Streptococcus pneumoniae

Gram Stain

• Gram positive elongated diplococci in chains (+/- capsule) (aerobic)

Clinical Significance

This organism often colonizes the nasopharynx, especially of children.

It is associated with pneumonia, septicemia, meningitis, otitis media, sinusitis, and acute excerbations of chronic obstructive pulmonary disease.

It has rarely been associated with genitourinary infections (cervicitis, amnionitis, post-partum infections, UTI in children), endocarditis (and other endovascular infections), as well as skin/soft tissue infections.

 

Usual Susceptibility Pattern

Nonsusceptibility to penicillin – (intermediate (I) and high level (R)) is dependent on geographic location. All penicillin nonsusceptible (I/R) strains exhibit decreased susceptibility to all oral cephalosporins. Amoxicillin retains the best coverage of all oral beta-lactam agents.

The following beta-lactams are listed in descending order of activity against pen (I) strains:

amoxicillin (best)
cefuroxime
cefprozil
cefixime (not recommended for S. pneumoniae)
cephalexin (not recommended for S. pneumoniae)

Note: Pen-R isolates are resistant to all oral cephalosporins.

Although most strains remain susceptible to cefotaxime/ceftriaxone (ceftriaxone may be more active), ceftazidime does not have reliable activity against S. pneumoniae.

There is significant TMP/SMX and macrolide resistance and increasing resistance to tetracycline and clindamycin.

Note: erythromycin resistance predicts resistance to azithromycin and clarithromycin.

Although typically susceptible to levofloxacin and moxifloxacin, first step mutations resulting in quinolone resistance may not be detected by routine susceptibility testing.  These agents should be avoided or used with caution if patient has received quinolone therapy in previous 3-6 months.

Note: ciprofloxacin is not active against S. pneumoniae.

Vancomycin tolerance, possibly due to defective autolytic enzymes, has recently been described.

Empiric Therapy
Otitis Media:
Amoxicillin
Respiratory Tract Infections:
Amoxicillin
or
Doxycycline
Meningitis:
Ceftriaxone
+/-
Vancomycin