MICROBIO 3.2 - FUNDAMENTALS OF ABX

• The learning objectives covered include describing the mechanisms of action, major adverse effects, and common clinical uses for six antibiotic classes.
• Resistance mechanisms for each antibiotic class will also be covered, along with the importance of antibiotic stewardship and conservative treatment.

Little History

• Alexander Fleming discovered Penicillin by accident in 1928.
• On September 28, 1928, upon returning from holiday, Fleming found Penicillium notatum mold growing in his petri dishes containing Staph.
• Albert Alexander became the first patient treated with Penicillin in 1941.
• Alexander had a life-threatening infection from a thorn scratch, improved but died when the medication ran out.
• Pfizer executive, John Smith said, "The mold is as temperamental as an opera singer," referencing challenges in yield, isolation, and purification.

Antibiotic Considerations

• Key questions to consider are:
• What differentiates a human cell from a bacteria?
• Are all bacteria the same?
• Do bacteria always respond to antibiotics as expected?
• Do people always respond to antibiotics as expected?

Antibiotic Targets

• Antimicrobial therapy targets:
• Folic acid synthesis via dihydrofolate reductase (DHF) reduction using sulfonamides, sulfamethoxazole, sulfisoxazole, sulfadiazine, trimethoprim, and metronidazole
• Membrane integrity using daptomycin and polymyxins
• Cell wall synthesis via peptidoglycan using glycopeptides (vancomycin, bacitracin)
• Peptidoglycan cross-linking using penicillinase-sensitive penicillins (penicillin G, V, ampicillin, amoxicillin), antipseudomonal (ticarcillin, piperacillin), carbapenems (imipenem, meropenem, ertapenem, doripenem), cephalosporins (I-V), and monobactams (aztreonam)
• mRNA synthesis using Rifampin
• DNA integrity using PABA
• DNA gyrase using fluoroquinolones (ciprofloxacin, levofloxacin) and quinolone (nalidixic acid)
• Protein synthesis by binding to the 50S subunit using chloramphenicol, clindamycin, linezolid, macrolides (azithromycin, clarithromycin, erythromycin), and streptogramins (quinupristin, dalfopristin)
• Protein synthesis by binding to the 30S subunit using aminoglycosides (gentamicin, neomycin, amikacin, tobramycin, streptomycin), glycylcycline (tigecycline), and tetracyclines (tetracycline, doxycycline, minocycline)

Classes of Antibiotics

• The classes of antibiotics to be discussed are:
• Penicillins
• Cephalosporins
• Aminoglycosides
• Tetracyclines
• Macrolides
• Fluoroquinolones
• The intended discussions for each class:
• Mechanism of action
• Adverse effects and important considerations, and
• Common clinical uses

Penicillins

• Mode of action:
• B-lactam antibiotic
• Binds penicillin-binding proteins (transpeptidase) via the B-lactam ring, blocking cross-linking of peptidoglycan in cell walls.
• This leads to osmotic imbalance, ultimately causing cell death (bactericidal).
• Adverse effect:
• Hypersensitivity
• Clinical use:
• Effective against Gram-positive aerobes such as S. pyogenes and S. pneumoniae.

Clinical Case I

• A 9-year-old female presents with a sore throat beginning two days prior, accompanied by fever and difficulty swallowing.
• Examination reveals discomfort during swallowing and a temperature of 100.3°F, with otherwise normal vitals.
• HENT exam results showed strep throat and the patient was perscribed pennicillin
• She returned within the day with urticaria, showing a hypersensitivity reaction to Penicillin

Cephalosporins

• Mode of action:
• B-lactam antibiotic that inhibits cell wall synthesis similarly to Penicillins and is bactericidal.
• Adverse effects:
• Hypersensitivity
• There is theoretically a cross-over penicillin allergy.
• Clinical Use:
• The generation class determines its use.
• 1st: Cefazolin, Cephalexin - Gram (+) Coverage
• 2nd: Cefaclor, Cefotetan, Cefoxitin, Cefuroxime
• 3rd: Cefixime, Cefotaxime, Ceftazidime, Ceftriaxone
• 4th: Cefepime - Gram (-) Coverage
• Ceftaroline: "5th generation" or "advanced generation" with similar to 3rd generation, but added MRSA coverage

Clinical Case II

• A 17-year-old male is brought in for altered mental status.
• The patient lives in dorms and did not receive meningococcal vaccines due to parental hesitancy.
• The patient presents with a week-long history of headache, fever, nausea, and vomiting.
• The patient is disoriented to person, place, and time and winces at light with neck stiffness due to a positive Brudzinski sign.
• A blood culture grows Gram-negative diplococci, indicating meningitis secondary to N. meningitidis infection.
• Ceftriaxone is the treatment due to great CNS penetration.

Aminoglycosides

• Mode of action:
• Binds to the 30S bacterial ribosome subunit, inhibiting protein synthesis and bactericidal
• Requires O₂ for uptake, making them ineffective against anaerobes.
• Adverse effects:
• Nephrotoxic, ototoxic, and teratogenic
• Clinical use:
• Used in severe Gram-negative rod infections, but its clinical use is limited due to adverse effects and resistance.

Tetracyclines

• Mechanism of Action:
• Bind to the 30S ribosome subunit to inhibit protein synthesis and are bacteriostatic.
• Should not be administered with divalent cations to avoid inhibited drug absorption.
• Adverse Effects:
• Discoloration of teeth and inhibition of bone growth in children
• Photosensitivity
• Teratogenic
• Clinical Use:
• These are versatile antibiotics
• Classic examples: Borrelia burgdorferi, Mycoplasma pneumoniae, Rickettsia, Chlamydia

Clinical Case III

• A 22-year-old female presents to the clinic for rash on her back that has appeared 3 days prior and getting worse.
• The patient recently had a hiking trip with friends in Maine leading to backpacking in densely wooded areas for a week.
• Symptoms now include rash and patients is experiencing flu-like symptoms.
• Lyme disease secondary to B. burgdorferi infection
• Treatment shown from course of oral doxycycline

Lyme Disease

• Borrelia burgdorferi = Lyme disease
• Ticks are vectors
• 3 stages:
• Stage I: 7-14 days out
• Stage II: 3-10 weeks out
• Stage III: months to years out
• The first stage is early localized Lyme disease (erythema chronicum migrans).
• The second stage is early disseminated Lyme disease (migratory arthralgia; Bell's palsy; myocarditis).
• The third stage is late Lyme disease (chronic arthritis, progressive encephalomyelitis).
• Annually 8.5 cases per 100,000 US populations have Lyme disease
• Preventative measure:
• Avoid endemic areas and exposure
• Instant tick removal
• Protective clothing and tick repellents
• Most commonly reported vector-borne disease in the US

Macrolides

• Mechanism of Action
• Binds to the 50S ribosome subunit to inhibit protein synthesis and are bacteriostatic.
• Adverse Effects:
• Arrythmia – prolonged QT interval
• Rash and GI upset
• Clinical Use:
• These are versatile antibiotics.
• Classic examples: Atypical pneumonia (ex: Mycoplasma), STIs (Chlamydia), Gram-positive cocci (alternative to penicillin)

Clinical Case IV

• A 19-year-old female presents to the clinic with a thick, whitish-green vaginal discharge for the past week.
• Patient is sexually active with 3 new partners in the last 6 months and uses condoms infrequently.
• Pelvic exam with speculum + otherwise normal vitals.
• Nucleic acid testing is positive for Chlamydia trachomatis.
• Treatment:
• Oral course of Azithromycin (single dose)
• +/- co-treatment of Gonorrhea
• Treatment of partners

Fluoroquinolones

• Mechanism of Action:
• Inhibits prokaryotic Topoisomerase II (DNA gyrase) and IV, which impairs DNA synthesis, and is bactericidal.
• Adverse Effects:
• Tendonitis or tendon rupture - contraindicated in children, pregnant/nursing women, and elderly.
• Arrythmia – prolonged QT interval
• Clinical Use:
• Gram-negative rods of urinary and Gl tracts.
• Otitis externa

Clinical Case V

• An 8-year-old male in clinic for ear pain and discharge on right side for 2 days + occurring after returning home from swim lessons.
• Decreased hearing and a yellowish discharge.
• The child begins to express extreme pain and cry when the right ear is tugged up and back.
• Otoscopy shows a normal and intact tympanic membrane.
• Diagnosis:
• Otitis externa likely secondary to Pseudomonas infection
• Treatment:
• Fluroquinolone drops specifically as Ciprodex otic suspension

Antibiotic Resistance

• Nearly as quickly as life-saving antibiotics are created, new drug-resistant infections appear:
• Pneumonia
• Meningitis
• Skin, bone, joint, stomach, blood, and heart valve infections
• Treats pneumonia, acne, infections of respiratory tract, genitals, urinary systems and stomach ulcers.
• Treats bronchitis, diphtheria, Legionnaires' disease, whooping cough, pneumonia, rheumatic fever, venereal disease, and many others.

Timeline of Antibiotic Resistance

• Timeline:
• 1943 - Penicillin Introduced
• 1950 - Tetracycline Introcuced
• 1953 - Erythromycin Introduced
• 1960 - Methicillin Introduced
• 1967 - Gentamicin Introduced
• 1972 - Vancomycin Introduced
• 1985 - Imipenem and Ceftazidime Introduced
• 1996 - Levofloxacin Introduced
• 2000 - Linezolid Introduced
• 2010 - Ceftaroline Introduced
• Timeline of Antibiotic Resistance Identified:
• 1940 - Penicillin-resistant Staphylococcus
• 1959 - Tetracycline-R Shigella
• 1962 - Methicillin-R Staphylococcus
• 1965 - Penicillin-R pneumococcus
• 1968 - Erythromycin-R Streptococcus
• 1979 - Gentamicin-R Enterococcus
• 1987 - Ceftazidime-R Enterobacteriaceae
• 1988 - Vancomycin-R Enterococcus
• 1996 - Levofloxacin-R pneumococcus
• 1998 - Imipenem-R Enterobacteriaceae
• 2001 - Linezolid-R Staphylococcus
• 2002 - Vancomycin-R Staphylococcus
• 2011 - Ceftaroline-R Staphylococcus
• Yearly Antibiotic-Resistant Infections:
• 2,000,000 illnesses with 23,000 deaths
• Antibiotics in Agriculture:
• 80 percent by weight are used in agriculture, primarily to fatten and protect animals

Mechanisms of Resistance

• Penicillins and Cephalosporins resistance:
• B-lactamases cleaves B-lactam rings
• Mutations in penicillin-biding-proteins
• Countering the counter: B-lactamase inhibitors
• Ex: Clavulanic acid (Augmentin)
• Aminoglycosides resistance:
• Bacterial transferase enzymes inactivate the drug
• Macrolides resistance:
• Alteration of 50S subunit binding site prevents drug binding
• Fluoroquinolones resistance:
• Mutations in Topoisomerase genes alter drug-protein interaction
• Efflux pumps
• Tetracyclines resistance:
• Transport pumps decrease uptake and/or increase efflux out of cells
• Bacteria Unique:
• Gene resistance encoding plasmids
• Conjugation, transformation, etc.

In Summary

• Practice good antibiotic stewardship,
• Not every infection requires an antibiotic, and
• Choose the right antibiotic for the right infection.