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SYNOPSIS Members of a newly recognized group of hospital staphylococci, which are believed to have arisen from 83A staphylococci by lysogenization, differ from them in several cultural characters. Some but not all of these characters appear to be determined by the carriage of phage.In 1960, a new group of Staphylococcus aureus strains not lysed by any of the basic set of typing bacteriophages made their appearance in British hospitals. These organisms gave inhibition reactions with some of the group III phages applied at 1,000 times the routine test dilution. This suggested that they were related to each other, and possibly also to staphylococci that were lysed only by phage 83A, which gave similar inhibition reactions and had first been recognized about two years earlier as causes of endemic infection in British hospitals. Jevons and Parker (1964) produced evidence that the new untypable staphylococci had arisen from the 83A organism by lysogenization with a phage which blocked the reaction with phage 83A. The blocking phages obtained from several distinct strains of the new organisms were, however, all different in host range, and included members of several serological groups. Strains from different places also differed in their susceptibility to lysis by a set of experimental phages. It was concluded that the new organisms had arisen by a number of separate lysogenizations, and probably not all from the same 83A strain. They did not constitute a 'type', but rather a group or complex of related strains.In 1963, several authors reported that the new untypable staphylococci had unusual cultural characters. Willis and Turner (1963) in Leeds found that many Staph. aureus strains that were resistant both to penicillin and to tetracycline formed a lemon-yellow pigment on glycerol monoacetate agar. According to Jacobs, Willis, Ludlam, and , most of these lemon-yellow organisms were untypable, but gave inhibition reactions with group III phages at routine test dilution x 1,000. In this they resembled the new untypable organisms prevalent in Glasgow Received for publication January 1966 and Liverpool (Temple and Blackburn, 1963;Turner, 1963;Willis, Jacobs, and Goodburn, 1963). Further investigations showed that lemon-yellow, tetracycline-resistant cultures differed from most others in that they were usually not 'proteolytic', i.e., did not cause darkening of heated blood agar (99 %), but were often f-lysin positive (33 %) and staphylokinase (fibrinolysin) negative (68 %); the incidence of these characters in other Staph. aureus cultures was, for absence of protease 21 %, for ,B-lysin production 3 %, and for absence of staphylokinase 24 %. It was later shown that the new untypable staphylococci seldom hydrolysed Tween 80 (Smith, Willis, and O'Connor, 1965). Robertson (1963) found that most of them were resistant to neomycin (see also Lowbury, Babb, Brown, and Collins, 1964). It seemed, therefore, that the new organisms were characteristically lemon-yellow, non-'proteolytic', ,B-lysin positive, staphylokinase-negat...

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Earlier investigations in St. Bartholomew's Hospital showed that wound sepsis rates were lowest in patients who did not carry Staphylococcus aureus in the nose during their stay in hospital. highest in those who acquired a staphyloooccus in the ward, and intermediate in those who retained the strain they carried on admission (Williams et al., 1962 ResultsWe made observations on 412 patients, of whom 276 were first admitted to the pre-operative side and 136 to the post-operative side. The scheme was more difficult to work than we had anticipated. There was often need for post-operative beds at a time when there were not enough patients awaiting operation to fill the beds on the pre-operative side. Therefore, 102 of the 205 patients admitted to the pre-operative side and subsequently operated upon were returned from the theatre to the same side, and only 23 of them were later transferred. At other times the pre-operative side was full, and 40 patients were first admitted to the post-operative side for this reason only.The investigation lasted for 10 months. We tried to assess the effectiveness of our ward division by considering how it interfered with air movements between the two sides, by comparing the staphylococci isolated from the air of the two sides, by recording the acquisition of new strains of staphylococci by patients in the two sections of the ward, and by observing the sepsis rate. Air MovementsOn 211 occasions observations were made of the direction of air movement around the doors between the two parts of the ward. using titanium tetrachloride smoke. On 112 (530%) of these occasions there was a substantial flow of air from the post-operative to the pre-operative side and only on 36 (17%) was the flow reversed. The air movement was slight and irregular on the remaining 63 occasions (30%).Measurements were also made on two occasions of the extent to which a gas tracer (nitrous oxide) liberated on the post-operative side reached the pre-operative side when the air flow was in this direction. The exposure to tracer (LidDEc. 21, I-963 PRE-OPERATIVE SEGREGATION 1567.