Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds with a structure consisting of carbon and hydrogen atoms that have more than two fused aromatic rings. Most PAHs have carcinogenic effects on animal or humans and induce various cancers. Polycyclic aromatic hydrocarbons are a consequence of environmental pollutants, imperfect burning or pyrolysis of organic substances during industrial processing. Additionally, foods can be contaminated during their processing and preparation through different heat treatments. This review highlights the formation, occurrence and health impacts of PAHs in milk and milk products, and analytical technique used for their determination in dairy products.

Antibiotic resistance signifies a safety hazard to public health. Lactic acid bacteria, particularly, Streptococcus thermophilus and Lactobacillus bulgaricus, are useful organisms responsible for dairy fermentation. In keeping with this, they may transfer antibiotic resistance to human population. We conducted a study exanimated the antibiotic resistance pattern and distribution of antibiotic resistance genes of the S. thermophilus and L. bulgaricus strains isolated from traditional yogurt samples. Fifty-five traditional yogurt samples were collected, and S. thermophilus and L. bulgaricus strains were isolated using the microbial culture. The disk diffusion method in agar wells was utilized to assess the antibiotic resistance pattern of isolates against 13 antibiotic agents. The distribution of antibiotic resistance genes was assessed using conventional PCR. Lactobacillus bulgaricus and S. thermophilus were identified in 94.54% (52/55) and 87.27% (48/55) of yogurt samples, respectively. Both L. bulgaricus and S. thermophilus bacteria were simultaneously identified in 72.72% of samples. Streptococcus thermophilus isolates harbored the highest antibiotic resistance rate against tetracycline (31.25%), ampicillin (31.25%), gentamicin (25%), erythromycin (25%), penicillin (12%), and ciprofloxacin (20.83%). Lactobacillus bulgaricus isolates harbored the highest resistance rate against tetracycline (9.61%), ampicillin (9.61%), gentamicin (9.61%), and erythromycin (7.69%). Streptococcus thermophilus (33.33%) isolates harbored the higher distribution of multidrug resistance than L. bulgaricus (11.53%). aacA-D (20.83%), tetK (16.66%), ermA (14.58%), blaZ (14.58%), and gyrA (12.50%) were the most commonly detected antibiotic resistance genes in S. thermophilus. AacA-D (3.84%) and tet K (3.84%) were the most commonly detected antibiotic resistance genes in L. bulgaricus. Lactobacillus bulgaricus isolates did not harbor tetM, cat1, rpoB, vanA, linA, and strA-strB antibiotic resistance genes. Streptococcus thermophilus and L. bulgaricus strains used in traditional yogurt production can harbor antibiotic resistance genes and subsequently disseminate the resistance to human beings. Monitoring antibiotic resistance in fermented foods should be a common inspection for food quality.

Purpose: Given the increasing use of antibiotics on humans and livestock for treatment or as a growth stimulant, antibiotic resistance has become a general concern. The food chain and specially fermented foods could be a source of antibiotic-resistant bacteria and resistance genes. Lactic Acid Bacteria (LAB) and Lactobacilli are considered safe to use as starter culture or probiotic strains. Recently, however, antibiotic-resistant genes isolated from LABs showed the necessity of setting international regulations to reduce the risk of antibiotic resistance genes transmission via the food chain. The current study aimed to investigate the antibiotic resistance of Lactobacilli isolated from traditional yogurt samples from Zanjan province in Iran.Methods: Lactobacilli characterization and identification were carried out through biochemical and molecular methods. The disk diffusion method was applied to determine phenotype resistance using 13 antibiotic disks resistance genes presence were investigated in the isolates to determine transferability risk, respectively.Results: Based on biochemical and molecular methods, 24 isolates have been identified as Lactobacilli with multiple antibiotic-resistant phenotypes. Vancomycin resistance was a typical phenotype and genotype among isolates. On investigated Lactobacilli chromosome, Tetracycline resistance genes Chloramphenicol (cat), beta-lactam, aminoglycosides (aph (3’)-III), and aadA resistance genes have been detected. While the examined resistance genes have not been detected on the plasmids, they were all on the bacterial chromosome.Conclusion: The results showed that the investigated isolates did not carry the resistance genes on their plasmids. It, therefore, would be a good point since they probably do not transfer resistance genes to other bacteria, and they would be proper candidates to do more investigation for introducing new safe starter culture or probiotic strain to food industries.