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Journal of Clinical Microbiology, October 1998, p. 3105-3110, Vol. 36, No. 10
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Extended-Spectrum
-Lactamase-Producing Klebsiella
pneumoniae Strains Causing Nosocomial Outbreaks of Infection
in the United Kingdom
Kevin
Shannon,1,*
Paul
Stapleton,1
Xiaoqin
Xiang,1,
Alan
Johnson,2
Hamish
Beattie,2
Fatima
El
Bakri,2,
Barry
Cookson,2 and
Gary
French1
Department of Microbiology, United Medical
and Dental Schools, St. Thomas's Campus, London SE1
7EH,1 and
Laboratory of Hospital
Infection, PHLS Central Public Health Laboratory, London NW9
5HT,2 United Kingdom
Received 21 January 1998/Returned for modification 12 May
1998/Accepted 9 July 1998
 |
ABSTRACT |
Representative isolates from 10 distinct extended-spectrum
-lactamase-producing strains of Klebsiella pneumoniae
that caused hospital outbreaks in the United Kingdom from 1991 to 1994 were examined for relationships between their enzymes and plasmids. The
-lactamases were identified by a combination of isoelectric focusing
and gene sequencing. SHV-2
-lactamase was produced by isolates from
four outbreaks, SHV-5 was involved in three, and SHV-4, TEM-15, and
TEM-26 were involved in one outbreak each. All of the extended-spectrum
-lactamases were encoded by self-transmissible plasmids, with sizes
ranging from about 70 to 160 kb. No similarities between the
restriction digest patterns of the extended-spectrum
-lactamase-encoding plasmids were detected, except to some extent between those that produced TEM-15 and TEM-26. Thus, outbreaks of
hospital infection with these organisms in the United Kingdom from 1991 to 1994 involved distinct organisms and resistance plasmids and
appeared to be unrelated.
 |
TEXT |
Members of the family
Enterobacteriaceae expressing extended-spectrum
-lactamases conferring resistance to ceftazidime and other
cephalosporins and derived from TEM-1 or SHV-1 enzymes (15) have become an increasing problem during the past two decades. During
the 1980s, occurrences were rare and most reports involved single
isolates (32), although there were a few outbreaks, most notably of TEM-3-producing Klebsiella pneumoniae in France
(38). However, in the 1990s there have been many outbreak
reports, most frequently of single strains of Klebsiella
spp., including SHV-5-producing Klebsiella strains, in
Australia (25), Germany (3), Austria (33), Great Britain (10), Italy (31),
and the United States (27, 41). In addition, an
SHV-5-encoding plasmid has spread among several strains of
Klebsiella in Greece (21) and Austria, where
three outbreaks caused by distinguishable klebsiellae carrying the same
plasmid were reported (33). Other outbreaks have included SHV-3-producing Klebsiella in Great Britain (17),
Klebsiella and other Enterobacteriaceae producing
the related
-lactamases TEM-10B, TEM-12B, and TEM-26B in Great
Britain (13), Klebsiella producing an
extended-spectrum
-lactamase that was not identified but that spread
between two hospitals in Great Britain (9), SHV-3- and
SHV-4-producing klebsiellae in France (2, 4, 7, 28),
TEM-26-producing K. pneumoniae in the United States (27, 40), and TEM-10-plus-TEM-12-producing K. pneumoniae in the United States (6). Thus, no single
extended-spectrum
-lactamase has predominated. However,
interhospital spread of extended-spectrum
-lactamase-producing
K. pneumoniae has been demonstrated in the United States
(24).
Since 1991, outbreaks of infection or colonization with distinct
strains of cephalosporin-resistant K. pneumoniae have
occurred in a number of hospitals in the United Kingdom, in addition to those already reported (9, 10, 13, 17). The epidemiology of
a number of these outbreaks is to be described by other workers (18a).
Organisms, outbreaks, and susceptibility.
In the present
study, representative isolates of 10 distinct strains of
cephalosporin-resistant K. pneumoniae producing hospital outbreaks in the United Kingdom between 1991 and 1994 were investigated to determine the relationships between their extended-spectrum
-lactamases and the plasmids encoding them. These organisms had been
submitted to the Central Public Health Laboratory by hospitals who had
epidemiological evidence of clinical outbreaks. All the outbreaks had
been characterized by capsular serotyping and either bacteriophage
typing or DNA fingerprinting by pulsed-field gel electrophoresis in the
Laboratory of Hospital Infection. The isolates chosen for study were
representative of the outbreaks and were distinct from each other by
the typing methods used (18a).
MICs were determined by broth or agar dilution in Iso-Sensitest broth
or agar (Oxoid, Basingstoke, United Kingdom) as described previously
(17, 19, 35). National Committee for Clinical Laboratory
Standards criteria were used to categorize strains as susceptible,
intermediately resistant, or resistant (26).
-Lactamases
were characterized by isoelectric focusing as described previously
(22). Plasmids were extracted by use of either the method of
Kado and Liu (18) or the alkaline lysis method of Birnboim
and Doly (5). Extracted plasmids were digested with the
restriction enzymes EcoRI, ClaI,
BamHI, and HindIII (Life Technologies,
Paisley, United Kingdom), and the resulting fragments were separated by
agarose gel electrophoresis. Each clinical isolate was mated with the
recipient strain, Escherichia coli K-12 J62.1 (nalidixic
acid resistant), or a rifampin-resistant mutant of it, in broth as
described previously (22). Transconjugants were selected on
medium containing ceftazidime (4 µg/ml) plus nalidixic acid (100 µg/ml) or rifampin (200 µg/ml). Transconjugants were assessed for
plasmid content and their antibiotic susceptibility.
Isolates from 10 distinct hospital outbreaks of infection or
colonization with extended-spectrum
-lactamase-producing klebsiellas in the United Kingdom that occurred during the period 1991 to 1994 were
investigated. Representative isolates (chosen on the basis of their
typical antibiogram and serotype), which were all K. pneumoniae, were designated D1 to D10 and are listed in
Table 1. The strains were considerably
more resistant to ceftazidime, cefotaxime, and cefepime than were
strains producing non-extended-spectrum
-lactamases.
Clavulanic acid (2 µg/ml) substantially reduced the MICs of
ceftazidime for all strains. Although the MICs of cefoxitin for some of
the strains were higher than those usually found for
Klebsiella, none was very high, and all strains were susceptible to carbapenems. The
-lactam resistance patterns of the transconjugants were similar to those of the
corresponding donors, although sometimes with a lower degree of
resistance (Table 1). Only one strain (D2) was susceptible to all the
aminoglycosides tested (Table 2), but
most strains were susceptible to amikacin. The strains were mostly
susceptible to ciprofloxacin and trimethoprim but resistant to
chloramphenicol and tetracycline.
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TABLE 1.
MICs of -lactam antibiotics and sizes of
-lactamase-encoding plasmids for Klebsiella outbreak
strains and their E. coli transconjugants
|
|
Single-plasmid transconjugants were obtained from each of the clinical
strains, and their plasmids were extracted and compared
by restriction
endonuclease digestion with
EcoRI,
ClaI,
BamHI,
or
HindIII. The plasmids in the
transconjugants were large, 70
to 170 kb (Table
1). With each of these
enzymes, the fragment
patterns appeared distinct from the patterns for
transconjugants
obtained from donors D1 and D5. With
EcoRI
digestion, a number
of common bands were noted for these two
transconjugants (Fig.
1). However,
greater diversity was noted with
ClaI and
HindIII
digestion. Neither plasmid appeared to be
digested by
BamHI.

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FIG. 1.
Agarose gel electrophoresis of restriction digests of
plasmids from the transconjugants of strains D1 and D5. Lane 1, D1
digested with ClaI; lane 2, D5 digested with
ClaI; lane 3, D1 digested with EcoRI; lane 4, D5
digested with EcoRI; lane 5, D1 digested with
HindIII; lane 6, D5 digested with
HindIII; lane 7, molecular weight markers (with weights
indicated, in thousands, to the right of the gel).
|
|
DNA sequences of
-lactamases.
PCR was used to amplify parts
of SHV or TEM gene sequences in whole-cell DNA preparations as
described previously (22). DNA preparations were made
from the klebsiellae for detection of TEM gene sequences but from
the transconjugants for detection of SHV gene sequences because of the
chromosomal SHV-1 gene usually present in K. pneumoniae. An
automated laser fluorescent DNA sequencer (Pharmacia Biotech, St.
Albans, Hertfordshire, United Kingdom) was used to sequence the
TEM PCR product, which had been labelled by the quick annealing
method, as described previously (39). A similar
procedure was used for SHV PCR products except that cycle
sequencing was performed on 1 µg of purified PCR product obtained
from transconjugants and with the reagents supplied in a
Thermo Sequenase fluorescently labelled primer cycle sequencing kit
(Amersham International, Buckinghamshire, United Kingdom). Reactions were performed as described in the manufacturer's
instructions, with 2 pmol of fluorescently labelled primer OS-1
(22) or a primer we have designated SHV-i
(5'-CCAGATCGGCGAACAACGTCACC-3'; bases 447 to 468 of the
SHV structural gene) and the following cycling conditions: 25 cycles of
30 s at 60°C and 30 s at 98°C.
Thermostable DNA polymerase from
Thermus brockianus
(DynaZyme), 10× polymerase buffer, and magnesium chloride were
supplied
by Flowgen (Lichfield, Staffordshire, United Kingdom).
Nucleotides
were obtained from Sigma (Poole, Dorset, United
Kingdom). Sterile
distilled water was molecular biology grade (Bio-Rad,
Hemel Hempstead,
Hertfordshire, United Kingdom). Synthetic
oligonucleotide primers,
AutoRead sequencing kits, and automated
laser fluorescence-grade
urea were supplied by Pharmacia Biotech.
Hydrolink Long Ranger
gel was obtained from Hoefer
(Newcastle-under-Lyme, Staffordshire,
United Kingdom). A Thermo
Sequenase fluorescently labelled primer
cycle sequencing kit with
7-deaza-dGTP was purchased from Amersham
International. All other
reagents were ANALAR grade obtained from
BDH (Lutterworth,
Leicestershire, United Kingdom).
The properties of the

-lactamases found in the outbreak strains are
summarized in Table
3. Apart from strain
D7, which produced
TEM-1 in addition to an extended-spectrum

-lactamase, the strains
possessed only one
transferable

-lactamase. Two strains (D1 and
D5) produced TEM-group
extended-spectrum

-lactamases (TEM-26
and TEM-15, respectively).
The other eight strains produced SHV-group
extended-spectrum

-lactamases (SHV-2 by four, SHV-5 by three,
and SHV-4 by one).
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TABLE 3.
Isoelectric points and deduced amino acid sequence
changes for -lactamases from Klebsiella outbreak strains
|
|
In this study, we investigated the extended-spectrum

-lactamases and
the plasmids encoding them in a series of distinct outbreak
strains of
K. pneumoniae isolated in the United Kingdom between
1991 and 1994. SHV-group extended-spectrum

-lactamases were more
common
than TEM-group enzymes. The identification of the former
was
straightforward, but the nomenclature of one of the TEM enzymes
requires some comment. The amino acid changes detected in the
enzyme
from strain D5 were identical to those given by Jacoby
and Medeiros
(
15) and Knox (
20) for TEM-15 on the basis of
oligotyping (
23). However, this enzyme has been omitted from
the most recently published list of TEM enzymes produced by Bush
and
Jacoby (
8), presumably because it had not at that time
been
fully sequenced. However, it has been reinstated in their
list, which
is accessible on the World Wide Web (at
http://www.lahey.org/studies/webt.htm),
as an enzyme with changes of
glutamic acid to lysine at position
104 and of glycine to serine at
position 238. We found some variability
in the codon corresponding to
the amino acid at position 240 in
SHV

-lactamases, with glutamic
acid encoded by GAG or GAA and
lysine encoded by AAA or AAG (Table
3);
such variability has
been reported previously (
29).
Since most strains of
K. pneumoniae synthesize a
chromosomally encoded

-lactamase with an isoelectric point of 7.6 that is
closely related to SHV-1 (
11,
22), surveys of

-lactamases
in this species that do not take the location of the
gene encoding
the enzyme into account are impossible to interpret.
Consequently,
there is little information on the frequencies of
plasmid-encoded

-lactamases in this organism. Although
extended-spectrum SHV

-lactamases appear to have evolved from SHV-1,
it is not known
whether their genes are derived from the chromosomal
gene and
have subsequently moved on to plasmids or whether mutation of
plasmid genes has occurred.
Although TEM-1 and TEM-2 can be transposon encoded (
34) as
can plasmid-encoded SHV-1 (
30), extended-spectrum

-lactamases
have generally not been found on transposons
(
16). However,
genes for TEM-12 (
12) and TEM-16
(
37) have been reported to
be located on transposons. It is
not known whether the

-lactamases
from the outbreak strains reported
in this paper are transposon
encoded, but the apparent lack of
relatedness of the plasmids
suggests that they are not, except perhaps
for the TEM-group enzymes.
On the basis of National Committee for Clinical Laboratory Standards
criteria (
26), eight of the strains were susceptible
to
cefotaxime and one had intermediate resistance (Table
1),
although all
the strains were less susceptible than typical klebsiellae
that do not
produce extended-spectrum

-lactamases. However, extended-spectrum

-lactamase producers can readily mutate to hyperproduction of
the
enzyme and higher degrees of resistance (
42), so we believe
that therapy of infections caused by such organisms would not
be
appropriate. Similarly, although most of the strains were susceptible
or had intermediate resistance to amoxicillin-clavulanic acid,
mutation
to hyperproduction may result in resistance to this and
other

-lactam-

-lactamase inhibitor combinations.
All of the strains were multiply drug resistant. As has been reported
previously for extended-spectrum

-lactamase producers
(
16), they were usually resistant to the aminoglycosides,
with
only one strain, D2, being susceptible to all four aminoglycosides
tested. Five of the 10 strains were fully amikacin susceptible,
a
proportion that is slightly higher than the 9 of 15 reported
by Jacoby
and Sutton (
16). Resistance to streptomycin was uncommon;
this contrasts with the situation 20 years ago, when 86% of
gentamicin-resistant
enterobacteria were also resistant to streptomycin
(
36), and
presumably reflects the reduced selective pressure
resulting in
loss of genes encoding streptomycin resistance from
plasmids.
The carbapenems (imipenem and meropenem) were the only agents
tested that were active against all the strains, but seven strains
were
ciprofloxacin susceptible. However, greater use of this and
other
quinolones may lead to selection of resistant mutants.
In conclusion, hospital outbreaks of
K. pneumoniae producing
extended-spectrum

-lactamases in the United Kingdom between
1991 and
1994 have been caused by distinct single strains. Two
outbreak strains
produced TEM enzymes (TEM-15 and TEM-26), three
produced SHV-2, three
produced SHV-5, and one produced SHV-4.
These enzymes were encoded on
large transferable plasmids that
appeared to be distinct from each
other. The organisms were variably
multiply resistant to other
antimicrobial agents and were usually
resistant to gentamicin and
sometimes to other aminoglycosides.
 |
ACKNOWLEDGMENTS |
This study was supported in part by a grant (no. 804) from the
Special Trustees of St. Thomas' Hospital and by a Sino-British Friendship Scheme Scholarship (to X.X.).
 |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Microbiology, United Medical and Dental Schools, St. Thomas's Campus, London SE1 7EH, United Kingdom. Phone: 44-171 922 8383. Fax: 44-171 928 0730. E-mail: k.shannon{at}umds.ac.uk.
Present address: Department of Infectious Diseases, Chongqing
University of Medical Sciences, Chongqing 630042, People's Republic of
China.
Present address: Southampton Public Health Laboratory, Southampton
SO16 6YD, United Kingdom.
 |
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Journal of Clinical Microbiology, October 1998, p. 3105-3110, Vol. 36, No. 10
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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