Clonal expansion of Staphylococcus epidermidis strains causing Hickman catheter-related infections in a hemato-oncologic department

Abstract

The detailed analysis of 411 strains of coagulase-negative staphylococci (CoNS) obtained from 40 neutropenic hemato-oncologic patients (61 Hickman catheter episodes) on intensive chemotherapy is described. By random amplification of polymorphic DNA (RAPD) analysis, a total of 88 different genotypes were detected: 51 in air samples and 30 in skin cultures prior to insertion, 12 in blood cultures after insertion, and only 5 involved in catheter-related infections (CRI). Two RAPD genotypes of Staphylococcus epidermidis predominated, and their prevalence increased during patient hospitalization. At insertion, these clones constituted 11 of 86 (13%) CoNS isolated from air samples and 33 of 75 (44%) CoNS isolated from skin cultures. After insertion, their combined prevalence increased to 33 of 62 (53%) in catheters not associated with CRI and 139 of 188 (74%) in catheters associated with CRI (P = 0.0041). These two predominant S. epidermidis clones gave rise to a very high incidence of CRI (6.0 per 1,000 catheter days) and a very high catheter removal rate for CRI, 70%, despite prompt treatment with vancomycin. A likely source of S. epidermidis strains involved in CRI appeared to be the skin flora in 75% of cases. The validity of these observations was confirmed by pulsed-field gel electrophoresis (PFGE) of SmaI DNA macrorestriction fragments of blood culture CoNS isolates. Again, two predominant CoNS genotypes were found (combined prevalence, 60%). RAPD and PFGE yielded concordant results in 75% of cases. Retrospectively, the same two predominant CoNS clones were also found among blood culture CoNS isolates from the same hematology department in the period 1991 to 1993 (combined prevalence, 42%) but not in the period 1978 to 1982. These observations underscore the pathogenic potential of clonal CoNS types that have successfully and persistently colonized patients in this hemato-oncology department.

FIG. 1

Distribution of RAPD genotypes of CoNS during Hickman catheter usage in hemato-oncologic patients. Eighty-eight RAPD genotypes among 411 CoNS isolates from 61 Hickman catheter episodes in 40 patients were detected. Each sector of an individual pie chart represents the contribution of a single RAPD CoNS genotype to the total number of CoNS isolated at the indicated time, site, and infection status. †, number of strains/number of RAPD genotypes isolated; ‡, two-letter codes correspond to codes in Table 1 while numbers are the numbers of strains isolated; §, number of single unique RAPD genotypes isolated at the indicated time, site, and infection status; ¶, number of catheter episodes at the indicated time and infection status.

FIG. 2

RAPD analysis of CoNS isolated from patients fitted with Hickman catheters. For patient 9 (A and B), eight strains derived from blood cultures were analyzed in two separate assays with two different primer species in RAPD (ERIC 1 and ERIC 2), as indicated below the panels. The patient was sampled daily for a full week, and all blood samples were culture positive for CoNS. After catheter removal, catheter tip cultures were also found to be positive. All RAPD fingerprints obtained were identical, demonstrating persistent infection by a single genotype (predominant strain A-D [see also Table 1]). For comparison, panel C displays typing data for strains derived from patient 18. Increased diversity in ERIC 2 fingerprints is shown. Strains were obtained from the catheter exit site, skin, and urine on various occasions spanning a period of more than 3 months. Lanes M display molecular length markers (100-bp ladder; Gibco BRL). The fragment indicated by a black dot on the left of each panel is 800 bp long.

FIG. 3

PFGE of SmaI DNA macrorestriction fragments from CoNS obtained from blood cultures of patients fitted with Hickman catheters. Strains (numbered 1 through 14) were obtained from seven patients, who are indicated by number at the bottom (corresponding with numbering in Table 1). PFGE types are given below the lanes and correspond to PFGE types in Table 1. The positions of some of the reference DNA size markers are indicated on the right.

FIG. 4

PFGE of SmaI DNA macrorestriction fragments from CoNS obtained from blood cultures of patients fitted with Hickman catheters during three different time periods (one isolate per genotype per catheter episode). †, number of strains/number of PFGE genotypes isolated; ‡, one-letter codes correspond to codes in Table 1 while numbers are the numbers of strains isolated.