National Center for Biotechnology Information NCBI NLM MEDLINE Virginia gel humans pubmed abstract nih national institutes of health national library of medicine treatment outcome middle aged drug resistance case-control studies disease outbreaks microbial hospitals hospital bed capacity electrophoresis pulsed-field gentamicins / pharmacology* cross infection / microbiology* veterans gram-positive bacterial infections / microbiology* gram-positive bacterial infections / epidemiology beta-lactamases / biosynthesis* pmid:1733382 doi:10.7326/0003-4819-116-4-285 v d wells e s wong s m markowitz enterococcus faecalis* / drug effects enterococcus faecalis* / enzymology enterococcus faecalis* / genetics 500 and over