FINAL DIAGNOSIS Roseomonas Gilardii
The genus Roseomonas was first described in 1993 by Rihs et al. The genus was based on phenotypic features, and DNA relatedness of 42 strains. These are nonfementative, weakly staining gram-negative plump coccoid rods. These bacteria phenotypically and genotypically resemble Methylobacterium species but are separable from the latter by their inability to oxidize methanol, to assimilate acetamide and by lack of absorption of long wave UV light. They grow on 5% sheep blood agar, chocolate agar, BCYE agar, Sabouraud's agar, and almost always on MacConkey agar. Growth appears as pinpoint, pale-pink, shiny, raised and often mucoid. All strains are catalase-positive and urease positive.
Infection by Roseomonas is exceedingly rare. Roseomonas species have been isolated from human sources such as blood, genitourinary sites, wounds, respiratory tract, body fluids, eye, and bone. Most of the isolates have been from blood.
Roseomonas infections tend to occur in the immunocompromised or debilitated host. Most patients recover completely from their infections. Bacteremia is the most common clinical presentation reported in the literature. The patients generally present with fever and typically involve the immunocompromised host. Other rare presentations reported in the literature have been peritonitis, septic arthritis, ventriculitis, left ventricular assist device (LVAD) infection, vertebral osteomyelitis and keratitis.
Susceptibility in vitro and in vivo
All isolates have been susceptible in vitro to the aminoglycosides; gentamicin, tobramycin, and amikacin. Most strains are susceptible to imipenem, tetracycline, and ciprofloxacin. They are rarely susceptible to the penicillins, including the extended-spectrum penicillins. All isolates are resistant to cefepime. No in vivo data for these organisms is available.
Antimicrobial therapy: drug of choice
Until a final identification and susceptibilities are available the drug of choice is gentamicin. All clinical isolates have been susceptible and organisms within the genus Methylobacterium are also susceptible in vitro to gentamicin. Standard dosing for gram-negative sepsis can be used, 1.7 - 2.0 mg/kg IV q8h. Alternatively, once-daily dosing can be used 5.0 mg/kg or 7.0 mg/kg, although postantibiotic effect (PAE) has not been studied.
Catheter removal may be required. Antibiotics alone can fail to clear catheter related sepsis despite achieving therapeutic levels.
Prevention or infection control measures
The natural reservoir of Roseomonas is not well known, however potable water and skin are likely. Bacteremia associated with central venous catheters is the predominant presentation. Strict adherence to sterile technique when manipulating the catheter and keeping the insertion site clean and dry should reduce the potential for this opportunistic infection. Minimizing the patient's contact with potable water can also decrease the risk of CAPD peritonitis caused by water-born gram-negative rods. Water baths used to preheat dialysis bags have been implicated in these infections. The use of dry heat (microwave or heating blankets) is now recommended for this purpose.
Contributed by by Shveta Hooda, MD, Ken Ho, MD and William Pasculle, ScD