Microbiological safety of spices and their interaction with antibiotics: implications for antimicrobial resistance and their role as potential antibiotic adjuncts

Objectives: A study was undertaken to: 1. examine contaminating bacteria on a variety of spices purchased at retail market; 2. investigate if spice bacterial enrichments alter the phenotype of 13 bacterial foodborne and clinical pathogens and 1 probiotic organism; and 3. investigate if spices can alter antimicrobial activity of seven clinical antibiotics against 16 bacterial foodborne/clinical pathogens. Materials and Methods: Microbiological examination was undertaken employing 27 spice varieties with four antibiotics and 15 bacterial pathogens. Results: Bacteriological contamination levels varied amongst spice varieties, ranging from Kasmin chilli powder (7.5 x 10(6) cfu/g; log(10) 6.88 cfu/g) to ginger (1.5 x 10(4) cfu/g; log(10) 4.18 cfu/g); mean contamination was 1.38 x 10(6) cfu/g (log(10) 6.14 cfu/g). Four species within the genus Bacillus were identified (Bacillus megaterium, Bacillus subtilis, Bacillus licheniformis, and Bacillus cereus). There was no phenotypic difference with the 14 bacteria, with bacterial colony growth/proliferation, pigment production, or with adhesin and mucoid production. None of the spice cultures inhibited any of the 14 bacterial species examined. In the case of doxycycline, amoxicillin, colistin, erythromycin, and piperacillin/tazobactam, the zone of inhibition increased with the inclusion of the 26 spice varieties, suggesting that the spices were interacting synergistically with the antibiotic, thus making the antibiotic more potent against the bacteria tested. Conclusions: This study demonstrates a positive interaction between spices and conventional antibiotics. Given the burden of antimicrobial resistance (AMR) worldwide, but particularly in South Asian countries (India and Pakistan), any food-related innovation that can help maximize the potency of existing antibiotics is to be encouraged and developed. The specific mechanism as to how spices increase the potency of antibiotics needs to be elucidated, as well as novel food (spice) delivery modalities including novel medicinal foodstuffs or functional foods, that can harness this beneficial effect for medicine and society.