A comparison of immunomagnetic separation, direct culture and polymerase chain reaction for the detection of verocytotoxin-producing Escherichia coli O157 in human faeces
Verocytotoxin-producing Escherichia coli O157 (O157 VTEC) has become well recognised as an important enteric pathogen. The number of organisms present in environmental and clinical samples may be low and efforts have been made to increase the sensitivity of O157 VTEC detection. Immunomagnetic separation (IMS) has been shown to improve O157 VTEC detection in bovine faeces and food samples. A milk-borne outbreak of O157 VTEC infection allowed us to compare the isolation rates from human faeces by IMS, direct faecal culture on sorbitol-MacConkey agar and a PCR test for verotoxin gene carriage. Of 142 faecal samples examined, 20 were positive on both direct culture and IMS and a further 13 on IMS alone. Therefore, IMS increased the detection rate of individual cases of O157 VTEC infection and also compared well with PCR. We recommend IMS for use in routine diagnostic laboratories where a more sensitive method than direct faecal culture is required for O157 VTEC isolation.
KarmaliM. A.,
PetrieM.,
SteeleB. T.,
LimC. Sporadic cases of haemolytic uraemic syndrome associated with faecal cytotoxin and cytotoxin-producing Escherichia coli in stools. Lancet1983; 1:619–620
GrossR. J.Escherichia coli diarrhoea. In
SmithG. R.,
EasmonC. S. F.
(eds) Topley and Wilson’s Principles of bacteriology, virology and immunity 8th edn London: Hodder and Stoughton; 1990469–487
MarchS. B.,
RatnamS. Sorbitol MacConkey medium for the detection of Escherichia coli O157:H7 associated with haemorrhagic colitis. J Clin Microbiol1986; 23:869–872
ScotlandS. M.,
RoweB.,
SmithH. R.,
WillshawG. A.,
GrossR. J. Verocytotoxin-producing strains of Escherichia coli from children with haemolytic uraemic syndrome and their detection by specific DNA probes. J Med Microbiol1988; 25:237–243
ChapmanP. A.,
SiddonsC. A.,
ZadikP. M.,
JewesL. An improved selective medium for the isolation of Escherichia coli O157. J Med Microbiol1991; 35:107–110
RitchieM.,
PartingtonS.,
JessopJ.,
KellyM. T. Comparison of a direct shiga-like toxin assay and sorbitol MacConkey agar culture for laboratory diagnosis of enterohaemorrhagic Escherichia coli infection. J Clin Microbiol1992; 30:461–464
PatonA. W.,
PatonJ. C.,
GoldwaterP. N.,
ManningP. A. Direct detection of Escherichia coli shiga-like toxin genes in primary faecal cultures by polymerase chain reaction. J Clin Microbiol1993; 31:3063–3067
ChapmanP. A.,
WrightD. J.,
SiddonsC. A. A comparison of immunomagnetic separation and direct culture for the isolation of verocytotoxin-producing Escherichia coli O157 from bovine faeces. J Med Microbiol1994; 40:424–427
WrightD. J.,
ChapmanP. A.,
SiddonsC. A. Immunomagnetic separation as a sensitive method for isolating Escherichia coli O157 from food samples. Epidemiol Infect1994; 113:31–39
OkrendA. J. G.,
RoseB. E.,
LattuadaC. P. Isolation of Escherichia coli O157:H7 using O157 specific antibody coated magnetic beads. J Food Protect1992; 55:214–217
MortlockS. Recovery of Escherichia coli O157:H7 from mixed suspensions: evaluation and comparison of pre-coated immunomagnetic beads and direct plating. Br J Biomed Sci1994; 51:207–214
PollardD. R.,
JohnsonW. M.,
LiorH.,
TylerS. D.,
RozeeK. R. Rapid and specific detection of verotoxin genes in Escherichia coli by the polymerase chain reaction. J Clin Microbiol1990; 28:540–545
TarrP. I.,
NeillM. A.,
ClausenC. R.,
WatkinsS. L.,
ChristieD. L.,
HickmanR. O.Escherichia coli O157:H7 and the haemolytic uraemic syndrome: importance of early cultures in establishing the etiology. J Infect Dis1990; 162:553–556
A comparison of immunomagnetic separation, direct culture and polymerase chain reaction for the detection of verocytotoxin-producing Escherichia coli O157 in human faeces