The human oral cavity is a complex and dynamic microbial ecosystem, encompassing distinct niches such as the buccal mucosa, tongue, and palate, which collectively support a dense and diverse microbiota (Lu and Xuan, 2019). While predominantly inhabited by commensals, shifts in microbial balance, particularly under hospitalization or immunocompromised conditions, can facilitate colonization by clinically significant Gram-negative bacilli, including Klebsiella (K.) pneumoniae (Zaatout, 2021; Katkowska et al., 2023).

Klebsiella species are diverse, with relatively large genomes that confer metabolic flexibility, biochemical diversity, and the ability to colonize clinical and environmental niches such as soil, plants, surface water, and medical devices (Choby et al., 2020; Mendes et al., 2023). In humans, these bacteria are typically found within the microbiota of healthy individuals and inconspicuously inhabit the digestive systems (Dong et al., 2022; Muraya et al., 2022; Li et al., 2023).

Recent studies have frequently reported the presence of K. pneumoniae in oral samples (Le et al., 2020; Wei et al., 2021; Haruta et al., 2023), although its role as a true member of the oral flora remains under debate (Tsuzukibashi et al., 2023; Liu et al., 2024). This organism is known to colonize the oral cavity in specific contexts, particularly in hospitalized patients or those with poor hygiene or reduced salivary flow, thereby creating opportunities for nosocomial transmission via saliva or oropharyngeal secretions (Amaral et al., 2009; Needleman et al., 2013; Altayar et al., 2020).

Currently, most research has focused on K. pneumoniae, which accounts for approximately 95% of Klebsiella infections and is recognized as the most common human pathogen within this genus (Effah et al., 2020; Wyres et al., 2020; Shah et al., 2025).

This opportunistic pathogen represents a major global health threat due to the rise of hospital-acquired infections associated with multidrug resistance, particularly in intensive care units (ICUs), as well as community-acquired infections linked to its high virulence (Wei et al., 2021; Zhu et al., 2024; Shah et al., 2025). A substantial percentage of K. pneumoniae infections occur in newborns, the elderly, and those with compromised immune systems and can cause a range of infections, including pneumonia, soft tissue and surgical wound infections, urinary tract infections, bloodstream infections, pyogenic liver abscesses, and sepsis (Muraya et al., 2022; Li et al., 2023; Spadar et al., 2023; Zhu et al., 2024).

A significant proportion of infections caused by Klebsiella species can be attributed to two primary pathotypes: Multidrug-resistant (MDR) and hypervirulent (hv) clones (Dong et al., 2022; García-Cobos et al., 2025). Carbapenemase-producing Enterobacterales pose a serious threat to global health, creating urgent challenges in clinical settings. Among these, Klebsiella pneumoniae carbapenemase (KPC), New Delhi metallo-β-lactamase (NDM), and oxacillinase-48 (OXA-48)-like enzymes are the most critical carbapenemases in terms of their spread and clinical impact (Alvisi et al., 2025; Ragueh et al., 2025). Typically, carbapenemases are encoded on mobile genetic elements, such as plasmids, which can be readily transferred between species through horizontal gene transfer (Xie et al., 2025). The World Health Organization (WHO) has listed K. pneumoniae producing carbapenemase and extended-spectrum beta-lactamases (ESBL) among the “priority pathogens” given their multidrug-resistant phenotype (World Health Organization, 2024). The prevalence of antimicrobial resistance (AMR) genes carried on plasmids and mobile genetic elements has earned K. pneumoniae its reputation as a “key trafficker” of AMR genes between Klebsiella species and other Enterobacterales, highlighting its significance in the spread and development of AMR (Muraya et al., 2022).

In contrast to multidrug-resistant K. pneumoniae, hypervirulent K. pneumoniae (hvKp) has emerged as a significant pathogen primarily associated with severe and invasive community-acquired infections in healthy individuals, such as endophthalmitis and liver abscesses (Hussain et al., 2023; Spadar et al., 2023). They have also been increasingly reported in hospital-acquired infections. These isolates are generally sensitive to most antibiotics but exhibit high virulence (Russo et al., 2024). The virulence factors include the capsule (K1, K2, K20 capsular types), lipopolysaccharide (LPS) with regulatory genes rmpA and rmpA2, and siderophores, predominantly aerobactin (Effah et al., 2020; Spadar et al., 2023).

In recent years, hypervirulent K. pneumoniae (hvKp) strains have evolved through the acquisition of carbapenem resistance, representing a concerning convergence that poses a significant public health threat (Douradinha, 2023; Hussain et al., 2023; García-Cobos et al., 2025). Multiple evolutionary pathways contribute to the emergence of these strains, primarily through the acquisition of resistance plasmids by hvKp, resulting in carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKp), the acquisition of virulence plasmids by carbapenem-resistant K. pneumoniae, resulting in hypervirulent carbapenem-resistant K. pneumoniae (hv-CRKp), or the acquisition of hybrid plasmids carrying both virulence and resistance genes (Arcari and Carattoli, 2023; Mendes et al., 2023; García-Cobos et al., 2025). These strains not only combine hypervirulence and multidrug resistance but also exhibit high transmission rates, making them a serious public health concern (Hussain et al., 2023). Although hvKp and carbapenem-resistant K. pneumoniae (CRKp) populations are recognized for their distinct clonal groups and sequence types (STs), primarily circulating in community and hospital settings respectively, virulence- and resistance-associated genes can be horizontally transferred and exchanged between these populations (Dong et al., 2022; Kochan et al., 2023; Spadar et al., 2023). Genomic analysis of K. pneumoniae strains reveals that these bacteria are classified into sequence types that form high-risk clones globally: the multidrug-resistant (MDR) clones (ST258, ST147, ST101) predominantly circulating in the Western world and hypervirulent clones (ST23, ST65, ST86) mainly in Eastern regions (Arcari and Carattoli, 2023; Byarugaba et al., 2023). The most common MDR-hvKP strains worldwide include the KPC-producing ST11 strain. However, due to the dissemination of mobile genetic elements encoding NDM-1 and OXA-48-type carbapenemases, hvKP strains harboring these determinants have increasingly emerged in recent years (Mendes et al., 2023; García-Cobos et al., 2025). These strains have been reported in several African countries, including Algeria (Zemmour et al., 2021), Egypt (Ahmed et al., 2021; Mendes et al., 2023), Kenya, and Sudan (Ofosu-Appiah et al., 2024).

In Algeria, OXA-48 represents the most common carbapenemase type circulating (Touati and Mairi, 2020). Several studies have reported the isolation of OXA-48-producing K. pneumoniae from clinical samples (Agabou et al., 2014; Bouguenoun et al., 2016; Loucif et al., 2016; Yousfi et al., 2019; Abderrahim et al., 2022), the hospital environment (Bouguenoun et al., 2016), and different ecological niches (Mairi et al., 2019; Loucif et al., 2022a).

Our study aimed to investigate the presence, genetic diversity, resistance mechanisms, and virulence traits of K. pneumoniae colonizing the oral cavity of hospitalized patients in Algeria, with a specific focus on the emergence of high-risk clones exhibiting convergence of multidrug resistance and hypervirulence.

Klebsiella pneumoniae is continuously evolving by acquiring resistance, virulence, and other traits that enable it to survive under antimicrobials and immune defenses. This study represents the first genomic characterization of multidrug-resistant (MDR) K. pneumoniae isolates from the oral cavity of hospitalized patients in Algeria. We assessed their genetic diversity, resistome, and virulome to evaluate the potential threat posed by international high-risk clones, particularly those combining resistance and hypervirulence.

We reported in this study oral colonization by carbapenem-resistant K. pneumoniae in 16 out of 180 hospitalized patients (8.88%) in a medical ward, with ages ranging from 18 to 89 years. Recent investigations have shown that Gram-negative bacteria resistant to third-generation cephalosporins or carbapenems such as Acinetobacter, Pseudomonas, and Enterobacterales can be isolated from the oral cavities of various populations. These include elderly individuals in long-term care facilities (Haruta et al., 2023; Kajihara et al., 2023; Nishihama et al., 2025), healthy adolescents (Kawayanagi et al., 2024), and healthy subjects with no prior antibiotic exposure, such as neonates and breastfed infants (Milanović et al., 2020). Understanding the oral resistome provides valuable insights into the most prevalent antimicrobial resistance genes (ARGs), their mobilization potential, and transmission risk via oral bacteria (Sukumar et al., 2024). The oral cavity is particularly important for investigation due to its anatomical and physiological features, which favor microbial proliferation and transmission through oropharyngeal secretions and saliva droplets when talking, coughing, sneezing, breathing, or kissing (De Paula Campêlo et al., 2022; Sukumar et al., 2024). Effectively, carbapenemase-producing K. pneumoniae were detected in patients, their environment, and their oral and rectal samples, highlighting potential hospital-associated environmental contamination (Wei et al., 2021). In this study, the majority of K. pneumoniae strains (14/20) were isolated from oral mucosa, while six were isolated from saliva samples, with six patients harboring multiple distinct resistant strains in their oral cavity (Supplementary Table 1). In healthy individuals, Gram-negative bacilli sporadically colonize the oral cavity and are not considered natural components of the oral microbiota. However, colonization by Enterobacteriaceae is a dynamic process influenced by hospitalization, compromised immunological response, poor oral hygiene, reduced salivary flow, and impaired mastication (Leão-Vasconcelos et al., 2015). Their incidence is variable and may increase under specific conditions such as diabetes (Li et al., 2000; Ashreen et al., 2020), advanced age (Li et al., 2000; Cruz et al., 2022), cancer (Santibañez-Bedolla et al., 2023), and HIV (Arirachakaran et al., 2019), confirming that their presence can be a marker of clinical severity. In the present study, despite limited clinical information, diabetes mellitus was the most frequently documented comorbidity among patients colonized with carbapenem-resistant K. pneumoniae, consistent with previous studies showing that diabetes significantly increases the risk of colonization and infection by CRKp (Pattolath et al., 2024; Wang et al., 2025).

Gram-negative bacteria have been associated with several oral diseases, including periodontitis, caries, and gingivitis, as well as systemic conditions of clinical relevance (Zaatout, 2021; Bridon, 2024). Inappropriate antibiotic use for these diseases may favor the selection and persistence of resistant bacteria in the oral cavity, including ESBL and carbapenemase-producing strains (Katkowska et al., 2023; Bridon, 2024). Cruz et al. (2022) reported that pathogenic microorganisms can colonize the oral cavity within 48 h of hospital admission, with host-related factors such as age, frailty, and comorbidities playing a greater role than hospitalization duration (Cruz et al., 2022). In contrast, De Paula Campêlo et al. (2022) reported a rapid shift in the oral microbiota of critically ill adult patients, characterized by the predominance of multidrug-resistant hospital-associated Gram-negative and/or Gram-positive bacteria. These studies suggest that these microorganisms can regularly colonize the oral cavity, but it is not well established whether this presence is transient (Cruz et al., 2022). These findings suggest that multidrug-resistant bacteria may be present in the oral cavity of both hospitalized patients and the general population. Given the potential for both community and hospital acquisition, the source of the K. pneumoniae isolates identified in this study cannot be definitively determined. Nevertheless, one possible route of entry for these bacteria is through water and food, as the incidence of coliforms and other bacteria in these sources may contribute to oral colonization (Leão-vasconcelos et al., 2015). Supporting this hypothesis, K. pneumoniae producing OXA-48 and ESBL have been detected in fresh vegetables in Algeria, in the same city as our hospitalized patients, highlighting the widespread occurrence of multidrug-resistant Gram-negative bacteria in agri-food chains, particularly in vegetables and fruits consumed raw (Touati et al., 2017). In addition, long-term dietary habits may contribute to the presence of antibiotic resistance genes in the mouths of healthy adults, reflecting the widespread use of antibiotics in humans, animals, and agriculture (Milanović et al., 2020).

Notably, 65% of the isolates were multidrug-resistant (MDR), with 85% reaching a resistance score of 2, exhibiting resistance across up to five antibiotic classes and highlighting the oral cavity as a hidden reservoir of MDR K. pneumoniae in hospitalized patients (Table 2, Figure 1). Approximately 80% of isolates were resistant to at least one of the tested carbapenems, with the majority carrying the blaOXA-48 gene (94.11%), while only one isolate (K21) harbored blaNDM-5. Half of the isolates co-produced extended-spectrum β-lactamase (ESBL), primarily blaCTX-M-15. Remarkably, the K21 strain was classified as extensively drug-resistant (XDR), exhibiting resistance to more than five antibiotic classes and harboring 20 resistance genes (Table 2), underscoring the complexity of resistance mechanisms in oral K. pneumoniae. The emergence of carbapenemase-producing bacteria has become a major public health concern in recent years. Carbapenemases are most often encoded on mobile genetic elements such as plasmids that can be easily transferred across species, including among Enterobacteriaceae, through horizontal gene transfer (Xie et al., 2025).

The high prevalence of carbapenemase-producing isolates observed in this study is consistent with the alarming levels of antimicrobial resistance (AMR) reported by the Algerian Antibiotic Resistance Surveillance Network.¹ Increasing rates of carbapenem and ESBL resistance, particularly among K. pneumoniae, confirm that antibiotic resistance in Algeria has reached critically concerning levels. Several studies have shown that the OXA-48 enzyme is the predominant carbapenemase among hospitalized patients, confirming its endemicity in Algeria (Abderrahim et al., 2017; Bourafa et al., 2018; Zemmour et al., 2021; Abderrahim et al., 2022). This enzyme is also widely disseminated across the Mediterranean region and African countries (Mathlouthi et al., 2017; Peyclit et al., 2018; Touati and Mairi, 2020; Chelaru et al., 2024). In parallel, the NDM-5 gene, first reported in multidrug-resistant E. coli from Algeria in 2014 (Sassi et al., 2014), has since been detected in human, animal, and environmental sources within the country, including pets (Yousfi et al., 2015), clinical isolates (Khaldi et al., 2022; Nabti et al., 2022), and migratory birds (Loucif et al., 2022b), highlighting its extensive dissemination across One Health compartments. The detection of NDM-5 in the oral cavity of a hospitalized patient in our study further underscores the widespread circulation of this carbapenemase in Algeria.

Phylogenetic analysis of the oral K. pneumoniae isolates revealed substantial clonal and phenotypic diversity, particularly among samples from Akbou hospital (Figure 3), suggesting local adaptation driven by antibiotic pressure and environmental factors. This heterogeneity between isolates from different hospitals likely reflects distinct selective pressures and horizontal gene transfer dynamics, contributing to the emergence of multiple clonal lineages within the same species. Whole-genome sequencing revealed genome sizes ranging from 5.45 to 6.02 Mb, consistent with previous reports describing the large, plastic genomes of Klebsiella species enriched in mobile genetic elements (Wyres and Holt, 2018; Rocha et al., 2022). The K. pneumoniae genome contains approximately 5,500 genes, of which about 3,500 constitute the accessory genome, encoding numerous resistance and virulence factors (Wyres and Holt, 2018; Rocha et al., 2022). Liu et al. (2024) reported that Klebsiella species are among the few oral and nasal bacteria characterized by remarkable metabolic versatility that enables adaptation to multiple environments. This genomic flexibility underpins the species’ ability to acquire resistance and virulence genes, supporting its opportunistic and adaptive lifestyle. In line with this, our assemblies identified genes associated with siderophore production, antimicrobial resistance, and diverse virulence functions that collectively enhance bacterial persistence under adverse conditions. This genomic plasticity was further illustrated by the detection of resistance genes with variable phenotypic expression. The detection of the blaOXA-48 gene in K. pneumoniae K36, despite its low MIC (2 mg/L) to both meropenem and imipenem, highlights a notable discrepancy between genotype and phenotype. Notably, this finding underlines an important limitation of phenotype-based definitions of carbapenem-resistant K. pneumoniae (CRKp), as it harbors the carbapenemase gene blaOXA-48 while remaining phenotypically susceptible to imipenem and meropenem. This highlights that phenotypic testing, although rapid and clinically indispensable, may fail to identify genotypic resistance determinants that are highly relevant for therapeutic decision-making and epidemiological surveillance. Similar observations have been reported in previous studies, where OXA-48 producers frequently exhibit low-level carbapenem resistance, often falling below EUCAST (≤2 mg/L) and CLSI (≤1 mg/L) clinical breakpoints (Boyd et al., 2022; Meekes et al., 2025). This inconsistency may result from low-level expression of the gene, potentially influenced by its promoter context, plasmid copy number, or the absence of permeability defects (porin loss) that are often required to achieve full carbapenem resistance. Such silent carriers pose a risk, as they can evade routine susceptibility testing while still contributing to the spread of resistance genes. Alternatively, the strain may carry a non-functional or weakly active blaOXA-48 allele, further explaining the low phenotypic resistance. The contrasting resistance and virulence profiles observed among the two ST6436 (K21 and K27) isolates may also reflect the population heterogeneity within K. pneumoniae in the oral cavity. This heterogeneity, arising from genetic variation and phenotypic plasticity, represents an adaptive “bet-hedging” strategy that enhances bacterial survival under fluctuating environmental conditions, including antibiotic exposure (Cho et al., 2025). The identification of a convergent ST6436 (K21) strain in the oral cavity, carrying both resistance and virulence determinants, raises important clinical concerns. Oral bacteria can enter the bloodstream during routine activities or dental procedures such as tooth brushing, chewing, or periodontal surgery, potentially leading to systemic infections such as bacteremia or pneumonia (Gendron et al., 2000; Kawayanagi et al., 2024). Moreover, the oral cavity may facilitate horizontal gene transfer to gut microbiota, promoting the dissemination of antimicrobial resistance and virulence traits within and beyond the host, particularly in hospitalized or immunocompromised patients (Kawayanagi et al., 2024).

Resistance and virulence in K. pneumoniae are frequently linked to specific clonal lineages (Aghamohammad et al., 2023). While global attention has mainly focused on well-known high-risk clones, other multidrug-resistant lineages capable of disseminating carbapenem resistance remain underexplored. In this study, whole-genome sequencing revealed the ongoing spread of two OXA-48-producing high-risk clones, ST13 and ST48, which harbor a substantial repertoire of resistance and virulence determinants. ST13 K. pneumoniae is an internationally disseminated high-risk clone associated with the spread of several ESBL and carbapenemase genes, including blaOXA-48 (Fursova et al., 2020; Österblad et al., 2012; Wrenn et al., 2014), blaKPC (Elias et al., 2023; Mendes et al., 2023), and blaCTX-M-15 (Marcade et al., 2013) across Europe. In Algeria, ST13 represents the most prevalent K. pneumoniae strains producing the OXA-48 lineage, recovered from diverse environmental and clinical sources (Touati and Mairi, 2020), including human fecal carriage, river water, farm animal feces, wild fish intestines, milk, wild bird feces, and various food products. This lineage was reported from both Bejaia (the same city as our study) and Tizi Ouzou province indicating a potential regional dissemination of this clone (Mairi et al., 2019; Touati and Mairi, 2020; Zemmour et al., 2021). Moreover, ST13 has been identified in hospital environments in Constantine province, carrying CTX-M-15, aac(6’)Ib-cr, and aadA2 genes conferring resistance to β-lactams, quinolones, and aminoglycosides (Zenati et al., 2017).

ST 48 was the founder ST of the clonal complex CC48 (Naha et al., 2021). In Algeria, Chaalal et al. (2021) showed the clonal expansion of K. pneumoniae isolates with the dissemination of ST48 among OXA-48-producing strains in chicken meat from three poultry farms in Western Algeria, indicating that these Klebsiella isolates could be easily transmitted to humans from food animals and their products. ST48 was also previously detected in an urban wastewater treatment plant in Algeria (Chaalal et al., 2021). This ST was also reported in the clonal dissemination of K. pneumoniae producing KPC-2 among hospitalized patients in China (Gu et al., 2019) and from K. pneumoniae isolates harboring the blaOXA-181 gene in neonates in India (Naha et al., 2021).

K. pneumoniae ST307 is a globally disseminated high-risk clone commonly associated with ESBL production (blaCTX-M-15) and a strong ability to acquire carbapenemase genes such as blaOXA-48, blaKPC, and blaNDM (Núñez-Samudio et al., 2022; Aghamohammad et al., 2023). In the present study, the ST307 isolate harbored a similar resistance profile and showed high genetic relatedness to strains previously reported in tertiary healthcare settings in Uganda (Byarugaba et al., 2023). However, in contrast to the Ugandan isolates, our strain lacked virulence-associated genes, suggesting local genomic variation and possible early-stage adaptation of this lineage to the local environment. Comparable intra-lineage diversity has been described in other globally circulating clones, including ST307, ST147, and ST15, underscoring the remarkable genetic plasticity of K. pneumoniae under diverse ecological and selective pressures (Wyres and Holt, 2018; Núñez-Samudio et al., 2022). Iron acquisition through siderophore production represents a key adaptive and virulence-associated trait in Klebsiella pneumoniae. Several siderophore systems, including yersiniabactin, aerobactin, and the Klebsiella ferric uptake system (kfu), have been described in clinical isolates, with highly heterogeneous distribution across sequence types (Di Mento et al., 2022). In the present study, the predominance of yersiniabactin (17/20), followed by colibactin (8/20), among oral isolates highlights their role in adaptation to the oral environment and suggests a contribution to enhanced bacterial fitness and persistence rather than overt invasiveness. We also confirmed the presence of the same iron uptake system genes in ST13 (ybt10), ST48 (ybt17 and clb3), as well as the absence of iron chelation mechanism genes in ST34, ST606-1LV, and ST307 strains. Interestingly, intra-lineage variability was observed within ST6436. K. pneumoniae K21 displayed yersiniabactin (ybt9) and aerobactin (iuc1) and hypermucoidy (rmp1) genes, whereas K. pneumoniae K27 harbored only yersiniabactin (ybt9). These findings illustrate the virulome divergence among K. pneumoniae strains from the oral cavity of hospitalized patients in Bejaia province, Algeria. Furthermore, multidrug-resistant lineages ST13 (OXA-48; CTX-M-15), ST48(OXA-48), and ST6436 (NDM-5; CTX-M-15) were associated with ybt10/ICEKp4, ybt17/ICEKp10, and ybt 9/ICEKp3, respectively. This heterogeneity confirms that siderophore acquisition is lineage-specific and primarily shaped by local ecological and selective pressures, rather than being universally conserved among multidrug-resistant clones, as previously reported by Di Mento et al. (2022).

We also report for the first time the predominance of integrative conjugative elements ICEKp (80%) variants carrying the blaOXA-48 gene associated with yersiniabactin variants in our strains. Integrative conjugative elements carrying antimicrobial resistance and/or virulence determinants are common in the opportunistic pathogen K. pneumoniae, which is a leading cause of highly drug-resistant infections in hospitals (Lam et al., 2018). The widespread detection of the yersiniabactin gene and its associated ICEKp among clinical K. pneumoniae producing OXA-48 has been reported in Spain and the Netherlands (Jati et al., 2023) but never in Algeria. Here, we also report the co-existence of ICEKp3 and KpVP-1 in the convergent K. pneumoniae K21 producing NDM-5 and harboring the iron acquisition systems yersiniabactin (ybt9), aerobactin (iuc1), and rmpA (rmp1).

The capsular types commonly associated with hvKp/CR-hvKp are, in order of frequency, K1, K2, and K57 (García-Cobos et al., 2025). In our study, K57 was associated with ST13 strains harboring yersiniabactin, blaOXA-48, and blaCTX-M-15 genes and other determinants.

Notably, the capsular type K27 was identified in two ST6436 isolates showing remarkable intra-lineage divergence. One isolate (strain K21) represented a convergent hv-CRKp harboring blaNDM-5, blaCTX-M-15, yersiniabactin (ybt9), aerobactin (iuc1), rmp1, and wzi, whereas the other isolate (strain K27) carried only blaCTX-M-15, yersiniabactin (ybt9), and wzi, illustrating divergent virulence profiles within the same clonal lineage sharing the same capsular type. The wzi gene, essential for capsular polysaccharide synthesis, was detected in 11 isolates, underscoring its role in antimicrobial resistance and biofilm formation (Alnaqeeb and Gergees, 2024). Additionally, most isolates possessed the lipopolysaccharide serotype O1v1, while O2afg was observed only in two isolates (K22 and K36). Importantly, the O2a and O2afg serotypes are prevalent in most multidrug-resistant K. pneumoniae strains and have been shown to induce poor inflammatory immune responses, promoting immune evasion and subsequent survival of CR-Kp strains (Bulati et al., 2021; Di Mento et al., 2022). These observations underscore the complexity of the mechanisms employed by multidrug-resistant K. pneumoniae to persist within the host and promote onward transmission among patients. These findings contribute to the growing body of evidence on convergent strains emerging across Africa. In countries such as Egypt, Nigeria, and Ghana, the combination of MDR and hypervirulence has been documented, with ST11-KL47 and ST147-K67 being the most notable examples (García-Cobos et al., 2025). In Algeria specifically, diverse capsular types including K1 (ST23), K2 (ST14 and ST86), K3 (ST13), K31 (ST2108), K6 (ST348), and K151 (ST405) have been identified in ESBL-producing and virulent K. pneumoniae from hospitalized patients at Oran hospital (Zemmour et al., 2021), highlighting the capsular diversity within the country. The identification of K57 and K27 types in our study from Bejaia further underscores this regional variability.

In conclusion, this study provides the first genomic characterization of oral carbapenemase-producing K. pneumoniae in hospitalized patients in Algeria, revealing widespread dissemination of OXA-48 and NDM-5 among high-risk lineages. The oral cavity serves as a reservoir of highly pathogenic strains with transmission potential via droplets and contamination. The discovery of convergent strains, such as ST6436-K21 harboring NDM-5, iuc1, and rmpA, in the oral cavity supports the hypothesis of hidden reservoirs outside the gut, challenging the paradigm that MDR and hvKp strains are separate or only gut-associated.

Our results demonstrate that greater attention should be given to oral bacteria for antimicrobial resistance prevention, highlighting the importance of maintaining oral health as a preventive measure. This identification is of utmost importance due to the fact that for a long time, MDR-Kp and hvKp have been considered distinct phenotypes associated with different patient populations. Whole-genome sequencing has proven valuable for characterizing K. pneumoniae, enabling monitoring of genetic changes, understanding transmission, and tackling the spread of hvKp. Our findings highlight the risk of MDR and hypervirulent convergent strains within Algerian hospitals. While carbapenem resistance detection is routine, virulence gene detection is not, and phenotypic methods such as the string test lack sensitivity. The convergence of hypervirulence and multidrug resistance is no longer confined to the gut or bloodstream but also extends to the oral ecosystem, representing an unrecognized risk for nosocomial and community transmission.