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Let's say I get an ear piercing over the cartilaginous area of pinna. Now due to traumatic perforation and inoculation, there will be perichondritis.

According to my logic it should be Staph aureus or some common skin organism. To my surprise the textbook says it's Pseudomonas. So Ciprofloxacin has to be given and not Amoxi-Clav.

I don't understand this.

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    Hi A Nandi, could you please edit your question with the name of the textbook and a quote of the section that makes the assertion about the most common pathogen?
    – Ian Campbell
    Commented Aug 17, 2022 at 12:05

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My edition of Mims' Medical Microbiology (3rd edition, 2005, p. 213) has this to say about otitis externa (emphasis mine):

Causes of otitis externa are Staph. aureus, Candida albicans and Gram-negative opportunists.

Infections of the outer ear can cause irritation and pain, and must be distinguished from otitis media. In contrast to the middle ear, the external canal has a bacterial flora similar to that of the skin (staphylococci, corynebacteria and, to a lesser extent, propionibacteria), and the pathogens responsible for otitis media are rarely found in otitis externa. The warm moist environment favours Staph. aureus, Candida albicans and Gram-negative opportunists such as Proteus and Pseudomonas aeruginosa

Now this is referring to otitis externa - inflammation of the ear canal itself, not the pinna. However, the presence of a pathogen such as P. aeruginosa in the ear canal could result in opportunistic infections of wounds to the pinna. I too would expect Staph infection to be the prime cause of an infection of a wound on the cartilaginous part of the pinna, apart from possibly the tragus or choncha.

Reference:

Mims, C; Dockrell, HM; Goring, RV; Roitt, I; Wakelin, D; Zuckerman, M; (2005) Medical Microbiology 3rd Edition. Elsevier Mosby, Edinburgh, UK, ISBN 0323035752

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