Surveillance of Dihydropteroate Synthase Genes inStenotrophomonas maltophiliaby LAMP: Implications for Infection Control and Initial Therapy.
Stenotrophomonas maltophiliais a common nosocomial pathogen that causes high morbidity and mortality. Because of its inherent extended antibiotic resistance, therapeutic options forS. maltophiliaare limited, and sulfamethoxazole/trimethoprim (SXT) is the only first-line antimicrobial recommended. However, with the spread of dihydropteroate synthase (sul1andsul2) genes, global emergence of SXT resistance has been reported. There is an urgent need to develop a rapid and sensitive but cost-efficient method to monitor the dissemination ofsulgenes. In this study, we developed loop-mediated isothermal amplification (LAMP) assays forsul1andsul2using real-time turbidity and hydroxy naphthol blue coloration methods. The assays could quickly detectsulgenes with high sensitivity and specificity. The LAMP detection limit was 0.74 pg/reaction of extracted genomic DNA forsul1and 2.6 pg/reaction forsul2, which were both 10-fold more sensitive than the corresponding traditional PCR assays. Additionally, the LAMP assays could positively amplify DNA fromsul1-producing strains, but not from the negative controls. We then used the LAMP assays to investigate the dissemination ofsulgenes amongS. maltophiliaisolates from patients in three hospitals in Beijing, China. Among 450 non-duplicated samples collected during 2012-2014, 56 (12.4%) strains were SXT-resistant. All these SXT-resistant strains were positive forsulgenes, with 35 (62.5%) carryingsul1, 17 (30.4%) carryingsul2, and 4 (7.1%) carrying bothsul1andsul2, which indicated thatsulgenes were the predominant resistance mechanism. Of 394 SXT-susceptible strains, 16 were alsosul-positive. To provide epidemiological data for the appropriate choice of antimicrobials for treatment ofsul-positiveS. maltophilia, we further tested the susceptibility to 18 antimicrobials. Among these,sul-positive strains showed the highest susceptibility to tetracycline derivatives, especially minocycline (MIC50/MIC90, 0.5/4; susceptibility rate, 95.4%). Ticarcillin-clavulanate and new fluoroquinolones (moxifloxacin and levofloxacin) also showed somein vitroactivity. Apart from these three kinds of antimicrobials, other agents showed poor activity againstsul-positive strains.
Department of Respiratory Diseases, Chinese PLA General Hospital Beijing, China.
Jin
J
Zhao
Department of Infection Management and Disease Control, Chinese PLA General Hospital Beijing, China.
Yubin
Y
Xing
Testing Center of HMI, Chinese PLA General Hospital Beijing, China.
Wei
W
Liu
Department of Respiratory Diseases, Chinese PLA General Hospital Beijing, China.
Wentao
W
Ni
Department of Respiratory Diseases, Chinese PLA General Hospital Beijing, China.
Chuanqi
C
Wei
Department of Clinical Pharmacology, Chinese PLA General Hospital Beijing, China.
Rui
R
Wang
Department of Infection Management and Disease Control, Chinese PLA General Hospital Beijing, China.
Yunxi
Y
Liu
Department of Respiratory Diseases, Chinese PLA General Hospital Beijing, China.
Youning
Y
Liu
LAMP; Stenotrophomonas maltophilia; dihydropteroate synthase; loop-mediated isothermal amplification; minocycline; sul gene; sulfamethoxazole