11. Write short notes on: 
a. mechanism of action of aminoglycosides 
b. pathogenic fungi 
c. necrotizing fasciitis 

The aminoglycosides are bactericidal antibiotics that irreversibly inhibit protein synthesis and ribosome function. 

There are effective against aerobic Gram negative bacilli for example pseudomonas and hospital acquired Gram negative bacteria. 

They have a narrow therapeutic index and need monitoring to detect accumulation if given intravenously. The main toxicity associated with systemic use are nephrotoxicity and ototoxicity.

In ophthalmology, only gentamicin and amikacin are commonly used. 
Gentamicin is given usually for corneal ulcer in combination with cefuroxime to cover Gram negative bacilli.

Both gentamicin and amikacin can be given intravitreously for post-operative endophthalmitis. However, amikacin is preferable as it is less toxic and therefore a lower incidence of retinal necrosis.

Neomycin is often incorporated with topical steroid drop for post-surgical use. Neomycin can give rise to contact dermatitis in a significant amount of patients.


Fungal infections or mycoses are classified depending on the degree of tissue involvement and mode of entry into the host. These are: 

Superficial - localized to the skin, the hair, and the nails. 
Subcutaneous - infection confined to the dermis, subcutaneous tissue or adjacent structures. 
Systemic - deep infections of the internal organs. 
Opportunistic - cause infection only in the immunocompromised. 

Human fungal infections in the United Kingdom are uncommon in normally healthy persons, being confined to conditions such as candidiasis (thrush) and dermatophyte skin infections such as athlete's foot. However, in the immunocompromised host, a variety of normally mild or nonpathogenic fungi can cause potentially fatal infections. Furthermore, the relative ease with which people can now visit "exotic" countries provides the means for unusual fungal infections to be imported into this country. 


Necrotizing fasciitis results from infection of the soft tissue below the dermis, spreading with alarming rapidity along the facial planes causing disruption of the blood supply hence necrosis and gangrene This infection is caused mainly by Streptococcus pyogenes (B-haemolytic Group A) and micro aerophilic Streptotococci with anaerobic bacteria.

The patient is usually in a toxic shock state necessitating rapid action in terms of antibiotic treatment which should be intravenous Benzyl Penicillin and Clindamycin with or without Metronidazole, in addition to tissue debridment. This situation usually follow trauma to the skin such as wounds after surgery.

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