A high percentage of non-typable (NT) Staphylococcus aureus strains was isolated in Spanish hospitals during 1984 and 1985. Several alternative methods of typing were employed to study these isolates. These were: phage-typing at 1000 × RTD, phage-typing after heat-treatment (48 °C), thermal shock (56 °C), reverse-typing and induction of additional phages. Using these methods the number of NT isolates was reducedby 60%. Best results were obtained with heat-treatment. Additional phages and reverse-typing were also useful.
A scheme for the study of outbreaks and sporadic cases caused by NT strains is proposed using the methods described.