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Polyclonal bacteremic episodes are caused by more than one genotype of the same species. We conducted a study to estimate the frequency and to describe the epidemiology of polyclonal Gram-negative bacteremia in our patient population. We reviewed the patients' medical records. We also did pulsed field gel electrophoresis on 66 Gram-negative isolates obtained from the 28 patients (29 episodes) who had more than one morphologically different isolate of the same Gram-negative species in a blood culture obtained between January 1, 1989 and December 31, 1993. Nine of 29 (31%) bacteremic episodes evaluated were polyclonal. The source of bacteremia was not significantly different among patients with polyclonal and monoclonal bacteremic episodes. Patients with polyclonal bacteremic episodes were younger and were more likely to have rapidly fatal diseases than were those with monoclonal bacteremic episodes; however, neither of these differences reached statistical significance. Patients with polyclonal bacteremic episodes were significantly more likely to have leukemia than were those with monoclonal bacteremic episodes (odds ratio = 18.67; 95% confidence interval, 1.92 to 255.80). Three of nine patients who had polyclonal bacteremia died compared with 2 of 19 patients who had monoclonal bacteremia (odds ratio = 4.25; 95% confidence interval, 0.41 to 50.80). Polyclonal Gram-negative bacteremia is more common than previously thought. Despite their younger age, patients with polyclonal bacteremic episodes were more likely to die than those with monoclonal bacteremic episodes. Thus, polyclonal bacteremia may be either an indicator or a risk factor for poor prognosis.

Ribotyping and macrorestriction analysis of chromosomal DNA using pulsed-field gel electrophoresis (PFGE) are among the more useful molecular epidemiologic typing methods. Because these techniques are labor intensive, automation of one or more steps may allow clinical laboratories to apply molecular typing methods. We compared the recently developed automated ribotyping system, the RiboPrinter Microbial Characterization System (DuPont), with PFGE as a means of typing clinical isolates of E. coli and P. aeruginosa. A total of 22 E. coli and 24 P. aeruginosa were typed by both PFGE and the RiboPrinter. When compared with PFGE typing of E. coli and P. aeruginosa, the RiboPrinter was less sensitive in identifying different strains, particularly among the isolates of P. aeruginosa. The RiboPrinter was completely automated and allowed up to 32 isolates to be typed within an 8-hour period. The pattern of results obtained in this study suggests that a heirarchical approach to molecular typing using the RiboPrinter Microbial Characterization System plus PFGE might be feasible. The RiboPrinter Microbial Characterization System promises to be a very useful addition to the expanding molecular typing armamentarium.

The relationship between nasal and skin colonization with Staphylococcus aureus and subsequent infection in continuous ambulatory peritoneal dialysis (CAPD) patients in Brazil has been documented by restriction endonuclease analysis of plasmid DNA. However, S. aureus strains without detectable plasmids have been identified. Using restriction endonuclease analysis of chromosomal DNA hybridized with an rRNA gene probe, we document the diversity of S. aureus strains without detectable plasmids colonizing CAPD patients. Ten paired strains without detectable plasmids from five patients were studied by restriction endonuclease analysis of chromosomal DNA and by phage typing. Five different profiles were obtained by restriction endonuclease analysis of chromosomal DNA. Although four of the ten paired isolates were nontypeable by phage typing, all were discriminated by restriction endonuclease analysis of chromosomal DNA. These results demonstrate that restriction endonuclease analysis of chromosomal DNA is a useful epidemiologic tool and complements the restriction endonuclease analysis of plasmid DNA of S. aureus by providing a means of typing strains without detectable plasmids.

Using simple, readily available typing methods, we evaluated 108 strains of coagulase-negative staphylococci that were causally related to bloodstream infections: 95% (103 of 108) of the isolates were identified as Staphylococcus epidermidis and were divided into 18 biotypes by API Staph-Trac. A single biotype (biotype A, 6606113) accounted for greater than 50% of the isolates of S. epidermidis. Biotype A was further divided into seven subtypes by slime production and synergistic hemolysis; however, 66% of the isolates in biotype A remained in two major subtypes, 1a (strongly slime-positive and synergistic hemolysis-positive) and 2a (strongly slime-positive and synergistic hemolysis-negative). The addition of the antibiotype further separated the isolates into individual strains or into small groups of organisms. A significant correlation was noted between synergistic hemolysis and the three most resistant antibiotypes (p = 4.2 X 10(-5); OR = 5.8; CI95, 2.2-15.2). Each biotype, subtype, and antibiotype was further divided into multiple unique strains by plasmid pattern analysis. In most clinical situations the combination of API Staph-Trac, antibiotic profile, slime production, and synergistic hemolysis provides adequate strain discrimination. Plasmid pattern analysis adds important information in specific clinical situations and may be invaluable for epidemiologic investigations.