Bacteriology

Lecture 1

bacterium/bacteria

single celled organisms

ubiquitous and the majority of bacteria are beneficial or harmless

some can invade the body and cause diseases

bacteria are prokaryotes

no nucleus

single celled organisms with a single circular chromosome and a rigid complex cell wall

they reproduce asexually though binary fission (cell*2)

bacteria shapes

etiology

cause of disease

pathogen

microbe that can cause disease (bacteria, fungi, virus, parasite)

transmission

the spread of the infectious agents from a host to another susceptible host

colonization

presence of microbes in the body without any disease

infection

invasion or growth of disease causing microbes in the body

transmission of disease diagram

pathogenesis

mechanisms by which a pathogen causes a disease

pathogenicity

ability of a pathogen to cause disease in a host

predisposition

condition of the host that makes it susceptible to infections

virulence

a pathogen’s ability to cause disease or damage

virulence factors

properties or traits found in isolates that cause disease but not found in isolates of the same species that lack the ability to cause disease

consequences of pathogen-host interaction

no colonization or colonization—the presence of bacteria on body surface without causing disease

infection

invasion of a host organism’s tissues by disease-causing organisms

what follows after infxn

disease followed by recovery

disease, death, or disability

disease followed by persistence:subclinical/chronic infection

obligate pathogen

obligatory—required

highly virulent microbe

small number of bacteria is enough to cause infection and a distinct dz without any host predisposition can cause a distinct dz

ex. Bacillus anthracis=Anthrax

primary pathogen

moderately virulent bacteria in moderate numbers with some level of host predisposition can cause a distinct dz

ex. Staphylococcus aureus skin infxn

opportunist pathogen

a bacteria with no virulence can cause nonspecific dz where this is host predisposing factors

ex. wound and burn infections caused by nonpathogenic bacteria

invades and then causes infxn; wide variety

endotoxin

bacteria has to die for toxin to be released in the body

sequence of events in bacterial pathogenesis

1. entry into host

2. evade host defenses

3. colonize the host systems

4. multiply

5. exert damage in host

6. transmission to other others

infectious vs contagious

🦠 Infectious

• Definition: Refers to diseases caused by pathogenic microorganisms (like bacteria, viruses, fungi, or parasites) that invade and multiply in the host.

• Key Point: Not all infectious diseases are easily spread from person to person.

• Examples: Tetanus (caused by Clostridium tetani) is infectious but not contagious—it enters through wounds and doesn’t spread between individuals.

🤝 Contagious

• Definition: A subset of infectious diseases that are easily transmitted from one individual to another.

• Key Point: All contagious diseases are infectious, but not all infectious diseases are contagious.

• Examples: Influenza, COVID-19, and measles are both infectious and highly contagious.

disease triangle of tragedy

host

pathogen

environmental

how do microbes cause disease

combination of specific virulence determinants that will allow them to invade, multiply, and persist in the host and conditions of the host that permits their survival

infection may result in

1. changing physiology by direct damage to the host cell (toxins)

2. depleting the host’s nutrients by using them

3. as a result of immune response (inflammation) to the infecting agent

   1. a combination of all the above affects

microbiome

collection of all microbes, such as bacteria, fungi, viruses, and their genes that naturally live on our bodies and inside a living body

they play a role essentially in all aspects an individual’s development immunity, mood, and disease development (obesity, chronic inflammation)

gram positive bacteria

thick peptidoglycan cell wall

lipoteichoic acid

no outer membrane

colored pink

gram negative

thin peptidoglycan wall

outer membrane containing lipopolysaccharide (LPS)

colored purple

acid fast bacteria

mycolic acid

they are **gram positive as they do not have an outer membrane

during gram-negative bacterial infection, bacteria dies and release

lipid a component or endotoxin to the bloodstream>stimulate the immune system>resulting in endotoxin or septic shock

what happens during gram negative bacterial infections

endotoxin releases immune factors

exceptions of bacteria without a cell wall

mollicutes: mycoplasm ureaplasma L forms are cell wall deficient bacteria

cannot see them using gram stain

cannot use cell well targeting therapy when treating infections caused by this bacteria

some bacteria have this type of flagella

endoflagella

pili/fimbrae

small thread-like structures on the bacterial surface

virulence factor

facilitate adherence to the host tissue through specific receptors

contibute to antigenicity and protection, and can be used as components of diagnostic test and vx

capsule

some bacteria have an outer coating usually made of a polysaccharide

capsule helps bacteria evade phagocytosis

a significant virulence factor

components of diagnostic test and vx

endospores

dormant form of bacteria

highly resistant to destruction

produced when bacteria are expose to adverse conditions and when essential nutrients are depleted

survival mechanism during adverse conditions

exotoxins

proteins produced inside pathogenic bacteria which are secreted into the surrounding medium

ex. tetanus

endotoxins

constitutive elements of the bacteria membrane

they are only liberated when the bacteria die

heat stable—components of bacteria that can induce inflammation by stimulating the immune system

superantigens

produced by pathogenic microbes (bacteria, mycoplasma, and viruses)

bind and crosslink indiscriminately to MHC class II molecule on the antigen presenting cells (macrophages) and T helper cell receptor

results in T cell activation and massive cytokine release leading to nausea, vomiting, fever and may end up in shock

ex. staphylococcal toxic shock syndrome toxin-1 (TSST-1)

biofilms

extracellular polymeric substances (EPS) produce when bacteria come together in masses and allowing bacteria to cling to surfaces

promote chronicity and reduce antimicrobial penetration and susceptibility and difficult to treat

ex. dental plaque, biofilm formation in implants, Pseudomonas aeruginosa biofilsm in cystic fibrosis patients

quorum sensing

molecular communication systems used by to synchronize the expression of certain genes

more likely to attack the host—individual behaviors vs group behaviors ex. fire ants

plasmids

circular extrachromosomal elements containing virulence factors

transferred between bacteria through a process called conjugation

ex. Tetanus neurotoxin

staphylococcus enterotoxin

bacteriophages

virus particles which attack bacteria

they transfer virulence factors or mutate virulence factors through a process called transduction

ex. Diphtheria toxin

Botulinum toxin

bacterial location

classification (taxonomy) of bacteria

best achieved by evaluating both genotypic and phenotypic properties (polyphasic taxonomy)

classification and nomenclature are subject to change

phylogeny

science dealing with evolutionary relationship between living organisms based on the sequences of macromolecules such as DNA, RNA, and protein

highly conserved **16s ribosomal gene is used most commonly