A study of chicken meat and ready-to-eat sprouted moong bean sold by poultry shops and local street vendors in Mumbai has revealed the presence of large number of antibiotic-resistant bacteria.
The research was small-scale — 14 chicken meat and 13 ready-to-eat mung samples — but it presented clear evidence, its authors say in a journal article.
Common food-borne pathogens such as Streptococcus, Shewanella, Pseudomonas, Aeromonas hydrophila, Staphylococcus, E. coli, Acinetobacter, Enterobacter, Klebsiella were found. The disease-causing bacteria, Enterobacter sp (23%), E. coli (22%), K. pneumonia (20%) were predominant among the 100 antibiotic-resistant microorganisms that were isolated and studied. Those belonging to Enterobacteriaceae family were predominant in both food types — 60% in chicken and 88% in mung sprouts. The results are reported in a paper to be published on July 10 in the journal Current Science.
Resorting to metagenomic analysis
The conventional method of studying microorganisms is by culturing. But there is an inherent problem as only a certain percentage of bacteria can be cultured. “So we resorted to metagenomic analysis, which is culture-independent, to detect microbes. In this, the total DNA from the sample is isolated. This helped us detect all microbes present in the samples. This is the first time metagenomic analysis has been done in these food types in India,” says Dr. Archana Rath from the Department of Biotechnology, University of Mumbai and the corresponding author of the paper.
E. coli and K. pneumoniae were resistant to 12 of the 13 antibiotics tested.
The microorganisms were then cultured to study antibiotic resistance. “Most of the 50-plus different microorganisms for each food type were resistant to one or more of the 13 clinically relevant antibiotics chosen for the study,” she says. More than 10 disease-causing pathogens were resistant to 5-12 antibitoics. E. coli and K. pneumoniae were resistant to 12 of the 13 antibiotics tested. Earlier studies did not find bacteria being resistant to so many antibiotics.
Reflection of resistance severity
The 50-plus antibiotic-resistant strains were found to have high antibiotic resistance index of 0.3-0.9. (Antibiotic resistance index is the number of antibiotics that the bacteria are resistant to divided by the total number of antibiotics studied.) “The index is very high. It is a reflection of the severity of resistance,” says Dr. Rath.
There was higher diversity of antibiotic-resistant bacteria in chicken than mung sprouts — 66 species in chicken samples compared with 21 species in mung sprouts. There is greater risk when antibiotic-resistant bacteria are found in mung sprouts, as they are consumed raw. Though chicken is cooked before eating, cross-contamination is likely when vessels and appliances used for cleaning and cooking are not thoroughly cleaned.
Presence of 18% bacteria common to both food types could be a reflection of their ubiquity or cross-contamination. “Untreated organic manure from chicken farms applied as manure in fields and the use of contaminated water for irrigation and for cleaning chicken might be responsible for cross-contamination,” says Onkar A. Naik, from the Department of Biotechnology, University of Mumbai and the first author of the paper.
“The study suggests that we are continuously exposed to a wide range of multiple antibiotic-resistant, food-borne bacteria. This poses a serious challenge to health and we should take steps to improve the quality of food,” Dr. Rath says.