Achromobacter xylosoxidans is a gram-negative bacillus first described in 1971.1 It is an opportunistic bacterium that usually infects immunocompromised patients.2,3 The incidence of A. xylosoxidans ocular infections in these patients is low, but their incidence in immunocompetent patients is extremely low.4 We present a case of keratitis due to A. xylosoxidans infection in an immunocompetent contact lens user diagnosed in our department in January 2016. We also conducted a review of the literature to facilitate diagnostic suspicion and empirical therapeutic management.
A 28-year-old man presented at Accident and Emergency Department/Unit because of photophobia and intense foreign body sensation in the right eye for 24 hr before the visit. He had been wearing silicone hydrogel contact lenses for 1 year (PureVision; Bausch & Lomb, Rochester, NY; lens care solution Clear Care; CIBA VISION, Atlanta, GA).
Two weeks previously, he had returned from travelling in Australia, Indonesia, and Singapore, where temperatures range from 28°C to 30°C and humidity is high. While travelling, he came into contact with warm waters and reported overuse of contact lenses (over 16 hr daily).
The patient's corrected visual acuity was 20/30 in the right eye and 20/20 in the left eye. Biomicroscopy (Fig. 1) showed mild hyperemia and multiple scattered star-shaped epithelial defects measuring 0.3 × 0.3 mm, with sublesional stromal infiltrates. During the visit, in view of the patient's history and the atypical clinical presentation (disproportionate symptoms and viral appearance of the lesions), topical anesthesia (Colircusí anestésico doble; Alcon, Fort Worth, TX) was applied, specimens were collected through corneal scrape using a 30-G needle and conjunctival smear, and these, together with the patient's lenses and lens case, were sent for microbiological study. After moderate growth in MacConkey agar, A. xylosoxidans was isolated using the Vitek 2 GN system (BioMérieux, Durham, NY).
Symptoms resolved after 7 days after empirical treatment with topical moxifloxacin 0.5% every 3 hr (Vigamox; Alcon, Fort Worth, TX), fluorometholone 0.1% every 8 hr (Allergan, Irvine, CA), and hyaluronic acid tears (Fig. 2). In the second week after treatment, visual acuity was 20/20 in both eyes.
Based on the antibiogram, A. xylosoxidans was sensitive to moxifloxacin, ciprofloxacin, ceftazidime, gentamicin, tobramycin, vancomycin, chloramphenicol, and clotrimazole, but resistant to tetracyclines and rifampicin.
A. xylosoxidans, also known as Alcaligenes xylosoxidans, is a nonfermenting, cytochrome oxidase-positive gram-negative bacillus that was first described in 1971. The incidence of infection in humans is very low2. A. xylosoxidans is an opportunistic bacterium that can cause sepsis, meningitis, pneumonia, urinary tract infections, and peritonitis in immunocompromised patients.4,5 The exact mechanism of transmission of the bacterium is unknown,4 but the most likely mode is contact with a contaminated element.6A. xylosoxidans is found in the normal bacterial flora of the auditory canal and digestive tract.7 It has also been isolated in fluids used in hospitals (dialysis fluid, distilled water, disinfectant solutions), in the home (humidifiers), and in humid environments (swimming pools).8 Being such a widespread organism, some authors have suggested that the incidence of A. xylosoxidans is underestimated.3 This bacterial group is not easily identified, and is even elusive using the latest proteomic techniques (MALDI-TOF).3
Opinions about the best treatment vary, and therapy can be complicated, given the fact that the bacterium is often drug-resistant. Previous studies have noted the sensitivity of A. xylosoxidans to broad-spectrum penicillins (carbenicillin, piperacillin, and ticarcillin), ceftazidime, imipenem, and trimethoprim/sulfamethoxazole9 and its resistance to first-generation aminoglycoside and cephalosporins.10 In some cases, it can also be sensitive to quinolones.4
We conducted a detailed review of the literature in MEDLINE and PubMed. As shown in Table 1, 24 cases of keratitis due to A. xylosoxidans4–6,9–19 have previously been reported, 23 of them in immunocompetent patients—14 men (58.3%) and 9 women (37.5%), 14 were unilateral (58.3%) and 2 bilateral (8.3%); mean age was 38.25 years. Twenty-eight patients presented risk factors, specifically, nine wore contact lenses.5,6,10–12,16,17 Of these nine cases, four had a history of corneal damage (2 cases of laser in situ keratomileusis,11 1 case of keratoplasty,16 and 1 case of pseudophakic bullous keratopathy10).
The mean follow-up period was 58 days, at which time 9 cases had resolved (50%) and 4 cases presented a corneal opacity (22%). Our patient, who was young and otherwise healthy, presented three risk factors for keratitis due to A. xylosoxidans: contact lens user (1) with misuse of lenses (poor hygiene and overuse) (2) who had come in contact with contaminated warm waters (3). The patient had no history of corneal damage. The disproportionate severity of the symptoms and star-shaped morphology of the lesions were striking. This led us to suspect an atypical etiology and prompted us to order microbiological analysis of corneal scrapings, conjunctival swabs, contact lenses, liquid, and lens case. As mentioned above, there is no consensus on the best treatment for this type of infection. According to our experience and the literature review, we emphasize the sensitivity of A. xylosoxidans to quinolones and ceftazidime. Regarding the pathogenesis, hypoxia due to contact lens use causes elevated lactic acid levels and glycogen deficiency, leading to defects in the corneal epithelium.5A. xylosoxidans, a motile bacterium with peritrichous flagella found in still, warm waters, would have penetrated the eye through the epithelial defect.11 The bacterium also secretes an extracellular polymer that is extremely resistant to the body's immune system, antibiotic drugs, and disinfection mechanisms.11
In conclusion, A. xylosoxidans is an uncommon etiological agent that should be suspected even in immunocompetent patients with no history of keratopathy when the patient reports contact with warm waters and presents additional risk factors such as contact lens use.
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