GRAM NEGATIVE BACILLI
|
spp Salmonella |
|
|
Characteristics |
·
Gr –ve bacilli ·
Non sporing , motile bacilli ·
All exept S.typhi are non – capsulate bacilli ·
Facultative anaerobes |
|
Habitat |
·
Animal gut ·
Human is the only natural host for S. typhi
& S paratyphi |
|
Transmission |
·
Foodborne
roote ·
Faecal-oral route |
|
Pathogenesis |
·
Endotoxin=cause fever , leukemia , hypotension
&shock ·
Capsule=antiphagocytosis ·
Can survive within macrophages |
|
Diseases |
·
Typhoid fever (Enteric fever) 1.
bacteria rich small
intestine and then enter lymphatics& blood streem 2.
cause fever , malaria ,
headache , constipation etc 3.
spleen &liver become enlarged ·
Enterocolitis
(gastroenteritis or food poisoning ) ·
septicemia |
|
Laboratory Identification |
·
Oxidase – ve
, non –lactose fermentation ·
Produce acid &gas from glucose ·
Grow well on macConnkey
agar , DCA , .S.S agar ·
Commercial kits available for full identification |
|
Shigella |
|
|
Characteristics |
·
Gram –Ve
bacillus ·
Faculitatie anaerobic ·
Most shigella pathogen is S.sonnei ·
Non lactose fermentive . ·
Non motile
. |
|
Pathogenesis |
·
Endotoxin ·
Capsule ·
Antigenic phase variation . |
|
Diseases |
·
Gastroenteritis (( shigellosis )) ·
S.dysenteriae cause bacterial dysenteria |
|
Laboratory Identification |
·
Oxidase –
Ve ·
Isolation from specimens
requires use of selective media . |
Vibrio
-the second major group of
gram-negative ,facultative anaerobic, fermentative rods.
- Were separated
from Enterobacteriaceae on the basis of positive oxidase reaction and the
presence of polar flagella.
-the most important members of Vibrio spp are:
1) Vibrio cholera.
2) Vibrio parahaemolyticus.
3)Vibrio vulnificus.
-Vibrio species can grow on a
variety of simple media within temp rate (14-40C).
V.cholerae can
grow in the absence of salts(most other species of vibrio that are pathogenic
in human require salt [halophilic species]).
-Vibrio tolerate a wide range of
PH (e.g.PH of 6.5-9.0) but are susceptible to stomach acids. If gastric acid
production is reduced or neutralized , patients are more susceptible to Vibrio
infection.
-most vibrio have
asingle polar flagella (in contrast with peritrichous flagella in the family
Enterobacteriaceae.
-vibrio have also various pili
that are important for virulence.
-epidemic
strains of V.cholerae the etiologic agent of cholera
|
cholerae Vibrio |
|
|
Characteristics |
·
Small , curved (comma – shapped ) ·
Gr –ve bacilli ·
Non sporing , motile
bacilli , non capsulate bacilli ·
Facultative anaerobes ·
Were separated from Enterobacteriaceae on the basis of positive oxidase
reaction and the presence of polar flagella. |
|
Habitat |
·
Contaminated water
(usually) or food (sometimes ) |
|
Transmission |
·
Foodborne route ·
Faecal – oral route |
|
Pathogenesis |
·
Choleragen enterotoxin =
hypersecretion of electrolytes andwater. |
|
Diseases |
·
Cholera 1.
bacteria colonize the
intestinal tract in very high numbers 2.
bacteria attach to but do not invade the intestinal mucosa 3.
intese vomiting & diarrhea 4. severe
loss of water &electrolytes *gastroenteritis |
|
Laboratory Identification |
·
Oxidase +ve ·
Commercial kits available for full identification ·
Special selective media for vibrio thiusulfate citrate bile
salts sucrose(TCBS). ·
Do not require salts for growth. But can
tolerate it. |
|
|
·
Vibrio cholerae are rarely
seen in Gram-stained stool or
wound specimens. ·
By using darkfield
microscope may able to detect the motile bacteria in stool specimen. |
Enterobacteriaceae SPP.
-the family Enterobacteriaceae is the largest,
most heterogeneous collection of medically important gram-negative rods.
-fewer than
20 species are responsible for more than 95% of the infection.
-Enterobacteriaceae are ubiquitous organisms, found
worldwide in soil,water,vegetation.
-Enterobacteriaceae
part of the normal intestinal flora of most human.
-these bacteria cause a variety of human diseases
including 30-35% of all septicemia, more than 70% of urinary tract infection ,
and many intestinal infections.
-some organisms(e.g.salmonella typhi, shiglla,
yersinia pestis) are always associated with disease.
-while other organisms(e.g. E.coli, klebsiella
pneumoniae, protus mirabilis) are members of the normal commensal flora that
can cause opportunistic infections.
-members of the Enterobacteriaceae family are
moderately in size, gram-negative rods .
-they share a co
mmon antigen (enterobacterial common antigen)
-are either nonmotile or motile with peritrichous
flagella
-do not form spore.
-all members can grow rabidly, facultative
anaerobic) on variety of nonselctive media(e.g.blood agar) and selective
(e.g.macConkey agar).
-the Enterobacteriaceae have simple nutritional
requirements, ferment glucose.
-catalase
+ve, oxidase –ve.
-the absence of cytochrome oxidase activity is
important characteristic , because it can be measured rabidly with simple test
and is used to distinguish the Enterobacteriaceae from many other fermentative
and nonfermentative gram-negative rods.
-a few exceptions to these rules exits (e.g.
plesiomonas shigelloides is oxidase +ve, klebsiella
granulomatis can not be cultured on traditional
media.
-the ability to ferment lactose has been used to differentiate
lactose-fermenting strains(e.g.
Echerichia, klebsiella, enterobacter, citrobacter ,
serratia spp) from strains that do not ferment lactose or do so slowly(e.g.
proteus, salmonella, shiglla, yersinia spp).
-resistance to bile salts in some selective media
has been used to separate enteric pathogen(e.g. shigella, salmonella) from
commensal organisms that are inhibited by bile salts(e.g. gram+ve and some
gram-ve bacteria present in the gastrointestinal tract)
-some Enterobacteriaaceae have prominent capsules
(e.g. most klebsiella, some Enterobacter, Escherichia strains),
-the heat-stable lipopolysaccharide(LPS) is the
major cell wall antigen.
-most the Enterobaceriaceae are motile with the
exception of the common isolates Klebsiella, shigella, yersinia.
-the motile strains posses peritrichous flagella.
-there are other species of Enterobacteriaceae :
1)Enterobacter
2)Citrobacter 3)Serratia 4)Morganella
-These species subdivide as lactose fermenter Enterobacteriaceae.
-these
species caused infections rarely in immunocompetent patients.
-they are more common causes of immunocompromised
patients.
-e.g.
citrobacter koseri cause meningitis and brain abscesses in neonates.
|
coli Escherichia |
|
|
Characteristics |
·
Gr –ve bacilli ·
Non sporing , motile , non
capsulated bacilli but some strains are capsulate ·
Facultative anaerobes |
|
Habitat |
·
Common normal flora of human intestinal tract |
|
Transmission |
·
Foodborne route ·
Faecal – oral route ·
Endogenous
spread |
|
Pathogenesis |
·
Endotoxin = cause fever , leucopenia ·
Capsule (in some strains ) = antiphagocytosis ·
Enterotoxin = cause diarrhea |
|
Diseases |
·
Urinary tract infection (UTI) ·
Diarrhoeal
disease ·
Neonatal
meningitis ·
Septicemia ·
Gastroenteritis. |
|
Laboratory Identification |
·
Oxidase –ve , lactose fermentive ·
Grow well on macConkey
agar , DCA , XLD agar ·
Commercial kits available for full identification |
|
spp Proteus |
|
|
Characteristics |
·
Gr –ve bacilli ·
Non sporing highly motile , non capsulate bacilli ·
Facultative anaerobes ·
P.mirabilis is the most common species. ·
Produce large quantitiesof
urease.(this process raises the urine PH and facilitates the formation of
renal stones , the increased alkalinity of the
urine is also toxic. |
|
Habitat |
Common normal flora of the human intestinal tract |
|
Transmission |
·
Foodborne route ·
Faecal – oral route ·
Endogenous
spread |
|
Pathogenesis |
Endotoxin = cause fever , leucopenia |
|
Diseases |
·
UTI ·
Septicemia |
|
Laboratory Identification |
·
Oxidase –ve , non lactose fermentive ·
Grow well on macConkey
agar , DCA , XLD agar ·
Swarming colonies on solid media ·
Commercial kits available for full identification |
|
pestis Yersinia |
|
|
Characteristics |
·
Gr –ve bacilli
(cocobacilli ) (facultative
anaerobes) ·
Have a tendency for bipolar staining (in which the endof
the bacilli stain darker than the central part) ·
Nonsporing , non motile
bacilli . capsulate bacilli ·
Some species (e.g.Y.enterocolitica)
can grow at cold temp. |
|
Habitat |
·
Animal reservoirs are rodents such as rats |
|
Transmission |
·
Bacteria spreads between anmals by fleas ·
Major outbreaks in humans
result from exposure to infected rats ·
The rat flea carries
infection from rat to rat &
from rat to human ·
Bubonic plague is not transmitted from person to person ·
Pneumonic plague spread
from person to person by droplets
(airborne route ) |
|
Pathogenesis |
·
Intracellular murine toxin
= causing irreversible shock and
death ·
Capsule (f1) = antiphagocytosis ·
The V/M antigen = specific protein act as antiphagocytosis & promote
intracellular growth of the bacteria |
|
Diseases |
PLAGUE : 1.
is normally
azoonotic disease of rodents that exists in 2 kinds of epidemic centers 2.
permanent but relatively
resistant rat population (wild rat) 3.
temporary but susceptible
rat population (domestic rats ) 4.
epidemics of plague
usually occur in crowded areas
poor sanitation ·
bubonic plague : 1.
bacteria multiply at the entery site in the
skin 2.
bacteria spread via the
lymphatics to lymph
nodes 3.
2 to 6 days after the flea bite occurs , lymph nodes become very tender , and enlarge to form buboes with haemorrhagic
inflammation 4.
death rate is about 75% in untread bubonic plague ·
pneumonic plague (black death) : 1.
bacteria disseminates from lymph nodes by way of the |
|
|
bloodstream
to the spleen , liver ,l lungs 2.
pneumonic plague can be transmitted by respriatory route but Iis 3.
death tate is nearly
100%in untreaed pneumonic plague |
|
Laboratory Identification |
·
stained smears should show bipolar staining ·
organism can be grow from
aspirtes of enlarged buboes , or from sputum in case of pneumonic plague ·
colonies are grayish ,
mucoid & rough colonies may be noted ·
the organism are not
fastidious ; it can be rrown on
routine media ·
oxidase –ve . |
|
Pasteurella |
|
|
Characteristics |
·
Garm –Ve
bacillus ·
Non spore
forming ·
Non motile ·
Faculitative anaerobic ·
Fermentative coccobacilli . ·
Most common P.multocida and P.canis |
|
Habitat |
|
|
Transmission |
|
|
Pathogenesis |
|
|
Diseases |
·
Bite wound infection . ·
Chronic pulmonary disesase ·
Bacteremia ·
Meningitis |
|
Laboratory Identification |
·
Grow well in blood and choclate agar . and poorly in macConkey agar . ·
After over night
incubation in blood agar large
buttery colonies with musty odor cuase by product indole |
|
pneumoniae Klebsiella |
|
|
Characteristics |
·
Gr –ve bacilli ·
Non sporing , non motile ,
prominent capsulate that responsible for the
mucoid. ·
Facultative anaerobes ·
Formerly called (Donovaina granulomatis) |
|
Habitat |
·
Common normal flora of the
human intestinal tract & oropharynx |
|
Transmission |
·
Foodborne
route ·
Faecal – oral route ·
Endogenous
spread |
|
Pathogenesis |
·
Endotoxin = cause fever , leucopenia ·
Capsule =
antiphagocytosis |
|
Diseases |
·
UTI ·
Neonatal
meningitis ·
Septicemia ·
Pneumonia (Rare ) |
|
|
·
Oxidase –ve , lactose fermentive |
|
Laboratory Identification |
·
Grow well on macConkey agar , DCA , XLD
agar |
|
|
·
Large mucoid colonies |
|
|
·
Commercial kits available for full identification |
|
spp Brucella |
|
|
Characteristics |
·
Gr –ve small coccibacilli ·
Non sporing ,non motile , non capsulated bacilli ·
Intracellular pathogen ·
Slow growth requirements ·
Fastidious. ·
Is member of the alpha –proteobacteria group ·
Strictly
aerobic ·
Does not ferment carbohydrates. ·
Four species: 1)Brucella
abortus 2)Brucella melitensis. 3)Brucella
suis 4)Brucella canis |
|
Habitat |
·
Chronic infection in domestic animals |
|
Transmission |
·
Contaminated milk or other unpasteurized dairy
products ·
Direct contact |
|
Pathogenesis |
·
Invasion of the body by
brucella results in lymphatic
dissemination of the bacteria ·
As regional lymph nodes
become infected , the brucella are phagocytized , but they are capable of survive & intracellular
multiplication inside phagocytic cells ·
As phagocytic cells die ,
brucella , are released into the blood stream and intracellularly , establish
localized infection in bone marrow
, liver &spleen , and thus hide from host defence |
|
Diseases |
·
Undulant fever (malta fever or brucellosis ) 1. patients
frequently present with PUO 2.
chronic , debilitating
febrile illness usually without any localizing signs 3.
intracellularly , bacteria localize and cause |
|
|
granulomas
lesions in the spleen , liver bone marrow & lymph nodes 4.
patients presents with
intermittent fever & profound
weakness , chills , sweats , headache , backache 5.
two types of infection
occur ; (acute infection ) or (chronic infection – lasting 12 months ) |
|
Laboratory Identification |
·
requiring complex growth
media like :glucose serum or liver infusion broth or agar ·
usuakky require 3-5 days incubation ·
blood provides the best material for culture ·
grow occasionally on MacConkey agar. ·
Oxidase +ve ·
Urease+ve |
|
tularensis Francisella |
|
|
Characteristics |
·
Gr – Ve small bacilli (coccobacilli) ·
Often showing bipolar staining ·
Non motile , non sporing , capsulate , coccobacilli ·
Strick aerobic ·
Fastidious. ·
Two species of Francisella spp: 1)F.tularensis 2)F.philomiragia *require cystein for growth. |
|
Habitat |
Widely found in animal reservoirs |
|
Transmission |
·
biting arthropods ·
direct contact with infected animal tissue ·
ingestion of contamination food or water ·
inhalation of aerosols |
|
Pathogenesis |
·
F.tularensis is highly infection ; penrtration of the
skin or mucous membranes or inhalation of 50 organism can result in infection ·
F.tularensis is an intracellular pathogen of
phagocytosis cells ·
Capsule= phagocytosis |
|
Diseases |
·
tularemia (sometimes
called rabbit fever or glandular fever or tick fever or deer fly fever ): 1- clinical presentation dependes on the route of infection 2- a
plague – like disease of rodents |
|
Laboratory Identification |
·
blood is
taken for serological tests ·
growth dose not occur in most ordinary bacteriological media
but small colonies appear in 1-3
day on glucose , blood agar incubated at 37
C under aerobic conditions ·
culture on
cystein-supplemented media(e.g.choclate agar, BCYE agar ) is specific. ·
Culture on cystin blood agar. ·
Culture on cystin glucose agar ·
BCYT= buffered charcoal yeast extract. |
Haemophilus
-the family
pasteurllaceae spp are 1)Haemophilus
2)Actinobacillus 3)Pasteurella
-the members
of this family are:
*Small
gram-negative
*Non-spore
*Nonmotile
*Aerobic or facultative anerobic rods
-most members of this
family have fastidious growth
needs, requiring enriched media for growth.
-members of the genus Haemophilus
are the most commonly and
significant human pathogen.
|
influenzae Haemophilus |
|
|
Characteristics |
·
Gr –ve bacilli (coccobacilli) ·
Non sporing , non moitile
, ·
The surface of many(but
not all) strains of H.influenzae is covered with polysaccharide capsule. ·
Facultative anaerobes ·
Haemophillic bacteria ·
Pyogenic (pus –producing ) bacteria ·
Plemorphic. ·
Is the most species of
Haemophilus that cause disease. ·
The cell wall structure is typical of other gran- negative rods(lipopolysaccharide with endotoxin
activity is present in thecell wall. ·
Is fermentive. |
|
Habitat |
·
Human upper respiratory
tract as anormal flora but many also cause respiratory disease , usually as
secondary invader |
|
Transmission |
·
Airborne
route |
|
Pathogenesis |
·
Endotoxin = causing damage
to the epithelial cell of the upper respiratory tract ·
Capsule =
antiphagocytosis ·
IgAase = degrades IgA
antibodies that is key host
defense mechanism in mucous membrane ·
H.influenzae type b is most virulent with RPR(polyribitol
phosphate) in capsule ·
Pili=adhere to host cells. |
|
Diseases |
·
Cause severe infection in children ( acute meningitis ) ·
H.influenzae serotype was
responsible for more than 95% of all Haemophilus infection. ·
Serotypes C and F and noncapsulated |
|
|
H.influenzae diseases. ·
Cause chronic , less
severe infection beyond age 6
(,pneumonia,Otitis media ,
sinusitis , bronchitis ) in older
children and adult ·
This bacteria is the most common cause of bacterial
meningitis in children from 5
months to 5 years of age ·
Mortality rate of
untreated H. influenzaw meningitis may be
up to 90% ·
Act synergistically with viral
infection , predisposing to severe
haemophilus infection , the incidwnce increase during influenza outbreaks |
|
Laboratory Identification |
·
Require enriched media such as blood or chocolate agar
or(Levinthals agar) ·
Need both od tow growth factor (factor V-X) 1.
heat stable X factor = hemin or some other iron
– containing prophrin 2.
heat stable V factor = nicotinamide adenine nucleotide (NAD) ·
grow poorly in the absence of oxygen & growth is enhancedin
an atmosphere with add CO2 ·
on chocolate or blood agar
: a streak of staph . aureus across the plate produce V factor and enlarges
the size of adjacent colonies of H . inflluenzae = satellitism phenomena ·
colonies are small , translucent , non hemolytic ·
microscopy is sensitive test for detecting H.influenzae
in(cerebrospinal fluidCSF .synovial fluid, and lower respirtory specimens. |
|
aeruginosa Pseudomonas |
|
|
Characteristics |
·
Gr –ve bacilli arranged in pairs. ·
Non sporing , motile , capsulate (polysaccharide) ·
Obligae aerobes ·
Nonfermentative. ·
The presence of cytochrome
oxidase(detected in rabid,5minute
test) in pseudomonas species is used to differentiate them from the
Enterobacteriaceae ·
Some pseudomonas produce
diffusible pigments (e.g.pyocyanin
[blue],fluorescein[yellow],pyorubin[raddish- brown] ·
P.aeruginosa is the most common type. |
|
Habitat |
·
Widley distributed in water , soil & moist areas ·
Carriage as a part of normal gut flora in higher proporation of hospital inpatients |
|
Transmission |
·
Direct contact ·
Endogenous
spread |
|
Pathogenesis |
·
Exdotoxin = cause fever , leucopenia ·
Exdotoxin A = inhibit protein synthesis ·
Exdotoxin S = inhibit protein synthesis ·
Protease & Elastase = destruction of tissue ·
Capsule=inhibits
antibiotics+suppresses neutrophil and lymphocyte activity. ·
Pili=adhesin |
|
Diseases |
·
UTI ·
Septicemia ·
Pneumonia ·
Burn wounds & wound infection ·
Ear and eye infection |
|
Laboratory Identification |
·
Oxidase +ve , lactose fermentive ·
Identified by colonial
characteristics(e.g. hemolytic, green pigment, grape like odor) ·
Grow well on macConkey
agar , DCA , XLD agar ·
Commercial kits available for full identification |
|
spp Acinetobacter |
|
|
Characteristics |
·
Gr –ve bacilli (plump coccobacilli) ·
Non sporing , non moitile
, capsulated coccobacilli ·
Strictly
aerobic ·
The genus can be subdivided into two groups: 1)glucose
oxidizing species(A.baumannii) 2)glucose nonoxidizing species(A.lwoffii) |
|
Habitat |
Survive
in moist surfaces. Including respiratory therapy equipment . And survive on dry surface including human skin(the latter feature is unusual for gram-negative rods) |
|
Transmission |
·
Direct contact ·
Indirect contact via invasive devices |
|
Pathogenesis |
·
It has ability to colonize on internal surfaces of the
invasive devices |
|
Diseases |
*pulmonary infection. *opportunistic pathogens that cause: Respiratory tract unfection and urinary tract infection and wound and
septicemia. |
|
Laboratory Identification |
·
Oxidase –ve ·
Grow well on simple media |
|
Bacteriodes |
|
|
Characteristics |
·
Gram –Ve bacillus . ·
Obligate anaerobic . ·
Most common species is b.fragilis . ·
Polymorphic in size and shape . · |
|
Diseases |
·
Intraabdominal infection . ·
Gynecologic . ·
Skin and soft tissues infection . ·
Bacteremia . |
|
Laboratory Identification |
·
Grow rapidly (( detected in 2 days )) . ·
Stimulated growth in 20% bile . |
|
pertussis Bordetella |
|
|
Characteristics |
·
Gr –Ve extremely smaal bacilli ·
Non sporing , non motile bacilli ·
Capsulate
bacilli ·
Obligate
aerobes |
|
Habitat |
Human respairatory tract |
|
Transmission |
·
airborne
route ·
direct contact |
|
Pathogenesis |
·
tracheal cytotoxin =
inhibits DNA synthesis in ciliated cells ·
fimbrial antigen (pili ) =
permit the adherence of bacteria to the
ciliated epithelium of the respiratory tract ·
endoxin = causing damage
to the epithelial cells of the
upper respiratory tract ·
pertussis
toxin |
|
Diseases |
·
whooping cough (pertussis
) by Bordetella pertussis. ·
Mild pertussis by Bordetella para pertissis. ·
Respirtory disease in dogs by Bordetella bronchiseptica. |
|
Laboratory Identification |
·
slow growing &
fastidious in its growth
requirement ·
bordet – gengous agar or blood – charcoal agar ·
requires media supplemented with charcoal,
starch, blood, or albumin. |
|
|
·
requires 3-5 day incubation in moist atmosphere ·
it dose not require X and V
factors on culure ·
oxidase amino acids. ·
Not ferment carbohydrates. |
Differential
characteristics of Bordetell species
|
characteristics |
B.pertussis |
B.parapertussis |
B.bronchiseptica |
|
oxidase |
+ |
- |
+ |
|
urease |
- |
+ |
+ |
|
motility |
- |
- |
+ |
|
On sheep agar |
- |
+ |
+ |
|
On macConkey agar |
- |
-/+ |
+ |
|
|
|
|
|
