Evaluation of Three Molecular Typing Techniques for Nonfermentative Gram-Negative Bacilli

Abstract

AbstractObjective:To evaluate three different DNA techniques for typing nonfermentative gram-negative bacilli isolated from Latin American hospitals.Design:One hundred twenty-six nonfermentative gram-negative bacilli were typed.Participants:Pseudomonas aeruginosa(n = 64) andAcinetobacter baumannii(n = 42) samples were obtained from blood cultures of patients admitted to 10 medical centers in Latin America during 1998 andStenotrophomonas maltophilia(n = 20) samples were obtained from patients admitted to the Hospital São Paulo between 1999 and 2001.Methods:All samples were typed using automated ribotyping, PFGE, and ERIC-PCR. The discriminatory power for each technique was calculated using Hunter's generalized formula.Results:All strains could be typed by automated ribotyping and ERIC-PCR, but two strains (1.6%) were not typeable by PFGE. All three techniques showed 100% reproducibility. The time to obtain the results was shorter for automated ribotyping and ERIC-PCR compared with PFGE. Likewise, the costs for ERIC-PCR and PFGE were lower than those for automated ribotyping. The interpretation of results was more complicated and more difficult with ERIC-PCR than with both PFGE and automated ribotyping. All techniques presented excellent discriminatory power forP. aeruginosa(0.98). PFGE presented the highest discriminatory power (0.94) forA. baumannii,and both PFGE and ERIC-PCR showed higher discriminatory power (0.90 for both) than automated ribotyping (0.82) for S.maltophilia.Conclusions:PFGE showed the highest discriminatory power for typing these nonfermentative gram-negative bacilli. However, automated ribotyping and ERIC-PCR can provide results in a shorter time period with similar discriminatory power.