Legionella, Listeria
and Corynebacteria
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Also
www.amm.co.uk,
Legionella
52 genetically defined species and about
half are pathogenic to humans. Thin Gram
negative rods with unusual complex
nutritional requirements :
eg high Fe and cysteine.
Not related to other respiratory
pathogens.
Legionella
Legionella pneumophila
Others associated with infection in the
compromised :
L. micdadei
L. bozemanii
L. longbeachae
L. dumoffii
Legionella
Legionella pneumophila:
First recognised as a pathogen in 1976
following a major outbreak amongst
American Legionnaires in Philadelphia >180 affected.
Subsequently recognised as a cause of
disease as far back as 1947 and an
outbreak in 1957.
Legionella
Ubiquitous in nature and can be isolated from
terrestrial and aquatic habitats and from patients
with LD. Isolated from lakes, streams and soil in
small numbers.
It is relatively resistant to heat and chlorine. (It
appears to go into some form of suspended
animation in adverse conditions.) It is normally
spread through water distribution or air
conditioning systems in which high numbers
may be found.
Legionella
Outbreaks seem to occur at the end of the
summer but cases may occur all year
round as it is found in hot water tanks,
and whirlpool spas (where it multiplies
readily at 35-45oC).
Spread by inhalation of aerosols from
showers etc.
NOT spread from person to person.
Legionella
Annual prevalence in US is steady at about
0.5 per 100,000. It is likely that many
cases are undiagnosed.
Legionella
Prevention is by:
Maintenance and cleaning of A/C systems.
Improved design of water systems and
elimination of dead legs,
Hyperchlorination,
Heating water to 63oC.
Legionella
Pathogenesis.
L. pneumophila is an intracellular parasite that
grows in alveolar macrophages and monocytes.
Phagocytosed cells are protected from
intracellular killing by lysosomal fusion and
acidification.
Virulent strains are difficult to distinguish from
avirulent strains. Virulence seems to depend on
proteolytic enzymes, lipases, phosphatases and
nucleases.
Legionella
Pontiac Fever :
A mild self-limiting disease - mild cough,
sore throat, mild headache and fever.
No treatment necessary and it resolves in
2-5 days. Possibly due to inhalation of
antigen rather than bacterial invasion.
Sometimes shows high attack rates (95%)in
outbreaks
Legionella
Legionnaires Disease:
In the elderly - often who are
immunocompromised for some reason a
more severe disease which is an atypical
pneumonia.
There are 18 serotypes– serogroup 1 is the
most pathogenic and seems to cause 95%
of such infections in these islands.
Low attack rates in outbreaks (0.5-5.0%)
Legionella
Predisposing factors:
Smoking, malignancy, diabetes, Aids, endstage renal disease, and alcohol abuse.
Male : Female 2.5 : 1
Very rare in those under 20
Legionella
Legionnaires Disease cont’d
Prior to the onset of pneumonia intestinal
disorders are common followed by high
fevers and chills and muscle aches.
Followed by dry cough, and chest and
abdominal pains.
Fatality at about 10% usually as a result of
respiratory failure
Legionella
Diagnosis
Culture of bronchial washings, pleural fluid
and possibly other body fluids. Culture
using buffered charcoal yeast extract agar
with iron and cysteine.
Growth may take 5 (L. pneumophila)-10
days (other species).
Legionella
Antigen detection in patient’s urine – ELISA
for Serotype 1 only.
Serology for retrospective diagnosis: FAT,
Rapid microagglutination Test, RIA or ELISA.
Antibody response in 8 days
4-fold rise in titre or a titre of 1:256 is
usually diagnostic.
Legionella
Treatment:
Conventional sensitivity tests are unreliable but
L. pneumophila is susceptible to
rifampicin, erythromycin, quinolones and
tetracyclines. All these have good intracellular
penetration.
Beta lactams and aminoglycosides are ineffective
IV erythromycin is preferred.
Listeria
Two species may be pathogenic – mostly
Listeria monocytogenes and occasionally
L. ivanovii.
L. innocua, L. welshimeri and L. seeligeri are
non pathogenic.
Up to 5% of healthy adults carry Listeria.
Listeria
Widespread in nature but infections are rare in the
general population but may cause life
threatening infections usually bacteraemia or
meningo-encephalitis in susceptible groups
which are:
Post 20 weeks of pregnancy,
neonates
and the immunosuppressed.
Mortality highest in infants of septic mothers or the
severely immunocompromised.
Listeria
Short intracellular Gram-positive rods, but in
clinical specimens may appear Gram variable
and look like diphtheroids or cocci. Motile with
tumbling motility.
Grow on blood agar – There are no identifiable
toxins but virulent strains are haemolytic. Animal
studies suggest the production of listeriolysin
which protects the organism after phagocytosis
and facilitates the extraction of iron
Listeria
Grow best at 30 – 37oC but can grow at
4 -10oC. Some claim it may grow at 0oC.
Definitive identification by biochemistry or
serology
Listeria
Neonatal disease:
Early onset: acquired transplacentally.
Disseminated abscesses and granulomas
with high mortality if untreated.
Late onset: 2-3 weeks after birth meningitis
or meningoencephalitis and septicaemia
Listeria
Treatment: Penicillin or ampicillin alone or
with an aminoglycoside.
No vaccine is available and because of the
ubiquitous nature of the organism and the
sporadic infections, prevention and control
are difficult.
Listeria
Reservoir: Domestic and wild animals, water
and mud.
Contaminated silage gives rise to listeriosis
in animals.
Faecal carriage in man in about 5%
Listeria
Listeria is found in a wide range of foods
including fish, meat and vegetables and
consequently in food products such as
soft cheeses and those not made with
pasteurised milk.
A relatively recent outbreak involved pork
pate from Brussels.
Listeria
Its ability to grow at 4oC and survive
temperatures of 70oC has implications in
the management of cook chill catering.
Also in ready prepared meals bought in
supermarkets.
Corynebacteria
The genus includes the diphtheria bacillus
as well as a number of commensals and
pathogens of man and animals.
These are usually referred to as coryneforms
or diphtheroids.
These are pleomorphic gram-positive rods
arranged as pallisades.
Corynebacteria
C. diphtheriae is the type strain It is aerobic
and facultatively anaerobic non-sporing
non-motile and non-capsulate.
It is grown on media containing blood or
serum and produces characteristic black
colonies on blood tellurite medium.
Corynebacteria
Three types of colonies may be observed :
Large – gravis
Medium – intermdius
Small – mitis.
Historically these reflected the severity of
the infection. Gravis and intermedius are
usually toxigenic due to the presence of a
bacteriophage
Corynebacteria
Diphtheria is an acute infection of the
tonsils, pharynx, nose and other mucous
membranes or even skin and on occasion
the conjunctiva and genitals.
A greyish membrane covers much of the
throat and is surrounded by inflammation.
The throat is moderately sore and the
patient will have enlarged cervical lymph
nodes.
Corynebacteria
Diphtheria should be differentiated from
other causes of sore throat and premature
use of antibiotics may delay diagnosis with
fatal results.
Specific treatment with antibiotics and
antitoxin is indicated even if lab results are
negative.
Corynebacteria
Man is the reservoir of this bacterium. The
disease is normally manifest in the colder
months. Usually unvaccinated children of
less than 15 y. This is a story of a very
successful vaccination programme.
It used to be very common but now
diphtheria is very rare.
Corynebacteria
Spread is by direct contact with patient or
articles soiled with discharges. Raw milk
has been a vehicle.
Incubation is 2-5 days.
Communicability depends on the success of
the treatment which if good, will prevent
carriage and spread. Rarely carriers may
shed for 6 months or more.
Corynebacteria
Non diphtheria coryneforms include :
C.ulcerans
C. haemolyticum
Acute pharyngitis
C.minutissimum
C.jeikeium
Cutaneous infections
Corynebacteria
C.pseudotuberculosis causing
Granulomatous lymphadenitis.
C.jeikeium
Infective endocarditis
C.xerosis
C.pseudodiphtheriticum
C.bovis
Corynebacteria
C.jeikeium
C.xerosis
C.bovis
Line shunt and cannula
C.equi
necrotising pneumonia
CDC group D-2 Complicated UTI
(abnormality or stones)