Epidemiology of Antibiotic and Heavy Metal Resistance in Bacteria: Resistance Patterns in Staphylococci Isolated from Populations in Iraq Exposed and Not Exposed to Heavy Metals or Antibiotics

Abstract

Staphylococci were isolated from rural and urban populations in Iraq, which were not known to be exposed to either heavy metals or antibiotics. The antibiotic and heavy metal resistance patterns of these strains were analyzed in both mannitol-fermenting and nonfermenting strains. Over 90% of the strains were resistant to at least one of the following antibiotics: penicillin, chloramphenicol, erythromycin, tetracycline, cephalothin, lincomycin, or methicillin. In general, mannitol-fermenting strains were resistant to penicillin and cupric ions. Mannitol-negative strains were more frequently associated with mercuric ion and tetracycline resistance. Although resistance to penicillin and tetracycline can coexist, the combination of penicillin resistance and tetracycline resistance usually occurred in mannitol-negative strains. The possibility of selection of heavy metal-resistant strains due to exposure to toxic levels of methylmercury was examined. No significant increase in mercuric ion-resistant strains of staphylococci or Escherichia coli were detected in exposed populations as compared to control groups. The possible reasons for this result are discussed.The current interest in subtle effects of environmental contaminants on ecosystems has resulted in a renewed emphasis on the interactions of pollutants with microorganisms. As man further contaminates his own environment, he alters the milieu of those organisms for whom he is the host. For example, selection of antibiotic-resistant strains in human patients (4,8,19) and live stock (18) is a well recognized phenomenon. There is also evidence to indicate that there may be a correlation between the emergence of resistance to antibiotics and heavy metals. Thus the exposure of industrial workers to metallic mercury or inorganic mercury has been shown to be associated with an increased colonization by antibiotic-or mercury-resistant staphylococci in the nasal passages (7). Even in populations that had not been known to have been exposed to mercury, there is a high correlation between certain types of antibiotic resistance patterns and resistance to heavy metals.Recent studies have demonstrated an association between resistance to penicillin, copper ions, and the production of coagulase, whereas resistance to mercury was more commonly noted in strains that were resistant to tetracycline and coagulase negative (6; D. Groves and F.. Young, manuscript in preparation). 6Because there was an increased incidence of intercurrent infections leading to death in patients poisoned with methylmercury at Minimata (14), it was considered particularly relevant to determine the effects of exposure to toxic amounts of heavy metals on resistance patterns in microorganisms. In the period from September 1971 to mid-January 1972, a severe epidemic of methylmercury poisoning of farmers and their families occurred in Iraq, due to the consumption of home-made bread prepared from seed grain treated with a methyl mercurial fungicide. A total of 6,530 cases were admitted to hospitals, and there...

Mechanisms of microbial resistance and detoxification of mercury and organomercury compounds: physiological, biochemical, and genetic analyses.

“…Populations exposed to methylmercury from grains coated with the compound exhibited no significant increase in the incidence of mercury resistance. However, a higher incidence of Hgr isolates was found in the urban than in the rural populations (34). In all cases cited above, a clear distinction between mercurysusceptible and -resistant populations is demonstrated, with MIC levels of 10 to 50 ,ug ml-'.…”

Bacteria with dual resistance to elevated concentrations of heavy metals and antibiotics in Nigerian contaminated systems

“…A correlation between heavy metal tolerance/resistance and antibiotic resistance in Escherichia coli (Spain 2003) and Staphylococcus sp. (Groves et al 1975) has been reported. Alonso et al (2000) implicated a cluster of genes to be involved in antibiotic and heavy-metal resistance of a clinical isolate of Gram-negative bacterium, Stenotrophomonas (Xanthomonas) maltophilia.…”

Epidemiology of Antibiotic and Heavy Metal Resistance in Bacteria: Resistance Patterns in Staphylococci Isolated from Populations Not Known to be Exposed to Heavy Metals

“…Second, the perturbations of the normal patterns of distributions of heavy metal resistance in microorganisms inhabiting man could serve as an assay for heavy metal contamination. An attempt has been made to determine the effect of heavy metal loads in changing these patterns with microorganisms isolated from populations "at risk" from heavy metal exposure, as well as "normal" control populations (12). Now that the epidemiologic patterns have been identified in clinical isolates, further studies utilizing deoxyribonucleic acid-mediated transformation are in progress to determine the molecular bases for the interspecific and intraspecific relationships between determinants for antibiotic and heavy metal resistance in the staphylococci described in this study.…”