International Journal of Antimicrobial Agents 28 (2006) 532–536
Activity of tigecycline against clinical isolates of Staphylococcus aureus
and extended-spectrum ␤-lactamase-producing
Escherichia coli in Granada, Spain
A. Sorl´ozano , J. Guti´errez , A. Salmer´on , J.D. Luna ,
F. Mart´ınez-Checa , J. Rom´an , G. Pi´edrola
a Department of Microbiology, University of Granada, Spain
b Pharmacy Services, Hospital Universitario San Cecilio, Granada, Spain
c Department of Biostatistics, University of Granada, Spain
d Microbiology Services, Hospital Universitario San Cecilio, Granada, Spain
Received 2 June 2006; accepted 17 July 2006
We evaluated the in vitro activity of tigecycline using the Etest and disk diffusion method according to Clinical and Laboratory Standards
Institute guidelines against clinical isolates of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus(MRSA) as well as for CTX-M-9 extended-spectrum ␤-lactamase (ESBL)-producing Escherichia coli and SHV ESBL-producing E. coli. All isolates were susceptible to tigecycline according to US Food and Drug Administration cut-off points. There were no differences in theactivity of tigecycline between MSSA and MRSA isolates or between the presence of either type of ESBL. For each type of microorganismstudied, we established the equation relating the minimum inhibitory concentration to the diameter of the zone of inhibition. 2006 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. Keywords: Tigecycline; Staphylococcus aureus; Escherichia coli; ESBL
tetracycline- and minocycline-resistant microorganisms anddoes not present cross-resistance with other antibiotics
Tigecycline is a semi-synthetic tetracycline (glycylcy-
such as ␤-lactams or fluoroquinolones Nevertheless,
cline) derived from minocycline It is active against
in vitro studies show that it is not active against Pseu-
Gram-positive cocci and Gram-negative rods, includ-
domonas aeruginosa, Proteus mirabilis or Providencia spp.
ing methicillin-resistant Staphylococcus aureus (MRSA),
vancomycin-resistant Enterococcus spp., macrolide- or
Tigecycline crosses the external membrane of bacteria
penicillin-resistant Streptococcus pneumoniae, extended-
through porins via passive diffusion and reaches the cyto-
spectrum ␤-lactamase (ESBL)-producing Enterobacteri-
plasm by an energy-dependent mechanism. It binds to the
aceae and carbapenem-resistant Acinetobacter spp. It is
ribosome thereby inhibiting protein synthesis. This effect is
also active against anaerobic bacteria (Bacteroides spp.,
produced by blocking binding of the tRNA aminoacyl site
Clostridium perfringens and Peptostreptococcus spp.), intra-
to the 30 S ribosomal subunit. The association is reversible,
cellular microorganisms and non-tuberculous mycobac-
which explains its bacteriostatic effect The absence of
teria Furthermore, tigecycline is active against
anti-eukaryotic activity means that it has selective antibacte-rial properties.
Several cases of reduced sensitivity to this antibiotic have
Corresponding author. Present address: Departamento de Microbiolog´ıa,
Facultad de Medicina, Avda. de Madrid 11, E-18012 Granada, Spain.
been reported in Enterobacteriaceae owing to induction of
E-mail address: (J. Guti´errez).
0924-8579/$ – see front matter 2006 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. doi:
A. Sorl´ozano et al. / International Journal of Antimicrobial Agents 28 (2006) 532–536
Tigecycline is administered parenterally as a 1 h infusion
cisco Soria Melguizo S.A., Madrid, Spain) the clinical
twice daily and is only available as an injectable formulation.
microbiology laboratory of Hospital ‘San Cecilio’, Granada,
It crosses the placental barrier and is generally eliminated in
high concentrations in breast milk. It is metabolised in the
One hundred and five isolates were identified as S.
liver and the main routes of elimination are via the biliary
aureus. Resistance to methicillin was confirmed using
the Mueller–Hinton agar diffusion procedure (bioM´erieux,
To date, the indications approved by the US Food and Drug
Marcy l’Etoile, France) with 1 g oxacillin disks, as recom-
Administration (FDA) are treatment of complicated skin and
mended by the Clinical and Laboratory Standards Institute
soft tissue infections and complicated intra-abdominal infec-
(CLSI) Fifty-four MSSA and 51 MRSA isolates were
In recent years in Spain we have observed a marked
The remaining 115 isolates were ESBL-producing E.
increase in the number of infections produced by multiresis-
coli in which the presence of the enzyme in each isolate
tant microorganisms as well as in the morbidity and mortality
was confirmed by the diffusion method with disks con-
of infections caused by MRSA and ESBL-producing Enter-
taining cefotaxime (30 g), cefotaxime/clavulanic acid
(30/10 g), ceftazidime (30 g) and ceftazidime/clavulanic
In Spain, the increased incidence of MRSA (from
acid (30/10 g), as recommended by the CLSI ollow-
1.5% in 1986 to 31.2% in 2002) was accompanied by
ing phenotypic confirmation, determination of the existing
a marked increase in resistance to other antibiotics such
␤-lactamase and clonality was carried out by means of
as macrolides, lincosamides, aminoglycosides or fluoro-
biochemical (determination of the isoelectric point) and
quinolones Although this is not currently a significant
molecular (polymerase chain reaction) studies following
problem in Europe, there have been reports of infections
the procedures previously described by our group
caused by S. aureus with reduced susceptibility to glycopep-
Sixty-seven isolates produced the CTX-M-9 enzyme and 48
tides (glycopeptide-intermediate S. aureus (GISA)) This
situation is particularly problematic given the lack of avail-
Isolates were stored at −40 ◦C until the susceptibility
ESBLs are plasmid-borne enzymes produced by Gram-
negative rods that confer resistance to all the penicillins,
cephalosporins (with the exception of cephamycins) andmonobactams. The plasmids encoding these enzymes can
After checking the purity of the isolates, a 0.5
also carry genes for resistance to other antibiotics such as co-
McFarland suspension was prepared and inoculated onto
trimoxazole, aminoglycosides and tetracyclines and cross-
Mueller–Hinton agar plates (bioM´erieux). An agar plate was
used for each isolate and the Etest and disk diffusion proce-
isms are also resistant to fluoroquinolones more frequently
than other non-ESBL-producing isolates Therefore,
Tigecycline Etest strips (AB Biodisk, Solna, Sweden)
sometimes the only possibility of treatment is using carbapen-
were used to determine the minimum inhibitory concentra-
ems However, these should be used in moderation as
tion (MIC) of tigecycline. To determine the diameter of the
they have been associated with an increase in infections by
zone of inhibition, the agar diffusion method was used with
carbapenem-resistant Acinetobacter baumannii or P. aerug-
15 g tigecycline disks (BBL, Becton Dickinson, Franklin
inosa with the result that treatment of these infections
The control strains used in all procedures were K. pneu-
Tigecycline may therefore be an alternative in the treat-
moniae ATCC 700603, E. coli ATCC 25922 and S. aureus
ment of skin and soft tissue infections caused by S. aureus
and intra-abdominal infections caused by Enterobacteriaceae(especially ESBL-producing Escherichia coli and Klebsiellapneumoniae) in hospitalised patients. This study used dif-
ferent methods to describe the activity of tigecycline againstclinical isolates of methicillin-sensitive S. aureus (MSSA),
MRSA and ESBL-producing E. coli.
Using the cut-off established by the FDA in 2005 for S.aureus (MIC ≤ 0.5 g/mL), 100% of the S. aureus isolates
2. Material and methods
were susceptible to tigecycline. They were all inhibited by aconcentration of ≤0.19 g/mL and presented a zone of inhi-
bition around the disk ≥18 mm. For S. aureus ATCC 29213,the values were 0.125 g/mL and 20 mm, respectively.
We evaluated the in vitro activity of tigecycline against 220
The MIC range and the MIC for 50% and 90% of the
clinical isolates identified using the WIDER system (Fran-
organisms (MIC50 and MIC90, respectively) obtained by the
A. Sorl´ozano et al. / International Journal of Antimicrobial Agents 28 (2006) 532–536
Table 1MIC range and MIC for 50% and 90% of the organisms (MIC50 and MIC90, respectively) obtained by the Etest, and range, mean and S.D. of the diameter ofthe zone of inhibition obtained by the disk diffusion method for Staphylococcus aureus isolates
MIC, minimum inhibitory concentration; S.D., standard deviation; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-susceptible S. aureus.
Table 2Percentage of clinical isolates at each minimum inhibitory concentration (MIC) of tigecycline obtained by the Etest
ESBL, extended-spectrum ␤-lactamase; MSSA, methicillin-susceptible S. aureus; MRSA, methicillin-resistant S. aureus.
Table 3MIC range and MIC for 50% and 90% of the organisms (MIC50 and MIC90, respectively) obtained by the Etest, and range, mean and S.D. of the diameter ofthe zone of inhibition obtained by the disk diffusion method for isolates of extended-spectrum ␤-lactamase (ESBL)-producing Escherichia coli
MIC, minimum inhibitory concentration; S.D., standard deviation.
Etest, and the range, mean and standard deviation (S.D.)
were 0.5 g/mL and 23 mm, and for E. coli ATCC 25922 they
of the diameter of the zone of inhibition obtained by the
were 0.38 g/mL and 22 mm, respectively.
disk diffusion method for the 105 S. aureus isolates are
The range, MIC50 and MIC90 obtained by the Etest, and
shown in The MIC values obtained by Etest show
the range, mean and S.D. of the diameter of the zone of inhibi-
the excellent activity of tigecycline against these clinical
tion obtained by disk diffusion for the 115 ESBL-producing
isolates (range 0.047–0.19 g/mL, MIC50 = 0.094 g/mL,
E. coli isolates are shown in The MIC values
MIC90 = 0.125 g/mL). These values were observed both inthe MSSA and MRSA isolates.
ws the percentage of S. aureus isolates at each
tigecycline MIC determined by the Etest.
Finally, we studied the relationship between the MIC val-
ues and the zone of inhibition around the 15 g disks for S. aureus. The equation relating MIC (y) and the diameter ofthe zone of inhibition (x) was y = 0.4566–0.0162x and thecorrelation coefficient was r = −0.808, which demonstrates asignificant relationship between both variables (
Using the cut-off established by the FDA in 2005 for
Enterobacteriaceae (MIC ≤ 2 g/mL), 100% of the ESBL-producing E. coli isolates were susceptible to tigecy-cline. All the isolates were inhibited by a concentration
Fig. 1. Scattergram comparing zones of inhibition around 15 g tigecycline
≤0.75 g/mL and presented a zone of inhibition around the
disks (x) with the tigecycline minimum inhibitory concentration (MIC) (y)
disk ≥19 mm. For K. pneumoniae ATCC 700603, the values
determined by the Etest method for all the isolates of Staphylococcus aureus. A. Sorl´ozano et al. / International Journal of Antimicrobial Agents 28 (2006) 532–536
Table 4Activity of tigecycline against species of Staphylococcus aureus (MRSA and MSSA) and Escherichia coli (ESBL-producing and non-ESBL-producing) indifferent studies
Minimum inhibitory concentration (g/mL)
MRSA, methicillin-resistant S. aureus; MSSA, methicillin-susceptible S. aureus; ESBL, extended-spectrum ␤-lactamase.
obtained by the Etest show the excellent activity of tigecy-
studies show that tigecycline is as active as imipenem in the
cline against these clinical isolates (range 0.047–0.75 g/mL,
treatment of intra-abdominal infections (where it is neces-
MIC50 = 0.125 g/mL, MIC90 = 0.38 g/mL). Similar val-
sary to cover the presence of Gram-negative pathogens such
ues were obtained for isolates producing CTX-M-9 or SHV
as Enterobacteriaceae) and as active as the combination of
vancomycin and aztreonam in skin and soft tissue infections
shows the percentage of isolates of ESBL-
(where it is necessary to cover the presence of MRSA and
producing E. coli for each tigecycline MIC determined by
shows the results of susceptibility to tigecy-
The equation relating the MIC value (y) and the diam-
cline among S. aureus isolates (MRSA and MSSA) and
eter of the zone of inhibition around the 15 g disks (x)was y = 1.8656–0.0674x and the correlation coefficient wasr = −0.845, which, once again, shows a significant relation-ship between both variables (
4. Discussion Staphylococcus aureus and ESBL-producing E. coli
are two important causes of nosocomial and community-acquired infections. Carbapenems are sometimes the onlytherapeutic alternative against infections caused by ESBL-producing pathogens owing to the resistance associated withother groups of antibiotics Glycopeptides such as van-comycin or teicoplanin are generally the antibiotics of choice
Fig. 2. Scattergram comparing zones of inhibition around 15 g tigecycline
for the treatment of MRSA infections. The emergence of
disks (x) with the tigecycline minimum inhibitory concentration (MIC) (y)
GISA that the use of glycopeptides may be lim-
determined by the Etest method for all the isolates of extended-spectrum
ited and it may be necessary to look for alternatives. Several
␤-lactamase-producing Escherichia coli. A. Sorl´ozano et al. / International Journal of Antimicrobial Agents 28 (2006) 532–536
ESBL-producing E. coli in different studies
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Title Sensitivity Analysis of a Meta-analysis with Unpublished butAuthor Noory Y. Kim. Advisors: Shrikant I. Bangdiwala, Gerald Gartlehner. Maintainer Noory Y. Kim <[email protected]>Description This package contains R functions to gauge the impact of unpublished stud-ies upon the meta-analytic summary effect of a set of published studies. (Credits: The re-search leading to these result
IUED Comments to the Public Hearing held on June 16, 2010 Introduction Adam Teva V'Din - the Israel Union for Environmental Defense (IUED) is a non-governmental organization of lawyers, scientists, urban planners and environmental specialists dedicated to protecting Israel's natural resources and public health. Since its founding in 1990, IUED has amassed a long record of achievements