Vibrio parahaemolyticus
gram negative, motile, curved,
and
non-sucrose bacilli. They are
halophilic (salt –loving) in
tolerating 2-11 % NaCl
cause diarrhoea in some
countries with sea water
The diarrhoea is usually a self
limiting condition and may be
associated with nasea,
vomiting and fever.
broad spectrum
anti-microbial may be
required as
co-trimoxazole.
Aeromonas:
These m.o. are gram
negative, comma-shaped,
motile, and sucrose-
fermenter bacilli. Some
species cause diarrhoea,
wound infection, UTI,
cellulitis, osteomylitis and
septicaemia. They are NLF
bacilli.
A. Hydrophila (water-lover)
may cause human diseases
Plesiomonas:
These m.o. have similar
morphology to Aeromonas,
but are non-sucrose
fermenter. They may cause
diarrhoea, neonatal menigitis,
cellulitis, septic arthritis, and
acute cholycystitis.
P. shigelloides
is an
important species that may
cause human diseases and
is LF m.o..
Treatment for Aeromonas & Plesiomonas:
Anti-microbial agents effective against gram negative m.o. or broad spectrum drugs
Genus: Campylobacter
Species that can cause human infection:
1. C. jejuni.
2. C. coli.
Genus: Helicobacter
only a single species is important to
humans which is H. pylori. The latter m.o.
is now a well-known cause of gastritis,
duodenal and gastric ulcer and is linked
to gastric carcinoma and MALT (Mucosal
Associated Lymphoid Tumours).
Helicobacter are different in being urease positive, while Campylobacter are urease
negative. Campylobacters are motile with one polar flagellum, while H. pylori have
multiple polar flagella.
Genus: Campylobacter
Morphology
Small gram negative rods
comma-shaped or S-shaped.
Motility is of darting type. These m.o.
have a single polar flagellum.
Cultural charictristic
These microorganisms are
microaerophilic (requires 5% O2, 10%
CO2, and 85% N2) . Also these m.o. are
thermophilic (tolerate temperature up to
42-43 C which is useful characteristic in
their isolation and differentiation.
The important media used for cultivation
is:
1. Skirrow’s medium: Contains blood
agar and anti-microbials including
vancomycin, polymyxin B, and
trimethoprim to make it selective for the
m.o.
2. Campy-BAP: Similar to (1) but with
cephalothin.
Biochemical activity
Campylobacter are oxidase positive,
catalase positive , these m.o. are urease
negative (versus Helicobacter).
Genus: Helicobacter
Morphology
H. pylori are gram negative m.o., spiral in
shape, actively motile by multiple
flagellae.
Cultural charictristic
H. pylori can grow on the same media
mentioned for Campylobacter.
Biochemical activity
m.o. are catalase positive, oxidase
positive and urease positive.
Pathogensis of camylobactet
Pathogenesis of H. pylori infection
a) The m.o. are acquired by oral route
b) The m.o. are quite sensitive to gastric
juice
c) In the intestine, they multiply and
invade the intestinal wall (similar to-
but less than Shigella).
d) The m.o. liberate exotoxin and
enterotoxin (V. cholerae- ike) causing
damage to the intestinal tissue.
e) This results in an acute onset of
grossly bloody diarrhoea which is
associated with cramps of abdominal
pain.
f) The stool contains R.B.C. and
leucocytes (pus cells).
g)
h) Occasionally, the m.o. invade to the
blood stream and giving picture of
enteric fevers.
a) These m.o. attaches to the mucous-
secreting cells deep in the gastric
mucosa away from the acidity of the
stomach.
b) The production of ammonia from urea
by the organism’s urease, coupled
with an inflammatory response leads
to damage of the mucosa.
c) Loss of the protective mucous
coating, predisposes to gastritis and
peptic ulcer.
d) The ammonia also neutralizes gastric
acidity, allowing the organism to
survive.
e)
f) It is worth to mention that the m.o.
prefer pH of 6-7, but sensitive to
gastric juice.
g)
H. pylori is responsible for 85% of peptic
ulcers. However, 80- 90 % of people in
developing counties carry this m.o., while
in developed counties the rate is 20-
40%. The main factors of pathogenicity
are the active motility, proteases
(damage mucosa) & urease.
Treatment of Campylobacter:
A. Replacement of fluid and electrolytes
is an essential step in the
management.
B.
C. The m.o. are sensitive to erythromycin
and nalidixic acid.
D.
Complications of camylobacter :
Gullian –barre syndrome ( acute
demyelinating peripheral neuropathy with
ascending flaccid paralysis)
Treatment of H. pylori infection:
Peptic ulcers and gastritis could be
treated by combination of the following
drugs:
Triple Therapy:
Metronidazole + clarithromycin or
amoxicillin or tetracycline + bismuth
subcitrate (pepto-bismol).
This treatment results in eradication of H.
pylori in
70 – 95 % of patients and decreases
recurrence rate of peptic ulcers.
Immunity to H.pylori :
antibodies have no active role in
bactericidal effect against H. pylori.
Diagnosis of H. pylori Infection:
1. Gastric Biopsy specimens:
A. Microscopical examination show the curved or spiral organism.
B. Culture
2. Detection of H. pylori Antibodies in patient’s serum: These antibodies are of 3
classes (IgM, IgG, and IgA).
3. Detection of H. pylori Antigens in the stool (ELISA).
4. Rapid urease test:. If H. pylori is present, the urease splits the urea and results in
shift of pH leading to colour change (from yellow to red).
5. Urease Breath Test: If the m.o. is present, the urease activity generates
radiolabelled CO2 that can be detected in patient’s breach (by detector).
Genus : Yersinia
Yersinia pestis:
Rats and rodents are the natural host of this m.o. which is transmitted to man by the
rat-flea Xenopsylla cheopis.
Morphology:
1. Gram negative short ovoid, non-motile bacilli.
2. In tissue it forms a capsule-like outer envelop.
3. it shows marked bipolar staining “ safety pin appearance).
Cultural characteristics:
Facultative anaerobe. Optimum temp. 30 C. It grows on nutrient agar, however, better
growth on blood agar.
Pathogenicity:
The m.o. have pathogenic factors as LPS, F1 antigen, V-W antigens and endotoxins;
F1 & V-W are anti-phagocytic.
Plague:
1. Plague is a disease of wild rodents and is transmitted to man by bite of infected
fleas.
2. The m.o. multiplies in the draining L.N. (tender) causing bubonic plague.
3. From there, it can spread to the blood causing septicaemic plague .
4. then to the lungs causing pneumonic plague which can spread from person to
person by droplets
5. The patient have painful lymphadenopathy specially in the groins and axillae.
6. the patient may have nausea, vomiting, diarrhoea, DIC, or meningitis.
7. Mortality rate of plague is 50%, but from pneumonia is almost 100%.
Diagnosis:
1. Detection and isolation
of the m.o. from aspirate of
L.N., sputum or blood.
2. Serological diagnosis by
ELISA or agglutination
tests for rising antibody
titers.
Treatment:
1. Streptomycin is the
drug of choice.
2. Tetracycline is an
alternative.
3. They may be used in
combination.
Prophylaxis:
1. Anti-rat anti-flea
measures
2. prevention of rats
coming in ships,
3. prophylactic
tetracyclines & killed
vaccine.
Y. Enterocolica & pseudotubrerculosis:
They cause enterocolitis and mesenteric adenitis even some times suspected as
appendicitis. They are transmitted to humans by contamination of food
Morphology and culture:
Similar to Y. pestis, and for culture the m.o. can tolerate temprature 4-30 C. Therefore, to
isolate the m.o. culture at 4 C (cold enrichment) motile at low temperature and not at 37 C.
Clinical picture Y. enterocolitica and pseudotuberculosis:
Both m.o. are important causes of diarrhoea (watery to bloody) in countries with cold
climate and pork consumption, but not in Iraq (1-2%). Early symptoms are fever, abdominal
pain, and diaarhoea.At times, the abdominal pain is severe and localized in the right lower
quadrant, suggesting appendicitis.
Treatment:
Aminoglycosides as nitilmicin & gentamycin.
Francisella tularensis & tularaemia
transmissible to humans by biting arthropods, direct contact with animals, inhalation of
aerosols, or ingestion of contaminated food or water.
The m.o. is small, gram negative, pleomorphic rod.
small colonies appear in 1-3 days aerobically at 37 C on:
1. Glucose cysteine blood agar.
2. Glucose blood agar.
When m.o. enter through skin abrasions, an ulcerating papule develops, and regional L.Ns.
enlarge,
when inhaled pneumonitis occurs, and oculoglandular tularaemia may develop via the
conjunctiva.
Treatment:
Streptomycin, or gentamicin .
Pasteurella
These m.o. are primarily animal pathogens, but the can produce human diseases.
P. Mutocida is the most common m.o. in cat or dog bites. The other m.o. may cause man
infections as wound, respiratory or suppurative.
The common presentation is animal bite followed by an acute onset of redness, swelling and
pain.
Treatment:
Aminoglycosides or tetracyclines.