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Klebsiella pneumoniae , a member of the autochthonous human gut microbiota, utilizes a variety of virulence factors for survival and pathogenesis. Consequently, it is responsible for several human infections, including urinary tract infections, respiratory tract infections, liver abscess, meningitis, bloodstream infections, and medical device-associated infections. The main studied virulence factors in K. pneumoniae are capsule-associated, fimbriae, siderophores, Klebsiella ferric iron uptake, and the ability to metabolize allantoin. They are crucial for virulence and were associated with specific infections in the mice infection model. Notably, these factors are also prevalent in strains from the same infections in humans. However, the type and quantity of virulence factors may vary between strains, which defines the degree of pathogenicity. In this review, we summarize the main virulence factors investigated in K. pneumoniae from different human infections. We also cover the specific identification genes and their prevalence in K. pneumoniae , especially in hypervirulent strains., Competing Interests: Conflict of interestThe authors declare no conflicts/competing interests., (© Association of Microbiologists of India 2024. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)

Multidrug-resistant gram-negative bacteria, such as carbapenem and colistin-resistant Klebsiella pneumoniae (ColR-CRKP), represent a major problem for health systems worldwide and have high lethality. This study investigated the genetic relationship, antimicrobial susceptibility profile, and resistance mechanisms to ColR-CRKP isolates from patients infected/colonized in a tertiary hospital in Salvador, Bahia/Brazil. From September 2016 to January 2018, 46 patients (56 ColR-CRKP positive cultures) were enrolled in the investigation but clinical and demographic data were obtained from 31 patients. Most of them were men (67.7%) and elderly (median age of 62 years old), and the median Charlson score was 3. The main comorbidities were systemic arterial hypertension (38.7%), diabetes (32.2%), and cerebrovascular disease (25.8%). The average hospitalization stay until ColR-CRKP identification in days were 35.12. A total of 90.6% used mechanical ventilation and 93.7% used a central venous catheter. Of the 31 patients who had the data evaluated, 12 had ColR-CRKP infection, and seven died (58.4%). Previous use of polymyxins was identified in 32.2% of the cases, and carbapenems were identified in 70.9%. The minimum inhibitory concentration (MIC) for colistin was > 16 μg/mL, with more than half of the isolates (55%) having a MIC of 256 μg/mL. The bla KPC gene was detected in 94.7% of the isolates, bla NDM in 16.0%, and bla GES in 1.7%. The bla OXA- 48 , bla VIM , and bla IMP genes were not detected. The mcr-1 test was negative in all 56 isolates. Alteration of the mgrB gene was detected in 87.5% ( n = 49/56) of the isolates, and of these, 49.0% (24/49) had alteration in size probably due to IS 903B , 22.4% (11/49) did not have the mgrB gene detected, 20.4% (10/49) presented the IS 903B , 6.1% (3/49) had a premature stop codon (Q30*), and 2.1% (1/49) presented a thymine deletion at position 104 - 104delT (F35fs). The PFGE profile showed a monoclonal profile in 84.7% of the isolates in different hospital sectors, with ST11 (CC-258) being the most frequent sequence type. This study presents a prolonged outbreak of ColR-CRKP in which 83.9% of the isolates belonged to the same cluster, and 67.6% of the patients evaluated had not used polymyxin, suggesting the possibility of cross-transmission of ColR-CRKP isolates., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Rocha, Barbosa, Leal, Silva, Sales, Monteiro, Azevedo, Malheiros, Ataide, Moreira, Reis, Bahia and Reis.)

Introduction. Sickle cell disease (SCD) children have a high susceptibility to pneumococcal infection. For this reason, they are routinely immunized with pneumococcal vaccines and use antibiotic prophylaxis (AP). Hypothesis/Gap Statement. Yet, little is known about SCD children's gut microbiota. If antibiotic-resistant Enterobacterales may colonize people on AP, we hypothesized that SCD children on AP are colonized by resistant enterobacteria species. Objective. To evaluate the effect of continuous AP on Enterobacterales gut colonization from children with SCD. Methodology. We analysed 30 faecal swabs from SCD children on AP and 21 swabs from children without the same condition. Enterobacterales was isolated on MacConkey agar plates and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) (bioMérieux, Marcy l'Etoile, France). We performed the antibiogram by Vitek 2 system (bioMérieux, Marcy l'Etoile, France), and the resistance genes were identified by multiplex PCR. Results. We found four different species with resistance to one or more different antibiotic types in the AP-SCD children's group: Escherichia coli , Klebsiella pneumoniae , Citrobacter freundii , and Citrobacter farmeri . Colonization by resistant E. coli was associated with AP (prevalence ratio 2.69, 95 % confidence interval [CI], 1.98-3.67, P <0.001). Strains producing extended-spectrum β-lactamases (ESBL) were identified only in SCD children, E. coli , 4/30 (13 %), and K. pneumoniae , 2/30 (7 %). The ESBL-producing Enterobacterales were associated with penicillin G benzathine use (95 % CI, 22.91-86.71, P <0.001). CTX-M-1 was the most prevalent among ESBL-producers (3/6, 50 %), followed by CTX-M-9 (2/6, 33 %), and CTX-M-2 (1/6, 17 %). Conclusion. Resistant enterobacteria colonize SCD children on AP, and this therapy raises the chance of ESBL-producing Enterobacterales colonization. Future studies should focus on prophylactic vaccines as exclusive therapy against pneumococcal infections.