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GRAM-NEGATIVE INFECTIONS

Pseudomonas infections

Pseudomonas aeruginosa is a common cause of gram-negative bacterial infections (Table 24.5). One clinical clue to its presence is the bluish green color it may impart to pus, the wound (Fig.24.35), or dressings (Fig.24.36). It is implicated in several patterns of infection, which include the following.

Figure 24.35 Pseudomonas infection. Note the typical green stain to the dressing.

Figure 24.36 Pseudomonas infection of a leg ulcer was diagnosed from the typical blue-green color staining of the overlying bandage in this patient.

Hot tub folliculitis

Etiology and pathogenesis

The typical patient with hot tub folliculitis develops the disorder several days after using a hot tub or pool contaminated by Pseudomonas . It has been shown that Pseudomonas proliferates in warm water when the level of added chlorine drops below that recommended for antimicrobial effect. The heat of the water in the hot tub helps to dissipate the chlorine more rapidly. Prolonged hydration and occlusion of the skin (e.g. by a tight bathing suit) promote infection. The family bath or shower may be the source of infection, for example via loofah sponge or rubber bath toys.

Clinical

The typical patient with hot tub folliculitis develops multiple pustules on top of urticarial bases scattered on the trunk or buttocks (Fig. 24.37).

Figure 24.37 (a,b) Hot tub folliculitis. The typical patient develops multiple pustules on top of urticarial bases several days after using a hot tub contaminated by the gram-negative bacterium Pseudomonas aeruginosa. Note the prominent inflammation, which is typical. The trunk and buttocks are favored sites.

Differential diagnosis

See differential for follicular pustules earlier (Table 24.2).

Treatment

The disease is usually self-limited. Once the skin is allowed to dry out and kept from the infectious source, clearing is expected. Persistence has, rarely, been noted in very sweaty individuals. If treatment is desired, oral ciprofloxacin (500mg twice a day) may be given. The hot tub or spa should be more aggressively maintained, with adequate chlorination and pH level checks.

Malignant otitis externa

This condition is infective rather than neoplastic, and is due to Pseudomonas ; the term malignant is applied, as it can be locally destructive, leading to cranial nerve damage, and may be fatal if septicemia develops (Fig.24.38). Diabetes is a risk factor.

Figure 24.38 Malignant otitis externa in a diabetic woman. This is an aggressive infection due to Pseudomonas aeruginosa.

Ecthyma gangrenosum

Ecthyma gangrenosum is a serious infection by P. aeruginosa . It is usually seen in association with pseudomonal sepsis. The classic adult with ecthyma gangrenosum is a very ill, immunocompromised, intensive care unit patient. Much less commonly, infants may be affected in the diaper area. Pseudomonas infection may develop in the setting of cancer chemotherapy, prolonged administration of antibiotics, diabetes, neutropenia, hematologic malignancies, immunosuppression (e.g. in a transplant patient), or prolonged bathing. The diagnosis may be made by either blood or tissue culture. Of note, ecthyma gangrenosum-like necrotic lesions have occurred with other infections (e.g. Aspergillus niger , Citrobacter freundii , and primary cutaneous mucormycosis).

    The initial lesion is often a bulla or hemorrhagic pustule that expands to a larger area of necrotic tissue. The end result is the establishment of solitary or multiple, well-defined areas of necrosis and ulceration (Fig.24.39). The flexural areas, such as the axilla and groin, are typically affected.

    Aggressive antibiotic therapy (e.g. ciprofloxacin) is needed, along with local wound care.

Figure 24.39 Ecthyma gangrenosum. A well-defined area of necrotic tissue in the axilla of an intensive care unit patient is shown. The patient died 4 days after the photograph was taken.

Other Pseudomonas infections

Colonization of leg ulcers, pressure sores, and other chronic wounds by Pseudomonas is common, particularly on buttocks or legs. Frank infection, manifest by local cellulitis, may also occur.

    Rarely, the skin may take on a greenish hue due to infection or colonization by Pseudomonas . This is most common on the toes (see Fig. 24.41) or foot, where the initial infection may be from under the nail or in the web spaces. Gram-negative web space infection, of which Pseudomonas is one cause, is discussed in this chapter.

    Nail infection by Pseudomonas is really colonization of an onycholytic space, with characteristic greenish black staining of the undersurface of the nail plate (see Ch.29).

Figure 24.41 Gram-negative toe web infection. Note the green color, which is characteristic of infection by Pseudomonas.

PRACTICE POINTS

Gram-negative toe web infection

Etiology and pathogenesis

Most patients wear their shoes most of their waking hours. This leads to an environment in the toe webs of constant wetness and maceration. It appears that dermatophytes secrete a penicillin-like substance that inhibits the growth of gram-positive bacteria, thus allowing for the overgrowth of gram-negatives.

Clinical

Initially, the toe web becomes white and macerated (Fig.24.40). Later, wetness, inflammation, and odor develop (Fig.24.41). In the full condition, the web spaces of all toes are eroded, malodorous, and inflamed (Fig.24.42).

Figure 24.40 Dermatophytosis complex. Constant wetness and maceration in the toe webs, along with a penicillin secreted by dermatophytes, allows overgrowth of the gram-negative organisms.

Figure 24.42 (a–c) Gram-negative toe web infection. As the infection takes hold, the distal foot and toes become swollen, inflamed, and malodorous. Proteus and Pseudomonas are often found.

Differential diagnosis

An allergic contact dermatitis or tinea pedis (which may contribute) might, in unusual circumstances, be confused with gram-negative toe web infection, but the diagnosis is usually clear.

Treatment

Approaches that dry out the web spaces, kill the bacteria, and allow healing are needed. Soaks (just warm water) twice daily are very helpful. How much of the day closed shoes are worn should be ascertained and the time reduced. The wearing of sandals or going barefoot may be helpful. Cotton in between the toes may decrease occlusion and maceration. Often, the discussion of the patient's work comes up, and in severe cases the patient's work environment must be altered for several weeks as healing occurs.

    A culture of the toe web should be done initially and periodically at follow-up visits. Gentamicin topically twice a day after soaking can be very helpful, as it has excellent gram-negative coverage. An oral antibiotic may be considered after the culture and determination of sensitivities.

    The foot should be assessed for the presence of dermatophytes. A topical antifungal may be needed after the initial inflammation and gram-negative infection have been controlled. Alternatively, an oral antifungal (e.g. terbinafine or itraconazole) may be indicated. Indeed, these patients are subject to recurrence, and any amount of onychomycosis should be cleared with oral therapy.

    Recurrences do occur, especially if any fungal infection is not prevented or prolonged occlusion of the toes is reinstituted. Antiperspirant sprayed between toes to desiccate has been successful. Alternatively, a superabsorbent powder may be used every morning.

Meningococcemia, acute

Neisseria meningitidis is a gram-negative coccus that can cause fulminant bacteremia and meningitis (Fig.24.43). The classic patient is a child or teenager who acutely develops a severe headache, nausea, vomiting, and fever. Meningeal symptoms may occur, and the mental state may deteriorate to disorientation or even coma. Hypotensive shock and death may ensue rapidly.

    A petechial rash, often on the extensor hands, arms, and feet, is characteristic. It is often a helpful diagnostic feature. Early lesions may be discrete macules or papules that later become hemorrhagic. Purpura fulminans (Fig.24.44) may be a complication. Prompt treatment is necessary. Intravenous penicillin is the treatment of choice. Rifampin may be given to close family members as prophylaxis.

Figure 24.43 (a,b) Neisseria meningitidis: distal purpura. This young woman presented to the emergency room with a fever, meningeal symptoms, and a distal purpuric rash.

Figure 24.44 Purpura fulminans may follow meningococcemia. This patient lost the finger and a leg. (Courtesy of Angelito Arias, M.D.)

Disseminated gonococcal infection

Neisseria gonorrhoeae is a gram-negative diplococcus that causes one of the most common sexually transmitted diseases: gonorrhea. Some patients go on to have disseminated gonococcal infection, in which pustular skin lesions are associated with arthritis, arthralgias and fever.

    Scattered hemorrhagic vesicopustules are seen acrally, often over the joints (Figs 24.45 and 24.46). Lesions typically heal after several days, leaving small scars.

Figure 24.45 Disseminated gonococcal infection. Hemorrhagic pustule over the ankle. (Courtesy of Michael O. Murphy, M.D.)

Figure 24.46 Disseminated gonococcal infection. Lesions often develop over bony areas (e.g. the fingers). (Courtesy of Michael O. Murphy, M.D.)

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.