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N A Johnston

Publications and source records attributed to N A Johnston.

15 recordsLinked to original sources
PubMed1999

Application of a quantitative algorithm to restriction endonuclease analysis of Aujeszky's disease (pseudorabies) virus from a geographically localized outbreak.

A retrospective epidemiologic study was conducted to evaluate the application of an objective quantitative algorithm for estimating genetic similarity from restriction endonuclease analysis data. The analysis was performed to assist the determination of chronologic trends in an Aujeszky's disease viral epidemic in a geographic region. DNA from each viral isolate obtained during the epidemic was digested with 4 restriction endonucleases and molar ratio labeled to generate separate fragment patterns that were simultaneously compared using the algorithm. The resultant estimates of genetic similarity were then used in conjunction with time of virus isolation and specific geographic location of the outbreaks to identify the probable sources of infection and the patterns of spread among swine herds. This type of quantitative analysis enabled a more precise and objective approach than previously has been applied to the interpretation of restriction endonuclease data, thereby demonstrating the benefit of this methodology for the investigation of infectious disease outbreaks.

Algorithms↗
PubMed1997

Evaluation of serum gamma-glutamyltransferase activity as a predictor of passive transfer status in crias.

OBJECTIVE: To determine the relationship between serum gamma-glutamyltransferase (GGT) activity and serum IgG concentration in neonatal crias. DESIGN: Prospective observational study. ANIMALS: 21 llama and 4 alpaca crias from 0 to 5 days old. PROCEDURE: Serum GGT activity was measured, using a commercially available kit. Serum IgG concentration was determined by use of radial immunodiffusion. With a serum IgG concentration of 1,000 mg/dl (considered adequate passive transfer), specificity and sensitivity of serum GGT activity in the detection of failure of passive transfer were determined. Regression models were developed to determine the relationship between serum GGT activity and serum IgG concentration. RESULTS: Sensitivity ranged from 0.56 to 0.89, and specificity ranged from 0.88 to 0.31, depending on the value of serum GGT activity chosen as a threshold. Proportion of crias correctly classified ranged from 0.76 to 0.52. Regression models failed to demonstrate a significant relationship between serum GGT activity and serum IgG concentration. CLINICAL IMPLICATIONS: Passive transfer status in crias cannot be accurately predicted on the basis of serum GGT activity.

Aging↗
PubMed1987

Plasmid profile of Neisseria gonorrhoeae in Nigeria and efficacy of spectinomycin in treating gonorrhoea.

The prevalence of penicillinase producing Neisseria gonorrhoeae (PPNG) strains has been steadily rising in Nigeria since 1979, and now about 80% of the strains of gonococci isolated in Ibadan are found to produce penicillinase. Spectinomycin has consequently become widely used in treating these infections. To ascertain the emergence of spectinomycin resistance, this study was undertaken to assess the in vivo susceptibilities of gonococcal strains to spectinomycin and other common antibiotics. Five hundred and twenty seven isolates were tested, of which 452 (85.5%) were PPNG strains. None of the strains were found to be resistant to 100 micrograms spectinomycin discs in vitro, whereas all 370 patients treated with the antibiotic were bacteriologically cured. Plasmid analysis shows that both "Asian" and "African" PPNG types are circulating in Nigeria. For the moment spectinomycin remains highly effective in treating gonococcal infections in west Africa.

Drug Resistance, Microbial↗
PubMed1985

Penicillinase-producing Neisseria gonorrhoeae: epidemiology, antimicrobial susceptibility and plasmid types.

Between 1976 and 1984 204 infections by penicillinase-producing Neisseria gonorrhoeae (PPNG) were seen in the Whitechapel Clinic. In 1984 PPNG were isolated from 4.7% of all patients attending with gonorrhoea. Three infections were homosexually acquired; 140 infections (68%) were acquired in the U.K. Strains that were tested were fully sensitive to spectinomycin (190), cefuroxime (177), kanamycin (170), amoxycillin combined with clavulanic acid (24) and rosoxacin (18). Of 135 strains 61% were resistant to co-trimoxazole, 69% of 169 to tetracycline (MIC greater than or equal to I mg/l) and 32% of 75 to streptomycin. Of 109 strains subjected to plasmid typing, 72(66%) were Asian strains. Of these, 55 (50% of the total) were without and 17 (16% of the total) possessed the 24.5 Mdal transfer plasmid; 27 (25%) were African strains without and 10 (9%) with the transfer plasmid. Of the Asian strains 10 were acquired in Africa. All four plasmid-containing strains are now endemic in the U.K. On the basis of the sensitivity tests, spectinomycin, cefuroxime and kanamycin should be effective in treatment, but not co-trimoxazole and tetracycline.

Drug Combinations↗
PubMed1984

Epidemiology of penicillinase-producing Neisseria gonorrhoeae in Liverpool from 1977 to 1982.

After the 1976 outbreak of penicillinase-producing Neisseria gonorrhoeae (PPNG) infections had been controlled, less than 1 per cent of cases of gonorrhoea in Liverpool in 1977 and 1978 were caused by PPNG. Thereafter the steady increase in PPNG infections to 5.6 per cent of all cases in 1982 was associated with marked changes in epidemiological pattern, plasmids and auxotypes. In 1976 nearly all PPNG infections were acquired by young black males living in the inner city from women frequenting clubs; the PPNG were all of the African 3.2 megadalton (MD) plasmid type and of arginine-requiring auxotype. Between 1977 and 1982 female patients were increasingly ship girl prostitutes associating with seamen who constituted more than 50 per cent of the male patients. These men and other travellers introduced PPNG into Liverpool from the Far East and West Africa. In 1978 PPNG of the Asian type with 4.4 MD plasmid with or without 24.5 MD transfer plasmids were isolated in Liverpool where in 1979 all PPNG carried 4.4 MD and 24.5 MD plasmids. In 1982 strains of the 'new' African type with 3.2 and 24.5 MD plasmids were isolated as were PPNG of the Asian type that had been acquired in West Africa. Auxotyping of the 1982 isolates showed that none were arginine-requiring but three other types were identified: proline-requiring: proline-arginine-requiring; non-requiring. For the control of PPNG, a strategy based on constant vigilance, appropriate diagnostic procedures, rapidly effective treatment and determined contact tracing is needed.

Adolescent↗
PubMed1983

Essential mixed cryoglobulinaemia with false-positive serological tests for syphilis.

Analysis of serum from a patient with cutaneous leukocytoclastic vasculitis showed a mixed cryoglobulin with a monoclonal IgM kappa-antiglobulin component (6.5 mg/ml), strong rheumatoid factor activity (latex titre 1/5000), and positive serological tests for syphilis (fluorescent treponemal antibody-absorbed and Treponema pallidum haemagglutination assay). After removal of antiglobulin activity by immunoabsorption with heat-aggregated gammaglobulin all serological test results for treponemal infection became negative. Serological tests for syphilis and rheumatoid factor on the supernatant from whole serum (minus cryoglobulin) remained positive though at a lower titre (latex 1/1250). Cryoglobulin isolated from whole serum retained rheumatoid and TPHA reactivity but was negative in the FTA-ABS test. The IgM and IgG cryoglobulin components purified by gel filtration on Sepharose showed no antitreponemal reactivity even when tested individually. Reducing the concentration of cryoglobulin to 1.5 mg/ml by plasma exchange converted the test results for syphilis to doubtful-positive or negative. These results indicated that high concentrations of antiglobulin activity may be associated with falsely positive specific antitreponemal test results and that this phenomenon depends on the concentration of cryoglobulin in the test sample.

Cryoglobulinemia↗
PubMed1981

A survey of beta-lactamase-producing gonococcal isolates reported in the United Kingdom 1979--80. The present trend.

104 strains of penicillinase-producing Neisseria gonorrhoeae (P.P.N.G) from England, Scotland, and Wales were reported to the V.D. Reference Laboratory and the Communicable Disease Centre, Colindale, in 1979. By contrast, there were only 15 reported cases in 1977 and 31 in 1978. The majority of patients each year contracted their infections overseas, primarily in South-East Asia and West Africa, but in 1979 41 patients (39%) reported contracting their infections in the United Kingdom. Of these 17 were secondary contacts of patients who had acquired their infection outside the U.K., but in 8 cases the primary contact was in the United Kingdom. The current incidence of P.P.N.G. in the U.K. is low compared with that in Singapore and the Philippines, but continued epidemiological assessment is essential because not all laboratories use this reference reporting system. The number of P.P.N.G. strains reported up to October, 1980, shows a considerable increase over those seen during 1979.

Adolescent↗
PubMed1981

Evaluation of the coagglutination test for the identification of Neisseria gonorrhoeae in primary cultures.

The coagglutination (COA) test for the identification of Neisseria gonorrhoeae was compared with immunofluorescence and sugar degradation tests on 1710 gonococcal isolates, 72 of which produce beta-lactamase. The COA test gave a positive result for 98.6% of the strains. Treatment of suspensions with Streptomyces enzyme reduced the incidence of inconclusive results due to autoagglutination to 1.2%. Cross-reactivity of the gonococcal antiserum was minimised by absorption with meningococci and Moraxella species. The COA provide a simple, quick, and reliable method for identifying N gonorrhoeae in culture.

Agglutination Tests↗
PubMed1975

A comparison between sorbent and Reiter sonicate in the absorbed fluorescent treponemal antibody test.

Some syphilitic sera still fluoresce with Reiter treponemes as the antigen after treatment with the sorbent used in the FTA-ABS test; this finding indicates incomplete removal of group antitreponemal antibody. Levels of this antibody in normal sera have been studied in relation to the titration of sorbent for use in the test. A comparison has been made of the results of FTA-ABS tests with sorbent and Reiter sonicate and the TPI test on 1141 selected problem sera. Results with the sonicate displayed closer agreement (60.9%) with those of the TPI test than did tests with sorbent 40.8%). The use of sonicate as the sorbing agent is thought to improve the performance of the FTA-ABS test without diminishing its sensitivity.

Absorption↗
PubMedDate not supplied

Rhamnus cathartica (buckthorn) hepatocellular toxicity in mice.

The toxicity of the plant Rhamnus cathartica was assessed in mice after the plant was identified as a potential cause of an idiopathic neurologic disease in horses. Another member of the Rhamnaceae family, Karwinskia humboldtiana, is neurotoxic to mammals and birds and can induce hepatic degeneration and necrosis. To investigate the toxicity of R. cathartica, a 34-day feeding trial in mice was conducted using a complete rodent diet with 0, 5, or 25% added R. cathartica. No clinical signs or gross lesions were seen, and all major tissues were histologically normal except the liver. The livers of mice fed R. cathartica had marked hepatocellular swelling. Results from periodic acid-Schiff reaction staining and from electron microscopy confirmed that the swelling was due to deposits of monoparticulate glycogen (beta particles) in the cytoplasm. Glycogen deposition is an uncommon toxic change in cells. Apparently, compound(s) in R. cathartica directly or indirectly interfered with glycogen metabolism (either glycogenesis or glycogenolysis). Mechanistic and chronicity studies with R. cathartica are needed to investigate the pathophysiology of the glycogen disturbance and to determine if hepatic injury progresses and if other organs will be injured.

Animal Feed↗