Heterogeneous antimicrobial resistance patterns in polyclonal populations of coagulase-negative staphylococci isolated from catheters

Most cases of nosocomial bacteremia are catheter related, and coagulase-neg ative staphylococci (CoNS) are the microorganisms most frequently associate d with these infections. Subtle morphological differences are frequently fo und among CoNS colonies cultured from infected catheters. The aim of this s tudy was to analyze the significance of the morphological heterogeneity obs erved in these CoNS populations. With this purpose in mind? the clonal comp osition of the CoNS populations obtained from a selection of nine catheters ,vas analyzed by two different molecular techniques, arbitrarily primed-PCR and DNA macrorestriction analysis by pulsed-field gel electrophoresis, Twe nty CoNS morphotypes were included for analysis, and four single colonies r epresentative of each morphotype were selected. Morphological differences b etween colonies mere found to correlate in all cases with differences at th e molecular level. Unique fingerprints were also obtained for some isolates which mere indistinguishable from other representatives of the same morpho types, Differences in the molecular patterns among the isolates were associ ated in most of the cases with differences in the antimicrobial susceptibil ity patterns. The frequent isolation of polyclonal CoNS populations from ca theters, with heterogeneous antimicrobial susceptibility patterns, has rele vant epidemiologic and therapeutic implications in the contest of catheter- related infections.