Resistance trends of Acinetobacter

International Journal of Infectious Diseases (2004) 8, 284 291 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,c a Laboratório Especial de Microbiologia Clínica, Disciplina de Doenças Infecciosas e Parasitárias, Universidade Federal de São Paulo-SP, CEP 04025-010, Brazil b Departamento de Análises Clínicas, 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 Antimicrobial Surveillance Program and also to evaluate the dissemination of multi-drug resistant Acinetobacter spp. strains in the region. Methods: A total of 826 isolates of Acinetobacter spp. from multiple infection sites were collected from January 1997 to December 2001 in ten medical centers and susceptibility tested to >25 selected agents by broth microdilution. Multi-drug resistant Acinetobacter spp. 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 susceptibility 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 eight Acinetobacter spp. strains isolated from three distinct Latin American countries. Conclusions: This study found that antimicrobial resistance is still a major issue among Acinetobacter 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: lemcdipa@terra.com.br (S.S. Andrade). 1201-9712/$30.00 2004 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijid.2003.11.009

Resistance trends of Acinetobacter spp. in Latin America 285 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 Acinetobacter spp. 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. Although carbapenems remain the mainstay of therapy for severe suspected Acinetobacter infections, resistance to this antimicrobial class has been increasingly reported. Thus, therapeutic options can become markedly limited. 2 4 Major hospital outbreaks related to multi-drug resistant (MDR) Acinetobacter spp. have been recently described in several countries, 5 7 making surveillance of antimicrobial susceptibility an important public health task. Although limited data on the antimicrobial susceptibility of Acinetobacter spp. available, previous studies have demonstrated 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 frequency of occurrence and the antimicrobial susceptibility of Acinetobacter spp., as well as to determine the possibility of the spreading of MDR isolates among the Latin American medical centers participating of the SENTRY Antimicrobial Surveillance Program. Material and methods Study design The SENTRY Antimicrobial Surveillance Program monitors the frequency of occurrence and antimicrobial resistance patterns of pathogens causing nosocomial and community-acquired infections worldwide. Participating countries in Latin America 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 monitored 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 coordinator 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 standard reference methods when needed. Protocols for species identification upon receipt at the coordinator center were previously described. 9 Antimicrobial susceptibility testing of isolates was performed by reference broth microdilution methods as described by the National Committee for Clinical Laboratory Standards (NCCLS). 10 Microdilution trays were purchased from TREK Diagnostic Systems Inc. (Westlake, OH, USA). Antimicrobial agents were obtained 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, tetracycline, and tobramycin. Antimicrobial susceptibility testing was performed according to the reference broth microdilution method recommended by the NCCLS. 10,11 Quality control was performed by testing Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, Pseudomonas aeruginosa ATCC 27853, and Enterococcus faecalis ATCC 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 centers located in Argentina, Brazil, Chile, and Colombia were randomly selected for rybotyping. The isolates were ribotyped using the RiboPrinter Microbial Characterization System (Qualicon, Wilmington, DE).

286 M.C.B. Tognim et al. Chromosomal DNA was digested with EcoRI and the DNA fragments were then hybridized with a labeled DNA probe. 12 The bands were detected using chemiluminescent substrate and the image was captured using a customized CCD camera and electronically transferred to the computer system. Each lane of sample data was normalized to a standard marker set and band intensity. This normalized output 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 coefficient 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. Statistical analysis was performed with Epi-Info version 6.04b software package (Centers for Disease Control and Prevention, Atlanta, GA). Results A total of 826 Acinetobacter isolates were collected between January 1997 and December 2001. Brazil contributed the largest number of isolates (n = 400) followed by Argentina (185);Chile (102);Venezuela (58);Colombia (43);Uruguay (20);and Mexico (18). The majority of isolates were identified as A. calcoaceticus-baumannii complex (85.3%) while 9.5% of isolates were not identified to the species level. Other, less frequently isolated, species included Acinetobacter lwoffii (5.0%) and A. junii (0.2%). The number of isolates and their respective susceptibility profile according to the year of isolation are shown in Table 1. Overall, the highest susceptibility rates were achieved by meropenem (86.8%) and imipenem (86.9%). However, a significant 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 collected in 1997. Other -lactams showed poor in vitro activity against the isolates tested, with susceptibility rates ranging from 17.7% (piperacillin) to 35.2% (cefepime). Similarly, the tested fluoroquinolones (ciprofloxacin, gatifloxacin and levofloxacin) demonstrated low susceptibility rates (<40.0%). Polymyxin B showed excellent activity (MIC 50, 1 g/ml;96.4% susceptibility), but this compound was only evaluated against pathogens collected in 2001. Six isolates categorized as resistant to polymyxin B (MIC 4 g/ml) 13 were recovered from hospitalized patients with bloodstream Table 1 Antimicrobial susceptibility of Acinetobacter spp. isolates in Latin America as reported in the SENTRY Antimicrobial Surveillance Program, 1997 2001. Antimicrobial agents % susceptible by year (n tested) MIC ( g/ml) 1997 (193) 1998 (215) 1999 (129) 2000 (123) 2001 (166) Total (826) MIC 50 MIC 90 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 Piperacillintazobactam 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 Ticarcillinclavulanate 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 96.4 a 1 2 a Isolates exhibiting MICs 2 g/ml were considered susceptible to polymyxin B. 13

Resistance trends of Acinetobacter spp. in Latin America 287 Table 2 Susceptibility of Acinetobacter spp. isolates to carbapenems in selected Latin American countries as reported in the SENTRY Antimicrobial Surveillance Program, 1997 2001. Country/year a (n tested) Imipenem Meropenem MIC 50 /MIC 90 % Susceptible % Resistant MIC 50 /MIC 90 % 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 Colombia b 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 a Includes only countries contributing more than 40 isolates. b Colombian 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 Acinetobacter isolates resistant to carbapenems isolated in selected Latin American countries. Overall, the highest resistance rate to imipenem was detected in Argentina (20.0%), followed by Colombia (14.0%) and Brazil (8.5%). In Brazil, imipenem resistance 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 isolates (<40) in the evaluated period. Resistance to imipenem was found to be rare in Chilean centers, with 98.0% of isolates susceptible to this antimicrobial. 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 resistance rate (40% resistance) 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 respiratory 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% vs. 6.4%; p < 0.001) (Table 4).

288 M.C.B. Tognim et al. Table 3 Antimicrobial susceptibility of Acinetobacter 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 (n tested) a Imipenem Meropenem MIC 50 /MIC 90 % Susceptible % Resistant MIC 50 /MIC 90 % 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 a Includes only infection sites with more than 100 isolates over the study period. A total of 35 and 74 Acinetobacter spp. isolates were collected, respectively, from skin/soft tissue and urinary tract infections. Table 4 Carbapenem susceptibility of Acinetobacter spp. isolates from intensive care units a as reported in the SENTRY Antimicrobial Surveillance Program, Latin America, 1997 2001. Intensive care unit (415 isolates) a Non-intensive care unit (264 isolates) a MIC 50 /MIC 90 % Susceptible % Resistant MIC 50 /MIC 90 % 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% a The origin of 147 isolates was not known. Eighteen different ribotyping patterns were identified among the 39 Acinetobacter spp. isolates evaluated (Table 5). The most frequent ribotype was 521-1, which was detected among eight isolates from three medical centers located in Argentina, 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). Discussion Acinetobacter spp. is generally an opportunistic nosocomial pathogen often resistant to multiple therapeutic agents. 1 In the present study we evaluated the susceptibility profile of Acinetobacter spp. isolates to selected antimicrobials in Latin American centers as part of a global surveillance program. Our study results were similar to previous Table 5 Distribution of ribotypes found in more than one Acinetobacter spp. 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

Resistance trends of Acinetobacter spp. in Latin America 289 reports that showed a decreased antimicrobial susceptibility profile for Acinetobacter spp. 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 Acinetobacter 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 permeability. 16,17 Although quinolones were initially considered 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 isolates, 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 centers in North America and Europe have demonstrated markedly higher susceptibility rates to carbapenems and quinolones. 21 In this study, the antimicrobial susceptibility of Acinetobacter spp. varied significantly among Latin American 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 Acinetobacter spp. 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 distinct 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 indicate 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 isolates. In fact, the Brazilian institutions harbored most of the distinct resistant genotypes, especially 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. Nevertheless, 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 typing results, especially in countries that submitted 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 antimicrobial agents among Acinetobacter spp. isolates has become a major international public health problem. 16,25 The geographic variation of resistance patterns emphasizes the importance 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 disseminating important up-to-date local data to guide the correct management of antimicrobial prescribing strategies in the nosocomial and community environment. Acknowledgements We express our appreciation to all medical technicians 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 (Laboratorio Lâmina, Rio de Janeiro, Brazil);Cássia Zoccoli (Laboratório Médico Santa Luzia Laboratory, Florianopolis, Brazil);Afonso Barth (Hospital de Clinicas, Porto Alegre, Brazil);Julival Ribeiro (Hospital de Base, Brasília, Brazil);José M. Casellas (Centro de Estudios en Antimicrobianos, San Isidro, Argentina);

290 M.C.B. Tognim et al. 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 (Hospital Maciel, Montivideo, Uruguay);Jaime A. Robledo (Corporation Para Investigaciones Biologicas, Medellin, Colombia);Jose Sifuentes-Osornio (Instituto Nacional de la Nutricion, Ciudade del Mexico, Mexico);and Manuel Guzmán-Blanco (Hospital Vargas, Caracas, Venezuela). Rodrigo E. Mendes and Juliana 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 declared. References 1. Bergogne-Berezin E, Towner KJ. Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features. Clin Microbiol Rev 1996;9:148 65. 2. Bou G, Cervero G, Dominguez MA, Quereda C, Martinez- Beltran J. Characterization of a nosocomial outbreak caused by a multiresistant Acinetobacter baumannii strain with a carbapenem-hydrolyzing enzyme: high-level carbapenem resistance in A. baumannii is not due solely to the presence of beta-lactamases. J Clin Microbiol 2000;38:3299 305. 3. Mahgoub S, Ahmed J, Glatt AE. Completely resistant Acinetobacter baumannii strains. Infect Control Hosp Epidemiol 2002;23:477 9. 4. Levin AS. Multiresistant Acinetobacter infections: a role for sulbactam combinations in overcoming an emerging worldwide problem. Clin Microbiol Infect 2002;8: 144 53. 5. Villegas MV, Hartstein AI. Acinetobacter outbreaks, 1977 2000. Infect Control Hosp Epidemiol 2003;24:284 95. 6. Corbella X, Montero A, Pujol M, Dominguez MA, Ayats J, Argerich MJ, et al. Emergence and rapid spread of carbapenem resistance during a large and sustained hospital outbreak of multiresistant Acinetobacter baumannii. J Clin Microbiol 2000;38:4086 95. 7. Manikal VM, Landman D, Saurina G, Oydna E, Lal H, Quale J. Endemic carbapenem-resistant Acinetobacter species in Brooklyn, New York: citywide prevalence, interinstitutional spread, and relation to antibiotic usage. Clin Infect Dis 2000;31:101 6. 8. Sader HS, Jones RN, Andrade-Baiocchi S, Biedenbach DJ. Four-year evaluation of frequency of occurrence and antimicrobial susceptibility patterns of bacteria from bloodstream infections in Latin American medical centers. Diagn Microbiol Infect Dis 2002;44:273 80. 9. Gales AC, Jones RN, Forward KR, Linares J, Sader HS, Verhoef J. Emerging importance of multidrug-resistant Acinetobacter species and Stenotrophomonas maltophilia as pathogens in seriously ill patients: geographic patterns, epidemiological features, and trends in the SENTRY Antimicrobial Surveillance Program (1997 1999). Clin Infect Dis 2001;32:S104 13. 10. National Committee for Clinical Laboratory Standards. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically. Approved standard M7-A6. 6th ed. Wayne, PA: NCCLS;2003. 11. National Committee for Clinical Laboratory Standards. Performance Standards for Antimicrobial Susceptibility Testing. Twelfth Informational Supplement M100-S13. 13th ed. Wayne, PA: NCCLS;2003. 12. Hollis RJ, Bruce JL, Fritschel SJ, Pfaller MA. Comparative evaluation of an automated ribotyping instrument versus pulsed-field gel electrophoresis for epidemiological investigation of clinical isolates of bacteria. Diagn Microbiol Infect Dis 1999;34:263 8. 13. Gales AC, Reis AO, Jones RN. Contemporary assessment of antimicrobial susceptibility testing methods for polymyxin B and colistin: review of available interpretative criteria and quality control guidelines. J Clin Microbiol 2001;39:183 90. 14. Goncalves CR, Vaz TM, Araujo E, Boni R, Leite D, Irino K. Biotyping, serotyping and ribotyping as epidemiological tools in the evaluation of Acinetobacter baumannii dissemination in hospital units, Sorocaba, Sao Paulo, Brazil. Rev Inst Med Trop Sao Paulo 2000;42:277 82. 15. Bantar C, Famiglietti A, Goldberg M. Three-year surveillance study of nosocomial bacterial resistance in Argentina. The Antimicrobial Committee and the National Surveillance Program (SIR) Participants Group. Int J Infect Dis 2000;4:85 90. 16. Quale J, Bratu S, Landman D, Heddurshetti R. Molecular epidemiology and mechanisms of carbapenem resistance in Acinetobacter baumannii endemic in New York City. Clin Infect Dis 2003;37:214 20. 17. Urban C, Segal-Maurer S, Rahal JJ. Considerations in control and treatment of nosocomial infections due to multidrug-resistant Acinetobacter baumannii. Clin Infect Dis 2003;36:1268 74. 18. Pascual A, Lopez-Hernandez I, Martinez-Martinez L, Perea EJ. In-vitro susceptibilities of multiresistant strains of Acinetobacter baumannii to eight quinolones. J Antimicrob Chemother 1997;40:140 2. 19. Reis AO, Luz DA, Tognim MC, Sader HS, Gales AC. Polymyxin-resistant Acinetobacter spp. isolates: what is next? Emerg Infect Dis 2003;9:1025 7. 20. Gales AC, Jones RN, Silbert S, Sader HS. SENTRY participant group Latin America. Assessment of the antimicrobial activity of polymyxin B against contemporary Gram-negative bacilli isolated in Latin America: results of SENTRY antimicrobial surveillance program - 2001. [abstract C-312] In: Program and abstracts of the 42nd Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego,CA: American Society for Microbiology;2002. 21. Pfaller MA, Jones RN, Biedenbach DJ. Antimicrobial resistance trends in medical centers using carbapenems: report of 1999 and 2000 results from the MYSTIC program (USA). Diagn Microbiol Infect Dis 2001;41:177 82. 22. Weinstein RA. Controlling antimicrobial resistance in hospitals: infection control and use of antibiotics. Emerg Infect Dis 2001;7:188 92. 23. Rahal JJ, Urban C, Segal-Maurer S. Nosocomial antibiotic resistance in multiple gram-negative species: experience at one hospital with squeezing the resistance balloon at multiple sites. Clin Infect Dis 2002;34:499 503. 24. Gales AC, Jones RN, Pfaller MA, Gordon KA, Sader HS. Two-year assessment of the pathogen frequency and antimicrobial resistance patterns among organisms isolated from skin and soft tissue infections in Latin American hospitals: results from the SENTRY antimicrobial surveillance

Resistance trends of Acinetobacter spp. in Latin America 291 program, 1997 98. SENTRY Study Group. Int J Infect Dis 2000;4:75 84. 25. Smolyakov R, Borer A, Riesenberg K, Schlaeffer F, Alkan M, Porath A, et al. Nosocomial multi-drug resistant Acinetobacter baumannii bloodstream infection: risk factors and outcome with ampicillin-sulbactam treatment. J Hosp Infect 2003;54:32 8. 26. Felmingham D. The need for antimicrobial resistance surveillance. J Antimicrob Chemother 2002;50: S1 7. 27. Richet HM, Mohammed J, McDonald LC, Jarvis WR. Building communication networks: international network for the study and prevention of emerging antimicrobial resistance. Emerg Infect Dis 2001;7:319 22.