Evaluation of animal blood sources to enable Group A Streptococcus culture detection in low-resource settings

Preventative measures are urgently required to reduce the burden of group A Streptococcus (GAS) and its complications, especially in low- and middle-income and remote settings. Diagnostic identification of GAS from the oropharynx and skin involves growth of swab cultures on blood agar plates. The use of horse and sheep blood is the gold standard to enable visualisation of characteristic β-haemolytic colonies. We sought to compare gold-standard culture methodology with blood agar made from a wider variety of animal sources to inform situations where horse and sheep blood are unavailable and other local animals can be used. Citrated blood from six animal species was obtained and was measured for shelf life and evaluated for streptococcal morphology. Blood agar was made from each blood type for 8 successive weeks or until blood reached insufficient quality. Streptococcal morphology was evaluated using overnight agar plate culture of clinical Group A, C and G Streptococcus and Staphylococcus aureus strains and a ‘mock-positive’ throat culture containing oropharyngeal commensals and GAS. Jersey cattle (dairy cattle) blood was the best alternative blood source compared to gold-standard sheep and horse blood due to comparative shelf life to horse blood and stability in agar form equal to sheep blood. Blood from other animals were also suitable for GAS culture but had a shorter shelf life. With a catalogue of alternative blood sources available, lower-resource or isolated settings may be better enabled to continue with low-cost throat and skin culture.