Micromodules Gram positive rods

Question 1

Do the Bacillus family need oxygen?

Answer 1

Not necessarily; they’re facultative anaerobes/aerobes, so they can survive without oxygen if they have to

Question 2

Do the Bacillus family form endospores? Do the Costridium family form endospores?

Answer 2

Yes and yes

Question 3

What disease does Bacillus anthracis cause, and where does it originate?

Answer 3

It causes anthrax, and is a disease of livestock/grazing animals

Question 4

What disease does Bacillus cereus cause, and where does it originate?

Answer 4

It’s a cause of food poisoning, and originates in poorly cooked/reheated rice dishes

Question 5

In what three ways are Gram positive rod bacteria classified?

Answer 5

1. Relationship with oxygen
2. Morphology
3. Whether they form endospores or not

Question 6

When are endospores formed and what’s their purpose?

Answer 6

Form when bacteria encounter adverse environmental conditions, and act as a tough shell which can resist heat and drying. These allow bacteria to survive for long periods of time in poor conditions

Question 7

What does the term actinomycetes refer to?

Answer 7

Gram positive rod species with filamentous/branching morphology

Question 8

What are the three routes of acquisition of Bacillus anthracis, and which one has the highest untreated mortality?

Answer 8

Cutaneous - 20% UM
Inhalation - 100% UM
Gastrointestinal - 100% UM

Question 9

What are the four most important species of Clostridium which cause severe disease?

Answer 9

C. perfringens, C.tentani, C.botulinum and C.difficile

Question 10

What does Clostridium perfringens cause, and where does it originate?

Answer 10

Some strains cause gas gangrene (liquefactive necrosis of skin and underlying muscle), some cause food poisoning
C.perfringens is found in the soil, spores may contaminate wounds

Question 11

What are the different forms of enteric disease caused by C.perfringens?

Answer 11

Clostridial food poisoning: bacteria in beef/pork/chicken, which cause crampy abdominal pain and diarrhoea which is self limiting.

Necrotizing bowel disease, which is associated with inadequately cooked pork inNew Guinea feasts. It causes necrosis of the Bowel or Bowel segment

Question 12

What disease does C.tetani produce and what is the mechanism of doing so?

Answer 12

Produces tetanus, characterised by muscle rigidity and severe spasms that can persist for weeks. It has a high mortality in absence of intensive care.
Mechanism: C. tetani produces a powerful neurotoxin which blocks inhibitory nerve impulses

Question 13

What disease does C.botulinum produce and what is the mechanism of doing so?

Answer 13

Produces Botulism, which involves flaccid paralysis of the eye, face and limb muscles, which can extend to the muscles of respiration, causing respiratory failure.

Mechanism: produces a powerful neurotoxin which blocks release of acetyl choline from motor nerve endings

Question 14

What does Clostridium difficile do?

Answer 14

Causes diarrhoea, which can range from severe to mild, and can be complicated by megacolon - a distended colon which may rupture.
Contraction of C difficile is associated with current/recent use to antibiotics, old age, hospitalisation or recent surgery

Question 15

What are some of the non-endospore forming, gram positive rods?

Answer 15

Lactobacillus, Listeria, Corynebacterium, Nocardia and Actinomyces

Question 16

Describe Lactobacillus

Answer 16

Large, regular gram positive rods. They’re facultative anaerobes, though some are obligate anaerobes.
Some are commensals of human GIT, vagina and mouth.
They are characterised b ability to convert glucose into lactic acid, lowering their environments pH

Question 17

In which body part do Lactobacilli play an important role?

Answer 17

The vagina. They maintain vaginal pH at 3.8-4.7, which prevents growth of some vaginal pathogens

Question 18

Where are Listeria found, which foods do they most often contaminate and why are they particularly tricky to kill off in food?

Answer 18

• Found in soil and water, and frequently carried by a number of animal species
• Raw cabbage, pasteurised milk, soft cheeses, undercooked chicken
• They can grow at 4 degrees, so refrigerated food may still contain live Listeria

Question 19

What type of pathogen are members of the Listeria genus?

Answer 19

Opportunistic

Up to 20x greater risk of contraction if you’re pregnant

Question 20

Which species of Listeria causes the most human disease?

Answer 20

Listeria monocytogenes

Question 21

What are outcomes of Listeria infection in healthy people?

Answer 21

• Asymptomatic

- Flu-like illness, with fever aches and pains

Question 22

What are outcomes of Listeria in pregnant women and a neonate?

Answer 22

Pregnant women:
Asymptomatic/flu-like
or
miscarriage, prematurity or stillbirth.

Neonate:
Severe disease with 2-30% mortality, sepsis, pneumonia, meningitis, granulomatous infantiseptica - a rare form of disseminated disease, with widespread microabscesses and granulomas, pneumonia and hepatosplenomegaly.

Question 23

Describe the morphology of Corynebacterium and where they are found on the human body

Answer 23

Tiny, irregular gram positive rods
Commensals at various body sites ,especially the skin.
Opportunistic infections if can penetrate outer defenses

Question 24

Which organism causes Diphtheria?

Answer 24

Corynebacterium diphtheriae

Question 25

What is the current mortality rate for Diphtheria, and in which time period did it cause more deaths than any other infectious disease?

Answer 25

• Mortality reaches 30%

- In the early 1900s in Australia

Question 26

Describe manifestations of infection by Diphtheria

Answer 26

-Primarily infects Pharynx, but also causes severe systemic disease due to toxin production.
-It causes inflammation, swelling and exudation that leads to the formation of an adherent, obstructive ‘membrane’ which may extend down the trachea, making asphyxiation a common cause of death
-The organism growing in the pharynx also produces a powerful exotoxin, which is absorbed into the body and affects the heart and cranial and peripheral nerves.
This can lead to myocarditis and cardiac arrhythmias which may lead to cardiac failure, and neuritis and paralysis

Question 27

Describe the classification of Actinomycetes

Answer 27

Filamentous or branching bacteria which may resemble fungi microscopically, or when growing on agar plates

Question 28

What are the differences in naming of mycetomas?

Answer 28

Name depends on whether grown by bacteria: Actinomycotic mycetoma or by fungi: Eumycotic mycetoma.

Question 29

What is a mycetoma?

Answer 29

Chronic, slowly developing lesions of the skin and underlying tissue, that typically result from minor trauma during which soil or organic material penetrates the skin.
This produces an infection with the following characteristics:
-Slow development (months/years)
-Swelling and thickening
-Destruction of skin, subcutaneous tissue, facia and bone
-Pus discharging from multiple sinuses
-Deformity of affected part, usually the foot = Madura foot.

Question 30

What types of disease does the genus Nocardia cause?

Answer 30

It’s an aerobic Actinomycetes, so can produce a mycetoma in a host, but is more likely to cause opportunistic infections in immunocompromised hosts. If inhaled, can cause a slowly progressing lung infection, and often disseminates to the brain

Question 31

Which anaerobic Actinomycetes causes Actinomycosis?

Answer 31

Usually A.israelii.
Actinomycosis is a very chronic, slowly developing disease which occurs when there’s a mucosal breach, allowing access to submucosal tissue. The infection is usually polymicrobial

Question 32

What are the three forms of Actinomycosis?

Answer 32

Cervicofacial, thoracic and abdominal/pelvic.

Inflammatory responses to the bacteria usually result in a suppurative, granulomatous mass