An outbreak of staphylococcal infection involving umbilical cords of seven newborn babies was repoed in the nursery. Bacteriological survey reveals that two nurses have a large number of Staphylococcus aureus in the nasopharynx. What test should be performed to determine whether these nurses may have been responsible for the outbreak?

Typing of S. aureus Bacteriophages of S. aureus have narrow host range For epidemiological studies, strains of S. aureus can be distinguished by their patterns of lysis by internationally recognized set of 23 standard typing phages The phage type of the strain is expressed by the designations of all the phages that lyse it S. aureus are divided into 5 lytic groups Phage type 80/81 are known to cause hospital infections throughout the world