Resistance trends of
Acinetobacter
spp. in Latin
America and characterization of international
dissemination of multi-drug resistant strains:
five-year report of the SENTRY Antimicrobial
Surveillance Program
Maria Cristina Bronharo Tognim
a,b,
Soraya Sgambatti Andrade
a,*
,
Suzane Silbert
a,
Ana Cristina Gales
a,
Ronald N. Jones
c,
Hélio S. Sader
a,ca
Laboratório Especial de Microbiologia Cl´ınica, Disciplina de Doenças Infecciosas e Parasitárias, Universidade Federal de São Paulo-SP, CEP 04025-010, Brazil
b
Departamento de Análises Cl´ınicas, Universidade Estadual de Maringá, Maringá, PR, Brazil
c
The Jones Group/JMI Laboratories, North Liberty, IA, USA
Received 23 July 2003 ;received in revised form 10 November 2003;accepted 11 November 2003
Corresponding Editor:Richard Oberhelman, New Orleans, USA
KEYWORDS
Acinetobacter; Antimicrobial resistance;
Carbapenem resistance; Latin America; Polymyxin; SENTRY
Summary Objectives:To analyze the antimicrobial susceptibility of Acinetobacter spp. isolates collected from Latin American medical centers as part of the SENTRY An-timicrobial Surveillance Program and also to evaluate the dissemination of multi-drug resistantAcinetobacterspp. strains in the region.
Methods:A total of 826 isolates ofAcinetobacterspp. from multiple infection sites were collected from January 1997 to December 2001 in ten medical centers and sus-ceptibility tested to >25 selected agents by broth microdilution. Multi-drug resistant Acinetobacterspp. isolates were molecular typed.
Results:Resistance rates to carbapenems varied significantly among countries. A continued annual increase occurred in the Argentinean medical centers. In contrast, carbapenem resistance was rare in Chilean centers, and decreased significantly in the Brazilian institutions.Acinetobacter spp. isolates recovered from lower respiratory tract and bloodstream infections were associated with lower antimicrobial suscepti-bility rates. Resistance rates to imipenem were higher among isolates collected from intensive care units (13.5%) than among isolates from other units. A major ribogroup pattern (521-1) was detected among eightAcinetobacterspp. strains isolated from three distinct Latin American countries.
Conclusions: This study found that antimicrobial resistance is still a major issue amongAcinetobacter spp. isolates collected from some Latin American countries.
*Corresponding author. Tel.:+55-11-5081-2819/5571-5180/5081-2965;fax:+55-11-5081-2819/5571-5180/5081-2965.
E-mail address:[email protected] (S.S. Andrade).
The dissemination of a major bacterial cluster in different regions reinforces the importance of longitudinal surveillance programs, such as SENTRY, as valuable tools for monitoring antimicrobial susceptibility rates and guiding local interventions. © 2004 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
Introduction
Acinetobacterspp. represents an important cause of nosocomial infections, including pneumonia, bacteremia, and meningitis. These opportunistic organisms have emerged as pathogens, especially
among critically ill patients.1 Resistance rates to
fluoroquinolones, aminoglycosides, cephalosporins, and ureidopenicillins are high in several regions. Al-though carbapenems remain the mainstay of
ther-apy for severe suspectedAcinetobacterinfections,
resistance to this antimicrobial class has been in-creasingly reported. Thus, therapeutic options can
become markedly limited.2—4
Major hospital outbreaks related to multi-drug
resistant (MDR) Acinetobacterspp. have been
re-cently described in several countries,5—7 making
surveillance of antimicrobial susceptibility an im-portant public health task. Although limited data
on the antimicrobial susceptibility of
Acinetobac-ter spp. available, previous studies have
demon-strated that isolates from the Latin American region are considerably less susceptible to antimicrobial agents than isolates collected from either North
America or Europe.8,9
This study was undertaken to determine the fre-quency of occurrence and the antimicrobial
suscep-tibility ofAcinetobacterspp., as well as to
deter-mine the possibility of the spreading of MDR iso-lates among the Latin American medical centers participating of the SENTRY Antimicrobial Surveil-lance Program.
Material and methods
Study design
The SENTRY Antimicrobial Surveillance Program monitors the frequency of occurrence and antimi-crobial resistance patterns of pathogens causing nosocomial and community-acquired infections worldwide. Participating countries in Latin Amer-ica included Argentina (1997—2001);Brazil (1997— 2001);Chile (1997—2001);Colombia (1997—2000); Mexico (1997—2001);Uruguay (1997 only) and Venezuela (1998—2001). Isolates were considered to be clinically significant based on the evaluation of the local physicians. In this study, all isolates were collected from hospitalized patients and only
one isolate per patient was included. The moni-tored body sites of infections were bloodstream, lower respiratory tract, skin and soft tissue, and
urinary tract.8,9
Identification and susceptibility tests
The isolates were identified at the participating institutions by the routine methodology in use at each laboratory and forwarded to the coordinator laboratory (Iowa, USA). Upon receipt at the co-ordinator laboratory, isolates were subcultured on blood agar to ensure viability and purity. Species identifications were confirmed with the use of the
Vitek system (bioMérieux Vitek®, Hazelwood, MO)
or API (bioMérieux Vitek®, Hazelwood, MO) or
stan-dard reference methods when needed. Protocols for species identification upon receipt at the
coor-dinator center were previously described.9
Antimi-crobial susceptibility testing of isolates was per-formed by reference broth microdilution methods as described by the National Committee for Clinical
Laboratory Standards (NCCLS).10Microdilution trays
were purchased from TREK Diagnostic Systems Inc. (Westlake, OH, USA). Antimicrobial agents were ob-tained from their respective manufacturers.
Tested antimicrobial agents included amikacin, cefepime, ceftazidime, ciprofloxacin, gatifloxacin, gentamicin, imipenem, levofloxacin, meropenem, piperacillin, piperacillin/tazobactam, polymyxin B, ticarcillin, ticarcillin/clavulanic acid, tetracy-cline, and tobramycin. Antimicrobial susceptibility testing was performed according to the reference broth microdilution method recommended by the
NCCLS.10,11Quality control was performed by
test-ing Escherichia coli ATCC 25922, Staphylococcus aureusATCC 29213,Pseudomonas aeruginosaATCC
27853, andEnterococcus faecalisATCC 29212.
Ribotyping
Thirty-nine MDR Acinetobacter isolates recovered
from unique patients with bloodstream infections hospitalized at distinct intensive care units (ICUs) from seven different Latin American medical cen-ters located in Argentina, Brazil, Chile, and Colom-bia were randomly selected for rybotyping. The
isolates were ribotyped using the RiboPrinter®
Chromosomal DNA was digested with EcoRI and the DNA fragments were then hybridized with a
la-beled DNA probe.12 The bands were detected
us-ing chemiluminescent substrate and the image was captured using a customized CCD camera and elec-tronically transferred to the computer system. Each lane of sample data was normalized to a standard marker set and band intensity. This normalized out-put was compared with all previously run samples and reference patterns. Similarity coefficients were calculated based on both position and relative band weight. Isolates were considered to have the same
RiboPrinter®pattern, ribotype, if the similarity
co-efficient between their patterns was≥0.90.12
Data analysis
Differences in group proportions were assessed with the Chi-square and Fisher’s exact tests. Two-tailed
tests of significance at the p ≤ 0.05 level were
used to determine statistical significance. Statis-tical analysis was performed with Epi-Info version 6.04b software package (Centers for Disease Con-trol and Prevention, Atlanta, GA).
Results
A total of 826Acinetobacterisolates were collected
between January 1997 and December 2001. Brazil
contributed the largest number of isolates (n=400)
Table 1 Antimicrobial susceptibility ofAcinetobacterspp. isolates in Latin America as reported in the SENTRY Antimicrobial Surveillance Program, 1997—2001.
Antimicrobial agents
% susceptible by year (ntested) MIC (g/ml)
1997 (193) 1998 (215) 1999 (129) 2000 (123) 2001 (166) Total (826) MIC50 MIC90
Meropenem 91.3 87.0 89.1 82.9 81.9 86.8 2 >8
Imipenem 91.2 87.0 88.4 82.9 83.7 86.9 1 >8
Cefepime 33.7 27.4 48.8 38.2 30.4 35.2 >16 >16
Ceftazidime 29.0 17.7 37.2 35.0 45.8 28.5 >16 >16
Piperacillin 18.1 11.6 26.4 18.7 17.5 17.7 >128 >128
Piperacillin-tazobactam
24.9 19.5 36.4 30.1 27.7 26.6 >64 >64
Ticarcillin 23.8 14.4 30.2 22.0 19.9 20.2 >128 >128
Ticarcillin-clavulanate
19.2 20.0 32.6 28.5 23.5 24.8 >128 >128
Ciprofloxacin 27.5 29.3 34.9 35.8 28.3 30.5 1 >4
Levofloxacin 29.0 30.7 37.2 39.8 28.9 32.3 >4 >4
Gatifloxacin 30.6 34.0 41.1 39.8 30.1 34.4 4 >4
Tetracycline 68.4 49.8 52.7 46.7 33.7 50.9 8 >8
Amikacin 35.8 27.0 37.2 35.0 38.0 34.0 >32 >32
Gentamicin 33.7 30.2 40.3 31.7 30.7 32.9 >8 >8
Tobramycin 35.8 40.5 51.2 — 45.8 41.5 16 >16
Polymyxin B — — — — 96.4 96.4a ≤1 2
aIsolates exhibiting MICs≤2g/ml were considered susceptible to polymyxin B.13
followed by Argentina (185);Chile (102);Venezuela (58);Colombia (43);Uruguay (20);and Mexico (18). The majority of isolates were identified as
A. calcoaceticus-baumanniicomplex (85.3%) while 9.5% of isolates were not identified to the species level. Other, less frequently isolated, species
in-cluded Acinetobacter lwoffii (5.0%) and A. junii
(0.2%). The number of isolates and their respec-tive susceptibility profile according to the year of
isolation are shown inTable 1. Overall, the highest
susceptibility rates were achieved by meropenem (86.8%) and imipenem (86.9%). However, a signif-icant decrease in the carbapenem susceptibility rates was noticed throughout the study period. Isolates recovered in 2001 were considerably more
resistant to imipenem (p=0.02;OR: 2.01, 95% CI:
1.01—4.03) and meropenem (p=0.006;OR=2.13,
95% CI: 1.16—4.53), when compared to those
col-lected in 1997. Other -lactams showed poor in
vitro activity against the isolates tested, with sus-ceptibility rates ranging from 17.7% (piperacillin) to 35.2% (cefepime). Similarly, the tested fluo-roquinolones (ciprofloxacin, gatifloxacin and lev-ofloxacin) demonstrated low susceptibility rates
(<40.0%). Polymyxin B showed excellent activity
(MIC50, ≤1g/ml;96.4% susceptibility), but this
compound was only evaluated against pathogens collected in 2001. Six isolates categorized as
resis-tant to polymyxin B (MIC≥4g/ml)13 were
Table 2 Susceptibility of Acinetobacterspp. isolates to carbapenems in selected Latin American countries as reported in the SENTRY Antimicrobial Surveillance Program, 1997—2001.
Country/yeara (ntested)
Imipenem Meropenem
MIC50/MIC90 % Susceptible % Resistant MIC50/MIC90 % Susceptible % Resistant
Argentina
1997 1/2 97.7 0.0 1/4 97.7 0.0
1998 1/>8 84.8 15.2 2/>8 82.6 15.2
1999 1/2 95.2 0.0 2/2 95.2 0.0
2000 2/>8 60.0 40.0 4/>8 60.0 37.1
2001 1/>8 60.0 40.0 2/>8 57.5 32.5
Total (185) 1/>8 78.9 20.0 2/>8 78.4 17.8
Brazil
1997 1/>8 77.8 13.6 1/>8 84.0 14.8
1998 1/>8 85.6 12.5 1/>8 87.5 12.5
1999 0.5/2 95.5 4.5 1/2 95.5 3.0
2000 0.5/>2 91.4 8.6 1/4 91.4 5.2
2001 0.5/>2 97.8 2.2 2/4 96.7 3.3
Total (400) 1/4 90.8 8.5 1/4 90.8 8.3
Chile
1997 0.5/8 96.7 3.3 1/4 100.0 0.0
1998 1/2 100.0 0.0 2/4 94.3 2.9
1999 0.5/2 100.0 0.0 0.5/2 100.0 0.0
2000 0.12/>2 100.0 0.0 0.25/2 100.0 0.0
2001 0.5/2 100.0 0.0 2/>8 95.5 4.5
Total (102) 0.5/2 98.0 0.7 2/4 96.1 2.0
Colombiab
1997 0.5/>8 87.5 12.5 0.5/8 87.5 12.5
1998 1/>8 80.0 20.0 1/2 90.0 10.0
1999 0.5/2 75.0 25.0 1/>8 75.0 25.0
2000 0.12/>0.25 100.0 0.0 1/4 100.0 0.0
Total (43) 0.25/>8 86.0 14.0 1/8 88.4 9.3
aIncludes only countries contributing more than 40 isolates.
bColombian medical center did not participate in the SENTRY Program in 2001.
infections from three different Brazilian medical centers and only one of those was also resistant to carbapenems.
Table 2 shows the prevalence of
Acinetobac-ter isolates resistant to carbapenems isolated
in selected Latin American countries. Overall, the highest resistance rate to imipenem was de-tected in Argentina (20.0%), followed by Colombia (14.0%) and Brazil (8.5%). In Brazil, imipenem re-sistance rates decreased significantly during the five-year period, from 13.6% in 1997 to 2.2% in 2001
(p=0.001, chi-square for trend test). Carbapenem
resistance was not detected in the Mexican and Uruguayan medical centers (data not shown), but these institutions contributed small numbers of
iso-lates (<40) in the evaluated period. Resistance to
imipenem was found to be rare in Chilean centers, with 98.0% of isolates susceptible to this antimicro-bial. Actually, no isolate resistant to the evaluated
carbapenems could be detected in Chile in the last four years of the study (1998—2001). Although the mean resistance to imipenem in Argentina was 20% over the five-year period, an increasing resis-tance rate (40% resisresis-tance) was documented in the last two years of the study. Moreover, resistance rates to carbapenems in Argentina (2000 and 2001) were significantly higher than those displayed by other Latin American nations in the same period (p<0.05).
Resistance rates to carbapenems were also higher among isolates recovered from the lower respira-tory tract (9.2—19.6%) than among those isolated from the bloodstream (5.7—17.2%) skin/soft tissue
(11.0—13.7%) or the urinary tract (0.0%) (Table 3).
Imipenem resistance rates were at least two-fold higher among isolates from intensive care units (ICU) when compared to non-ICU isolates (13.5%
Table 3 Antimicrobial susceptibility ofAcinetobacter spp. isolates to imipenem and meropenem according to the site of infection as reported in the SENTRY Antimicrobial Surveillance Program, Latin America 1997—2001.
Infection site/Year (ntested)a
Imipenem Meropenem
MIC50/MIC90 % Susceptible % Resistant MIC50/MIC90 % Susceptible % Resistant
Bloodstream
1997 (87) 0.5/2 92.0 6.9 1/4 93.1 5.7
1998 (107) 1/8 89.7 8.4 1/4 91.6 7.5
1999 (61) 0.5/2 90.2 8.2 1/2 91.8 8.2
2000 (58) 0.5/>8 82.8 17.2 1/>8 82.8 12.1
2001 (67) 0.5/>8 88.1 10.4 1/>8 85.1 11.9
Lower respiratory tract
1997 (65) 1/8 89.2 9.2 1/8 89.2 9.2
1998 (75) 1/>8 81.3 18.7 2/>8 78.7 18.7
1999 (48) 1/>8 89.6 10.4 1/8 89.6 8.3
2000 (51) 0.5/>8 80.4 19.6 2/>8 80.4 19.6
2001 (60) 1/>8 86.7 13.3 2/>8 85.0 13.3
aIncludes only infection sites with more than 100 isolates over the study period. A total of 35 and 74Acinetobacter
spp. isolates were collected, respectively, from skin/soft tissue and urinary tract infections.
Table 4 Carbapenem susceptibility ofAcinetobacterspp. isolates from intensive care unitsaas reported in the SENTRY Antimicrobial Surveillance Program, Latin America, 1997—2001.
Intensive care unit (415 isolates)a Non-intensive care unit (264 isolates)a
MIC50/MIC90 % Susceptible % Resistant MIC50/MIC90 % Susceptible % Resistant
Imipenem 1/>8 85.1% 13.5% 0.5/2 92.8% 6.4%
Meropenem 2/>8 84.8% 13.0% 1/4 92.4% 6.1%
aThe origin of 147 isolates was not known.
Eighteen different ribotyping patterns were
iden-tified among the 39 Acinetobacter spp. isolates
evaluated (Table 5). The most frequent ribotype
was 521-1, which was detected among eight iso-lates from three medical centers located in Ar-gentina, Brazil, and Colombia. Six other ribotypes were detected in more than one medical center, and two of them were detected in medical centers
located in different countries (Table 5).
Table 5 Distribution of ribotypes found in more than oneAcinetobacterspp. isolate according to medical center and nation as reported in the SENTRY Antimicrobial Surveillance Program, 1997—2001.
Ribotype No. of isolates Medical center (No. of isolates) Nations
521-1 8 40(5);44(1);48(2) Argentina, Brazil, Colombia
531-3 4 41(1);42(1);46(1);48(1) Brazil, Chile
815-2 4 39(2);40(1);46(1) Argentina, Brazil
1008-2 3 48(3) Brazil
1242-5 3 46(1), 48(2) Brazil
218-1 2 46(1);48(1) Brazil
1380-1 2 46(1);48(1) Brazil
1414-5 2 46(2) Brazil
1395-4 2 42(2) Chile
Discussion
Acinetobacter spp. is generally an opportunistic nosocomial pathogen often resistant to multiple
therapeutic agents.1In the present study we
eval-uated the susceptibility profile of Acinetobacter
reports that showed a decreased antimicrobial
sus-ceptibility profile forAcinetobacterspp. isolates in
the Latin American region.14,15
Overall, resistance rates were very high for most antimicrobial agents, with the exception of the carbapenems, (imipenem and meropenem) and
polymyxin B. Among clinical isolates of
Acine-tobacter spp., several antimicrobial resistance mechanisms have been described, including the production of chromosomally- or plasmid-mediated
-lactamase, aminoglycoside-modifying enzymes
and alteration in the outer membrane
permeabi-lity.16,17 Although quinolones were initially
con-sidered promising antimicrobial agents to treat
Acinetobacter infections, these compounds did not show adequate coverage against this pathogen
in the Latin American region.18 These data were
also in agreement with previous studies, which demonstrated that quinolone resistance has rapidly
emerged among Acinetobacter spp. clinical
iso-lates, probably reflecting the ability of this pathogen to acquire resistance determinants via
several mechanisms.17
Although polymyxin B was very active against
Acinetobacter spp. isolates, emerging resistance to this compound has been reported especially in
Brazil.19,20 This fact is very worrisome, since very
few therapeutic options are clinically available to treat infections caused by this multi-drug resistant pathogen.
Isolates recovered from SENTRY participant cen-ters in North America and Europe have demon-strated markedly higher susceptibility rates to
carbapenems and quinolones.21 In this study,
the antimicrobial susceptibility of
Acinetobac-ter spp. varied significantly among Latin
Amer-ican countries, among centers and even among wards of a given hospital (ICU versus non-ICU). These discrepancies may reflect differences in the environmental factors and also in patterns of local antimicrobial usage or infection control
policies.9,22
There has been a consensus that hospitalization in ICU is an important factor influencing emergence
of antimicrobial resistance.23 This pattern was
corroborated by this study, which demonstrates
higher rates of carbapenem-resistant
Acinetobac-terspp. in these high-risk units.
Molecular typing results clearly indicate clonal dissemination of multi-drug resistant strains of
Acinetobacter spp. Inter-hospital dissemination could be identified in Argentina and Brazil through the presence of identical or similar ribotypes in dis-tinct institutions in the same country. In addition, the finding of isolates with an identical ribotype (521-1) in medical centers from different countries
may indicate the international spread of multi-drug resistant (MDR) clones. The wide dissemination of MDR pathogens has already been documented for other organisms in Latin America and may in-dicate that control measures should be designed to avoid the greater worldwide dissemination of these bacteria harboring important mechanisms of
resistance.24
In addition to clonal dissemination, selection of other resistant mutants was indicated by the genetic diversity found among evaluated MDR iso-lates. In fact, the Brazilian institutions harbored most of the distinct resistant genotypes, espe-cially clustered in two medical centers (46 and 48). This indicates that antimicrobial use policies must be reviewed and appropriate interventions implemented in the respective institutions. Nev-ertheless, the data have some limitations that are inherent to laboratory-based surveys. The small
number of Acinetobacter spp. isolates collected
and tested from some Latin American countries may have influenced the susceptibility and typ-ing results, especially in countries that submit-ted a small number of isolates, such as Mexico, Venezuela, and Colombia. Further studies, testing
a larger number of Acinetobacter spp. isolates,
are necessary in these regions to address such questions.
Emergence of resistance to multiple
antimi-crobial agents among Acinetobacter spp. isolates
has become a major international public health
problem.16,25 The geographic variation of
resis-tance patterns emphasizes the imporresis-tance of local surveillance in determining the most adequate
therapy for Acinetobacter spp. infections.26,27
Epidemiology-based surveillance studies, such as SENTRY, have a crucial role in disseminat-ing important up-to-date local data to guide the correct management of antimicrobial prescrib-ing strategies in the nosocomial and community environment.
Acknowledgements
We express our appreciation to all medical techni-cians who have worked in SENTRY. The SENTRY Latin America Study Group in 1997–2001 includes: Helio S. Sader and Ana C. Gales (São Paulo, Brazil - Latin America Coordinator);Jorge Sampaio
(Laborato-rio Lˆamina, Rio de Janeiro, Brazil);Cássia Zoccoli
Jorgelina Smayevsky (Laboratorio C.E.M.I.C., Buenos Aires, Argentina);Valeria Prado (Faculdad de Medicina de Chile, Santiago, Chile);Elizabeth Palavecino/Patricia Garcia (Universidad Catolica del Chile, Santiago, Chile);Homero Bagnulo (Hos-pital Maciel, Montivideo, Uruguay);Jaime A. Rob-ledo (Corporation Para Investigaciones Biologicas, Medellin, Colombia);Jose Sifuentes-Osornio (Insti-tuto Nacional de la Nutricion, Ciudade del Mexico, Mexico);and Manuel Guzmán-Blanco (Hospital Var-gas, Caracas, Venezuela). Rodrigo E. Mendes and Ju-liana B. Silva provided excellent support in the data analysis. The SENTRY Antimicrobial Surveillance Program is sponsored by a research/educational grant from Bristol-Myers Squibb.
Conflict of interest: No conflict of interest de-clared.
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