Proteus mirabilis

Proteus mirabilis is a Gram-negative bacillus which belongs to a family of bacteria called the Enterobacteriaceae. It is widely distributed in soil and water and can also be found in the normal human intestinal flora.

In humans, it causes urinary tract infections, or UTIs for short.Now, Proteus mirabilis has a thin peptidoglycan layer, so it doesn’t retain the crystal violet dye during Gram staining.

Instead, like any other Gram-negative bacteria, it stains pink with safranin dye.And since it’s a Gram-negative bacillus, it looks like a little pink rod under the microscope.Alright, now Proteus mirabilis is non-spore forming and highly motile.

It’s also facultative anaerobic which means it can survive in both aerobic and anaerobic environments, non-lactose fermenter, oxidase negative which means it doesn’t produce this enzyme, and urease positive which means it can produce an enzyme called urease.Now, it grows well on blood agar and MacConkey agar.

On blood agar, it has a swarming growth, so it moves and forms a thin filmy layer of concentric circles, which look like the ripples after you throw a rock into a lake.

On MacConkey agar, however, it doesn’t swarm so it forms smooth, pale or colourless colonies.Finally, the triple sugar iron test, or TSI for short can be done to assess hydrogen sulfide production.

This medium contains three sugars - lactose, glucose and sucrose, as well as iron and a pH sensitive dye. Proteus mirabilis produces hydrogen sulfide, that reacts with the iron, and a black precipitate forms in the test tube.Ok, now Proteus mirabilis has a number of virulence factors, that are like assault weaponry that help it attack and destroy the host cells, and evade the immune system.First, Proteus mirabilis has flagella, which are lash-like appendages that comes out from the cell body, and confer the bacteria its motility.

Now, when Proteus mirabilis comes in contact with solid surfaces, especially urinary catheters, it has the ability to differentiate from short swimmer cells into elongated swarm cells that express hundreds to thousands of flagella, and interact with each other to form multicellular rafts.This process is known as swarming motility and it helps the bacteria migrate along the catheter surface.

If the catheter is introduced in a person’s urinary tract, the bacteria is inoculated and it uses its flagella to ascend from the bladder to the kidneys and come in close contact with the uroepithelial cells lining the urinary tract.

Once there, it uses its fimbriae, which are tiny projections on the bacterial surface, and attach to the cells. After attaching, it makes a hemolysin, which cause formation of tiny holes in the cell membrane, leading to cell damage.Additionally, Proteus mirabilis produces a ZapA protease, a toxic protein that can destroy immunoglobulin A, or IgA and immunoglobulin G, or IgG.

IgA and IgG are immune system proteins that normally opsonizes invading bacteria, meaning it tags them so neutrophils can recognize and destroy them.

So ZapA protease neutralizes the first line of defense.Finally, in the urinary tract, Proteus can also use urease to convert the urea that’s normally present in urine to ammonia and carbon dioxide.

Ammonia can then combine with hydrogen to form ammonium, which increases urine PH - so the urine becomes more alkaline. Alkaline urine promotes the precipitation of phosphate, calcium and magnesium which can combine with ammonium to form struvite stones, that often form large staghorn renal calculi, or kidney stones.

Finally, this leads to urinary stasis, which starts a vicious circle, promoting bacterial multiplication, urinary alkalinization, and the deposition of new layers of struvite.

Proteus mirabilis causes urinary tract infections, or UTIs for short, such as urethritis and cystitis, when the urethra and bladder are involved, prostatitis, which is a prostate infection, or pyelonephritis, when the kidneys themselves get inflamed.

Struvite kidney stones may also develop. A rare complication of chronic Proteus mirabilis infections is xanthogranulomatous pyelonephritis, which, aside from making you sound really smart, happens when the infected struvite calculi cause chronic obstruction and, in turn, massive destruction of the kidney, characterized by necrotic, hemorrhagic masses containing foamy macrophages.

These masses are often mistaken for tumors on imaging studies! Ok, now, zebras aside - Proteus mirabilis UTIs are most common found in elderly people who are hospitalized, and have a couple of risk factors, like urinary tract procedures, such as such as surgery or catheterization, or underlying medical conditions like chronic kidney disease or neurogenic bladder, which is a bladder dysfunction caused by neurological damage.

Other risk factors may include multiple prior UTIs, prior use of antibiotics and also sexual activity, because it can cause Proteus to move from the end of the GI tract and the perineum up the urethra.Symptoms depend on the infection.

With urethritis, there’s dysuria, or pain during urination, pyuria, which is pus in the urine and increased urinary frequency, or needing to urinate more often than usual.

Cystitis, on the other hand, associates dysuria, urinary frequency and also urinary urgency which means strong need to urinate, and suprapubic pain.

The urine also has a particular ammonia smell. Prostatitis has the same symptoms as cystitis, but there may also be fever and chills, and on physical examination, the prostate may be swollen and tender.

Finally, with pyelonephritis there’s dysuria, urinary frequency and urinary urgency, and there may also be flank pain and systemic symptoms like fever, chills, nausea and vomiting.

Now, Proteus mirabilis can be identified by doing a urine culture. Urinalysis may show pyuria, which are white blood cells in the urine, bacteriuria, or that there are bacteria in the urine, and urinary PH above 7.

With pyelonephritis or prostatitis, a complete blood count may show leukocytosis, or increased numbers of white blood cells.

Finally, struvite stones appear radiopaque on an X-ray.Now, cystitis can be treated with trimethoprim-sulfamethoxazole, or TMP/SMX for short, quinolones and fosfomycin.

Pyelonephritis can be treated with fluoroquinolones, cephalosporins or gentamicin. Finally, surgery may be done to remove the struvite stones.

##SummaryAlright, as a quick recap, Proteus mirabilis is a Gram-negative bacillus which belongs to a family of bacteria called the Enterobacteriaceae.

It’s non-spore forming, highly motile, facultative anaerobic, non-lactose fermenter; oxidase negative, urease positive, produces hydrogen sulfide on TSI agar and has a swarming growth on blood agar.

It has virulence factors such as flagella, fimbriae, hemolysin and ZapA protease involved in the colonization of the urinary tract and evasion of immune system and it also produce urease which is involved in the formation of struvite stones.

It causes urinary tract infections such as urethritis, cystitis, prostatitis and pyelonephritis. Proteus mirabilis can be identified in a urine culture, and treatment is done with trimethoprim-sulfamethoxazole,