GPB

Question 1

What cellular feature do the genera Bacillus and Clostridium have in common?

Answer 1

Large (brick-shaped) rods

Question 2

If a gram smear result was described as pallisading GPB, what does this mean? (i.e. what would you see?)

Answer 2

form groups that look like Chinese lettering or picket fence (III=LV)

Question 3

(a) Which GPB produces sulphur granules and (b) in what type of specimen would they normally be found? (c) Describe the microscopic composition of the granules.

Answer 3

a) Actinomyces israelii
b) (chronic) Abcess in pus
c) microcolonies of GPB embedded in Ag-Aby complexes

Question 4

(a) What incubation conditions does A.israelii require for growth and (b) how could you recognise this organism in the clinical microbiology laboratory?

Answer 4

a) AnO2

b) Media: small gel clumpy colonies on agar (long incubation). Microscopy: branching/filamentous rods. Catalase neg

Question 5

Describe the main lab. characteristics of Nocardia asteroides. i.e. How would you identify/suspect its presence both microscopically and in culture?

Answer 5

• Weak GPB (beaded) w/ branching filaments
• wet/damp soil odour
• catalase pos
• Weak/partial acid fast
• yellow/orange to grey/white colonies w/ irregular shapes & folds

Question 6

(a) What is the name of the infection caused by Erysipelothrix rhusiopathiae? (b) How is this disease best diagnosed? (c) treatment

Answer 6

a) Erysipeloid (cutaneous infection of skin on hands, forearms)
b) biopsy specimen
c) self-limiting 2-4wks

Question 7

What significant laboratory features would allow you to presumptively identify each of the 4 main pathogens if no MALDI-TOF were available?
- Actinomyces, Nocardia, Erysipelothrix, Propionibacterium

Answer 7

• Actinomyces: Branching/filamentous rods, catalase neg, AnO2
• Erysipelothrix: curved rods, catalase neg, facultative
• Nocardia: branching rods, catalase pos, O2

Question 8

For each of the four main pathogens, list the clinical site/conditions that these organisms are usually associated with in respect of human infection?

Answer 8

• Actinomyces: above shoulder (head, face, neck)
• Erysipelothrix: Cutaneous infection (hands, fingers, forearms)
• Nocardia: lungs or skin lesions
• Propionibacterium: acne

Question 9

What is the HACEK group?

Answer 9

* org. responsible for infective endocarditis 
Haemophilus parainfluenzae
Actinobacillus/Aggrigatebacter
Ccardiobacterium hominis
Eikenella corrodens
Kingella sp.

Question 10

a) Generally, what is the main clinical Hx that preceeds infection with the HACEK group? (b) What is the common type of systemic infection that all are usually associated with?

Answer 10

(a) HACEK = human oropharyngeal flora (=> blood stream via)
- infection from poor oral hygiene &/or
- immunocompromised and/or
- having dental procedures
- bite wounds
(b) Edocardial infections

Question 11

You identify a GNB in a blood culture with a typical HACEK Hx by direct microscopy. It takes a several days to grow so you suspect that it is one of these organisms. Once culture plates are available, summarise/explain how you could separate the 7 orgs from this lecture in the clinical laboratory using the minimal number of tests. Assume that each grows with a typical colony morphology and exhibits any typical odours.

Answer 11

Haemophilus sp: GNCB, only grow CHOC @ CO2
Aggregatibacter actinomycetemcomitans: GNCB, small colonies w/ ~star, catalase pos* (only pos in group)
A. aphorophilus & A. paraphrophilus: GNCB, yellowish w/ glue smell
Cardiobacterium hominis: GNB w/ purple poles (lollipop)/ rossette, colonies w/ rough zone,
Eikenella corrodens: GNB, bleach smell, clear colonies w/ spreading growth
Kingella sp.: GNB/GNCB, NG MAC, catalase neg, oxidase pos

Question 12

Given the mobility of the blood stream, what virulence factors are likely associated with the ability of the HACEK organisms to colonise, persist and cause infectious endocarditis?*

Answer 12

• fimbrae= attachment
• pili & lectin = adherance
• enzymes: collagenase, protease, Ig degrading
• toxins: leucotoxins, LPS (enterotoxin)

Question 13

In what clinical situations should blood culture be requested as a routine investigation?*

Answer 13

• Hx of dental procedures/ infection in mouth/ bite wounds
• immunocompromised
• Detection of bacteremia/septicemia

Question 14

Why are 100% of blood cultures positive in patients with IE (infectious endocarditis)?*

Answer 14

Bc travel in blood (bacteremia)

Question 15

Name 4 antimicrobials that have been demonstrated to have a 100% effectiveness against all of the HACEK organisms?*

Answer 15

B-lactams: Pc*, AMC, 3GC

Doxycyline

Question 16

Based on the discussion within this lecture, what is the main impediment(issue) to obtaining an accurate organism ID for members of the HACEK group by MALDI-TOF?

Answer 16

the species of an organism must be in the database for it to be ID accurately