Anti-Infective Agents
DR. JAMA

Learning objectives
• Know (generally) the micro-organisms and the diseases they cause
• Know what microbe each antibiotic is effective against
• Know the names of antimicrobials
• Know the major adverse effects of each antimicrobial

Classification
1) Antibacterial
2) Antiviral
3) Antifungal
4) Antiprotozoal
5) Anthelminthic

Definitions
• Bateriostatic – inhibit bacterial multiplication
• Bactericidal – kill bacteria
Note, some “Bateriostatic” drugs are
“bactericidal” at high concentrations

Sites of Action (on target organism)
1. Cell wall (protection, maintains osmotic pressure)
• Penicillins, cephalosporins
2. Cytoplasmic membrane (biochemical activity)
• Azoles, amphotericin
3. Protein synthesis (peptide chains)
• Erythromycin, aminoglycosides
4. Nucleic acid metabolism (DNA or RNA synthesis/replication/repair)
• Quinolones, metronidazole

Principles of antimicrobial therapy
1. Make the correct diagnosis
2. Decide if antibiotics are necessary
3. Select the appropriate drug
Specificity

Principles of antimicrobial therapy
• Make the correct diagnosis
• Decide if antibiotics are necessary
• Select the appropriate drug
I. Specificity
II. Pharmacokinetic factors (eg. reaching site of infection)
III. Patient

Why combine drugs?
1) Avoid development of resistance
2) Broaden spectrum of antibacterial activity
3) Gain synergistic effect
4) Enable reduction of dose of one of the drugs (therefore reducing
risks of adverse drug reactions)

Chemoprophylaxis
• As suppressive therapy
1. Prevention of primary infection (strep pharyngitis - rheumatic fever)
2. Prevention of opportunistic infections (HIV)
3. Prevention of spread amongst contacts

Chemoprophylaxis
• Prior to surgery
• Gastrointestinal surgery
• Gynecological surgery
• Amputations
• Insertion of prosthetic joints
• Patient risk factors (prosthetic valves)

Problems
• Resistance
• Naturally resistant strains
• Spontaneous mutations
• Transmission of genes from other organisms
• Super infection
• From suppression of normal bacterial flora (eg. Clostridium
Difficile colitis)

Gram-positive bacteria
I’m positively blue over you!!

Gram-positive bacteria
• Streptococcus (groups A,B,C,G) (ie. Strep.)
Group A Strep = Strep pyogenes
Viridans streptococcus
Streptococcus pneumoniae (ie. pneumococcus)
• Enterococcus species (sp.)
• Staphlococcus aureus (ie. Staph. Aureus)
Staphylococcus epidermidis
• Corynebacteria sp.
• Listeria monocytogenes

Gram-negative bacteria

Gram-negative bacteria
• Neisseria gonorrhoeae
• Neisseria meningitidis
• Morraxella catarrhalis
• Haemophilus influenzae (ie. H. flu)
• Escherichia coli (ie. E. coli)
• Klebsiella sp.
• Enterobacter sp.
• Serratia sp.
• Salmonella sp.
• Shigella sp.
• Proteus sp

Gram-negative bacteria
• Aeromonas sp.
• Acinetobacter sp.
• Pseudomonas aeruginosa
• Legionella sp.
• Providencia sp.
• Morganella sp.
• Citrobacter sp.
• Stenotrophomonas maltophilia
• Yersinia sp.
• Pasteurella multocida
• Haemophilus ducreyi

Other
• Chlamydia sp.
• Mycoplasma pneumoniae

Anaerobes
1) Actinomyces
2) Bacteroides fragilis
3) Clostridium difficile
4) Peptostreptococcus
5) Fusobacterium sp.

• Sinusitis :
Streptococcus pneumoniae
Haemophilus influenzae
 Streptococcus pyogenes (group A strep),
Moraxella catarrhalis
• Otitis media :
usually viral
Streptococcus pneumoniae
Haemophilus influenzae
 Streptococcus pyogenes
Moraxella catarrhalis
 Staphylococcus aureus

Pharyngitis :
•usually viral
•Streptococcus pyogenes
Bronchitis
•usually viral
•Streptococcus pneumoniae
• Haemophilus influenzae

• The acute dental abscess is usually polymicrobial (anaerobes
and streptococci).

Pneumonias
• Community acquired :
• Streptococcus pneumoniae
• Haemophilus influenzae
• Following influenza – Staphylococcus aureus
• Atypical:
• Mycoplasma pneumonaiae
• Chlamydia pneumoniae
• Legionella pneumophilia
• Coxiella burnetii
• Hospital-associated (nosocomial) – Staphlyococcus aureus,
Enterobacteria sp., Streptococcus pneumoniae, Pseudomonas
aeruginosa, Haemophilus influenzae

Pneumonias, cont
• Patients with chronic lung disease – Klebsiella
pneumoniae (also in alcholics and elderly), Moraxella
catarrhalis
• Immunocompromised – staphylococcus aureus,
Streptococcus pneumoniae, Enterobacteria sp.,
Klebsiella, VIRUSES, FUNGI
• Aspiration – Aerobic & anaerobic streptococci,
Bacteroides sp., Fusobacterium
• Tuberculosis – Mycobacterium tuberculosis
Endocarditis – Strep sp., Enterococci sp, Staph sp.

•Meningitis
•Neonates
• E. coli, Group B strep., Listeria
monocytogenes
•Children (<5 years old)
• Neisseria meningitidis, H. flu, Strep.
Pneumoniae
•All ages over 5 yrs old
• Neisseria meningitidis, strep.
pneumoniae

• Bacterial causes of diarrhea
• diarrhea with a *multitude* of causes; many
of which DO NOT warrant antibiotics.
• Antibiotics can make some diarrheal
disease WORSE.
• Bacterial causes of diarrhea
• Campylobacter jejuni, Shigella, Salmonella,
E. coli, Vibrio cholerae, C. Diff

• Urinary Tract Infections – E. coli, Proteus sp.,
Klebsiella sp, Enterobacter, Pseudomonas
aeruginosa, Enterococcus sp, Staphylococcus
saprophyticus
• Genital Tract Infections
• Gonorrhea – Neisseria gonorrhoeae
• Chlamydia – Chlamydia trachomatitis
• Pelvic inflammatory disease – Neisseria
gonorrhoeae, Chlamydia trachomatis,
Mycoplasma sp.
• Syphilis – Treponema pallidum
• Chancroid – Haemophilus ducreyi
• Bacterial vaginosis – Gardnerella vaginalis,
Bacteroides sp.