In Vitro Antimicrobial Susceptibility of Aerococcus urinae

Abstract

Aerococcus urinae may cause urinary tract infections, bacteremia, and endocarditis. No standardized susceptibility test methods or interpretive criteria have been proposed for this organism. This study reports the MIC results for 128 A. urinae isolates tested by broth microdilution. The isolates had low MICs to amoxicillin, cefotaxime, ceftriaxone, doxycycline, linezolid, meropenem, penicillin, rifampin, tetracycline, trimethoprim-sulfamethoxazole, and vancomycin. However, 55% of the isolates had MICs to clindamycin of >0.25 g/ml, 44% had MICs to erythromycin of >0.25 g/ml, and 16% had MICs to levofloxacin of >2 g/ml.A erococcus urinae is a Gram-positive coccus that colonizes the human urinary tract and may cause symptomatic urinary tract infections (1-3). Importantly, A. urinae is also described as the cause of invasive infections, such as endocarditis and bacteremia (4-17), and has been reported to demonstrate resistance to a variety of commonly used classes of antimicrobial agents, in particular, trimethoprim-sulfamethoxazole (SXT) and fluoroquinolones (18,19). In the laboratory, A. urinae, particularly when isolated from urine, may be misidentified as an alpha-hemolytic Streptococcus strain due to several shared phenotypic properties, including colony morphology and negative catalase reactions (13,20). However, improved diagnostic technologies, such as matrixassisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) (21), are allowing clinical laboratories to correctly identify A. urinae with increasing frequency.The lack of standardized susceptibility test methods and interpretive criteria for Aerococcus spp. are problematic for clinical laboratories and clinicians. There are a limited number of published studies that address susceptibility testing of A. urinae, and these usually include a small number of isolates. A variety of test methods have been reported, and interpretive criteria for streptococci (2), staphylococci (22), and even enterococci (R.M.H., personal observation) have been applied. The Clinical and Laboratory Standards Institute (CLSI) has described a broth microdilution MIC test for Streptococcus pneumoniae and Streptococcus spp. that utilizes Mueller-Hinton broth supplemented with 2.5 to 5% lysed horse blood (23). In this study, we report the results of antimicrobial susceptibility testing for a collection of 128 unique A. urinae isolates, performed using this method, against 14 antimicrobial agents. Based on information in the literature and the MIC distributions obtained in our study, we propose the use of CLSI viridans group streptococci MIC interpretive criteria for A. urinae.All A. urinae strains were isolated from urine specimens at concentrations of Ն10 5 CFU/ml between January 2005 and December 2013 by the UCLA Health System Clinical Microbiology Laboratory. Identification was performed using the API 20 Strep (bioMérieux, Durham, NC). Antimicrobial susceptibility testing was performed at the time of isolation using the CLSI reference broth microdilution (BM...

Aerococcus urinae: An Emerging Cause of Urinary Tract Infection in Older Adults with Multimorbidity and Urologic Cancer

“…In vitro, A. urinae is susceptible to amoxicillin, cefotaxime, ceftriaxone, doxycycline, linezolid, meropenem, penicillin, rifampin, trimethoprim-sulfamethoxazole, and vancomycin. It had variable resistance to clindamycin, erythromycin, and levofloxacin 5 . Several other studies have indicated that it is also resistant to sulfonamides and it may have variable resistance to vancomycin and trimethoprim-sulfamethoxazole 1 .…”

In vitro susceptibility of Aerococcus urinae isolates to antibiotics used for uncomplicated urinary tract infection

“…3 By broth microdilution, Humphries et al reported susceptibility rates of 84% for levofloxacin (LEV) and 97% for trimethoprim-sulfamethoxazole (SXT) using the Clinical Laboratory Standards Institute (CLSI) interpretive criteria. 4 As stated in a recent review by Rasmussen et al, the fosfomycin (FOS) susceptibility rate for A. urinae was 90% 1 ; however, these data were only based on twenty isolates. In an older study from 1997, which may not represent our current situation, Schuur et al reported that their collection of A. urinae was uniformly susceptible to nitrofurantoin (NIT).…”

“…1,3 However, using a broth microdilution MIC test with broth supplemented with 2.5% LHB, Humphries et al reported that most of their isolates were susceptible. 4 The thymidine present in conventional media is able to inhibit SXT. The addition of 2.5% LHB, however, modulates SXT susceptibility in that it provides endogenous thymidine phosphorylase which converts thymidine to thymine and thus restores the in vitro activity of the drug.…”

“…The addition of 2.5% LHB, however, modulates SXT susceptibility in that it provides endogenous thymidine phosphorylase which converts thymidine to thymine and thus restores the in vitro activity of the drug. 4 Senneby et al reported that most of their A. urinae isolates were resistant to SXT by Etest on Mueller-Hinton agar although 5% LHB was added. 7 In line with these findings, Etest results of almost all of our isolates indicated resistance to SXT even though we supplemented CAMH agar with LHB.…”

Mise au point : les uropathogènes émergents

“…Les Aerococcus spp., sont sensibles aux glycopeptides, à la rifampicine, aux cyclines, au linézolide et à la gentamicine. Ils sont inconstamment sensibles aux macrolides [1,2,7,12]. Les études portant sur la sensibilité d'A.…”