Assessment of Similarity among Coagulase-Negative Staphylococci from Sequential Blood Cultures of Neonates and Children by Pulsed-Field Gel Electrophoresis

Abstract

One of the criteria used to determine the clinical importance of coagulase-negative staphylococci (CoNS) is isolation of the bacteria from sequential blood cultures. Pulsed-field gel electrophoresis was used to characterize sequential blood isolates of CoNS collected within a 7-day period from neonates and children with bacteremia. Of 18 episodes among neonates, 6 (33%) involved unrelated strains of CoNS. All unrelated strains were from neonates who received antimicrobial therapy after the first culture and who had a second culture > or = 36 h later. Among older children, 5 (19%) of the 27 episodes of presumed central venous (CV) catheter-related sepsis involved unrelated isolates. All of the unrelated isolates were from patients who had blood samples obtained through CV catheters only. Thus, even repeated isolation of CoNS from blood cultures may represent contamination if samples are drawn through CV catheters only or if second samples are obtained > 1 day after appropriate antimicrobial therapy.

A blinded, randomized, multicenter study of an intravenous Staphylococcus aureus immune globulin

“…13,14 It is acknowledged that the definitions for CoNS are imperfect and uncertain, and these definitions would influence the reported cumulative incidence of CoNS infection. CRP levels to assist in the classification of CoNS infections were not obtained.…”

Clonal Diversity in Episodes with Multiple Coagulase-Negative Staphylococcus Bloodstream Isolates Suggesting Frequent Contamination

“…Different clinical-and/or laboratory-based algorithms have demonstrated variable discriminatory power between true bacteremia and contamination [4][5][6][7][8]. Therefore, in clinical practice, if only one of two or more sets is positive for CoNS, the positive result is presumed to be a contaminant, while if two or more blood cultures yield CoNS, a true bacteremia is assumed [9][10][11] and systemic antimicrobial treatment with vancomycin is initiated [12]. The validity of this commonly used clinical practice is not well defined.…”

“…A true bacteremia may be more likely if CoNS isolates are recovered from two or more positive sets of blood cultures and the isolates are demonstrated to be the same clone by molecular typing studies. Conversely, if two or more CoNS isolates are shown to be different clones, contamination is likely [2,[11][12][13].…”

Evaluation of Quantitative Antibiotic Susceptibility Testing by Vitek 2 as a Routine Method To Predict Strain Relatedness of Coagulase-Negative Staphylococci Isolated from Blood Cultures

“…Ninety-eight (82.4%) of these pairs were identified as belonging to the same staphylococcal species, while 21 Among 119 CoNS pairs, isolates from 66 (55.5%) pairs were found to be genetically identical (60 pairs) or closely related (6 pairs) and 53 (44.5%) pairs comprised isolates that showed at least seven band differences and were considered genetically distinct based on PFGE results (Fig. 1).…”

“…Comparison of AST patterns has been evaluated previously using different susceptibility testing methods such as the Dade MicroScan WalkAway-40 system, the Vitek system, and broth microdilution as well as different gold standards such as plasmid typing and PFGE for comparisons (5,11,21). Quantitative antibiogram analysis involving the calculation of a similarity coefficient or cluster analysis and based on the measurement of the diameters of agar diffusion inhibition zones of CoNS isolates was also investigated (2,16).…”