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M J Prentice

Publications and source records attributed to M J Prentice.

7 recordsLinked to original sources
PubMed1997

A graphical method for detecting recombination in phylogenetic data sets.

Current phylogenetic tree reconstruction methods assume that there is a single underlying tree topology for all sites along the sequence. The presence of mosaic sequences due to recombination violates this assumption and will cause phylogenetic methods to give misleading results due to the imposition of a single tree topology on all sites. The detection of mosaic sequences caused by recombination is therefore an important first step in phylogenetic analysis. A graphical method for the detection of recombination, based on the least squares method of phylogenetic estimation, is presented here. This method locates putative recombination breakpoints by moving a window along the sequence. The performance of the method is assessed by simulation and by its application to a real data set.

Computer Simulation↗
PubMed1979

Ureaplasma urealyticum and Mycoplasma hominis in chlamydial and non-chlamydial nongonococcal urethritis.

Urethral specimens from 726 patients with nongonococcal urethritis (NGU) were examined for Chlamydia trachomatis, Ureaplasma urealyticum, and Mycoplasma hominis. Chlamydiae were isolated from 35.9% of ureaplasma-positive patients and from 36.5% of ureaplasma-negative patients. Ureaplasmas were isolated from 52.5% of chlamydia-positive patients and from 53.1% of chlamydia-negative patients, an observation which contrasts with that of some workers who have suggested that ureaplasmas are significantly associated with chlamydia-negative NGU. Furthermore, the numbers of ureaplasmas isolated from patients who did or did not harbour chlamydiae were not significantly different nor was there a particular association of ureaplasmas with chlamydia-negative NGU in patients experiencing their first episode of disease. In addition, M. hominis was not isolated more frequently from those from whom chlamydiae were or were not isolated. The only significant associations were the isolation of M. hominis from patients who were ureaplasma-positive and of ureaplasmas from those who were M. hominis-positive. These findings do not necessarily mitigate against ureaplasmas being responsible for some cases of chlamydia-negative NGU.

Chlamydia trachomatis↗
PubMed1977

Survival of chlamydiae after cooling to -196 degrees C.

Factors influencing the survival of chlamydiae after freezing were reexamined. From the data presented, it is suggested that preservation of laboratory-grown chlamydiae is best achieved through the use of sucrose as the cryoprotective agent, in the presence of 10% serum. Dimethyl sulfoxide and glycerol are more toxic. The period of exposure to sucrose before freezing must be kept as short as possible and be at 4 degrees C rather than at room temperature. The rate of cooling during freezing in sucrose is not important; however, cooling at a rate slower than 1 degrees C/min should be avoided. Since chlamydial survival is increased by rapid thawing, the volume of the sample should be kept to a minimum. Thawed suspensions should be inoculated onto cell monolayers without delay. The application of these methods may increase the proportion of stored clinical specimens in which chlamydiae can be found.

Blood↗
PubMed1977

A microbiological study of neonatal conjunctivae and conjunctivitis.

To investigate the importance of chlamydiae, ureaplasmas, Mycoplasma hominis, and anaerobic bacteria in the pathogenesis of neonatal conjunctivitis in the Harrow population conjunctival specimens from 104 infants with conjunctivitis and 104 similar healthy neonates were examined. The incidence of neonatal conjunctivitis was 8-2%, and no case of neomycin-resistant disease occurred during the study. Staphylococcus aureus, viridans Streptococci, and Escherichia coli were the only micro-organisms isolated significantly more frequently from affected than from control eyes, which suggests that these bacteria may be a cause of the conjunctivitis. All cultures for chlamydiae, M. hominis, Neisseria gonorrhoeae, and anaerobic bacteria were negative. The mother's race, social status, illness, and obstetric events were found to have no effect on the incidence, time of onset of conjunctivitis, or micro-organisms isolated. The clinical characteristics of conjunctivitis were also not related to the micro-organisms isolated. No potential pathogens were isolated from 63-5% of the eyes showing conjunctivitis. The results suggest that some of these cases may be caused by chemical irritation, and the possibility of an infectious aetiology is also discussed.

Conjunctiva↗
PubMed1976

Non-specific urethritis. A placebo-controlled trial of minocycline in conjunction with laboratory investigations.

The results of a double-blind therapeutic trial on 81 men suffering from non-specific urethritis (NSU) show that minocycline was more effective than a placebo. Before treatment Chlamydia trachomatis was isolated from 31 per cent. of the men, ureaplasmas from 58 per cent., and Mycoplasma hominis from 7-5 per cent. There is evidence that chlamydiae are a cause of urethritis. However, after minocycline therapy improvement in the clinical response of patients from whom only ureaplasmas were isolated was less significant, so that the evidence that these organisms are pathogenic is less convincing. Possible reasons for this are discussed, as are the implications of finding minocycline-resistant ureaplasmas in at least 6 per cent. of the patients who harboured these organisms. The symptoms and signs of patients from whom micro-organisms were not isolated also improved after minocycline therapy, implying that the aetiological agents in this group of patients are antibiotic-sensitive. However, the results do not exclude the possibility that a minocycline-resistant agent is the cause of urethritis in a minority of patients.

Chlamydia↗