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R R Colwell

Publications and source records attributed to R R Colwell.

300 records · Page 17Linked to original sources
PubMed1966

Structure of a marine bacteriophage as revealed by the negative-staining technique.

Valentine, Artrice F. (Georgetown University, Washington, D.C.), Peter K. Chen, Rita R. Colwell, and George B. Chapman. Structure of a marine bacteriophage as revealed by the negative-staining technique. J. Bacteriol. 91:819-822. 1966.-The morphology of a marine bacteriophage has been determined by negative-staining techniques and electron microscopy. The virus possesses a head, 600 A in diameter, and a tail which may be from 860 to 1,000 A in lenght. No tail sheath is seen. The appearance of the terminal tail structure is discussed.

Bacteriophages↗
PubMed1966

Properties of two marine bacteriophages.

Chen, Peter K. (Georgetown University, Washington, D.C.), Ronald V. Citarella, Omar Salazar, and Rita R. Colwell. Properties of two marine bacteriophages. J. Bacteriol. 91:1136-1139. 1966.-Various properties have been determined for two bacteriophages, NCMB 384 and 385, and their host, NCMB 397, a Cytophaga sp., isolated from the marine environment. The purified bacteriophages have been subjected to serological analysis, results of which indicate a high degree of relatedness. Purified, highly polymerized deoxyribonucleic acid (DNA) prepared from the host strain showed an overall base composition of 37 moles% guanine + cytosine (buoyant density of 1.696 g/cc). The bacteriophage DNA, in the native configuration, from NCMB 384 and 385 banded at 1.691 g/cc in a CsCl gradient and the denatured bacteriophage DNA demonstrated a bimodal peak. Stability tests of the bacteriophages in various buffers and diluents suggest a requirement for inorganic cations, most likely Na(+) and Mg(++), for retention of viability.

Bacteriophages↗
PubMedDate not supplied

Association of Vibrio cholerae O1 with the cyanobacterium, Anabaena sp., elucidated by polymerase chain reaction and transmission electron microscopy.

It has been hypothesized that Vibrio cholerae is an autochthonous flora of the estuarine and brackish water environment. Zooplankton and phytoplankton have been considered as possible reservoirs. The present study was carried out in microcosms to confirm the role of a cyanobacterium, Anabaena sp., as a reservoir of V. cholerae O1 using culture, polymerase chain reaction (PCR) and immunoelectron microscopy. Survival of culturable V. cholerae in microcosms was monitored by using tellurite taurocholate gelatin agar. Culturable V. cholerae were detected for up to 1 h in association with Anabaena sp. from a microcosm. However, viable but nonculturable (VBNC) V. cholerae O1 were detected for up to 25 months using PCR and immunoelectron microscopy. Results also showed that VBNC V. cholerae can multiply and maintain their progeny in the mucilaginous sheath of Anabaena sp. This is the first time that PCR and immunoelectron microscopy have been used to detect nonculturable V. cholerae in association with Anabaena sp. This study further clarifies the role of Anabaena sp. as a possible reservoir of cholera.

Anabaena↗
PubMedDate not supplied

Alice C. Evans: breaking barriers.

Despite severe and persistent criticism of her research, Alice Evans persevered in her pioneering work on the bacterial contamination of milk, identifying the organism that caused undulant fever and demonstrating that drinking unpasteurized cow's milk could transmit the disease, undulant fever, to humans. The opprobrium that Alice Evans endured was unrelenting, even after her election as the first President of the Society of American Bacteriologists, (now the American Society for Microbiology), but she remained undeterred, a true heroine of American microbiology and a magnificent public health worker.

Animals↗
PubMedDate not supplied

Evaluation of radiolabeled and colorimetric DNA probes in comparison with an antigen screening assay for the detection of Salmonella from poultry farms.

A total of 48 environmental drag-swab samples from various poultry farms were tested for the presence of Salmonella spp. by culture, an enzyme-linked immunosorbent assay-based Salmonella antigen screening (SAS) assay, and two DNA probes (radiolabeled and colorimetric). The radiolabeled DNA probe was allowed to hybridize with culture-positive samples (n = 8) and was found to detect Salmonella spp. in all cases (100%). Both of the probes, subsequently hybridized with culture-negative samples (n = 8), were observed to yield good agreement (91%) with the culture findings. The remaining samples (n = 32) were tested by the SAS assay, and where there was no agreement between the culture and SAS, samples were further examined by the DNA probes. Results using both probes agreed with those obtained by culturing the samples but did not agree with the SAS assay result when the ratio of samples tested to samples positive (S/P) cutoff value used was 0.5.

Animals↗
PubMedDate not supplied

Plasmid profile as a useful marker of a Shigella dysenteriae type 1 strain causing an epidemic of shigellosis.

Plasmid profiles of 60 Shigella dysenteriae type 1 isolates obtained during an epidemic period (April - October 1983) were compared with that of 74 other Shigella species isolated during the same period of time and also with that of 20 S. dysenteriae type 1 isolates obtained before the epidemic period (1969 - 1982). All samples were collected during an epidemic of shigellosis from diarrhoeal patients being treated at the Dhaka Treatment Centre of the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B) between April and October 1983. Approximately 4% of the patients were sampled. The isolated showed varied patterns of resistance to several antimicrobial agents. Ninety-two per cent of the 60 S. dysenteriae type 1 strains showed a typical profile of four plasmids with masses of 140, 6, 4 and 2 megadaltons (Mdal). The finding is in contrast with that of a previous study at the ICDDR,B, in which 14 different plasmid profiles were observed in 23 strains of S. dysenteriae type 1 isolated during a 10 - month period in 1982. The profile typical for this study was different from those found in other species of Shigella isolated at the same time. There was a strong association between the possession of this plasmid profile and resistance to chloramphenicol, streptomycin, tetracycline and trimethoprim - sulphamethoxazole. Twenty S. dysenterae type 1 strains isolated from the faeces of patients at the ICDDR,B during 1969 - 1982 were also analysed for their plasmid profiles. The finding is in contrast with that of the epidemic strains. The typical epidemic plasmid pattern, i.e. the 140, 6, 4 and 2 Mdal, was absent in isolates obtained before 1983 epidemic.(ABSTRACT TRUNCATED AT 250 WORDS)

Bangladesh↗