Small gram negatives and gram negative anaerobes Flashcards
Brucella- general characteristics
Small gram negative coccobacili
non-motile, non-sporing, non-fermentative, aerobe
oxidase positive
visualized by modified Z-N stain
requires complex media for growth (i.e. blood)
growth enhanced by CO2
predilection for male and female repro tracts
organism can be acquired via inhalation, ingestion or direct contact
B. abortus
Cattle: contagious bovine abortion, orchitis,
Sheep goats pigs: sporadic abortion
humans: undulant fever- remitting fever localized to musculoskeletal system
B. melitensis
Sheep and goats: orchitis and obrtion
HumansL malta fever
B. ovis
Sheep: abortion and epidiymitis
B. canis
dogs: abortion, epididymitis and arthritis
Humans: mild infection
B. suis
pigs: abortion, infertility, orchitis, arthritis
humans: undulant fever
B. neotomae
rodents
Brucella pathogenesis
Prevention of phagolysosome fusion to allow intracellular survival
Penetrate mucosa (usually GI)–> move to regional LN via macrophages and multiply in LN
Phaogcytosis/invasion–> proliferation/persistence/ bacteremia–> dissemination
tropism for repro tissue
Milk becomes infectious if disseminated to udder.
B. melitensis genome
2 chromosomes with 2300 genes.
closest relatives are plant symbionts and plant pathogens
Lacks many of the expected virulence systems: no TTSS, no fimbriae, no secreted toxins, no capsule
Pathogenesis depends on intracellular survival.
Putative virulence genes identified
Type IV secretion system- diff. in structure but it also injects effector proteins.
Brucella pathogenesis
We don’t know a lot about brucella virulence
intracellular pathogen- many cell types
survives within the macrophages (and also epithelial and endothelial cells)
-inhibits phagolysosome fusion and actively replicates in macrophore cells.
Preferred carbon source is erythritol- present in high concentration in placenta of cattle, sheep goats and pigs, however, if you knock out erythritol in mice, doesn’t change the outcome, but erythritol isn’t the predominant CHO in mouse placenta.
Siderophore, iron uptake.
Brucella: persistent infection
Surivival within the macrophages: inhibits phagolysosome fusion
Type IV secretion system
Cylic Beta 1,2-glucan in brucella virulence factor required for intracellular survival
Doesn’t alarm the host- brucella LPS 1000 times less pro-inflammatory than E. coli. Body doesn’t recognized it well–>stealth pathogen.
Bovine brucellosis in GB: eradication
1934- ~40% of cattle herds brucella positive
a a free calf vax scheme S19 vaccine in 1962
voluntary attested herd scheme 1967
compulsory area eradication 1971
disease free, vaccine program ended in 1979
brucellosis free status gained in 1991 from EU
Human brucellosis
no human to human transmission
zoonosis via direct contact or unpasteurized dairy products
One of the leading zoonoses worldwide.
Brucella screening
detect antibody in serum (milk against brucella LPS)
Milk ring test: test milk using labelled antibodies–> get precipitation if there are anti-brucella antibodies.
ELISA, Serum agglutination test
False positives: ABs cross react with LPS of other bacteria; shares similar O group to Yersinia enterocolitica
Brucella vaccines
live vaccines, chemical mutagens
smooth strain: not attenuated for humans due to intact LPS
rough strain: non intact LPS- lack O side chain. look rough on culture.
useful to distinguish between vaccinated animals and naturally infected. rough strain is obviously vaccinated.
Bordetella-general characteristics
small gram negative coccobacilli strict aerobe oxidase positive non-sporing, most motile don't ferment CHOs respiratory tract pathogens mammals and birds
B. bronchiseptica
Dogs: kennel cough
Cats: resp infections/ acute pneumonia
Pigs: progressive atropic rhinitis with Pasturella multocida, bronchopneumonia
Many species: respiratory infections
B. parapertussis
Sheep: resp infections
Humans: whooping cough
not zoonotic infection- separate sheep/human strains
B. avium
turkeys: resp infections
B. pertussis
human whooping cough
B. bronchiseptica cultural characteristics
grows on macconkey agar
NLF–> produces urease, lowers pH–Characteristic yellow.
since it grows on macconkey agar and doesn’t produce pink colonies (NLF)–useful to distinguish from most gram negative resp. pathogens
Strategies of extracellular pathogens
Likes to survive outside cells counteract complement counteract phagocytes acquire nutrients bordetella has toxins involved with pathogenesis.
Adhesion of B. bronchispetica to ciliated respiratory cells
ciliated epithelial cells trap organisms–> get swallowed.
bordetella adheres to these cells
organisms not being swept back. bordetella gets stuck to the mucociliary elevator.
Pathogenesis of bordetella
Initial attachment of B. bronchiseptica to ciliated cells- done by specific adhesins
Tight adhesion to cilia
Production of toxins
paralyse cilia
Loss of cilia
interference with innate and specific IR
Accumulation of mucus–> presentation of disease in kennel cough
Bordetella virulence factors
Fimbriae: bind to tissue
Filamentous hemagglutinin (FHA)
Pertactin- outer membrane protein
These three act as adhesins to attach to host tissue.
Adenylate cyclase toxin, tracheal cytotxin and dermonecrotoxin all cause tissue dmage and counteract host defences
TTSS: subversion of host defense mechanisms
Adenylate cyclase toxin
adenylate cyclase= bacterial enzyme RTX toxin (repeat structure): hemolysin, damages WBCs
RTX binds to host cell surface. Adenylate cyclase enters and activates calmodulin. This increases the cAMP in tissue causing a fluid influx into the tissue (edema). This decreases chemotaxis, and decreases phagocytosis
Tracheal cytotoxin
not a classic toxin. sheds TCT (fragment of peptidoglycan) and LPS. These have effect on epithelial cells. Bind and internalize into epithelial cells. Increase IL-1 which increases nitric oxide. The nitric oxide is responsible for the cilia loss.
Increases susceptibility to other respiratory infection as well–> secondary bacterial pneumonia.
Regulation of bordetella virulence
2 compoonent regulatory system
BvgS- sensor kinase- phosphorylate and de-phosphorylate- present in membrane and
BvgA- present in cytoplasm- transcriptional activator. BvgA acts as a thermostat. At 37 degrees, S phosphorylates A and virulence genes are expressed. At 25 degrees, A is de-phosphorylated and the virulence genes are not expressed.
Having the virulence genes on all the time is wasteful.
Pathogeneis of atropic rhinitis in pigs
Synergistic infection with pasturella multocida and bord. bronchiseptica
Initial attachment of B. bronch to ciliated cells
Tight adhesion to the cells–> production of toxin–> paralyse cilia
loss of cilia–> interference with innate and specific IR, accumulation of mucus.
Colonisation of toxigenic p. multocida types A or D–> P. mutlocida toxin responsible for destruction of turbinates.
Bronchiseptica vaccines
available for cats and dogs
live attenuated, not defined
administered intranasally- produces mucosal immunity where organism tries to infect.
mucosal IgA important for immunity
Gram negative anaerobes
non-sporing, gram negatives, anaerobic
Anaerobic bacterial infections
Anaerobic bacteria require anaerobic conditions, need negative redox potential Eh for growth.
They can grow in lumen of the LI and rumen. Also found on any mucosal surface. Large numbers in the mouth, gut, genitourinary system
Elsewhere (if not on mucosal surface), they require loss of blood supply or necrotic conditions or population of aerobes/facultative anaerobes which reduces the oxygen tension.–> often cause mixed infection.
Anaerobic, non-sporing gram negative species
Fusobacterium necrophorum Dichelobacter nodosus Bacteroides sp. Prevotella sp. Porphyromonas sp.
Polymicrobial infections
Foot rot: dichelobacter nodusus (mainly caused by this but need damage from other bacteria)
fusobacterium necrophorum
a. pygoenes
spirochetes, and others
Abscesses: bacteroides fragilis and e. coli (facultative aerobe)
Pathogenesis of foot rot
Predisposing conditions: wetting, trauma, etc
primary colonisation: facultative anaerobe (e.g. trueperella pyogenes)
secondary colonisation: F necrophorum–local superficial inflammation (dermatitis)
Tertiary colonisation: Dichelobacter nodosus- causes severe symptoms- ulceration, hoof destruction–> chronic lameness
Dichelobacter nodosus
strict anaerobic gram negative, non-sporing
long-clubbed ends
footrot in sheep
type IV fimbriae- can’t be pathogenic w/out this
Several proteases to digest hoof tissue
pathogenicity island?
Fusobacterium necrophorum infections
Cattle: calf diphtheria- necrotic laryngitis, post-partum metritis, hepatic abscesses, black spot of teat.
Pig: necrotic rhinitis
horses: necrobacilliosis of lower limb, thrush of hoof.
Fusobacterium
obligate anaerobe, non-sporing, gram negative (pleomoprhic) rods
virulence factors: leukotoxin, hemolysins and proteases
Bacteroids, prevotella and porphyomonas species
gram negative rods, obligate anaerobes
All pyogenic, may cause abscesses, soft tissue infections
pus is foul smelling
Some bacteroides fragilis strains produce an enterotoxin and cause cause diarrhea in lambs, calves, piglets, foals and children.
produce BLACK pigment on culture.
