Acid tolerance of Shigella sonnei and Shigella flexneri.
OBJECTIVE
Determination of the behaviour of Shigella sonnei and Sh. flexneri under acid conditions.


RESULTS
The growth and survival of Shigella spp. (9 isolates) in acidified Brain Heart Infusion (BHI) (pH 5.0-3.25 with pH intervals of 0.25) was determined after 6, 24 and 30 h incubation at 37 degrees C. Subsequently, survival of shigellae was studied in apple juice and tomato juice stored at 7 degrees C and 22 degrees C for up to 14 days and in strawberries and a fresh fruit salad, kept at 4 degrees C for 4 and 48 h.


CONCLUSIONS
The minimum pH for growth in acidified BHI for Sh. flexneri and Sh. sonnei was, respectively, pH 4.75 and pH 4.50. Survival in fruit juices and fresh fruits depended upon their pH, the type of strain and the incubation temperature. Shigella spp. Survived for up to 14 days in tomato juice and apple juice stored at 7 degrees C. The shortest survival time (2-8 d) was observed in apple juice at 22 degrees C. Sh. sonnei but not Sh. flexneri was recovered after 48 h from strawberries and fruit salad kept at 4 degrees C.


CONCLUSIONS
Acid foods, especially if kept at refrigeration temperatures, support survival of Shigella spp. and may cause Shigella food poisoning.
Bagamboula
C F
CF
Laboratory of Food Microbiology and Food Preservation, University of Gent, Gent, Belgium.
Uyttendaele
M
M
Debevere
J
J
D001628:Beverages / Q000382:microbiology*; D015169:Colony Count, Microbial; D003470:Culture Media; D005638:Fruit / Q000382:microbiology*; D006863:Hydrogen-Ion Concentration; D018551:Solanum lycopersicum / Q000382:microbiology*; D027845:Malus / Q000382:microbiology; D012763:Shigella flexneri / Q000254:growth & development*; D012764:Shigella sonnei / Q000254:growth & development*; D013696:Temperature
D003470:Culture Media