| Antibiotic resistance doesn't just
make pathogens(病原体) difficult to treat, It also makes them harder to track
Traditionally, epidemiologists(流行病专家)following the paths of disease-causing
microbes have identified their suspects by features of bacterial
polysaccharide(多糖) coats, susceptibility to different antibiotics, or other
schemes But these tracking techniques "are losing their relevance (相关性,实用性),
"says Alexander Tomasz, a microbiologist at Rockefeller University in New York
City. With the increase in drug resistance, a variety of resistant microbes can
now wear the same coat or be resistant to the same drugs, making it harder and
harder to keep tabs on individual strains (菌株). Epidemiologists, therefore, are increasingly turning to more precise molecular typing techniques, such as DNA fingerprinting, to distinguish resistant strains. DNA typing tools are, of course, not new. Indeed, some DNA-based methods, such as comparing plasmids (质体)(small rings of DNA outside the chromosomes 〈染色体〉), have been used by epidemiologists to track infections since the 1970s. but since plasmid DNA is transferred easily and often between different strains, that technique too has its limitations. More recent techniques use restriction enzymes to cut apart entire bacterial chromosomes into strain-specific fragment patterns, Another method uses specific radiolabeled (放射标汇的) DNA probes, in a technique known as Southern hybridization(杂交), to test for the presence of a particular drug-resistance gene in a bacterial strain. "Such tools give epidemiologists, unprecedented resolving power for identifying reservoirs and transition routes of genes and pathogens, "says Tomasz. That has helped researchers track a number of drug-resistant clones as they travel vast distances. Such tracking methods also "help us learn about the mechanism of resistance, "says CDC(疾病控制和预防中心) epidemiologist Robert Breiman. Resistance grows, he explains, either as one resistant organism spreads from one location to the next—as in the Brazilian MRSA(耐甲氧苯青素金黄色葡萄球菌)—or as different strains and even species of microbes share the genes responsible for drug resistance, as a series of studies of vancomycin(万古霉素) resistance recently demonstrated. That knowledge also helps public health officials combat the spread. If resistance spreads "horizontally'as a microbe increases its range, Breiman says it's important to focus prevention efforts on minimizing person-to-person spread in hospitals and day-care centers. If, however, resistance genes are jumping between organisms, that suggests that overly aggressive antibiotic treatment is encouraging nonresistant bugs to acquire new genes. "In such cases, the focus needs to be on controlling anti-microbial use, "says Breiman. The hoped-for result: fewer infections to track. |