Bacillus cereus causing brain abscess in an immunocompetent patient with craniotomy

Introduction

Bacillus cereus is a motile, aerobic or facultative anaerobic, sporulating, Gram‑positive bacilli. As a human pathogen, it usually causes self‑limited foodborne acute gastroenteritis. It can cause opportunistic infections such as bacteraemia, pneumonia, ophthalmitis, osteomyelitis, cutaneous-soft tissue infections and meningitis among neonates, immunocompromised and sometimes immunocompetent hosts with high risk or implants.1, 2, 3 The route of transmission is usually via indwelling catheters or foreign bodies. The occurrence of B.cereus in hematological malignancies ranges from 0.07% to 2%.4, 5 Mortality can be as high as 42%6 to 52%.7

Case Report

A 44 years old, immunocompetent male patient was admitted to the hospital with fever and left hemiparesis in March 22. He had history of right parieto-occipital intracranial haemorrhage (ICH) and subarachnoid haemorrhage (SAH) one month back. On examination pupil reacted to light, but he couldn’t obey commands to open the eyes. The rest of the findings were as expected.

In Feb ’22, he was admitted with left sided giddiness, slurring of speech and headache at another hospital. MRI brain showed right parieto-occipital intracranial haemorrhage with midline shift and uncal herniation. He underwent decompressive craniotomy and partial clot evacuation for the same. One week later arteriovenous embolization was done. The patient was brought to our institute 4 weeks after the craniotomy.

CT scan was done on the day of admission, showed peripherally enhancing brain abscess in right parietal lobe with surrounding oedema. This was at the surgical site. Patient was started with treatment for management of SAH and ICH along with meropenem and vancomycin. Patient was put on ventilator. Laboratory investigations were done as appropriate which included blood culture and urine culture.

Exploration and evacuation of abscess was done on 2^nd day of admission. Pus collected during surgery showed gram positive bacilli on smear examination and further grew Bacillus cereus on 5% Sheep blood agar which was identified by Vitek MS (MALDIToF, Biomerieux, France). Antimicrobial susceptibility was done on Vitek2 and breakpoint of Bacillus sp. By EUCAST (The European Committee on Antimicrobial Susceptibility Testing) were followed.19 It was sensitive to vancomycin (MIC1), linezolid (MIC1), clindamycin (MIC0.5). Penicillin and levofloxacin were found to be resistant. Antimicrobial therapy was deescalated to only vancomycin once the reports were available. Blood culture on admission grew Candida tropicalis which was fluconazole resistant. Caspofungin was added to antimicrobial treatment for candidemia. Urine culture grew Candida auris which was considered as coloniser as patient’s symptoms were attributed mostly to the brain abscess. Vacomycin and caspofungin each were continued for 14 days. His clinical condition improved. Blood culture did not grow Candida tropicalis after seven days of caspofungin. The patient remained in the hospital for approximately six months for rehabilitation therapy and then was discharged.

Discussion

Brain abscess due to B.cereus are reported from India1 and other countries6, 20, 17, 16, 8 but brain abscess at surgical site in immunocompetent patient is not reported. The reported cases of brain abscess are summarised in Table 1.

Conventionally, the detection of Bacillus spp. in clinical specimens is considered as contaminant due to its ubiquitous presence in environment.3 Evaluating the clinical settings and predisposing factors3 of the patient is crucial to identify it as pathogen and reduce the turnaround time to report. Repeated isolations are useful but it takes up the additional time. In our case, pus specimen collected during surgery grew B.cereus hence it was considered as a pathogen.

Surgical drainage is significant in the treatment of individuals with brain abscesses by B.cereus along with antimicrobial therapy for improved outcome.1, 5

Often B.cereus is found to be resistant to penicillin.5, 17, 8 Antimicrobial susceptibility reporting for B.cereus is done as per EUCAST Guidelines19 of Bacillus sp. or sometimes, breakpoints for staphylococcus are extrapolated for B.cereus.17, 21 Hence, appropriate standardisation for susceptibility is imperative.

Patient was a middle-aged healthy person before SAH. It was crucial to make an attempt to give him his previous pre-morbid life back. Hence, aggressive surgical drainage to relieve symptoms and bacterial load along with vancomycin was used for our patient.

Patient also had candidemia at the time of admission to our hospital and was treated as per susceptibility pattern. It is important to mention that since our patient had candidemia at the time of admission and if he was treated presuming Candida tropicalis also as brain abscess pathogen without draining or culturing the pus or if B.cereus was considered as contaminant, the patient’s outcome could have been compromised.

Candida auris in urine was considered to be a coloniser as described. Contact isolation however, was maintained.

Patient was further provided extensive rehabilitation therapy to improve his mobility and was discharged from the hospital after about six months.

Conclusion

Brain abscess is one of the important non-gastrointestinal manifestation of B.cereus. It is imperative to achieve a microbiologic diagnosis of B.cereus quickly. Antimicrobial susceptibility needs standardisation. Clinico-Microbiological correlation to ensure that it is not a contaminant along with appropriate surgical and antimicrobial treatment improves patient outcome.

Conflicts of Interest

None.

Ethics Approval

Patient’s informed and written consent was taken. Study is approved by Institutional Review Board.