Combination Antimicrobial Susceptibility Testing of Multidrug-Resistant Stenotrophomonas maltophilia from Cystic Fibrosis Patients

Abstract

Stenotrophomonas maltophilia is increasingly being isolated from the respiratory tract of individuals with cystic fibrosis, and, because of its multidrug-resistant nature, the selection of suitable treatment regimens can be problematical. Etest methodology was used to facilitate MIC and antimicrobial combination testing on 80 isolates of S. maltophilia cultured from the respiratory tract of Scottish individuals with cystic fibrosis between 2001 and 2010. The overall rate of susceptibility for the 1,410 MIC tests was 23.1%, and resistance was 68.9%. The most active antimicrobials were minocycline, co-trimoxazole, and doxycycline, with 92.4%, 87.3%, and 58.8% of isolates being susceptible, respectively. Of the 517 combinations, 13.2% were synergistic, with the most synergistic being ticarcillin/clavulanate plus aztreonam (91.7% synergistic), ticarcillin/clavulanate plus colistin (40%), and ticarcillin/clavulanate plus levofloxacin (19.4%). Colistin plus tobramycin was the only antagonistic combination (0.2%). By the median susceptible breakpoint index, the most active combinations were minocycline plus co-trimoxazole (median index, 20), minocycline plus piperacillin-tazobactam (median, 20), and co-trimoxazole plus ceftazidime (median, 16.5). The increasing problem of multidrug resistance in organisms recovered from the respiratory tracts of individuals with cystic fibrosis is not going to go away. Current susceptibility testing methods do not address the slow-growing organisms associated with chronic infection, and interpretive standards are based on achievable blood levels of antimicrobials. Addressing these issues specifically for organisms recovered from the respiratory tracts of individuals with cystic fibrosis should lead to better therapeutic outcomes and improved wellbeing of individuals with cystic fibrosis.

Type II Secretion-Dependent Degradative and Cytotoxic Activities Mediated by Stenotrophomonas maltophilia Serine Proteases StmPr1 and StmPr2

“…Community-acquired S. maltophilia infections, especially in the high-risk populations mentioned, have been reported (5), and recently, a communityacquired skin infection was reported for the first time in an immunocompetent individual (6). The multidrug-resistant nature of S. maltophilia makes treatment of infections highly difficult (7), and in recent years, an increased resistance to the preferred antibiotic trimethoprim-sulfamethoxazole has been reported (8)(9)(10). These findings emphasize the need to better understand the virulence mechanisms employed by S. maltophilia.…”

Antibiotic susceptibility of sulfamethoxazole-trimethoprim resistant Stenotrophomonas maltophilia strains isolated at a tertiary care centre in Hungary

“…Several studies tested in vitro antibiotic combinations on SXT-susceptible S. maltophilia isolates, but only few ones focused on SXT-resistant ones [21]. By different methods, a lot of synergistic combinations were described; including those we tested [8,11,[22][23][24][25]. According to our results, synergy is strain dependent.…”

“…Resistance rates of SXT ranges from 2 to 10% globally; however studies from Turkey (15%), Spain (27%), Taiwan (25%) and China (30-48%) reported higher resistance rates [4,[6][7][8]. In patients suffering from cystic fi brosis (CF), the frequency of SXT-resistant S. maltophilia is higher (24-84%) [2,[9][10][11]. Resistance level of isolates from patients with cancer and those treated in intensive care unit (ICU) might be also higher [4].…”

Screening of Anti-Infectives against <i>Leishmania donovani</i>

“…Multi-drug susceptibility tests do not only give results for susceptibility, but also qualifies the activity of the combined anti-infective agents [11].…”