Evaluation of an immunofluorescent-antibody test for rapid identification of Pseudomonas aeruginosa in blood cultures.

An immunofluorescent-antibody test was developed for rapid detection of Pseudomonas aeruginosa in blood cultures. The test uses a murine monoclonal antibody specific for all strains of P. aeruginosa. In initial tests, bright uniform immunofluorescence signals were seen when each of the 17 international serotypes, as well as 14 additional isolates of P. aeruginosa, were examined. No immunofluorescent staining was observed when 37 other gram-negative and 15 gram-positive species were studied. In a clinical study, the assay was applied to broth smears of 86 gram-negative bacilli isolated from 74 bacteremic patients and 28 additional clinical isolates of Pseudomonas sp. and other oxidase-positive gram-negative bacilli recovered from various body sites. Smears were made directly from blood cultures which were positive for gram-negative bacilli by Gram staining. Eleven (15%) of 74 patients with gram-negative bacteremia had a positive test for P. aeruginosa. Including the results of these 11 isolates recovered in a prospective study and an additional 10 isolates from a retrospective study, we obtained a sensitivity and specificity of 100% (21 positive specimens and 103 negative specimens, respectively). These preliminary results suggest that this is a useful reagent for rapid presumptive identification of P. aeruginosa in blood cultures. With the immunofluorescent-antibody test, P. aeruginosa could be identified within 1 h of Gram stain evidence of gram-negative bacteremia.     

Use of real-time PCR with multiple targets to identify Pseudomonas aeruginosa and other nonfermenting gram-negative bacilli from patients with cystic fibrosis

Pseudomonas aeruginosa and other gram-negative isolates from patients with cystic fibrosis (CF) may be difficult to identify because of their marked phenotypic diversity. We examined 200 gram-negative clinical isolates from CF respiratory tract specimens and compared identification by biochemical testing and real-time PCR with multiple different target sequences using a standardized combination of biochemical testing and molecular identification, including 16S rRNA partial sequencing and gyrB PCR and sequencing as a "gold standard." Of 50 isolates easily identified phenotypically as P. aeruginosa, all were positive with PCR primers for gyrB or oprI, 98% were positive with exotoxin A primers, and 90% were positive with algD primers. Of 50 P. aeruginosa isolates that could be identified by basic biochemical testing, 100% were positive by real-time PCR with gyrB or oprI primers, 96% were positive with exotoxin A primers, and 92% were positive with algD primers. For isolates requiring more-extensive biochemical evaluation, 13 isolates were identified as P. aeruginosa; all 13 were positive with gyrB primers, 12 of 13 were positive with oprI primers, 11 of 13 were positive with exotoxin A primers, and 10 of 13 were positive with algD primers. A single false-positive P. aeruginosa result was seen with oprI primers. The best-performing commercial biochemical testing was in exact agreement with molecular identification only 60% of the time for this most difficult group. Real-time PCR had costs similar to those of commercial biochemical testing but a much shorter turnaround time. Given the diversity of these CF isolates, real-time PCR with a combination of two target sequences appears to be the optimum choice for identification of atypical P. aeruginosa and for non-P. aeruginosa gram-negative isolates.     

Routine aerobic terminal subculturing of blood cultures in a cancer hospital.

Routine terminal aerobic subcultures of macroscopically negative blood culture bottles were evaluated during a 15-month period when 30,000 blood cultures were processed. Each blood culture set consisted of a vented and an unvented 50-ml broth bottle. Forty-eight pathogens and 47 contaminants were isolated only from terminal subcultures. Twenty-two of the significant isolates were yeasts (usually recovered from vented bottles), and 10 were Pseudomonas aeruginosa (usually recovered from unvented bottles). Blood cultures that were positive by terminal subculture provided clinically relevant information in many cases, whether other blood cultures were positive or not. Microbiology laboratories, particularly those in hospitals where yeasts and P. aeruginosa are commonly isolated from blood specimens, should evaluate carefully the need for terminal subcultures of blood culture bottles before abandoning their use.     

Rapid differentiation of fermentative from nonfermentative gram-negative bacilli in positive blood cultures by an impedance method

Rapid differentiation of fermentative gram-negative bacilli (fermenters) from nonfermentative gram-negative bacilli (nonfermenters) in positive blood cultures may help physicians to narrow the choice of appropriate antibiotics for empiric treatment. An impedance method for direct differentiation of fermenters from nonfermenters was investigated. The bacterial suspensions (or positive culture broths containing gram-negative bacteria) were inoculated into the module wells of a Bactometer (bioMérieux, Inc., Hazelwood, Mo.) containing 1 ml of Muller-Hinton broth. The inoculated modules were incubated at 35 degrees C, and the change in impedance in each well was continuously monitored. The amount of time required to cause a series of significant deviations from baseline impedance values was defined as the detection time (DT). The percent change of impedance was defined as the change of impedance at the time interval from DT to DT plus 1 h. After testing 857 strains of pure cultures (586 strains of fermenters and 271 strains of nonfermenters), a breakpoint (2.98%) of impedance change was obtained by discriminant analysis. Strains displaying impedance changes of greater than 2.98% were classified as fermenters; the others were classified as nonfermenters. By using this breakpoint, 98.6% (340 of 345) of positive blood cultures containing fermenters and 98% (98 of 100) of positive blood cultures containing nonfermenters were correctly classified. The impedance method was simple, and the results were normally available within 2 to 4 h after direct inoculation of positive blood culture broths.     

Controlled clinical comparison of Isolator and BACTEC 9240 Aerobic/F resin bottle for detection of bloodstream infections.

A controlled clinical comparison was carried out with the BACTEC 9240 Aerobic/F resin bottle and the Isolator system with adult patients suspected of having bloodstream infections. A total of 10,500 paired specimens were collected, of which 1,122 from 520 patients were positive. There were 68 false-positive BACTEC bottles; 259 positive cultures that were excluded from analysis because the bottle, the Isolator, or both failed to meet the minimum volume criterion of 8 ml of blood; and 207 positive cultures that were excluded because the isolates were found to be clinically insignificant or of indeterminate clinical significance on the basis of patient assessment. A total of 656 positive cultures from 258 patients formed the basis of the analysis. Significantly more Staphylococcus aureus isolates (P = 0.03), Staphylococcus epidermidis isolates (P = 0.03), members of the family Enterobacteriaceae (P = 0.03), and Pseudomonas aeruginosa isolates (P = 0.04) were recovered from the resin bottle, and there was no category of organism that was recovered significantly more frequently from the Isolator system. With patients receiving antibiotics at the time of blood culture, S. aureus, S. epidermidis, and gram-negative bacilli were recovered significantly more frequently from the resin bottle. No significant differences between systems were found with cultures from patients not receiving antibiotics at the time of blood culture. Only 12 clinically significant organisms were recovered from the bottle on terminal subcultures, and only 1 of these had not been previously isolated from another blood culture set (10 of the 12) or from the companion Isolator (1 of 12).(ABSTRACT TRUNCATED AT 250 WORDS)     

Direct susceptibility testing of positive blood cultures by using Sensititre broth microdilution plates

Traditional susceptibility testing of blood cultures requires overnight incubation in order to obtain isolated colonies. Susceptibility results can be reported up to 24 h sooner by using a bacterial pellet from the blood culture broth. This study evaluated the accuracy of direct susceptibility testing from positive ESP blood culture broths by using Sensititre broth microdilution plates compared to testing with isolated colonies. Practical inclusion criteria were applied to gram-positive organisms to avoid reporting susceptibilities for probable contaminants. All gram-negative organisms were tested directly. An aliquot of the blood culture was centrifuged, and the resulting pellet was used to make a 0.5 McFarland suspension. Microdilution plates were inoculated and interpreted according to the manufacturer's instructions. Colony counts were performed to ensure proper colony density was achieved. A total of 199 patient and seeded blood cultures were evaluated for both essential (within +/-1 twofold dilution) and categorical (sensitive, intermediate, or resistant) agreement. Testing of 93 gram-positive isolates (1,214 antimicrobial agent-organism combinations) yielded 98% essential agreement and categorical error rates of 0.3% minor, no major (false resistance), and 1.7% very major (false susceptibility) errors. For 106 gram-negative isolates (1,828 antimicrobial agent-organism combinations), the essential agreement was 99%. Categorical error rates were 0.5, 0, and 2.0% for minor, major, and very major errors, respectively. Performance was comparable for both gram-positive and gram-negative isolates, as well as for both aerobic and anaerobic media. Using this direct testing methodology, reliable susceptibility results can be reported to physicians 24 h sooner, allowing earlier appropriate modification of antimicrobial therapy.     

Identification of Pseudomonas aeruginosa by pyocyanin production on Tech agar.

Pseudomonas aeruginosa is the only gram-negative bacillus capable of producing the very distinctive water-soluble pigment pyocyanin. We evaluated the reliability of this characteristic as a unique test for the identification of this organism by using Tech agar (BBL Microbiology Systems, Cockeysville, Md.) medium. A retrospective and prospective analysis was performed with a total of 835 strains of P. aeruginosa; 818 (98%) produced pigment within 48 h of incubation, and 96% of those which produced pigment were positive after overnight incubation. Seventeen strains (2.0%) failed to produce pigment; 15 were mucoid strains from patients with cystic fibrosis. Tech agar is an effective, simple, and inexpensive medium for P. aeruginosa identification and may be used as a unique test for all potential P. aeruginosa isolates (beta hemolytic on blood agar; lactose-negative, oxidase-positive colonies). Nonpigmented mucoid strains, as well as other nonpigmented organisms, will require additional testing to ensure proper identification.     

Evaluation of detection of positive blood cultures by pH changes.

We observed that the pH of positive blood culture broths was significantly lower than that of negative broths. However, significantly pH changes were generally not observed for subculture-positive, macroscopically negative blood culture broths. Therefore, although the pH of most positive blood culture broths was reduced significantly, this change was generally not useful for the early detection of positive cultures.     

Effect of volume of blood cultured on detection of bacteremia.

The rates of recovery of bacteria from vented vacuum blood culture bottles containing 50 and 100 ml of a soybean-casein digest broth were compared. Overall, more isolates were recovered from the larger bottle; moreover, gram-negative bacilli and especially Pseudomonas aeruginosa were recovered significantly more frequently (P less than 0.01) from the 100-ml bottle.     

Oropharyngeal and fecal carriage of Pseudomonas aeruginosa in hospital patients.

This prospective study was designed to determine the incidence of rectal and/or oropharyngeal colonization rates of patients with Pseudomonas aeruginosa upon admission to a general hospital and the risk of becoming colonized while hospitalized. Consecutive 186 admissions (180 patients) to one medical ward, one surgical ward, and the intensive care unit were studied over a period of 5 months. Rectal and oropharyngeal swabs for P. aeruginosa were obtained on admission, weekly thereafter, and/or upon discharge. Forty-two patients (22.6%) were colonized on admission, 20 patients (10.8%) acquired P. aeruginosa during hospitalization. Colonization on admission was observed twice as frequently on the surgical ward and in the intensive care unit as on the medical ward. Positive rectal cultures were more frequent than oropharyngeal cultures throughout the study (P less than 0.01). For patients admitted culture positive or culture negative, the probabilities of remaining culture positive or culture negative, respectively, remained at 44 and 72% after 35 days of hospitalization. The most common P. aeruginosa serotypes were 1, 6, and 10, and pyocin types 1, 3, and 10 were predominant. There was no statistical difference in the serotypes or pyocin types detected on admission or acquired during hospitalization. Except for two hospital-acquired first isolates which were resistant to moxalactam, all first isolates were susceptible to the four antibiotics tested. During the study, one isolate became resistant to azlocillin, gentamicin, and tobramycin, while two isolates became resistant to moxalactam. A statistical analysis was performed for 13 risk factors for all colonized and noncolonized patients. Colonization detected at the time admission was positively associated with age ( > 65 years), previous surgery of the gastrointestinal tract for neoplasm, and anemia ( P< 0.05). In contrast, for patients who entered the study culture negative, none of the analyzed 13 risk factors was associated with an increased probability for colonization. This observation included the administration of antimicrobial agents singly or in combination or both.     

Incidence of Neisseria gonorrhoeae isolates negative by Syva direct fluorescent-antibody test but positive by Gen-Probe accuprobe test in a sexually transmitted disease clinic population.

To determine the accuracy of the Syva (Palo Alto, Calif.) direct fluorescent-antibody (DFA) test in comparison with the Gen-Probe (San Diego, Calif.) Accuprobe culture confirmation test, we tested 395 isolates of Neisseria gonorrhoeae from cultures obtained from patients attending a sexually transmitted disease clinic from 1 July 1991 through 30 June 1992. All isolates were tested for DFA reactivity with a polyclonal reagent (Difco Laboratories, Detroit, Mich.) and a monoclonal reagent (Syva, Inc., direct specimen test) and for specific molecular probe reactivity by the Gen-Probe Accuprobe culture confirmation test for N. gonorrhoeae. The 395 isolates gave positive results for the Gen-Probe culture confirmation test and the Difco polyclonal direct specimen test. However, 18 (4.6%) of the isolates were negative for N. gonorrhoeae by the Syva DFA test. With the exception of six beta-lactamase-positive isolates, all isolates that were negative by Syva DFA were sensitive to penicillin, tetracycline, spectinomycin, and ceftriaxone by disk-diffusion susceptibility testing. Auxotyping and serotyping studies indicated that strains negative by Syva DFA consisted of several variants. The frequency of N. gonorrhoeae isolates showing negative results by Syva DFA in this patient population ranged from 0 to 11.5%/month. Laboratories using only the Syva DFA test for confirmation of N. gonorrhoeae may incur a significant risk of misidentification.     

Evaluation of the Hyplex BloodScreen Multiplex PCR-Enzyme-linked immunosorbent assay system for direct identification of gram-positive cocci and gram-negative bacilli from positive blood cultures

We evaluated the Hyplex BloodScreen PCR-enzyme-linked immunosorbent assay (ELISA) system (BAG, Lich, Germany), a new diagnostic test for the direct identification of gram-negative bacilli and gram-positive cocci from positive blood cultures, with 482 positive BACTEC 9240 blood culture bottles. The test involves amplification of the bacterial DNA by multiplex PCR and subsequent hybridization of the PCR product to specific oligonucleotide probes in an ELISA-based format. The available probes allow the separate detection of Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, Klebsiella spp., Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis/Enterococcus faecium, Streptococcus pyogenes, and Streptococcus pneumoniae and the staphylococcal mecA gene. The Hyplex BloodScreen test showed an overall sensitivity of 100% for the identification of gram-negative bacilli and 96.6 to 100% for the identification of gram-positive cocci (S. aureus, 100%; S. epidermidis, 97.2%; Enterococcus faecalis/Enterococcus faecium, 96.6%; and Streptococcus pneumoniae, 100%). The specificities of the test modules ranged from 92.5 to 100% for gram-negative bacilli and 97.7 to 100% for gram-positive cocci (Escherichia coli, 92.5%; Pseudomonas aeruginosa, 98.5%; Klebsiella spp., 100%; Enterobacter aerogenes, 100%; S. aureus, 100%, S. epidermidis, 97.7%; Enterococcus faecalis/Enterococcus faecium, 99.6%; Streptococcus pyogenes, 100%; and Streptococcus pneumoniae, 99.3%). The result of the mecA gene detection module correlated with the result of the phenotypic oxacillin resistance testing in all 38 isolates of Staphylococcus aureus investigated. In conclusion, the Hyplex BloodScreen PCR-ELISA system is well suited for the direct and specific identification of the most common pathogenic bacteria and the direct detection of the mecA gene of Staphylococcus aureus in positive blood cultures.     

Microbial skin flora of selected cancer patients and hospital personnel.

The bacterial flora of the skin from five anatomical sites on 10 leukemia patients, 10 patients with malignant melanoma, and a control group of 10 medical personnel was examined quantitatively and qualitatively. This was done to determine whether malignant disease results in changes in skin flora and to establish carrier rates of gram-negative bacteria on the skin of personnel in hospital environments. Gram-negative bacteria were isolated more frequently (74 isolates from 100 cultures) from the skin of leukemia patients than from either patients with malignant melanoma (8 isolates from 100 cultures) or the medical personnel (9 isolates from 100 cultures). Klebsiella pneumoniae and Pseudomonas aeruginosa were isolated exclusively from leukemia patients. Relative proportions of gram-negative bacteria in total populations were determined. The axilla was the only site with a uniformly high proportion of gram-negative bacteria. From all other sites cultured, gram-negative populations were low (1 to 5 bacteria/cm2 of skin), although a high proportion of gram-negative populations occurred randomly throughout all subject groups. It was concluded that leukemia patients tend to carry gram-negative bacteria on the skin. The factors permitting colonization of skin by gram-negative bacteria are discussed.     

Blood culture gram stain,acridine orange stain and direct sensitivity-based antimicrobial therapy of bloodstream infection in patients with trauma

Purpose: The purpose of this study was to ascertain if the simple practice of Gram stain, acridine orange stain and direct sensitivity determination of positive blood culture bottles could be used to guide early and appropriate treatment in trauma patients with clinical suspicion of sepsis. The study also aimed to evaluate the error in interpreting antimicrobial sensitivity by direct method when compared to standard method and find out if specific antibiotic–organism combination had more discrepancies. Findings from consecutive episodes of blood stream infection at an Apex Trauma centre over a 12-month period are summarized. Materials and Methods: A total of 509 consecutive positive blood cultures were subjected to Gram staining. AO staining was done in BacT/ALERT-positive Gram-stain negative blood cultures. Direct sensitivity was performed from 369 blood culture broths, showing single type of growth in Gram and acridine orange staining. Results of direct sensitivity were compared to conventional sensitivity for errors. Results: No ‘very major’ discrepancy was found in this study. About 5.2 and 1.8% minor error rates were noted in gram-positive and gram-negative bacteria, respectively, while comparing the two methods. Most of the discrepancies in gram-negative bacteria were noted in β lactam – β lactamase inhibitor combinations. Direct sensitivity testing was not reliable for reporting of methicillin and vancomycin resistance in Staphylococci. Conclusions: Gram stain result together with direct sensitivity testing is required for optimizing initial antimicrobial therapy in trauma patients with clinical suspicion of sepsis. Gram staining and AO staining proved particularly helpful in the early detection of candidaemia.     

Evaluation of the IDI-MRSA assay for detection of methicillin-resistant staphylococcus aureus from nasal and rectal specimens pooled in a selective broth

Rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) by PCR can be performed directly from nasal specimens with the IDI-MRSA assay. To improve the efficiency of screening, we evaluated the performance of the IDI-MRSA assay for the detection of MRSA from pooled and unpooled specimens cultured in a selective broth. Of the 287 specimens evaluated, 71 were culture and PCR positive, 203 were culture and PCR negative, 3 were culture positive and PCR negative, 8 were culture negative and PCR positive, and 2 remained inhibited. A methicillin-susceptible Staphylococcus aureus isolate was recovered from five of the eight specimens with false-positive PCR results. Compared to the results of culture, the sensitivity, specificity, and positive and negative [corrected] predictive values of the IDI-MRSA assay for detection of MRSA from broth were 96%, 96%, 90%, and 98%, respectively. Following implementation of the IDI-MRSA assay, PCR-positive broths were subcultured for evaluation of assay performance. Of the 298 IDI-MRSA assay-positive broths, the results for 103 could not be confirmed by culture. A methicillin-susceptible S. aureus (MSSA) isolate was recovered from 77 of these 103 broths. Repeat testing by the IDI-MRSA assay directly with the MSSA isolates confirmed the original positive PCR result. The positive predictive value of the IDI-MRSA assay fell from 90% during the evaluation phase to 65% postimplementation. The IDI-MRSA assay performed well for the detection of MRSA from a selective broth compared to the performance of the detection of MRSA from culture. However, because of the burden associated with implementation of infection control precautions, cultures remain essential in confirming positive IDI-MRSA results.     

Controlled clinical evaluation of BACTEC Plus Aerobic/F and BacT/Alert Aerobic FAN bottles for detection of bloodstream infections.

A total of 7,190 blood culture sets were obtained from adult patients with a suspected bloodstream infection. A 20-ml sample of blood was distributed equally between the aerobic FAN bottle which was monitored in the BacT/Alert system and a Plus Aerobic/F bottle which was monitored in the BACTEC 9240 system. A total of 988 positive cultures were obtained from 483 patients; however, only 453 positive cultures from 173 patients met the criteria for volume ( > or = ml per bottle) and clinical significance on the basis of concurrent case review required for data analysis. There were 25 and 68 false positives from the FAN and Plus Aerobic/F bottles, respectively. There were no statistically significant differences between systems in the number of positive cultures or septic episodes by species; however, the total number of Enterobacteriaceae and Pseudomonas aeruginosa isolates combined was significantly greater in the FAN bottle (P = 0.04). Detection times did not differ significantly between systems for positive cultures; however, episodes of Staphylococcus aureus bacteremia were detected significantly more rapidly from the FAN bottle (P = 0.005). There was no significant difference between systems in the detection of bloodstream infections in patients receiving antibiotics at the time of blood culture.     

Comparison of commercial slide agglutination kits with a tube coagulase test for the rapid identification of Staphylococcus aureus from blood culture.

Eighty clinical specimens of BACTEC 9240 blood culture vials, culture positive for staphylococci (38 Staphylococcus aureus and 42 coagulase negative staphylococci), were tested directly for the presence of clumping factor/protein A and free coagulase. Seven commercial slide agglutination kits were compared with a direct-tube coagulase (DTC) method. All tests were performed on blood culture pellets. Sensitivity, specificity, and negative and positive predictive values for the seven commercial kits were extremely variable, whereas a two-hour DTC test was highly predictive of S aureus. There was no significant difference between a two-, six- or 24-hour DTC test. Three (8%) S aureus isolates remained DTC negative even after 24 hours' incubation. Staphylococcal slide agglutination kits should not be used directly on blood culture broths. In contrast, a two-hour DTC test is a useful, rapid screening test for S aureus bacteraemia, provided isolates from DTC negative blood culture broths are re-tested using standard laboratory techniques.     

Clinical experiences of bacteremia caused by metallo-beta-lactamase-producing gram-negative organisms.

The emergence of acquired metallo-beta-lactamase (MBL) in gram-negative bacilli is regarded as a therapeutic challenge since such enzymes are capable of hydrolyzing all beta-lactams in vitro except the monobactams. The clinical characteristics and outcome of 8 episodes of gram-negative bacteremia caused by MBL-producing isolates from January 1997 through December 2000 (Klebsiella pneumoniae, 6 isolates; Pseudomonas stutzeri, 4; Pseudomonas aeruginosa, 1; and Pseudomonas putida, 1) were analyzed. The median age of the patients was 61 years (range, 2-95 years). Most patients (n = 6, 75%) had more than 1 comorbid illness or condition and 6 patients acquired bacteremia in the intensive care unit. The median time from admission to the first positive culture was 34.5 days (range, 1-99 days). Pneumonia was the most common site of infection. Five patients (62.5%) received a carbapenem to treat bacteremia. The median time to defervescence was 6 days (range, 2-12 days). No bacteriologic failure was noted during or after antimicrobial therapy. The overall mortality rate from bacteremia caused by gram-negative, MBL-producing organisms was nil at 14 or 28 days.     

Audit of Pseudomonas aeruginosa in a general hospital in Saudi Arabia

All isolates of Pseudomonas aeruginosa in our laboratory from hospitalised patients were collected over a 4-month period in 1993/94. Details of the patients including length of stay, transfer from another hospital, nationality, diagnosis and antibacterial treatment were noted. Each patient was assessed as to whether the first isolate during the study period was of clinical significance and whether the infection or colonization was nosocomially acquired. The isolates of P. aeruginosa were identified and sensitivity was determined by recognized methods. Isolates were serotyped. 108 different patients were included in the study (median age 50 years, 58% males). 57/77 (74%) isolates where information was noted were nosocomial acquired. Length of patient stay for the nosocomial acquired isolates ranged from less than 1 day to more than 1 year. 19% of patients were transfers from other hospitals. Clinical significance was graded 31% isolates were judged to be highly significant and 44% to have little or no clinical significance. 41% isolates were from superficial sites including wounds, 27% from respiratory sites, 23% from urine and 6% were from blood cultures. Heavy growth of P. aeruginosa was correlated with clinical significance. Coliforms were the other organisms most frequently isolated with the P. aeruginosa but highly significant isolates were usually in pure culture. Serotypes 11, 2 and 4 were the dominant isolates. Serotype 11 was also the most common environmental isolate from the hospital. 60% patients were receiving antibacterial agents when the sample was taken but only 12% patients were receiving potentially anti-pseudomonal agents.     

转座子tnpU基因在多重耐药革兰阴性杆菌中的分布情况

目的研究转座子tnpU基因和β-内酰胺酶在多重耐药革兰阴性杆菌中的分布情况。方法用纸片扩散初筛试验、扩散确证试验进行超广谱β-内酰胺酶（ESBLs）表型检查,头孢西丁三维试验进行AmpC β-内酰胺酶的表型检查,纸片协同试验筛选产金属β-内酰胺酶（MBL）菌株;用多重聚合酶链反应（PCR）技术扩增转座子tnpU基因,并进行DNA测序;用MIC药敏法分析多重耐药革兰阴性杆菌的药物敏感性。结果转座子tnpU的总检出率为25．5％。在各菌种的检出率分别为大肠埃希菌占6.3％（3株）、肺炎克雷伯菌占8．3％（1株）、鲍曼不动杆菌占33-3％（20株）、铜绿假单胞菌占43．2％（16株）;β-内酰胺酶表型检测中,ESBLs的检出率最高,转座子tnpU基因阳性的菌株大多数B．内酰胺酶表型为阳性;转座子tnpU基因阳性菌株对抗生素的耐药率显著高于转座子阴性菌株（P〈0．05）。结论转座子tnpU基因在非发酵菌中的分布较广泛,可能在多重耐药机制中起重要作用。