Predictive biomarkers for drug-resistant Acinetobacter baumannii isolates with bla(TEM-1), AmpC-type bla and integrase 1 genotypes.

BACKGROUND AND PURPOSE: We tested whether antibiotic susceptibilities of drug-resistant Acinetobacter baumannii isolates could be used to predict the clinically important genotypes bla(TEM-1), AmpC-type bla, and integrase 1 gene (IntI1).

METHODS

We analyzed 401 A. baumannii isolates obtained at Changhua Christian Hospital between April 2001 and March 2002. The isolates were all from blood cultures, and identification of A. baumannii was confirmed by API-20NE. Antibiotic susceptibility testing (phenotype) was performed by disk diffusion method. Polymerase chain reaction was used to detect the genes bla(TEM-1), AmpC-type bla and IntI1.

RESULTS

Of 32 A. baumannii isolates, 10 possessed bla(TEM-1), 21 AmpC-type bla, and 26 IntI1. Resistance to ceftazidime (CAZ) predicted bla(TEM-1) genotype with 63.6% sensitivity, 100% specificity, 55.6% positive predictive value (PPV) and 0% negative predictive value (NPV). Trimethoprim-sulfamethoxazole (SXT) and gentamicin (GM) resistance predicted IntI1 genotype with 83.3% sensitivity, 71.4% specificity, 95.2% PPV and 45.4% NPV. No resistance phenotype could predict the AmpC-type bla genotype.

CONCLUSIONS

CAZ resistance predicted the bla(TEM-1) genotype with 100% specificity, and SXT and GM resistance predicted the IntI1 genotype with 92.5% PPV. Therefore, antibiotic susceptibilities to CAZ, SXT, and GM can be utilized clinically to detect critical genotypes in A. baumannii.