Activity of carbapenems and tigecycline against ESBL- producing Escherichia coli and Klebsiella spp.

Universidade de Santa Cruz do Sul (Unisc), Rio Grande do Sul, Brazil

Endereço para correspondência

Caio Fernando de Oliveira
Avenida Independência, 2293, prédio 42, sala 4208; Bairro Universitário
CEP: 96816-501; Santa Cruz do Sul-RS, Brasil
e-mail: caiofarm@yahoo.com.br

INTRODUCTION

In recent years, the uncritically use of carbapenems for treating multidrug resistant (MDR) gram-negative infections has boosted the global dissemination of carbapenem-resistant Enterobacteriaceae⁽¹⁾. Extended-spectrum beta-lactamases (ESBL)-producing Escherichia coli and Klebsiella spp. isolates with acquired carbapenemases are the most prevalent gram-negative species among the MDR bacteria in the Americas^(2-4) and also other continents^{(5, 6)}. Furthermore, the emergence of cefotaximase-Munich (CTX-M) ESBL-producing bacteria evidenced these days poses significant challenge for antibiotic treatment, since this ESBL family often exhibits a MDR profile^(7-9).

The combination of ESBL production and carbapenem resistance in MDR Gram-negative isolates limits the antimicrobial therapy to few antimicrobial agents, such as colistin and tigecycline^{(9, 10)}. Due to its low toxicity and to reduce induction of carbapenem resistance, tigecycline has been suggested as an alternative to carbapenems for the treatment of infections caused by ESBL-producing strains⁽⁶⁾. Resistance to tigecycline is not widely disseminated, but was already found in multicenter studies from some countries such as the United States⁽¹¹⁾, United Arab Emirates⁽¹⁰⁾, and Brazil⁽⁴⁾, mainly in K. pneumoniae isolates.

In this study, we examine the in vitro activity of carbapenems and tigecycline against all ESBL-producing E. coli and Klebsiella spp. isolated in a single hospital at two different periods eight years apart. The hospital has a total number of 232 beds (10 intensive care unit beds) and is a regional reference center located in the central region of Rio Grande do Sul, Brazil. The first period runs from April to November 2007 (before the use of tigecycline in the mentioned hospital). The second period, from April 2015 to January 2016. All ESBL-producing E. coli and Klebsiella spp. isolated during both periods were selected to be included in this study; ESBL production was assessed in routine susceptibility testing by combined disc method using discs of cefotaxime (30 µg), ceftazidime (30 µg) and cefpodoxime (30 µg) placed at a distance of 20 mm distant from amoxicillin-clavulanic acid (30/10 µg) discs (Sensidisc, DME, Brazil). ESBL test and susceptibility of the isolates to carbapenems and tigecycline was determined by the Kirby-Bauer disc diffusion technique on Mueller-Hinton agar plates using discs of ertapenem (10 µg), imipenem (10 µg) and meropenem (10 µg) (Sensidisc, DME), and tigecycline strips (Oxoid M.I.C. Evaluator, England) according to the European Committee of Antimicrobial Susceptibility Testing (EUCAST) breakpoints. Quality control was performed using K. pneumoniae ATCC 700603 and E. coli ATCC 25922.

The species distribution, clinical source and antimicrobial resistance of isolates selected in both periods evaluated in this study are shown in the Table. The high prevalence of K. pneumoniae and E. coli isolated from urinary tract infections (UTI) found in our study were also reported in other studies^{(3, 10)}. These two species are quite common in hospitalized patients UTI, and especially K. pneumoniae sometimes appears as a MDR strain even possessing the Klebsiella pneumoniae carbapenemase (KPC) gene⁽⁸⁾.

Overall resistance to carbapenems in our study was 18.7% in 2007 and 19.1% in 2015/2016. Recent multicenter studies have shown decreasing in vitro susceptibility of ESBL-producing K. pneumoniae isolates to carbapenems^(3,8), mainly meropenem⁽³⁾. We also found a higher prevalence of K. pneumoniae resistant to carbapenems, but mainly to ertapenem. Moreover, we found an interesting prevalence of E. coli isolates resistant to imipenem (24%). Interestingly, for E. coli isolates, other studies reported better susceptibility to imipenem^{(4, 10)} and higher resistance to meropenem⁽³⁾.

Regarding the clinical source of each isolate, the body fluid and site which presented more isolates resistant to carbapenems were urine (n = 7) and respiratory tract (n = 3) in 2007; and urine (n = 8) in 2015/2016. All isolates resistant to carbapenems in the 2015/2016 period were from urine samples. Skin wound and fluids had reduced number of isolates and did not present any isolate resistant to carbapenems.

Tigecycline presented a very good in vitro activity against all isolates included in this study. The only two isolates (one E. coli and one K. pneumoniae) with intermediate profile to this antimicrobial agent [minimum inhibitory concentration (MIC) = 2 µg/ml] were both found in the 2015/2016 period. In other studies, resistance to tigecycline is higher in K. pneumoniae when compared to E. coli isolates^{(4, 5)}. Both isolates in our study were from male patients with chronic kidney disease and history of previous UTI. The E. coli isolate was from a 49-yearold patient, paraplegic by spinal cord injury, indwelling urinary catheter user, hypertensive, with recent history of septicemia and use of ciprofloxacin, nitrofurantoin and meropenem. The K. pneumoniae isolate was recovered from a 72-year-old hypertensive patient with peripheral vascular disease, type 2 diabetes mellitus, with repeated admissions including 20 days in intensive care unit in October 2015 and use of levofloxacin (prolonged curse), ampicillin + sulbactam, azithromycin and nystatin.

In this study we confirm the absence or low occurrence of E. coli and Klebsiella spp. nosocomial isolates resistant to tigecycline reported by other investigators^{(1, 10, 11)}. As limitations, we highlight the absence of molecular tests to confirm phenotypic results or evaluate clonality, the prevalence of urinary isolates and the low reproducibility of tigecycline strips. However, in the hospital environment, the ESBL-resistant genes are easily transferable to other microorganisms through plasmids and, subsequently, the resistance to carbapenems is induced by its extensive use. The resistance to carbapenems found in our study, along with a recent report of KPC-producing Klebsiella spp. in another city hospital⁽⁸⁾, demonstrates the importance of antimicrobial resistance surveillance and further researches into the presence of KPC-type carbapenemases in all Enterobacteriaceae family.

CONFLICT OF INTEREST

None to declare.

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