A multiple protocol to improve diagnosis and isolation of Shiga toxin-producing Escherichia coli from human stool specimens.
Many infections caused by Shiga toxin-producing Escherichia coli (STEC) are undiagnosed, particularly non-O157 STEC. We evaluated the use of a multiple protocol approach to improve diagnosis, isolation, and characterization of STEC strains. Among 18 presumptive STEC-positive stool samples received by the INOVA Fairfax Hospital, Falls Church, VA, in 2006, 16 were Shiga toxin positive. From these 16 stool samples, 8 O157:H7 and 5 non-O157 STEC were isolated by plating onto sorbitol MacConkey (SMAC) agar. The remaining 5 stool samples that did not yield colonies on SMAC agar plates were enriched. All enriched samples were Shiga toxin positive, and 2 O157:H7 and 1 non-O157 STEC were subsequently isolated. The 2 remaining enriched samples did not yield isolates; however, based on polymerase chain reaction (PCR) analysis, both samples contained STEC genes. Based on PCR analysis of non-O157 strains, 3 strain types were identified. Samples from 3 patients, received within 2 days of one another, had a similar gene profile-eae and stx(1) negative and stx(2) positive-suggesting that these patients were likely infected with the same strain. Our results indicate that a multiple protocol approach is necessary to reliably diagnose and isolate STEC strains, and that PCR profiling of strains could allow for more rapid identification of outbreaks.
Environmental Microbial Safety Laboratory, U.S. Department of Agriculture, Animal and Natural Resources Institute, Agricultural Research Service, Beltsville, MD, USA. dan.shelton@ars.usda.gov
Daniel R
DR
Shelton
Jeffrey S
JS
Karns
Choong H
CH
Park
D015373:Bacterial Typing Techniques; D001431:Bacteriological Techniques; D003470:Culture Media / Q000737:chemistry; D004927:Escherichia coli Infections / Q000175:diagnosis* / Q000382:microbiology; D019453:Escherichia coli O157 / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D006463:Hemolytic-Uremic Syndrome / Q000175:diagnosis* / Q000382:microbiology; D006801:Humans; D016133:Polymerase Chain Reaction / Q000379:methods*; D022621:Shiga Toxin / Q000096:biosynthesis; D054323:Shiga-Toxigenic Escherichia coli / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*
D003470:Culture Media; D022621:Shiga Toxin