Application of infrequent-restriction-site PCR to clinical isolates of Acinetobacter baumannii and Serratia marcescens

Abstract

We applied infrequent-restriction-site PCR (IRS-PCR) to the investigation of an outbreak caused by 23 isolates of Acinetobacter baumannii in an intensive care unit from November 1996 to May 1997 and a pseudoepidemic caused by 16 isolates of Serratia marcescens in a delivery room from May to September 1996. In the epidemiologic investigation of the outbreak caused by A. baumannii, environmental sampling and screening of all health care workers revealed the same species from the Y piece of a mechanical ventilator and the hands of two health care personnel. IRS-PCR showed that all outbreak-related strains were genotypically identical and that three strains from surveillance cultures were also identical to the outbreak-related strains. In a pseudoepidemic caused by S. marcescens, IRS-PCR identified two different genotypes, and among them one genotype was predominant (15 of 16 [93.8%] isolates). Extensive surveillance failed to find any source of S. marcescens. Validation of the result of IRS-PCR by comparison with that of field inversion gel electrophoresis (FIGE) showed that they were completely concordant. These results suggest that IRS-PCR is comparable to FIGE for molecular epidemiologic studies. In addition, IRS-PCR was less laborious and less time-consuming than FIGE. To our knowledge, this is the first report of the application of IRS-PCR to A. baumannii and S. marcescens.

FIG. 1

(A) Representative results of IRS-PCR for S. marcescens. Lane 1, molecular weight marker; lanes 2 to 7, strains from the OB/GYN ward (lane 2, strain 9803; lane 3, strain 9823; lane 4, strain 9685; lane 5, strain 9870; lane 6, strain 9857; lane 7, strain 9858). (B) Representative result of FIGE with SpeI for S. marcescens. Lane 1, molecular size marker, lanes 2 to 7, strains from the OB/GYN ward (the strains in each lane are as described for panel A.

FIG. 2

Dendrogram by cluster analysis of the band patterns produced by IRS-PCR of S. marcescens. Fifteen of 16 isolates in the OB/GYN ward (strains 9563 to 9858) had a single pattern. One strain from the OB/GYN ward (strain 9870) and those from the other wards (strains 9623 to 9645) had distinct patterns.

FIG. 3

Representative results of IRS-PCR for A. baumannii. (A) Lane 1, molecular size marker; lanes 2 to 7, clinical strains from the ICU. (B) Comparison with strains from the surveillance study and epidemiologically unrelated strains. Lane 1, molecular size marker; lane 2, a strain from the outbreak; lane 3, a strain from a hand of a member of the medical staff; lane 4, a strain from the Y piece of a mechanical ventilator; lanes 5 and 6, epidemiologically unrelated clinical strains.