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Journal of Clinical Microbiology, Jan 1997, 179-183, Vol 35, No. 1
A Bubert, J Riebe, N Schnitzler, A Schonberg, W Goebel and P Schubert
Two catalase-negative Listeria monocytogenes serovar 1/2b strains were
isolated from listeriosis patients in 1995 in Germany. The infections
appeared in individuals from different cities at different seasons and were
caused by L. monocytogenes strains of different clonal types. In
particular, the catalase reaction of one strain isolated from blood was
consistently negative, whereas this reaction was only reversibly blocked
when the strain was freshly isolated from ascitic fluid. After
subculturing, the catalase-positive reaction was restored. Initially,
identification of these isolates was difficult to achieve not only because
of the lack of a catalase reaction, which generally distinguishes L.
monocytogenes from other morphologically similar pathogenic gram-positive
bacteria, but also because other routinely used biochemical tests such as
CAMP and the commercial API test gave unclear results. However, rapid and
unequivocal identification of these strains was possible by analyzing
secretions of the p60 protein in culture supernatants by enzyme-linked
immunosorbent assay or Western blot (immunoblot) analysis with our recently
developed Listeria- and L. monocytogenes-specific anti-p60 antibodies.
Additionally, the identifications were confirmed by Listeria- and L.
monocytogenes- specific PCR analyses with primers derived from the iap,
hly, and prfA genes. Immunoanalyses also allowed for the differentiation of
these two strains, whereas no differentiation was possible by PCR when the
internal, variable repetitive iap gene portion was analyzed. However, size
variations of the PCR products comprising these gene portions which were
obtained from a number of L. monocytogenes strains belonging to the same
serotypes indicated that this type of PCR is not only useful for specific
identifications but may be used in parallel as an additional marker for
epidemiological studies. In conclusion, the data suggest that catalase
production should not be taken as a strict criterion for the identification
of listeriae. Furthermore, at least the infection caused by the stably
catalase-negative strain supports the notion that catalase does not seem to
be necessary for the intracellular growth of L. monocytogenes.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Isolation of catalase-negative Listeria monocytogenes strains from listeriosis patients and their rapid identification by anti-p60 antibodies and/or PCR
Lehrstuhl fur Mikrobiologie, Theodor-Boveri-Institut fur Biowissenschaften, Universitat Wurzburg, Germany. bubert@biozentrum.uni- wuerzburg.de
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