ATCC 4352 Klebsiella Pneumoniae, Subsp. pneumoniae

In the vast world of microbiology, reference strains play a crucial role in standardizing research, quality control, and clinical testing. One such strain, designated ATCC 4352, stands out as a cornerstone for studies on bacterial pathogens. Initially misidentified as Escherichia coli, ATCC 4352 is now known as Klebsiella pneumoniae subsp. pneumoniae (Schroeter) Trevisan, a Gram-negative, encapsulated rod-shaped bacterium known for causing opportunistic infections in humans. Isolated from cow's milk, this strain has become a benchmark in antimicrobial susceptibility testing, biofilm research, and epidemiological studies due to its well-characterized genome and consistent phenotypic properties.

The story of ATCC 4352 begins with a taxonomic confusion. Recorded in the American Type Culture Collection (ATCC) catalog as an Escherichia coli strain, it was routinely used in early microbiological analyses. However, detailed phenotypic and genotypic analyses conducted in the late 20th century revealed the strain's true identity to be Klebsiella pneumoniae. A study confirmed this reclassification through biochemical testing, including positive reactions for distinguishing features of Klebsiella species such as urease, citrate utilization, and glucose-to-gas production.

This strain, also known by various synonymous names, was isolated from bovine milk and has highlighted its zoonotic potential. Because its entire genome sequence is publicly available, it has become an invaluable resource for genomic comparisons and molecular biology experiments. The redefinition, supported by advances in whole-genome analysis, emphasizes the evolution of microbial taxonomy, ensuring that reference strains like ATCC 4352 remain reliable tools for global research.

Klebsiella pneumoniae subsp. pneumoniae ATCC 4352 exemplifies the defining characteristics of the genus: a non-motile, facultative anaerobe that thrives in nutrient-rich media. On agar plates, colonies appear mucous due to the production of a polysaccharide capsule, a virulence factor that evades phagocytosis. The strain ferments lactose, forming pink colonies, and exhibits resistance to some environmental stressors such as desiccation and moderate pH changes. Genomically, ATCC 4352 spans approximately 5,3 million base pairs, encoding genes for antibiotic resistance determinants, efflux pumps, and biofilm formation. This strain is ideal for modeling infections such as pneumonia, urinary tract infections, and sepsis, which are frequently caused by Klebsiella pneumoniae in immunocompromised patients.

The versatility of ATCC 4352 in research and industrial applications encompasses many disciplines. In quality control laboratories, it is a standard for the validation of culture media, reagents, and antimicrobial discs under guidelines such as USP <62> for microbiological testing of non-sterile products. Some commercial products distribute derivatives of this strain in lyophilized form for easy and traceable use, limited to only two passages from the original, and maintaining its authenticity.

In antimicrobial research, this strain is a resource used to evaluate new treatments.

In addition to plant-based antimicrobials, ATCC 4352 is also involved in vaccine development and phage therapy trials, and its genomic stability helps in evaluating efficacy. Inclusion in international culture collections ensures the provision of globally consistent standards.

The enduring importance of ATCC 4352 lies in its role as a gold standard in the context of increasing antimicrobial resistance. Since Klebsiella pneumoniae is classified as a critical priority pathogen by the World Health Organization due to its carbapenem-resistant strains, this reference strain facilitates the development of diagnostic and therapeutic approaches.

ATCC 4352 (Klebsiella pneumoniae subsp. pneumoniae) is one of the most widely used reference strains in microbiology, and its importance stems from several key factors:

• It is the long-standing gold standard for quality control: an official control strain in numerous pharmacopoeias and regulatory standards worldwide (USP, EP, ISO). It is used in the following areas:
• Tests of cultural environments that promote growth.
• Validation of antimicrobial susceptibility test discs and systems.
• Microbiological examination of non-sterile drugs (USP <61>/<62>).
• Suitability of the sterility test method (USP <71>).

Because it has been used under the same ATCC number for decades, results from laboratories worldwide have remained comparable over time.

• Historical misidentification has been turned into an advantage: For many years it was mistakenly labeled as Escherichia coli. In 1988 it was correctly identified as Klebsiella pneumoniae. This history makes it a teaching tool in clinical microbiology and a cautionary tale about relying on outdated catalog names.
• It is well-characterized and genomically stable: The complete genome sequence is publicly available (multiple high-quality assemblies). It exhibits predictable phenotypic behavior: lactose-positive, mucous colonies, consistent antibiotic susceptibility profile (susceptible to most common antibiotics, making it ideal as a susceptible control). Low passage history in commercial products guarantees genetic stability.
• It is a benchmark for antimicrobial and biofilm research: It is frequently used as a sensitive reference in testing novel antibiotics, disinfectants, or natural compounds against multidrug-resistant Klebsiella pneumoniae clinical isolates. Because it forms strong biofilms in vitro, it is a popular model for biofilm studies. It is used as a control in hundreds of published studies on plant extracts, bacteriophages, nanoparticles, and novel anti-Klebsiella agents.
• Global availability and traceability: ATCC is distributed by cultural collections under many synonyms. It is included in the World Federation of Cultural Collections reference list.

In conclusion, ATCC 4352 is the microbiological equivalent of a calibrated standard, which every laboratory uses to ensure its methods and reagents perform correctly. Even as new strains emerge, its decades of documented performance and regulatory approval make it indispensable.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services to businesses in accordance with the “ATCC 4352 Klebsiella pneumoniae, subsp. pneumoniae” standard.