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Biomedical subjects

B R Davis

Publications and source records attributed to B R Davis.

At least 163 records · Page 9Linked to original sources
PubMed1980

Hemolytic activity in enterotoxigenic and non-enterotoxigenic strains of Escherichia coli.

We screened 223 strains of Escherichia coli belonging to serotypes previously associated with the production of enterotoxin for hemolytic activity, using horse erythrocytes in liquid and in agar media. Thirty-eight were hemolytic. They belonged to nine different serotypes; most (65.8%) belonged to one serotype, O6: H-. Additionally, all 38 strains were specifically assayed for a filterable, heat-labile hemolytic activity previously associated with a hemolysin plasmid. A comparison of hemolytic activity and enterotoxicity showed that none of 32 strains hemolytic in both media was enterotoxigenic; 28 of the 32 expressed heat-labile hemolytic activity. Four of the six strains hemolytic in only one of the media were enterotoxigenic; none of these six expressed heat-labile hemolytic activity. Of 223 strains, 176 that were of human origin and isolated in the United States were further assayed for three traditionally plasmid-mediated characteristics: heat-labile enterotoxin, heat-stable enterotoxin, and colonization factors. The interrelationships of these characteristics, including hemolytic activity, may reflect varying degrees of plasmid compatibility.

Animals↗
PubMed1980

Antibiotic resistance in Enterotoxigenic and non-enterotoxigenic Escherichia coli.

Antibiotic disk susceptibility tests were done on 220 strains of Escherichia coli belonging to serotypes reported in the literature to be associated with the production of enterotoxin. A total of 128 (58%) were resistant to one or more antibiotics, sulfa drugs, or chemotherapeutic agents. An analysis of these strains revealed primary, secondary, and tertiary drug resistance patterns that indicated a selective pattern in the formation of multiple drug resistance in E. coli. Resistances to certain antibiotics were more likely to occur in pairs and triads (secondary resistance patterns) that were often combined or coexisted in a single strain of E. coli to produce tertiary drug resistance patterns, conferring drug resistance to five or six different antibiotics. Among enterotoxin-associated serotypes, single and multiple drug resistance was less frequently associated with enterotoxin-produced strains than with strains from the same serotype that were not enterotoxigenic. Within the enterotoxigenic E. coli, single and multiple resistance to antibiotics was more frequent in strains producing only heat-stable enterotoxin (ST) than in strains producing only heat-labile enterotoxin (LT) or both. The number of resistances to different antibiotics per resistant strain averaged approximately 1.4 for LT plus ST or LT strains, and 3.9 for ST strains and nonenterotoxigenic strains. Phenotypic characterization of 170 strains for four usually plasmid-mediated characteristics showed that the number of antibiotics to which a strain was directly resistant varied with the type and number of plasmid-mediated characteristics present.

Anti-Bacterial Agents↗
PubMed1979

Ureolytic Escherichia coli of human origin: serological, epidemiological, and genetic analysis.

Forty-five strains of ureolytic Escherichia coli of human origin, isolated in the United States between 1956 and 1977, were characterized by geographical distribution, site of infection, serotype, resistance to antibiotics, and biochemical reactions. All strains were studied for the ability to generate clones of nonureolytic E. coli (segregants), and a subset of these were selected for plasmid analysis and a variety of bacterial matings. There did not appear to be a common geographical distribution, serotype, antibiogram, or other aberrant biochemical reactions other than the hydrolysis of urea among these strains. The predominance of urinary tract isolates (46.7% total) may reflect a relationship between urea hydrolysis and pathogenesis at this site. Ten of the strains (22.2%) did segregate nonureolytic E. coli colonies, and all possessed at least one common plasmid species with a molecular weight of about 65 X 10(6). Only strain 1138-77 serotype O16:H6 conjugally transfered the ability to hydrolyze urea, ferment sucrose, and resist inhibition by sulfadiazide simultaneously. The resulting, recombination-deficient E. coli K-12 tranconjugant was found to possess a plasmid with a molecular weight of about 80 X 10(6) to 90 X 10(6).

Anti-Bacterial Agents↗
PubMed1976

Detection of Serratia outbreaks in hospital.

Infections due to Serratia marcescens were studied in 23 different hospitals. A retrospective study was done in 4 hospitals; all isolates were compared by serological typing, antibiograms, bacteriocin production, and bacteriocin sensitivity. 2 of the hospitals were having cross-infection problems due to antibiotic-resistant strains, but the other 2 had little or no cross-infection. Outbreaks were studied in 19 other hospitals. 9 of these outbreaks were classified as "common source" since contaminated "sterile solutions" were incriminated as the cause in each. One hospital had a "pseudo-outbreak," in which Serratia from E.D.T.A. blood-collecting tubes contaminated blood-cultures as they were collected. All 10 of these strains from common-source outbreaks were generally sensitive to antibiotics. Outbreaks in 9 other hospitals resulted from cross-infection and were caused by strains which were very resistant to antibiotics. Guidelines for detecting outbreaks are given and control measures are suggested.

Alabama↗
PubMed1975

Response of rat lung to 3,4-benzpyrene administered by intratracheal instillation in infusine with or without carbon black.

In a controlled experiment groups of SPF Wistar rats were give 18 once-fortnightly doses of 0-5, 1-0 or 2-0 mg 3,4-benzpyrene (BP) suspended in infusine (I) or in carbon black (CB) + I by intratracheal instillation. Of rats examined post mortem, 1/16 given I+CB only, 0/16 given I only, 15/51 given BP in I+CB and 24/48 given BP in I developed squamous neoplasms of the lung. The incidence of tumours was significantly related to dose of BP. At the 1 or 2 mg dose levels BP in I only was more productive of tumours than BP in I+CB. Other changes encountered included squamous metaplasia of alveolar and bronchiolar epithelium (Sq.M), but not of bronchial epithelium, and cuboidal and columnar metaplasia of alveolar epithelium in the vicinity of terminal bronchioles (CCM). Sq.M was associated with exposure to BP or I+CB. CCM was strongly associated with exposure to I+CB but only weakly with exposure to BP.

Adenocarcinoma↗
PubMed1975

Response of rat lung to tobacco smoke condensate or fractions derived from it administered repeatedly by intratracheal instillation.

The repeated intratracheal instillation of cigarette smoke condensate (SWS) in rats at close to maximum tolerated dose levels failed to induce squamous neoplasms in the lungs although such treatment was associated with an increased incidence of cuboidal/columnar metaplasia (CCM) and squamous metaplasia (Sq.M) of alveolar epithelium. With one exception, various fractions of SWS had no effect on lung tumour incidence though some were more effective than SWS in increasing the incidence of CCM and Sq.M. The exceptional fraction, Fraction P, which contains most of the polycyclic aromatic hydrocarbons of smoke and is the most effective of the fractions tested in producing tumours in mouse skin, gave rise to 4 squamous tumours of doubtful malignancy and one metastasizing squanmous carcinoma among 3 groups of 18 animals exposed at 3 different dose levels. The results are discussed in relation to the possible development of a method for comparing condensates for relative lung carcinogenicity.

Animals↗
PubMed1975

Response of rat lung to inhaled vapour phase constituents (VP) of tobacco smoke alone or in conjunction with smoke condensate or fractions of smoke condensate given by intratracheal instillation.

In a controlled experiment, 6 groups of SPF rats were given cigarette smoke condensate (SWS) in solid form without a vehicle once fortnightly by intratracheal instillation, at 3 dose levels with or without additional exposure to the vapour phase of smoke (VP) from 10 plain cigarettes each week. Treatment continued for life. Six other groups were similarly treated with one of 3 fractions of condensate with or without VP. Exposure to VP was associated with a significant reduction in body weight, but not signficantly with the incidence or severity of any observed pathological change in the lungs. A significant dose-related assoication was seen between SWS or its fractions and the incidence and degree of chronic respiratory disease (CRD), cuboidal or columnar metaplasia (CCM) and squamous metaplasia of alveolar epithelium (Sq.M) produced. No neoplasms, however, were elicited. A significant correlation was found between the degrees of CCM and of Sq.M produced in the 24 groups exposed to SWS or fractions. The results are discussed in the light of studies in which rats were exposed to tobacco smoke by inhalation and of studies in which the same condensate and fractions were applied to mouse skin.

Animals↗
PubMed1975

Response of rat lung to inhaled tobacco smoke with or without prior exposure to 3,4-benzpyrene (BP) given by intratracheal instillation.

SPF rats were exposed to the smoke from 10 cigarettes per week from the age of 10 weeks until they died. Survival, body weight, tumour incidence and histopathological appearances of the lungs were compared with those for untreated sham exposed rats. Two further groups were given a single dose of 3,4-benzyprene (BP) by intratracheal instillation. One of these was then exposed to the smoke of 10 cigarettes per week till death. Compared with untreated or sham exposed rats, exposure to smoke was associated with a significant reduction in incidence of mammary tumours. Exposure to smoke was associated with an increasing incidence of collections of macrophages laden with golden-brown pigment (GBM) and of areas of cuboidal or columnar metaplasia (CCM) or squamous metaplasia (Sq.M) of alveolar epithelium. In control rats there was virtually no GBM, a low incidence of CCM and Sq.M. Four out of 406 smoke exposed rats which came to post mortem had squamous neoplasms in the lungs, 3 having lesions of doubtful malignancy and one having a squamous carcinoma. In contrast, no squamous neoplasms were seen in 197 control rats. This difference was not statistically significant. The findings in rats given a single dose of BP were, in all the above respects, similar to those in untreated rats, except that one developed a squamous carcinoma of the lung. The effects of a single dose of BP followed by smoke exposure were in general similar to those of smoke exposure only. Three rats on this treatment regimen developed squamous cancers of the lung. None of the treatments increased the incidence of adenomata of the lungs. The results are discussed in relation to other studies of the effects of smoke exposure on rats and other species.

Adenoma↗
PubMed1974

Biochemical and serological characterization of hydrogen sulfide-positive variants of Escherichia coli.

Over 200 H(2)S-positive, gram-negative rods have been characterized by standard biochemical and serological techniques. The results indicate that the isolates are H(2)S-positive variants of Escherichia coli. Comparison of the variants with biochemically typical E. coli suggests that they represent a rather limited subgroup within the species. The H(2)S-positive strains were more resistant to antibiotics than the typical strains; 54% of the H(2)S-positive isolates were resistant to three or more antibiotics compared with only 25% of the typical strains. Similar differences were also seen in the distribution of O and H antigens and in the results of certain biochemical tests.

Agglutination Tests↗
PubMed1973

The crystal structures of 2,5-piperazinediones having epipolysulfide bridges between c3 and c6: the structures of n,n'-dimethyl-3,6-epitetrathio-2,5-piperazinedione.

The crystal and molecular structure of N,N'-dimethyl-3,6-epitetrathio-2,5-piperazinedione (C(6)H(8)O(2)N(2)S(4)) has been determined from three-dimensional x-ray diffraction data collected by counter techniques. The substance crystallizes in the orthorhombic space group Fdd2, with a = 15.352(5), b = 20.432(7), and c = 6.635(2) A; V = 2081.2(8) A(3), D(meas) = 1.72(2) g/cm(3), and z = 8 molecules per unit cell. The molecule lies on a crystallographic 2-fold axis, the piperazinedione ring is in the boat conformation, and the deviation from planarity is 18 degrees . The bonds of the tetrasulfide chain alternate in length so that the S-S distances are 2.0244(9), 2.076(1), and 2.0244(9) A. The structural data were refined by least-squares methods to an R(F) of 2.5% by use of the 1089 independent reflections (2theta </= 71 degrees ; MoKalpha) for which F(0) (2) >/= 3sigma (F(0) (2)). Since this molecule is chemically identical with the active center of the recently isolated natural product sporidesmin G, our structural study constitutes a description of the epitetrathio-2,5-piperazinedione fragment of that molecule.

Journal Article↗