Chapter 25
Foodborne Listeriosis
The suddenness with which Listeria monocytogenes emerged as the etiological agent of a foodborne
disease is unparalleled. The acquired immunodeficiency syndrome (AIDS) and legionellosis are examples of two other human diseases that appeared suddenly, but unlike foodborne listeriosis, the
etiological agents of these syndromes were previously unknown as human pathogens, and they proved
to be difficult to culture. Not only is L. monocytogenes rather easy to culture, but also listeriosis was
well documented as a disease of many animal species, and human cases were not unknown. For more
information on the listeriae, see references 26 and 69.
TAXONOMY OF LISTERIA
The listeriae are Gram-positive, non-spore-forming, and non-acid-fast rods that were once classified
as “Listerella.” The generic name was changed in 1940 to Listeria. In many ways they are similar to
the genus Brochothrix. Both genera are catalase positive and tend to be associated in nature, along with
Lactobacillus. All three genera produce lactic acid from glucose and other fermentable sugars, but
unlike Listeria and Brochothrix, the lactobacilli are catalase negative. At one time the listeriae were
believed to be related to coryneform bacteria and, in fact, were placed in the family Corynebacteriaceae,
but it is now clear that they are more closely related to Bacillus, Lactobacillus, and Streptococcus.
From 16S ribosomal RNA (rRNA) sequence data, Listeria places closest to Brochothrix, and these
two genera, together with Staphylococcus and Kurthia, occupy a position between the Bacillus group
and the Lactobacillus/Streptococcus group within the Clostridium–Lactobacillus–Bacillus branch,
where the mol% G + C of all members is less than 50.
65 Genetic transfers occur among Listeria,
Bacillus, and Streptococcus, and immunological cross-reactions occur among Listeria, Streptococcus,
Staphylococcus, and Lactobacillus. Brochothrix shares 338 common purine and pyrimidine bases with
Listeria.
85 Although Erysipelothrix is in the Mycoplasma line, it shares at least 23 oligonucleotides in
common with Listeria and Brochothrix.
85 Listeria spp. contain teichoic and lipoteichoic acids, as do
the bacilli, staphylococci, streptococci, and lactobacilli, but unlike these groups, their colonies form a
blue–green sheen when viewed by obliquely transmitted light.
Six species of Listeria are recognized, and they, with some differentiating characteristics, are listed
in Table 25–1. The former L. murrayi has been merged with L. grayi.
107 It can be seen from Figure
25–1 that the two former species occupy a position away from the other five species. L. ivanovii is
represented by two subspecies—L. ivanovii subsp. ivanovii and L. ivanovii subsp. londoniensis.
10 The
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Foodborne Listeriosis
The suddenness with which Listeria monocytogenes emerged as the etiological agent of a foodborne
disease is unparalleled. The acquired immunodeficiency syndrome (AIDS) and legionellosis are examples of two other human diseases that appeared suddenly, but unlike foodborne listeriosis, the
etiological agents of these syndromes were previously unknown as human pathogens, and they proved
to be difficult to culture. Not only is L. monocytogenes rather easy to culture, but also listeriosis was
well documented as a disease of many animal species, and human cases were not unknown. For more
information on the listeriae, see references 26 and 69.
TAXONOMY OF LISTERIA
The listeriae are Gram-positive, non-spore-forming, and non-acid-fast rods that were once classified
as “Listerella.” The generic name was changed in 1940 to Listeria. In many ways they are similar to
the genus Brochothrix. Both genera are catalase positive and tend to be associated in nature, along with
Lactobacillus. All three genera produce lactic acid from glucose and other fermentable sugars, but
unlike Listeria and Brochothrix, the lactobacilli are catalase negative. At one time the listeriae were
believed to be related to coryneform bacteria and, in fact, were placed in the family Corynebacteriaceae,
but it is now clear that they are more closely related to Bacillus, Lactobacillus, and Streptococcus.
From 16S ribosomal RNA (rRNA) sequence data, Listeria places closest to Brochothrix, and these
two genera, together with Staphylococcus and Kurthia, occupy a position between the Bacillus group
and the Lactobacillus/Streptococcus group within the Clostridium–Lactobacillus–Bacillus branch,
where the mol% G + C of all members is less than 50.
65 Genetic transfers occur among Listeria,
Bacillus, and Streptococcus, and immunological cross-reactions occur among Listeria, Streptococcus,
Staphylococcus, and Lactobacillus. Brochothrix shares 338 common purine and pyrimidine bases with
Listeria.
85 Although Erysipelothrix is in the Mycoplasma line, it shares at least 23 oligonucleotides in
common with Listeria and Brochothrix.
85 Listeria spp. contain teichoic and lipoteichoic acids, as do
the bacilli, staphylococci, streptococci, and lactobacilli, but unlike these groups, their colonies form a
blue–green sheen when viewed by obliquely transmitted light.
Six species of Listeria are recognized, and they, with some differentiating characteristics, are listed
in Table 25–1. The former L. murrayi has been merged with L. grayi.
107 It can be seen from Figure
25–1 that the two former species occupy a position away from the other five species. L. ivanovii is
represented by two subspecies—L. ivanovii subsp. ivanovii and L. ivanovii subsp. londoniensis.
10 The
591