Maryn McKenna

Journalist and Author

Industrial farming, bacterial spread 2 – or: Flies. Ick.

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There’s a brand-new paper in the journal Science of the Total Environment that has some unnerving things to say about the link between very large scale farming, use of antibiotics in food animals, development of resistant organisms, and transmittal out into the larger environment.

Via flies.

Not to be unscientific, but: Ick.

A team from the Bloomberg School of Public Health at Johns Hopkins (who have done a number of studies on the spread of antibiotic-resistant organisms from farms to the outside world) decided to test the links in a chain of hypothesis that goes like this:

  • Antibiotics are used in large amounts in poultry production.
  • Antibiotic-resistant organisms are produced within the birds.
  • Antibiotic-resistant organisms leave the batteries via poultry litter (“excreta, feathers, spilled feed, bedding material, soil and dead birds“).
  • Poultry litter is stored in open sheds until it can be used as a soil amendment.
  • Flies have unrestricted access to poultry litter.

The tests were: sampling poultry litter from three farms in the Delmarva Peninsula (for non-US readers, that’s a portmanteau word for contiguous areas of the states Delaware, Maryland and Virginia, home to about 600 million chickens each year); trapping flies at 8 locations within 100 meters of farm boundaries; and assaying both litter and flies for the presence of resistant organisms and resistance genes.

And the findings were: Oh, lots and lots. Litter piles at all three farms contained resistant organisms — E. faecium, E. faecalis and our particular interest, Staphylococcus (multiple species, including three strains of S. aureus) — throughout the 120-day study period. All 8 fly traps did as well. All of the litter contained enterococci and staph strains that were resistant to 3 or more antibiotic classes. Seven of the 8 fly traps yielded multi-drug resistant enterococci, and 3 yielded multi-drug resistant staph. The resistance factors identified were for drugs that the FDA classifies as “critically or highly important” to human medicine: “penicillin, tetracyclines, macrolides, lincosamides, aminoglycosides and streptogramins.” Oh, and the fly species captured in the traps had an average range of 2 miles.

Of note, among the isolates discovered was one staphylococcus with high-level resistance to vancomycin.

The authors say:

This study strongly suggests that flies in intensive poultry production areas, such as the Delmarva Peninsula, can disperse antibiotic resistant bacteria in their digestive tracts and on their exterior surfaces. Dispersion of resistant bacteria from poultry farms by flies could contribute to human exposures, although at present it is difficult to quantify the contribution of flies. Flies may also transfer bacteria from fields amended with poultry waste.

The cite is: Graham JP et al., Antibiotic resistant enterococci and staphylococci isolated from flies collected near confined poultry feeding operations, Sci Total Environ (2009), doi:10.1016/j.scitotenv.2008.11.056. The ahead-of-print abstract is here.

Despite stewardship efforts, antibiotic use increasing

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Well, this is bad news.

I hope we can all agree that antibiotic use creates antibiotic resistance. (Proof, if any were needed, that the universe has a captious sense of humor; but then it has had millennia to practice. OK, sorry for the anthropomorphizing.) The more pressure bacteria are placed under, the more resistant mutants emerge and survive. So the challenge in using antibiotics is to use them sufficiently and not too much: enough to quell infection and save lives, but not so much that the benefit of successful treatment is outweighed by the cost of increased resistance.

That’s the theory, anyway. In practice, according to a paper published today in the Archives of Internal Medicine, we’re not living up to the plan.

Amy L. Pakyz, Pharm.D. and colleagues at Virginia Commonwealth University surveyed antibiotic use at 22 academic medical centers — tertiary care teaching hospitals, ones that would be most likely to have high awareness of the dangers of resistance and good antibiotic stewardship programs — between 2002 and 2006. And found: Despite all that awareness, antibiotic use is going up, and the use of broad-spectrum agents and vancomycin, MRSA’s drug of last resort, is going up most of all.

The third significant observation is the marked increase in vancomycin use during the 5-year period such that it became the single most commonly used antibacterial in this sample of hospitals from 2004 to 2006. …
The reasons for the continued increase in vancomycin use are likely multifactorial, including the increasing numbers of hospital-acquired infections caused by MRSA and the emergence of community-associated MRSA, all of which encourage greater empirical use of vancomycin.

With only a few new drugs of comparative effectiveness on the market, and none that are significantly better, this is bad news, the authors underline:

Vancomycin use is a risk factor for emergence of vancomycin-intermediate S aureus and vancomycin-resistant S aureus, although these strains are rare in the United States. Of greater concern may be the emergence of low-level resistance in MRSA to vancomycin, referred to as minimum inhibitory concentration (MIC) “creep,” and this is far more common. Strains of MRSA having vancomycin MICs of 2.0 μg/mL are associated with longer median times to clearance of bacteremia compared with strains having MICs of 1.0 μg/mL or less, as well as frank treatment failures.

The cite is: Pakyz, AL et al. Trends in Antibacterial Use in US Academic Health Centers 2002 to 2006. Arch Intern Med. 2008;168(20):2254-2260.

Breaking MRSA news from the ICAAC meeting 1

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There are 15,000+ people at the 48th Interscience Conference on Antimicrobial Agents and Chemistry (known as ICAAC – yes, “Ick-ack”) and 46th Infectious Diseases Society of America Annual Meeting, and at least half of them seem interested in MRSA. At the keynote address last night, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at NIH, referred to MRSA as a “global pandemic.”

Here are some highlights — a few of very, very many — from the first two days:

  • MRSA is truly a global phenomenon: Researchers here are reporting on local epidemics in Argentina, Australia, Botswana, Canada, Colombia, Ecuador, Greece, Japan, Nigeria, Peru, South Korea, Sweden and Taiwan.
  • In the United States, USA300 — the virulent community strain that is crowding out all other community strains — continues its dominance. It first appeared in the San Francisco jail in 2001 and now is the only cause of community MRSA infections there. (Tattevin, P. et al. “What Happened After the Introduction of USA300 in Correctional Facilities?” Poster C2-225.)
  • And MRSA continues to demonstrate its protean ability to cause unexpected forms of illness: The number of cases of sinusitis caused by MRSA seen at Georgetown University tripled between 2001-03 and 2004-06. (I. Brook and J. Hausfeld. “Increase in the Frequency of Recovery of Methicillin-Resistant Staphylococcus aureus in Acute and Chronic Maxillary Sinusitis.” Poster C2-228.)
  • Meanwhile, treatment options are shrinking. Hospitalization for vancomycin-resistant pathogens (that is, resistant to vancomycin, the drug of last resort for MRSA) doubled between 2003 and 2005 according to national healthcare utilization databases. (A.M. Ramsey et al. “The Growing Burden of Vancomycin Resistance in US Hospitals, 2000-2005.” Poster K-560.)
  • But, new drugs are beginning to emerge from the pipeline. Early results from a privately held company called Paratek Pharmaceuticals (co-founded by resistance guru Dr. Stuart Levy) showed that their new tetracycline relative PTK 0796 scored as well or slightly better than linezolid (Zyvox) in safety, tolerability and adverse events, and is advancing to a full Phase 3 trial. (R.D. Arbeit et al. “Safety and Efficacy of PTK 0796.” Poster L-1515.)

More as the meeting goes on.