Microbio

Question 1

Name two (2) different types of fungal infection that diabetics are prone to (1) & For each, name two (2) anatomical sites where the fungus typically causes infection (2)

Answer 1

• Candidiasis: Oral cavity, vagina, oesophagus, skin, nails etc. (any 2 appropriate sites)
• Mucormycosis (zygomycosis): Nasal sinuses, occasionally GIT via ingestion or skin via inoculation

Question 2

Outline the pathogenesis of mucormycosis (3) (NB)

Answer 2

Spores are ubiquitous and inhaled (½), implants in nose/ sinuses (½). Hyphae grow & invade blood vessels (½). This results in thrombosis (½) & tissue destruction (½). Can extend into eye & brain (½)

Question 3

Two months later Mr Ramon experiences acute abdominal pain and undergoes surgery for a perforated appendix. The surgeon is concerned about the possibility of anaerobic organisms contributing to his appendicitis.

Define what is meant by an anaerobic organism (1)

Answer 3

An anaerobe is an organism which derives its energy entirely by fermentation and does not use oxygen as a terminal electron acceptor.

Question 4

State where most anaerobic infections originate (1)

Answer 4

Endogenous - own flora e.g. GIT

Question 5

Name three (3) anatomical sites where anaerobes can be found as normal flora (1½)

Answer 5

Colon, oral cavity, nasopharynx, lower urogenital tract

Question 6

Outline the two (2) predisposing factors that are usually required for anaerobes to establish an infection (2)

Answer 6

• Breach in the mucosal or cutaneous barrier to allow anaerobes in
• Reduced oxygen tension in tissues/ devitalised tissue to allow anaerobes to grow

Question 7

Give two (2) reasons (unrelated to his diabetes) why he might be at risk of an anaerobic infection (2)

Answer 7

Infection at site where anaerobes are part of normal flora
Perforation of viscus allowing spillage of normal flora
Concurrent polymicrobial infection, resulting in reduced oxygen availability

Question 8

Name four (4) infections commonly caused by anaerobes (apart from infected wounds) (2)

Answer 8

Peritonsillar abscess, Tubo-ovarian abscess, Dental infections, Peritonitis (esp after colonic perforation), Perirectal abscess, Lung abscess, Aspiration pneumonia

Question 9

Name two (2) clinical conditions that typically involve anaerobes (1)

Answer 9

Peritonsillar cellulitis or abscess, dental and jaw infections, brain abscess, aspiration pneumonia, lung abscess or bronchiectasis, peritonitis or peritoneal abscess following colonic surgery or perforation, perirectal abscess, tubo-ovarian abscess, necrotising cellulitis or fasciitis (with or without gas gangrene)

Question 10

State the optimal specimen the surgeon could send to the microbiology laboratory to detect anaerobes (½)

Answer 10

Pus/ tissue

Question 11

List the features on the Gram stain that might suggest the presence of anaerobes (1)

Answer 11

Plenty of pus cells, pleomorphic/mixed organisms

Question 12

Name an antibiotic that is commonly used to treat anaerobic infections (½)

Answer 12

Metronidazole

Question 13

Name two (2) antibiotics that may be used to treat anaerobic infections (1)

Answer 13

Metronidazole, clindamycin, penicillin, co-amoxiclav, cefoxitin, carbapenems

Question 14

Name two (2) antibiotics that would be suitable for empiric treatment of anaerobic infections associated with intra-abdominal infections (1)

Answer 14

Metronidazole, co-amoxiclav, etc.

Question 15

Briefly describe how metronidazole kills bacteria (1)

Answer 15

Inhibits nucleic acid synthesis/interferes with bacterial DNA

Question 16

Explain why metronidazole is not active against aerobic bacteria (1)

Answer 16

Requires anaerobic conditions to be activated/ to achieve sufficient concentration in bacterial cell.

Question 17

Outline two (2) different types of common side-effects of metronidazole (2)

Answer 17

Gastro-intestinal: Nausea/ vomiting/ metallic taste

Disulfiram-like reaction when taking alcohol concurrently

Neurological: Peripheral neuropathy, seizures

Question 18

The diabetic patient’s infected foot is probably due to a variety of bacteria, including anaerobes.

Name in full one (1) anaerobe that may be involved in this infection (1)

Answer 18

E.g. Bacteroides fragilis

Question 19

List three (3) organisms commonly involved in diabetic foot ulcers (1½)

Answer 19

Anaerobes e.g. clostridium perfringens, Staphylococcus aureus, Pseudomonas aeruginosa

Question 20

Discuss the pathogenesis of a diabetic foot ulcer (4½)

Answer 20

Peripheral neuropathy  loss of sensation  injury

Microvascular and Macrovascular disease  poor blood supply  poor healing

Poor glycaemic control  immune suppression  infection

Question 21

List three (3) complications of a diabetic foot ulcer (1½)

Answer 21

Abscess, cellulitis, gangrene, osteomyelitis

Question 22

State what else should be done to treat the diabetic patient’s infected foot, apart from antibiotic therapy (½)

Answer 22

Debridement of any dead/ devitalised tissue – antibiotics will not penetrate dead tissue.

Question 23

Outline five (5) non-pharmacological interventions which should be part of management of a diabetic foot ulcer (5)

Answer 23

Debridement of all necrotic tissue
Resting the foot
Elevation of the foot
Well-fitting shoes
Relief of pressure on the foot– crutches or wheelchair, total contact casting, removable walking brace or “half shoe”
Provide a warm moist environment protected from contamination – saline wet – dry dressings
Daily foot inspection with prompt treatment of any lesion
Foot hygiene
Well-fitting shoes
Regular foot care with debridement of calluses and ingrown toenails
Elective surgery to correct deformities

Question 24

Patients with diabetes mellitus are at risk of various infections, including fungal infections and “diabetic foot”. Various anaerobes have been associated with infections in diabetic foot, including Clostridium perfringens.

Describe the typical Gram stain appearance of Clostridium perfringens (1)

Answer 24

Large Gram-positive bacilli

Question 25

Gram stain of the pus shows large gram-positive bacilli (some showing spore formation). On culture these organisms only grow anaerobically. Give the most likely identity of this organism (full name) (1)

Answer 25

Clostridium perfringens

Question 26

Outline the important pathogenic processes involved in Clostridial infections (3)

Answer 26

Organisms are anaerobes, thus infect ischaemic or necrotic tissues. Produce a variety of enzymes which diffuse into tissues, causing further necrosis and allow for further spread of organism

Question 27

Name three (3) clinical manifestations associated with C. perfringens (1½)

Answer 27

Wound contamination, Soft tissue infections, Anaerobic cellulitis, Gas gangrene, Bacteraemia

Question 28

Describe the clinical syndrome that could result from a more severe invasive infection caused by this organism (4)

Answer 28

Gas gangrene – spread of toxins into healthy tissue leading to cell death – myonecrosis, gas in the tissues. Severe local pain without high fever. Tensely swollen tissue with haemorrhagic bullae. Mental alertness and anxiety despite toxaemia and hypotension ending in renal failure and coma. AND Death [if your anat path]

Question 29

Whilst in hospital the attending doctor notices that Mr Molefe has developed a foul smelling necrotic infection of his distal foot and toes. On palpation of the area there seems to be a lot of gas in the tissues.

Name in full the most likely organism responsible for this infection (1)

Answer 29

Clostridium perfringens

Question 30

Name the causative organism of gas gangrene. Give the full name (1)

Answer 30

Clostridium perfringens

Question 31

Briefly describe the pathogenesis of this infection (2)

Answer 31

Poor blood supply to the area thus less oxygen anaerobes proliferate (1), also exotoxins produced by organism (1)

Question 32

State what laboratory condition this organism requires in order to be cultured (1)

Answer 32

Anaerobic

Question 33

Outline how you would manage this case (2)

Answer 33

Treat underlying cause/ diabetes (1), Remove necrotic tissue (1), Penicillin or metronidazole (1) (any 2)