Department Of Pathogenic Biology, School Of Basic Medical Sciences, Tongji Medical College, Huazhong University Of Science And Technology, Wuhan, 430030, PR China

ObjectiveTo investigate the antimicrobial resistance trends among Acinetobacter baumanniiisolated from Taihe hospital affiliated to Yunyang medical college between 2001 and2007.To analyze the epidemiology and drug resistance of multidrug-resistant andimipenem-resistant strains,Detection of the molecular mechanism ofβ-lactam drugsand aminoglycosides resistance in multi-drug-resistant strains;the rate of classâ… integron integrase gene in multiple drug-resistant strains.To establish bases for clinicalusage of antimicrobial agents reasonable and reducing the prevalence of drug-resistantstrains.MethodsA total of 332 non-repeated strains of Acinetobacter baumannii from January2001 to December 2007 were collected from Taihe hospital.The infection distribution and the drug resistance of 13 kinds of antimicrobials were retrospective analyzed byWHONET5.4 software.The prevalence of multi-drug resistant and imipenem-resistantAcinetobacter baumannii was analyzed.The minimum inhibition concentration (MICs)of the clinical isolates to 16 kinds of antimicrobial agents was tested by agarosedilution method.The phenotype of ESBLs (extended spectrum beta-lactamases)producing strains were detected by standard disk diffusing test according to Clinical andLaboratory Standards Institute (CLSI).AmpC beta-lactamases carriers were screened byimproved three-dimensional test,metallo-β-1actamase carriers were screened bythree-dimensional test.The genetype ofβ-1actamases genes,aminoglycoside-modifyingenzyme genes and sulfonamides resistance gene qacEΔ1-sull and integrase gene intllwere detected by polymerase chain reaction (polymerase chain reaction,PCR).ResultsDuring the 7-year period from 2001 to 2007,a total of 332 A.baumannii strainswere isolated.All strains were distributed at ward,especially at neurosurgery ward(29.8%),breath internal medicine department(17.4%),intensive care unit (ICU,15.3%)and orthopedic trauma(12.4%).These 4 wards accounted for 75% of the total numberof isolates.The most infectious age was bigger than 60 year-old,accounted for 31.9%,next was 30～60 year-old of group,accounted for 49.2%.The respiratory infectionsoccupied the overwhelming majority,which achieved 66%,next was each kind ofwound infection and the urinary tract infection,accounted for 15.7% and 6.3%.During this period,infections caused by Acinetobacter baumannii has increasedyear by year,the antimicrobial resistance rates to all tested antimicrobial agents weregetting higher and higher.Imipenem was the most active agent against A.baumannii,although the resistance rate was increased to 15.4% in 2007.The least active agent wascefoperazone / sulbactam,the resistance/intermediate rate was increased from9.8%/19.6% in 2004 to 17.3%/28.8% in 2007.In this period,aztreonam had a slightly increasing resistance/intermediate rate from 51.7%/34.5% to 57.7%/30.8% and had ahigher rate of intermediary.The resistance rate of Ceftazidime was highest in2004(74.5%),while before and after it fluctuated between 42.6% and 66.7%.Ampicillinhas a higher rate of drug resistance,and the trend has increased year by year,from69.0% to 88.5%.Cefoxitin,in general,had the highest resistance to A.baumannii,withmean resistance rate of 90.8%.The resistance rates of other antimicrobials had greatlyimproved,with mean resistance rates from 32.5% in 2001 to 73.1% in 2007.During the studied period,a total of 42 multi-drug resistant strains were isolatedfrom variety of specimens.Overall,multidrug-resistance increased from 4.8% in2001 to 28.6% in 2007,total detection rate of 12.65%.Multi-drug resistantAcinetobacter baumannii were all sensitive to polymyxin B and polymyxin E,theMIC₅₀ and MIC₉₀ were 0.5ug/ml,all at the range of susceptibility.The other relativelylow rates of resistance of antimicrobial agents were meropenem and imipenem,theresistance rates were 50.0% and 52.3%,the MIC₅₀ and MIC₉₀ were in the range ofresistance.The resistance and intermediate rate of cefoperazone/sulbactam were 35.7%,26.2%,respectively.To other 12 kinds of antimicrobial drugs,the resistance rates wereof 78.6%～100%,and the MIC₅₀ and MIC₉₀ were all in the range of resistance.A total of 24 strains of imipenem-resistant Acinetobacter baumannii were detected,with a total detection rate of 7.23%.Imipenem-resistant Acinetobacter baumannii wereresistant to meropenem at the same time.The highest active antimicrobials werepolymyxin B and polymyxin E,with no resistance,the MIC₅₀ and MIC₉₀ were 0.5ug/ml,followed by the cefoperazone/sulbactam,the resistance/intermediate rate reached to62.5%/16.7% and the MIC₉₀ up to128ug/ml.To the other 13 kinds of antimicrobialdrugs,the resistance rates were of 75～100%,and the MIC₅₀ and MIC₉₀ were all inthe range of resistance.The phenotypes were detected in 42 strains of multi-drug resistant Acinetobacterbaumannii,five strains producing ESBLs,the detection rate was 11.9%,36 strains produced AmpC enzyme,the detection rate was 85.7%,no strains produced metallo-β-lactamase.The genetypes of 42 strains of multi-drug resistant Acinetobacter baumannii wereperformed by PCR.37 strains were detected as the bla TEM,the positive rate of 88.1%,bla OXA-23 group of 24,the positive rate of 57.1%;bla ADC 36 strains,the positiverate of 85.7%,bla PER 4,the positive rate of 9.5%,not detected SHV,VEB,OXA-24,OXA-58,IMP and VIM-typeβ-lactamase gene.Aminoglycoside modifying enzymegene detection situation,AAC (3)-Ia 32 strains,the positive rate of 76.2%,AAC (6')-Ib22 strains,the positive rate of 52.4%,ANT (3")-I 11 strain The positive rate of 26.2%.42 bacteria were detected qacEâ–³1-sull gene 26,intll gene 25,the positive rateswere 61.9%,59.5%.Conclusions1.During the 7-year period from 2001 to 2007,a total of 332 A.baumannii strains wereisolated.All strains were distributed at ward,especially at neurosurgery ward(29.8%),breath internal medicine department(17.4%),intensive care unit(ICU,15.3%) and orthopedic trauma(12.4%).These 4 wards accounted for 75% ofthe total number of isolates.The most infectious age was bigger than 60 year-old,accounted for 31.9%.The respiratory infections occupied the overwhelmingmajority,which achieved 66%.2.During this period,infections caused by Acinetobacter baumannii has increasedyear by year,the antimicrobial resistance rates to all tested antimicrobial agentswere getting higher and higher.Imipenem was the most active agent against A.baumannii.The least active agent was cefoperazone/sulbactam.3.During the studied period,a total of 42 multi-drug resistant strains were isolated fromvariety of specimens.Overall,multidrug-resistance increased from 4.8% in 2001to 28.6% in 2007,total detection rate of 12.65%.Multi-drug resistant Acinetobacter baumannii were all sensitive to polymyxin B and polymyxin E,the MIC₅₀ and MIC₉₀were 0.5ug/ml,all at the range of susceptibility.The other relatively low rates ofresistance of antimicrobial agents were imipenem,meropenem and cefoperazone/sulbactam,however,the sensitive rates of these three antimicrobials all less than50% and the MIC₅₀ and MIC₉₀ were all in the range of resistance.4.A total of 24 strains of imipenem-resistant Acinetobacter baumannii were detected,with a total detection rate of 7.23%.Imipenem-resistant Acinetobacter baumanniiwere resistant to meropenem at the same time.The highest active antimicrobials werepolymyxin B and polymyxin E,with no resistance,the MIC₅₀ and MIC₉₀ were0.5ug/ml,followed by the cefoperazone/sulbactam,the resistance/intermediate ratereached to 62.5%/16.7% and the MIC₉₀ up to128ug/ml.5.The phenotypes were detected in 42 strains of multi-drug resistant Acinetobacterbaumannii,five strains producing ESBLs,the detection rate was 11.9%,36 strainsproduced AmpC enzyme,the detection rate was 85.7%,no strains producedmetallo-β-lactamase.6.The genetypes of 42 strains of multi-drug resistant Acinetobacter baumannii wereperformed by PCR.37 strains were detected as the bla TEM,the positive rate of88.1%,bla OXA-23 group of 24,the positive rate of 57.1%;bla ADC 36 strains,thepositive rate of 85.7%,bla PER 4,the positive rate of 9.5%,not detected SHV,VEB,OXA-24,OXA-58,IMP and VIM-typeβ-lactamase gene.Aminoglycoside modifyingenzyme gene detection situation,AAC (3)-Ia 32 strains,the positive rate of 76.2%,AAC (6')-Ib 22 strains,the positive rate of 52.4%,ANT (3")-I 11 strain The positiverate of 26.2%.42 bacteria were detected qacEΔ1-sull gene 26,intll gene 25,thepositive rates were 61.9%,59.5%.