Growth responses of Candida and Staphylococci to Noradrenaline

Candida and Staphylococci are frequently involved in opportunistic oral infections, either alone or as co-infective species (Hermann et al, 1999 Mycoses 42: 619-627). Microorganisms possess the ability to recognise stress hormones produced by the host, such as Noradrenaline (NOR) and utilise them to adapt to their surroundings (Lyte et al, 1993 J Endocrin. 137: 343-5). Salivary NOR is released during human stress responses in saliva (Mitome et al, 1997 J Clin Pediatr Dent 21: 255-9) and may act as an environmental cue to alter the growth of individual oral organisms (Roberts et al, 2002 Oral Micro & Immunol. 17: 296-303). Objective:- To investigate the growth response to NOR of C. albicans (Strains 350/0I & EDH23), S. aureus (ATCC 29523) and S. warneri (ATTC 27836). Methods:- Initial cultures were established (Staphylococci: anaerobic, 37°C, trypticase soy broth; Candida: 5%CO₂-air, 37°C, yeast nitrogen base medium) and allowed to grow to turbidity. Organisms were inoculated into a minimal medium (serum-SAPI) containing 30% serum and grown at 37°C until visible growth was seen. Organism growth was assessed by optical density readings (OD600nm) with test and control cultures performed in triplicate. Test cultures were supplemented with 50µM NOR (Freestone et al, 1999 FEMS Microbiol. Lett. 172(1): 53-60). Non-inoculated cultures ± 50µM NOR were used as controls for spectrophotometry. Results:- The observed effects of NOR on growth from control cultures were: C.albicans (350/0I); +65.7%; C.albicans (EDH23); -11.2 %; S. aureus; –49.3%; S. warneri; +27.2%. Conclusion:- Candida and Staphylococci vary in their in-vitro growth responses to noradrenaline. Such variation in growth response to catecholamine hormones may influence their pathogenicity during periods of stress and is worthy of further investigation.