The Vitek analyser for routine bacterial identification and susceptibility testing: protocols, problems, and pitfalls

Automated and semiautomated technology in microbiology has seen great advances in recent years. The choice of automated equipment for the identification and susceptibility testing of bacteria in a routine diagnostic laboratory depends on speed, accuracy, ease of use, and cost factors. The Vitek analyser (bioMerieux, UK) was installed in a busy diagnostic teaching hospital laboratory in London. This report describes one year's experience. Changes to work practice as a result of incorporating the equipment into the laboratory, and the advantages and disadvantages of automation in key areas are described in detail, together with possible solutions to problems. The Vitek analyser was found to be valuable for the speed and accuracy with which results were available for the common bacterial pathogens. Results of susceptibility testing were standardised according to NCCLS guidelines and used breakpoint MICs to ascertain susceptibility and resistance; they were an improvement on disc testing. This equipment is not a reference facility for difficult to identify organisms and many manual techniques, including some disc susceptibility testing, will have to be retained by the laboratory.

The in-vitro activity of grepafloxacin against Chlamydia spp., Mycoplasma spp., Ureaplasma urealyticum and Legionella spp

The activity of grepafloxacin, a new orally active fluoroquinolone, was compared with the activities of ofloxacin, clarithromycin and doxycycline against Chlamydia pneumoniae, Chlamydia trachomatis, Mycoplasma pneumoniae, Mycoplasma hominis and Ureaplasma urealyticum, and with the activities of ofloxacin, clarithromycin and rifampicin against Legionella spp. Grepafloxacin (MIC range 0.06-0.12 mg/L) was some 8-16 times more active than ofloxacin against the chlamydiae, showing activity similar to that of doxycycline, and equal or two- to four-fold less active than clarithromycin. Grepafloxacin was four-fold more active than ofloxacin against M. pneumoniae (MIC 0.06-0.5 mg/L) and U. urealyticum (MIC 0.12-1.0 mg/L), but 16 times more active against M. hominis (MIC 0.015-0.05 mg/L). Grepafloxacin was highly active against Legionella spp. (MIC 0.008-0.03 mg/L), showing equivalent activity to ofloxacin, clarithromycin and rifampicin.

In-vitro activity of trovafloxacin, a new fluoroquinolone, against recent clinical isolates

Trovafloxacin (CP-99,219) was very active against Gram-negative species examined including Haemophilus influenzae, Moraxella catarrhalis, Legionella spp., Neisseria spp. and Escherichia coli (MIC90s < or = 0.03 mg/L). In general trovafloxacin was twice as active as ofloxacin but only half as active as ciprofloxacin against Gram-negative species. Trovafloxacin was active against Gram-positive organisms, including Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes and Enterococcus faecalis (MIC90s < or = 0.25 mg/L). Against these organisms activity was eight to 16 times greater for trovafloxacin than for either ofloxacin or ciprofloxacin. In addition, Chlamydia spp., Mycoplasma spp. and Ureaplasma urealyticum were eight to 16 times more susceptible to trovafloxacin than to either ofloxacin or ciprofloxacin. These in-vitro data show that trovafloxacin is a broad-spectrum fluoroquinolone with greater activity against clinically important Gram-positive species compared with ofloxacin or ciprofloxacin.

Modern diagnosis and management of genital Chlamydia trachomatis infection

Chlamydia trachomatis infection is now the commonest bacterial, sexually transmitted infection in the UK. Uncomplicated genital chlamydial infection often does not produce symptoms in men or women, but patients may present with sequelae. New diagnostic techniques are available to identify C. trachomatis more easily and new antibiotic regimens provide effective treatment. These factors, together with heightened awareness within the medical profession and the general population, should help to reduce the prevalence of this infection.

Comparison of the ligase chain reaction with cell culture for the diagnosis of Chlamydia trachomatis infection in women

OBJECTIVE

To determine the sensitivity and specificity of ligase chain reaction (LCR) analysis of cervical and urine specimens from women compared with cell culture of cervical and urethral specimens for the diagnosis of genitourinary chlamydial infection.

METHODS

Women (n = 624) attending the Genitourinary Medicine Clinic at University College London Hospitals, were enrolled. Patients who had received antibiotics within the previous two weeks were excluded. Specimens were obtained from the urethra and cervix for chlamydial culture, and from the cervix for LCR. A specimen of first void urine was also obtained for LCR. Discrepancies were resolved by direct immunofluorescence or a major outer membrane protein targeted LCR, or both.

RESULTS

The prevalence of Chlamydia trachomatis in 600 patients, using an expanded standard of a positive cell culture or two confirmed positive non-culture tests, was 13.2% (79/600). Cervical culture detected 68.4% and urethral culture 62% of all positive results compared with 81% detected by cervical LCR and 69% by urine LCR. Cervical and urethral culture combined detected 87.3% whereas cervical and urine LCR combined detected 91.1% of positive cases. Specificity of LCR was 100% in the cervix and 99.8% in urine.

CONCLUSION

This study demonstrates that LCR analysis of cervical and urine specimens is a reliable method for the diagnosis of chlamydial genital infection in women. However, the study also demonstrates that no single test will detect all chlamydial infections. Conventional non-culture tests and cell culture may grossly underestimate the prevalence of chlamydial infection. LCR analysis of a cervical specimen was superior to conventional cell culture without blind passage as a single test for diagnosing chlamydial infection in women, followed by LCR of a urine specimen.

Azithromycin in the management of Chlamydia trachomatis infections

The unique pharmacological profile of the azalide macrolide azithromycin, coupled with its in vitro activity against both Chlamydia trachomatis and the ureaplasmas, suggested that genital infections caused by these bacteria could be successfully treated with a single dose of the antibiotic. This has now been confirmed in worldwide clinical studies. A single oral dose of azithromycin 1 g eradicates C. trachomatis in almost 100% of cases of non-gonococcal urethritis and cervicitis. Unfortunately, there are no specific clinical signs for genital chlamydial infection. It is therefore necessary to use therapy effective against known and unknown pathogens for treating lower genital tract infection. Clinical cure rates for both chlamydial and non-chlamydial, non-gonococcal infections compare favourably with standard 7-day doxycycline therapy, being in excess of 85%. Side effects are few (< 20%) and essentially minor.

Assessment of the efficacy of a low temperature hydrogen peroxide gas plasma sterilization system

The STERRAD 100 sterilization system (Johnson & Johnson Medical Ltd) uses low temperature hydrogen peroxide gas plasma for sterilization of heat labile equipment. The efficacy of the machine was tested by contaminating a standard set of instruments with different organisms and using a filtration method to assess recovery of organisms from the wash fluids of instruments post-sterilization. Experiments were performed under clean (the organism only) and dirty (organism mixed with egg protein) conditions. A parallel study conducted using a 3M STERIVAC ethylene oxide sterilizer could not be completed owing to closure of the ethylene oxide plant. For sterilization of instruments with long and narrow lumens, hydrogen peroxide adaptors are necessary. The STERRAD 100 sterilizer can achieve effective sterilization of heat labile instruments with a reduction of 6 log10 cfu/mL of organisms tested. This method has the advantages over ethylene oxide sterilization of safety, ease of maintenance and no requirement for aeration time.

Clinical, laparoscopic and microbiological findings in acute salpingitis: report on a United Kingdom cohort

OBJECTIVE

To determine the clinical features and microbial aetiology of acute salpingitis in women attending an inner city teaching hospital.

DESIGN

Prospective, longitudinal cohort study.

SUBJECTS

One hundred and forty-seven women presenting consecutively with acute abdominal pain and clinical signs of acute salpingitis were evaluated microbiologically and laparoscopically.

RESULTS

One hundred and four women (70.7%) had acute salpingitis diagnosed at laparoscopy. Other pathological conditions were identified in 20 women (13.6%). No visually identifiable pathology was found in 23 (15.6%). Thirty-five women with acute salpingitis had evidence of pelvic adhesions (33.7%). Bilateral tubal occlusion was present in 6 (5.8%) cases. Chlamydia trachomatis was identified in the genital tract in 40 (38.5%) of the women with acute salpingitis and Neisseria gonorrhoeae in 15 (14.4%). A dual infection was present in eight cases (7.7%). Serological evidence suggested that a further seven women (6.7%) had acute chlamydial infections at the time of diagnosis. C. trachomatis was identified in the genital tract of 5/23 (21.7%) of the women who had no laparoscopic evidence of intra-abdominal pathology.

CONCLUSIONS

The responsible care of women with suspected acute salpingitis depends on establishing an accurate diagnosis, so that appropriate therapy can be instigated. This study provides evidence to challenge the outpatient management of acute salpingitis on clinical grounds alone as potentially inadequate. Early laparoscopy in hospitalised women improves diagnostic precision and accurately determines disease severity, providing prognostic information for future fertility. In this urban population, sexually transmitted micro-organisms were the commonest pathogens found in the genital tract of women with acute salpingitis. The high prevalence of C. trachomatis in these women suggests that appropriate chemotherapy for acute salpingitis should always include a specific antichlamydial agent.

Varicella gangrenosa with toxic shock-like syndrome due to group A streptococcus infection in an adult: case report

Varicella gangrenosa is a rare and serious complication of chickenpox that has been described in children only. We describe a case of an adult with varicella gangrenosa that presented as necrotizing fasciitis of a limb. This infection is caused by group A streptococcal superinfection of the skin lesions due to chickenpox. It can be misdiagnosed, with fatal consequences. Because of prompt recognition and aggressive surgical and medical treatment, the patient survived without loss of the affected limb.

Quinolones in sexually transmitted diseases. Global experience

The role of quinolones in sexually transmitted diseases is still being defined. In vitro and in vivo efficacy of established agents against gonorrhoea after a single oral dose is well established, although problems with emerging resistance have been identified. However, among these agents only ofloxacin is reliably active against Chlamydia trachomatis infection, and only as a course of treatment. Preliminary trials with sparfloxacin are encouraging. Other new agents show potentially useful in vitro activity, but clinical studies are awaited. To date, clinical activity of quinolones in bacterial vaginosis has been disappointing. The efficacy of newer agents with anaerobic activity will be of interest. Chancroid can be cured with ciprofloxacin or ofloxacin; resistance has been reported, but is not yet clinically significant. Ofloxacin appears to be effective therapy for pelvic inflammatory disease, without the need for additional anaerobe cover. The possibility of improved clinical efficacy justifies further in vitro and in vivo studies.

Chlamydial urethritis in heterosexual men attending a genitourinary medicine clinic: prevalence, symptoms, condom usage and partner change

A prospective study of 356 consecutive heterosexual male patients attending the Department of Genitourinary Medicine at University College Hospital was carried out to determine the prevalence of Chlamydia trachomatis. Patients were asked about their symptoms, use of condoms and change of sexual partner. The prevalence of non-gonococcal urethritis (NGU--chlamydia positive and negative urethritis) was 37% (131 of 356). C. trachomatis was shown to be the causative organism in 24% (31 of 131) of patients with NGU. The prevalence of other STDs in men with C. trachomatis and with non-chlamydial urethritis was 15% and 10% respectively. Men with C. trachomatis were significantly more likely than men with non-chlamydial urethritis to be asymptomatic (56% vs 35%). The prevalence of C. trachomatis was highest in men who had changed partner in the previous 3 months (20 of 32 men). A third of men never used condoms in the first 3 months of a new relationship and over half failed to use them after 3 months. There was no evidence that the reported use of condoms reduced the rate of infection with C. trachomatis.

Endoscope decontamination: a comparison of the Wolf 35100 and DSD-91 systems

The Wolf 35100 and DSD-91 endoscope disinfection machines were compared. Using a total viable count method, the degree of contamination of an Olympus GIFXQ20 endoscope was assessed following inoculation with a suspension of Pseudomonas aeruginosa and again following disinfection cycles in each machine, using 2% glutaraldehyde as the disinfectant. Both machines performed satisfactorily, with an average reduction of between 7 and 8 log10 cfu ml-1 P. aeruginosa following disinfection. The dilution effect on the glutaraldehyde of repeated disinfection cycles was also assessed for each machine. After 40 cycles in the DSD-91 and 25 cycles in the Wolf 35100 machines, the dilution of glutaraldehyde may give rise to concern, especially if adequate pre-cleaning of the endoscope is not carried out. The DSD-91 machine has certain advantages over the Wolf 35100 in terms of endoscope capacity, running costs and ease of maintenance. Both machines give similar results for endoscope disinfection.

Antibiotic chemotherapy of bacterial sexually transmitted diseases in adults: a review

Treatment regimens for sexually transmitted infections continue to evolve. The natural history of syphilis in HIV-infected patients is leading to more aggressive policies in terms of both investigation and treatment. In particular, treatment protocols for late syphilis, especially neurosyphilis, are under scrutiny. Epidemiological change typified by the spread of penicillinase-producing Neisseria gonorrhoeae (PPNG) has led to a search for new agents to treat gonorrhoea, with a more extensive use of cephalosporin and quinolone antibiotics emerging. The problem of compliance with the antibiotic courses presently required for chlamydial infection may be close to being solved with the development of newer macrolide agents. Single dose azithromycin, although expensive, seems to be as effective as longer courses with other agents. Furthermore, its efficacy in gonococcal infection is also encouraging. Increased understanding of the pathogenesis and natural history of pelvic inflammatory disease (PID) and bacterial vaginosis (BV) has led to rationalization of treatment policies for these conditions.