Bacterial Cell Structure Flashcards

Question

What are the types of genetic mutations that can occur in bacteria?

Answer 1

May occur via one of three mechanisms: Conjugation Transformation (COMPETENCE) Transduction * Resistance genes may be shared in the above ways

Answer 2

The ability to conjugate is conferred by the F plasmid (fertility factor) Bacterial cells that contain an F plasmid are called “F+”. Bacteria that don’t have an F plasmid are called “F-”. F+ cells grow special tubes called “sex pilli” from their bodies. When an F+ cell bumps into an F- cell, the sex pilli hold them together, and a copy of the F plasmid is transferred from the F+ to the F-. Now both cells are F+. F plasmids can be spontaneously lost.

Answer 3

Competent cell takes up naked DNA from the environment Source of DNA from lysed donor cell DNA transported into cell through transmembrane channel using DNA translocase DNA incorporated into bacterial chromosome by RecA protein

Answer 4

Generalized: Caused by lytic phages (bacteriophage). Any genes from the host chromosome may be incorporated into future cells by bacteriphages Specialized: Caused by lsogeny phages. Genes close to the prophage insertion site may be transduced

Answer 5

The means by which transferred DNA is incorporated into the bacteria’s chromosomal DNA. Can be classified as: * Homologous (legitimate) recombination Occurs between closely related DNA sequences and generally substitutes one sequence for another. * Non-homologous (illegitimate) recombination. These generally occur between dissimilar sequences and generally produces insertions, deletions or both. These usually require special enzymes such as those produced by transposons and lysogenic bacteriophages.

Answer 6

Conjugative Transposons are self-transmissible - have all genes necessary to connect and transmit themselves to other bactera. Mobile sections of DNA that can move within or between genomes. (cut & paste model, conservative replication). Alternatively, it can be copied, with the copy being inserted at a second site, in a process known as replicative transposition.

Answer 7

* Constitutive Genes: Always active (expressed continuously). Necessary for basic cellular functions (e.g., metabolism, protein synthesis). Examples: Genes for ribosomal RNA, ATP synthesis * Adaptive Genes: Expressed in response to environmental changes or specific signals. Enable the cell to adapt to changing conditions (e.g., stress, nutrient availability). Expression is regulated (turned on/off as needed). Examples: Heat shock proteins, lactose operon in E. coli.

Answer 8

* Inducible Genes Activated (turned on) in response to specific environmental stimuli. Typically off but can be induced when a substrate or condition is present. Allow the organism to conserve resources by producing enzymes or proteins only when needed. Example: Lac operon in E. coli, activated by the presence of lactose * Repressible Genes Turned off when the end product or specific condition reaches a certain level. Typically on, but repressed when sufficient levels of a substance (usually a product of a biosynthetic pathway) are available. Helps to prevent overproduction of a substance. Example: Trp operon in E. coli, repressed when tryptophan levels are high.

Answer 9

Promoters and Operators These are nucleotide sequences that control the expression of a gene by influencing which sequences will be transcribed into mRNA. Operans Groups of one or more structural genes, expressed from a particular promoter and ending at a transcriptional terminator. E.g.. The E. coli lac operan includes all the genes necessary for lactose metabolism.

Answer 10

* Normal flora - microbes that colonize the body and usually do not cause disease * Opportunistic pathogens – generally don’t cause disease, but may under certain circumstances. * Frank pathogens - always cause disease.

Answer 11

* First introduction of human microbiome occurs at birth (a fetus in utero should be microbe-free) * Typically, from the mother’s vaginal flora * Infants born by caesarean section have significantly different microbiota than those born vaginally. Infants born by caesarean section tend to have a high proportion of bacteria normally found on the skin

Answer 12

* CoNs (S. epidermidis) - major inhabitant of the skin More than 90 percent of the resident aerobic flora in some areas. * Staphylococcus aureus - nose and perineum are the most common sites for S. aureus colonization Also prevalent (67 percent) on vulvar skin S. aureus is extremely common (80 to 100 percent) on the skin of patients with certain dermatologic diseases such as atopic dermatitis. Reason for this finding is unclear * Micrococci - not as common as staphylococci and diphtheroids; However, frequently present on normal skin. Mainly Micrococcus luteus, (20 to 80 percent of the micrococci) from the skin * Diphtheroids (Coryneforms) Denotes bacteria belonging to the genus Corynebacterium. Corynebacterium acnes - originally used to describe skin anaerobic diphtheroids: * Re-classified as Propionibacterium acnes and as P. granulosum P. acnes 8x more frequent than P. granulosum in acne Possibly involved in acne pathogenesis Children <10 years :- rarely colonized with P. acnes.

Answer 13

* Many variations in oral flora, based on: Time, individual, oral cavity site Healthy oral cavity (human): * Gram positive Cocci – Abiotrophia, Peptostreptococcus, Streptococcus, Stomatococcus Rods – Actinomyces, Bifidobacterium, Corynebacterium, Eubacterium, Lactobacillus , Propionibacterium, Pseudoramibacter, Rothia * Gram negative Cocci – Moraxella, Neisseria, Veillonella Rods – Campylobacter, Capnocytophaga, Desulfobacter, Desulfovibrio, Eikenella, Fusobacterium, Hemophilus, Leptotrichia, Prevotella, Selemonas, Simonsiella, Treponema, Wolinella Non-bacteria Oral cavity contains diverse forms of microbes such as protozoa, fungi and viruses Protozoa (commonly seen) Entamoeba gingivalis and Trichomonas tenax Fungi (Candida most common) Candida, Cladosporium, Aureobasidium, Saccharomycetales, Aspergillus, Fusarium and Cryptococcus Histatins - antimicrobial peptides secreted by salivary glands.

Answer 14

Pharynx and trachea contain bacterial genera commonly found in the oral cavity. * Common organisms: α- and β-hemolytic streptococci, anaerobes, staphylococci, neisseriae, diphtheroids. * Potential Pathogens present in the pharynx: Haemophilus spp. Mycoplasmas Pneumococci * Upper respiratory tract is often the first site of colonization for pathogens like: Neisseria meningitidis Corynebacterium diphtheriae Bordetella pertussis Lower Respiratory Tract (small bronchi and alveoli) is typically sterile

Answer 15

* Duodenum and Jejunum: Low bacterial levels (approximately 10³ organisms/ml) Streptococci, lactobacilli, and Bacteroides. * Ileum: Bacterial populations increase at the ileocecal junction to around 10⁶ to 10⁸ organisms/ml. * Common bacteria: Streptococci, lactobacilli, Bacteroides, and bifidobacteria. * Colon and Faeces: Highest bacterial concentrations (10⁹ to 10¹¹ organisms/g), with over 400 species identified. -Anaerobes: Bacteroides, Bifidobacterium, Clostridium, and others.

Answer 16

* The composition of vaginal flora varies based on age, pH, and hormonal levels of the host. Yeasts (e.g., Candida) are occasionally present in the vagina (10-30% of women). - Yeast overgrowth can cause vaginitis. * Anterior Urethra Flora: Common bacteria: S. epidermidis, Enterococci, Diphtheroids. Occasionally present: E. coli, Proteus, Nonpathogenic Neisseria (10-30%). * Clinical Relevance: Urine cultures may contain these organisms if a midstream (clean-catch) sample is not obtained, leading to potential contamination.

Answer 17

Conjunctival flora is sparse. Tears may have a role in spare flora Corynebacteria, Neisseriae, and Moraxellae have been cultured. Staphylococci and streptococci also present.

Answer 18

Believed that isopropyl alcohol dehydrates the bacterial cell and denatures its proteins Concentration difference of water and alcohol on either side of the cell wall 70% alcohol enters the cell to denature both enzymatic and structural proteins * 99% isopropanol evaporates very quickly and results in almost immediate coagulation of surface or cell wall proteins, preventing penetration of cell walls and killing bacteria

Answer 19

1. Infectivity: The organism's ability to invade, survive within, multiply, and spread in the host. 2. Pathogenicity: The ability of a microorganism to cause disease in a host. Parasitism: A relationship where one organism lives on or within another. Different types of host-parasite interactions exist. - Commensalism: The parasite resides in or on the host without causing harm or disease. - - Symbiosis: A mutually beneficial relationship between two organisms. 3. Opportunistic Pathogen: Normally harmless, but can cause disease when it enters different tissues or sites. 4. Obligate Pathogen: Always causes disease when present in a host.

Answer 20

Infection begins with exposure to a pathogen from its natural reservoir, which can be either animate (humans or animals) or inanimate (water, soil, food). Carriers may spread pathogens without showing symptoms. Zoonosis: Diseases transmitted from animals to humans. Nosocomial Infection: Infections acquired in hospitals.

Answer 21

1. Direct Contact: Transmission through person-to-person contact (e.g., kissing, sexual intercourse), or from mother to child during pregnancy or birth. 2. Droplet Transmission: Spread through respiratory droplets from coughing or sneezing, typically over short distances. 3. Indirect Contact: Pathogens transferred via contaminated objects (fomites) or by healthcare workers between patients. 4. Airborne Transmission: Pathogens carried in small particles over long distances (e.g., fungal spores in the air).Fecal-Oral Transmission: Pathogens in contaminated food or water are consumed by the next host. 5. Vectorborne Transmission: Arthropod vectors (e.g., mosquitoes, ticks) spread pathogens by biting infected hosts and transferring the agent to others.

Answer 22

A measure of an organism's ability to cause disease; the degree of pathogenicity. It is often used to compare the disease-causing potential between different strains of the same species. LD50: Lethal dose required to kill 50% of inoculated hosts. ID50: Infectious dose required to infect 50% of inoculated hosts.

Answer 23

Molecules produced by microorganisms that cause harm to the host. These factors assist pathogens in: 1. Invading the host 2. Causing disease 3. Evading host defenses

Answer 24

1. Factors promoting bacterial colonization: -Adherence factors -Invasion or spreading factors -Nutrient competition (e.g., iron) -Evasion of immune responses 2. Factors causing damage to the host: - Exotoxins - Endotoxins

Answer 25

Biofilms: Bacteria within a sticky polysaccharide web, binding cells together and to surfaces (e.g., surgical implants, catheters). -Facilitates colonization -Biofilm production requires adequate numbers of bacteria (quorum). Example: Pseudomonas aeruginosa produces a biofilm once the bacterial colony size is large enough. Example: Dental plaque is another form of biofilm. Biofilm Advantages: Protects bacteria from host defenses and antibiotics, promoting persistence in the host.

Answer 26

Bacteria pathogens must survive and multiply in the host There are two main types of toxins: - Endotoxins - Exotoxins

Answer 27

* Lipopolysaccharides (LPS) in the outer membrane of Gram-negative bacteria. Released when bacterial cells die or lyse, usually in the late growth stages. * Toxic Effects: Only occur after endotoxins are released into the medium. * Effects of LPS-Endotoxins - Fever and Inflammation - Tissue Destruction and Respiratory Distress - Capillary Damage: Leading to petechial rash, capillary leakage, and hypovolemia.

Answer 28

Heat-sensitive soluble proteins secreted by living bacteria. - Highly potent and can cause damage distant from the original infection site. - Associated with specific diseases, with toxin genes often carried on plasmids or prophages. - Examples of exotoxin-related diseases: Botulism, Tetanus, Diphtheria.

Answer 29

Type I: Cell surface-active toxins. Bind to cell receptors and stimulate cell responses. Example: Superantigens – Stimulate T cells excessively, causing massive inflammation and tissue damage. Type II: Membrane-damaging toxins. Form pores in the host cell membrane, leading to cell lysis and loss of osmotic balance. Type III: Intracellular toxins. Enter the host cell and disrupt internal processes. Example: AB toxins – The B subunit binds to the cell, and the A subunit disrupts cell function (e.g., Tetanus toxin).

Answer 30

Superantigens: - Stimulate T cells to produce excessive cytokines (IL-1; TNF), leading to massive immune responses. - Trigger systemic effects such as Toxic Shock Syndrome (S. aureus, Group A Streptococci). - Cause symptoms like inflammation, shock, diarrhea, and vomiting when ingested in contaminated food. Superantigens can bind without processing to MHCII receptors on APC's. Superantigens acts as polyclonal stimulators of T cells.

Answer 31

Target host cell membranes, forming pores that cause cell lysis. Example: Clostridium perfringens alpha-toxin, a lecithinase that causes red blood cell (RBC) hemolysis. Commonly observed in aggressive pathogens (S. aureus, Group A Streptococcus, E. coli).

Answer 32

AB Toxins: Composed of two subunits: - B subunit: Binds to specific host cell receptors (determines host cell specificity). - A subunit: Enters the cell and modifies target proteins through enzymatic reactions. Common reaction: ADP-ribosylation, where ADP-ribose is attached to a target protein, inhibiting its function. Example: Cholera toxin inactivates G proteins in intestinal cells, causing hypersecretion of electrolytes and diarrhea. Tetanus toxin cleaves synaptobrevin in neurons, leading to reduced neurotransmitter release and spastic paralysis

Bacterial Cell Structure Flashcards

(60 cards)