Z Infection types of bacteria

Question 1

Community-Acquired Pneumonia (CAP)

Answer 1

S. pneumonia, H.influenza, Intracellular atypical organisms (Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella), Respiratory viruses.

• S.aureus if IV drug user, recent influenza.
• Pseudomonas if structural lung disease (e.g. bronchiectasis, COPD with frequent steroid use).

Question 2

Hospital, Healthcare- Associated, or Ventilator-Associated Pneumonia
(HAP, HCAP, VAP)

Answer 2

S.aureus (including MRSA) and aerobic gram negative rods including Pseudomonas aeruginosa, E.coli, Klebsiella pneumonia, and Enterobacter species. Multi-drug resistant (MDR) gram negatives are common in ICU patents.
*Role of anaerobes, even in nosocomial aspiration pneumonia, is unclear (but reasonable to add anaerobic coverage in that scenario).

Question 3

Aspiration Pneumonia

Answer 3

Oral anaerobes, enteric gram negative rods, S.aureus, Streptococcus species

Question 4

Appendicitis, Diverticulitis, Intraabdominal Abscess, Secondary Peritonitis

Answer 4

Polymicrobial GI flora including gram negative rods (especially E.coli) and anaerobes (especially Bacteroides).
For bowel perforation, microbiology depends on site. Upper GI tract (e.g. perforated duodenal ulcer) mainly Streptococcus species. Lower GI tract mainly gram negative rods and anaerobes.
Enterococcus and Candida species usually less important, except in healthcare-associated cases.

Question 5

Spontaneous Bacterial Peritonitis (SBP) in patients with ascites

Answer 5

Gram negative rods including E.coli, Klebsiella, Enterobacter. Also, enteric Streptococci and Enterococci.

Question 6

Cholangitis

Answer 6

Polymicrobial GI flora. Anaerobes if biliary-enteric anastomosis.
Enterococcus coverage usually not required.

Question 7

Acute cystitis

Answer 7

E.coli is most common, followed by also other gram negatives (Proteus, Klebsiella, Serratia, Enterobacter) and Staph saphrophyticus

Question 8

Acute pyelonephritis

Answer 8

Same as for acute cystitis

Question 9

Complicated UTI (defined by presence of anatomic or functional abnormality in GU tract, or urinary catheter)

Answer 9

More likely to be due to resistant gram negatives including ESBL’s and Pseudomonas. Staph aureus is possible if chronic urinary catheters or stents. Also: Enterococcus, Candida.

Question 10

Cellulitis

Answer 10

Streptococcus species (most commonly Group A), S.aureus including MRSA.
 More unusual pathogens are possible depending on risk factors (i.e. water exposures, animal bites, neutropenia).

Question 11

Infected Diabetic Foot Ulcer

Answer 11

Streptococcus species, S.aureus including MRSA, Gram negative rods (E.coli, Klebsiella, Proteus, Pseudomonas), anaerobes.

Question 12

Necrotizing Fasciitis

Answer 12

Type I is polymicrobial (Streptococci, Gram negatives) and also involves anaerobes.
Type II is due to beta-hemolytic strep (usually group A strep), less commonly CA-MRSA.

Question 13

Septic Arthritis

Answer 13

S.aureus including MRSA, Streptococcus species (especially Group B strep in diabetics), N.gonorrhoeae (triad of pustular skin lesions, tenosynovitis, arthritis), Gram negative rods (Pseudomonas if IVDU).

Question 14

Bacterial Meningitis, Community-Acquired

Answer 14

S.pneumo, N.meningitidis, H.influenza species.

Listeria if risk factors: Age >50, Immunocompromised

Question 15

Nosocomial Meningitis

Answer 15

S.aureus, Coagulase-negative staph, Gram negative rods including P.aeruginosa

Question 16

Catheter-associated bloodstream infection

Answer 16

S.aureus, Coagulase-negative staph, Enterococci, Gram negative rods (more likely with femoral lines or ICU patient), Candida (especially if on TPN)

Question 17

Neutropenic fever

Answer 17

Oral and enteric streptococci, gram negative rods including Pseudomonas, Candida. S.aureus or coagulate-negative staph in patients with indwelling lines.

Question 18

Severe Sepsis of Unknown Source

Answer 18

Unknown Source

Both gram positive and gram negative organisms should be targeted