This document discusses infectious diseases and treatment of various bacterial infections. It begins with an introduction to antibiotics and how the bacteria that cause disease remain the same but the antibiotics used to treat them can change. It then discusses treatment of methicillin-sensitive and methicillin-resistant Staphylococcus aureus infections. The remainder of the document covers various classes of antibiotics including penicillins, cephalosporins, carbapenems, fluoroquinolones, aminoglycosides and others; the bacteria and infections they treat; and treatments for central nervous system infections like meningitis and encephalitis.

1. Infectious Diseases

2. Introduction to Antibiotics
 The organisms associated with particular diseases do not change over
time, but
 the antibiotics that treat the infections can change.

3. Treatment of Staphylococcus
 “methicillin-sensitive Staphylococcus aureus” (MSSA)
 “methicillin-resistant Staphylococcus aureus” (MRSA)

4. Sensitive Staphylococcal Isolates
 First agents:
 Intravenous: oxacillin, nafcillin, cefazolin
 Oral: dicloxacillin, cephalexin, cefadroxil
 Additional agents:
 Intravenous: any cephalosporin, any carbapenem, beta-lactam/beta
lactamase combinations
 Oral: amoxicillin/clavulanate, any oral cephalosporin

5. Resistant Staphylococcal Isolates
 First agents:
 Intravenous: vancomycin, linezolid, daptomycin, ceftaroline,
 Oral: linezolid, TMP/SMZ, doxycycline•
 Additional agents:
 Intravenous: oritavancin, telavancin, dalbavancin
 Oral: clindamycin, tedizolid

7. Beta-lactam Antibiotics: Penicillins,
Cephalosporins,
Carbapenems, Aztreonam

8. Penicillins
 Penicillin (G, VK, benzathine):
 viridans group streptococci, Streptococcus pyogenes, oral anaerobes,
syphilis, Leptospira
 Ampicillin and amoxicillin: cover the same organisms as penicillin, as
well as
 E. coli, Lyme disease, and a few other gram-negative bacilli.

10.  Amoxicillin is the “best initial therapy” for:
 Otitis media•
 Dental infection and endocarditis prophylaxis
 Lyme disease limited to rash, joint, or seventh cranial nerve involvement
 Urinary tract infection (UTI) in pregnant women
 Listeria monocytogenes
 Enterococcal infections

11. Penicillin's-resistant penicillins
 oxacillin, cloxacillin, dicloxacillin, and nafcillin.
 These drugs are used to treat:
 Skin infections: cellulitis, impetigo, erysipelas
 Endocarditis, meningitis, and bacteremia from staphylococci
 Osteomyelitis and septic arthritis only when the organism is proven
 sensitive
 They are not active against methicillin-resistant Staphylococcus aureus
(MRSA) or Enterococcus.

12. Antipsudomonal Penicillins
 Piperacillin, ticarcillin, azlocillin, mezlocillin
 These agents cover gram-negative bacilli (e.g., E. coli, Proteus) from
the large Enterobacteriaceae group as well as pseudomonads.
 They are the “best initial therapy” for:
 Cholecystitis and ascending cholangitis
 Pyelonephritis
 Bacteremia
 Hospital-acquired and ventilator-associated pneumonia

14. Cephalosporins
 The amount of cross-reaction between penicillin and cephalosporins is very small
(<3%).
 All cephalosporins, in every class, will cover group A, B, and C streptococci,
viridans group streptococci, E. coli, Klebsiella, and Proteus mirabilis.

15. First Generation: Cefazolin, Cephalexin,
Cephradrine, Cefadroxyl
 Staphylococci: methicillin sensitive = oxacillin sensitive = cephalosporin
sensitive
 Streptococci (except Enterococcus)
 Some gram-negative bacilli such as E. coli, but not Pseudomonas
 Osteomyelitis, septic arthritis, endocarditis, cellulitis

16. Second Generation: Cefotetan, Cefoxitin,
Cefaclor, Cefprozil, Cefuroxime,
Loracarbef
 These agents cover all the same organisms as first-generation
cephalosporins and add coverage for anaerobes and more gram-
negative bacilli.
 Warning: Cefotetan and cefoxitin increase the risk of bleeding and give a
disulfiramlike reaction with alcohol.
 Cefuroxime, loracarbef, cefprozil, cefaclor: Respiratory infections such as
bronchitis, otitis media, and sinusitis.

17. Third Generation: Ceftriaxone, Cefotaxime,
Ceftazidime
 Ceftriaxone: First-line for pneumococcus, including partially insensitive
organisms
 Meningitis
 Community-acquired pneumonia (in combination with macrolides)
 Gonorrhea
 Lyme involving the heart or brain
 Avoid ceftriaxone in neonates because of impaired biliary
metabolism.

18.  Cefotaxime
 Superior to ceftriaxone in neonates
 Spontaneous bacterial peritonitis
 Ceftazidime has pseudomonal coverage.

19. Fourth Generation: Cefepime
 Cefepime has better staphylococcal coverage compared with the
third- generation cephalosporins.
 It is used to treat:
 Neutropenia and fever
 Ventilator-associated pneumonia

20. Fifth Generation: Ceftaroline
 Gram-negative bacilli and MRSA, not Pseudomonas

21. Carbapenems (Imipenem, Meropenem,
Ertapenem,
Doripenem)
 Carbapenems cover gram-negative bacilli, including many that are
resistant,
 anaerobes, streptococci, and staphylococci.
 They are used to treat neutropenia and fever.

22. Aztreonam
 This is the only drug in the class of monobactams.
 Exclusively for gram-negative bacilli including Pseudomonas
 No cross-reaction with penicillin

23. Fluoroquinolones (Ciprofloxacin, Gemifloxacin,
Levofloxacin,
Moxifloxacin)
 Best therapy for community-acquired pneumonia, including penicillin-resistant
pneumococcus (except ciprofloxacin)
 Gram-negative bacilli including most pseudomonads
 Ciprofloxacin for cystitis, pyelonephritis, and ventilator-associated
 pneumonia.
 Diverticulitis and GI infections, but ciprofloxacin, gemifloxacin, and
 levofloxacin must be combined with metronidazole because they don’t cover
anaerobes
 Moxifloxacin can be used as a single agent for diverticulitis and does not need
metronidazole

24. Aminoglycosides (Gentamicin, Tobramycin,
Amikacin)
 Gram-negative bacilli (bowel, urine, bacteremia)
 Synergistic with beta-lactam antibiotics for enterococci and staphylococci
 No effect against anaerobes, since they need oxygen to work
 Nephrotoxic and ototoxic

25. Doxycycline
 Chlamydia
 Lyme disease limited to rash, joint, or seventh cranial nerve palsy
 Rickettsia
 MRSA of skin and soft tissue (cellulitis)
 Primary and secondary syphilis in those allergic to penicillin
 Borrelia, Ehrlichia, and Mycoplasma
 Adverse effects: tooth discoloration (children), Fanconi syndrome (Type II
RTA proximal), photosensitivity, esophagitis/ulcer

26. Trimethoprim/Sulfamethoxazole
 Cystitis
 Pneumocystis pneumonia treatment and prophylaxis
 MRSA of skin and soft tissue (cellulitis)
 Besides rash, it causes hemolysis with G6 PD deficiency and bone
marrowsuppression because it is a folate antagonist.

27. Beta-Lactam/Beta-Lactamase
Combinations
 Amoxicillin/clavulanate
 Ampicillin/sulbactam
 Ticarcillin/clavulanate
 Piperacillin/tazobactam
 Ceftazidime/avibactam
 Ceftolozane/tazobactam
 Beta-lactamase adds coverage against sensitive staphylococci to these agents.
 They cover anaerobes and are a first choice for mouth and GI abscess.

28. Anaerobes
 Oral (above the diaphragm) Penicillin (G, VK, ampicillin, amoxicillin)
 Clindamycin
 Abdominal/gastrointestinal
 Metronidazole, beta-lactam/lactamase combinations, carbapenems

29. Gram-Negative Bacilli (E. coli, Klebsiella, Proteus,
Pseudomonas, Enterobacter, Citrobacter)
 These organisms cause infections of the bowel (peritonitis, diverticulitis);
 urinary tract (pyelonephritis); and liver (cholecystitis, cholangitis).
 All of these agents cover gram-negative bacilli:
 Quinolones
 Aminoglycosides
 Carbapenems
 Piperacillin, ticarcillin
 Aztreonam
 Cephalosporins
 Polymyxin (used last because of renal toxicity)

30. Central Nervous System
Infections

31.  All central nervous system (CNS) infections may present with
 fever, headache, nausea, and vomiting.
 All of them can lead to seizures.

33. Meningitis
 Meningitis is an infection or inflammation of the covering or meninges of
the central nervous system
 Streptococcus pneumonia (60%),
 group B streptococci (14%),
 Haemophilus influenzae (7%),
 Neisseria meningitidis (15%),
 Listeria (2%) account for over 95% of cases. Staphylococcus occurs
in those with recent neurosurgery.

34. Presentation
 fever, headache, neck stiffness (nuchal rigidity), and photophobia.
 Acute bacterial meningitis develops over several hours.
 Focal neurological abnormalities occur in up to 30% of patients.

36. Diagnostic tests

37. CT ?
 Papilledema
 Seizures
 Focal neurological abnormalities
 Confusion interfering with the neurological examination

38. Bacterial Antigen Detection (Latex Agglutination
Tests)
 These tests are similar to a Gram stain.
 If antigen detection methods are positive, they are extremely specific.
 If they are negative, the person could still have the infection.
 Sensitivity ranges from 50% to 90% depending on the organism.
 .

39.  When is a bacterial antigen test indicated?
 When the patient has received antibiotics prior to the LP and the
culture may be falsely negative

40. What is the Most Accurate
Diagnostic Test?
 Tuberculosis: Acid fast stain and culture on 3 high-volume lumbar
punctures.
 Lyme and Rickettsia: Specific serologic testing, ELISA, western blot, PCR.
 Cryptococcus: India ink is 60% to 70% sensitive. Cryptococcal
antigen is more than 95% sensitive and specific.
 Culture of fungus is 100% specific.
 Viral: Generally a diagnosis of exclusion.

42. Treatment
 The best initial treatment for bacterial meningitis is
 ceftriaxone, vancomycin, and steroids.
 You will base your treatment answer on the cell count.
 Add ampicillin if immunocompromised for Listeria.

43. Listeria monocytogenes
 Elderly
 Neonates
 Steroid use
 AIDS or HIV
 Immunocompromised, including alcoholism
 Pregnant

44. Neisseria meningitidis: Additional
Management
Respiratory isolation
Rifampin, ciprofloxacin, or ceftriaxone
to the close contacts to decrease nasopharyngeal carriage

46. Encephalitis
 acute onset of fever and confusion.
 Although there are many causes of encephalitis, herpes simplex is by far
the most common cause

48. Treatment
 Acyclovir is the best initial therapy for herpes encephalitis.
 Famciclovir and valacyclovir are not available as intravenous formulations.
 Foscarnet is used for acyclovir-resistant herpes.