A new screen test and selective medium for the rapid detection of epidemic strains of Staph. aureus

An inclusive study to elucidation the heavy metals-derived ecological risk nexus with antibiotic resistome functional shape of niche microbial community and their carbon substrate utilization ability in serpentine soil

Heavy metals (HMs) contained terrestrial ecosystems are often significantly display the antibiotic resistome in the pristine area due to increasing pressure from anthropogenic activity, is complex and emerging research interest. This study investigated that impact of chromium (Cr), nickel (Ni), cobalt (Co) concentrations in serpentine soil on the induction of antibiotic resistance genes and antimicrobial resistance within the native bacterial community as well as demonstrated their metabolic fingerprint. The full-length 16S-rRNA amplicon sequencing observed an increased abundance of Firmicutes, Actinobacteriota, and Acidobacteriota in serpentine soil. The microbial community in serpentine soil displayed varying preferences for different carbon sources, with some, such as carbohydrates and carboxylic acids, being consistently favored. Notably, 27 potential antibiotic resistance opportunistic bacterial genera have been identified in different serpentine soils. Among these, Lapillicoccus, Rubrobacter, Lacibacter, Chloroplast, Nitrospira, Rokubacteriales, Acinetobacter, Pseudomonas were significantly enriched in high and medium HMs concentrated serpentine soil samples. Functional profiling results illustrated that vancomycin resistance pathways were prevalent across all groups. Additionally, beta-lactamase, aminoglycoside, tetracycline, and vancomycin resistance involving specific bio-maker genes (ampC, penP, OXA, aacA, strB, hyg, aph, tet(A/B), otr(C), tet(M/O/Q), van(A/B/D), and vanJ) were the most abundant and enriched in the HMs-contaminated serpentine soil. Overall, this study highlighted that heavy-metal enriched serpentine soil is potential to support the proliferation of bacterial antibiotic resistance in native microbiome, and might able to spread antibiotic resistance to surrounding environment.

Co-selection mechanism for bacterial resistance to major chemical pollutants in the environment

Bacterial resistance is an emerging global public health problem, posing a significant threat to animal and human health. Chemical pollutants present in the environment exert selective pressure on bacteria, which acquire resistance through co-resistance, cross-resistance, co-regulation, and biofilm resistance. Resistance genes are horizontally transmitted in the environment through four mechanisms including conjugation transfer, bacterial transformation, bacteriophage transduction, and membrane vesicle transport, and even enter human bodies through the food chain, endangering human health. Although the co-selection effects of bacterial resistance to chemical pollutants has attracted widespread attention, the co-screening mechanism and co-transmission mechanisms remain unclear. Therefore, this article summarises the current research status of the co-selection effects and mechanism of environmental pollutants resistance, emphasising the necessity of studying the co-selection mechanism of bacteria against major chemical pollutants, and lays a solid theoretical foundation for conducting risk assessment of bacterial resistance.

Unraveling the Role of Metals and Organic Acids in Bacterial Antimicrobial Resistance in the Food Chain

Antimicrobial resistance (AMR) has a significant impact on human, animal, and environmental health, being spread in diverse settings. Antibiotic misuse and overuse in the food chain are widely recognized as primary drivers of antibiotic-resistant bacteria. However, other antimicrobials, such as metals and organic acids, commonly present in agri-food environments (e.g., in feed, biocides, or as long-term pollutants), may also contribute to this global public health problem, although this remains a debatable topic owing to limited data. This review aims to provide insights into the current role of metals (i.e., copper, arsenic, and mercury) and organic acids in the emergence and spread of AMR in the food chain. Based on a thorough literature review, this study adopts a unique integrative approach, analyzing in detail the known antimicrobial mechanisms of metals and organic acids, as well as the molecular adaptive tolerance strategies developed by diverse bacteria to overcome their action. Additionally, the interplay between the tolerance to metals or organic acids and AMR is explored, with particular focus on co-selection events. Through a comprehensive analysis, this review highlights potential silent drivers of AMR within the food chain and the need for further research at molecular and epidemiological levels across different food contexts worldwide.

Plasmid Genomes Reveal the Distribution, Abundance, and Organization of Mercury-Related Genes and Their Co-Distribution with Antibiotic Resistant Genes in Gammaproteobacteria

Mercury (Hg) pollution poses human health and environmental risks worldwide, as it can have toxic effects and causes selective pressure that facilitates the spread of antibiotic resistant genes (ARGs) among microbes. More and more studies have revealed that numerous Hg-related genes (HRGs) can help to resist and transform Hg. In the present study, we systematically analyzed the HRG distribution, abundance, organization, and their co-distribution with ARGs, using 18,731 publicly available plasmid genomes isolated from a Gammaproteobacteria host. Our results revealed that there were many Hg-resistant (mer) operon genes but they were not extensively distributed across plasmids, with only 9.20% of plasmids harboring HRGs. Additionally, no hgcAB genes (which methylate Hg to create methylmercury) were identified in any of the analyzed plasmids. The host source significantly influenced the number of HRGs harbored by plasmids; plasmids isolated from humans and animals harbored a significantly smaller number of HRGs than plasmids isolated from the wastewater and sludge. HRG clusters displayed an extremely high organizational diversity (88 HRG cluster types), though incidences of more than half of the HRG cluster types was <5. This indicates the frequent rearrangement among HRGs in plasmids. The 1368 plasmids harboring both HRGs and ARGs, were dominated by Klebsiella, followed by Escherichia, Salmonella, and Enterobacter. The tightness of the HRG and ARG co-distribution in plasmids was affected by the host sources but not by pathogenicity. HRGs were more likely to co-occur with specific ARG classes (sulfonamide, macrolide-lincosamide-streptogramin, and aminoglycoside resistance genes). Collectively, our results reveal the distribution characteristics of HRGs in plasmids, and they have important implications for further understanding the environmental risks caused by the spread of ARGs through the plasmid-mediated co-transfer of ARGs and HRGs.

Heavy metal-induced selection and proliferation of antibiotic resistance: A review

Antibiotic resistance is recognized as a global threat to public health. The selection and evolution of antibiotic resistance in clinical pathogens was believed to be majorly driven by the imprudent use of antibiotics. However, concerns regarding the same, through selection pressure by a multitude of other antimicrobial agents, such as heavy metals, are also growing. Heavy metal contamination co-selects antibiotic and metal resistance through numerous mechanisms, such as co-resistance and cross-resistance. Here, we have reviewed the role of heavy metals as antimicrobial resistance driving agents and the underlying concept and mechanisms of co-selection, while also highlighting the scarcity in studies explicitly inspecting the process of co-selection in clinical settings. Prospective strategies to manage heavy metal-induced antibiotic resistance have also been deliberated, underlining the need to find specific inhibitors so that alternate medicinal combinations can be added to the existing therapeutic armamentarium.

Organomercurial lyase (MerB)-mediated demethylation decreases bacterial methylmercury resistance in the absence of mercuric reductase (MerA)

The mer operon encodes enzymes that transform and detoxify methylmercury (MeHg) and/or inorganic mercury (Hg(II)). Organomercurial lyase (MerB) and mercuric reductase (MerA) can act sequentially to demethylate MeHg to Hg(II) and reduce Hg(II) to volatile elemental mercury (Hg⁰) that can escape from the cell, conferring resistance to MeHg and Hg(II). Most identified mer operons encode either MerA and MerB in tandem or MerA alone, however, microbial genomes were recently identified that encode only MerB. Yet, the effects of potentially producing intracellular Hg(II) via demethylation of MeHg by MerB, independent of a mechanism to further detoxify or sequester the metal is not well understood. Here, we investigate MeHg biotransformation in Escherichia coli strains engineered to express MerA and MerB, together or separately, and characterize cell viability and Hg detoxification kinetics when these strains are grown in the presence of MeHg. Strains expressing only MerB are capable of demethylating MeHg to Hg(II). Compared to strains that express both MerA and MerB, strains expressing only MerB exhibit a lower minimum inhibitory concentration with MeHg exposure, which parallels a redistribution of Hg from the cell-associated fraction to the culture medium, consistent with cell lysis occurring. The data support a model whereby intracellular production of Hg(II), in the absence of reduction or other forms of demobilization, results in a greater cytotoxicity compared to the parent MeHg compound. Collectively, these results suggest that in the context of MeHg detoxification, MerB must be accompanied by an additional mechanism(s) to reduce, sequester, or re-distribute generated Hg(II). Importance: Mercury is a globally distributed pollutant that poses a risk to wildlife and human health. The toxicity of mercury is influenced largely by microbially mediated biotransformation between its organic (methylmercury) and inorganic (Hg(II) and Hg⁰) forms. Here we show in a relevant cellular context that the organomercurial lyase (MerB) enzyme is capable of MeHg demethylation without subsequent mercuric reductase (MerA)-mediated reduction of Hg(II). Demethylation of MeHg without subsequent Hg(II) reduction results in a greater cytotoxicity and increased cell lysis. Microbes carrying MerB alone have recently been identified but have yet to be characterized. Our results demonstrate that mer operons encoding MerB but not MerA put the cell at a disadvantage in the context of MeHg exposure, unless subsequent mechanisms of reduction or Hg(II) sequestration exist. These findings may help uncover the existence of alternative mechanisms of Hg(II) detoxification in addition to revealing the drivers of mer operon evolution.

Antimicrobials and Food-Related Stresses as Selective Factors for Antibiotic Resistance along the Farm to Fork Continuum

Antimicrobial resistance (AMR) is a global problem and there has been growing concern associated with its widespread along the animal-human-environment interface. The farm-to-fork continuum was highlighted as a possible reservoir of AMR, and a hotspot for the emergence and spread of AMR. However, the extent of the role of non-antibiotic antimicrobials and other food-related stresses as selective factors is still in need of clarification. This review addresses the use of non-antibiotic stressors, such as antimicrobials, food-processing treatments, or even novel approaches to ensure food safety, as potential drivers for resistance to clinically relevant antibiotics. The co-selection and cross-adaptation events are covered, which may induce a decreased susceptibility of foodborne bacteria to antibiotics. Although the available studies address the complexity involved in these phenomena, further studies are needed to help better understand the real risk of using food-chain-related stressors, and possibly to allow the establishment of early warnings of potential resistance mechanisms.

Biotic and Abiotic Degradation of Methylmercury in Aquatic Ecosystems: A Review

Mercury (Hg) methylation and demethylation is supposed to simultaneously exist in the environment and form a cycle, which determines the net production of methylmercury (MeHg). Exploring the mechanisms of MeHg formation and degradation, and its final fate in the natural environment is essential to understanding the biogeochemical cycle of Hg. However, MeHg demethylation has been less studied in the past years comparing with Hg methylation, particularly in anaerobic microorganisms whose demethylation role has been under-evaluated. This review described the current state of knowledge on biotic (microorganisms) and abiotic demethylation (photodegradation, chemical degradation) of MeHg. The decomposition of MeHg performed by microorganisms has been identified as two different pathways, reductive demethylation (RD) and oxidative demethylation (OD). Anaerobic and aerobic microorganisms involved in the process of RD and OD, influencing factors as well as research background and histories are systematically described in this review. It is predicted that the photodegradation mechanism, as well as anaerobic microorganisms involved in MeHg formation and degradation cycle will be the focus of future research.

Co-selection of multi-antibiotic resistance in bacterial pathogens in metal and microplastic contaminated environments: An emerging health threat

Misuse/over use of antibiotics increases the threats to human health since this is a main reason behind evolution of antibiotic resistant bacterial pathogens. However, metals such as mercury, lead, zinc, copper and cadmium are accumulating to critical concentration in the environment and triggering co-selection of antibiotic resistance in bacteria. The co-selection of metal driven antibiotic resistance in bacteria is achieved through co-resistance or cross resistance. Metal driven antibiotic resistant determinants evolved in bacteria and present on same mobile genetic elements are horizontally transferred to distantly related bacterial human pathogens. Additionally, in marine environment persistent pollutants like microplastics is recognized as a vector for the proliferation of metal/antibiotics and human pathogens. Recently published research confirmed that horizontal gene transfer between phylogenetically distinct microbes present on microplastics is much faster than free living microbes. Therefore, microplastics act as an emerging hotspot for metal driven co-selection of multidrug resistant human pathogens and pose serious threat to humans which do recreational activities in marine environment and ingest marine derived foods. Therefore, marine environment co-polluted with metal, antibiotics, human pathogens and microplastics pose an emerging health threat globally.

Heavy metal resistance in bacteria from animals

Resistance to metals and antimicrobials is a natural phenomenon that existed long before humans started to use these products for veterinary and human medicine. Bacteria carry diverse metal resistance genes, often harboured alongside antimicrobial resistance genes on plasmids or other mobile genetic elements. In this review we summarize the current knowledge about metal resistance genes in bacteria and we discuss their current use in the animal husbandry.

Metal Resistance and Its Association With Antibiotic Resistance

Antibiotic resistance is recognised as a major global threat to public health by the World Health Organization. Currently, several hundred thousand deaths yearly can be attributed to infections with antibiotic-resistant bacteria. The major driver for the development of antibiotic resistance is considered to be the use, misuse and overuse of antibiotics in humans and animals. Nonantibiotic compounds, such as antibacterial biocides and metals, may also contribute to the promotion of antibiotic resistance through co-selection. This may occur when resistance genes to both antibiotics and metals/biocides are co-located together in the same cell (co-resistance), or a single resistance mechanism (e.g. an efflux pump) confers resistance to both antibiotics and biocides/metals (cross-resistance), leading to co-selection of bacterial strains, or mobile genetic elements that they carry. Here, we review antimicrobial metal resistance in the context of the antibiotic resistance problem, discuss co-selection, and highlight critical knowledge gaps in our understanding.

Application of internal standard method in recombinant luminescent bacteria test

Mercury and its organic compounds have been of severe concern worldwide due to their damage to the ecosystem and human health. The development of effective and affordable technology to monitor and signal the presence of bioavailable mercury is an urgent need. The Mer gene is a mercury-responsive resistant gene, and a mercury-sensing recombinant luminescent bacterium using the Mer gene was constructed in this study. The mer operon from marine Pseudomonas putida strain SP1 was amplified and fused with prompterless luxCDABE in the pUCD615 plasmid within Escherichia coli cells, resulting in pTHE30-E. coli. The recombinant strain showed high sensitivity and specificity. The detection limit of Hg(2+) was 5nmol/L, and distinct luminescence could be detected in 30min. Cd(2+), Cu(2+), Zn(2+), Ca(2+), Pb(2+), Mg(2+), Mn(2+), and Al(3+) did not interfere with the detection over a range of 10(-5)-1mM. Application of recombinant luminescent bacteria testing in environmental samples has been a controversial issue: especially for metal-sensing recombinant strains, false negatives caused by high cytotoxicity are one of the most important issues when applying recombinant luminescent bacteria in biomonitoring of heavy metals. In this study, by establishing an internal standard approach, the false negative problem was overcome; furthermore, the method can also help to estimate the suspected mercury concentration, which ensures high detection sensitivity of bioavailable Hg(2+).

Bacterial antimicrobial metal ion resistance

Metals such as mercury, arsenic, copper and silver have been used in various forms as antimicrobials for thousands of years with until recently, little understanding of their mode of action. The discovery of antibiotics and new organic antimicrobial compounds during the twentieth century saw a general decline in the clinical use of antimicrobial metal compounds, with the exception of the rediscovery of the use of silver for burns treatments and niche uses for other metal compounds. Antibiotics and new antimicrobials were regarded as being safer for the patient and more effective than the metal-based compounds they supplanted. Bacterial metal ion resistances were first discovered in the second half of the twentieth century. The detailed mechanisms of resistance have now been characterized in a wide range of bacteria. As the use of antimicrobial metals is limited, it is legitimate to ask: are antimicrobial metal resistances in pathogenic and commensal bacteria important now? This review details the new, rediscovered and 'never went away' uses of antimicrobial metals; examines the prevalence and linkage of antimicrobial metal resistance genes to other antimicrobial resistance genes; and examines the evidence for horizontal transfer of these genes between bacteria. Finally, we discuss the possible implications of the widespread dissemination of these resistances on re-emergent uses of antimicrobial metals and how this could impact upon the antibiotic resistance problem.

Bacterial mer operon-mediated detoxification of mercurial compounds: a short review

Mercury pollution has emerged as a major problem in industrialized zones and presents a serious threat to environment and health of local communities. Effectiveness and wide distribution of mer operon by horizontal and vertical gene transfer in its various forms among large community of microbe reflect importance and compatibility of this mechanism in nature. This review specifically describes mer operon and its generic molecular mechanism with reference to the central role played by merA gene and its related gene products. The combinatorial action of merA and merB together maintains broad spectrum mercury detoxification system for substantial detoxification of mercurial compounds. Feasibility of mer operon to coexist with antibiotic resistance gene (ampr, kanr, tetr) clusters enables extensive adaptation of bacterial species to adverse environment. Flexibility of the mer genes to exist as intricate part of chromosome, plasmids, transposons, and integrons enables high distribution of these genes in wider microbial gene pool. Unique ability of this system to manipulate oligodynamic property of mercurial compounds for volatilization of mercuric ions (Hg2+) makes it possible for a wide range of microbes to tolerate mercury-mediated toxicity.

A study of post-operative wound infection in a provincial general hospital

1. A survey of post-operative wound infection was done in 1959–60 on 559 surgical patients admitted to a provincial general hospital.

2. Clinical evidence of post-operative wound sepsis was observed in 71(12·7 %), suppuration in 51(9·1 %) and staphyloccocal wound sepsis in 48 (8·6 %).

3. Seventeen of the patients died in hospital. Although 5 of these had septic wounds, the sepsis did not appear to have been the cause of death.

4. Contrary to some reported findings, the post-operative wound sepsis rate was considerably lower in patients who were staphylococcal nasal carriers on admission to hospital than in non-carriers. Nine out of 153 carriers (5·9 %) developed wound sepsis and 36 out of 385 non-carriers (9·4 %). When allowance is made for 3 highly probable self-infections, the incidence of wound cross-infection was 3 % in carriers and 9 % in non-carriers.

5. The excess of sepsis in non-carriers could not be explained in terms of different age or sex distribution in carrier and non-carrier groups, nor by differences in the types of operation undergone or in degree of exposure to staphylococcal contamination.

6. The excess of sepsis in non-carriers was accounted for by the patients whose wounds had drains rather than by clean-stitched wounds.

7. Those carriers who harboured a staphylococcus of the 80/81 group in the nose on admission to hospital had a higher incidence of wound sepsis than carriers of other phage types or staphylococcus.

8. Three probable instances of wound self-infection occurred, and in the early stages of the survey at least 5 wound infections were probably directly caused by two members of the theatre staff carrying staphylococci of the 80/81 group in the nose and with existing skin sepsis or a recent history.

9. The survey findings and a study of the literature suggested: (a) that the acquisition of a nasal staphylococcus in hospital was probably, as a rule, evidence of exposure to staphylococeal contamination and not a determinant of wound sepsis, unless the patient also became a skin carrier; (b) that a small proportion of patients are self-infected, some are directly infected by theatre personnel, and the wounds of other patients are directly or indirectly contaminated by staphylococci from the ward environment; (c) that wool or cotton fluff contaminated with staphyloccoci may cause wound sepsis by falling into open wounds and as foreign bodies induce a significant reduction in the minimum pus-forming dose of staphylococci; (d) that before ascribing high or low sepsis rates to factors such as the nasal carrier state, the relevant groups should be shown not to differ materially in respect of other factors known to influence the incidence of wound sepsis.

We gratefully acknowledge the help and encouragement of our surgical colleagues Mr H. P. Guerrier, Mr P. J. W. Monks, Mr J. Macpherson and Mr C. C. Jeffery; and of Dr C. P. Warren, consultant pathologist to the Torbay Hospital, Mrs M. Stamp, Matron, Sister E. M. Cottrell, first Infection Control Sister at the Torbay Hospital, and her successor Mr H. Street.

Acknowledgement is also due to the South Western Regional Hospital Board for its encouragement and for a research grant for technical aid, without which the surveys described would not have been possible.

Crystal structures of the organomercurial lyase MerB in its free and mercury-bound forms: insights into the mechanism of methylmercury degradation

Bacteria resistant to methylmercury utilize two enzymes (MerA and MerB) to degrade methylmercury to the less toxic elemental mercury. The crucial step is the cleavage of the carbon-mercury bond of methylmercury by the organomercurial lyase (MerB). In this study, we determined high resolution crystal structures of MerB in both the free (1.76-A resolution) and mercury-bound (1.64-A resolution) states. The crystal structure of free MerB is very similar to the NMR structure, but important differences are observed when comparing the two structures. In the crystal structure, an amino-terminal alpha-helix that is not present in the NMR structure makes contact with the core region adjacent to the catalytic site. This interaction between the amino-terminal helix and the core serves to bury the active site of MerB. The crystal structures also provide detailed insights into the mechanism of carbon-mercury bond cleavage by MerB. The structures demonstrate that two conserved cysteines (Cys-96 and Cys-159) play a role in substrate binding, carbon-mercury bond cleavage, and controlled product (ionic mercury) release. In addition, the structures establish that an aspartic acid (Asp-99) in the active site plays a crucial role in the proton transfer step required for the cleavage of the carbon-mercury bond. These findings are an important step in understanding the mechanism of carbon-mercury bond cleavage by MerB.

Comparative genomics of regulation of heavy metal resistance in Eubacteria

BACKGROUND

Heavy metal resistance (HMR) in Eubacteria is regulated by a variety of systems including transcription factors from the MerR family (COG0789). The HMR systems are characterized by the complex signal structure (strong palindrome within a 19 or 20 bp promoter spacer), and usually consist of transporter and regulator genes. Some HMR regulons also include detoxification systems. The number of sequenced bacterial genomes is constantly increasing and even though HMR resistance regulons of the COG0789 type usually consist of few genes per genome, the computational analysis may contribute to the understanding of the cellular systems of metal detoxification.

RESULTS

We studied the mercury (MerR), copper (CueR and HmrR), cadmium (CadR), lead (PbrR), and zinc (ZntR) resistance systems and demonstrated that combining protein sequence analysis and analysis of DNA regulatory signals it was possible to distinguish metal-dependent members of COG0789, assign specificity towards particular metals to uncharacterized loci, and find new genes involved in the metal resistance, in particular, multicopper oxidase and copper chaperones, candidate cytochromes from the copper regulon, new cadmium transporters and, possibly, glutathione-S-transferases.

CONCLUSION

Our data indicate that the specificity of the COG0789 systems can be determined combining phylogenetic analysis and identification of DNA regulatory sites. Taking into account signal structure, we can adequately identify genes that are activated using the DNA bending-unbending mechanism. In the case of regulon members that do not reside in single loci, analysis of potential regulatory sites could be crucial for the correct annotation and prediction of the specificity.

Staphylococcal cassette chromosome mec (SCCmec) typing of methicillin-resistant Staphylococcus aureus strains isolated in 11 Asian countries: a proposal for a new nomenclature for SCCmec elements

A description of staphylococcal cassette chromosome mec (SCCmec) elements carried by 615 methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in 11 Asian countries is reported, and a novel nomenclatural system based on their structures is proposed. The 615 strains were classified as type 3A (370 strains), type 2A (207 strains), type 2B (32 strains), type 1B (1 strain), and nontypeable (5 strains). The previously reported type III SCCmec (DDBJ/EMBL/GenBank accession no. AB037671) carried by the MRSA strain 85/2082 was ascertained to be composed of two SCC elements, type 3A SCCmec and SCCmercury. PCR analysis indicated that 310 of 370 type 3A SCCmec strains carried both SCC elements. These strains were prevalent in eight countries: Thailand, Sri Lanka, Indonesia, Vietnam, Philippines, Saudi Arabia, India, and Singapore. The remaining 60 type 3A SCCmec strains differed with respect to the left extremity polymorphism or to the presence of ccrC. Among these, two were identified as carrying only type 3A SCCmec elements, but their left extremities differed. Type 2A SCCmec strains predominated in Korea and Japan, although the frequency of the presence of ant(4')-1 gene downstream of mecA varied (53% for Korean strains; 93% for Japanese strains). Various SCCmec elements were identified in the tested strains, and limited numbers were identified by their multilocus sequence typing genotypes. These data suggest that numerous MRSA clones are disseminated in Asian hospitals, and these consist of minor clones that are presumed to have arisen locally and major clones that are presumed to have been introduced from other countries.

Mercury tolerance of thermophilic Bacillus sp. and Ureibacillus sp

Although resistance of microorganisms to Hg(II) salts has been widely investigated and resistant strains have been reported from many eubacterial genera, there are few reports of mercuric ion resistance in extremophilic microorganisms. Moderately thermophilic mercury resistant bacteria were selected by growth at 62 degrees C on Luria agar containing HgCl(2). Sequence analysis of 16S rRNA genes of two isolates showed the closest matches to be with Bacillus pallidus and Ureibacillus thermosphaericus. Minimum inhibitory concentration (MIC) values for HgCl(2) were 80 microg/ml and 30 microg/ml for these isolates, respectively, compared to 10 microg/ml for B. pallidus H12 DSM3670, a mercury-sensitive control. The best-characterised mercury-resistant Bacillus strain, B. cereus RC607, had an MIC of 60 microg/ml. The new isolates had negligible mercuric reductase activity but removed Hg from the medium by the formation of a black precipitate, identified as HgS by X-ray powder diffraction analysis. No volatile H(2)S was detected in the headspace of cultures in the absence or presence of Hg(2+), and it is suggested that a new mechanism of Hg tolerance, based on the production of non-volatile thiol species, may have potential for decontamination of solutions containing Hg(2+) without production of toxic volatile H(2)S.

Bacterial mercury resistance from atoms to ecosystems

Bacterial resistance to inorganic and organic mercury compounds (HgR) is one of the most widely observed phenotypes in eubacteria. Loci conferring HgR in Gram-positive or Gram-negative bacteria typically have at minimum a mercuric reductase enzyme (MerA) that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic Hg(0) vapor and a membrane-bound protein (MerT) for uptake of Hg(II) arranged in an operon under control of MerR, a novel metal-responsive regulator. Many HgR loci encode an additional enzyme, MerB, that degrades organomercurials by protonolysis, and one or more additional proteins apparently involved in transport. Genes conferring HgR occur on chromosomes, plasmids, and transposons and their operon arrangements can be quite diverse, frequently involving duplications of the above noted structural genes, several of which are modular themselves. How this very mobile and plastic suite of proteins protects host cells from this pervasive toxic metal, what roles it has in the biogeochemical cycling of Hg, and how it has been employed in ameliorating environmental contamination are the subjects of this review.

Observations on the distribution of Staphylococcus aureus in the atmosphere of a surgical ward

The environment of two contiguous surgical wards was examined over a period of twelve months by means of a slit sampler, settle plates and blanket sweep plates. At the same time, nasal swabs were taken each week from the patients and all cases of sepsis examined bacteriologically.

Phage typing of more than 3600 isolations ofStaph. aureusshowed that there was one predominant strain in the air, bedding, patients' noses and infected wounds.

There was no relationship between the total number of bacteria in the ward air and the numbers ofStaph. aureus.

The recovery of large numbers ofStaph. aureusfrom the air at certain periods was associated with a high contamination rate in the blankets and with an increased incidence of staphylococcal sepsis.

Not all nasal carriers ofStaph. aureuscontaminated their bedding. There was evidence that some patients became nasal carriers of strains of staphylococci previously isolated from their bedding.

Some evidence was obtained that blankets may play a role in the transmission of staphylococci from patient to patient.

This work was supported by a grant from the Australian National Health and Medical Research Council. Our thanks are due to Mrs Elisabeth Bradshaw for her technical assistance and to Prof. John Loewenthal for his interest and for permission to study his wards.

Mercury sensitivity of staphylococci

The technique devised by Moore (1960) for determining the sensitivity of staphylococci to mercuric chloride was investigated and the effect of variations in the medium determined. An alternative technique, in which paper discs impregnated with phenyl mercuric nitrate are used, was found to give identical results. Three hundred and eighty-six out of 717 staphylococci from various sources in hospital were resistant to mercuric chloride, most of the strains belonging to phage types that have commonly produced epidemics. Only five of 73 strains from septic lesions in R.A.F. recruits and only three of 380 strains from healthy nasal carriers among R.A.F. recruits were resistant to mercury.

THE EGG YOLK REACTION OF STAPHYLOCOCCUS AUREUS ISOLATED FROM BURNS

Staph. aureusfrom burns of in-patients were tested for egg yolk reaction during three periods; in 1958 and in 1960 approximately 80 % of the strains gave a negative reaction (EY-), but in 1962 only 36 % of the strains were egg yolk negative.

Staphylococci of phage group III were more commonly EY- than those of other groups isolated from burns. Within each of groups I and III, however, there were patterns predominantly EY- and others predominantly egg yolk positive (EY+); in group I the majority of strains isolated in 1960 were of phage type 52 and EY-, while those isolated in 1962 were predominantly of phage type 80 or related patterns which were always EY+.

Most of the staphylococci in burns were resistant to penicillin, tetracycline and erythromycin; within groups I and III, the staphylococci which were EY- were also more commonly resistant than EY+ strains to these three antibiotics.

Most of the staphylococci from burns were mercuric chloride resistant (presumptive epidemic strains); of the mercuric chloride sensitive staphylococci, the proportion of EY+ strains was greater than that of EY- strains.

Selection for mercurial resistance in hospital settings

The frequency of resistance to Hg2+ in 1980 to 1981 collections from Barnes Hospital, St. Louis, Mo., was only 2% for Staphylococcus aureus and 9% for Escherichia coli. The frequency of Hg2+ resistance in E. coli isolates from Jikei University Hospital, Tokyo, Japan, was 57% during 1972 to 1977 and decreased to 29% in 1979 to 1982; for S. aureus the frequency of Hg2+ resistance dropped from 36% in 1972 to 1977 to 10% in 1979 to 1982. Frequencies of resistances to cadmium (S. aureus) and arsenic (S. aureus and E. coli) remained approximately constant during this time. The decrease in frequency of mercurial resistance is attributed to the termination of the use of organomercurials (largely phenylmercury and thimerosal) in hospital liquid detergents and disinfectants. It is proposed that selection for mercurial resistance occurred within the hospital setting when there was widespread use of mercurials. The resistance patterns and phage types for each of four new mercurial-resistant S. aureus isolates from St. Louis were distinct, indicating that no single type of "hospital staph" predominates. Furthermore, resistance to thimerosal, merbromin, and methylmercury and the ability to volatilize 14C from [14C]methylmercury were found with the new isolates and never with previously known mercurial resistance plasmids in S. aureus.

Gentamicin-resistant Staphylococcus aureus strains isolated in Denmark in 1979

In 1979 seven gentamicin (G)-resistant (res.) Staphylococcus aureus strains caused epidemic episodes in eight Danish hospitals. Furthermore, a total of 37 resistant strains were isolated from separate incidents. All the G-res. strains were resistant to kanamycin, sisomicin and tobramycin, five to amikacin and two to cephalothin. None were resistant to netilmicin. Twelve out of the total of 44 strains were multiply-res. (resistant to penicillin, streptomycin and tetracyclines), and 10 of these were also resistant to methicillin (M). All phage groups/complexes were represented, group III by 13, and the 83A complex by seven strains. Multiply-res. strains, resistant to both M and G were all resistant to mercury, but sensitive to arsenate, whereas such strains resistant to either M or G usually have been found resistant to both metals. Twenty-three strains lost resistance to G upon storage, among them only one multiply-res. Loss of resistance did not influence the metal resistance pattern. From one patient only, the various isolates (nine) differed in respect to bacteriological properties. It was concluded, however, that they all were descendants of the same unstable strain. In the majority of the cases treatment with G had preceded isolation of the resistant strain.

Cervicofacial abcesses of unknown origin. A survey of eighty-one cases

A survey of eighty-one patients with cervicofacial abscesses of unknown origin is presented. The salient clinical features and the treatment of the abscesses are described. Mainly affected were children under 4 years of age, and the submandibular and submental regions were the most common sites of involvement. Staphylococcus aureus was the predominant pathogenic organism, and epidemic strains were implicated in some cases. A high incidence of resistance to penicillin was noted. The nasal vestibule is postulated to be reservoir of the organisms, and the possible relationship between infection, malnutrition, and a mild degree of anemia is examined.

Antibiotic resistance patterns of metal-tolerant bacteria isolated from an estuary

Estuarine bacteria isolated on metal-containing media were also found to be antibiotic resistant; ampicillin and chloramphenicol were the antibiotics to which resistance was most common. Patterns of antibiotic resistance were found associated with a variety of taxa.

The identification of staphylococci in clinical and food microbiology laboratories

A comprehensive review of the methods which have been utilized for the identification of staphylococci is presented. Biochemical characteristics which have assisted in the primary isolation of staphylococci, such as pigmentation, hemolytic activity, the egg yolk phenomenon, and deoxyribonuclease and coagulase production, are also analyzed. The potential applicability of advanced techniques to identify staphylococci, such as the detection of enterotoxin production, base ratio analysis, cell wall analysis, phage typing, and serology, is discussed. The following procedures are recommended for routine use: Idnetification of Staphylococcus sp. (clinical laboratories): microscopic observation, catalase activity, coagulase production, lysostaphin sensitivity, and (optional) facultative growth in thioglycolate medium. Identification of Staphylococcus aureus (food laboratories): microscopic observation, catalase activity, coagulase production, thermonuclease production, and (optional) lysostaphin sensitivity.

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

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.

Human pharmacology of carbenicillin, a semisynthetic penicillin active against Pseudomonas aeruginosa

Staphylococci were isolated from clinical specimens obtained from patients not known to be exposed to abnormal levels of heavy metals. The antibiotic and heavy metal resistance patterns of these strains were determined by using a disk diffusion test and computer sorting. Though not absolute, an association of resistance to mercury and tetracycline in coagulase-negative strains was found, in contrast to resistance to copper and penicillin in coagulase-producing strains. A high degree of correlation was observed between the resistance to phenyl mercury and inorganic mercury, but no correlation was obtained between resistance to methylmercury and other metals. In general, strains resistant to many agents were usually coagulase negative. A possible mechanism and implications of these associations are considered.

Mechanism of plasmic-mediated resistance to cadmium in Staphylococcus aureus

The mechanism of plasmid-mediated resistance to cadmium in Staphylococcus aureus was investigated. Protein synthesis in cell-free extracts from resistant or susceptible bacteria was equally susceptible to inhibition by Cd(2+), but spheroplasts from resistant bacteria retained their resistance. Resistant bacteria did not have a decreased affinity for cations in general, nor was active metabolism required for exclusion of Cd(2+). The kinetics of Cd(2+) uptake into susceptible and resistant bacteria suggested that the conformation of membrane proteins in resistant bacteria may be important in the exclusion of Cd(2+).