriction patterns (similarity coefficient 58 to 93%) and five different patterns were detected. In contrast, the outbreak isolates were closely related (similarity coefficient 90 to 100%). Genomic DNA macrorestriction analysis correlated well with ribotyping, but PFGE was more discriminating. CONCLUSIONS: PFGE is a useful method for epidemiological comparison and differentiation of EIEC 0124 isolates.