Haemophilus

Haemophilus:
Haemophilus bacteria are G- coccobacilli that are frequently distinguished by their X and V factor requirements. X factor is hemin, an iron containing porphyrin molecule, and V factor is nicotinamide adenine dinucleotide (NAD). NAD is a common coenzyme involved in electron transport. Both X and V factor are in chocolate agar but only X factor is in SBA. Haemophilus species can be differentiated by their need for X and V factors, see the table below.

Haemophilus species	X Factor needed	V factor needed	Beta-hemolysis on horse or rabbit blood	ALA conversion
H. influenza	+	+	-	-
H. ducreyi	+	-	-	-
H. haemolyticus	+	+	+	-
H. aphrophilus	-	-	-	+
H. parainfluenzae	-	+	-	+

Again, there’s a strategy to how I setup the table which makes it as easy as possible to remember. The species can be listed as IDHAP based on the first letter of the species name. The X factor requirement is 3 +’s followed by 2 –‘s and the V factor alternates +/-. H. haemolyticus is the only species with 3 +’s, and ALA conversion is the opposite of X factor. When you have all of the flow charts to remember on top of all the other subjects, the easier it is to recall things like this, the better.

Haemophilus sattelliting:
Bacteria such as Staph aureus produce V factor (NAD) when grown on SBA. Haemophilus species will use that V factor along with the X factor in SBA, and tiny colony growth can be observed. The NAD is a small amount, so small colonies of Haemophilus result.

How is the X and V factor test run?
The test can be run on a plate lacking X and V factors such as trypticase soy broth. Discs like the ones used in antibiotic testing are used but in this case they have X factor, V factor, and one with both X and V factor (3 discs total).

What does the porphyrin test mean?
The porphyrin test is a confirmation test for X factor. Species that need X factor are unable to convert delta-amino-levulinic acid (ALA) into porphyrins or protoporphyrins and species that don’t need X factor are able to convert ALA in porphyrins or protoporphyrins. So if you have a + in the X factor column it will be negative for the porphyrin test.

Other notes for Haemophilus species:

H. influenza:
Serotype B responsible for most infections; strains that are resistant to ampicillin and/or penicillin produce beta-lactamase; associated with pinkeye

H. aphrophilus:
Can be associated with endocarditis

H. ducreyi:
Associated with genital ulcers