The Prevalence Studies Of Integrons And ISCR1 Of Stenotrophomonas Maltophilia In Anhui Area And The Effects Of Combined Treatment Of Its MSW

ObjectiveTo analyze clinical distribution characteristics and drug resistance of Stenotrophomonas maltophilia collected in 2010- 2011 from The First Affiliated Hospital of Anhui Medical University.To learn the presence of integrons、ISCR1 and the resistance genes of strains and to explore its relationship with resistance among 115 clinical strains of stenotrophomonas maltophilia which were isolated from Anhui Province from 2010 to 2013.To determine the mutant prevention concentration of sulfamethoxazole-trimethoprim alone and combination with levo?oxacin against S. maltophilia and to determine if the combination can decrease the emergence of resistant mutants strains.MethodsThe susceptibility of 108 strains of stenotrophomonas maltophilia was tested by agar dilution. The results were judged according to the criteria recommended by Clinical and Laboratory Standards Institute(CLSI) 2012. Using WHONET5.4 for analyzing data.The amplification of qac E 1-sul1 gene, class 1,2 and 3 integrase, variable region of class 1 integron and ISCR1 as well as ISCR1 gene were detected by polymerase chain reaction(PCR).Minimal inhibitory concentrations of 19 antimicrobial agents were determined by agar dilution method.The MPC of 20 strains which were both susceptible to sulfamethoxazole-trimethoprim and levo?oxacin were determined by inhibiting visible growth among 1010 CFU on four agar plates after 72 hours incubation at 37 ℃.ResultsThe stains of stenotrophomonas maltophilia is most isolated from lower respiratory tract infection, mainly comes from sputum and swab specimens, accounting for 83.3%.The infection mainly occurred at department of respiratory and ICU(20.4% and 15.7%); Most patients are male and most of them are old people, the proportion of patients over 60 years old is 67.6%. Susceptibility results show that the most sensitive antimicrobial agents is minocycline and sensitivity was 80.6%(87/108), followed by levofloxacin 69.4%(75/108), chloramphenicol 61.1%(66/108), cefoperazone/sulbactam 52.8%(57/108) and 51.9%(56/108) of co-trimoxazole. Other drugs have shown resistance severely.74 strains(64.3%) of 115 S. maltophilia were Int1 gene positive; the number of ISCR1 positive strains was only 5 strains(4.3%). No Class 2 or 3 integron were detected. 6.8%(5) aac A4-cat B8-aad A1 gene cassette and 2.7%(2) aac(6’)-Ⅱ-bla CARB-8 gene cassette were identified in int1 positive strains. Resistance gene was not detected in the variable region of ISCR1. The detected rate of class 1 integron in multi-drug resistance(MDR) isolates was higher than non-MDR isolates(p<0.01). The MIC values of class 1 integron positive group and sul1 gene positive group were significantly higher than the group that class 1 integron and sul1 gene both were negative among the trimethoprim–sulfamethoxazole(TMP/SMZ) resistant strains.5 All except two strains(18/20) showed a MPC exceed 152/8μg/m L for sulfamethoxazole-trimethoprim and the range of the MPC for the sulfamethoxazoletrimethoprim in combination with levo?oxacin is 9.5/0.5~608/32μg/m L. The MPC and MPC/MIC of 95%(19/20) strains demonstrate to reduce at least 1/2 fold after combination. The MSW were narrowed by sulfamethoxazole-trimethoprim in combination with levo?oxacin.ConclusionsStenotrophomonas maltophilia has become an important bacterial pathogen in nosocomial infection. We should take measures to prevent from risk factors. The surveillance of antimicrobial resistance S. maltophilia should be strengthened for purpose of preventing the production of multidrug resistant strains.This study showed that the presence of class 1 integron and sul1 gene in stenotrophomonas maltophilia isolates can enhance their resistance to TMP/SMZ. Class 1 integron and ISCR1 may increase the multi-drug resistance of SMA and accelerate the spreading of resistance genes in Anhui province.We consider the combination can decrease the enrichment of mutant bacterial populations. More clinical data are needed to verify the use of drug combinations can restrict or even block the MSW of S. maltophilia.