Lesson 3: Genus Actinobacteria, Nocardia & Dermatophilus

Question 1

General description:

Answer 1

• Gram-positive bacteria many species with branching filaments
• Slow growth on laboratory media
  -Opportunistic pathogens producing diverse inflammatory responses

Question 2

Species of actinobacteria:

Answer 2

Actinomyces, Arcanobacterium and Actinobaculum species

Question 3

-anaerobic or facultatively anaerobic
-morphologically heterogeneous
-non-spore-forming, non-motile
-require enriched growth media for growth

Question 4

modified

Answer 4

Ziehl-Neelsen-negative (MZN)

Question 5

colonize

Answer 5

mucous membranes

Question 6

usual habitat:

Answer 6

mucous membranes of animals

Question 7

surrounded by club-shaped structures. These structures are part of the host response to this chronic infection.

Answer 7

Actinomyces bovis

Question 7

o name changes:

Answer 7

-Trueperella pyogenes —–Arcanobacterium pyogenes

-Corynebacterium pyogenes Actinomyces pyogenes

Question 8

Nocardia species

Answer 8

o aerobic, non-motile
o Gram-positive
o spores from aerial filaments
o growth on Sabouraud dextrose agar
o modified Ziehl-Neelsen-positive (MZN) due to mycolic acid in cell wall
o long, slender, branching filaments with a tendency to fragment into rods and cocci in smears.

Question 9

habitat:

Answer 9

o soil saprophytes

Question 10

 Dermatophilus congolensis

Answer 10

o Gram-positive, filamentous and branching
o aerobic and capnophilic
o motile coccal zoospores about 1.5μm in diameter.
o no growth on Sabouraud dextrose agar
o found in scabs and in foci on skin of carrier animals

Question 10

o associated with equine nocardiform placentitis, leading to loss of the foal in approximately 50% of cases.

Answer 10

 Crossiella equi

Question 10

 Trueperrela pyogenes produces pyolisin,

Answer 10

a haemolytic exotoxin

Question 11

which is cytolytic for several cell types including neutrophils and macrophages, and is dermonecrotic and lethal for laboratory animals.

Answer 11

haemolytic exotoxin

Question 11

 T. pyogenes also produces

Answer 11

• produces adhesins such as
• neuraminidases, and other - extracellular matrix-binding proteins and fimbriae

Question 11

 The usual mode of infection by Nocardia sp. is by

Answer 11

• inhalation but it may also occur through skin wounds or via the teat canal.

Question 12

survive intracellularly

Answer 12

 Virulent strains of N. asteroides

Question 13

The production of superoxide dismutase and catalase and the presence of a thick peptidoglycan layer in the cell wall confer resistance to microbiocidal activity of phagocytes

Question 14

Invasion leads to an acute inflammatory response characterized by large numbers of neutrophils which ultimately form microabscesses in the epidermis.

Question 14

when activated, produce germ tubes and these develop into filaments which invade the epidermis.

Answer 14

 Dermatophilus congolensis zoopores

Question 14

Factors that depress specific immune responses, including

Answer 14

• intercurrent diseases and pregnancy,
  –may increase host susceptibility to dermatophilosis.

Question 15

A cyclical pattern of invasion of regenerating epithelial cells by the pathogen, together with serous exudation and microabscess formation, leads to the

Answer 15

development of raised scab- like crusts containing numerous branching filaments.

Question 15

Diagnosis

Question 16

Actinomycetaceae

Answer 16

 Gram-staining or modified Ziehl-Neelsen (MZN)

Question 17

 Histopathological examination of specimens from lesions caused by

Answer 17

• A. bovis reveals aggregates of filamentous organisms surrounded by eosinophilic club- shaped structures.

Question 18

 Identification criteria for isolates:

Answer 18

 Pitting of a Loeffler’ s serum slope ( T. pyogenes)

 Urease production (A. suis).

Question 19

Nocardia sp.

Answer 19

 Gram-staining and MZN methods

 Bacterial culture on blood agar or on selective growth-enhancing media such as charcoal– yeast extract medium