H. Miyamoto et al., TEMPERATURE EFFECTS ON LEGIONELLA-PNEUMOPHILA KILLING BY AND MULTIPLICATION IN PHAGOCYTES OF GUINEA-PIGS, Microbiology and immunology, 39(9), 1995, pp. 647-654
We examined the effects of temperature on the interaction between Legi
onella pneumophila and phagocytes of guinea pigs. The body temperature
s of guinea pigs infected with a sublethal dose (1.2 x 10(4) CFU) or a
lethal dose (1.0 x 10(5) CPU) of L. pseumophila elevated from 38.4 0.15 C to 40.2 +/- 0.42 C or 40.3 +/- 0.62 C, respectively. The intrac
ellular bacterial killing by and bacterial proliferation in the phagoc
ytes were examined at 33, 37, 40, and 42 C, using in vitro culture sys
tems of peritoneal macrophages or polymorphonuclear leukocytes (PMN) o
f guinea pigs. In all the macrophages incubated at different temperatu
res, significant intracellular bacterial killings were observed at 4 h
r after in vitro phagocytosis. After 24 hr of incubation, there was ab
out a 100-fold increase of CFU and the number reached a maximum after
48 hr of incubation in the macrophages incubated at 42 C as well as 37
and 40 C, suggesting that macrophages support the intracellular bacte
rial growth in hyperthermia. In the PMN, L. pneumophila CFU 4 hr or 12
hr after the infection were significantly lower at 42 C than those at
37 C (P< 0.05), indicating that the bactericidal capacity of PMN was
enhanced at 42 C compared to 37 C. However, in all the PMN incubated a
t different temperatures, there were about 10-fold increases of CFU 24
hr after the infection, suggesting that PMN as well as macrophages su
pport intracellular bacterial growth in hyperthermia. The extracellula
r bacterial growth was examined at 33, 37, 40, and 42 C in buffered ye
ast extract (BYE) broth or RPMI 1640 medium containing 50% guinea pig
serum as a permissive or non-permissive liquid medium for the bacteria
l growth, respectively. Inhibition of bacterial growth in BYE broth at
42 C, and a decrease of CFU in RPMI 1640 medium containing 50% guinea
pig serum at 42 C were observed. In conclusion, hyperthermia may be b
eneficial by restricting extracellular bacterial survival, but it exer
ts no beneficial effect on the restriction of intracellular bacterial
growth in phagocytes, though PMN showed enhanced initial killing at 42
C. These results suggest that fever, or hyperthermia itself, may not
largely contribute as a nonspecific host defense early in the course o
f legionellosis.