Bacterial Oxygen Requirements

Question 1

Oxygen is essential for

A - obligate aerobes

B - obligate anaerobes

Answer 1

A

Question 2

Why is oxygen is essential for obligate aerobes?

Answer 2

Serves as the final electron acceptor in electron transport chains which produce most of the ATP in these organisms.

By contrast oxygen is a deadly poison for obligate anaerobes

Question 3

How can oxygen be essential for one group of organisms and yet be a fatal toxin for others?

Answer 3

Neither gaseous atmospheric oxygen (O2) nor the covalently bound oxygen in compounds such as carbohydrates or water is poisonous
The forms of oxygen that are toxic are those that are highly reactive.

Question 4

Why are highly reactive forms of oxygen toxic?

Answer 4

because in the same way that oxygen is the final oxygen acceptor for aerobes, they are excellent oxidizing agents,
i.e. they steal electrons from other compounds

Question 5

How toxic forms of oxygen cause a chain reaction that damages cells?

Answer 5

The electron depleted compounds then steal electrons from other compounds
Resulting in a chain of vigorous oxidation
Causing irreparable damage to cells by oxidising important compounds including proteins and lipids

Question 6

Singlet oxygen (¹O₂)

Answer 6

toxic form of oxygen - A very reactive oxidizing agent

Molecular oxygen – electrons boosted to a higher energy state – during aerobic metabolism

Phagocytic cells – certain human white blood cells use it to oxidize pathogens

Question 7

Superoxide radical (O₂^-)

Answer 7

Superoxide radicals form

• during incomplete reduction of O₂ during electron transport in aerobes
• during metabolism by anaerobes in the presence of oxygen

Question 8

How aerobic organisms detoxify superoxide radicals

Answer 8

Produce superoxide dismutase – lacking in anaerobes

Have active sites that contain metal ions e.g. Zn²⁺ and Fe²⁺

Combine 2 superoxide radicals and 2 protons to form hydrogen peroxide (H₂O₂) and oxygen

Question 9

Peroxide anion O₂^2-

Answer 9

Hydrogen peroxide produced during reactions catalysed by superoxide dismutase

Peroxide anion makes hydrogen peroxide an antimicrobial agent

Question 10

What do aerobes have to detoxify the peroxidase anion?

Answer 10

either catalase or peroxidase

Question 11

Hydroxyl radical (OH)

Answer 11

Hydroxyl radicals result from ionising radiation and from incomplete reduction of hydrogen peroxide

Question 12

What is the most reactive of the 4?

Answer 12

Hydroxyl radicals

Due to catalase and peroxidase effect eliminated in aerobes

Question 13

other antioxidants aerobes can use

Answer 13

Vitamin C & E

Again, provide electrons that reduce toxic forms of oxygen

Question 14

Facultative anaerobes

Answer 14

Can live in various oxygen concentrations

Question 15

How do facultative anaerobes maintain life

Answer 15

Can maintain life via fermentation or anaerobic respiration

Question 16

Metabolic efficiency in absence of oxygen for facultative anaerobes

Answer 16

reduced

Question 17

Example of facultative anaerobe

Answer 17

E.coli

Question 18

Aerotolerant anaerobes

Answer 18

Do not use aerobic metabolism

Have some detoxifying enzymes

Question 19

example of a Aerotolerant anaerobe

Answer 19

lactobacilli

Question 20

Microaerophiles

Answer 20

Microaerophiles are damaged by the 21% concentration of atmospheric oxygen

Some organisms require oxygen levels of 2% to 10%

Question 21

Example of microaerophile

Answer 21

Helicobacter pylori

ulcer causing pathogen

concentration of oxygen in stomach 2-10%

Question 22

Injecting Drug User (IDU) Infections

Answer 22

40% of IDU hospital admissions due to infections, 20% result in death

Intravenous, intra-muscular or subcutaneous injection

Minor bacterial infections usually result in local abscess formation

Question 23

Severe IDU infections

Answer 23

Severe illness if the injected material or paraphernalia, are contaminated with certain clostridial spores

Question 24

Clostridia

Answer 24

Gram positive anaerobic spore-forming rods

Question 25

Where is Clostridia found?

Answer 25

Widely distributed in soil and gut

Question 26

How does Clostridia exist?

Answer 26

exo-spores Resistant to environmental conditions Spores germinate when introduced into an oxygen-reduced environment

Question 27

Pathogenic Clostridia species

Answer 27

* C. perfringens* * C. septicum* * C. sordellii* * C. novyi* * C. histolyticum* * C. tetani* * C. botulinum* * C. difficile*

Question 28

IDU Outbreak, 2000

Answer 28

Cases of serious illness and deaths amongst IDUs recorded in parts of UK 60 IDUs in Scotland acquired a severe infection at or near an injection site

Question 29

clinical manifestations of IDU outbreak

Answer 29

Spread rapidly Extensive skin and muscle damage Hypotension Multi-organ failure 23 deaths

Question 30

origin of IDU outbreak

Answer 30

Association with a batch of heroin in circulation at the time and the practice of skin or muscle “popping”

Question 31

Clinical Presentation of Clostridia infection; Soft tissue inflammation at injection site

Answer 31

Abscess, Cellulitis, Fasciitis, Myositis

Question 32

Clinical Presentation of Clostridia infection; Local inflammatory reaction has varied

Answer 32

Minimal pain and swelling at injection site

Question 33

Clinical Presentation of Clostridia infection; Severe local symptoms

Answer 33

Extensive swelling, Pain, Oedema, Erythema with blackening/blistering at centre, Extensive necrosis, Necrotising fasciitis

Question 34

*C.novyi* Type A

Answer 34

Widely distributed in soil Gram-variable rods, some with sub-terminal spores

Question 35

Identifying *C.novyi* Type A

Answer 35

Examine anaerobic cultures after 24h incubation for small, flat, rough or rhizoidal, translucent, haemolytic colonies with a spreading edge Exposure to air toxic to micro-colonies that haven’t begun sporulation After 48-72h, colonies often coalesce to give a fine spreading growth Unreactive in commercial anaerobe identification kits (API Anaerobe)

Question 36

*C.perfringens*

Answer 36

Post-mortem contaminant Straight-sided, gram variable rods, no spores

Question 37

Identifying *C.perfringens* morphological appearance

Answer 37

Large discrete colonies after 24h incubation Flat and rough-edged, or smooth and domed Non-haemolytic or with a narrow zone of complete haemolysis inside a larger zone of partial haemolysis

Question 38

*C.septicum*

Answer 38

Gram variable rods, numerous sub-terminal spores Most common source of isolates from blood cultures of patients with malignancies of the colon

Question 39

Culture growth of *C.septicum*

Answer 39

Grows rapidly Thick, swarming growth, haemolytic

Question 40

*C.botulinum*

Answer 40

Profuse sub-terminal and free spores, gram variable bacilli Implicated in food-borne illnesses and cases of wound botulism

Question 41

Culture growth of *C.botulinum*

Answer 41

Proteolytic types A,B and F initially produce discrete rhizoidal colonies that spread and coalesce Haemolysis is variable

Question 42

*C.tetani* history in human disease

Answer 42

Uncommon in recent decades Outbreak between July ‘03 and March ‘04, 22 cases in IDUs

Question 43

Culture growth and identification of *C.tetani*

Answer 43

Colonies may produce a fine swarming growth Gram stain of overnight cultures can give readily over-decolorised long bacilli without spores Classical ‘drumstick’ appearance of cells with terminal, round spores after further incubation

Question 44

Outbreak of *C.histolyticum*

Answer 44

December ’03 to March ’04 First case, 35 year old female IDU from Glasgow, presented at hospital with a necrotic lesion at injection site Outbreak on-going

Question 45

Identifying the organism responsible for the outbreak

Answer 45

Molecular typing and PCR ribotyping revealed them all to be indistinguishable Isolated organism referred to Anaerobe Reference Lab(ARL), identified as *C.histolyticum*

Question 46

*C.histolyticum*

Answer 46

Member of the gas gangrene group, may be isolated from soil, bone-meal and gelatin Produces potent exotoxins causing severe localized necrosis

Question 47

Treatment of *C.histolyticum* infection

Answer 47

_Early surgical intervention_ * Exploration, Drainage, Extensive debridement _Microbiological sampling_ _Patients presenting with compartment syndrome_ * Urgent decompression, Excision of surrounding oedematous tissues _Antimicrobial therapy_ * Penicillin, Metronidazole, Clindamycin