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Antimicrobial Agents and Chemotherapy, January 2002, p. 216-219, Vol. 46, No. 1
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.46.1.216-219.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Postneurosurgical Meningitis Due to Proteus penneri with Selection of a Ceftriaxone-Resistant Isolate: Analysis of Chromosomal Class A ß-Lactamase HugA and its LysR-Type Regulatory Protein HugR
Nadia Liassine,1* Stéphanie Madec,2 Béatrice Ninet,1 Catherine Metral,1 Martine Fouchereau-Peron,3 Roger Labia,2 and Raymond Auckenthaler1
Central Laboratory of Bacteriology, University Hospital, Geneva, Switzerland,1
Centre National de la Recherche Scientifique, Unité FRE 2125, Quimper,2
Centre de Biologie Marine, Unité FRE 2125, Concarneau, France3
Received 30 January 2001/
Returned for modification 29 May 2001/
Accepted 29 September 2001

ABSTRACT
We report on a case of a postneurosurgical meningitis due to
ceftriaxone-susceptible
Proteus penneri, with selection of a
ceftriaxone-resistant isolate following treatment with ceftriaxone.
The isolates presented identical patterns by pulsed-field gel
electrophoresis and produced a single ß-lactamase
named HugA with an isoelectric point of 6.7. The ceftriaxone-resistant
isolate hyperproduced the ß-lactamase (increase in
the level of production, about 90-fold). The sequences of the
hugA ß-lactamase gene and its regulator,
hugR, were
identical in both
P. penneri strains and had 85.96% homology
with those of
Proteus vulgaris. The HugA ß-lactamase
belongs to molecular class A, and the transcriptional regulator
HugR belongs to the LysR family.

TEXT
The clinical significance of
Proteus penneri, described in 1982
as a new species (
9) and previously known as
Proteus vulgaris indole negative, is poorly documented (
13,
17). Like
P. vulgaris,
P. penneri is naturally resistant to ampicillin, narrow-spectrum
cephalosporins, and cefuroxime by the production of a ß-lactamase
commonly named cefuroximase (
7,
15,
16). Only the ß-lactamase
of
P. vulgaris has been sequenced and characterized (
6,
11).
Named CumA (
6), it belongs to molecular class A and functional
group 2 e (
4) of the ß-lactamases and is regulated
by a system common to class C of the ß-lactamases
(
6,
11).
We report on a postneurosurgical infection due to P. penneri complicated by the emergence of a ceftriaxone-resistant isolate during treatment with ceftriaxone. Our purpose was to characterize the isolates of P. penneri and to understand the emergence of a ceftriaxone-resistant isolate of P. penneri by sequencing the ß-lactamase gene and its regulator.
Case report.
After a severe cranial trauma, a reconstruction of the frontal and cranial basis with a muscular homograft and prosthetic material was performed in a 34-year-old patient. Four days later, because of suspected bronchopneumonia while the patient was under ventilation, a bronchoalveolar lavage (BAL) showed the presence of Staphylococcus aureus at 105 CFU/ml and P. penneri (isolate S08) at 104 CFU/ml. The bronchopneumonia resolved spontaneously. At day 22 a cerebral computed tomography scan followed by neurosurgical intervention showed a basal frontal breach and a cerebral abscess containing a pure culture of P. penneri (isolate S29) susceptible to ceftriaxone. Treatment with ceftriaxone (2 g twice a day [b.i.d.]), amikacin (500 mg b.i.d.), and metronidazole was instituted. Twelve days later, a P. penneri strain resistant to ceftriaxone (isolate R15) was isolated from the cerebrospinal fluid (CSF). A third neurosurgical intervention showed a frontal epidural infection and osteomyelitis due to a P. penneri strain resistant to ceftriaxone. With treatment with imipenem (500 mg four times a day) and gentamicin (120 mg b.i.d.) for 6 weeks, the patient healed without neurologic sequelae.
The isolates (S08 from BAL fluid, S29 and R15 from CSF) were identified as P. penneri with the API Rapid ID 32E gallery (bioMérieux, Marcy lEtoile, France). They showed completely identical banding patterns by molecular typing, performed by pulsed-field gel electrophoresis after digestion with SfiI and NotI (New England Biolabs, Beverly, Mass.).
The results of antimicrobial susceptibility testing, performed according to the guidelines of NCCLS (18), are reported in Table 1. The isolate from CSF, P. penneri R15, was resistant to ceftriaxone; and synergy between the amoxicillin-clavulanic acid disk and the ceftriaxone disk and/or the cefepime disk was presented for this isolate, whereas such synergy was not found for isolate P. penneri S29, susceptible to ceftriaxone. According Le Comité de lAntibiogramme of the French Society for Microbiology (1), this pattern of synergy for P. penneri suggests hyperproduction of a ß-lactamase instead of production of an extended-spectrum ß-lactamase.
Specific activities of ß-lactamase.
Bacterial strains were obtained from 4-liter cultures grown
in brain heart infusion broth. Cells were harvested by centrifugation
at 5,800
x g for 30 min. The pellets (about 12 g [wet weight])
were washed by resuspension in 24 ml of a 0.1 M NaCl solution
and centrifuged as described above, and the supernatant was
discarded. Then the pellets were resuspended in 24 ml of the
same solution and lysed by ultrasonic treatment. The crude extracts
were cleared by centrifugation at 48,000
x g for 30 min at 4°C.
These extracts were used for specific activity determinations
by computerized microacidimetry (
14).
P. penneri S29 and R15
both produced a single ß-lactamase of pI 6.7, as determined
by analytical isoelectric focusing, but the ß-lactamases
had different specific activities (
2). These activities were
determined with cephalothin as the substrate for crude extracts.
The resistant strain increased its level of ß-lactamase
production 91-fold compared with that for the susceptible strain,
with production of 8.5 ± 1 and 0.093 ± 0.01 U/mg,
respectively. The kinetic parameters of the highly purified
(>97%) ß-lactamase from
P. penneri R15 (Table
2)
showed high degrees of activity for most cephalosporins, with
kcat values ranging from 376 s
-1 for cefamandole to 65 s
-1 for
ceftriaxone. The level of hydrolysis of ceftazidime was very
low (0.5 s
-1), a value comparable to that for ticarcillin. The
enzyme was inhibited by clavulanic acid and tazobactam, with
Ki values of 0.15 and 0.12 µM, respectively. In terms
of
kcat/
Km values, cephalothin appears to be the best substrate
and ceftriaxone is hydrolyzed about two times more rapidly than
cefotaxime.
Sequencing of the ß-lactamase.
The DNAs of
P. penneri S29 and R15 were extracted by mechanical
lysis and amplified with five pairs of primers chosen according
to the sequences of the ß-lactamase gene of
P. vulgaris (
cumA gene) and its transcriptional regulator gene (
cumR gene)
(
6) (pair 1, 5'-GTCAACTCGTGAAGGGAA-3' and 5'-TTTTTGACTCCTCACGTT-3';
pair 2, 5'-AGCGCTTCATTCATTAGCCAT-3' and 5'-TGAAGCTTCAGCAAGGCACCT-3';
pair 3, 5'-CGATCTTCTAACATCCTC-3' and 5'-AAGCTCACTTAATTGCGC-3';
pair 4, 5'-TATGAGCAACAATGACTATG-3' and 5'-ACCACTGCCAGTTTTATC-3';
pair 5, 5'-TCAAGCATTAACATTAGG-3' and 5'-TATTTTGTTTGAGGTGAA-3').
Three independent PCR products from each amplification were
then analyzed by direct cycle sequencing with ABI dye terminator
TaqFSkit (Applied Biosystems, Rotkreuz, Switzerland) and the
ABI 373A apparatus (Applied Biosystems). Both strands of DNA
were sequenced. The sequences coding for the ß-lactamase,
named HugA, and an LysR-type regulator, named HugR, were identical
in the susceptible and the resistant isolates (Fig.
1). The
gene sequences had 85.96% homology with those of
P. vulgaris. The deduced amino acid sequence of the ß-lactamases
of the two isolates of
P. penneri showed structural features
typical of a class A ß-lactamase (
12): active-site
serine S*-T-S-K and its limiting elements S-D-N, E-P-E-L-N,
and K-T-G. A serine was present at position 237 (
21). The protein
alignments of ß-lactamase HugA of
P. penneri and the
CumA ß-lactamase of
P. vulgaris (
6) showed great similarities,
with 282 of 298 (94.6%) residues being identical.
The cerebral infection due to
P. penneri described here is,
to our knowledge, the first to be described and emphasizes the
virulence (
20) and the opportunistic character of
P. penneri (
18). The microorganism invaded the brain from the respiratory
tract through a breach of the cranial basis. The interest of
the present case is understanding of the emergence of a ß-lactamase-hyperproducing
mutant of
P. penneri during treatment with ceftriaxone. The
HugA ß-lactamase of
P. penneri, sequenced for the
first time in the present study, belongs to structural class
A of the ß-lactamases and was regulated by an equivalent
of the
amp system, a regulation system of class C ß-lactamases
(
15). The
ampR gene encodes a transcriptional regulator, like
hugR for
P. penneri and
cumR for
P. vulgaris, whereas
ampD encodes
an enzyme that controls the induction of the ß-lactamase
(
3,
10). A mutation of the
ampD gene results in high-level constitutive
expression of the ß-lactamase and resistance to broad-spectrum
cephalosporins. These mutants can be selected in vivo (
5,
15).
In the present case, both the ß-lactamase and transcriptional
regulator genes of the ceftriaxone-susceptible isolate and the
ceftriaxone-resistant isolate of
P. penneri have similar sequences.
This indicates that the ceftriaxone resistance is linked to
a mutation elsewhere within the
amp system and probably involves
a mutation of the equivalent of the
ampD gene in
P. penneri.
Previously, Datz et al. (
6) restored the ceftriaxone susceptibility
of a ceftriaxone-resistant isolate of
P. vulgaris by introducing
an
ampD gene. In the present case, the selection of a ß-lactamase-hyperproducing
mutant could be explained by several factors: (i) the cerebral
localization of the infection, in which the concentration of
ceftriaxone (
8) is not sufficient to inhibit the growth of mutants;
(ii) the presence of a prosthetic material, which allowed the
adherence of microorganisms; and (iii) the large bacterial inoculum,
which at the beginning contained a certain proportion of ß-lactamase-hyperproducing
mutants. The present case emphasizes the necessity to carefully
prescribe extended-spectrum cephalosporins as monotherapy for
the treatment of severe infections due to
P. penneri.
Nucleotide sequence accession number.
The sequence coding for the ß-lactamase, named HugA, and a LysR-type regulator, named HugR, can be found in the GenBank database under accession number AF324468.

ACKNOWLEDGMENTS
We thank Wladimir Sougakoff for determination of the isoelectric
point of the ß-lactamase, Reno Frei for the typing
of isolates by pulsed-field gel electrophoresis, and Isabelle
Jan for technical assistance.

FOOTNOTES
* Corresponding author. Present address: Laboratoire Bioanalytique-Riotton, 53 avenue Blanc, 1211 Geneva 2, Switzerland. Phone: (41) (22) 716 20 04. Fax: (41) (22) 716 20 07. E-mail:
nliassine{at}unilabs.ch.


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Antimicrobial Agents and Chemotherapy, January 2002, p. 216-219, Vol. 46, No. 1
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.46.1.216-219.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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