Endemic carbapenem-resistant Acinetobacter baumannii in a London hospital

Rohini J. Manuel*, Gee Yen Shin, N. Farrag and Richard Holliman

Department of Medical Microbiology, St George’s Hospital, Blackshaw Road, London SW17 0QT, UK

Keywords: carbapenem-resistant, Acinetobacter baumannii

Sir,

We read with interest the report by Towner et al.1 of a carbapenem-resistant strain of Acinetobacter baumannii imported from Spain. We would like to share our experience with multi-resistant strains of A. baumannii and add to the current knowledge base regarding this important marker of cross-infection.

In a number of London hospitals, including our own, A. baumannii isolates (three distinct clones) susceptible only to meropenem, amikacin and colistin have been endemic for several years, particularly in the intensive therapy unit (ITU) setting. Recently, however, A. baumannii isolates resistant to meropenem and amikacin have emerged in our institution, most likely through broad-spectrum antibiotic therapy and selection pressure. The carbapenem-resistant strain has become established in the general ITU, which, like most ITUs in this country, has high levels of antibiotic use.

Despite strict infection control measures, enhanced environmental cleaning, extra vigilance and education of ITU medical and nursing staff, this carbapenem-resistant A. baumannii strain is now endemic. Over a 2 month period, the carbapenem-resistant A. baumannii spread to the cardiothoracic ITU (geographically disparate), and then to a general ward (through patient transfer from the general ITU).

Environmental testing was carried out on the general ITU following the first isolation of carbapenem-resistant A. baumannii, and this organism was found on a patient’s bed, drip stand and wash bowl. The isolate was initially found in sputum, blood cultures or intravascular catheter tips from seven patients. Subsequent typing of carbapenem- and aminoglycoside-resistant A. baumannii isolates by pulsed-field gel electrophoresis has shown that a distinct clone is represented in the outbreak (Table 1). All clinical isolates were significant, and patients were treated for ventilator-associated pneumonia or line-associated bacteraemia with intravenous colistin.2 There were no side effects to colistin therapy, and all patients responded well.


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Table 1.  Molecular comparison of A. baumanii isolates by pulsed-field gel electrophoresis of ApaI chromosomal DNA digests
 
To the best of our knowledge, there has been only one report of endemic carbapenem-resistant A. baumannii in the UK.3 Other reports of carbapenemase producing Acinetobacter have been of single isolates.1,4

The carbapenem resistance appears to be due to metallo-ß-lactamase. We have recent evidence of the transfer of the multiple antibiotic resistance (possibly via an integron) to other bacterial species including Escherichia coli, Enterobacter cloacae and Klebsiella aerogenes (further studies of this phenomenon are in hand).

Multidrug-resistant (including carbapenem-resistant) Gram-negative bacteria pose a serious problem due to the lack of therapeutic options and the potential transfer of antibiotic resistance to more virulent pathogens. The continuing evolution of Acinetobacter spp. demands our continued surveillance of at-risk units, considered antibiotic use and a redoubling of multi-disciplinary infection control efforts.

Acknowledgements

We thank the Infection Control Team, the Laboratory of Hospital Infection and the Antibiotic Resistance Monitoring and Reference Laboratory (ARMRL) for collection, typing and susceptibility testing of the isolates.

Footnotes

* Corresponding author. Tel: +44-20-8725-5676; Fax: +44-20-8725-5694; E-mail: rmanuel{at}doctors.org.uk Back

References

1 . Towner, K. J., Gee, T. & Boswell, T. (2002). An unwanted import to the UK: a carbapenem-resistant clinical isolate of Acinetobacter baumannii producing metallo-ß-lactamase. Journal of Antimicrobial Chemotherapy 50, 1092–3.[Free Full Text]

2 . Levin, A. S., Barone, A. A., Penco, J. et al. (1999). Intravenous colistin as therapy for nosocomial infections caused by multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii. Clinical Infectious Diseases 28, 1008–11.[ISI][Medline]

3 . Das, I., Lambert, P., Hill, D. et al. (2002). Carbapenem-resistant Acinetobacter and role of curtains in an outbreak in intensive care units. Journal of Hospital Infection 50, 110–4.[CrossRef][ISI][Medline]

4 . Tysall, L., Stockdale, M. W., Chadwick, P. R. et al. (2002). IMP-1 carbapenemase detected in an Acinetobacter clinical isolate from the UK. Journal of Antimicrobial Chemotherapy 49, 217–8.[Free Full Text]