Basics in Abx therapy

Question 1

Gram Positive coverage

Answer 1

nafcillin (IV) and dicloxacillin (PO) provide excellent coverage and are not destroyed by penicillinases (beta- lactamases)

1st gen Cephalosporins (cephalexin and cefazolin) are effective against most skin infections

Question 2

Gram Negative coverage

Answer 2

3rd generation Cephalosporins are good, and not destroyed by cephalosporinases. They also penetrate CNS
Cephalosporins and penicillins may enhance the activity of aminoglycosides against Gram - neg. Combo of Amp and Gent provides good coverage of both positive and negatives.
Trimethoprim-sulfamethoxazole (Bactrim/Septra) is active against most UTI’s.
Amoxicillin is used for otitis media and other bact. URI’s

Question 3

Pseudomonas coverage

Answer 3

Ticarcillin or ceftazidime cover most Gm neg including Pseudomonas but fail to tx some Gram positive

Imipenem and meropenem good against pseudomonas

Question 4

Anaerobic coverage

Answer 4

Metronidazole or clindamycin cover most

mouth anaerobes are adequately coverage by penicillin

Question 5

Mycoplasma coverage

Answer 5

Macrolides (erythro, clarithro, azithro) tx mycoplasma pneumonia along with other organisms that cause community acquired pneumonia

Question 6

Systemic fungi coverage

Answer 6

Amphotericin is DOC for fungemia. (only for use in severe systemic infections)

Question 7

Bactericidal

Answer 7

abx that kill bacteria

Question 8

Bacteriostatic

Answer 8

only inhibit bacterial proliferation while host’s immune system does the killing.
(not very effective in immunocompromised patients: cancer, HIV, diabetes, or in overwhelming infections).

Question 9

Gram positive cocci: the basics

Answer 9

Have developed resistance to basic penicillins and some specialized penicillins

Have a peptidoglycan cell wall that surrounds bacteria, makes the cell impermeable (unlike gm -), Will stain blue

Effective tx: penicillins, cephalosporins, bacitracin, vanco, and cycloserine inhibit the synthesis of the peptidoglycan cell wall.

Question 10

Examples of Gram positive cocci

Answer 10

staph aureus and staph epidermidis: inhabit skin, most likely to infect wounds, surgical sites, and indwelling catheters

Strep pneumo is often cause of community-acquired pneumonia and adult bact. meningitis

Strep throat is caused by Group A beta-hemolytic Streptococcus (if left untx –> cause rheumatic fever)

Question 11

Anaerobes basics

Answer 11

common anaerobes: Bacteroides fragile, C. diff, and Fusobacterium.

C. botulinum and C. tetani produce toxins responsible for botulism and tetanus.

Metronidazole, chloramphenicol or clindamycin are effective against anaerobic infections

Appearance: mixed gm + and - compost of most anaerobic infections. Frequently are encased in abcess wall.

Question 12

Common sites of anaerobic invasion

Answer 12

mouth, GI, and skin

infections occur when anaerobes penetrate poorly oxygenated tissues (diabetic foot) or tissues that are normally sterile (peritoneum). C. diff flourishes in bowel when broad spectrum abx diminish normal flora. C. diff proliferates and releases a toxin that causes pseudomembranous colitis

Question 13

4 groups of gram negative pathogens

Answer 13

1. enterics, organism that normally inhabit GI (escherichia, shigella, salmonella, klebsiella, enterobacter, Serrate, proteus).
2. H. influenzae
3. Neisseria
4. Pseudomonas

Question 14

Appearance of gm - cells

Answer 14

Enterics and H. influenzae are red and elongated
Plasma membrane is protected by an adjacent rigid peptidoglycan cell wall which is encased by an outer membrane. This membrane is made of lipopolysaccharides interrupted by transmembrane protein pores (which prohibit entry of most penicillins and cephalosporins).

Question 15

Are penicillins good tx for gm - bacteria?

Answer 15

Depends, penicillins must first penetrate outer membrane in order to act on inner cell wall. Broad spectrum penicillins and 3rd gen cephalosporins are more hydrophilic and able to get through pores but even so some strains are resistant to penicillins b/c they produce B-lactamases that are concentrated in space between outer membrane and cell wall.

Neisseria meningitides and N. gonorrhea are the only gm - that are susceptible to penicillin G and other narrow spectrum penicillins.
*ceftriaxone is DOC for N. gonorrhea due to resistant penicillin strains

Question 16

Common sites of gm - infections?

Answer 16

Enterics responsible for UTIs and aspiration pneumonia

N. gonorrhea is responsible for sexually transmitted gonorrhea

N. menigitides and H. influenzae both cause meningitis

H. influenza causes pneumonia more commonly in the elderly

Pseudomonas aeruginosa is sometimes responsible for hospital acquired infections.