Salmonella culture. Drug resistant Salmonella
were obtained from B. germanica and grown to
mid-log phase. Five gram of foods were inoculated
with 1 ml of culture medium (106 CFU/ml) and fed
to cockroaches. The number of Salmonella in dry
and wet food (without any cockroaches as blanks)
and the food of contaminated and uncontaminated
cockroaches was estimated.
Antibiotic resistance. The disk diffusion test was
used for determining bacteria susceptibility to
antimicrobials. In this method, standard paper disks
impregnated with known amounts of antibiotics
(10-30 µg) are placed on Muller-Hinton agar. After
48 h incubation, antibiotic activity was determined
by the width of the zone of no growth around the
antibiotic disk. In seven experiments, the most
resistant salmonella was isolated for transmission
study