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Biomedical subjects

A P Johnson

Publications and source records attributed to A P Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Multiple components are involved in the efficient joining of double stranded DNA breaks in human cell extracts.

We describe a rapid and efficient in vitro system for the rejoining of double stranded breaks in DNA based on extracts of human 293 cells. Using this system as an assay, we have separated the nuclear extract into several components involved in break rejoining. The unfractionated system can convert approx. 100% of the input DNA, linearized with a restriction enzyme, to high molecular weight material at low temperature (17 degrees C), and at the physiological temperature of 37 degrees C we have shown that competing activities in the extract can also act on the DNA template. We present the fractionation of the extract and the partial purification of a novel factor which will stimulate a crude rejoin activity and in addition increases the activity of purified DNA ligase I. We have also partially purified the break joining activity and show that the chromatographic properties do not directly correspond with the three DNA ligases previously described, indicating that the activity observed may not be due to a single enzyme species. By studying the rejoining of double stranded DNA breaks as a biochemical process, we have demonstrated that the efficient joining of such breaks requires factors in addition to DNA ligases.

Cell Extracts↗
PubMed1992

Multiresistant Klebsiella pneumoniae in a neonatal nursery: the importance of maintenance of infection control policies and procedures in the prevention of outbreaks.

During a 3-week period, nine babies in the neonatal unit of a large teaching hospital in Durban were infected or colonized with Klebsiella pneumoniae resistant to a range of antimicrobial agents including amikacin and cefotaxime. Resistance to cefotaxime was reduced by clavulanic acid in vitro suggesting production of extended-spectrum beta-lactamase activity. All the isolates had the same antibiotic resistance profile, belonged to the same serotype (K17), were non-typable with bacteriophages, and had identical plasmid profiles indicating that they belonged to the same strain. During a 1-day microbiological survey of the ward, the outbreak strain was isolated from the nose and hands of a doctor based in the nursery and from the hands of a nurse and the mother of an infected baby. The strain was also isolated from nine of 67 environmental samples. Investigation revealed that infection control practices which had been instituted following a previous outbreak in the nursery with multi-resistant methicillin-resistant Staphylococcus aureus (MRSA) were not being adhered to. The re-introduction and strict enforcement of these procedures under the supervision of an Infection Control Nurse resulted in the abrupt end of the outbreak.

Amikacin↗
PubMed1992

Outbreak of infection in two UK hospitals caused by a strain of Klebsiella pneumoniae resistant to cefotaxime and ceftazidime.

During an 8-month period, Klebsiella pneumoniae resistant to cefotaxime and ceftazidime were isolated from 18 elderly patients in two closely-situated UK hospitals. Amongst these 18 patients, the organisms were isolated from urine samples of 17, from blood cultures of two and from a wound swab of one. The infected patients were located in nine different wards and several of the patients had been transferred between wards, within and between the two hospitals. All the bacterial isolates belonged to serotype K62, were non-typable or reacted only weakly with bacteriophage, showed similar plasmid profiles and were resistant to tetracycline and trimethoprim, thus indicating they were the same strain. Resistance to cefotaxime and ceftazidime was inhibited by clavulanic acid suggesting the involvement of extended-spectrum beta-lactamase (ESBL) enzyme activity. This was confirmed by analytical isoelectric focusing, which showed that isolates each produced two beta-lactamases with isoelectric points of 7.0(SHV-3) and 7.6 (SHV-1/2) respectively.

Cefotaxime↗
PubMed1992

Binding of Haemophilus ducreyi to extracellular matrix proteins.

A collection of Haemophilus ducreyi isolates were screened for the ability to bind to fibrinogen, fibronectin, collagen, gelatin and laminin by a particle agglutination test using latex beads coated with the individual proteins. Thirteen of 21 isolates reacted with all five extracellular matrix proteins. Binding of organisms to protein-coated latex beads was inhibited by pretreatment of the bacteria with detergent, trypsin or boiling. Two isolates did not bind to collagen and gelatin with one of these not reacting with laminin either. Seven strains which failed to react with laminin did not express pili when examined by electron microscopy. This observation suggests a specific interaction with the pili of H. ducreyi.

Agglutination Tests↗
PubMed1992

Lack of immunoglobulin A1 protease production by Haemophilus ducreyi.

A collection of 20 strains of Haemophilus ducreyi including freshly isolated, low-passage and multi-passage reference strains was examined for immunoglobulin A1 protease production by SDS-PAGE and immunoblotting. None of the strains demonstrated IgA1 protease activity despite the fact that different culture media were used. By direct immunofluorescence testing, binding of IgA to Haemophilus ducreyi organisms could be demonstrated.

Blotting, Western↗
PubMed1992

Milk nasendoscopy in the assessment of dysphagia.

The bedside assessment of dysphagia may be difficult, due to the inability to witness the act of swallowing directly. The milk test described in this paper gives a good assessment of swallowing, is cheap and easily portable and allows an instant decision to be made without recourse to special investigations.

Animals↗
PubMed1992

Prevalence of a plasmid-mediated type II dihydrofolate reductase gene among trimethoprim-resistant urinary pathogens in Greek hospitals.

The genetic basis of trimethoprim resistance was examined in 24 Klebsiella pneumoniae, 27 Enterobacter cloacae, five Enterobacter aerogenes and nine Serratia marcescens urinary isolates from five hospitals in Greece. Analysis of the 65 isolates by serotyping and phage-typing identified 53 distinct strains. Thirty-eight isolates (15 K. pneumoniae, 19 E. cloacae, two E. aerogenes and two S. marcescens) hybridized with a probe specific for a gene encoding type II dihydrofolate reductase (DHFR). Three of the K. pneumoniae and four of the E. cloacae isolates which reacted with this probe also hybridized with probes specific for type I DHFR and transposon Tn7. Two E. cloacae isolates hybridized only with the probe for type I DHFR, while a further three isolates hybridized only with the type I DHFR and Tn7 probes. None of the isolates hybridized with a probe for type V DHFR. The plasmids in transconjugants derived from 40 isolates were analysed by digestion with restriction enzymes and Southern blotting. Eighteen (45%) of the donors (12 K. pneumoniae and 6 E. cloacae) produced transconjugants containing plasmids of about 95 kb in size, while transconjugants from the other donors had plasmids in the range 100-185 kb. Of the 18 transconjugants containing a 95 kb plasmid, 15 had similar restriction endonuclease digest patterns, although they varied in terms of the range of antimicrobial resistances which they encoded. When EcoRI digests of these 15 plasmids were hybridized with the type II DHFR probe, a 23 kb common band reacted with the probe.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross Infection↗
PubMed1991

Absence of extracellular enzyme activity and cytotoxicity in cell-free culture filtrates of Haemophilus ducreyi.

Ten isolates of Haemophilus ducreyi, including seven clinical isolates and three laboratory reference strains, were assessed for their ability to produce extracellular enzymes which might contribute to their pathogenicity. Protease, elastase, lecithinase, lipase or collagenase enzyme activity were not detected in culture filtrates from any of the isolates tested using either plate or spectrophotometrical assays. Furthermore, cell-free culture filtrates did not exhibit cytotoxic activity in vitro when tested using either an established tissue culture cell line (Vero) or a primary cell culture of human keratinocytes. These results suggest that extracellular products do not play a role in host invasion or production of tissue damage by H. ducreyi.

Cell-Free System↗
PubMed1991

Distribution and transferability of plasmids encoding trimethoprim resistance in urinary pathogens from Greece.

Of 505 strains of Enterobacteriaceae responsible for significant bacteriuria and isolated from hospital patients in two Greek cities in 1989, 151 strains (30%) were resistant to trimethoprim (MIC greater than or equal to 4 mg/L) and 220 (44%) were resistant to sulphamethoxazole (MIC greater than or equal to 64 mg/L); 127 (84%) of the trimethoprim-resistant strains exhibited high-level resistance (MIC greater than 1024 mg/L) and 121 (80%) were additionally resistant to four or more other antibiotics. Plasmids were detected in 141 (93%) of the trimethoprim-resistant strains. Trimethoprim resistance was encoded on self-transmissible plasmids in 79 (52%) of the resistant strains, and in a further seven strains (5%), plasmids coding for trimethoprim resistance could be mobilised by X+ factor. Co-transfer of various other antimicrobial resistances with trimethoprim resistance was observed, tetracycline resistance being the most common. The low degree of linkage observed between trimethoprim resistance and resistance to streptomycin and spectinomycin suggests that Tn7 is relatively uncommon in Greece. Classification of trimethoprim-resistance plasmids on the basis of their antimicrobial-resistance patterns and molecular mass revealed 39 different profiles. Overall, these findings differ from those from other European countries where the prevalence of transferable high-level trimethoprim resistance is low and where chromosomal Tn7-encoded trimethoprim resistance is common.

Bacteriuria↗
PubMed1991

Patterns of epithelial migration in the unaffected ear in patients with a history of unilateral cholesteatoma.

Epithelial migration in a centrifugal manner is an established phenomenon in the normal human tympanic membrane. This pattern of migration is symmetrical in both ears of any one individual. We present a prospective study on the pattern of tympanic ink dot migration on the normal drum, in patients with a history of cholesteatoma in one ear. It was demonstrated that patients who develop cholesteatoma have a normal migratory pattern and rate in the unaffected ear. The conclusion from this study is that defective migration is not the initiating factor in the development of acquired cholesteatoma.

Cell Movement↗
PubMed1990

Effect of iron limitation on protein composition and ultrastructure of Haemophilus ducreyi.

Protein profiles of whole cells of Haemophilus ducreyi grown in the presence or absence of the iron chelator desferal, were compared by polyacrylamide gel electrophoresis. Each of four strains produced novel proteins in the range 43-160 kDa when cultured under conditions of reduced iron availability. At some sub-inhibitory concentrations, desferal produced enhanced growth, possibly due to it functioning as an exogenous siderophore. Organisms grown under conditions of reduced iron availability ultrastructurally showed also large periplasmic spaces between cytoplasm and outer membrane.

Bacterial Proteins↗
PubMed1990

The evolutionary watershed of susceptibility to gonococcal infection.

Gonococci do not cause genital infection in any convenient experimental animal, but all too easily cause genital infection in humans. To determine the 'evolutionary watershed' of gonococcal infections (the point on the evolutionary tree at which susceptibility to gonococcal infection begins) we extended previous studies of the interaction of gonococci with animal oviduct mucosa to include chimpanzees and baboons. Gonococci attached to, damaged, and invaded the oviduct (fallopian tube) mucosa of chimpanzees (which are apes) but not the oviduct mucosa of baboons (which are monkeys). Thus, the pattern of gonococcal infection in chimpanzees was identical to that in humans, whereas the pattern in baboons was like that in other animals. These studies indicate that the point in evolution at which susceptibility to gonococcal infection commences is between baboons and chimpanzees (or between monkeys and apes). Susceptibility to gonococcal disease appears to require the presence on genital epithelial cells of receptors for gonococcal ligands such as pili, receptors for gonococcal lipopolysaccharide, or both. The physiological role of these receptors may be to interact with more useful, as yet unidentified molecules.

Animals↗