Abstract
AimsThis study was carried to reveal the genetic mechanisms of trimethoprim/sulfamethoxazole (SXT) resistance.MethodsAmong 300 clinical Stenotrophomonas maltophilia isolates from China, resistance determinants such as sul and dfrA genes, integrons and transposase were examined using PCR, DNA sequencing and thermal asymmetric interlaced PCR (TAIL-PCR). Data were analyzed using SPSS 20.0.ResultsOf the 300 isolates, 116 (38.7%) were resistant to SXT. An alarming trend of increased resistance to SXT were found over the 10-year period. The positive rates of sul and class 1 integrase (intI1) increased gradually with the development of SXT resistance over the 10-year period. Multiple logistic regression analyses indicated that the genes of qacEΔ1-sul1 (81% vs 46.2%, p = 0.000), sul2 (50.9% vs 9.8%, p = 0.000), intI1 (83.6% vs 65.8%, p = 0.000), dfrA12 (25% vs 3.3%, p = 0.000), dfrA17 (15.5% vs 3.8%, p = 0.000) and dfrA27 (4.3% vs 1.6%, p = 0.01) were more prevalent in SXT-resistant isolates than SXT-susceptible isolates except dfrA1(p = 0.83) and dfrA5(p = 0.18). Sequencing data revealed 12 types of resistance gene cassettes (aar-3-dfrA27, dfrA12–aadA2, dfrA17–aadA5, cmlA1, aacA4, aadA5, arr-3-aacA4, aadA1, aadB–aadA4, aacA4–catB8–aadA1, aadB–aac(6′)-II–blaCARB-8 and aac(6′)-II–blaCARB-8) located in the class 1 integron in 163 isolates (87% SXT-resistant vs 33.7% SXT-susceptible isolates, p = 0.000). A novel finding was the aar-3-dfrA27 (KC748137) gene cassette. The gene of sul2 linked to transposase in 50 SXT- resistant and 7 SXT- susceptible isolates was detected by TAIL-PCR.ConclusionsThe findings demonstrated a higher prevalence of sul, dfrA, intI1 and resistance gene cassettes in class 1 integron in SXT-resistant clinical S. maltophilia isolates in China. The sul1 and dfrA genes located in integrons and the sul2 linked to transposase may imply wide and rapid dissemination of resistance gene in bacteria.
Highlights
S. maltophilia, a non-fermentative gram-negative bacterium, is generally regarded as an important opportunistic pathogen, especially in immunocompromised patients with underlying disease, and can cause a number of clinical syndromes, such as bacteraemia, sepsis, pneumonia, meningitis, endocarditis, septic arthritis, urinary infections, and endophthalmitis [1,2,3].S. maltophilia has been recognized as one of the leading multidrug resistant organisms in hospital settings due to its resistance to a broad array of antimicrobial agents afforded by the existence of intrinsic and acquired resistance mechanisms [4]
The findings demonstrated a higher prevalence of sul, dfrA, intI1 and resistance gene cassettes in class 1 integron in SXT-resistant clinical S. maltophilia isolates in China
The sul1 and dfrA genes located in integrons and the sul2 linked to transposase may imply wide and rapid dissemination of resistance gene in bacteria
Summary
S. maltophilia, a non-fermentative gram-negative bacterium, is generally regarded as an important opportunistic pathogen, especially in immunocompromised patients with underlying disease, and can cause a number of clinical syndromes, such as bacteraemia, sepsis, pneumonia, meningitis, endocarditis, septic arthritis, urinary infections, and endophthalmitis [1,2,3].S. maltophilia has been recognized as one of the leading multidrug resistant organisms in hospital settings due to its resistance to a broad array of antimicrobial agents afforded by the existence of intrinsic and acquired resistance mechanisms [4]. Trimethoprim/sulfamethoxazole (SXT) is traditionally recommended as the first choice against S. maltophilia infections; increasing resistance to SXT has complicated the treatment. Resistance determinants such as sul and dfrA genes, class 1 integrons and mobile genetic elements have been reported to contribute to SXT resistance [5,6], but these determinants were sometimes detected in SXT- susceptible S. maltophilia isolates. The in vitro susceptibility of SXT against 300 clinical S. maltophilia isolates were examined to reveal the evolution of SXT resistance, SXT resistance determinants such as the sul and dfrA genes and resistance gene cassettes in integrons were determined, and their contribution to SXT resistance were analysed by multivariate statistics
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