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R R Colwell

Publications and source records attributed to R R Colwell.

At least 55 records · Page 3Linked to original sources
PubMed1999

Analysis of 16S-23S rRNA intergenic spacer regions of Vibrio cholerae and Vibrio mimicus.

Vibrio cholerae identification based on molecular sequence data has been hampered by a lack of sequence variation from the closely related Vibrio mimicus. The two species share many genes coding for proteins, such as ctxAB, and show almost identical 16S DNA coding for rRNA (rDNA) sequences. Primers targeting conserved sequences flanking the 3' end of the 16S and the 5' end of the 23S rDNAs were used to amplify the 16S-23S rRNA intergenic spacer regions of V. cholerae and V. mimicus. Two major (ca. 580 and 500 bp) and one minor (ca. 750 bp) amplicons were consistently generated for both species, and their sequences were determined. The largest fragment contains three tRNA genes (tDNAs) coding for tRNAGlu, tRNALys, and tRNAVal, which has not previously been found in bacteria examined to date. The 580-bp amplicon contained tDNAIle and tDNAAla, whereas the 500-bp fragment had single tDNA coding either tRNAGlu or tRNAAla. Little variation, i.e., 0 to 0.4%, was found among V. cholerae O1 classical, O1 El Tor, and O139 epidemic strains. Slightly more variation was found against the non-O1/non-O139 serotypes (ca. 1% difference) and V. mimicus (2 to 3% difference). A pair of oligonucleotide primers were designed, based on the region differentiating all of V. cholerae strains from V. mimicus. The PCR system developed was subsequently evaluated by using representatives of V. cholerae from environmental and clinical sources, and of other taxa, including V. mimicus. This study provides the first molecular tool for identifying the species V. cholerae.

Base Sequence↗
PubMed1998

A proposal to transfer Vibrio marinus (Russell 1891) to a new genus Moritella gen. nov. as Moritella marina comb. nov.

The taxonomic positions of Vibrio marinus and 11 related natural isolates were examined. Their phylogenetic positions on the basis of almost complete 16S rRNA sequences were determined by maximum likelihood, maximum parsimony and neighbor-joining analyses. V. marinus and the 11 isolates fell into a single cluster that was clearly distinct from other genera. There is now strong evidence that V. marinus should be reclassified as Moritella marina gen. nov., comb. nov.

Base Sequence↗
PubMed1998

Mercury-resistant actinomycetes from the Chesapeake Bay.

Two actinomycete strains, CHR3 and CHR28, were isolated from metal-contaminated sediments from Baltimore Inner Harbor. The isolates were classified as Streptomyces spp. Agar diffusion assays showed both isolates to be resistant to mercuric chloride and phenylmercuric acetate. Hybridization experiments indicated that genes homologous to the mercuric reductase and organomercurial lyase of Streptomyces lividans 1326 were present in strains CHR3 and CHR28. Strain CHR28 grew at both low and high salt concentrations; however, strain CHR3 showed enhanced growth in the presence of salt, evidence of its habitat being marine or estuarine sediment.

Baltimore↗
PubMed1997

Microbial diversity: the importance of exploration and conservation.

Microbial diversity is fundamental to maintenance and conservation of global genetic resources. As extreme environments are explored, the richness of microbial diversity is increasingly evident. Measures must be taken to estimate, record, and conserve microbial diversity, not only to sustain human health but also to enrich the human condition globally through wise use and conservation of genetic resources of the microbial world.

Animals↗
PubMed1997

Systematic study of the genus Vogesella gen. nov. and its type species, Vogesella indigofera comb. nov.

A blue-pigmented colony that had a metallic copper-colored sheen was isolated in 1973 from a standard spread plate count preparation of oxidation pond sediment. Over the next 11 years, an additional 12 strains of blue-pigmented bacteria were isolated from freshwater samples and compared to several reference strains of bacteria. Morphological and biochemical tests revealed that these 13 isolates were very similar to [Pseudomonas] indigofera ATCC 19706T (T = type strain) and ATCC 14036. A numerical analysis (in which simple matching similarity coefficients were clustered by the unweighted pair group mathematical averaging method) of morphological and biochemical characteristics revealed 90.0% relatedness between the 13 isolates and [P.] indigofera ATCC 19706T and ATCC 14036 and 73.6% relatedness between the 13 isolates and a cluster containing Burkholderia cepacia ATCC 25416T, Janthinobacterium lividum ATCC 12473T, and the Pseudomonas species tested. A phylogenetic analysis, in which both 5S rRNA and 16S rRNA were used, also revealed that the 13 isolates were closely related to each other and to strains ATCC 19706T and ATCC 14036. In addition, both 5S rRNA and 16S rRNA analyses demonstrated that the isolates and strains ATCC 19706T and ATCC 14036 were members of the beta subdivision of the Proteobacteria and were closely related to Chromobacterium violaceum ATCC 12742T but sufficiently distinct to warrant placement in a new genus. Accordingly, we propose that the 13 isolates and strains ATCC 19706T and ATCC 14306 be placed in the genus Vogesella gen. nov., which is named in honor of Otto Voges, who first isolated and described this blue-pigmented eubacterium in 1893. We also propose that [P.] indigofera be renamed Vogesella indigofera comb. nov. and designated the type species of the genus; strain ATCC 19706 is the type strain of this species.

Bacteriological Techniques↗
PubMed1997

Effect of alum on free-living and copepod-associated Vibrio cholerae O1 and O139.

The effects of alum [KAl(SO4)2] on free-living and copepod-associated Vibrio cholerae O1 and O139 were investigated by using plate counts and immunofluorescence direct viable counting (DVC). Growth of alum-treated cells in 0.5/1000 Instant Ocean seawater was inhibited, i.e., no growth was obtained on Luria-Bertani (LB) agar or thiosulfate-citrate-bile salt-sucrose (TCBS) agar. However, a significant number of the inhibited cells maintained viability, as measured by DVC. In comparison, a significant number of V. cholerae organisms associated with zooplankton, most of which were crustacean copepods, were viable but nonculturable, with only a small number of cells retaining culturability on LB and TCBS agar. Both DVC and viable plate counts (CFU) were significantly greater for V. cholerae O1 and O139 associated with zooplankton than for V. cholerae in water alone, i.e., without copepods. It is concluded that alum is an effective coagulant but not an effective killing agent for V. cholerae and that association with copepods offers protection for V. cholerae O1 and O139 against alum and chlorine treatments.

Alum Compounds↗
PubMed1997

Effect of aerosolization on culturability and viability of gram-negative bacteria.

Estimations of the bacterial content of air can be more easily made now than a decade ago, with colony formation the method of choice for enumeration of airborne bacteria. However, plate counts are subject to error because bacteria exposed to the air may remain viable yet lose the ability to form colonies, i.e., they become viable but nonculturable. If airborne bacteria exhibit this phenomenon, colony formation data will significantly underestimate the bacterial populations in air samples. The objective of the study reported here was to determine the effect of aerosolization on viability and colony-forming ability of Serratia marcescens, Klebsiella planticola, and Cytophaga allerginae. A collision nebulizer was used to spray bacterial suspensions into an aerosol chamber, after which duplicate samples were collected in all-glass impingers over a 4-h period. Humidity was maintained at ca. 20 to 25%, and temperature was maintained at 20 to 22 degrees C for each of two replicate trials per microorganism. Viability was determined by using a modified direct viable count method, employing nalidixic acid or aztreonam and p-iodonitrotetrazolium violet (INT). Cells were stained with acridine orange and observed by epifluorescence microscopy to enumerate total and viable cells. Viable cells were defined as those elongating in the presence of antibiotic and/or reducing INT. CFU were determined by plating on tryptic soy agar and R2A agar. It was found that culture techniques did not provide an adequate description of the bacterial burdens of indoor air (i.e., less than 10% of the aerosolized bacteria were capable of forming visible colonies). It is concluded that total cell count procedures provide a better approximation of the number of bacterial cells in air and that procedures other than plate counting are needed to enumerate bacteria in aerosol samples, especially if the public health quality of indoor air is to be estimated.

Aerosols↗
PubMed1996

Global climate and infectious disease: the cholera paradigm.

The origin of cholera has been elusive, even though scientific evidence clearly shows it is a waterborne disease. However, standard bacteriological procedures for isolation of the cholera vibrio from environmental samples, including water, between epidemics generally were unsuccessful. Vibrio cholerae, a marine vibrio, requiring salt for growth, enters into a dormant, viable but nonculturable stage when conditions are unfavorable for growth and reproduction. The association of Vibrio cholerae with plankton, notably copepods, provides further evidence for the environmental origin of cholera, as well as an explanation for the sporadic and erratic occurrence of cholera epidemics. On a global scale, cholera epidemics can now be related to climate and climatic events, such as El Niño, as well as the global distribution of the plankton host. Remote sensing, with the use of satellite imagery, offers the potential for predicting conditions conducive to cholera outbreaks or epidemics.

Animals↗
PubMed1996

Effect of seawater on Escherichia coli beta-galactosidase activity.

An investigation of beta-galactosidase activity of Escherichia coli strain H10407, under different physiological and environmental conditions, e.g. induced and uninduced osmotic stress, light, etc., was undertaken. In this study E. coli was employed as a model for faecal coliforms in waste water. beta-Galactosidase activity was induced by isopropyl-beta-D-thiogalactoside (IPTG). Enzyme activity (U cell-1)/cell for sewage bacteria and for induced E. coli was similar, i.e. log U cell-1 = -8.5 whereas uninduced E. coli yielded log U cell-1 = -12.1. Initial enzyme activity was not dependent on phase of growth of the cell (exponential vs stationary phase) or whether marine or fresh water at the time of initial dilution. However, osmotic change resulted in a decrease in culturable cells, even though enzyme activity remained constant. A significant decrease in the number of culturable bacteria, followed by a decrease in beta-galactosidase activity, was observed after exposure of cells to visible light radiation. It is concluded that beta-galactosidase enzyme is retained in viable but non-culturable E. coli. Furthermore, beta-galactosidase appears to offer a useful and rapid (25 min) measure of the viability of faecal coliforms, and therefore, of the water quality of bathing and shellfishing areas.

Chloramphenicol↗
PubMed1996

Potential virulence of viable but nonculturable Shigella dysenteriae type 1.

We examined a virulent strain of Shigella dysenteriae type 1 after induction into the viable but nonculturable (VBNC) state for its ability to (i) maintain the Shiga toxin (stx) gene; (ii) maintain biologically active Shiga toxin (ShT); and (iii) adhere to intestinal epithelial cells (Henle 407 cell line). PCR was used to amplify the stx gene from VBNC cells of S. dysenteriae type 1, thereby establishing its presence even when cells are in the VBNC state. VBNC S. dysenteriae type 1 ShT was monitored by the enzyme-linked immunosorbent assay with mouse monoclonal antibodies against the B subunit of ShT and affinity-purified rabbit polyclonal antibodies against ShT. We used the Henle 407 cell line to study the adhesive property of VBNC S. dysenteriae type 1 cells in a series of tissue culture experiments. Results showed that VBNC S. dysenteriae type 1 not only maintained the stx gene and biologically active ShT but also remained capable of adhering to Henle 407 cells. However, S. dysenteriae type 1 cells lost the ability to invade Henle 407 cells after entering the VBNC state. From results of the study, we conclude that VBNC cells of S. dysenteriae type 1 retain several virulence factors and remain potentially virulent, posing a public health problem.

Animals↗
PubMed1996

Microbial ecology of Campylobacter jejuni in a United Kingdom chicken supply chain: intermittent common source, vertical transmission, and amplification by flock propagation.

A study of Campylobacter jejuni on a broiler chicken farm between 1989 and 1994 gave an estimated isolation rate of 27% (3,304 of 12,233) from a 0.9% sample of 1.44 million broiler chickens from six to eight sheds over 32 consecutive rearing flocks comprising 251 broiler shed flocks. During the study, C. jejuni was found in 35.5% of the 251 shed flocks but only 9.2% (23 of 251) had Campylobacter isolates in successive flocks, with 9 of those 23 sheds having the same serotype between consecutive flocks, indicating a low level of transmission between flocks. Analysis of a systematic sample of 484 of 3,304 (14.6%) C. jejuni isolates showed that 85% were of 10 serotype complexes but 58% were of 3 serotype complexes, indicating a high degree of strain similarity throughout the entire study. The three commonest types were detected in 8 of 32 flocks during the 5-year study period, suggesting an intermittent common external Campylobacter source. This hypothesis was tested by a retrospective cohort analysis of C. jejuni rates and types by reference to hatchery supplier of the 1-day-old chicks. Isolation rates of C. jejuni and frequency distribution of types were determined in 6-week-old broiler chickens identified by the hatchery supplying the original chicks. The isolation rate of C. jejuni in broilers, supplied by hatchery A, was 17.6%, compared to 42.9% (P < 0.0001) for broilers reared from chicks supplied by hatchery B. In two instances, when both hatcheries were used to stock the same farm flock, Campylobacter isolates were found only in those sheds with chicks supplied by hatchery B. Thus, the frequency distribution of Campylobacter types for chickens supplied by the two hatcheries over the 5-year period showed marked dissimilarity. These findings suggest that the isolation rate and type of Campylobacter isolates in broiler chickens was associated with the hatchery supplying chicks. The lack of diversity of types and the intermittent high positivity of sheds is evidence for a common source of C. jejuni introduced by vertical transmission rather than contamination at the hatchery or during transportation.

Animals↗
PubMed1996

Retention of enteropathogenicity by viable but nonculturable Escherichia coli exposed to seawater and sunlight.

The effect of natural sunlight on culturability and persistence of pathogenicity of Escherichia coli was examined in the field, i.e., in the Morlaix Estuary, France, using an enterotoxigenic strain of Escherichia coli H10407. Results showed that E. coli responds to the estuarine diurnal solar cycle by entering the viable but nonculturable state upon exposure to sunlight. That is, direct counts of viable cells remained stable without significant change, but E. coli cells remained fully culturable only when exposed to seawater in control chambers in the dark, i.e., without solar irradiation. The effect of sunlight on the pathogenicity of E. coli H10407 was studied, using both the rabbit intestinal loop assay and ganglioside-enzyme-linked immunosorbent assay (GM1-ELISA), a sensitive procedure for testing for production of enterotoxin. Results of the GM1-ELISA demonstrated that strains of E. coli, after exposure to sunlight and entering the viable but nonculturable state, as well as culturable E. coli, retained pathogenicity, i.e., produced enterotoxin. The GM1-ELISA is concluded to be more sensitive than the rabbit intestinal loop assay for analysis of enterotoxin in natural water samples.

Animals↗
PubMed1996

Distribution of Vibrio vulnificus in the Chesapeake Bay.

Vibrio vulnificus is a potentially lethal human pathogen capable of producing septicemia in susceptible persons. Disease is almost always associated with consumption of seafood, particularly raw oysters, or with exposure of wounds to seawater. An oligonucleotide DNA probe (V. vulnificus alkaline phosphatase-labeled DNA probe [VVAP]), previously shown to be highly specific for V. vulnificus, was used to enumerate this species in environmental samples collected from the Chesapeake Bay between April 1991 and December 1992. Total aerobic, heterotrophic, culturable bacteria were enumerated by plate counts on nonselective medium. The number of V. vulnificus organisms was determined by colony lifts of spread plates for subsequent hybridization with VVAP. V. vulnificus was not detected in any samples collected during February and March (water temperature of < 8 degrees C) but was found in 80% of the water samples collected during May, July, September, and December (water temperature of > 8 degrees C), with concentrations ranging from 3.0 x 10(1) to 2.1 x 10(2)/ml (ca. 8% of the total culturable heterotrophic bacteria). In a multiple regression analysis, increased V. vulnificus concentrations were correlated with lower salinities and with isolation from samples collected closer to the bottom. Isolation from oysters was demonstrable when water temperatures were 7.6 degrees C, with concentrations ranging from 1.0 x 10(3) to 4.7 x 10(4)/g (ca. 12% of total culturable bacteria). In samples collected in May and July, V. vulnificus was identified in seven of seven plankton samples and four of nine sediment samples. Our data demonstrate that V. vulnificus is a widespread and important component of the bacterial population of the Chesapeake Bay, with counts that are comparable to those reported from the Gulf of Mexico.

Animals↗
PubMed1996

Effects of sunlight on bacteriophage viability and structure.

Current estimates of viral abundance in natural waters rely on direct counts of virus-like particles (VLPs), using either transmission or epifluorescence microscopy. Direct counts of VLPs, while useful in studies of viral ecology, do not indicate whether the observed VLPs are capable of infection and/or replication. Rapid decay in bacteriophage viability under environmental conditions has been observed. However, it has not been firmly established whether there is a corresponding degradation of the virus particles. To address this question, viable and direct counts were carried out employing two Chesapeake Bay bacteriophages in experimental microcosms incubated for 56 h at two depths in the York River estuary. Viruses incubated in situ in microcosms at the surface yielded decay rates in full sunlight of 0.11 and 0.06 h-1 for CB 38 phi and CB 7 phi, respectively. The number of infective particles in microcosms in the dark and at a depth of 1 m was not significantly different from laboratory controls, with decay rates averaging 0.052 h-1 for CB 38 phi and 0.037 h-1 for CB 7 phi. Direct counts of bacteriophages decreased in teh estuarine microcosms, albeit only at a rate of 0.028 h-1, and were independent of treatment. Destruction of virus particles is concluded to be a process separate from loss of infectivity. It is also concluded that strong sunlight affects the viability of bacteriophages in surface waters, with the result that direct counts of VLPs overestimate the number of bacteriophage capable of both infection and replication. However, in deeper waters, where solar radiation is not a significant factor, direct counts should more accurately estimate numbers of viable bacteriophage.

Bacteriophages↗
PubMed1996

Distribution of sewage indicated by Clostridium perfringens at a deep-water disposal site after cessation of sewage disposal.

Clostridium perfringens, a marker of domestic sewage contamination, was enumerated in sediment samples obtained from the vicinity of the 106-Mile Site 1 month and 1 year after cessation of sewage disposal at this site. C. perfringens counts in sediments collected at the disposal site and from stations 26 nautical miles (ca. 48 km) and 50 nautical miles (ca. 92 km) to the southwest of the site were, in general, more than 10-fold higher than counts from an uncontaminated reference site. C. perfringens counts at the disposal site were not significantly different between 1992 and 1993, suggesting that sewage sludge had remained in the benthic environment at this site. At stations where C. perfringens counts were elevated (i.e., stations other than the reference station), counts were generally higher in the top 1 cm and decreased down to 5 cm. In some cases, C. perfringens counts in the bottom 4 or 5 cm showed a trend of higher counts in 1993 than in 1992, suggesting bioturbation. We conclude that widespread sludge contamination of the benthic environment has persisted for at least 1 year after cessation of ocean sewage disposal at the 106-Mile Site.

Clostridium perfringens↗
PubMed1996

A simple filtration method to remove plankton-associated Vibrio cholerae in raw water supplies in developing countries.

Plankton to which cells of Vibrio cholerae O1 and/or O139 were attached was introduced into 0.5% Instant Ocean microcosms maintained at 25 degrees C. The bulk of the plankton and associated particulates was removed with a filter constructed from either nylon net and one of several different types of sari material, the latter being very inexpensive and readily available in villages in Bangladesh, where V. cholerae is endemic. V. cholerae was enumerated before and after filtration to evaluate the efficiency of the filtration procedure. The results obtained indicate that 99% of V. cholerae, i.e., those cells attached to plankton, were removed from the water samples. Epidemic strains of V. cholerae O1 and O139 from various geographical sources, including Bangladesh, Brazil, India, and Mexico, were included in the experiments. Removal of vibrios from water by this simple filtration method was found to yield consistent results with all strains examined in this study. Thus, it is concluded that a simple filtration procedure involving the use of domestic sari material can reduce the number of cholera vibrios attached to plankton in raw water from ponds and rivers commonly used for drinking. Since untreated water from such sources serves as drinking water for millions of people living in developing countries (e.g., Bangladesh), filtration should prove effective at reducing the incidence and severity of outbreaks, especially in places that lack fuel wood for boiling water and/or municipal water treatment plants. The results of this study provide the basis for determining such reductions, which are to be carried out in the near future.

Animals↗