Study On Antimicorobial Susceptibility Of Proteus And Detecting ESBL Producers And Study On ESBLs Genotype

IntroductionProteus belongs to Enterobacteriaceae.The genus Proteus currently consists of four named species(P. mirabilis, P. penneri, P. vulgaris and P. myxofaciens) and P. mirabilis is the most common clinical species of the four.Proteeae are widespread in the environment and make up part of the normal flora of the human gastrointestinal tract.Although Escherichia coli accounts for the largest percentage of cases of uncomplicated cystitis, pyelonephritis, and prostatitis,Proteus ranks third as the cause of these infections, particularly in hospital-acquired cases. P. mirabilis accounts for approximately 3% of nosocomial infections in the United States and is commonly isolated in clinical microbiology laboratories. Among Enterobacteriaceae, Proteus mirabilis is the second most common cause of urinary tract infections after E. coli,and is also an important cause of nosocomial infections.Wild-type strains of P. mirabilis are susceptible to all penicillins and cephalo- sporins.However,since 1990, the resistance of the species to ?-lactams has regularly increased.Producing extended-spectrumβ-lactamases(ESBLs) is one of the most important mechanisms of gram-negative bacteria resistant to spectrum cephalosporins. ESBLs not only result for the emergence of multi-drug-resistant strains but also result for the spreading of resistance gene. ESBLs are capable of hydrolyzing a wide range ofβ-lactams, including oxyimino-lactams and monobactam, but usually remain ineffective against cephamycins such as cefoxitin, cefmetazole, and cefotetan as well as carbapenems. These class Aβ-lactamases tend to be blocked byβ-lactamase inhibitors such as clavulanicacid.Among the Enterobacteriaceae, the TEM- and SHV-derived ESBLs are often the predominant enzyme.However, the reports of CTX-M enzymes are increased in recent years.The emergence of extended-spectrumβ-lactamases in gram-negative bacteria has become a major public health concern.Early detection of ESBLs is very important for controlling of their spreading and epidemic.Further more,the prevalent genotypes are diverse in different area.So,it is necessary to study on the best substrante of ESBLs-producing Proteus and genotype of the ESBLs.By now,there are few study on ESBL-producing Proteus in our country and there are no large-scale survey in Anhui province.We collected 125 clinical isolates of Proteus from the Center of Control and Supervision for Bacterial Resistance of Anhui Province(from Jan 2004 to May 2005) and investigate their antimicrobial resistance patterns and genotype of ESBLs.ObjectiveTo investigate the resistance patterns of the clinical isolates of Proteus and guide clinical reasonable usage of antibiotic and to avoid nosocomial outbreak infections by ESBL-producing Proteus.To examine the incidence of ESBL-producing Proteus and genotype of the ESBLs.Materials and Methods125 clinical isolates of Proteus were collected from the Center of Control and Supervision for Bacterial Resistance of Anhui Province(from Jan 2004 to May 2005).Identification test and antimicrobial susceptibility test were performed by MicroScan WalkAway-40 system.ESBLs producers were screened by ESBLs initial screening test and phenotype confirmatory test in accordance with the guidelines of NCCLS(now named Clinical and Laboratory Standards Institute,CLSI) in 2005.PCR were performed with eight pairs of primers which were designed(by Dr. Sheng Ji-lu) in accordance with the basic sequences of blaTEM,blaSHV,blaCTX,blaOXA and blaTOHO in the GenBank.Then the positive strains were performed conjugation test.Examined the extent of drug resistance by microdilution method.ResultMicroScan results showed the resistance rates of ampicillin and piperacillin are 64.6% and 32.0%.But the the resistance rates to ampicillin/sulbactam and piperacillin/ tazobactam are decreased to 59.6% and 4.2% respectively. The resistance rates to cefalotin,cefazolin and cefuroxime are 29.4%,27.7% and 25.4% respectively.Compared to cefotaxime(15.3%),ceftriaxone(14.9%) and cefepime(16.3%) ceftazidime had the lowest resistance rate of 10.3%.The resistance rate to amikacin(13.0%) is more lower than that of gentamicin(39.7%) and tobramycin(27.4%).All the clinical isolates are susceptible to imipenem.The incidence of ESBLs-producing Proteus was 7.2%.Identification rates of three substrates were 60.0%(cefotaxime),20.0% (ceftazidime)and 26.7%(cefpodoxime). Cefotaxime was the best detective substrate.Except for imipenem,the resistance rates of ESBLs producers were significant higher than non-ESBLs producers(P<0.05).Among ESBL-producing strains,CTX-M was the major genotype(3 CTX-M-13 and 1 CTX-M-3).To the best of our knowledge,this is also the first CTX-M ESBLs have been reported in P. mirabilis in China.TEM-1b spectrumβ-lactamase were also prevalence in P. mirabilis.ConclusionsCefotaxime was more susceptible in ESBLs screening and confirmatory test.So it was the best substrate to dectect ESBL-producing Proteus in our area.The antimicrobial susceptibility results clued us on that ESBL-producing strains and non-ESBL-producing strains should be differentiated when therapy different patients.The low-level resistence antimicrobials,such as cefoxitin,ceftriaxone, ceftazidime,cefotaxime,cefpirome and piperacillin/tazobactam can be selected to therapy the non-ESBLs resulting infections.To the ESBLs resulting infections, imipenem is the most reliable therapeutic drug.In this study,the genotypes of ESBLs-producing P. mirabilis include CTX-M-14, CTX-M-3 and TEM-1b.The diversity ofβ-lactamases in P. mirabilis and the emergency of multi-drug-resistance clinical strains will present serious threat to clinical therapy and even will lead to outbreak of nosocomial infections.Our study emphasize the need for enhanced supervision of ESBL-producing Protues. Reasonable drug-resistance data are important to clinical therapy.