A 52-year-old maintenance haemodialysis patient developed a catheter-related bloodstream infection caused by the water-associated Gram-negative bacterium Aeromonas dhakensis, according to a clinical case report. Medical staff identified the pathogen using MALDI-TOF mass spectrometry after the patient experienced recurrent chills, rigours, and right internal jugular vein catheter site tenderness during dialysis sessions at multiple regional centres.
Emergence of Aeromonas dhakensis in Haemodialysis Infections
According to the case report, water-associated Gram-negative organisms are increasingly recognized in haemodialysis settings where patients face repeated exposure to water systems, dialysis equipment, and disinfectants. Aeromonas dhakensis, which was reclassified as a distinct species in 2013 after previously being considered part of the Aeromonas hydrophila complex, naturally inhabits aquatic environments and aquaculture systems. Studies from Taiwan cited in the report indicate higher fatality rates for this species compared to other members of the A. hydrophila complex. In India, only one prior human infection case has been reported, which proved fatal, though researchers have identified the organism in local Indian water bodies and aquaculture environments.
Clinical Presentation and Diagnostic Challenges
The patient presented to the dialysis unit with a history of chronic kidney disease, diabetes mellitus, hypertension, and previous arteriovenous fistula failure requiring multiple central venous catheter insertions. Upon hospital admission to the Nephrology department, laboratory tests revealed leukocytosis at 16,384 cells/µL, a C-reactive protein level of 112 mg/L, and a procalcitonin level of 49.25 ng/mL, according to the findings. Paired blood cultures drawn simultaneously from the central venous catheter and a peripheral vein showed a differential time to positivity of greater than two hours. Microbiological analysis identified smooth, moist, greyish colonies with beta-haemolysis on sheep blood agar and non-lactose-fermenting colonies on MacConkey agar, verified as A. dhakensis via MALDI-TOF MS (bioMérieux, France).
Did you know? Aeromonas dhakensis can be misidentified as Aeromonas hydrophila in routine practice unless laboratories use MALDI-TOF mass spectrometry or specific conventional biochemical markers such as a positive oxidase reaction and glucose fermentation.
Antibiotic Susceptibility Versus Suboptimal Clinical Response
Initial antimicrobial susceptibility testing performed by disc diffusion according to CLSI M45 guidelines showed the isolate was susceptible in vitro to ceftazidime, piperacillin-tazobactam, cefepime, meropenem, imipenem, amikacin, and ciprofloxacin. Despite empirical treatment with intravenous ceftazidime, the patient remained febrile with only marginal inflammatory marker declines after 72 hours. According to the report, this suboptimal response occurred because A. dhakensis carries chromosomally encoded class B, C, and D beta-lactamases—including the species-specific AmpC enzyme blaAQU-1—which can cause treatment failure despite apparent in vitro susceptibility. Furthermore, environmental isolates from sewage water in India have demonstrated colistin resistance mediated by the mcr-1 gene.
Resolution Following Catheter Removal
Suspecting a persistent catheter-related infection with probable biofilm formation, clinicians removed and replaced the right internal jugular vein catheter. Culture of the removed catheter tip grew A. dhakensis with the same susceptibility profile as the blood isolate, according to the documentation. Following catheter removal, the patient showed rapid clinical improvement: leukocyte counts dropped to 7,500 cells/µL, C-reactive protein fell to 24 mg/L, and procalcitonin decreased to 4.38 ng/mL. Repeat blood cultures after catheter removal were sterile, and the patient was discharged in stable condition after completing five total days of ceftazidime therapy.
Frequently Asked Questions
What is Aeromonas dhakensis?
Aeromonas dhakensis is a water-associated Gram-negative bacterium found in aquatic environments that can cause severe human infections, including bacteraemia and necrotising fasciitis.
Why is accurate laboratory identification important for Aeromonas dhakensis?
According to the case report, accurate speciation using MALDI-TOF mass spectrometry prevents misidentification as Aeromonas hydrophila, ensuring clinicians recognize the higher virulence and potential resistance mechanisms associated with this specific pathogen.
What role does catheter removal play in treating catheter-related bloodstream infections?
When patients fail to improve despite appropriate antimicrobial therapy due to factors like possible biofilm formation on indwelling devices, early removal and replacement of the central venous catheter is essential for achieving source control and clinical recovery.
Pro Tip: Healthcare providers managing haemodialysis patients with persistent bacteraemia should maintain high clinical awareness of emerging water-borne pathogens and consider early catheter removal when standard antibiotic therapy yields a suboptimal response.
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