Development and evaluation of a real-time quantitative PCR for the detection of human cytomegalovirus

A novel real-time quantitative PCR (QPCR) assay is described for monitoring CMV DNA load in clinical specimens using the LightCycler. The assay is rapid (< 40 min), easy to carry out, robust, reliable and is capable of detecting from 10 to over 2 x 10(5) CMV DNA copies with a wide linear range. Amplification and detection occur simultaneously, avoiding the need for post-PCR analysis and thereby minimising the risk of carryover contamination. The assay proved to be accurate, specific and reproducible when evaluated in three different laboratories. In addition, LightCycler results were comparable with those of TaqMan, an independent real-time QPCR assay.

Epidemiology and molecular typing of an outbreak of tuberculosis in a hostel for homeless men

AIM

To investigate a possible outbreak of tuberculosis in a hostel for homeless men using IS6110 profiling, a polymerase chain reaction (PCR) based fingerprinting technique.

METHODS

Eight cases of tuberculosis were diagnosed in residents of the hostel over a period of 28 months. To provide epidemiological data, a heminested inverse PCR (HIP) assay targeting the insertion sequence IS6110 together with its upstream flanking region was used to fingerprint the eight isolates of M tuberculosis under investigation.

RESULTS

The HIP technique gave IS6110 profiles which showed that while three isolates were clearly distinct, the remaining five strains were indistinguishable, suggesting the latter were representatives of a single outbreak strain.

CONCLUSIONS

The HIP assay proved discriminatory and facilitated repeated testing for the direct comparison of strains as more patients presented over the protracted course of this outbreak.

Comparison of PCR detection of mecA with methicillin and oxacillin disc susceptibility testing in coagulase-negative staphylococci

The provisional BSAC method for the detection of methicillin sensitivity in coagulase-negative staphylococci (CNS) requires incubation of isolates for 48 h and raises the problem of timely reporting of susceptibility data. The forthcoming withdrawal of methicillin raises another difficulty. We evaluated 42 clinically significant CNS blood culture isolates by PCR, methicillin and oxacillin disc testing and by using methicillin Etests. Our results suggest that, although oxacillin disc susceptibility testing is a reasonable first line step, optimal and timely detection of resistance or susceptibility may require a combination of phenotypic and genotypic methods.

Rapid detection of methicillin-resistant staphylococci by multiplex PCR

A multiplex PCR was developed to detect the coagulase gene (coa; pathognomic of Staphylococcus aureus) and the mecA gene (characteristically encoding for methicillin resistance in staphylococci) in a single, rapid test. Suitable primers for the gene targets and an internal, amplification control were incorporated into a multiplex PCR assay, which was then optimized on a capillary air thermal cycler to improve the turnaround time of the test to approximately 1.5 hours. The assay was evaluated with 111 fresh clinical isolates of staphylococci. The multiplex PCR correctly distinguished between isolates of S. aureus, which were sensitive to methicillin (MSSA) and those resistant to it (MRSA). It also correctly differentiated between similar isolates of coagulase negative staphylococci (MSSE and MRSE respectively). It was concluded that this multiplex PCR was a rapid and reliable method for the detection of methicillin-resistant staphylococci.

Rapid identification of Mycobacterium bovis BCG by the detection of the RD1 deletion using a multiplex PCR technique

The BCG vaccine strain cannot, with confidence, be differentiated from other members of the Mycobacterium tuberculosis complex on phenotypic tests alone. Isolates from clinical sites not associated with vaccination may be confused with M. tuberculosis. A characteristic of BCG strains is the deletion of the genomic region RD1; detection of this forms the basis of a multiplex polymerase chain reaction (PCR) assay to distinguish BCG strains. In this study, 28 M. tuberculosis complex strains were analysed by the PCR assay. A DNA sequence displaying the characteristic deletion was detected in all eleven of the BCG strains tested and was not found in representatives of other members of the complex, including M. bovis. Thus, the assay affords a rapid, simple and effective method for the discrimination of the BCG vaccine strain from other members of the M. tuberculosis complex.

A rapid polymerase chain reaction technique for detecting M tuberculosis in a variety of clinical specimens

A rapid in-house polymerase chain reaction (PCR) assay is described for the direct detection of Mycobacterium tuberculosis complex in clinical material. Its performance is compared with two kit based systems. The results of the in-house assay were comparable with the commercial assays, detecting M tuberculosis in 100% of smear positive, culture positive samples. The in-house assay proved to be rapid, easy, and inexpensive to perform, and the inclusion of an internal inhibitor control permitted validation of the PCR results.

Differentiation of strains of Mycoplasma fermentans from various sources by pyrolysis mass spectrometry

Mycoplasma fermentans has attracted much interest both as a cofactor for the progression of AIDS and as a pathogenic agent in non-AIDS related diseases. Previous studies with serological and genetic techniques suggest that M. fermentans represents a homogeneous group of organisms, with no significant differences identified among the strains examined. In this study, 25 cultures of M. fermentans, including isolates from human sources and tissue culture cells, were compared by pyrolysis mass spectrometry (PMS). It was possible to distinguish the 'type' strain PG-18 from an AIDS-associated M. fermentans strain 'incognitus' by this technique. PMS was also able to differentiate laboratory-induced aminoglycoside-resistant variants from their fully susceptible parents. Four AIDS-associated isolates were distinguished from each other, whilst five European cell culture isolates were shown to be closely related, as were six M. fermentans isolates from an outbreak of acute respiratory infection in Canada. PMS has proved useful in distinguishing isolates of M. fermentans, providing epidemiological data. In addition, PMS may help in determining the likely origin of a given isolate, and in the future may be of use in assessing the role of this micro-organism in human disease.

Abnormal phagocytic function in children under one year of age

The action of white blood cells (WBC) against Proteus mirabilis was assayed in 22 children following meningitis or septicaemia and compared with that in control groups of: (1) adult volunteers, (2) children undergoing minor surgical procedures for non-infective conditions, and (3) children being investigated for suspected renal disease. WBC bacterial killing tests were normal in all 55 adult volunteers. Abnormal results were obtained in 11 of 22 (50%) children with meningitis or septicaemia, 10 of 21 (47.6%) children undergoing surgery and six of 13 (46%) children with suspected renal disease, thereby indicating that there were no significant differences in phagocytic function among these three groups. Of children aged 1 year or less, 75% had abnormal phagocytic function. The significance of this finding is discussed.

Nosocomial enterococci: resistance to heat and sodium hypochlorite

Six strains each of Enterococcus faecium and E. faecalis were investigated with respect to their resistance to heat and sodium hypochlorite. All enterococci survived the temperatures and holding times specified by the Department of Health (DoH) for the disinfection of 'foul and used' or 'infected' linen (65 degrees C for 10 min or 71 degrees C for 3 min). In addition, three strains (one E. faecium and two E. faecalis) could withstand 150 ppm available chlorine for 5 min, the treatment suggested by the DoH for the disinfection of heat labile materials. Further, our results showed that four strains of E. faecium were able to survive the British Standard for heat disinfection of bedpans (80 degrees C for 1 min). The significance of these findings with particular reference to the potential for enterococci to survive and disseminate in the hospital environment is discussed.

A study of three blood culture media for isolating genital mycoplasmas from obstetrical and gynaecological patients

Mycoplasma species are often found colonising the female genital tract. Their ability to become invasive and pathogenic, however, is often ignored, since attempts may not be made to culture these organisms from the bloodstream. We have investigated the ability of three types of blood culture media to support the growth of genital mycoplasmas. The media studied included brain-heart infusion broth, brain-heart infusion broth supplemented with 30% V/V sucrose and fastidious anaerobe broth. Genital mycoplasmas were cultured from the latter medium only. Since this was the sole medium which was liquoid-free, the inhibitory effects of liquoid on Mycoplasma spp. is discussed. This study comprised an investigation of 75 patients in obstetric and gynaecological wards with postpartum or post-operative fever. Genital mycoplasmas were isolated from five (6.7%) patients, four with Ureaplasma urealyticum and one with M. hominis. The value of considering these organisms in the differential diagnosis of fever in 'at risk' patients and of including appropriate media for their isolation is emphasised.

Failure of mebendazole to cure trichomonal vaginitis resistant to metronidazole: case reports

After a recent report showing the in vitro susceptibility to mebendazole of a strain of Trichomonas vaginalis that was resistant to metronidazole, we present two cases of metronidazole resistant infection, both of which failed to respond to oral mebendazole.

Bacteriology of chronic otitis media with effusion

Samples of middle ear effusions from 102 children with serous and mucoid otitis media were cultured for mycoplasmas and bacteria. No sample yielded mycoplasmas but bacteria were cultured from 48 (47 per cent). Organisms commonly regarded as pathogens were present in 25 samples (Haemophilus influenzae 17, Streptococcus pneumoniae four, other streptococci four). The only sample from which anaerobic bacteria were isolated was from a patient with cholesteatoma.