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Rhodococcus equi is an important pathogen of foals aged 1–6 months. Evidence exists that foals are exposed to a wide diversity of R. equistrains in their environment. However, limited data are available regarding the extent to which genotypic variation exists among isolates infecting individual foals. Therefore, electrophoresis of repetitive sequence–based polymerase chain reaction (rep-PCR) amplicons in an automated microfluidics chip format was used to genotype 9 virulent R. equiisolates obtained from distinct anatomic locations in a single foal. Four of the isolates were obtained from different regions of the lung, and 5 were from abscessed intra-abdominal lymph nodes (LNs). Six distinct genotypes were identified among the 9 isolates. None of the pulmonary isolates was identical; however, a pulmonary isolate was found to be identical to an isolate recovered from a small intestinal LN, and another pulmonary isolate was identical to an isolate from a mesenteric LN. These results indicate that foals can be infected with multiple strains of virulent R. equi.Furthermore, identical strains can be found in multiple, remote anatomic locations in an infected foal, and this can occur for >1 strain in the same foal. The automated system used in the current study provided a rapid, reproducible, and discriminating method for typing R. equiisolates.

ABSTRACTWe compared the results of typing methicillin-resistant Staphylococcus aureus(MRSA) isolates using the DiversiLab system (DL) to the results obtained using pulsed-field gel electrophoresis (PFGE). One hundred five MRSA isolates of PFGE types USA100 to USA1100 and the Brazilian clone, from the Centers for Disease Control and Prevention (CDC) and Project ICARE strain collections, were typed using DL. In addition, four unique sets of MRSA isolates from purported MRSA outbreaks that had been previously typed by DL, each consisting of six isolates (where five isolates were classified as indistinguishable by DL and one was an unrelated DL type) were typed by PFGE. DL separated the 105 MRSA isolates of known USA types into 11 clusters and six unique banding patterns. DL grouped most of the USA100, USA200, and USA1100 isolates into unique clusters. Multilocus sequence type 8 isolates (i.e., USA300 and USA500) often clustered together at >95% similarity in DL dendrograms. Nevertheless, USA300 and USA500 DL patterns could be distinguished using the pattern overlay function of the DL software. Among the hospital outbreak clusters, PFGE and DL identified the same “unrelated” organism in three of four sets. However, PFGE showed more pattern diversity than did DL, suggesting that two of the sets were less likely to represent true outbreaks. In summary, DL is useful for screening MRSA isolates to rule out potential outbreaks of MRSA in hospitals, but PFGE provides better discrimination of potential outbreak strains and is more useful for confirming strain relatedness and specific USA types.