Aprosamine Derivatives Active against Multidrug-Resistant Gram-Negative Bacteria

Novel aprosamine derivatives were synthesized for the development of aminoglycoside antibiotics active against multidrug-resistant Gram-negative bacteria. The synthesis of aprosamine derivatives involved glycosylation at the C-8' position and subsequent modification (epimerization and deoxygenation at the C-5 position and 1-N-acylation) of the 2-deoxystreptamine moiety. All 8'-β-glycosylated aprosamine derivatives (3a-h) showed excellent antibacterial activity against carbapenem-resistant Enterobacteriaceae and 16S ribosomal RNA methyltransferase-producing multidrug-resistant Gram-negative bacteria compared to the clinical drug, arbekacin. The antibacterial activity of 5-epi (6a-d) and 5-deoxy derivatives (8a,b and 8h) of β-glycosylated aprosamine was further enhanced. On the other hand, the derivatives (10a,b and 10h) in which the amino group at the C-1 position was acylated with (S)-4-amino-2-hydroxybutyric acid showed excellent activity (MICs 0.25-0.5 μg/mL) against resistant bacteria that produce the aminoglycoside-modifying enzyme, aminoglycoside 3-N-acetyltransferase IV, which induces high resistance against parent apramycin (MIC > 64 μg/mL). In particular, 8b and 8h showed approximately 2- to 8-fold antibacterial activity against carbapenem-resistant Enterobacteriaceae and 8- to 16-fold antibacterial activity against resistant Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, compared to apramycin. Our results showed that aprosamine derivatives have immense potential in the development of therapeutic agents for multidrug-resistant bacteria.

Exploration of Antibiotic Activity of Aminoglycosides, in Particular Ribostamycin Alone and in Combination With Ethylenediaminetetraacetic Acid Against Pathogenic Bacteria

The emergence of infections caused by bacterial pathogens that are resistant to current antibiotic therapy is a critical healthcare challenge. Aminoglycosides are natural antibiotics with broad spectrum of activity; however, their clinical use is limited due to considerable nephrotoxicity. Moreover, drug-resistant bacteria that cause infections in human as well as livestock are less responsive to conventional antibiotics. Herein, we report the in vitro antibacterial evaluation of five different aminoglycosides, including ribostamycin, against a panel of Gram-positive and Gram-negative pathogens. Eight of the tested bacterial strains are linked to gastrointestinal (GI) infections. The minimum inhibitory concentration (MIC) of ribostamycin against three different Escherichia coli strains is in the range of 0.9–7.2 μM and against a strain of Haemophilus influenzae is 0.5 μM. We also found that the MIC of ribostamycin was considerably enhanced from 57.2 to 7.2 μM, an 8-fold improvement, when bacteria were treated with a combination of ribostamycin and ethylenediaminetetraacetic acid (EDTA). These findings demonstrate a promising approach to enhance the clinical potential of ribostamycin and provide a rational for its antibiotic reclassification from special level to non-restricted level.

Development of 6'-N-Acylated Isepamicin Analogs with Improved Antibacterial Activity Against Isepamicin-Resistant Pathogens

The development of new aminoglycoside (AG) antibiotics has been required to overcome the resistance mechanism of AG-modifying enzymes (AMEs) of AG-resistant pathogens. The AG acetyltransferase, AAC(6′)-APH(2″), one of the most typical AMEs, exhibiting substrate promiscuity towards a variety of AGs and acyl-CoAs, was employed to enzymatically synthesize new 6′-N-acylated isepamicin (ISP) analogs, 6′-N-acetyl/-propionyl/-malonyl ISPs. They were all active against the ISP-resistant Gram-negative bacteria tested, and the 6′-N-acetyl ISP displayed reduced toxicity compared to ISP in vitro. This study demonstrated the importance of the modification of the 6′-amino group in circumventing AG-resistance and the potential of regioselective enzymatic modification of AG scaffolds for the development of more robust AG antibiotics.

Escherichia coli and Klebsiella pneumoniae bacteremia in patients with neutropenic fever: factors associated with extended-spectrum β-lactamase production and its impact on outcome

Escherichia coli and Klebsiella pneumoniae are main pathogens in neutropenic fever even if the proportion of Gram-positive cocci is increasing. Extended-spectrum β-lactamases (ESBL)-producing organisms are an emerging problem in nosocomial infection. Nevertheless, until now, information about risk factors for the acquisition and clinical outcomes of bacteremia due to ESBL-producing organisms is limited in neutropenic patients. From medical records collected between January 2007 and December 2008, we identified a total of 101 consecutive patients who developed bacteremia due to E. coli (n = 87) or K. pneumoniae (n = 14). Twenty-six (26 %) cases of bacteremia were caused by ESBL-producing organisms. A hospital stay of >2 weeks during the 3 months preceding bacteremia [adjusted odds ratio (OR), 5.887; 95 % confidence interval (CI), 1.572-22.041] and the use of broad-spectrum cephalosporins in the 4 weeks prior to bacteremia (adjusted OR, 6.186; 95 % CI, 1.616-23.683) were significantly related to the acquisition of ESBL. Twenty-four (92 %) of the ESBL-producing organisms were susceptible to either piperacillin-tazobactam or amikacin. Aminoglycosides (amikacin or isepamicin) were the main appropriate antimicrobial agents used against the ESBL-producing isolates during the initial empirical treatment (16/22, 73 %). However, the 30-day mortality rates for ESBL bacteremia and non-ESBL bacteremia were not significantly different (15 vs 5 %; p = 0.199). As alternatives to carbapenem, piperacillin-tazobactam plus amikacin or isepamicin combinations may be effective empirical therapeutic options for patients with neutropenic fever who are at high risk of developing bacteremia with ESBL-producing pathogens.

In vitro antimicrobial susceptibility to isepamicin of 6,296 Enterobacteriaceae clinical isolates collected at a tertiary care university hospital in Greece

The reevaluation of "forgotten" antibiotics can identify new therapeutic options against extensively drug-resistant Gram-negative pathogens. We sought to investigate isepamicin in this regard. We retrospectively evaluated the antimicrobial susceptibility to isepamicin of Enterobacteriaceae sp. isolates from unique patients, collected at the microbiological laboratory of the University Hospital of Heraklion, Crete, Greece, from 2004 to 2009. Susceptibility testing was done with the automated Vitek 2 system. The breakpoints for susceptibility to isepamicin, tigecycline, and other antibiotics were those proposed by the Comité de l'Antibiogramme de la Société Française de Microbiologie (CA-SFM), the FDA, and the CLSI, respectively. A total of 6,296 isolates were studied, including primarily 3,401 (54.0%) Escherichia coli, 1,040 (16.5%) Klebsiella pneumoniae, 590 (9.4%) Proteus mirabilis, and 460 (7.3%) Enterobacter sp. isolates. Excluding the species with intrinsic resistance to each antibiotic, antimicrobial susceptibility was highest for colistin (5,275/5,441 isolates [96.9%]) and isepamicin (6,103/6,296 [96.9%]), followed by meropenem (5,890/6,296 [93.6%]), imipenem (5,874/6,296 [93.3%]), and amikacin (5,492/6,296 [87.2%]). The antimicrobial susceptibility of the 1,040 K. pneumoniae isolates was highest for isepamicin (95.3%), followed by colistin (89.3%) and meropenem (63.0%). Regarding resistant K. pneumoniae isolates, susceptibility to isepamicin was observed for 91.1% of the 392, 87.7% of the 375, and 85.6% of the 111 isolates that were nonsusceptible to the carbapenems, all other aminoglycosides, and colistin, respectively. Isepamicin exhibited high in vitro activity against almost all of the Enterobacteriaceae species. It could particularly serve as a last-resort therapeutic option for carbapenem-resistant K. pneumoniae in our region, where it is endemic, as it does not show considerable cross-resistance with other aminoglycosides.