Bloodstream infection by Acinetobacter radioresistens: the first case report in Brazil

This report is the description of the first case in Brazil of community-acquired bloodstream infection caused by Acinetobacter radioresistens. A 73-year-old male patient with Alzheimer’s and Parkinson’s disease was hospitalized and diagnosed with pneumonia at a general hospital. MacConkey agar pure culture was obtained from blood cultures. Conventional tests identified the isolate as Acinetobacter baumannii complex. However, the matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) technique identified it as Acinetobacter radioresistens. The isolate was sensitive to all antibiotics tested by the disk diffusion method, including carbapenem. However, bla oxa-23 gene was detected by the polymerase chain reaction (PCR) assay. Acinetobacter radioresistens can be considered an important agent of opportunistic infections in immunocompromised patients, a potential disseminator of resistance genes.

Acinetobacter spp. has shown to be a potential opportunistic pathogen, which mainly affects patients with some comorbidity (1) . The Acinetobacter baumannii species, in particular, is in the first place of the "critical state" list of bacteria requiring special attention, according to the World Health Organization (2) . However, the special attention given to this species should also be directed towards other emerging members of this genus, such as Acinetobacter radioresistens. This species shows great adaptability to an environment with low relative humidity, and great persistence and survival in hospital environments, under such conditions (3) . It is also considered a possible reservoir and disseminator of genes that confer resistance to carbapenem (4) . To date, there are a few clinical case reports involving A. radioresistens (5)(6)(7) , of which only one describes a community-acquired bloodstream infection, from a human immunodeficiency virus (HIV)-positive patient (7) .

CaSE rEPort
A 73-year-old male patient was hospitalized at a general hospital localized in Natal, Brazil Northeast, presenting fever, respiratory secretions and wheezing on chest auscultation. The patient was diagnosed with pneumonia and was breathing with the aid of a 50% ventilation mask. He was hypertensive and presented Alzheimer's and Parkinson's disease. Urine, sputum and blood samples were collected for cultures in three different sites upon hospital admission. The urine culture on cystine-, lactose-, and electrolyte-deficient (CLED) agar (HiMedia, India) was negative, and the sputum culture on chocolate agar (HiMedia, India) showed growth (50,000 cfu/ml) with Gram-negative features (i.e. small and non-pigmented), however, this was considered a non-significant growth by the microbiology laboratory. Three blood samples were later inoculated on chocolate agar (HiMedia, India) and incubated at 37°C on microaerophilic environment for 18 h, and all of them yielded significant monomicrobial growth. After Gram staining performance, Gram-negative coccobacilli isolate was observed. Biochemical tests results revealed a non-fermenting isolate. In addition, the strain presented oxidase-negative, catalase-positive, detectado por la técnica de reacción en cadena de la polimerasa (RCP). Acinetobacter radioresistens puede ser considerado un agente importante de infecciones oportunistas en pacientes inmunocomprometidos, un potencial diseminador de genes de resistencia.
Polymerase chain reaction (PCR) assays screening for carbapenem-hydrolyzing class D β-lactamases encoding genes were performed, as previously published (9) . The strain showed positive results for bla oxa-23 gene. The amplicon was observed in an agarose gel electrophoresis at 2%, stained with ethidium bromide, visualized under ultra-violet (UV) transilluminator, and photographed. After bla oxa-23 gene was confirmed, NT 5376 strain was also screening for the insertion sequence ISaba1 by PCR assay, as previously described by Segal et al. (2005) (10) . The strain presented negative results for this insertion sequence.

DiSCuSSion
This is the first report of bloodstream infection by A. radioresistens in Brazil. Antimicrobial therapy was performed with ceftriaxone and the patient received hospital discharge in good clinical condition. This infection can be considered as a community-acquired infection since it was detected upon patient's hospital admission and was not related to any previous hospitalization (11) . Community infections associated to Acinetobacter spp. mainly affect patients with some morbidity (1) . The patient from this report presented Alzheimer and Parkinson's disease. In addition, diseases such as Alzheimer and Parkinson increase the risk of saliva aspiration, more prone to respiratory infections. The infection occurred, possibly, through the upper airways with subsequent dissemination through the bloodstream.
The respiratory systems are a gateway for Acinetobacter spp. bloodstream infection (12) , which is in agreement with the initial diagnosis of the case, which was pneumonia. The development of aspiration pneumonia with Alzheimer's disease is related to the reduced level of consciousness, dysphagia, and loss of reflexes, favoring the aspiration of commensal microorganisms from the environment to the airways, causing pneumonia with subsequent dissemination through the bloodstream (13) . Although the strain harbored bla oxa-23 gene, it was susceptible to the carbapenems tested and it showed absence of ISaba1 by PCR screening. Our findings agree with some other studies, which also detected bla oxa-23 gene and absence of ISaba1 in A. radioresistens sensitive to carbapenems. This phenomenon has been explained by relating this sensitivity to the absence of genetic elements in the genome, particularly the ISaba1 insertion sequences (5) .
rEfErEnCES Therefore, further studies will be needed to better understand the pathogenic potential of the Acinetobacter radioresistens species, since it may play a significant role as an infectious agent, especially in immunocompromised patients. Furthermore, additional experiments are required to understand the importance of harboring resistance genes in their genome, which show no expression, and their ability to disseminate them to other species.

aCknowLEDgMEntS
The authors thank to Dra. Beatriz Meurer Moreira for helping them identifying the A. radioresistens isolate and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) for the financial support.