Selection for antimicrobial resistance in the plastisphere

Microplastics and antimicrobials are widespread contaminants that threaten global systems and frequently co-exist in the presence of human or animal pathogens. Whilst the impact of each of these contaminants has been studied in isolation, the influence of this co-occurrence in driving antimicrobial resistance (AMR)1 in microplastic-adhered microbial communities, known as 'the Plastisphere', is not well understood. This review proposes the mechanisms by which interactions between antimicrobials and microplastics may drive selection for AMR in the Plastisphere. These include: 1) increased rates of horizontal gene transfer in the Plastisphere compared with free-living counterparts and natural substrate controls due to the proximity of cells, co-occurrence of environmental microplastics with AMR selective compounds and the sequestering of extracellular antibiotic resistance genes in the biofilm matrix. 2) An elevated AMR selection pressure in the Plastisphere due to the adsorbing of AMR selective or co-selective compounds to microplastics at concentrations greater than those found in surrounding mediums and potentially those adsorbed to comparator particles. 3) AMR selection pressure may be further elevated in the Plastisphere due to the incorporation of antimicrobial or AMR co-selective chemicals in the plastic matrix during manufacture. Implications for both ecological functioning and environmental risk assessments are discussed, alongside recommendations for further research.

Culturing the Plastisphere: comparing methods to isolate culturable bacteria colonising microplastics

Microplastics quickly become colonised by diverse microbial communities, known as the Plastisphere. There is growing concern that microplastics may support the enrichment and spread of pathogenic or antimicrobial resistant microorganisms, although research to support the unique role of microplastics in comparison to control particles remains inconclusive. Limitations to this research include the microbiological methods available for isolating adhered microbes. Culture-based methods provide some of the most established, accessible and cost-effective microbiological protocols, which could be extremely useful in helping to address some of the remaining key questions in Plastisphere research. Previous works have successfully cultured bacteria from plastics, but these have not yet been reviewed, nor compared in efficiency. In this study, we compared four common biofilm extraction methods (swabbing, sonication, vortexing, sonication followed by vortexing) to extract and culture a mixed community of bacteria from both microplastic (polyethylene, polypropylene and polystyrene) and control (wood and glass) particles. Biofilm extraction efficiency and viability of bacterial suspension was determined by comparing CFU/mL of four different groups of bacteria. This was verified against optical density and 16S rRNA qPCR. Overall, we found that all tested methods were able to remove biofilms, but to varying efficiencies. Sonicating particles with glass beads for 15 min, followed by vortexing for a further minute, generated the highest yield and therefore greatest removal efficiency of culturable, biofilm-forming bacteria.

Antifungal Exposure and Resistance Development: Defining Minimal Selective Antifungal Concentrations and Testing Methodologies

This scoping review aims to summarise the current understanding of selection for antifungal resistance (AFR) and to compare and contrast this with selection for antibacterial resistance, which has received more research attention. AFR is an emerging global threat to human health, associated with high mortality rates, absence of effective surveillance systems and with few alternative treatment options available. Clinical AFR is well documented, with additional settings increasingly being recognised to play a role in the evolution and spread of AFR. The environment, for example, harbours diverse fungal communities that are regularly exposed to antifungal micropollutants, potentially increasing AFR selection risk. The direct application of effect concentrations of azole fungicides to agricultural crops and the incomplete removal of pharmaceutical antifungals in wastewater treatment systems are of particular concern. Currently, environmental risk assessment (ERA) guidelines do not require assessment of antifungal agents in terms of their ability to drive AFR development, and there are no established experimental tools to determine antifungal selective concentrations. Without data to interpret the selective risk of antifungals, our ability to effectively inform safe environmental thresholds is severely limited. In this review, potential methods to generate antifungal selective concentration data are proposed, informed by approaches used to determine antibacterial minimal selective concentrations. Such data can be considered in the development of regulatory guidelines that aim to reduce selection for AFR.

Insertion of a casein kinase recognition sequence induces phosphorylation of ovine beta-lactoglobulin in transgenic mice

We have shown that the cellular mechanisms of the mammary gland can be used to produce a phosphorylated form of a normally unphosphorylated milk protein. This was achieved by the insertion of a beta-casein DNA sequence coding for a group of mammary gland casein kinase recognition sites into ovine beta-lactoglobulin. Transgenic mice carrying this modified gene were generated and lactating females were shown to produce a novel beta-lactoglobulin in their milk. The infrared spectrum, reactivity to antiphosphoserine antibody and reduction of electrophoretic mobility on treatment with alkaline phosphatase showed that the novel protein recovered from the milk whey (serum) was phosphorylated and molecular mass determination by mass spectrometry was consistent with the phosphorylation of one or two residues. A similar level of phosphorylation was measured by quantitative infrared spectroscopy. Centrifugation of the milk to pellet the casein micelles showed that most of the phosphorylated beta-lactoglobulin was in the whey and hence not incorporated into casein micelles.

HIV positive tests at Coronial Services in Victoria 1989-1996: lessons for HIV surveillance

Results of routine testing at other sites can supplement surveillance of the HIV epidemic in Australia which is largely based upon voluntary testing. Since 1989, systematic onsite HIV testing has been undertaken on all bodies taken to the Victorian Institute of Forensic Medicine (VIFM). Information was collected on all cases of HIV infection detected at VIFM between 1989 and 1996, and matched to surveillance databases. In 8 years, 75 people were diagnosed with HIV; all except one were male. The age range was 14-70 years, mean 37.4 years. The major causes of death were suicide 35%, AIDS 21%, drug toxicity 16%, natural causes 12% and injury 7%. The major exposure categories were male homosexual 51%, male bisexual 11%, homosexual/bisexual IDU 16%, IDU other 8%, and haemophiliac 7%. For only two was exposure information unavailable. Seropositivity for anti-HCV and HBsAg was 37% and 11% respectively. The deceased was recorded as having HIV/AIDS on the police report in 73% of cases, and at least 90% of subjects had been diagnosed with HIV prior to their death. The study suggests there is relatively little undiagnosed HIV infection in Victoria, that HIV infection has not moved outside traditional risk groups, and that many tests for HIV are undertaken using false namecodes. Many patients could not be matched on the HIV/AIDS databases, identifying a problem with HIV surveillance systems in Victoria, and the need to capture all information on HIV positives detected at VIFM.

The epidemiology of notified genital Chlamydia trachomatis infection in Victoria, Australia: a survey of diagnosing providers

Data on 259 notified cases of genital chlamydia infection diagnosed in Victoria Australia in January and February 1995 were augmented by call-back. Risk factor data was available for 221. Patients were primarily adolescents or young adults (median age 23 years); 66% were women. Men were more commonly symptomatic. Persons without symptoms were tested as a result of partner notification, sexual risk, termination of pregnancy, or because of abnormalities on genital examination. Limitations of antigen-based screening tests in low prevalence populations were rarely considered. Although antimicrobial treatment usually accorded with available guidelines, case management was not well geared to reducing the broader issue of risk of this infection in the community. Data management systems for handling name-coded data, and systems for recall and follow-up of diagnosed patients and their partners were often inadequate. Sexual history taking had not generally identified details of sexual partners. Partner notification was generally regarded as the patient's responsibility and professional help with contact tracing was rarely sought. Control of chlamydia will require much greater attention to management issues, particularly contact tracing.

Cryptosporidiosis in patients with AIDS

Cases of cryptosporidiosis in patients with the acquired immunodeficiency syndrome (AIDS) residing in Melbourne over a 6-year period (1990-1995) are described. During this period 85 cases occurred, while 979 new AIDS diagnoses were notified. Over this period temporal clustering in cryptosporidial detection was evident (P=0.007), but the pattern was not statistically associated with the season, rainfall (P=0.88), mean average maximal temperature (P=0.15) or mean average minimal temperature. Further studies should identify these risk factors and provide an opportunity to prevent this devastating disease.

Bovine beta-casein expressed in transgenic mouse milk is phosphorylated and incorporated into micelles

Transgenic mice carrying the bovine beta-casein gene linked to the promoter sequence of the sheep beta-lactoglobulin milk protein gene were produced. Four of seven lines expressed the transgene protein with mice from the two highest expressing lines producing 4 to 5 mg ml(-1) of this protein in their milk. The foreign protein was associated with the casein micelles and did not segregate into the whey fraction on centrifugation of milk samples. Following purification, the protein was characterized by amino acid analysis, gel electrophoresis, capillary zone electrophoresis, and trypsinolysis. The results showed that the transgene protein was authentic, phosphorylated bovine beta-casein A(1).

A profile of HIV testing in Victoria to the end of 1993. Victorian Collaborative Group on HIV and AIDS Surveillance (VCGHAS)

Examination of testing patterns for human immunodeficiency virus (HIV) in a population is important because it affects interpretation of surveillance data on new HIV diagnoses and can guide the targeting and evaluation of campaigns to encourage appropriate antibody testing. This report describes a relatively inexpensive mechanism of collecting information on who is being tested for HIV in Victoria (other than at the Blood Bank). The annual number of HIV tests performed in Victoria increased steadily throughout the 1980s but the rate of increase slowed in the early 1990s. By 1993, women accounted for almost half of HIV tests, although they made up only 8 per cent of positive tests. There were marked differences in the volume of testing and testing profiles of different laboratories. The information available on personal risk category and the reasons for HIV tests show that many people of low risk are tested, although conclusions are limited by inadequate information elicited or provided by many requesting doctors. For better information on what is occurring with respect to HIV testing, the fundamental requirement is better compliance from requesting doctors in supplying basic information on who they test and why.

Ascertaining exposure categories of HIV-infected individuals with previously unrecorded risk data

OBJECTIVES

To improve the quality of surveillance data for HIV in Victoria by following up all cases with an unknown exposure category; and to determine whether those with no exposure category included cases of transmission other than via the conventionally recognised routes.

METHODS

The Victorian HIV database records data on all people diagnosed with HIV in Victoria, including information on route of exposure to the virus. We identified all HIV diagnoses to which no exposure category had been attributed and, with the permission of the State Minister for Health, obtained access to namecoded testing records. Exposure categories, where possible, were obtained directly from these records. Otherwise, cases were checked against the namecoded AIDS database and, if necessary, an intensive process of call-back to laboratories, diagnosing doctors and HIV treatment centres was undertaken.

RESULTS

The database initially contained records for 289 people with unknown exposure categories (9.1% of Victorian people with HIV infection). We identified exposure categories for 155 of these people.

CONCLUSIONS

Exposure categories for those cases previously without data were similar to those for cases where exposure category was known. No instances of HIV transmission by previously unrecognised means were detected.