Biocide Susceptibility of Staphylococcus aureus CC398 and CC30 Isolates from Pigs and Identification of the Biocide Resistance Genes, qacG and qacC

Genomic analysis of multi-drug resistant coagulase-negative staphylococci from healthy humans and animals revealed unusual mechanisms of resistance and CRISPR-Cas system

BACKGROUND

Coagulase-negative staphylococci (CoNS) are evolving as major reservoirs and vectors of unusual and critical antimicrobial resistance (AMR) mechanisms.

MATERIALS AND METHODS

In this study, the genomic characterization of 26 multidrug-resistant (MDR)-CoNS (S. borealis, S. saprophyticus, S. sciuri, S. hominis, S. epidermidis, S. pasteuri, S. hyicus, S. simulans, S. haemolyticus, and S. arlettae) previously obtained from the nasal cavity of healthy nestling storks, humans who had no contact with animals, pigs, and pig farmers, as well as dogs and dog owners from Spain was performed. High-quality draft genomes obtained by Illumina sequencing technology were used to determine their resistome, virulome, mobile genetic elements, and CRISPR-Cas types. The relatedness of three CoNS species with publicly available genomes was assessed by core-genome single nucleotide polymorphisms (SNPs).

RESULTS

AMR genes to all classes of antibiotics in staphylococci were detected including unusual ones (mecC, ermT, and cfr), of which their corresponding genetic organizations were analyzed. About 96.1% of the MDR-CoNS strains harbored diverse adherence or immune evasion genes. Remarkably, one enterotoxin-C and -L-carrying S. epidermidis-ST595 strain from a nestling stork was detected. Moreover, various plasmid bound-biocide resistance genes (qacACGJ) were identified in 34.6% of the MDR-CoNS. Two genes that encode for cadmium and zinc resistance (cadD, czrC) were found, of which czrC predominated (42.3%). Complete CRISPR-Cas system was detected in 19.2% of the CoNS strains, of which cas-1, -2, and -9 predominated, especially in 75% of the S. borealis strains. The phylogenetic analysis identified clusters of related S. epidermidis lineages with those of other countries (SNP < 100). Also, highly related S. borealis isolates (SNP < 10) from pigs was confirmed for the first time in Spain.

CONCLUSION

These findings showed that various ecological niches harbor CoNS that presented MDR phenotypes mediated by multiple AMR genes carried by mobile genetic elements with relatively low frequency of intact CRISPR-Cas systems. Furthermore, the transmission of some CoNS species in humans and animals is strongly suggested.

Comparative genomics of Staphylococcus aureus strains from wild birds and pig farms elucidates levels of mobilomes, antibiotic pressure and host adaptation

OBJECTIVES

This study characterized the resistome, mobilome and phylogenomic relatedness of Staphylococcus aureus strains previously obtained from healthy nestling storks (HNS), pigs (HP) and pig farmers (HPF) to analyse possible transmission pathways of S. aureus with implications for the spread of antimicrobial resistance.

METHODS

The genomic contents of 52 S. aureus strains obtained from the nasal cavity of HNS, HP and HPF in Spain were sequenced using the Illumina NextSeq platform to characterize their resistome, virulome and mobile genetic elements. The relatedness of strains was assessed by core-genome single nucleotide polymorphisms (SNPs).

RESULTS

The frequencies of multidrug-resistance phenotype and transposons were significantly lower in strains from HNS than in those from HP and HPF (P < 0.005). However, the presence of human immune evasion cluster genes in S. aureus strains from HNS was significantly higher than in those from HP and HPF (P < 0.005). Interestingly, the frequencies of plasmids and phages were not significantly associated with the host (P > 0.05). The phylogenetic analysis identified a cluster of all the MSSA-CC398 strains carrying φSa3 and ermT on rep13 separately from the two MRSA-CC398 strains (carrying ermT on repUS18). Highly related MRSA-CC398 strains were detected in some pigs and related farmers (<10 SNPs).

CONCLUSION

This study confirms high-level antibiotic selection in S. aureus in HP and HPF in comparison to HNS. Furthermore, our findings highlight the continuous transmission of MRSA-CC398 in the pig-to-human interface and MSSA-CC398 with human adaptation markers in HNS. Molecular surveillance of S. aureus using the One Health model is required to establish appropriate control strategies.

A review of new emerging livestock-associated methicillin-resistant Staphylococcus aureus from pig farms

Methicillin-resistant Staphylococcus aureus (MRSA) is a S. aureus strain resistant to β-lactam antibiotics and is often associated with livestock, known as livestock-associated (LA)-MRSA. Using molecular typing with multi-locus sequence typing, MRSA clones have been classified in pigs, including clonal complex 398. Livestock-associated-methicillin-resistant S. aureus was first discovered in pigs in the Netherlands in 2005. Since then, it has been widely detected in pigs in other countries. Livestock-associated-methicillin-resistant S. aureus can be transmitted from pigs to pigs, pigs to humans (zoonosis), and humans to humans. This transmission is enabled by several risk factors involved in the pig trade, including the use of antibiotics and zinc, the size and type of the herd, and the pig pen management system. Although LA-MRSA has little impact on the pigs' health, it can be transmitted from pig to pig or from pig to human. This is a serious concern as people in direct contact with pigs are highly predisposed to acquiring LA-MRSA infection. The measures to control LA-MRSA spread in pig farms include conducting periodic LA-MRSA screening tests on pigs and avoiding certain antibiotics in pigs. This study aimed to review the emerging LA-MRSA strains in pig farms.

Airborne methicillin-resistant Staphylococcus aureus, other bacteria, fungi, endotoxin, and dust in a pigeon exhibition

Pigeon breeding is associated with exposure to airborne microorganisms and endotoxin and with symptoms of the airways. Antibiotic resistance is a threat to human health. Some pigeons participate in national and international indoor exhibitions. This study aims to obtain knowledge about the potential human exposure to dust, endotoxin, fungi, and bacteria including the methicillin-resistant Staphylococcus aureus (MRSA) in a pigeon exhibition in Denmark. In walking areas for visitors, airborne microorganisms in different size fractions able to enter the airways were sampled and following identified. The average concentrations were: 5000 cfu fungi/m³, 1.8 × 10⁴ cfu bacteria/m³, 37 endotoxin units/m³, and 0.18 mg dust/m³ air with the highest concentrations in-between rows with pigeon cages. The fungal species Wallemia sp. and Aspergillus versicolor and the bacterial species S. equorum and S. aureus were found in high concentrations. MRSA spa type t034 described to be associated with livestock was found in the air. Most of the S. aureus was present in the size fraction of 1.1-2.1 μm, which are particles able to enter the human terminal bronchi. In conclusion, fungi, bacteria, and endotoxin, respectively, were found in concentrations 10, 2000, and 200 times higher than outdoor references. The airborne bacteria in the exhibition were mainly species found previously in pigeon coops showing that the pigeons are the sources of exposure. The presence of airborne MRSA in the pigeon exhibition highlights the importance of also considering this environment as a potential place of exchange of resistant bacteria between animals and between animals and humans.

Towards a Harmonized Terminology: A Glossary for Biocide Susceptibility Testing

Disinfection is a key strategy to reduce the burden of infections. The contact of bacteria to biocides-the active substances of disinfectants-has been linked to bacterial adaptation and the development of antimicrobial resistance. Currently, there is no scientific consensus on whether the excessive use of biocides contributes to the emergence and spread of multidrug resistant bacteria. The comprehensive analysis of available data remains a challenge because neither uniform test procedures nor standardized interpretive criteria nor harmonized terms are available to describe altered bacterial susceptibility to biocides. In our review, we investigated the variety of criteria and the diversity of terms applied to interpret findings in original studies performing biocide susceptibility testing (BST) of field isolates. An additional analysis of reviews summarizing the knowledge of individual studies on altered biocide susceptibility provided insights into currently available broader concepts for data interpretation. Both approaches pointed out the urgent need for standardization. We, therefore, propose that the well-established and approved concepts for interpretation of antimicrobial susceptibility testing data should serve as a role model to evaluate biocide resistance mechanisms on a single cell level. Furthermore, we emphasize the adaptations necessary to acknowledge the specific needs for the evaluation of BST data. Our approach might help to increase scientific awareness and acceptance.

Detection and Genomic Characterisation of Clostridioides difficile from Spinach Fields

Despite an increased incidence of Clostridioides difficile infections, data on the reservoirs and dissemination routes of this bacterium are limited. This study examined the prevalence and characteristics of C. difficile isolates in spinach fields. C. difficile was detected in 2/60 (3.3%) of spinach and 6/60 (10%) of soil samples using culture-based techniques. Whole genome sequencing (WGS) analysis identified the spinach isolates as belonging to the hypervirulent clade 5, sequence type (ST) 11, ribotypes (RT) 078 and 126 and carried the genes encoding toxins A, B and CDT. The soil isolates belonged to clade 1 with different toxigenic ST/RT (ST19/RT614, ST12/RT003, ST46/RT087, ST16/RT050, ST49/RT014/0) strains and one non-toxigenic ST79/RT511 strain. Antimicrobial resistance to erythromycin (one spinach isolate), rifampicin (two soil isolates), clindamycin (one soil isolate), both moxifloxacin and rifampicin (one soil isolate), and multi-drug resistance to erythromycin, vancomycin and rifampicin (two soil isolates) were observed using the E test, although a broader range of resistance genes were detected using WGS. Although the sample size was limited, our results demonstrate the presence of C. difficile in horticulture and provide further evidence that there are multiple sources and dissemination routes for these bacteria.

Metagenomic evidence for co-occurrence of antibiotic, biocide and metal resistance genes in pigs

Antibiotic-resistant pathogens constitute an escalating public health concern. Hence a better understanding of the underlying processes responsible for this expansion is urgently needed. Co-selection of heavy metal/biocide and antibiotic resistance genes (ARGs) has been suggested as one potential mechanism promoting the proliferation of antimicrobial resistance (AMR). This paper aims to elucidate this interplay and exploit differences in antibiotic usage to infer patterns of co-selection by the non-antibiotic factors metals and biocides in the context of pig farming. We examined 278 gut metagenomes from pigs with continuous antibiotic exposure, only at weaning and at no exposure. Metals as growth promoters and biocides as disinfectants are currently used with little restrictions in stock farming. The pigs under continuous antibiotic exposure displayed the highest co-occurrence of ARGs and other genetic elements while the pigs under limited use of antibiotics still showed abundant co-occurrences. Pathogens belonging to Enterobacteriaceae displayed increased co-occurrence phenomena, suggesting that this maintenance is not a random selection process from a mobilized pool but pertains to specific phylogenetic clades. These results suggest that metals and biocides displayed strong selective pressures on ARGs exerted by intensive farming, regardless of the current use of antibiotics.

Repeated disinfectant use in broiler houses and pig nursery units does not affect disinfectant and antibiotic susceptibility in Escherichia coli field isolates

BACKGROUND

Disinfectants are frequently used in animal production to reduce or eliminate the load of infectious agents and parasites in buildings and equipment associated with the housing or transportation of animals. There are growing concerns that the use of disinfectants would select for resistance to antibiotics and disinfectants. The aim of this study was to determine the effect of repeated use of different disinfectants on the disinfectant and antibiotic susceptibility under practical conditions in a broiler and pig pilot farm. Therefore, the susceptibility of Escherichia coli (E. coli) to 14 antibiotics and 4 disinfectants was monitored over a one-year period.

RESULTS

High (20-50%) to very high (> 50%) resistance levels for ampicillin, sulfamethoxazole, trimethoprim and tetracycline were observed in both animal production types. Disinfectant susceptibility did not change over time and did not depend on the used disinfection product. Compared to in-use concentrations of formaldehyde, benzalkoniumchloride and a peracetic acid - hydrogen peroxide formulation, all E. coli strains remained susceptible indicating that the use of disinfectants did not select for disinfectant resistance. Moreover, no association could be found between the use of disinfectants and antibiotic resistance.

CONCLUSIONS

These findings suggest that repeated use of disinfectants in agricultural environments does not select for antibiotic resistance nor does it reduce disinfectant susceptibility.

Limited association between disinfectant use and either antibiotic or disinfectant susceptibility of Escherichia coli in both poultry and pig husbandry

BACKGROUND

Farm disinfectants are widely used in primary production, but questions have been raised if their use can select for antimicrobial resistance. The present study examined the use of disinfectants in poultry and pig husbandry and its contribution to the antibiotic and disinfectant susceptibility of Escherichia coli (E. coli) strains obtained after cleaning and disinfection. On those field isolates antibiotic susceptibility was monitored and susceptibility to commonly used active components of farm disinfectants (i.e. glutaraldehyde, benzalkoniumchloride, formaldehyde, and a formulation of peracetic acid and hydrogen peroxide) was tested.

RESULTS

This study showed a high resistance prevalence (> 50%) for ampicillin, sulfamethoxazole, trimethoprim and tetracycline for both production animal categories, while for ciprofloxacin only a high resistance prevalence was found in broiler houses. Disinfectant susceptibility results were homogenously distributed within a very small concentration range. Furthermore, all E. coli strains were susceptible to in-use concentrations of formaldehyde, benzalkoniumchloride and a formulation of peracetic acid and hydrogen peroxide, indicating that the practical use of disinfectants did not select for disinfectant resistance. Moreover, the results showed no indications for the selection of antibiotic resistant bacteria through the use of disinfectants in agricultural environments.

CONCLUSION

Our study suggests that the proper use of disinfectants in agricultural environments does not promote antibiotic resistance nor reduce E. coli disinfectant susceptibility.

Susceptibility of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) to chlorhexidine digluconate, octenidine dihydrochloride, polyhexanide, PVP-iodine and triclosan in comparison to hospital-acquired MRSA (HA-MRSA) and community-aquired MRSA (CA-MRSA): a standardized comparison

Background

Recent publications have raised concerns of reduced susceptibilities of clinical bacterial isolates towards biocides. This study presents a comparative investigation of the susceptibility of livestock-associated Methicillin-resistant Staphylococcus aureus (LA-MRSA), hospital-acquired MRSA (HA-MRSA) and community-aquired MRSA (CA-MRSA) to the commonly used antiseptics chlorhexidine (CHX), octenidine (OCT), polyhexanide (PHMB), PVP-iodine (PVP-I) and triclosan (TCX) based on internationally accepted standards.

Methods

In total, 28 (18 LA-, 5 HA- and 5 CA) genetically characterized MRSA strains representing a broad spectrum of hosts, clonal complexes and spa-types, as well as the reference methicillin-sensitive Staphylococcus aureus (MSSA) strain ATCC 6538, were selected. Minimal inhibitory concentration (MIC) and minimal microbicidal concentration (MBC) were determined in accordance with DIN 58940-7, 58940-8 and DIN EN ISO 20776-1. The microbicidal efficacy was determined in accordance with DIN EN 1040.

Results

Results from the MIC/MBC and quantitative suspension tests revealed differences between antiseptic substances but not between epidemiological groups of MRSA strains. OCT and PHMB were the most active substances with a minimal MIC of 1 mg/L, followed by CHX (2 mg/L), TCX (32 mg/L) and finally PVP-I (1024 mg/L). The MSSA reference strain showed a tendency to a higher susceptibility compared to the MRSA strains.

Conclusions

This investigation of the susceptibility of a range of LA-, HA- and CA-MRSA strains using standardized conditions gave no indication that LA-MRSA strains are less susceptible to commonly used antiseptics compared to HA- and CA-MRSA strains.

Antimicrobial Resistance among Staphylococci of Animal Origin

Antimicrobial resistance among staphylococci of animal origin is based on a wide variety of resistance genes. These genes mediate resistance to many classes of antimicrobial agents approved for use in animals, such as penicillins, cephalosporins, tetracyclines, macrolides, lincosamides, phenicols, aminoglycosides, aminocyclitols, pleuromutilins, and diaminopyrimidines. In addition, numerous mutations have been identified that confer resistance to specific antimicrobial agents, such as ansamycins and fluoroquinolones. The gene products of some of these resistance genes confer resistance to only specific members of a class of antimicrobial agents, whereas others confer resistance to the entire class or even to members of different classes of antimicrobial agents, including agents approved solely for human use. The resistance genes code for all three major resistance mechanisms: enzymatic inactivation, active efflux, and protection/modification/replacement of the cellular target sites of the antimicrobial agents. Mobile genetic elements, in particular plasmids and transposons, play a major role as carriers of antimicrobial resistance genes in animal staphylococci. They facilitate not only the exchange of resistance genes among members of the same and/or different staphylococcal species, but also between staphylococci and other Gram-positive bacteria. The observation that plasmids of staphylococci often harbor more than one resistance gene points toward coselection and persistence of resistance genes even without direct selective pressure by a specific antimicrobial agent. This chapter provides an overview of the resistance genes and resistance-mediating mutations known to occur in staphylococci of animal origin.

Survival of LA-MRSA in Dust from Swine Farms

Dust is suspected to be an important factor in transmission of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) between pigs and pig farmers and their families. The aim of this study was to determine the rate of decay for Staphylococcus aureus and LA-MRSA in dust from swine farms. Electrostatic dust fall collectors (EDCs) were used for passive sampling of settling airborne dust in 11 stable sections from six swine farms. Extraction, plating, identification, and enumeration of cultivable S. aureus and LA-MRSA from the EDCs were performed after storage for 0-30 days postsampling. The survival of S. aureus was measured in 196 dust samples from all farms, and data were used to estimate the decay constant λ according to a model for exponential decay: N(t) = N0 × e-λt. The number of S. aureus colonies was up to 600-fold higher than the number of LA-MRSA colonies on MRSA selective agar. The data showed a good fit to the model (λ = 0.13, r2 = 0.86) even with a large difference in initial concentrations of S. aureus between stables. The loads of S. aureus and LA-MRSA in the dust were significantly reduced by storage time, and the half-life was 5 days for both S. aureus and LA-MRSA. In dust samples with high initial concentrations, LA-MRSA and S. aureus could still be cultivated 30 days after sampling. On all farms MRSA isolates belonged to the clonal complex (CC) 398, and at one farm some isolates also belonged to CC30. A screening for other Staphylococcus species in the farm dust revealed 13 different species numerically dominated by Staphylococcus equorum. Based on the exponential decay model, S. equorum had a half-life of 4 days. In conclusion, the presence of MRSA in airborne dust from five of six farms indicates that dust might be an important vehicle for transmission of LA-MRSA. LA-MRSA and S. aureus was found to survive well in farm dust with half-lives of 5 days, and dependent on the initial concentration they could be found in farm dust for weeks. The 99.9% die-off rate was 66 days for LA-MRSA. Thus, farm dust can pose an exposure risk for humans in the farm environment, but also when transported to other environments. On the other hand, the risk will decrease by time. These results provide important knowledge to diminish spread from farm environments to other environments on, e.g., tools or clothing, and in relation to cleaning of emptied LA-MRSA-positive stables.

In vitro studies of the antibacterial activity of Copaifera spp. oleoresins, sodium hypochlorite, and peracetic acid against clinical and environmental isolates recovered from a hemodialysis unit

Background

Patients submitted to hemodialysis therapy are more susceptible to infection, especially to infection by Gram-positive bacteria. Various research works have attempted to discover new antimicrobial agents from plant extracts and other natural products.

Methods

The present study aimed to assess the antibacterial activities of Copaifera duckei, C. reticulata, and C. oblongifolia oleoresins; sodium hypochlorite; and peracetic acid against clinical and environmental isolates recovered from a Hemodialysis Unit. The Minimum Inhibitory Concentration and the Fractionated Inhibitory Concentration Index were determined; the ability of the tested compounds/extracts to inhibit biofilm formation was evaluated by calculating the MICB50 and IC50.

Results

C. duckei was the most efficient among the assayed Copaifera species, and its oleoresin was more effective than peracetic acid and sodium hypochlorite. Copaifera oleoresins and disinfectants did not act synergistically at any of the tested combinations. Certain of C. duckei oleoresin, peracetic acid, and sodium hypochlorite concentrations inhibited biofilm formation and eradicated 50% of the biofilm population.

Conclusion

C. duckei oleoresin is a potential candidate for disinfectant formulations. Based on these results and given the high incidence of multi-resistant bacteria in hemodialysis patients, it is imperative that new potential antibacterial agents like C. duckei oleoresin, which is active against Staphylococcus, be included in disinfectant formulations.

Susceptibility of vancomycin-resistant and -sensitive Enterococcus faecium obtained from Danish hospitals to benzalkonium chloride, chlorhexidine and hydrogen peroxide biocides

PURPOSE

In Danish hospitals, the number of infections caused by vancomycin-resistant Enterococcus faecium (VRE faecium) has dramatically increased in recent years. Hospital disinfectants are essential in eliminating pathogenic microorganisms, and reduced susceptibility may contribute to hospital-associated infections. We have addressed whether clinical VRE faecium display decreased biocide susceptibility when compared to vancomycin-sensitive Enterococcus faecium (VSE faecium) isolates.

METHODOLOGY

In total 12 VSE faecium and 37 VRE faecium isolates obtained from Danish hospitals over an extended time period were tested for susceptibility towards three commonly applied biocides, namely benzalkonium chloride, chlorhexidine and hydrogen peroxide.

RESULTS

For benzalkonium chloride, 89 % of VRE faecium strains had a minimal inhibitory concentration (MIC) of 8 mg l^-1, whereas for VSE faecium, only 25 % of the strains had an MIC of 8 mg l^-1. For chlorhexidine, the MIC of 95 % of VRE faecium strains was 4 mg l^-1 or higher, while only 33 % of VSE faecium strains displayed MIC values at the same level. In contrast, both VRE and VSE faecium displayed equal susceptibility to hydrogen peroxide, but a higher minimal bactericidal concentration (MBC) was found for the former. The efflux activity was also assessed, and this was generally higher for the VRE faecium strains compared to VSE faecium.

CONCLUSION

VRE faecium from Danish hospitals demonstrated decreased susceptibility towards benzalkonium chloride and chlorhexidine compared to VSE faecium, where the use of chlorhexidine is particularly heavy in the hospital environment. These findings suggest that biocide tolerance may characterize VRE faecium isolated in Danish hospitals.

Current and Emerging Topical Antibacterials and Antiseptics: Agents, Action, and Resistance Patterns

Bacterial skin infections represent some of the most common infectious diseases globally. Prevention and treatment of skin infections can involve application of a topical antimicrobial, which may be an antibiotic (such as mupirocin or fusidic acid) or an antiseptic (such as chlorhexidine or alcohol). However, there is limited evidence to support the widespread prophylactic or therapeutic use of topical agents. Challenges involved in the use of topical antimicrobials include increasing rates of bacterial resistance, local hypersensitivity reactions (particularly to older agents, such as bacitracin), and concerns about the indiscriminate use of antiseptics potentially coselecting for antibiotic resistance. We review the evidence for the major clinical uses of topical antibiotics and antiseptics. In addition, we review the mechanisms of action of common topical agents and define the clinical and molecular epidemiology of antimicrobial resistance in these agents. Moreover, we review the potential use of newer and emerging agents, such as retapamulin and ebselen, and discuss the role of antiseptic agents in preventing bacterial skin infections. A comprehensive understanding of the clinical efficacy and drivers of resistance to topical agents will inform the optimal use of these agents to preserve their activity in the future.

Assessment of the Risk to Public Health due to Use of Antimicrobials in Pigs-An Example of Pleuromutilins in Denmark

Antibiotic consumption in pigs can be optimized by developing treatment guidelines, which encourage veterinarians to use effective drugs with low probability of developing resistance of importance for human health. In Denmark, treatment guidelines for use in swine production are currently under review at the Danish Veterinary and Food Administration. Use of pleuromutilins in swine has previously been associated with a very low risk for human health. However, recent international data and sporadic findings of novel resistance genes suggest a change of risk. Consequently, a reassessment was undertaken inspired by a risk assessment framework developed by the European Medicines Agency. Livestock-associated methicillin-resistant Staphylococcus aureus of clonal complex 398 (MRSA CC398) and enterococci were identified as relevant hazards. The release assessment showed that the probability of development of pleuromutilin resistance was high in MRSA CC398 (medium uncertainty) and low in enterococci (high uncertainty). A relatively small proportion of Danes has an occupational exposure to pigs, and foodborne transmission was only considered of relevance for enterococci, resulting in an altogether low exposure risk. The human consequences of infection with pleuromutilin-resistant MRSA CC398 or enterococci were assessed as low for the public in general but high for vulnerable groups such as hospitalized and immunocompromised persons. For MRSA CC398, the total risk was estimated as low (low uncertainty), among other due to the current guidelines on prevention of MRSA in place at Danish hospitals, which include screening of patients with daily contact to pigs on admittance. Moreover, MRSA CC398 has a medium human–human transmission potential. For enterococci, the total risk was estimated as low due to low prevalence of resistance, low probability of spread to humans, low virulence, but no screening of hospitalized patients, high ability of acquiring resistance genes, and a limited number of alternative antimicrobials (high uncertainty). This assessment reflects the current situation and should be repeated if pleuromutilin consumption increases substantially, resulting in increased prevalence of mobile, easily transmissible resistance mechanisms. Continuous monitoring of pleuromutilin resistance in selected human pathogens should therefore be considered. This also includes monitoring of linezolid resistance, since resistance mechanisms for pleuromutilins and oxazolidones are often coupled.