Commonly:

• acute - Streptococcus pneumoniae; Haemophilus aegyptius (in tropical climates only); Neisseria gonorrhoeae and N. meningitidis; Haemophilus influenzae
• chronic - Staphylococcus aureus, often as a complication of dacrocystitis or obstruction of the nasolacrimal duct
  
  
  • infection among children is caused by Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus species
  • most adult cases of acute bacterial conjunctivitis are caused by gram-positive organisms. Staphylococcus species, including Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus species, and Gram-negative organisms such as Escherichia coli, and Pseudomonas species
  • Neisseria infection should be suspected when severe, bilateral, purulent conjunctivitis is present in a sexually active adult or in a neonate three to five days postpartum

Rarely:

• Streptococci pyogenes, Escherichia coli, Corynebacterium diphtheriae, Mycobacterium tuberculosis

Reference:

1. Morrow GL, Abbot RL. Conjunctivitis. Am Fam Physician. 1998 Feb 15;57(4):735-46.