Recombinant DNA Technology and Pathogenic Gram-Negative Bacteria: Study Guide

Recombinant DNA Technology

Genetic Engineering & Biotechnology

Genetic engineering involves the direct, deliberate modification of an organism’s genome. Biotechnology utilizes these altered organisms for commercial production, including pharmaceuticals and agriculture.

• Genetic Engineering: Modification of genetic material to achieve desired traits.

• Biotechnology: Application of genetically modified organisms in industry.

• Example: Production of human insulin using genetically engineered bacteria.

Tools & Techniques of Molecular Genetics

Several tools and techniques are essential for manipulating DNA and studying genes.

Restriction Enzymes

• Definition: Enzymes that recognize and cleave specific DNA sequences, often palindromic.

• Restriction Site: Specific sequence where the enzyme cuts (e.g., EcoRI recognizes GAATTC).

• Types of Ends: Cuts can produce blunt ends (straight cut) or sticky ends (overhanging single-stranded ends).

• Example: EcoRI produces sticky ends at GAATTC.

Enzyme	Restriction Site	Type of End
BAMHI	GGATCC	Sticky ends
HINDIII	AAGCTT	Sticky ends
EcoRI	GAATTC	Sticky ends

Palindromes: DNA sequences that read the same forward and backward on complementary strands.

Reverse Transcriptase

• Definition: Enzyme that synthesizes complementary DNA (cDNA) from an RNA template.

• Application: Allows insertion of eukaryotic genes (lacking introns) into prokaryotes for protein production.

• Example: Production of human insulin in bacteria using cDNA from human mRNA.

Vectors

• Definition: DNA molecules used to carry foreign genetic material into a host cell.

• Examples: Plasmids, bacteriophages, cosmids.

• Application: Used in gene cloning and recombinant DNA technology.

CRISPR-Cas9

• Definition: Gene editing tool derived from bacterial immune systems.

• Cas9: Endonuclease enzyme that cuts DNA at targeted locations.

• Applications: Potential treatment for genetic diseases, precise genome editing.

• Example: Correction of sickle cell anemia mutations.

Gel Electrophoresis

• Principle: Separation of DNA fragments by size using an electric field in agarose or polyacrylamide gel.

• Procedure: DNA samples loaded into wells; electric current moves DNA toward positive electrode; smaller fragments travel farther.

• Application: DNA fingerprinting, analysis of PCR products.

Sample	Size (bp)	Expected Band Position
A	2500	Middle
B	800	Farthest from well
C	6400	Closest to well
D	2500	Middle

Synthetic Nucleic Acids

• Definition: Artificially created short DNA or RNA sequences complementary to target sequences.

• Application: Used as probes in diagnostics, primers in PCR.

Polymerase Chain Reaction (PCR)

• Definition: Technique to amplify specific DNA sequences exponentially.

• Steps:

  1. Denature: DNA strands separated by heating (typically 94-98°C).

  2. Anneal (Priming): Primers bind to target sequence (typically 50-65°C).

  3. Extend: DNA polymerase synthesizes new DNA (typically 72°C).

• Real-time PCR: Quantitative method to measure DNA amplification.

• Multiplex PCR: Amplifies multiple targets in one reaction using multiple primer pairs.

Equation:

$\text{Number of DNA copies after n cycles} = 2^n \times \text{initial copies}$

Next Generation Sequencing (NGS)

• Definition: High-throughput sequencing to determine DNA base order.

• Features: Simultaneous sequencing of many DNA strands; uses fluorescently labeled dideoxynucleotides (ddNTPs) to terminate synthesis.

• Application: Whole genome sequencing, mutation analysis.

Recombinant DNA, Gene Cloning, & Product Retrieval

• Process:

  1. Isolate gene of interest.

  2. Insert gene into vector.

  3. Transform host cell with recombinant vector.

  4. Host cell expresses gene and produces desired protein.

  5. Retrieve and purify protein product.

• Example: Production of human growth hormone in bacteria.

Pharmaceutical and Therapeutic Applications

• Human Insulin: Recombinant insulin for diabetes treatment; reduces allergic reactions compared to animal insulin.

• Human Growth Hormone: Used to treat growth disorders; produced safely in bacteria.

Agricultural Applications

• Bt Crops: Genetically modified to express Bacillus thuringiensis toxin, providing pest resistance.

• Herbicide-Resistant Plants: Engineered to tolerate herbicides, allowing efficient weed control.

Gene Therapy

• Definition: Replacement of faulty genes with normal genes to cure genetic disorders.

• History: First gene therapy in 1990 for ADA deficiency.

• Current Status: Hundreds of ongoing clinical trials; challenges include delivery and immune response.

Pathogenic Gram-Negative Cocci and Bacilli

Neisseria Genus

Neisseria are gram-negative cocci, often occurring as diplococci. Virulent strains possess fimbriae, capsule, and lipid A.

• Distinguishing Features: Gram-negative, diplococci, capnophilic (require CO2), oxidase positive.

Neisseria gonorrhoeae

• Selective Media: Thayer Martin agar (contains antibiotics).

• Disease: Gonorrhea (urethritis, cervicitis, pelvic inflammatory disease, conjunctivitis in newborns).

• Symptoms: Painful urination, discharge, pelvic pain.

• Complications: Infertility, ectopic pregnancy, disseminated infection.

Neisseria meningitidis

• Carriage: Nasopharyngeal carriage in 3-40% of healthy people.

• Transmission: Respiratory secretions.

• Disease: Meningitis, meningococcemia (fever, headache, neck stiffness, petechiae).

• Vaccines:

  • MenACWY (conjugate): Recommended for 11-12 years and at-risk persons.

  • MenB: Recommended for 10+ years at increased risk.

Pseudomonas Genus

• Distinguishing Features: Gram-negative rods, aerobic, oxidase positive, motile, produce pigments.

Pseudomonas aeruginosa

• Resistance: Resistant to soaps, disinfectants, drugs.

• Habitat: Moist environments (pools, sinks, respiratory equipment).

• Pathogenicity: Opportunistic pathogen; rarely part of normal microbiota.

• At-risk Patients: Burn victims, cystic fibrosis, immunocompromised, hospitalized patients.

Burkholderia cepacia

• Significance: Important in cystic fibrosis; causes rapid lung decline, necrotizing pneumonia.

• Control: Strict infection protocols to prevent spread.

Legionella Genus

• Distinguishing Features: Gram-negative rods, aerobic, require special media.

Legionella pneumophila

• Habitat: Water environments (air conditioners, showers, misters).

• Transmission: Inhalation of aerosolized contaminated water.

• Disease: Legionnaires disease (pneumonia, fever, cough, confusion).

• Diagnosis: Culture, urinary antigen test.

Bordetella Genus

• Distinguishing Features: Gram-negative rods, aerobic.

Bordetella pertussis

• Transmission: Person-to-person via respiratory droplets.

• Disease: Whooping cough (pertussis): severe cough, copious mucus, paroxysms.

• Diagnosis: Culture, PCR.

• Prevention: DTaP (children), Tdap (adolescents).

Campylobacter Genus

• Distinguishing Features: Curved gram-negative rods, microaerophilic.

Campylobacter jejuni

• Reservoir: Domestic animals.

• Transmission: Foodborne (undercooked poultry, contaminated water).

• Disease: Campylobacteriosis (diarrhea, abdominal pain, fever).

• Diagnosis: Stool culture.

Helicobacter pylori

• Significance: Causes >90% of duodenal ulcers, up to 80% of gastric ulcers.

• Adaptation: Produces urease to neutralize stomach acid.

• Symptoms: Abdominal pain, nausea, vomiting.

• Diagnosis: Urea breath test, stool antigen, biopsy.

Enterobacteriaceae Family

• Distinguishing Features: Gram-negative rods, facultative anaerobes, ferment glucose, reduce nitrate, motile/non-motile, serological subtyping (O and H antigens).

• O Antigen: Outer membrane polysaccharide.

• H Antigen: Flagellar protein.

• IMViC Tests: Indole, Methyl Red, Voges-Proskauer, Citrate.

Genus	IMViC Pattern
Escherichia coli	++--
Klebsiella	--++
Enterobacter	--++
Proteus	-+--
Salmonella	-+--
Shigella	+-++
Additional info: Patterns inferred for illustration.

Escherichia coli

• Habitat: Intestines of humans and animals.

• Pathogenic Strains: Six diarrheagenic types; most common cause of urinary tract infections.

• Adherence: Fimbriae allow attachment to urethral epithelium.

Shiga toxin-producing E. coli (STEC)

• Example: E. coli O157:H7.

• Transmission: Undercooked beef, contaminated produce.

• Symptoms: Bloody diarrhea, abdominal cramps.

• Complication: Hemolytic Uremic Syndrome (HUS): kidney failure, anemia, thrombocytopenia.

Salmonella enterica

• Serotypes: Over 2,000.

• Transmission: Zoonotic, foodborne (contaminated food/water).

• Symptoms: Gastroenteritis: diarrhea, fever, abdominal cramps.

• Diagnosis: Stool culture.

Shigella sonnei

• Transmission: Person-to-person (fecal-oral).

• Symptoms: Shigellosis: fever, abdominal pain, bloody diarrhea.

• Diagnosis: Stool culture.

Miscellaneous Gram-Negative Organisms

Vibrio cholerae

• Distinguishing Features: Curved gram-negative rods, motile, oxidase positive.

• Transmission: Contaminated water/food.

• Symptoms: Cholera: profuse watery diarrhea, dehydration.

• Prevention: Clean water, sanitation, oral vaccine.

Vibrio vulnificus

• Disease: Wound infections, septicemia, diarrhea.

• Geographic Distribution: More common in warm coastal regions (e.g., Florida).

Haemophilus influenzae

• Growth Requirements: Chocolate agar, heme (X factor), NAD+ (V factor).

• Pathogenicity: Encapsulated strains resist phagocytosis.

• Disease: Meningitis in children (reduced by HIB vaccine).

• Prevention: HIB vaccine at 2, 4, 6, 12 months.

Chlamydia trachomatis

• Significance: Most common reportable STD in U.S.; curable with antibiotics.

• Complications: Infertility if untreated.

• Symptoms: Often asymptomatic.

• Screening: Sexually active women under 25, high-risk groups.

• Diagnosis: NAAT (nucleic acid amplification test).

• Treatment: Antibiotics (azithromycin, doxycycline).

Trachoma

• Transmission: Contact with eye/nose discharge, flies.

• Symptoms: Scarring of conjunctiva, corneal scarring, blindness.

• Global Impact: Endemic in 53 countries; 2.2 million visually impaired.

Treponema pallidum

• Distinguishing Features: Spirochete, motile, cannot be cultured on artificial media.

• Disease: Syphilis: primary (chancre), secondary (rash), tertiary (neurological/cardiovascular).

• Transmission: Sexual contact, vertical (mother to fetus).

• Diagnosis: Serology (RPR, VDRL, FTA-ABS).

Borrelia burgdorferi

• Distinguishing Features: Spirochete, transmitted by Ixodes tick.

• Disease: Lyme disease: erythema migrans (bull's-eye rash), fever, joint pain, neurological symptoms.

• Transmission: Tick bite.

• Diagnosis: Serology, clinical presentation.

Additional info: Some IMViC patterns and table entries inferred for completeness. Life cycle of Ixodes tick and some figures referenced but not described due to lack of image content.