Neisseria gonorrhoeae (small red dots) in pus from a man with a urethral discharge (Gram stain)
Rod-shaped Bacillus subtilis
Commensals vs pathogenic bacteria in COPD
Phylogenetic tree of Bacteria, Archaea and Eucarya. The vertical line at bottom represents the last universal common ancestor.
An abscess caused by opportunistic S. aureus bacteria.
Bacteria display many cell morphologies and arrangements
Protein structure of botulinum toxin.
The range of sizes shown by prokaryotes (Bacteria), relative to those of other organisms and biomolecules.
Structure and contents of a typical Gram-positive bacterial cell (seen by the fact that only one cell membrane is present).
An electron micrograph of Halothiobacillus neapolitanus cells with carboxysomes inside, with arrows highlighting visible carboxysomes. Scale bars indicate 100 nm.
Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface
Bacillus anthracis (stained purple) growing in cerebrospinal fluid
Many bacteria reproduce through binary fission, which is compared to mitosis and meiosis in this image.
A culture of ''Salmonella
A colony of Escherichia coli
Helium ion microscopy image showing T4 phage infecting E. coli. Some of the attached phage have contracted tails indicating that they have injected their DNA into the host. The bacterial cells are ~ 0.5 µm wide.
Transmission electron micrograph of Desulfovibrio vulgaris showing a single flagellum at one end of the cell. Scale bar is 0.5 micrometers long.
The different arrangements of bacterial flagella: A-Monotrichous; B-Lophotrichous; C-Amphitrichous; D-Peritrichous
Streptococcus mutans visualised with a Gram stain.
Phylogenetic tree showing the diversity of bacteria, compared to other organisms. Here bacteria are represented by three main supergroups: the CPR ultramicrobacterias, Terrabacteria and Gracilicutes according to recent genomic analyzes (2019).
Overview of bacterial infections and main species involved.
Colour-enhanced scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cells
In bacterial vaginosis, beneficial bacteria in the vagina (top) are displaced by pathogens (bottom). Gram stain.
Antonie van Leeuwenhoek, the first microbiologist and the first person to observe bacteria using a microscope.

Pathogenic bacteria are bacteria that can cause disease.

- Pathogenic bacteria

However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus and bubonic plague.

- Bacteria

7 related topics

Alpha

Testing the susceptibility of Staphylococcus aureus to antibiotics by the Kirby-Bauer disk diffusion method – antibiotics diffuse from antibiotic-containing disks and inhibit growth of S. aureus, resulting in a zone of inhibition.

Antibiotic

Testing the susceptibility of Staphylococcus aureus to antibiotics by the Kirby-Bauer disk diffusion method – antibiotics diffuse from antibiotic-containing disks and inhibit growth of S. aureus, resulting in a zone of inhibition.
Molecular targets of antibiotics on the bacteria cell
Protein synthesis inhibitors (antibiotics)
Scanning electron micrograph of a human neutrophil ingesting methicillin-resistant Staphylococcus aureus (MRSA)
This poster from the US Centers for Disease Control and Prevention "Get Smart" campaign, intended for use in doctors' offices and other healthcare facilities, warns that antibiotics do not work for viral illnesses such as the common cold.
Arsphenamine, also known as salvarsan, discovered in 1907 by Paul Ehrlich.
Paul Ehrlich and Sahachiro Hata
Penicillin, discovered by Alexander Fleming in 1928
Alexander Fleming was awarded a Nobel prize for his role in the discovery of penicillin
Phage injecting its genome into a bacterium. Viral replication and bacterial cell lysis will ensue.
Fecal microbiota transplants are an experimental treatment for C. difficile infection.
Share of population using safely managed sanitation facilities in 2015.

An antibiotic is a type of antimicrobial substance active against bacteria.

It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of such infections.

Microscopic image of gram-negative Pseudomonas aeruginosa bacteria (pink-red rods)

Gram-negative bacteria

Microscopic image of gram-negative Pseudomonas aeruginosa bacteria (pink-red rods)
Gram-negative cell wall structure
Gram-positive and -negative bacteria are differentiated chiefly by their cell wall structure

Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation.

The gram-negative bacteria include the model organism Escherichia coli, as well as many pathogenic bacteria, such as Pseudomonas aeruginosa, Chlamydia trachomatis, and Yersinia pestis.

A cluster of Escherichia coli bacteria magnified 10,000 times

Microorganism

Organism of microscopic size, which may exist in its single-celled form or as a colony of cells.

Organism of microscopic size, which may exist in its single-celled form or as a colony of cells.

A cluster of Escherichia coli bacteria magnified 10,000 times
Antonie van Leeuwenhoek was the first to study microscopic organisms.
Lazzaro Spallanzani showed that boiling a broth stopped it from decaying.
Vardhmana Mahavira postulated the existence of microscopic creatures in the sixth century BC.
Louis Pasteur showed that Spallanzani's findings held even if air could enter through a filter that kept particles out.
Robert Koch showed that microorganisms caused disease.
Staphylococcus aureus bacteria magnified about 10,000x
Euglena mutabilis, a photosynthetic flagellate
A tetrad of Deinococcus radiodurans, a radioresistant extremophile bacterium
The photosynthetic cyanobacterium Hyella caespitosa (round shapes) with fungal hyphae (translucent threads) in the lichen Pyrenocollema halodytes
Wastewater treatment plants rely largely on microorganisms to oxidise organic matter.
A laboratory fermentation vessel
The eukaryotic parasite Plasmodium falciparum (spiky blue shapes), a causative agent of malaria, in human blood

Two of the three domains Archaea and Bacteria, only contain microorganisms.

This rapid evolution is important in medicine, as it has led to the development of multidrug resistant pathogenic bacteria, superbugs, that are resistant to antibiotics.

False-colored electron micrograph showing a malaria sporozoite migrating through the midgut epithelium of a rat

Infection

Invasion of an organism's body tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce.

Invasion of an organism's body tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce.

False-colored electron micrograph showing a malaria sporozoite migrating through the midgut epithelium of a rat
Chain of infection; the chain of events that lead to infection
Infection of an ingrown toenail; there is pus (yellow) and resultant inflammation (redness and swelling around the nail).
This image depicts the steps of pathogenic infection.
A southern house mosquito (Culex quinquefasciatus) is a vector that transmits the pathogens that cause West Nile fever and avian malaria among others.
Four nutrient agar plates growing colonies of common Gram negative bacteria.
Nucleic acid testing conducted using an Abbott Laboratories ID Now device
A temporary drive-in testing site for COVID-19 set up with tents in a parking lot
Washing one's hands, a form of hygiene, is an effective way to prevent the spread of infectious disease.
Mary Mallon (a.k.a. Typhoid Mary) was an asymptomatic carrier of typhoid fever. Over the course of her career as a cook, she infected 53 people, three of whom died.
Deaths due to infectious and parasitic diseases per million persons in 2012
Great Plague of Marseille in 1720 killed 100,000 people in the city and the surrounding provinces
East German postage stamps depicting four antique microscopes. Advancements in microscopy were essential to the early study of infectious diseases.
Herrerasaurus skull.

Infections can be caused by a wide range of pathogens, most prominently bacteria and viruses.

Many pathogenic bacteria are easily grown on nutrient agar, a form of solid medium that supplies carbohydrates and proteins necessary for growth, along with copious amounts of water.

A photomicrograph of a stool that has shigella dysentery. This bacteria typically causes foodborne illness.

Pathogen

Any organism or agent that can produce disease.

Any organism or agent that can produce disease.

A photomicrograph of a stool that has shigella dysentery. This bacteria typically causes foodborne illness.
Magnified 100× and stained. This photomicrograph of the brain tissue shows the presence of the prominent spongiotic changes in the cortex, with the loss of neurons in a case of a variant of Creutzfeldt-Jakob disease (vCJD)
Two pinworms next to a ruler, measuring in 6 millimeters in length
Brown rot fungal disease on an apple. Brown rot typically target a variety of top-fruits.
A structure of Doxycycline a tetracycline-class antibiotic

Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.

However, a relatively small list of pathogenic bacteria can cause infectious diseases.

Shigella

Shigella is a genus of bacteria that is Gram-negative, facultative anaerobic, non-spore-forming, nonmotile, rod-shaped, and genetically closely related to E. coli.

After infection, Shigella cells multiply intracellularly and spread to neighboring epithelial cells, resulting in tissue destruction and characteristic pathology of shigellosis.

Skin blotching and inflammation due to sepsis

Sepsis

Life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs.

Life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs.

Skin blotching and inflammation due to sepsis
Blood culture bottles: orange cap for anaerobes, green cap for aerobes, and yellow cap for blood samples from children
Sepsis Steps. Training tool for teaching the progression of sepsis stages
Intravenous fluids being given
Personification of septicemia, carrying a spray can marked "Poison"
Phenotypic strategy switches of microbes capable of provoking sepsis

Infections leading to sepsis are usually bacterial but may be fungal, parasitic or viral.

The current terms are dependent on the microorganism that is present: bacteremia if bacteria are present in the blood at abnormal levels and are the causative issue, viremia for viruses, and fungemia for a fungus.