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Streptococcus pneumoniae

Featured Bug Details

Organism:

Streptococcus pneumoniae

Classification:

Normal habitat:

Colonizes the nasopharynx in humans.

Cultural characteristics:

•	a- hemolytic colonies on Blood and Chocolate Agar
•	Encapsulated strains are mucoid
•	Can appear grey
•	Flat “nail-head” appearance
•	Colonies with autolysis induced central depression on prolonged incubation is described as “checker piece”
•	It is sensitive to “Optochin” and is bile soluble.

Microscopic Appearance:

Gram positive diplococcus (lancet shaped)

Susceptibility testing:

In accordance with CLSI-recommendations for Betalactams MIC is best method. Disc sensitivity is not reliable

1.	Penicillin MIC: 1 µg Oxacillin disc . Zone >19mm indicates S. to penicillin, cephalosporins and Carbapenem. If zone <19mm could be sensitive, intermediate or resistant to penicillin and ceftriaxone. MIC should be determined
2.	Vancomycin
3.	Macrolide susceptibility to azithromycin and clarithromycin can be predicted by using erythromycin.
4.	Quinolones Check Gatifloxacin, Levofloxacin or Moxifloxacin. Does not report Ciprofloxacin
5.	Trimethoprim /sulphamethoxazole:

Virulence factors:

1.	Polysaccharide capsule resists ingestion and killing by phagocytic cells. Over 84 capsular types are identified
2.	Adhesins cause adherence to pharyngeal epithelial cells
3.	Pneumolysin inhibits bactericidal activity of phagocytic cells and arrests ciliary motility
4.	a-hemolysin
5.	Pneumococcal surface protein
6.	Autolysin lytic causes dispersal of both pneumolysin and a-hemolysin

Common infections:

Unusual infections:

Drug of choice:

Will depend on site of infection
OTITIS MEDIA/ UPPER RESP TRACT:
•	Amoxicillin/clavulanate, cefuroxime or 1-3 doses of parenteral ceftriaxone
PNEUMONIA:
•	Outpatient: Macrolide, ,Amoxicilin, Co Amoxiclav or a Quinolone
•	Inpatient (Antibiotic sensitivity is important)
•	3rd generation cephalosporin or ß-Lactam/ ß-Lactamase inhibitor Plus
Macrolide and Quinolone Or Quinolone MENINGITIS: Antibiotic sensitivity is very important Susceptible strain: Penicillin or Ceftriaxone Resistant strain: Vancomycin plus ß-Lactam (until susceptibility report is available)

Resistance:

•	Prevalence of penicillin intermediate susceptible or resistant strain is variable. Resistant isolates have Penicillin Binding Protein (PBP) with decreased affinity to Penicillin.
•	Macrolide and Quinolone resistant strains are also prevalent in varying levels.
•	Vancomycin and Linezolid : If isolates show zone size less than “S” , it must be confirmed from a reference laboratory.

Suggestions for empirical therapy have become difficult because of multidrug resistance. Proper culture and antibiotic susceptibility testing is highly recommended, especially in serious infections.