What Is Bacteriology? A Plain-Language Guide

Bacteriology is the scientific study of bacteria: the single-celled prokaryotes that live in soil, water, food, plants, animals and the human body, and that cause, prevent and treat a great deal of disease. Bacteriologists ask how bacteria grow, divide, exchange genes and sense their surroundings, how they are named and classified, how they cause infection, how laboratories detect them, and how they evolve resistance to the drugs used against them. This guide explains what bacteriology covers, its major subfields, the methods and culture collections the field depends on, a short history, how bacteriology research is funded, the societies and journals that serve it, the biosafety rules that govern bacterial work, and the usual training path into the field.

What Is Bacteriology?

Bacteriology is the branch of microbiology devoted to bacteria. Bacteria are prokaryotes: their cells have no membrane-bound nucleus, and most have a single circular chromosome, often supplemented by small mobile DNA elements called plasmids. They are one of the two prokaryotic domains of life; the other, the archaea, was recognized as a separate lineage in the late 1970s and is sometimes studied alongside bacteria. Bacteria are usually a few micrometres long and come in a handful of characteristic shapes, including spheres (cocci), rods (bacilli) and spirals.

The word “bacteriology” is older than the modern term “microbiology,” and the American Society for Microbiology itself was founded in 1899 as the Society of American Bacteriologists, taking its current name in 1960. Today bacteriology is usually treated as one of the main branches of microbiology, alongside virology, mycology and parasitology, and it overlaps with genetics, molecular biology, immunology and epidemiology.

It helps to separate the two things people mean by the word. In basic research, bacteriology is the study of bacteria as living systems and as models for general biology. In clinical and public-health work, a bacteriology laboratory is the place that isolates and identifies bacteria from patient specimens and tests which antibiotics will work against them. Both senses are covered below.

Major Subfields of Bacteriology

• Bacterial physiology and cell biology — growth, cell division, the cell envelope, motility, metabolism, stress responses, biofilm formation and communication between cells. Model organisms such as Escherichia coli and Bacillus subtilis have taught biology much of what it knows about gene expression and cell division.
• Bacterial genetics and genomics — how bacterial genomes are organized, how genes are regulated, and how DNA moves between cells by conjugation, transformation and transduction. Horizontal gene transfer is central to bacterial evolution and to the spread of resistance genes. Whole-genome sequencing is now routine for identifying and comparing isolates.
• Taxonomy and systematics — naming, describing and classifying bacteria. Sequencing of the 16S ribosomal RNA gene transformed classification, and genome-based comparison is increasingly used to define species.
• Medical and clinical bacteriology — bacterial infections of people, how they are diagnosed in the laboratory, and how they are treated. This is also where Gram staining, culture, identification and susceptibility testing are done every day.
• Bacterial pathogenesis and host–pathogen interaction — how bacteria attach, invade tissue, evade the immune system and produce toxins; closely linked to immunology.
• Antimicrobial resistance (AMR) research — the mechanisms, spread and consequences of resistance, and the search for new antibacterial drugs, diagnostics and vaccines. See the dedicated section below.
• Environmental and microbial ecology — the roles of bacteria in soil, water, nutrient cycling and the microbiomes of plants and animals.
• Veterinary, food and agricultural bacteriology — bacterial disease in animals, foodborne pathogens and food spoilage (see food microbiology testing), and plant-pathogenic bacteria.
• Industrial and applied bacteriology — fermentation, enzymes, bioremediation, probiotics and the use of bacteria as tools in biotechnology.

Antimicrobial Resistance: Why It Dominates Funding and Policy

Antimicrobial resistance occurs when microbes change so that medicines that once killed or inhibited them no longer work. For bacteria, resistance can arise by mutation or be acquired from other bacteria on mobile genetic elements. A 2022 systematic analysis published in The Lancet estimated that in 2019 there were 4.95 million deaths associated with bacterial AMR worldwide, including 1.27 million deaths directly attributable to it. In May 2024 the World Health Organization published an updated Bacterial Priority Pathogens List that groups 24 pathogens into critical, high and medium priority tiers to guide research and development. The critical group includes carbapenem-resistant Acinetobacter baumannii, third-generation cephalosporin-resistant and carbapenem-resistant Enterobacterales, and rifampicin-resistant Mycobacterium tuberculosis.

AMR research spans several kinds of work: basic studies of resistance mechanisms and bacterial physiology; surveillance of resistant organisms; discovery and development of new antibacterial compounds, alternatives such as phage therapy, and vaccines; rapid diagnostics; and clinical trials. In hospitals, the applied side shows up as antimicrobial stewardship programs, the antibiogram that summarizes local susceptibility patterns, and multidrug-resistant organism prevention.

Core Methods

• Culture and isolation — growing bacteria on selective and differential media, in liquid broth, and under the atmosphere (aerobic, anaerobic, microaerophilic) each organism needs. Many bacteria in nature have never been cultured in the laboratory, which is why culture-independent methods matter. Good aseptic technique underpins all of it.
• Microscopy and staining — the Gram stain, devised by Hans Christian Gram in 1884, divides most bacteria into Gram-positive and Gram-negative groups by the structure of the cell wall and remains a first step in many identifications. Acid-fast staining and fluorescence and electron microscopy extend the toolkit.
• Biochemical and mass-spectrometry identification — panels of metabolic tests and, in many clinical laboratories, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry for rapid species identification.
• Antimicrobial susceptibility testing — disk diffusion, gradient strips and broth microdilution to determine the minimum inhibitory concentration (MIC), interpreted against breakpoints published by standards bodies such as the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Bactericidal behaviour can be examined with time-kill assays.
• Molecular methods — PCR, 16S rRNA gene sequencing, whole-genome sequencing, and genetic tools for making and testing mutants and for gene editing.
• Omics and imaging — transcriptomics, proteomics, metabolomics and high-resolution live-cell imaging for studying how bacteria behave as populations and as individual cells.
• Contamination control — bacterial contamination, including mycoplasma, is a recurring problem in cell-culture laboratories; see cell culture contamination and mycoplasma testing methods.

Culture Collections and Biological Resource Centers

Reproducible bacteriology depends on being able to obtain the same, well-characterized strain that another group used. Public culture collections preserve, authenticate and distribute reference strains. Examples include ATCC (the American Type Culture Collection, a nonprofit established in 1925 that now holds collections in bacteriology, cell culture, molecular biology, mycology, protistology and virology), the German DSMZ (Leibniz Institute DSMZ–German Collection of Microorganisms and Cell Cultures), and the National Collection of Type Cultures (NCTC) in the United Kingdom. ATCC also manages BEI Resources, a repository supported by NIAID that supplies microbial reagents for research on priority pathogens and emerging infectious diseases.

For research offices, strain acquisition raises practical questions: who owns a derived strain, what a material transfer agreement allows, whether a permit or import authorization is needed, and whether a strain is a regulated agent. Deposit of a published strain in a recognized collection is also a common expectation of journals and funders, and a good reproducibility practice.

History in Brief

• 1670s — Antonie van Leeuwenhoek, using single-lens microscopes, describes tiny living “animalcules” in letters to the Royal Society, the earliest observations of bacteria.
• 1860s–1870s — Louis Pasteur’s work on fermentation and spontaneous generation and the germ-theory arguments of the period lay the ground for linking specific microbes to specific processes and diseases.
• 1880s — Robert Koch and colleagues develop solid culture media and pure-culture technique, identify the agents of anthrax, tuberculosis and cholera, and articulate the criteria now known as Koch’s postulates. Gram publishes his staining method in 1884.
• 1928 — Alexander Fleming observes that a Penicillium mold inhibits bacterial growth, the discovery that led to penicillin and the antibiotic era.
• 1977 — Carl Woese and colleagues use ribosomal RNA sequences to show that archaea are a distinct lineage, establishing sequence-based classification of prokaryotes.
• 1995 onward — the first complete bacterial genome sequences, followed by low-cost sequencing that has made genomics a routine tool in both research and public-health laboratories.

How Bacteriology Research Is Funded

In the United States, the largest single funder of bacteriology is the National Institutes of Health. The National Institute of Allergy and Infectious Diseases (NIAID) supports basic, translational and clinical research on bacterial pathogens and antimicrobial resistance. NIAID describes its AMR investments as including basic research on how microbes develop resistance, new and faster diagnostics, and clinical trials of vaccines and treatments for drug-resistant microbes; named efforts it has supported include the Systems Biology and Antibacterial Resistance Consortium and the Antibacterial Resistance Leadership Group. Investigator-initiated projects are most often funded through the R01 research project grant, and success rates are shaped by institute funding policy such as the NIAID payline. Training support comes through mechanisms such as the T32 institutional training grant. Always check the current NIH Guide notices and the institute’s own pages for open opportunities, because programs and priorities change from year to year.

Other funders include the National Science Foundation (for basic microbial biology, ecology and evolution), the U.S. Department of Agriculture (for agricultural and food-safety bacteriology), the Department of Defense and other federal agencies, public-private partnerships, philanthropic foundations and industry. Outside the U.S., national research councils and international programs fund comparable work.

Journals and Societies

The American Society for Microbiology (ASM), founded in 1899, is the largest U.S. professional society for the microbial sciences and publishes a large portfolio of journals. Those most relevant to bacteriology include Journal of Bacteriology, Antimicrobial Agents and Chemotherapy, Infection and Immunity, Journal of Clinical Microbiology, Applied and Environmental Microbiology and mBio. ASM also holds an annual scientific meeting. In the UK, the Microbiology Society serves the field; in Europe, the Federation of European Microbiological Societies (FEMS) brings national societies together. Specialist reference works, such as Bergey’s Manual of Systematics of Archaea and Bacteria, set out bacterial taxonomy, and the International Journal of Systematic and Evolutionary Microbiology is the journal where many new bacterial names are validly published.

Biosafety Considerations for Bacterial Work

Bacteria range from harmless laboratory strains to agents that can cause severe or fatal disease. Work is therefore assigned a biosafety level (BSL) based on a risk assessment of the organism, the procedure and the laboratory. Many teaching and nonpathogenic strains are BSL-1; many clinically important bacteria are handled at BSL-2; and some, such as Mycobacterium tuberculosis cultures, call for BSL-3 practices. The reference framework in the U.S. is the CDC and NIH publication Biosafety in Microbiological and Biomedical Laboratories (BMBL); see BMBL 6th edition: what changed and the overview of biosafety levels BSL-1 to BSL-4.

Institutional oversight usually runs through the institutional biosafety committee (see what is an institutional biosafety committee). Some bacteria are also federal select agents, which brings registration, security and reporting requirements; see the guide to Federal Select Agent Program registration. Research that could be misapplied is addressed under dual-use research of concern. This page gives orientation only; the rules that apply to a specific project come from the organism, the funder and your biosafety office.

Training and Career Paths

Most research bacteriologists have a bachelor’s degree in biology, microbiology or a related field, followed by a PhD in microbiology, molecular biology, genetics or a related program and postdoctoral training. Clinical laboratory roles follow a different route: medical laboratory scientists and technologists typically complete accredited laboratory-science education and certification, while physicians and doctoral-level laboratory directors may pursue board certification in medical microbiology or infectious diseases. Careers include academic and government research, clinical and public-health laboratories, hospital infection prevention, the pharmaceutical and biotechnology industries, food and agricultural safety, environmental consulting and culture-collection curation. Computational skills, especially genomics and bioinformatics, are now an expected part of the training.

Bacteriology and Research Administration

Bacteriology research brings a recognizable set of administrative questions: which NIH institute and mechanism fit the project, how the budget accounts for biosafety containment and specialized equipment, how institutional biosafety review is scheduled, how strains and sequence data are shared and deposited, and how clinical isolates and patient-derived materials are governed. Early contact with the biosafety office and the sponsored programs office avoids avoidable delays. The wider family of scientific disciplines is mapped on the Branches of Science guide.

Frequently Asked Questions

What is bacteriology in simple terms?

Bacteriology is the scientific study of bacteria: how they live, grow, evolve and interact with people, animals, plants and the environment, including the ways they cause disease and the ways they are controlled.

What is the difference between bacteriology and microbiology?

Microbiology is the broader field covering all microorganisms, including bacteria, viruses, fungi and protozoa. Bacteriology is the part focused on bacteria. See What Is Microbiology? for the wider picture.

What does a bacteriologist do?

Depending on the setting, a bacteriologist may study bacterial genetics and physiology, identify bacteria from clinical or environmental samples, test antibiotic susceptibility, investigate outbreaks, develop new antibacterial drugs or diagnostics, or curate bacterial collections.

What is clinical bacteriology?

Clinical bacteriology is the laboratory discipline that detects, identifies and characterizes bacteria in patient specimens and tests which antibiotics are likely to be effective, supporting diagnosis, treatment and infection control.

Are all bacteria harmful?

No. Most bacteria are harmless to humans, and many are beneficial: they help digestion, fix nitrogen for plants, drive nutrient cycles and are used to make foods and medicines. Only a minority cause disease.

Where can researchers obtain bacterial strains?

From public culture collections such as ATCC, DSMZ and NCTC, and for certain priority pathogens through BEI Resources. Check permits, material transfer terms and biosafety requirements before ordering or shipping.

Which agency funds bacteriology research in the U.S.?

Mainly NIH, especially NIAID for infectious disease and antimicrobial resistance, with NSF, USDA and other agencies supporting basic, agricultural and applied work.

What biosafety level is needed for bacteria?

It depends on the organism, the procedure and the facility. Nonpathogenic strains are often BSL-1 and many clinical isolates BSL-2, while some agents require BSL-3. Use the BMBL and your institutional biosafety office to decide.