1. Ability to Cause Disease: This is the defining feature of pathogenic bacteria. They possess mechanisms or factors that allow them to invade the host, multiply, and disrupt normal bodily functions, leading to illness.
2. Virulence Factors: Pathogenic bacteria often have specific virulence factors, which are molecules or structures that contribute to their disease-causing ability. These include:
* Toxins: Substances that can damage host cells or tissues (e.g., botulinum toxin, tetanus toxin).
* Adhesins: Molecules that allow bacteria to attach to host cells and surfaces (e.g., pili, fimbriae).
* Capsules: Protective layers that can evade host immune responses (e.g., Streptococcus pneumoniae).
* Enzymes: Proteins that break down host tissues or molecules to facilitate infection (e.g., hyaluronidase).
3. Host Specificity: Some pathogenic bacteria are highly specific to certain host species or even particular tissues or organs within a host.
4. Mode of Transmission: Pathogenic bacteria can spread through various means, including:
* Contact transmission: Direct contact with infected individuals or contaminated surfaces.
* Airborne transmission: Inhaling bacteria-laden droplets.
* Foodborne transmission: Ingestion of contaminated food or water.
* Vector transmission: Spread through insects or other animals.
5. Infectivity and Contagiousness: A highly infectious bacterium is easily spread from person to person. Contagiousness refers to the likelihood that an infected individual will transmit the bacteria to others.
Examples of Pathogenic Bacteria:
* Salmonella: Causes food poisoning.
* Staphylococcus aureus: Can cause skin infections, pneumonia, and toxic shock syndrome.
* Mycobacterium tuberculosis: Causes tuberculosis.
* Clostridium difficile: Causes severe diarrhea and colitis.
* Neisseria gonorrhoeae: Causes gonorrhea, a sexually transmitted infection.
It's important to note that not all bacteria are pathogenic. Many bacteria are beneficial or harmless to humans.
