Lacticaseibacillus spp., a Gram-positive facultative anaerobic bacterium, is a constituent of the natural human microbiota and is used in probiotic health supplements [1,2]. While these organisms are considered to be of low virulence and often does not cause harm; however, they can cause opportunistic infection in immunocompromised patients [1]. However, there has been a growing number of reports regarding the infections caused by Lacticaseibacillus spp., specifically Lacticaseibacillus casei and Lacticaseibacillus rhamnosus (L. rhamnosus). These include bacteraemia, endocarditis, pneumonia, intra-abdominal infections, peritonitis, chorioamnionitis, and abscesses in immunocompromised patients [1-11]. Here we present the first case report of L. rhamnosus infection in a patient who underwent a liver transplant and provide an overview of cases reported in literature.

A 63-year-old male underwent his first liver transplant (LTX) in 2021 due to hepatocellular cancer. He was maintained on tacrolimus immunosuppressive therapy post-transplant. Post first LTX he developed biliary anastomotic stricture of the graft and complete thrombosis of intrahepatic branches portal veins (Fig. 1A). Consequently, he underwent second LTX in January 2024. He received the liver graft from donation after brain death (DBD) with cold ischemia time of 12 hours and 22 minutes. Because of his deformed portal architecture, he needed a difficult anastomosis of the portal vein. Unfortunately, he developed primary non function graft within 24 hours, requiring laparotomy that confirmed necrosis of the 80% of the liver. As a result, the graft was removed and the patient stayed anhepatic for 24 hours. Patient was listed for a super urgent third LTX. He received the third liver graft DBD donor, with cold ischemia period of 11 hours and 15 minutes had a caval replacement, single arterial anastomosis and portal anastomosis with interposition graft. Post LTX he required repeated transfusions, because of more than 10 L blood loss during the transplant procedure. He received piperacillin-tazobactam, vancomycin, and anidulafungin, according to local antimicrobial protocol and he was re-started on standard immunosuppression of methylprednisolone and tacrolimus. The tacrolimus level was maintained between 5–10 ng/mL. On day 7 of post-transplant, his antibiotic regimen was escalated to meropenem due to pyrexia and worsening inflammatory markers (Fig. 2). On post-operative day 17, a computed tomography (CT) scan of the abdomen and pelvis performed for abdominal distension and tenderness (Fig. 1B) showed a colonic perforation. On post-operative day 18, he underwent re-laparotomy with a primary repair and a loop ileostomy. On day 20, a new ascending colonic perforation was identified, necessitating a repeat laparotomy and a right hemicolectomy. The possible causes of perforation was thought to be secondary to ischemic colitis following hypovolemic episodes, gastrointestinal mucosal injury, prolonged operative times and multiple abdominal surgeries.

Figure 1. CT imaging timeline. (A) Pre redo transplant computed tomography (CT) abdomen and thorax. (B) Day 17 post redo transplant day CT abdomen and thorax. (C) Day 44 CT abdomen and thorax prior to thoracotomy. (D) Day 114 CT thorax. (E) Post thoracotomy.

Figure 2. Rising inflammatory markers post-transplant. WCC, white cell count.

Intraoperative cultures from abdominal wall tissue and peritoneal fluid grew L. rhamnosus, despite being on meropenem. This isolate was identified multidrug resistant (MDR) including resistant to piperacillin-tazobactam, meropenem and vancomycin, the routinely used antibiotics in post-transplant period. It was only sensitive to metronidazole, and after susceptibility results were available, on day 25 metronidazole was added. As his condition did not improve, CT thorax, abdomen, and pelvis was repeated on day 44 (Fig. 1C), showing less peritoneal collection than previous imaging, but large bilateral pleural effusions. Pleural drainage was performed twice, on day 82 and day 99 and drained turbid, caramel-coloured fluid. These pleural fluid cultures grew L. rhamnosus, despite 60 days of metronidazole and meropenem treatment. CT thorax on day 114 (Fig. 1D) showed the persistent empyema. Therefore, on day 119, patient underwent right thoracotomy and decortication for the empyema. Intraoperatively, a connection between the transplanted liver and the pleural cavity was observed. He received a total of 4 months of meropenem and metronidazole. The patient recovered from the described infection postoperatively, evidenced by resolution of the empyema by radiological imaging (Fig.1E) but remained an inpatient for further management of his post LTX associated complications. The timeline of infections and treatment are shown in Fig. 3.

Figure 3. Timeline of infection and treatment. L. rhamnosus, Lacticaseibacillus rhamnosus; LTX, liver transplant.

The gut translocation and systemic dissemination are the likely underlying mechanisms of pathogenesis in most reported cases of L. rhamnosus intra-abdominal infections or bacteraemia [5]. In our case the infection was secondary to colonic perforation, which is triggered by ischaemic bowel and multiple abdominal surgeries. Despite being on antibiotics for more than 3 months and source control the intra-abdominal infection progressed to pleural empyema. This was likely due to MDR strain of L. rhamnosus for routinely used antibiotics in post-transplant patient and delay in starting the appropriate treatment. This delay in appropriate treatment of these opportunistic infections can be complicated due to long turnaround time because of difficult processing of the culture and sensitivity of anaerobic organisms in the laboratory. Although L. rhamnosus is a relatively low-pathogenicity organism, it has been consistently reported as a major cause of bacteraemia in both immunocompetent and immunocompromised patients, indicating that it has a higher level of pathogenicity than previously believed [1-11]. In a case series of 47 patients reported by Albarillo et al. [8], L. rhamnosus was isolated from various samples, such as blood cultures, wounds, urine, abdominal abscesses, and respiratory samples, and was associated with very high mortality of 55%. The likely risk factors for increased mortality were; these patients were critically ill with major comorbidities, had polymicrobial infections, and exposure to broad-spectrum antibiotic, which can disrupt the normal gut microbiota and potentially allowing opportunistic pathogens to cause infections [8]. In our case the patient did not have any other infection unlike in a case reported by Falci et al. [7] of L. rhamnosus bacteraemia in a kidney transplant recipient, who had multiple opportunistic infections including cytomegalovirus infection, cryptococcal meningitis and gastrointestinal tuberculosis. The patient underwent a bowel resection and received vancomycin, fluconazole, rifampicin and isoniazid. However, day 80 after bowel resection, developed L. rhamnosus bacteraemia, which was resistant to routinely use antibiotics cephalosporins and glycopeptides, nevertheless, patient was treated successfully with ampicillin for 21 days after sensitivity results were available [7].

In a case report by Kell et al. [5], a 76-year-old man with a complicated past medical history, empirically treated for urinary tract infection with IV piperacillin/tazobactam. The treatment was escalated to meropenem to treat infection due to extended spectrum beta lactamase Escherichia coli. However patient developed splenic abscess and bacteraemia due to L. rhamnosus. There was no history of probiotic supplementation suggesting the infection could have been acquired from diet or endogenous gut flora. The organism was susceptible to ampicillin, penicillin however resistant to vancomycin. The patient was treated successfully with piperacillin/tazobactam for eight-week period with source control [5]. Similar patterns of antibiotic resistance observed in most reported cases, can complicate initial treatment with empirical antibiotics, because of the varying degree of antimicrobial susceptibility [1,3,6].

Isolating and performing antibiotic susceptibility tests (AST) for L. rhamnosus is challenging due to their low relevance and unique growth requirements such as requiring capnophilic or anaerobic atmosphere and often extended culture times up to 48 hours, which may delay diagnosis [1,6,11]. There is also diagnostic dilemma among clinicians regarding interpretation of positive cultures for Lacticaseibacillus spp., where in some instances a single positive culture may be treated as a contaminant rather than true infection, underestimating the significance of infection and potential pathogenicity [1]. AST guidance lacks standardization for L. rhamnosus. However it is important to perform AST for these isolates in clinical and research settings, because of its increasing use as probiotics for its beneficial effect and in contrast its role as a potential opportunistic pathogen in immunocompromised patients [3,5]. The recommendations for AST for Lacticaseibacillus (Lactobacillus) spp. by two major organizations -Clinical Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST), are different [12,13]. The CLSI recommends testing for ampicillin, penicillin, imipenem, meropenem, vancomycin, daptomycin, erythromycin, clindamycin, and linezolid, whilst EUCAST recommends testing for ampicillin, gentamicin, streptomycin, and tetracycline [12,13]. The susceptibility pattern of Lactocaseibacillus spp. might exhibit variability depending on the strain and due to its intrinsic resistance [3,8]. Penicillin and ampicillin are generally effective against L. rhamnosus and there is inherent resistance to vancomycin, ciprofloxacin, tetracycline, meropenem, metronidazole, and sulphonamides [14]. This was evident in our case where the strain was only sensitive to metronidazole and our patient was on piperacillin-tazobactam, vancomycin and meropenam treatment, when the infection progressed. Consequently, the patient had a favourable response when metronidazole was incorporated into the therapy regimen. The duration of treatment for Lactocaseibacillus infections can vary significantly and is contingent upon the patient’s individual response and any pre-existing risk factors. An analysis of 85 cases revealed that the length of treatment can vary from a few days to several weeks (Table 1) [1,2,5,7-11,15].

Table 1 . Reported cases of Lacticaseibacillus rhamnosus infection.

Author	Sex	Age (yr)	Site of infection	Underlying condition	Treatment & duration	Outcome
Albarillo et al. [8]	47 patients		Intra-abdominal infection, bacteraemia, mediastinitis, others (empyema, septic arthritis, pneumonia, vascular graft, and mandibular abscess)	Gastrointestinal disruptions/gastrointestinal related procedures, malignancy, cardiovascular disease, immunosuppression, biliary disease, diabetes mellitus, renal disease, prior antibiotic exposure	Vancomycin, metronidazole, carbapenems, piperacillin-tazobactam, cephalosporins, others (daptomycin, linezolid, clindamycin, trimethoprim-sulfamethoxazole, amoxicillin-clavulanic acid, aztreonam, fluoroquinolones, and ampicillin-sulbactam) Mean duration of antibiotics: 3.7±2.2 weeks	57.1% clinical improvement; 56.2% mortality
Rubin et al. [2]	Male	56	Bacteraemia	Immunocompetent, consumed commercial probiotic presented with multi-trauma	No treatment, probiotic discontinued	Infection resolved with cessation of probiotics
Eze et al. [9]	Male	79	Bacteraemia	Parkinson’s disease, stage III chronic kidney disease, type II diabetes mellitus, hypertension, chronic anaemia, atrial fibrillation, pacemaker placement and bio prosthetic aortic valve replacement	Ampicillin-sulbactam and vancomycin	Deceased
Kell et al. [5]	Male	76	Bacteraemia, perisplenic fluid	Coronary artery disease, intracerebral haemorrhage, peripheral vascular disease, hypertension, type II diabetes mellitus, congestive heart failure and pacemaker	Piperacillin/tazobactam 1–2 months	Successfully treated
Karime et al. [10]	Male	60	Bacteraemia	Bio prosthetic aortic valve replacement, ulcerative colitis treated with balsalazide and probiotics containing six Lactobacilli strains including Lacticaseibacillus rhamnosus	Ampicillin 14 days	Successfully treated
Falci et al. [7]	Female	43	Bacteraemia	Kidney transplant recipient	Ampicillin 21 days	Successfully treated
Mikucka et al. [1]	Male	83	Bacteraemia	Acute respiratory failure and haemorrhagic shock due to polytrauma	Amoxicillin-clavulanate 10 days	Deceased
Mikucka et al. [1]	Female	74	Bacteraemia	Acute respiratory failure after mitral valve replacement, tricuspid valve annuloplasty and coronary artery bypass grafting	Ampicillin, not stated	Successfully treated
Aydoğan et al. [15]	Male	Infant	Bacteraemia	Aortic coarctation	Ampicillin	Successfully treated
Lilitwat et al. [11]	Male	14	Lung abscess	Cerebral palsy, epilepsy, asthma	IV ampicilin-sulbactam then oral amoxicillin-clavulanic acid 4 weeks	Successfully treated

There is increasing concern of developing infections from the use of probiotics especially in immunocompromised patients and in patients with multiple comorbidities [2,9,10]. Rarely can it cause infection in immunocompetent patient. In a case report by Rubin et al. [2], a 56-year-old immunocompetent multi-traumatised woman with a central venous catheter developed a bloodstream infection with L. rhamnosus after being administered the probiotic. The whole genome sequencing confirmed that the bloodstream strain matched the probiotic strain [2]. In contrast probiotic use for chronic diarrhoea in a 79-year-old man with numerous comorbidities developed L. rhamnosus bacteraemia resistant to empirically administered antibiotics [9]. This patient received targeted antibiotic therapy, but experienced multiple severe complications and deceased [9]. Similarly, a immunocompromised 60 years old patient with ulcerative colitis was on probiotics, developed L. rhamnosus sepsis and endocarditis with septic emboli to the brain [10]. The patient was treated intravenous ampicillin and gentamicin and discharged with long term suppressive therapy of oral amoxicillin [10]. Together, these cases emphasize the need for caution in administering probiotics to immunocompromised patients. The reported cases of L. rhamnosus in literature are shown in Table 1.

In our case, despite the use of appropriate antibiotics, the infection still disseminated, highlighting the crucial need for effective source control in managing anaerobic infections. The infection was successfully resolved through a combination of draining the empyema, repeated intra-abdominal washouts, and continued long-term antibiotic therapy. Acknowledging these diagnostic and therapeutic challenges, our case underscores the critical need for clinicians to maintain vigilance when they are presented with potential L. rhamnosus isolate with high index of suspicion for infections, particularly in immunocompromised patients.

This case highlights several key considerations for treating invasive Lactocaseibacillus spp.:

1. Given the variability in antibiotic susceptibility and resistance patterns, antimicrobial therapy should be tailored based on AST of the isolated strain.

2. Addressing the source of the infection is crucial, as antibiotics alone may not be sufficient to control the infection without effective source management.

3. Treatment duration should be individualized based on the patient’s response and underlying conditions, which can range from several days to weeks.

There was no funding related to this study.

All authors have no conflicts of interest to declare.

Conceptualization: AAH, AV. Data curation: AAH, AV. Formal analysis: AAH, AV. Investigation: AAH, AV, BM, FT. Methodology: AAH, AV. Project administration: AV. Resources: AAH, AV. Software: AAH, AV. Supervision: AV. Validation: AV. Visualization: AAH, AV. Writing – original draft: AAH, AV. Writing – review & editing: AAH, AV, BM, FT.