Any experience with persistent foot infection (abscess)? And final outcome?

My cat, Blix, has had a persistent foot infection since September 4 (24 days now). He is under a vet's care, and I was wondering if any one else here has had a similar experience, and, especially what was the final outcome? We have another vet visit tomorrow (Sept. 30), and I want to brace myself for possibilities.

That is my basic question. Here is the case history (I am relying on memory, so not sure about some dates):

On Saturday, Sept. 3rd, Blix was in our back yard. We have made it so that he cannot get out of the yard. But there was a feral cat who made it into the yard, and started a fight with Blix. I broke up the fight, and checked Blix for wounds. I didn't see anything. But he was limping, and, being an idiot, thought maybe he sprained his ankle in the fight.

On Sunday, I took a closer look at his foot and noticed a small hole in his paw (right front foot). It did not look deep, but I decided to take him to my vet on Tuesday (the vet was closed Monday due to being Labor Day). 

On Monday (Labor Day), I noticed there was pus coming out of the wound. With my vet being closed I drove him to the Purdue University Emergency Vet Clinic, about 8 miles away. They opened his wound, so that it would drain, and supplied Blix with antibiotics and pain meds. He did well, but dutifully took Blix my regular vet for a follow-up visit on Monday, Sept. 12. By that time his meds ran out. Everything looked good. 

However, on Friday or so, I noticed pus back on the wound, and took him back to the vet. An abscess had formed. My vet did some x-rays and ultrasound, made a couple of incisions to get the abscess to drain, and gave him a shot of antibiotics and pain meds.

So far, the abscess/infection has not abated. It waxes and wanes. We've been going back and forth to vet. Day before yesterday, my vet said that everything points to a foreign body that maybe worked its way into the wound after the original bite. It's wouldn't be part of a tooth, since it would have shown up in the x-rays. Anyway, tomorrow (Sept. 30), I'll be bringing Blix in again; they are going to inject some high contrast dye and do more x-rays.

So anybody with a similar experience, I would really like to know how thinks worked out. 

I thank everyone in advance for any insights or advice, suggestions, etc.

First I notice he only had one week on the first antibiotic, which is too short a time for it to finish the job.  Generally they are given 10 days to two weeks, or for three days after there are no symptoms like pus.  What was the first antibiotic they used?  Did they tell you to keep flushing the would with something like saline and not allowing it to close back up?

Did the second vet ask what medicine he had been on?  Did he do a culture and sensitivity of the wound (i.e. swab it and put it on a culture plate) to find out what bug is growing there before he just gave the cat a "shot of antibiotic"? (probably Convenia, a long-acting cephalosporin, which lasts for 2 weeks). 

I did once cure a cat who came in with abscesses inside his other abscesses from fighting for many years.  It took time.  It took culturing the wound to see what bug we were dealing with and what antibiotic would best treat it.  Sometimes we would have to switch when a second abscess opened up inside an older abscess that had healed on the first drug.  Personally, I don't think your cat is as likely to have a foreign body as he is likely to be on an antibiotic that doesn't kill the particular bacteria that is infecting him.  My first call would have been to do a culture and sensitivity back then, but since it has not been done, you might get it done now and see what superbug is still hanging around.  Once they culture it, they test various antibiotics with it to find out which one is the most effective and then they use that.

A culture was done but, believe it or not, the lab could not grow anything, which I found to be astonishing.

He has been on way more than one week on antibiotic... that is what I meant to imply by the "back and forth to the vet". At Purdue, they gave Blix Clavamox liquid, to be used until done. After the start of the secondary infection, my vet put him on Convenia  , which lasts for 10-14 days. Then my vet tried Clavamox tabs (which absolutely killed Blix's appetite), so now he is back on another dose of Convenia.

The two incisions in Blix's paws were for drainage, and my vet wanted to keep those incisions open for at least five days. 

I soak Blix's paws in Epsom salts and some medicine (I can't remember what it is called, but it is a blue liquid, that is diluted in water).