Effects of chilling on sampling of bacteria attached to swine carcasses

Two microbiological sampling techniques, excision and sponge swabbing, were compared by determining counts of aerobic bacteria, coliforms and injured coliforms from 20 de-haired swine carcasses before and after chilling. Exci sed jowl skin produced significantly greater counts of the three types of b acteria than sponge swabs. Aerobic bacteria, coliforms and injured coliform s recovered by sponge swabbing carcasses before chilling were 11.6%, 0.9% a nd 11.0% of excised samples, respectively; the corresponding percentages re covered after chilling were 23.9%, 11.1% and 5.0%. Numbers of all bacteria present on the post-chill carcasses were substantially lower than on the pr e-chill carcasses. Excision usually produced more countable plates for coli forms and injured coliforms on chilled carcasses than sponge swabbing and t herefore, is more suitable in estimating low numbers of faecal bacteria on chilled carcasses. To explore the possible structural bases for these findi ngs, skin samples were inoculated with 10(2)-10(7) cfu cm(-2) faecal bacter ia and examined by scanning electron microscopy. Chilled samples showed bac teria and biofilm embedded in superficial crevices, which underlies a possi ble reason for the lower recovery of bacterial cells by the sponge swabbing . The study indicates that the differences between sampling techniques may be a result of the chilling process of swine carcasses.