Abstract
Sheep and horse blood are the most commonly used blood for the isolation of microorganisms from human tissue and fluids. However, in many developing countries such as Nigeria, expired human blood from blood banks is still used despite the risk of exposure to HIV and other blood-borne infections, because it is easy to obtain. Blood agar made from blood of rams (similar to sheep), cows, chickens and goats, which are very common in Nigeria, were therefore evaluated. The isolation rates, colony size and morphology as well as haemolytic characteristics of common hospital pathogens such as Pseudomonas aeruginosa, Klebsiella pneumonae, Staphylococcus aureus, and Streptococcus spp, were tested on blood agar prepared from the different animal blood types. All reactions were observed at 24 hrs and 48 hrs respectively. Good growth was achieved by all isolates on rabbit, sheep and chicken blood agar though the best growth was achieved on ram blood agar but there was no significant variation in their morphology. There were differences in their abilities to distinguish haemolytic patterns. Beta Haemolytic Streptococci remained the same on all the blood agar, but the haemolysis of Staphylococci aureus and Pseudomonas aeruginosa varied on different media while haemolysis was least consistent on chicken and cow blood agar. Ram blood agar gave the best reactions in terms of good growth rates of organisms, good morphological characterization as well as good haemolytic reactions. Besides, it is easily available and large quantities of blood can be obtained. Despite the good qualities of ram blood agar observed in this study, however, there is a need for it to be tested further for its ability to support more fastidious organisms.
Highlights
The concept of isolating micro-organisms in culture media has remained virtually unchanged since they were first developed by Robert Koch more than 100 years ago [1]
All the blood agars prepared from animals and man supported the growth of all the isolates and there was no significant difference in the morphology and cultural characteristics on the various blood agar types
This was further confirmed by comparing with descriptions from Bergey’s Manual [10]. This is comparable to a study in Australia and Fiji which compared blood agar prepared by using citrated sheep blood, defibrinated non-citrated sheep blood, citrated human blood agar and defribrinated, non-citrated horse blood agar [12]
Summary
The concept of isolating micro-organisms in culture media has remained virtually unchanged since they were first developed by Robert Koch more than 100 years ago [1]. From the onset it was recognized that the addition of blood or serum provided the nutritional factors present in the human body which were required for the pathogens to grow [2]. Blood is added to blood agar base (small amount of natural carbohydrate, sodium chloride) to a concentration of 5% (v/w) and is useful as a growth medium but allows the diagnosis of organisms on the basis of their haemolytic patterns [3]. Defibrinated sheep blood is preferred because it inhibits the growth of the non-pathogenic commensal, Haemophillus haemolyticus, from throat cultures which may be mistaken for the clinically significant group A β-haemolytic Streptococci [4]. Some Streptococcus spp. produce alpha rather than beta haemolysis on human blood agar. It has been suggested that human blood may contain antibodies and anti-microbial agents which may inhibit growth or cause false haemolysis [5]-[7]
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