GRAM NEGATIVE BACILLI

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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	-	-/+	+

 

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