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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 101, Num. 7, 2006, pp. 741-748
Memórias do Instituto Oswaldo Cruz - Vol.101(7) November 2006

Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 101, No. 7, November ,2006, pp. 741-748

Increased resistance to first-line agents among bacterial pathogens isolated from urinary tract infections in Latin America: time for local guidelines?

Soraya S Andrade/+, Helio S Sader*, Ronald N Jones*, Andrea S Pereira, Antônio CC Pignatari, Ana C Gales

Laboratório Especial de Microbiologia Clínica, Universidade Federal de São Paulo, Rua Leandro Dupret 188, 04025-010 São Paulo, SP, Brasil *JMI Laboratories, North Liberty, IA, US

+Corresponding author: soraya.andrade@lemc.com.br

Received 5 April 2006
Accepted 31 July 2006

Code Number: oc06214

Emerging resistance phenotypes and antimicrobial resistance rates among pathogens recovered from community-acquired urinary tract infections (CA-UTI) is an increasing problem in specific regions, limiting therapeutic options.

As part of the SENTRY Antimicrobial Surveillance Program, a total of 611 isolates were collected in 2003 from patients with CA-UTI presenting at Latin American medical centers. Each strain was tested in a central laboratory using Clinical Laboratory Standard Institute (CLSI) broth microdilution methods with appropriate controls.

Escherichia coli was the leading pathogen (66%), followed by Klebsiella spp. (7%), Proteus mirabilis (6.4%), Enterococcus spp. (5.6%), and Pseudomonas aeruginosa (4.6%). Surprisingly high resistance rates were recorded for E. coli against first-line orally administered agents for CA-UTI, such as ampicillin (53.6%), TMP/SMX (40.4%), ciprofloxacin (21.6%), and gatifloxacin (17.1%). Decreased susceptibility rates to TMP/SMX and ciprofloxacin were also documented for Klebsiella spp. (79.1 and 81.4%, respectively), and P. mirabilis (71.8 and 84.6%, respectively). For Enterococcus spp., susceptibility rates to ampicillin, chloramphenicol, ciprofloxacin, and vancomycin were 88.2, 85.3, 55.9, and 97.1%, respectively. High-level resistance to gentamicin was detected in 24% of Enterococcus spp. Bacteria isolated from patients with CA-UTI in Latin America showed limited susceptibility to orally administered antimicrobials, especially for TMP/SMX and fluoroquinolones. Our results highlight the need for developing specific CA-UTI guidelines in geographic regions where elevated resistance to new and old compounds may influence prescribing decisions.

Key words: urinary tract infection - SENTRY - Latin America

Community-acquired urinary tract infections (CA-UTI) are a frequent problem worldwide. In the United States, surveys have estimated an incidence of eight million UTI episodes per year (Foxman 2002). These infections are usually caused by Escherichia coli, but other uropathogens, such as Klebsiella spp. and Staphylococcus saprophyticus, have also been frequently isolated (Ronald 2002, Lau et al. 2004).

Effective management of UTIs in the outpatient setting has been hampered by the fact that many strains have developed resistance to several oral antimicrobial agents. The increasing frequency of thrimetoprim/sulfamethoxazole (TMP-SMX) resistance is worrisome, since this agent is frequently prescribed for uncomplicated UTIs in many developed and developing countries (Talan et al. 2000, Hay et al. 2005, Sader et al. 2005). Reports from North America indicate an elevated prevalence of TMP-SMX-resistant isolates in this region associated with increased clinical failure rates (Manges et al. 2004). Although the Infectious Diseases Society of America (IDSA) guidelines and some studies have suggested that fluoroquinolones may be used as first-line therapy for treatment of uncomplicated bacterial cystitis in woman (Warren et al. 1999,Talan et al. 2004) reports of uro-pathogens resistant to these agents have increasingly been reported (Alos et al. 2005).

The continuous trend of empirically treating CA-UTI episodes poses a great challenge for researchers, since data on uropathogens prevalence and antimicrobial susceptibility have been increasingly more difficult to obtain. Moreover, regional variations in resistance patterns do occur, and must be as well documented (Gupta 2003). In Latin America, few data are available on the frequency and resistance rates of CA-UTI. In this study, we have evaluated the pathogen frequency and susceptibility patterns of CA-UTI in Latin American medical centers as part of the SENTRY Antimicrobial Surveillance Program.

MATERIALS AND METHODS

Bacterial strains - Each medical center was responsible to collect consecutive isolates from CA-UTI, including urinary pathogens from patients presenting to outpatient clinics or emergency department. Urinary specimens were collected in the course of routine clinical management, and infections were considered to be clinically significant and of community origin by local criteria. A number of demographic information, such as antibiotic use, and presence of complicated UTI, were not collected or might have not been available. A total of 611 non-duplicate bacterial isolates were collected from patients with CA-UTI presenting at Latin America medical centers participating in the SENTRY Program between January and December 2003 (Argentina, Chile, Brazil, Mexico, and Venezuela). All isolates were identified at the participating institution by the routine methodology in use at each laboratory. Upon receipt at the monitoring laboratory (JMI Laboratories, North Liberty, IA, US), isolates were subcultured onto blood agar to ensure viability and purity. Confirmation of species identification was performed with Vitek (bioMérieux Vitek, St Louis, MO) or conventional methods as required.

Participant medical centers - The medical centers were located in San Isidro and Buenos Aires (Argentina); Brasília, Florianópolis, Porto Alegre, São Paulo (Brazil); Santiago (two medical centers, Chile); Ciudade del Mexico, (Mexico); and Caracas (Venezuela).

Susceptibility testing - Antimicrobial susceptibility testing was performed and interpreted following the guidelines for reference broth microdilution method described by the Clinical and Laboratory Standards Institute (CLSI, formerly National Committee for Clinical and Laboratory Standards) (NCCLS 2003). The minimal inhibitory concentrations (MICs) were defined as the lowest antimicrobial concentration able to totally inhibit bacterial growth. The diverse antimicrobial agent powders were obtained from the respective manufacturers or purchased from Sigma (St Louis, MO, US). Dry-form microdilution panels and broth for inoculation were purchased from Trek Diagnostic Systems (Westlake, OH, US). Testing of quality control strains E. coli ATCC 25922 and 35218, S. aureus ATCC 29213, P. aeruginosa ATCC 27853, and Enterococcus faecalis ATCC 29212 was performed for quality assurance purposes. Isolates of E. coli and K. pneumoniae with increased MIC values (³ 2 µg/ml) for ceftazidime and/or ceftriaxone and/or aztreonam were considered as possible extended-spectrum b-lactamase (ESBL)-producing phenotypes according to CLSI criteria (2005). Production of ESBL was confirmed by disk-approximation test (Thomson & Sanders 1992).

RESULTS AND DISCUSSION

E. coli (66%) was the most common pathogen isolated from CA-UTI in Latin American countries, followed by P. mirabilis (6.4%) and K. pneumoniae (5.9%) (Table I). Enterococcus spp. was the most common gram-positive uropathogen, responsible for 5.6% of all CA-UTI. These data are similar to those presented by other surveillance studies, in which gram-negative agents were the most common pathogens associated with CA-UTI (Zhanel et al. 2000, Kahlmeter 2003).

Overall, the majority of isolates (75.6%) were collected from female patients with E. coli being also the most common uropathogen (Table II). The median age of patients with CA-UTI was similar in both groups: 41.4 years (female sex) and 43.7 years (male sex) (data not shown). The predominance of E. coli as the leading agent of CA-UTI in women had been also verified by other surveillance reports from distinct geographic regions, such as the ECO SENS report from Europe and Canada, and the TSN study from the United States (Kahlmeter 2000, Gupta et al. 2001).

Among gram-positive uropathogens, Enterococcus spp. and group B streptococci were the most common agents isolated from women, responsible for 5.2 and 2.8%, respectively, of all CA-UTI (Table II). In this study, however, only 8 isolates of S. saprophyticus were recovered. These results contrast with other reports, where S. saprophyticus remains a significant pathogen causing CA-UTI in women (Kahlmeter 2003, Muratani & Matsumoto 2004). This finding may indicate a distinct pattern of Gram-positive uropathogen distribution in the Latin American region.

The antimicrobial susceptibility results of the most frequent pathogens associated with CA-UTI in Latin America is shown in Table IIIa and Table IIIb . The b-lactam agents ceftriaxone (MIC50, £ 0.25 µg/ml), ceftazidime (MIC50, £ 1 µg/ml), and cefepime (MIC50, £ 0.12 µg/ml), displayed excellent activity against E. coli (98.3-98.5% susceptible). All of the 403 clinical isolates of E. coli were susceptible to imipenem and meropenem, indicating that carbapenem resistance is still an unusual phenotype among Enterobacteriaceae isolated from CA-UTI in the region. On the other hand, decreased susceptibility rates were detected among E. coli for common orally administered agents, such as ampicillin (46.2% susceptible), ciprofloxacin (77.4% susceptible), and TMP-SMX (59.6% susceptible). In fact, among the orally prescribed agents, cefuroxime (2.2% resistant), amoxicillin/clavulanate (1.2% resistant), and nitrofurantoin (6.9% resistant) achieved the lowest resistance rates for E. coli.

Our study have detected much higher resistance rates when compared to the ECO SENS and TSN Programs for some oral prescribed agents (Gupta et al. 2001, Kahlmeter 2003). Most surprisingly, the E. coli resistance rates found in the current study are even higher than those described by some surveillance programs evaluating hospitalized patients. The EARSS study in Spain reported lower resistance rates to ciprofloxacin (19.3%), and TMP/SMX (32.6%), among E. coli strains from Spanish hospitals (Oteo et al. 2005). The current study showed similar susceptibility rates for some orally prescribed agents among CA-UTI isolates similar to those showed by E. coli strains from other infection sites previously evaluated by the SENTRY Program in Latin America, such as bloodstream infections (Sader et al. 2002), and hospital-acquired UTI (Gales et al. 2002).

The increased resistance rates detected for TMP/SMX in Latin America is of great concern. These rates may reflect a possible widespread use of this low cost antimicrobial agent for treatment of CA-UTI in the region, or as a prophylactic agent against Pneumocystis jiroveci infections in the HIV-infected population.

Increased resistance rates of E. coli against the studied quinolones were also verified in contrast to other surveillance studies evaluating CA-UTI in United States and Europe, which have documented resistance rates of approximately 2% (Gupta et al. 2001, Kahlmeter 2003) for some fluoroquinolones (Table IIIa and b ). In fact, the susceptibility rates to the fluoroquinolones were lower than those observed for hospital-acquired E. coli isolates previously collected by the SENTRY in Latin America (Gales et al. 2002). These increased resistance rates among community-acquired E. coli was addressed by the EARSS study in Spain, where 19.3% of all invasive clinical isolates evaluated in 2003 were resistant to ciprofloxacin (Oteo et al. 2005). These high resistance rates were attributed to an increase in fluoroquinolone consumption over the years in Spain. Prior exposure to fluoroquinolones has been recently acknowledged to be an independent risk factor for ciprofloxacin-resistant E. coli from CA-UTI (Killgore et al. 2004).

Among the participating countries, Brazil and Chile displayed the highest susceptibility rates to the evaluated fluoroquinolones against E. coli (Table IV). Although Mexico contributed with only 36 E. coli isolates, very low susceptility rates were detected among all tested oral agents. Overall, rates of TMP/SMX resistance were significantly decreased for all Latin American countries. The current data may reflect the increased use of orally prescribed agents in some Latin American countries, to treat hospital or community-acquired infections, such as UTI or respiratory tract infections. This overuse may select for multidrug-resistant E. coli phenotypes, harboring the potential to disseminate within a specific region. Further antimicrobial consumption studies at community level are needed in the Latin American region to verify this assumption.

High resistance rates were also documented for TMP/SMX among the other Enterobacteriaceae causing CA-UTI, ranging from 19.4% for K. pneumoniae, to 28.2% for P. mirabilis (Table III). Resistance rates for the tested fluoroquinolones were lower than those described for E. coli, but also significantly elevated. Overall, more than 85% of clinical isolates of K. pneumoniae and P. mirabilis were susceptible to third- and fourth-generation cephalosporins. No isolate was found to be resistant to imipenem or meropenem. These two Enterobacteriaceae pathogens have been described as frequent uropathogens associated with CA-UTI among non-E. coli isolates, especially among adult and elderly patients (Gupta et al. 2001). Other surveillance studies, however, have found distinct and much lower resistance rates for orally administered antimicrobial agents for these pathogens (Gupta et al. 2001, Kahlmeter 2003).

A total of 88.2% of Enterococcus spp. isolates were susceptible to ampicillin (Table III). Among other orally administered agents, nitrofurantoin (94.1%) and chloramphenicol (85.3%) demonstrated the higher susceptibility rates. Linezolid was the only agent able to inhibit the growth of 100% of all Enterococcus spp. isolates, and 2.9% of isolates were resistant to both, teicoplanin and vancomycin (vanA phenotype). The majority of group B streptococci collected from CA-UTI were susceptible to the tested antimicrobial agents, including the tested fluoroquinolones.

Surprisingly, a total of 28 isolates of P. aeruginosa were reported (Table III). Previous surveillance studies have also documented P. aeruginosa among patients with CA-UTI (Barrett et al. 1999, Lau et al. 2004). These data may correspond, in the current study, to infections developed in the community setting from patients with recent hospitalization and/or antimicrobial treatment.

Rates of ESBL-producing isolates were 1.7, 16.3, and 5.1%, respectively, for E. coli, Klebisella spp., and P. mirabillis (data not shown). The increasing frequency of ESBL phenotypes in the community is an emerging problem (Pitout et al. 2005). Although we were not able to track demographic data on these patients, risk factors for the development of ESBL in the community have already been described, including recent hospitalization, previous antimicrobial treatment, and use of immunosuppressive therapy (Colodner et al. 2004). The current report further emphasizes the importance of routine screening, by clinical laboratories, of ESBL production among Enterobacteriaceae strains isolated from community-acquired infections.

In the Latin American region, international surveillance programs have already documented increased resistance rates for multiple pathogens among hospitalized patients (Andrade et al. 2003, Gordon & Jones 2003, Mendes et al. 2005), probably reflecting local antimicrobial usage patterns, leading to a high selective pressure, and/or dissemination of specific resistant clones. However, antimicrobial susceptibility among pathogens isolated from community-acquired infections is poorly investigated in this region.

Although this is the first surveillance study in the Latin American region to assess the frequency of pathogens from CA-UTI, a number of points should be raised. The classification of CA-UTI was based on local criteria, according to the study protocol, but some data, such as previous hospitalization, may not have been available for analysis. So, the presence of some pathogens, such as P. aeruginosa and Enterococcus spp., and the low prevalence of S. saprophyticus, might reflect infections acquired during hospitalization, followed by community-onset after hospital discharge. However, a larger surveillance study conducted in the US has also found even elevated frequencies of Enterococcus spp. (from 5 to 12%) and P. aeruginosa (from 1 to 4%) among CA-UTI in woman (Gupta et al. 2001). Since most cases of CA-UTI are treated empirically and cultures are not usually requested, we can predict that some urine cultures evaluated in the present study were submitted to the laboratory because of treatment failure or complicated UTI, and probably represent a different patient population from those with first episode of UTI. Although these limitations are inherent to the retrospective nature of large surveillance studies, the inclusion of such specimens may have overestimated the resistance rates for some organisms.

Even tough, the decreased susceptibility rates found for some agents in the current study is worrisome, since some of them are currently prescribed as first-line agents for treatment of CA-UTI in the Latin American region. As most orally administered agents prescribed for CA-UTI usually achieve high urinary concentrations, it was originally thought that in vitro resistance could not result into therapeutic failure. However, recent studies have demonstrated therapeutic failure in more than 50% of patients infected with TMP/SMX-resistant uropathogens (Gupta & Stamm 2002). The Infectious Diseases Society of America (IDSA) guidelines consider TMP/SMX as the current standard therapy for uncomplicated CA-UTI in women (Warren et al. 1999). The IDSA guidelines recommend that local antimicrobial susceptibility patterns of community-acquired pathogens must be taken into account before prescribing such agents. As demonstrated by this study, TMP/SMX may no longer be considered a first-line orally administered agent for CA-UTI in the specific geographic regions covered by the SENTRY Program in Latin America. Based on the results reported here, it has become a difficult task to choose the most suitable oral agent for empiric treatment of CA-UTI. Fluo-roquinolones, agents recommended for communities with elevated prevalence of TMP/SMX resistance, must be used with caution, since resistance rates may reach up to 21% among E. coli, as described in this study. Although cefuroxime and amoxicillin/clavulanate demonstrated lower resistance rates, b-lactam agents are less effective in bacteriuria erradication, leading to increased rates of recurrence (Daikos et al. 1987). Although nitrofurantoin had poor activity against P. mirabilis and only 51.2% of Klebsiella spp. were susceptible to this agent, it might constitute a good alternative agent for treatment of uncomplicated CA-UTI caused by E.coli.

The worldwide trend of empirically treating CA-UTI may not apply for specific geographical regions in which decreased susceptibility rates are documented for common uropathogens. In these communities with high rates of antimicrobial resistance, routine urine cultures may be necessary, since treatment failure is more likely to occur. International guidelines may no longer be suitable for some Latin American countries, where antimicrobial resistance rates for first-line agents were unexpectedly elevated in this study. The development of specific guidelines based on local susceptibility patterns may be necessary in these geographic regions. Continued surveillance programs, such as the SENTRY, are essential to provide local information for decision-makers and infectious diseases specialists developing CA-UTI guidelines.

ACKNOWLEDGMENTS

To all medical technicians who have worked in SENTRY. SENTRY Latin America Study Group in 2003 includes: Helio S Sader and Ana C Gales (São Paulo, Brazil - Latin America Coordinator); Cássia Zoccoli (Laboratório Médico Santa Luzia Laboratory, Florianópolis, Brazil); Afonso Barth (Hospital de Clínicas, Porto Alegre, Brazil); Julival Ribeiro (Hospital de Base, Brasília, Brazil); José M Casellas (Centro de Estudios en Antimicrobianos, San Isidro, Argentina); Jorgelina Smayevsky (Laboratorio C E M I C, Buenos Aires, Argentina); Valeria Prado (Faculdad de Medicina de Chile, Santiago, Chile); Patricia Garcia (Universidad Catolica del Chile, Santiago, Chile); Jose Sifuentes-Osornio (Instituto Nacional de la Nutricion, Ciudade del Mexico, Mexico); and Manuel Guzmán-Blanco (Hospital Vargas, Caracas, Venezuela).

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