R. Baselga et al., PHASE VARIATION OF SLIME PRODUCTION IN STAPHYLOCOCCUS-AUREUS - IMPLICATIONS IN COLONIZATION AND VIRULENCE, Infection and immunity, 61(11), 1993, pp. 4857-4862
Two methods commonly used for slime detection in coagulase-negative st
aphylococci (tube biofilm formation and colony morphology in Congo red
agar) were used to study 144 ruminant mastitis Staphylococcus aureus
strains. Slime production was detected in 21 strains. A majority of ce
lls (85%) in slime-producing (SP) strains and a minority of cells (5%)
in non-slime-producing (NSP) strains showed a condensed exopolysaccha
ride matrix (slime) surrounding the bacterial cell wall, as revealed b
y electron microscopy and immunofluorescence. In vivo slime production
was also detected immunohistochemically after experimental infection
of the mammary gland in sheep. Upon repeated subcultures in Congo red
agar, NSP variants were obtained from four ovine and four bovine SP st
rains at a frequency ranging from 0.5 x 10(-4) to 10(-4). Because SP v
ariants could not be obtained from NSP strains within this range or at
a higher frequency, they were obtained by the tube biofilm formation
(requiring repeated subculturing of NSP strains in tryptic soy broth c
ontaining 2% glucose for subsequent recovery of colonies adherent to t
he walls of the culture tubes). In experimental challenge, the SP vari
ant showed a significantly higher colonization capacity than did the N
SP variant of the same strain used (P < 0.001). However, the NSP varia
nt had a higher virulence than did the SP variant (P < 0.001). These r
esults may help to explain the different roles of S. aureus slime prod
uction cell types (SP and NSP) coexisting in disease.