PER-1 ß-lactamase-producing Pseudomonas aeruginosa in an intensive care unit

Geert Claeys*, Gerda Verschraegen, Thierry de Baere and Mario Vaneechoutte

Laboratory for Bacteriology and Virology, University Hospital, De Pintelaan 185, 9000 Ghent, Belgium

Sir,

New ß-lactamases are one of the mechanisms by which Gram-negative bacteria exhibit antibiotic resistance. Extended-spectrum ß-lactamases (ESBLs) account for many of these enzymes and are commonly found in Enterobacteriaceae. Although Pseudomonas aeruginosa easily acquires resistance to new ß-lactams, ESBLs are rarely responsible, and only PER-1, TEM-4 and -42, SHV-2a, VEB-1 and OXA-18 have been described so far.1,2 We recently discovered ESBL-producing P. aeruginosa isolates in our hospital, whose characteristics are described below.

In October 1998 our attention was drawn to the results of the disc diffusion susceptibility testing for a P. aeruginosa isolate (9809*06400) with the exceptional phenotype ‘piperacillin-S/ceftazidime-R’ (PIP-S/CAZ-R). This phenotype was characterized by the absence of an inhibition zone for ceftazidime and a clear inhibition zone for piperacillin. The isolate was also resistant to gentamicin, tobramycin, isepamicin, amikacin, quinolones and cefepime, but remained susceptible to imipenem. Because this CAZ-R/PIP-S phenotype is observed in many of the ESBL-producing Enterobacteriaceae at our hospital, the presence of an ESBL in this pseudomonal isolate was suspected and a disc approximation test was performed. A synergic ‘ghost zone’ could be observed between the CAZ 30 µg disc and the amoxycillin/clavulanic acid 20/10 µg (AMX-30) disc, but not between the PIP-100 and the AMX-30 discs.

Between October 1998 and April 1999 we obtained a total of 11 isolates from clinical specimens and also two isolates from environmental samples, all with the same susceptibility phenotype.

PER enzyme-mediated resistance was confirmed by amplification and sequencing, using the primers PER-1 (ATG AAT GTC ATT ATA AAA GC) and PER-2 (AAT TTG GGC TTA GGG CAG AA), as previously described.3

Ten of the 13 isolates tested were found positive for the PER gene. The sequence for the PER gene amplified from these 10 isolates was identical for all isolates and 100% identical to the known PER-1 sequence (GenBank Z21957).

After the first ESBL-producing P. aeruginosa was detected from a sputum specimen, 10 more isolates were recovered from urine specimens during the following 7 months, all from male neurotrauma patients treated in the same room of the intensive care unit (ICU). The isolates were detected only once in each patient, and in most of the cases the cultures were preceded or followed by other bacterial isolates. As no overlap was found in the ward stay of the patients concerned, direct patient-to-patient transmission was unlikely and a common source, linked to urinary catheter placement or care, was suspected.

Several environmental cultures were taken, which were negative, except for a jar, containing a densitometer in water, and another used as a fluid waste collector. The densitometer was used for determining the density of urine in screening for diabetes insipidus in the trauma patients. It was suspected that the jar had been filled with urine of a patient and, after density determination, had been inadequately decontaminated.

DNA fingerprinting of the P. aeruginosa isolates was carried out by means of arbitrarily primed PCR with primer ERIC2 (AAG TAA GTG ACT GGG GTG AGC G),4 using RAPD Ready-to-Go beads (Pharmacia/Amersham, Uppsala, Sweden),5 and it could be shown that all 11 isolates had the same fingerprint and thus were clonally related.

After instruction on the correct cleaning of the densitometer, no further PIP-S/CAZ-R P. aeruginosa isolates have been found. It can be concluded that all the CAZ-R/PIP-S P. aeruginosa isolates from patients in this ICU room were the result of pseudo-infection.

The first two isolates, however, were from sputum and a urine specimen from another room in the ICU, and probably represent true infection. The DNA-fingerprint of these first two isolates was similar to that of the pseudo-outbreak urinary isolates.

The first PER-1 ß-lactamase-producing P. aeruginosa was isolated in 1991 from a Turkish patient in Paris,1 and the enzyme was present in 15 P. aeruginosa isolates collected in Turkey between 1991 and 1993. In later studies,6 PER-1 was found also in other species, i.e. in K. pneumoniae, Acinetobacter spp. and Salmonella spp. Until now PER-1 has not been reported from other countries.

Although there is a sizeable Turkish population in Ghent, none of the patients involved were of Turkish origin and none of the first patients who harboured the PER-1 P. aeruginosa had recently travelled to Turkey. The findings reported here illustrate that the broad-spectrum ß- lactamase PER-1 can be found outside Turkey and that P. aeruginosa isolates with the CAZ-R/PIP-S phenotype should be suspected of carrying the PER-1 gene.

Acknowledgments

We thank Mr J. De Schuijmer, from the hospital hygiene department, for help in the epidemiological investigations.

Notes

J Antimicrob Chemother 2000; 45: 924–925

* Corresponding author. Tel: +32-92-403645; Fax: +32-92-403659; E-mail: Geert.Claeys{at}rug.ac.be Back

References

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