Pseudomonas Aeruginosa

by Sean Elliott, MD

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    00:01 Pseudomonas Aeruginosa, a bacteria.

    00:04 Pseudomonas are gram-negative aerobic rods.

    00:08 They have sometimes up to three flagella and they are non-fermenting.

    00:14 So when you hear them described in a case vignette, you will frequently hear this organism is a non-fermenting, gram negative rod.

    00:22 They will likely not mention the flagella.

    00:25 The organisms are oxidase and nitrate reduction test positive and this is important, they have a very characteristic grape fruity odor - some likened this very much to grape chewing gum or grape candy but it’s quite a prominent scent which actually is somewhat pleasant.

    00:43 Also, on culture, they appear greenish or blue greenish due to production of a pyocyanin, a pigment which appears blue or green.

    00:53 Transmission. Pseudomonas are important especially in hospital acquired infections because they are ubiquitous throughout the environment and especially in any reservoir that have some degree of moisture.

    01:06 You might think of dialysis equipment, a respiratory ventilator but also so too the sinks, the soap dispensers in the hospital setting or even at home.

    01:17 Whenever and wherever the moisture accumulates then infection too can develop, so it’s a difficulty for infection preventionists to address.

    01:28 Let's look at some of the mechanisms of pathogenesis for pseudomonas.

    01:33 The first has to do with the pili or the attachment points.

    01:37 These create a very strict adherence to respiratory epithelium.

    01:42 In addition, the antiphagocytic capsule is present which also binds very strongly to tracheal epithelium.

    01:50 So those two combine start the process known as biofilm formation, where the organism can start to coat the airway linings and build upon itself.

    02:03 Exotoxin A, typically is released as well, and this ribosylates, adenosine diphosphate, which is in the elongation factor known in cellular mechanics.

    02:14 If one inhibits the process of the elongation factor by ribosylating it, then protein synthesis and chain elongation cannot occur.

    02:26 This is one of the principle mechanisms by which Pseudomonas aeruginosa can cause disease.

    02:32 But in addition, Pseudomonas in a way is smart.

    02:36 Once one gets more than a couple of the Pseudomonas organisms or bacteria together, they start to sense the presence of other Pseudomonas in the region and they communicate in a way, no they're not using radio signals or something like that, but there's definite proof that a group of Pseudomonas when put together can start to navigate further biofilm production, further growth, and then uniform production of the exotoxins.

    03:07 In addition, exotoxins also exists which as the biofilm is being put down, can prevent phagocytic killing.

    03:15 And then there are degradative enzymes which do the specific damage to host tissues, so in a way, Pseudomonas, while being ubiquitous in the hospital setting, and water loving areas, is also quite a nasty challenge because it can create this biofilm which has many weapons to cause disease among host tissues.

    03:36 So what are some of the infections seen with Pseudomonas? Well, there are many.

    03:41 The first and perhaps the most common are the urinary tract infections especially in patients who have an indwelling catheter.

    03:49 Why? Because Pseudomonas loves plastic and it loves the micro areas protection which are induced by having an indwelling catheter in the urinary collecting system.

    04:00 So, patient’s with foley or catheter associated urinary tract infections are most likely to be growing pseudomonas aeruginosa.

    04:10 Then there are the patients suffering with burn and wound infections.

    04:14 Again, because the diseased tissues have limited immunosurveillance and they retain moisture, it is possible for Pseudomonas to evade immunologic detection and create further damage in the burn tissue secondarily followed by entrance into the blood system causing bacteremia and sepsis.

    04:35 A very common source in which one sees Pseudomonas are the otitis externa or swimmers ear infections.

    04:43 Now, these maybe benign but talk to any child and perhaps even yourself who suffered from this and it does not feel good.

    04:51 Painful Pseudomona’s discharge from the external canal of the ear, again, due to retention of moisture in that environment.

    05:00 Sometimes, that otitis external can get out of control creating something known as malignant external otitis or put the other way around, malignant otitis externa.

    05:11 This is sort of a swimmer’s ear gone really bad in which there’s extensive pain and then swelling and a very purulent discharge from the external auditory canal.

    05:22 If not recognized and not treated that infection can then become invasive going into the central nervous system causing cranial nerve damage, bacteremia and sepsis.

    05:34 In fact, many times, malignant external otitis is mistaken for mastoiditis, which is a different set of infection and a different type of bacteria but they look somewhat similar.

    05:47 The earlobe itself, the pinna protrude and are red, and very tender and the patients are many times quite sick.

    05:55 Skin infections. Ecthyma gangrenosum, roles trippingly off the tongue, but in itself is not a good process at all.

    06:04 Ecthyma gangrenosum is typically caused by presence of Pseudomonas in the capillary beds of an infected tissue creating an immunologic reaction which is uncontrolled.

    06:17 And so, one will frequently see ecthyma gangrenosum in patients who have a hematologic malignancy especially those with leukemia or lymphoma who are also neutropenic to the chemotherapy or about to become so.

    06:33 The lesions themselves are very focal, they look almost like a gangrene so blackened, ischemic lesions which start off as purpuric or hemorrhagic lesions and then progress to superficial necrosis.

    06:47 Folliculitis, this is also sometimes knows as hot tub folliculitis and again it makes sense because one has warm moist water retention in the areas of the hair follicles even after getting out of the hot tub and precipitates a local infectious cellulitis at those follicle roots, so most often, as you see in the areas of the apocrine sweat glands but also around the nipple, areola, arm pits -- you name it.

    07:19 Typical treatment with that is going to be topical and it would take sure time just waiting for it to resolve.

    07:26 And then pulmonary infections.

    07:29 These are perhaps the most commonly encountered in patients who have an otherwise underlying chronic pulmonary process such as those with cystic fibrosis or chronic obstructive pulmonary disease, COPD.

    07:43 These patients will typical have diffuse or bilateral bronchopneumonia lesions and it again comes from contamination of the airway with the Pseudomonas from other respiratory therapy equipment.

    07:57 Keratitis. Now looking toward the eye and this can be a fulminating process so typically patients will present with some ulceration or some injury of the cornea which then is secondarily infected by the pseudomonas.

    08:12 If it starts and ends simply at the cornea, it may only be a keratitis but the potential for this to extend to infect the entire eye, a panophthalmitis, is quite extensive.

    08:24 Disseminated infections. Typically coming from a point or a focal source such as the lungs or perhaps ecthyma gangrenosum as we talked about in leukemia patients, but any patient with altered immunity is at risk to develop disseminated infections.

    08:41 And then osteomyelitis or perhaps more accurately called costochondritis.

    08:47 This typically and classically is associated with a penetrating trauma such as a thorn or a nail or screw going through the sole of a shoe and typically, an athletic shoe which is warm and moist and sometimes stinky inside and then penetrating and inoculating the sole of the foot and the underlying cartilage in this bone structures with Pseudomonas.

    09:13 Treatment. All these very significant infectious processes while differing in severity, all can respond to systemic treatment and the most common start for antibiotic treatment is with an antipseudomonal beta lactam penicillin or a cephalosporin, depending on the susceptibility of the isolate.

    09:37 Now, Pseudomonas like increasingly other gram-negative bacteria, is acquiring more and more robust mechanisms of antibiotic resistance and so commonly, in those chronically ill patients, one will see a need for even more evolved and more aggressive antibiotic therapy but as a proper starting point, starting with the antipseudomonal beta lactam antibiotic or penicillin is appropriate.

    10:03 In some cases, double covering the treatment, adding two antibiotics to more rapidly or more perhaps aggressively reduce the organism load is appropriate.

    10:14 The typical antibiotic to add to the antipseudomonal beta lactam is an aminoglycoside, something like a tobramycin or a gentamycin; but the fluoroquinolones such as ciprofloxacin and others in that family will also be effective.

    10:32 So, as we look at the presence of Pseudomonas all around us, keep in mind that it again, is a water loving green culturing fruity grape juice smelling organism which has a potential to do nothing more than a swimmers ear or a hot tub folliculitis but has the potential to cause incredibly extensive opportunistic infections.

    11:00 Just say no to Pseudomonas.

    About the Lecture

    The lecture Pseudomonas Aeruginosa by Sean Elliott, MD is from the course Bacteria.

    Included Quiz Questions

    1. ,..pyocyanin and pyoverdine.
    2. ...prodigiosin.
    3. ...staphyloxanthin.
    4. ...violacein.
    5. ...granadaene.
    1. Grape juice odor
    2. Bleach odor
    3. Wet fur odor
    4. Burnt chocolate odor
    5. Butterscotch odor
    1. Adenosine diphosphate ribosylation of elongation factor 2
    2. Adenosine triphosphate ribosylation of elongation factor 2
    3. Adenosine monophosphate ribosylation of elongation factor 2
    4. Adenosine monophosphate hydroxylation of elongation factor 2
    5. Adenosine triphosphate hydroxylation of elongation factor 2
    1. exoenzyme S.
    2. ...endotoxin A.
    3. ...exoenzyme B.
    4. ...endotoxin Y
    5. ...exotoxin D.
    1. Cystic fibrosis
    2. Sarcoidosis
    3. Emphysema
    4. Idiopathic pulmonary fibrosis
    5. Hypersensitivity pneumonitis
    1. Gram-negative rods
    2. Gram-negative vibrios
    3. Gram-positive spirochetes
    4. Gram-positive diplococci
    5. Gram-negative spirochetes

    Author of lecture Pseudomonas Aeruginosa

     Sean Elliott, MD

    Sean Elliott, MD

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