3.5. Influence of temperature on PT

3.5. Influence of temperature on PT productionA wide range of temperatures is used to cultivate B. pertus-sis, without a clear optimum reported. In order to find an op-timum growth temperature for PT production the organism was cultivated between 32.6 and 39 C. The results of these cultures are shown in Fig. 5. At 39 C the B. pertussis strain 509 hardly grew, but at all other temperatures the cultures grew to comparable densities with comparable growth rates (Fig. 5a). This is to be expected for an organism that infects the respiratory tract, where inhaled air constantly cools the surface of the surrounding tissue somewhat, i.e. the ambient temperature in the respiratory tract is less than the body tem-perature of the host. Fig. 5b shows that PT production was fairly constant between 33 and 36 C. PT was largely associ-ated with the cell, while at 37 C the PT production was at least 30% lower. The maximum proteolytic activity coincided with the maximal PT production. At 32.6 C, the proteolytic activity declined to approximately 70%, while the PT produc-tion declined only 20%.Although the production of PT and therefore other viru-lence factors is optimal below 36 C, many producers and researchers cultivate B. pertussis at 37 C [12,14,21]. While B. pertussis grows well at temperatures below body tempera-ture (33e36 C), it does not grow well at temperatures higher than 37 C. Poor growth at these higher temperatures (38e 39 C), i.e. a situation corresponding with fever of the host, may seem curious, but fever is normally minimal during a per-tussis infection.