Bacteria: no caving in to antibiotics

20. June 2012
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Researchers have discovered, far removed from any human contact, deep in a Mexican cave which had until now never been visited, bacteria that are resistant to as many as 14 antibiotics.

When it comes to antibiotic resistance, people mostly think of humans as the cause: hospitals, poor sanitation and improper and indiscriminate use of drugs promoting the development of drug resistance and turning bacteria presumed to be harmless into dangerous pathogens. The World Health Organisation (WHO) is calling for global strategies to combat the growing bacterial infections which are beyond an effective antibiotic treatment.

The fact that bacteria have developed effective defence strategies in order to survive is already suggestive of naturally occurring resistance, even in bacteria which play no role in causing disease in humans or animals there. As a matter of fact Gerry Wright and staff at McMaster University in Hamilton, Ontario found, in the depths of Lechuguilla Cave discovered in 1986 in New Mexico, strains of bacteria that are resistant to antibiotics. The bacteria originate from an area up to 400 metres deep where humans had not yet entered. The bacteria here proved resistant not only to one or two antibiotics, but a large number were resistant to as many as 40 antimicrobial agents.

Resistance – natural, age-old and an integral part of the genome

In total, the researchers studied the effectiveness of 16 different antimicrobial agents on 92 strains of bacteria from the cave. The antibiotic agents included natural products, semisynthetic derivatives and synthetic substances.

Both Gram-positive and Gram-negative bacteria proved resistant against a multitude of currently employed antibiotics. Among the tested Gram-positive bacterial strains, on average 70 percent were resistant to three or four different classes of antibiotics. Three strains of Streptomyces spp. even resisted the attack of 14 different active ingredients. Among the agents used was Daptomycin, one of the last hopes for infections involving Gram-positive bacteria. No resistance was shown by Gram-positive bacteria to the synthetic antibiotics Ciprofloxacin and Linezolid, or against the semi-synthetic Rifampicin and Minocycline, as well as the natural substance Vancomycin.

Gram-negative bacteria are resistant to many classes of antibiotics from a structural perspective, so that only those antibiotics were examined for which effectiveness is recognised. 65 percent of the strains were resistant to three or four antibiotics. There was no tetracycline resistance observed, which is otherwise often found with outer-coated bacteria. However resistance to Sulfamethoxazole, Trimethoprim, and Fosfomycin was often indicated.

Competition: Man against bacteria

Antibiotic resistance is thus widespread in nature, even in the absence of human-used antibiotics. The cave which spawned the bacteria was isolated for millions of years. The entry of surface water was ruled out. Antibiotic resistance has been well anchored in the genome of the bacteria since prehistoric times. This suggests that in nature there also exists a variety of previously unknown antibiotic substances which may be discovered, but against any of which new antibiotic resistance can develop, because the information for this has lay dormant for eons in the bacterial genome.

The results change our understanding of the emergence of antibiotic resistance, and maybe unburden the shoulders of prescribing physician a little, even if they are still not then given carte blanche for the uncritical application of these medications. With regard to bacterial infection illness, a continuous contest between infectious agents and researchers is expected.

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Dr. Norman Pizano
Dr. Norman Pizano

Fascinanting and, for me, unexpected.

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