V. BACTERIOPHAGE TYPING OF SHICELLA
265
After phage application, plates are dried at' room temperature without
lids for 10-15 min before incubation at 37°C (to 38.5"C) for 5 h with the
agar down and the lids up.
7. Recording of results
Phage typing patterns have been recorded as phage types (Table
XVIII), although it is now preferred to report patterns instead of types.
Variation in one single phage reaction has the unfortunate effect that the
bacterium becomes referred to a completely different type. Reporting
patterns makes it easier for the recipient of the report to see slight differences in the reaction and thereby better include in the interpretation of
results the unavoidable experimental error or details of the method.
The total number of phage patterns observed is very large. Among
5386 cultures from world-wide sources, 3223 different lytic patterns have
been noted when any difference is accepted. Among these, a very substantial number have been found only in one or a few strains. Only about $
occur with any significant frequency.
Such large data masses are difficult to assess unless modern computer
technology is utilised. This has been done at the National Bacteriological
Laboratory, Stockholm, for all cumulative typing results at the laboratory,
including the data of Hammarstrom (Kallings and Sjoberg, 1975). For
this purpose, the phage reactions were coded as follows:
Phage reaction
Unknown
Negative
Less than 40 normal plaques ( + ,
Less than 40 large plaques ( + L, f L ) a
40-80 plaques ( + +)
More than 80 plaques (+ + + )
Semiconfluent lysis (SCL)
Opaque lysis (OL)
Confluent lysis (CL)
)
Computer score
a L = large plaques.
Each strain is identified by accession number, source, sampling data,
geographical origin (by numerical code), and the reaction strength of each
typing phage.
The lytic patterns of 3 178 cultures have been compared by computer to
see which differences in pattern reactions could be expected within the
framework of the errors inherent in the typing technique itself. Table
265
After phage application, plates are dried at' room temperature without
lids for 10-15 min before incubation at 37°C (to 38.5"C) for 5 h with the
agar down and the lids up.
7. Recording of results
Phage typing patterns have been recorded as phage types (Table
XVIII), although it is now preferred to report patterns instead of types.
Variation in one single phage reaction has the unfortunate effect that the
bacterium becomes referred to a completely different type. Reporting
patterns makes it easier for the recipient of the report to see slight differences in the reaction and thereby better include in the interpretation of
results the unavoidable experimental error or details of the method.
The total number of phage patterns observed is very large. Among
5386 cultures from world-wide sources, 3223 different lytic patterns have
been noted when any difference is accepted. Among these, a very substantial number have been found only in one or a few strains. Only about $
occur with any significant frequency.
Such large data masses are difficult to assess unless modern computer
technology is utilised. This has been done at the National Bacteriological
Laboratory, Stockholm, for all cumulative typing results at the laboratory,
including the data of Hammarstrom (Kallings and Sjoberg, 1975). For
this purpose, the phage reactions were coded as follows:
Phage reaction
Unknown
Negative
Less than 40 normal plaques ( + ,
Less than 40 large plaques ( + L, f L ) a
40-80 plaques ( + +)
More than 80 plaques (+ + + )
Semiconfluent lysis (SCL)
Opaque lysis (OL)
Confluent lysis (CL)
)
Computer score
a L = large plaques.
Each strain is identified by accession number, source, sampling data,
geographical origin (by numerical code), and the reaction strength of each
typing phage.
The lytic patterns of 3 178 cultures have been compared by computer to
see which differences in pattern reactions could be expected within the
framework of the errors inherent in the typing technique itself. Table