In recent years, clinical and laboratory data have been gathered to support the concept that of the S. saprophyticus biotypes it is mainly biotype 3 strains (Baird-Parker, 1974) which are involved in urinary tract infections. These infections are seen for the most part in domiciliary practice in young women. In several studies, S. saprophyticus biotype 3 has been found in 0 to 30 ~ of all urinary tract infections. Although S. saprophyticus biotype 3 is not as frequently found in urinary tract infections as E. coli, it forms a sizeable proportion of such infections and, moreover, the severity of the symptoms is not less. However, the epidemiology of these infections is still unknown and the question arises whether urinary tract infections caused by S. saprophyticus biotype 3 result from its prevalence on the skin of young women or whether specific and more virulent strains are involved.
In our preliminary studies we examined the frequency of urinary tract infections by S. saprophyticus biotype 3 in a general practice near Amsterdam.
S. saprophyticus biotype 3 strains composed 5 ~ of all the bacteria isolated from urinary tract infections. When strains were arranged according to the sex and age of the patients, this biotype composed 9 % of all the isolates from women of the age of 16-35 years.
Our epidemiological studies showed that S. saprophyticus biotype 3 made up only 5 ~ of the bacteria isolated from the skin of males and females and was not the predominant bacterial species. No significant differences were found in numbers of this biotype whether isolated from females or males. L Ds 0 determination of coagulase-negative staphylococci in neonatal mice revealed that strains of S. saprophyticus biotype 3 varied in virulence according to novobiocin sensitivity. Novobiocinresistant strains of S. saprophyticus biotype 3, whether isolated from urinary tract infections or from the skin, showed the same degree of virulence in neonatal mice, whereas novobiocin-sensitive skin isolates were significantly less virulent.
Although extrapolation from animal studies to the human situation is difficult, our LD 50 results suggested some differences in virulence. Therefore, a study of the resistance to phagocytosis and intracellular killing was carried out because these processes are of vital importance in the body defence system. This might point to biotypes with potentially enhanced virulence. The uptake of strains belonging to a given staphylococcal species or biotype by human polymorphonuclear leucocytes varied from 60 to 80 ~ with an average of 70 % after 20 min incubation at 37 ยฐC. Up to 95 ~ of intracellular bacteria were killed after 20 rain. In spite of the difference in LD s 0 values of novobiocinresistant S. saprophyticus strains compared with other staphylococcal strains (Namavar et al., 1978), there were no marked differences in their uptake and killing by human leucocytes.
Why S. saprophyticus biotype 3 should invade the urinary tract of young women is still unknown and further studies might be directed to a study of superficial antigens ofS. saprophyticus biotype 3 in relation to cell adherence.