In what is the first evidence of multidrug resistance in poultry sold in Indian markets, researchers in Hyderabad have isolated a bacterium in chicken that may well be the source of transmission of the drug-resistant pathogen to humans.
The pathogen, called Helicobacter pullorum , was found in broiler and free-range chickens from markets in the city, which — besides being untreatable — could also be cancer-causing.
H. pullorum is commonly found in the liver and gut of poultry birds and is believed to co-evolve with its natural host. Infected chicken, when consumed, are known to cause gastrointestinal infections in humans. The study by the Hyderabad researchers, published on November 4 in Applied and Environmental Microbiology , a journal of the American Society for Microbiology, is the first data on prevalence and isolation of H. pullorum in India.
The surprise findingsCorresponding author Niyaz Ahmed, senior director at the International Centre for Diarrhoeal Disease Research, Dhaka, said the greatest concern of news of resistance is H. pullorum ’s ability to cause cancer. “It is known to produce a cancer-causing agent called cytolethal distending toxin, which is the main concern. This toxin damages the DNA and interferes with the cell cycle. Since this bacterium also infects the liver, it increases the risk of cancer in the organ,” he says.
In the study, Dr. Ahmed, a Shanti Swarup Bhatnagar awardee who has also headed the Department of Biotechnology at University of Hyderabad, and his team of researchers described 11 hitherto unknown genetic sequences of the bacterium isolated from broilers and free-range chicken. They found about six well-marked antimicrobial resistant genes in the isolates. Besides administration of antibiotics in broilers, chicken feed is also being suspected to have turned H. pullorum resistant to antibiotics such as fluoroquinolones, cephalosporins, sulfonamides and macrolides.
Not expecting to find such resistance in isolates obtained from free-ranging birds, the researchers were surprised when they found that these birds too harboured multidrug-resistant H. pullorum . “We surmise that the feeding habits of free-ranging birds, including scavenging from the environment which is known to contain antibiotic residues, are driving resistance,” says Dr. Ahmed.
Computer modelling of the data further revealed as many as 182 virulence genes which make the bacterium infectious. “There a number of possibilities which are currently being investigated, including whether the bacterium can be passed down vertically through the egg, and the risk of bacterial transmission through the faecal-oral route,” adds Dr. Ahmed.
Not on the radarInstances of human H. pullorum infection aren’t numerous, and clinicians feel they are missing something. “The bacterium may be causing infections in humans and in all likelihood, we remain unaware of it until we test for it,” says Dr. K.S. Soma Sekhar Rao, a gastroenterologist with Apollo Hospitals in Hyderabad.
The National Research Centre on Meat in Hyderabad, which is working to thwart listeria and salmonella outbreaks, does not have H. pullorum on its radar. Additionally, studies that described finding H. pullorum in humans attribute the bacterium’s rather low-key presence to the difficulty in distinguishing it from Campylobacter jejuni, a related bacterium that is more commonly seen and is better understood. Dr. Rao attests infections of C. jejuni are seen more frequently.
Though chicken consumption is rising exponentially in Asia, Dr. Ahmed and his team do not consider H. pullorum capable of acute illness or outbreaks but have cautiously termed it an “emerging threat” capable of chronic health issues including malignancy.
All this notwithstanding, the investigators have offered a silver lining for the chicken aficionado, albeit with a caveat. “Cooking the Indian way — at temperatures higher than 60° Celsius — kills H. pullorum . However, eating uncooked or undercooked dishes like pickled chicken carries risk of infection,” says Dr. Ahmed.
rohit.ps@thehindu.co.in
