The qualification “resembling coliforms” is added if the technologist is confident that the organism viewed is likely to be a member of the family enterobacteriaciae see Gram negative bacilli. E.coli (the prototypic enterobacteriaciae) is one of the most common organisms found in blood cultures.

Other coliforms include Klebsiella spp., Serratia spp., Proteus spp., Citrobacter spp., and Enterobacter sp.. The last four genera are sometimes referred to as the “SPICE” group and are distinguished by higher levels of resistance to antibiotics, esp. Beta-Lactam antibiotics. These resistant organisms are more often seen in complicated hospital-associated infections esp. in ICUs.

Sources of coliform bacteremia

The most likely sources of coliform bacteremia discovered in a patient that has presented with an acute condition to hospital are:

  • The urinary tract i.e. pyelonephritis or prostatitis as cystitis is not usually associated with bacteremia.

  • The biliary tract i.e. ascending cholangitis generally secondary to obstruction by stones or tumors. Simple cholecystitis is less likely to be associated with bacteremia.

  • The colon Any process that results in leaking of colon contents provokes abscess formation that can be a source of bacteremia. Common conditions include appendiceal abscess and diverticulitis.

Often, by the time the blood culture is positive, the source is clear by symptoms, signs and other lab tests. Urinalysis and urine cultures may be positive. Abdominal surgery may have already been performed or is planned.

Likely effectiveness of empirical therapy

This is determined by assessing likely source, prior microbiology, local susceptibility patterns and response to therapy if already initiated.

Likely urinary source

And patient is already on:

  • Ceftriaxone
  • Piperacillin tazobactam

These are likely effective empirical choices except if the patient has recent evidence of resistant organisms (e.g. SPICE group) for which a carbapenem is indicated.

Therapy not initiated:

Ceftriaxone is an appropriate recommendation if resistant organisms have not been identified in the past.

Therapy with ceftriaxone or piperacillin tazobactam is ineffective:

Imipenem should be recommended. Surgical care may be required. (e.g. perinephric abscess, obstructed ureter)

Likely Biliary or Colon source

And patient already on:

  • Piperacillin tazobactam
  • Ceftriaxone

These are effective agents. Piperacillin tazobactam is often advocated because of excellent biliary levels and activity against some enterococci and anaerobes commonly found in GI infections. Ceftriaxone also achieves good biliary levels and is often given with metronidazole. If the patient is on ceftriaxone alone advise addition of metronidazole.

Therapy not initiated:

Piperacillin tazobactam is appropriate.

Therapy with ceftriaxone or piperacillin tazobactam is ineffective:

Imipenem should be recommended. Surgical care may be required.

See [Therapy Recommendations Cholecystitis-Cholangitis]( ‎) and Therapy Recommendations Diverticulitis