Klebsiella species, particularly Klebsiella pneumoniae and Klebsiella oxytoca, are Gram-negative, encapsulated, non-motile bacilli belonging to the Enterobacteriaceae family. These organisms are commonly found in the human gastrointestinal tract as part of the normal flora but are also well-recognized opportunistic pathogens in both community and hospital settings [1, 2]. In healthcare environments, Klebsiella species are frequently implicated in a wide range of infections, including pneumonia, urinary tract infections, bloodstream infections, wound infections, and device-associated infections such as catheter-associated urinary tract infections and ventilator-associated pneumonia [3-5].

The increasing incidence of multidrug-resistant (MDR) Klebsiella strains, particularly those producing extended-spectrum beta-lactamases (ESBLs) and carbapenemases, has become a serious global health concern. These resistance mechanisms render many first-line antibiotics ineffective, limiting therapeutic options and leading to prolonged hospital stays, increased morbidity and mortality, and higher healthcare costs. The problem is further compounded by the widespread and often indiscriminate use of antibiotics, which accelerates the emergence and dissemination of resistant strains [6-7].

Among the various resistance mechanisms, ESBL production is particularly notable for its ability to hydrolyze a wide range of β-lactam antibiotics, including third-generation cephalosporins and monobactams [8]. The rise in carbapenem-resistant Klebsiella pneumoniae (CRKP), often mediated by enzymes such as KPC (Klebsiella pneumoniae carbapenemase) and NDM (New Delhi metallo-β-lactamase), poses an even greater therapeutic challenge, as these strains are resistant to most available antibiotics, including β-lactams, fluoroquinolones, and aminoglycosides. In such cases, treatment options are often limited to less effective or more toxic alternatives like polymyxins and tigecycline [9-11].

The present study was undertaken to evaluate the antimicrobial resistance profile of Klebsiella species isolated from clinical specimens in a tertiary care hospital. By identifying the resistance trends and prevalence of ESBL and carbapenemase production, the study aims to inform antibiotic stewardship strategies and improve patient management in hospital settings [12, 13].

This cross-sectional study was conducted over a period of six months in the Department of Microbiology at a tertiary care hospital. This study was conducted at department of Microbiology, Government Medical College, Nalgonda, Telangana, India from February 2024 to January 2025. A total of 50 non-duplicate Klebsiella species isolates were obtained from various clinical samples, including urine, sputum, blood, wound swabs, and pus, submitted to the microbiology laboratory for routine culture and sensitivity testing. All samples were processed using standard microbiological procedures. Bacterial isolates were identified based on colony morphology, Gram staining, and a series of biochemical tests, including indole, citrate utilization, urease, and triple sugar iron agar tests. Identification was further confirmed using automated systems where necessary (e.g., VITEK 2).

Inclusion Criteria:

• Clinical samples yielding growth of Klebsiella species.
• Non-duplicate isolates from patients of all age groups and both sexes.
• Inpatients and outpatients attending the tertiary care hospital during the study period.

Exclusion Criteria:

• Repeat isolates from the same patient.
• Contaminated or improperly collected samples.
• Isolates showing mixed growth or not identified as Klebsiella species.

Antimicrobial Susceptibility Testing (AST):

The antimicrobial susceptibility of the isolates was determined using the Kirby-Bauer disk diffusion method on Mueller-Hinton agar, following the guidelines set by the Clinical and Laboratory Standards Institute (CLSI). The antibiotics tested included ampicillin, cefotaxime, ceftazidime, ceftriaxone, gentamicin, amikacin, ciprofloxacin, imipenem, meropenem, tigecycline, and colistin.

Detection of ESBL Production:

Isolates showing reduced susceptibility to third-generation cephalosporins were subjected to ESBL detection using the phenotypic confirmatory test (combined disc method) with cefotaxime (30 µg) and cefotaxime-clavulanic acid (30/10 µg).

Detection of Carbapenem Resistance:

Isolates showing reduced zones of inhibition for carbapenems (imipenem and meropenem) were considered carbapenem-resistant. Confirmatory testing for carbapenemase production was done using the modified Hodge test or other recommended phenotypic methods.

A total of 50 non-duplicate Klebsiella isolates were recovered from various clinical specimens over the study period. The isolates were identified as Klebsiella pneumoniae (86%) and Klebsiella oxytoca (14%). Detailed findings are presented in the tables below.

Table 1: Distribution of Klebsiella Isolates According to Sample Type

Urine was the most common sample type from which Klebsiella spp. were isolated, accounting for 36% of the total, followed by sputum (20%) and wound swabs (18%). This indicates a significant prevalence of Klebsiella-associated urinary and respiratory tract infections.

Table 2: Species Distribution of Klebsiella Isolates

The majority of isolates were identified as K. pneumoniae (86%), highlighting its predominant role in clinical infections compared to K. oxytoca.

Table 3: Antibiotic Susceptibility Pattern of Klebsiella Isolates

High resistance was observed to beta-lactams such as ampicillin, cephalosporins, and fluoroquinolones. However, colistin and tigecycline remained the most effective antibiotics, with 98% and 92% susceptibility, respectively. Carbapenem resistance was seen in 16–18% of isolates.

Table 4: Prevalence of ESBL-Producing Klebsiella Isolates

More than half of the isolates (56%) were confirmed as ESBL producers, indicating a significant resistance to extended-spectrum cephalosporins among the clinical Klebsiella population.

Table 5: Distribution of Carbapenem-Resistant Klebsiella Isolates by Sample Type

Carbapenem-resistant isolates were detected across all sample types, with the highest percentage in blood samples (25%), followed by sputum and pus. Overall, 18% of isolates were resistant to carbapenems, emphasizing the emerging threat of these multidrug-resistant strains.

The findings of the present study underscore the increasing burden of antimicrobial resistance (AMR) among Klebsiella species, particularly K. pneumoniae, which accounted for 86% of the isolates. This aligns with observations by Podschun and Ullmann (1998), who reported that K. pneumoniae is the predominant species associated with hospital-acquired infections, especially those involving the respiratory and urinary tracts [14, 15].

A notably high level of resistance was observed against several commonly used antibiotics, particularly beta-lactams such as ampicillin (100%) and third-generation cephalosporins, with resistance rates exceeding 80%. This trend is consistent with findings by Bush and Jacoby (2010), who explained that the intrinsic resistance of Klebsiella to ampicillin is due to the presence of chromosomal beta-lactamases, and that acquired beta-lactamase enzymes, especially extended-spectrum beta-lactamases (ESBLs), have further worsened the situation [16, 17].

The current study found ESBL production in 56% of isolates, which is consistent with earlier research from Indian healthcare settings. For example, Mathur et al. (2002) reported a similar high prevalence of ESBL-producing Klebsiella isolates in a tertiary care hospital, indicating an ongoing and widespread issue in nosocomial environments. Similarly, Shahid et al. (2009) highlighted that ESBL production among Enterobacteriaceae, including Klebsiella, is alarmingly frequent and contributes to resistance against cephalosporins and monobactams [18, 19]. Of equal concern is the emergence of carbapenem resistance in 18% of the isolates, with the highest rates seen in bloodstream infections. This is in line with global trends reported by Nordmann et al. (2011), who emphasized the rapid dissemination of carbapenemase-producing Klebsiella strains, particularly those harboring genes such as KPC, NDM, and OXA-48. According to Logan and Weinstein (2017), carbapenem-resistant Enterobacteriaceae (CRE), including K. pneumoniae, have become a global menace due to their association with high mortality rates and limited treatment options [20, 21].

On a more positive note, colistin and tigecycline were found to be highly effective against most isolates in this study, with susceptibility rates of 98% and 92% respectively. However, their use as last-resort antibiotics requires careful stewardship to avoid the development of resistance. Olaitan et al. (2014) warned that both acquired and intrinsic resistance mechanisms against polymyxins, including colistin, are emerging and could compromise the effectiveness of these drugs if overused [22].

The patterns observed in this study reflect the urgent need for continuous surveillance, strict infection control protocols, and implementation of antimicrobial stewardship programs to curb the spread of resistant strains. While the data provide important insights, the study's limitations include the relatively small sample size and the lack of molecular analysis for specific resistance genes, which could have added depth to the findings [23].

In conclusion, as also reported by previous researchers, Klebsiella species continue to evolve resistance to multiple drug classes, posing serious challenges for clinicians. An integrated approach involving diagnostics, surveillance, and policy is essential to mitigate the risks posed by these pathogens [24].

The present study underscores the alarming prevalence of multidrug-resistant Klebsiella species in clinical settings, particularly Klebsiella pneumoniae, which was the most frequently isolated pathogen. High resistance rates to commonly used antibiotics such as ampicillin, third-generation cephalosporins, and fluoroquinolones were observed, with over half of the isolates exhibiting extended-spectrum beta-lactamase (ESBL) production. The emergence of carbapenem-resistant strains further complicates therapeutic options, especially in critically ill patients. Although colistin and tigecycline remain effective against most isolates, their use must be carefully regulated due to the potential for resistance development. These findings highlight the urgent need for strict antimicrobial stewardship, regular surveillance programs, and implementation of infection control practices in healthcare facilities. Additionally, molecular characterization of resistance genes and large-scale multicenter studies are essential to better understand resistance mechanisms and guide empirical therapy. Effective management of drug-resistant Klebsiella infections requires coordinated efforts from clinicians, microbiologists, and policymakers to preserve the efficacy of existing antibiotics and safeguard public health.

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