A 2023 review provides a detailed examination of the Citrobacter species, focusing on the growing threat they pose to public health due to their increasing antimicrobial resistance. Among the species discussed, Citrobacter braakii is highlighted for its involvement in various infections, including urinary tract infections and meningitis. This species has been isolated from different clinical samples across the globe, including wound infections and cases presenting with severe underlying medical conditions such as diabetes and cardiovascular disease. The review emphasizes that Citrobacter braakii exhibits resistance to multiple antibiotics, including beta-lactams and fluoroquinolones, posing a significant challenge for treatment. The resistance is often mediated by chromosomal and plasmid mechanisms, complicating empirical treatment options and necessitating the use of combination therapies that are often costly and potentially hazardous. The 2023 review also explores the epidemiology and virulence factors associated with Citrobacter braakii, which contribute to its pathogenicity in causing opportunistic infections in immunocompromised patients. The study notes the species' capability to form biofilms and produce toxins, factors which enhance its ability to colonize and invade host tissues. These characteristics, coupled with its multidrug-resistant nature, underscore the critical need for improved infection control measures and comprehensive surveillance to mitigate the spread of Citrobacter braakii infections in healthcare settings. [1]
A 2020 publication detailed the genetic diversity, antimicrobial resistance, and virulence characteristics of Citrobacter spp., with a focus on Citrobacter braakii. This study involved the analysis of 128 Citrobacter isolates collected from human diarrheal patients, foods, and the environment in Shijiazhuang, Hebei Province, China. Among these, 45 isolates were identified as C. braakii, which were classified into 42 distinct sequence types (STs), indicating a high genetic diversity. Notably, Lineage III contained all C. braakii isolates and displayed the highest prevalence of quinolone resistance among the lineages, with 52.6% of the isolates showing resistance. The antimicrobial resistance profile revealed that C. braakii isolates exhibited multidrug resistance (MDR) with 46.7% being resistant to at least one antibiotic from three or more distinct classes. Additionally, the study identified significant quinolone resistance in C. braakii with several isolates harboring mutations in the quinolone resistance-determining regions (QRDR) of the gyrA gene. The isolates also carried various plasmid-mediated quinolone resistance (PMQR) genes, including qnr and aac(6')-Ib-cr. Furthermore, C. braakii isolates were also assessed for their virulence potential, with some isolates showing high cytotoxicity and adhesion properties, indicating a potential pathogenic role in causing diarrheal disease. [2]
According to a 2022 study, Citrobacter braakii was isolated from solid-organ transplant patients during a surveillance for multidrug-resistant Enterobacteriaceae. Among the 57 strains of cefpodoxime-resistant Citrobacter spp. identified, 10 were Citrobacter braakii. These strains displayed resistance to multiple antibiotics, including cephalosporins, aminoglycosides, and trimethoprim-sulfamethoxazole. Notably, one clinical isolate obtained from a urine specimen in the study was Citrobacter braakii, indicating its presence in both colonizing and potential infection scenarios. Pulsed-field gel electrophoresis (PFGE) revealed 36 unique strains of Citrobacter among 32 patients, highlighting the genetic diversity of these isolates. Moreover, Citrobacter braakii was recognized for its novel association with class I integrons in this study, marking the first report of integrons encoding resistance mechanisms in this species. Despite the prevalence of multidrug-resistant strains, the study noted that these low-virulence species only led to a single recorded infection with a colonizing strain over 18 months, suggesting limited pathogenic potential in the hospitalized, immunocompromised population. [3]
A 1997 clinical paper presents findings on Citrobacter braakii within a study conducted at the University Hospital St Rafael in Leuven, Belgium. This research involved the collection of 126 samples from 116 patients over a six-month period, during which the identification, differentiation, and susceptibility of various Citrobacter species were analyzed. Citrobacter braakii was identified as the second most common species, following Citrobacter freundii, with a prevalence of 21.6% among the isolates. This species demonstrated a significant presence in the urinary and respiratory tracts, and it was often associated with predisposing factors such as intubation, tracheostomy, or serious debilitating conditions. In terms of antimicrobial susceptibility, Citrobacter braakii exhibited resistance patterns that were comparable to those seen in the C. freundii complex. Specifically, the strains were generally resistant to ampicillin, amoxicillin-clavulanate, and cefazolin, with percentages of resistance being 96%, 96%, and 98%, respectively. However, these strains were found to be sensitive to newer antibiotics like ceftazidime, cefepime, and imipenem. The findings underscore the opportunistic nature of Citrobacter braakii as a pathogen in hospital settings, where it contributes to infections frequently encountered in patient populations with underlying health issues. [4]
A 2007 observational study examined the antibiotic sensitivity pattern of Citrobacter species isolated from various clinical specimens at Kasturba Medical College, Mangalore. Using the Kirby-Bauer disk diffusion method, the study evaluated 709 isolates to determine their antimicrobial susceptibility. Results revealed that all isolates were susceptible to Imipenem, demonstrating a 100% susceptibility rate, while there was a complete resistance to Ampicillin. The variability in susceptibility to third-generation cephalosporins was notable, with rates ranging from 29% to 43%, indicating a significant level of resistance. Further detailed investigation using agar dilution methods determined the minimum inhibitory concentration (MIC) of Cephotaxime, considering MIC values equal to or less than 8 µg/ml as susceptible. Among the assessed strains, 253 were fully susceptible, 71 exhibited intermediate susceptibility, and 385 were fully resistant to Cephotaxime. The study emphasized that the use of beta-lactamase inhibitor combinations with beta-lactam antibiotics increased sensitivity, suggesting a potential strategy to mitigate resistance. These findings underscore the complex nature of antibiotic resistance in Citrobacter species, highlighting the critical need for tailored antibiotic stewardship in clinical settings to effectively manage infections. [5]
A 2018 case report described a 67-year-old man with acute myeloid leukemia who developed septic shock due to Citrobacter braakii during chemotherapy with high-dose cytosine arabinoside. Treatment with cefepime led to rapid clinical improvement, highlighting the antibiotic’s effectiveness against this rare pathogen. The authors emphasized that reported cases of C. braakii sepsis are limited and that further case accumulation is needed to clarify risk factors. Additional details are unavailable as the full article is published in Japanese. [6]