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

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Abstract
Objective: 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) and Acinetobacter baumannii (n = 42) samples were obtained from blood cultures of patients admitted to 10 medical centers in Latin America during 1998 and Stenotrophomonas 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 for P. aeruginosa (0.98). PFGE presented the highest discriminatory power (0.94) for A. 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.

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