Empyema caused by MRSA ST398 with atypical resistance profile, Spain

Review of pork and pork products as a source for transmission of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is an opportunistic bacterium that can cause infection in animals and humans. Recently, MRSA from food-producing or farm animals has been identified as livestock-associated MRSA (LA-MRSA). The spread of LA-MRSA is particularly found in pork and pork products because LA-MRSA has been widely known to infect pigs. The most common type of LA-MRSA identified in pork and pork products is the clonal complex LA-MRSA 398 (LA-MRSA CC398). The MRSA strains on the surface of pork carcasses can be spread during the handling and processing of pork and pork products through human hands, cutting tools, and any surface that comes into direct contact with pork. Food infection is the main risk of MRSA in pork and pork products consumed by humans. Antibiotics to treat food infection cases due to MRSA infection include vancomycin and tigecycline. The spread of MRSA in pork and pork products is preventable by appropriately cooking and cooling the pork and pork products at temperatures above 60°C and below 5°C, respectively. It is also necessary to take other preventive measures, such as having a clean meat processing area and disinfecting the equipment used for processing pork and pork products. This review aimed to explain epidemiology, transmission, risk factors, diagnosis, public health consequences, treatment of food poisoning, and preventing the spread of MRSA in pork and pork products.

Identification and Validation of a Novel Antibacterial Compound MZ-01 against Methicillin-Resistant Staphylococcus aureus

The discovery of new classes of antibiotics is slow, and it is being greatly outpaced by the development of bacterial resistance. This disparity places us in an increasingly vulnerable position because we are running out of safe and effective therapeutic options to treat antibiotic-resistant infections. This is exemplified by the emergence and persistence of hospital-acquired and community-associated methicillin-resistant S. aureus (MRSA), which has markedly narrowed our options for treating life-threatening staph infections. Thus, there is an urgent need to develop novel, potent, preventive, and therapeutic agents. In our current study, we performed a whole-cell screening assay of synthetic libraries for antibacterial activity and identified a novel molecule, MZ-01. MZ-01 exhibited potent bactericidal activity against Gram-positive bacterial pathogens, including MRSA, Streptococcus pyogenes, and Streptococcus pneumoniae, at low concentrations. MZ-01 killed and lysed both the late exponential phase of an S. aureus population and bacteria inside mammalian cells. Furthermore, MZ-01 exhibited low cytotoxicity. These results indicate that MZ-01 is a promising scaffold to guide the development of novel, potent antibacterial agents against multidrug-resistant Gram-positive bacterial pathogens such as MRSA.

Human mecC-Carrying MRSA: Clinical Implications and Risk Factors

A new methicillin resistance gene, named mecC, was first described in 2011 in both humans and animals. Since then, this gene has been detected in different production and free-living animals and as an agent causing infections in some humans. The possible impact that these isolates can have in clinical settings remains unknown. The current available information about mecC-carrying methicillin resistant S. aureus (MRSA) isolates obtained from human samples was analyzed in order to establish its possible clinical implications as well as to determine the infection types associated with this resistance mechanism, the characteristics of these mecC-carrying isolates, their possible relation with animals and the presence of other risk factors. Until now, most human mecC-MRSA infections have been reported in Europe and mecC-MRSA isolates have been identified belonging to a small number of clonal complexes. Although the prevalence of mecC-MRSA human infections is very low and isolates usually contain few resistance (except for beta-lactams) and virulence genes, first isolates harboring important virulence genes or that are resistant to non-beta lactams have already been described. Moreover, severe and even fatal human infection cases have been detected. mecC-carrying MRSA should be taken into consideration in hospital, veterinary and food safety laboratories and in prevention strategies in order to avoid possible emerging health problems.

A Longitudinal Case Study on Dissemination of ST398 Methicillin-Resistant Staphylococcus aureus Within a Dairy Cow Herd

The study was conducted to describe the dynamics of ST398 methicillin-resistant Staphylococcus aureus (MRSA) on a dairy herd in northeastern Italy. MRSA was first identified in this herd of 120 cows in 2016, after which the herd was sampled once every 3 months for 1 year (April 2016-May 2017). Samples collected included nasal swabs and milk samples from cows and nasal swabs from farmworkers. In addition, pen fencing and teat milk liners were swabbed and air samples from cow pens and the milking parlor were collected. All samples were tested for MRSA using a selective medium; positive isolates were confirmed by mecA PCR. A representative set of MRSA isolates was genotyped using spa typing and multilocus sequence typing. Overall, 34 (mean 23%, range 16-30%) milking cows were found harboring MRSA in the mammary gland and only 6 recovered from infection or colonization. The mean incidence rate was 14% (range 8-20%), mean cure rate was 23% (range 13-43%), and estimated basic reproduction number (R₀) was 1.08. The average of positive quarters found was 35.1% and most of the positive quarters (82.4%) developed subclinical mastitis. The mean duration of MRSA colonization in quarters during the study was 247 days, but quarters affected by subclinical mastitis harbored MRSA for a longer time than healthy ones (285 days vs. 131 days). After the second sampling, the farmer segregated MRSA-positive cows from the uninfected cows and milked them last. Despite segregation, 25 newly infected or colonized cows were detected. MRSA isolates from cows, environment, and two farmworkers belonged to the same sequence type (ST398) and spa type (t034). This study highlights the ability of ST398 MRSA to cause a persistent infection of the mammary gland and to survive in the farm environment.

Methicillin-resistant Staphylococcus aureus in swine housed indoors in Galicia, Spain

INTRODUCTION

Livestock are known reservoirs of methicillin-resistant Staphylococcus aureus (MRSA) and this constitutes an important public health issue. The prevalence of nasal MRSA carriers in swine housed indoors in Galicia, Spain, was studied.

METHODS

197 samples from swine aged three, eight, 12, 16 and 24 weeks, and from adult pigs, were obtained from four farms. The cleaning procedures implemented to clean the barns and antimicrobial consumption were analyzed. Antimicrobial susceptibility and antimicrobial resistance genes were studied. PFGE, spa typing and MLST were used to classify the isolates. SCCmec, agr and pvl were analyzed.

RESULTS

MRSA prevalence was 12.7%. Swine younger than 16 weeks had a higher colonization rate; 22.9% vs 3.5% (OR, 8.16; 95% CI, 2.47-29.79; p<0.01). The only farm found to be MRSA-free used disinfectants as part of its cleaning procedure. All MRSA were tetracycline-resistant (identifying the tetK and tetM genes), 80% were resistant to erythromycin and clindamycin and 16% were only clindamycin-resistant. The ermC and vgaA genes were identified in these two phenotypes. A single genotype (PFGE type A) and ST398 - spa t011 (84%) and t1451 (16%) were identified. SCCmec type V and agrI were identified in all isolates, and all were pvl-negative.

CONCLUSION

A correlation between swine age and MRSA colonization was observed. Appropriate cleaning procedures could have an impact on MRSA colonization in farming. Resistance to antibiotics used in human health was identified. Clinicians should be aware if their patients have come into contact with farm animals.

MRSA in swine, farmers and abattoir workers in Southern Italy

Methicillin-resistant Staphylococcus aureus (MRSA) is an important medical issue, since it causes serious and sometimes fatal infections in humans. Intensively reared swine may serve as reservoirs for MRSA that can infect swine workers, and also consumers (via contaminated meat). In this study, MRSA strains were isolated from 55 of the 85 (64.7%) intensive pig farms surveyed, and prevalence was greater on pig fattening farms than on breeding farms. In addition, we included in the study 63 foreign pigs imported for slaughter. Overall, the prevalence of MRSA in the 418 sampled swine was 59.1%; 12 genotypes were identified among the isolates; ST398 (96.4%) was most prevalent, followed by ST97 (2%), ST9 (0.8%) and ST1 (0.8%). MRSA isolates were also detected in 26 (17.3%) of the 150 operators included in the study; the genotypes detected were ST398 (85%), ST9 (7.6%), ST5 (3.8%) and ST1 (3.8%). All the strains were pvl negative and pia positive. Both swine and human strains displayed a multi-resistance pattern, and almost all were resistant to tetracycline. The results obtained in this study confirm the high prevalence of MRSA in swine reared and slaughtered in Italy, and underline the public health risk linked to the spread of antimicrobial-resistant Staphylococcus aureus among intensively reared pigs.

Airborne MRSA and Total Staphylococcus aureus as Associated With Particles of Different Sizes on Pig Farms

Airborne methicillin-resistant Staphylococcus aureus (MRSA) have previously been found on pig farms, which may lead to nasal deposition of MRSA in humans via inhalation. The anterior nares are the main niche for S. aureus, and S. aureus can cause, e.g. wound infection and pneumonia. The aim of this study was to acquire knowledge about the potential deposition of airborne MRSA, specifically, and of total S. aureus (including both methicillin-sensitive S. aureus and MRSA, in the following called S. aureus) in the different parts of the airways during occupancy on pig farms. Measurements of airborne MRSA and S. aureus were performed on four pig farms using a six and a three-stage sampler during different work tasks, such as high-pressure cleaning and everyday inspection. MRSA were quantified using MRSA-selective agar, and S. aureus were quantified using Staphylococcus selective agar. The identity of the bacteria were confirmed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The geometric mean (GM) concentrations of MRSA and S. aureus were 447 cfu/m3 air and 1.8 × 103 cfu/m3 air, respectively. The highest concentrations of MRSA and S. aureus were found among pigs in a weaner stable and during high-pressure cleaning of an empty stable, respectively. The lowest concentrations of MRSA and S. aureus were found in a stable with sick pigs and in feed-storages, respectively. Most MRSA and S. aureus were associated with particles between 7 and 12 µm. On average, the particle size fractions potentially depositing in the upper airways constituted 70%, in the primary and secondary bronchi 22%, and in the terminal bronchi and alveoli 8% of the inhalable MRSA and S. aureus concentration. Across the sampled areas, the geometric mean diameter (Dg) of particles with MRSA and S. aureus were 7.2 and 6.4 µm, respectively, and no significant difference was found between these Dgs. The Dg of the airborne particles with the studied bacterium was significantly associated with the different locations on the farms. The largest Dgs were found in the air samples from the aisles and on the fence to the pens, while the smallest Dgs were found in samples from the pens among the pigs and in samples taken at greater distances from the pigs: in the hallway, feed-storage, and entry room. In conclusion, airborne MRSA and S. aureus were found in sample fractions potentially depositing in all six parts of the airways. However, the majority was found to potentially deposit in the upper airways. The concentration of airborne MRSA and S. aureus and MRSA, as well as the fraction potentially depositing in the different parts of the airways, depended on the specific work task being performed and the location on the farm.

Prevalence of colonization by methicillin-resistant Staphylococcus aureus ST398 in pigs and pig farm workers in an area of Catalonia, Spain

Background

A livestock-associated clonal lineage (ST398) of methicillin-resistant Staphylococcus aureus (MRSA) has been identified causing colonization or infection in farm workers. The aim of the study was to analyze the prevalence of MRSA-ST398 colonization in pigs and in pig farmers in an area with a high pig population (Osona, Barcelona province, Catalonia, Spain).

Methods

We performed a cross-sectional prevalence study in Osona (Catalonia, Spain), from June 2014 to June 2015. All pig farm workers from 83 farms were studied. Twenty of these farms were randomly selected for the study of both pigs and farmers: 9 fattening and 11 farrow-to-finish farms. All workers over the age of 18 who agreed to participate were included. Samples were analyzed to identify MRSA-ST398 and their spa type.

Results

Eighty-one of the 140 pig farm workers analyzed (57.9% (95% IC: 50.0–66.4%)) were MRSA-positive, all of them ST398. The mean number of years worked on farms was 17.5 ± 12.6 (range:1–50), without significant differences between positive and negative MRSA results (p = 0.763). Over 75% of MRSA-ST398 carriers worked on farms with more than 1250 pigs (p < 0.001). At least one worker tested positive for MRSA-ST398 on all 20 selected pig farms. Ninety-two (46.0% (95% IC: 39.0–53.0%)) of the nasal swabs from 200 pigs from these 20 farms were MRSA-positive, with 50.5% of sows and 41.4% of fattening pigs (p = 0.198) giving MRSA-positive results. All the isolates were tetracycline-resistant, and were identified as MRSA-ST398. The spa type identified most frequently was t011 (62%). Similar spa types and phenotypes of antibiotic resistance were identified in pigs and farmers of 19/20 tested farms.

Conclusions

The prevalence of MRSA-ST398 among pig farm workers and pigs on farms in the studied region is very high, and the size of the farm seems to correlate with the frequency of colonization of farmers. The similar spa-types and phenotypes of resistance detected in pigs and workers in most of the farms studied suggest animal-to-human transmission.

Occurrence of methicillin-resistant Staphylococcus aureus in dairy cattle herds, related swine farms, and humans in contact with herds

In this study we investigated the circulation of methicillin-resistant Staphylococcus aureus (MRSA) in 2 dairy cattle farms (farm A and B), previously identified as MRSA-positive in bulk tank milk samples, and epidemiologically related to swine farms. Collected specimens included quarter milk samples and nasal swabs from dairy cows, pig nasal swabs collected at both the farm and slaughterhouse level, environmental dust samples, and human nasal swabs from the farms' owners and workers. The prevalence of MRSA was estimated at the herd level by testing quarter milk samples. The prevalence of MRSA was 4.8% (3/63; 95% confidence interval=0-10.2%) and 60% (33/55; 95% confidence interval=47.05-72.95) in farm A and B, respectively. In farm A, MRSA was also isolated from humans, pigs sampled at both farm and slaughterhouse level, and from environmental samples collected at the pig facilities. The dairy cattle facilities of farm A tested negative for MRSA. In farm B, MRSA was isolated from environmental dust samples in both the cattle and pig facilities, whereas nasal swabs collected from cows and from humans tested negative. Sixty-three selected MRSA isolates obtained from different sources in farm A and B were genetically characterized by multilocus sequence typing, spa-typing, ribosomal spacer-PCR, and also tested for the presence of specific virulence genes and for their phenotypical antimicrobial susceptibility by broth microdilution method. Different clonal complex (CC) and spa-types were identified, including CC398, CC97, and CC1, CC already reported in livestock animals in Italy. The MRSA isolates from quarter milk of farm A and B mostly belonged to CC97 and CC398, respectively. Both lineages were also identified in humans in farm A. The CC97 and CC398 quarter milk isolates were also identified as genotype GTBE and GTAF by ribosomal spacer-PCR respectively, belonging to distinct clusters with specific virulence and resistance patterns. The GTBE and GTAF clusters also included swine, environmental, and human isolates from both farms. A high heterogeneity in the genetic and phenotypic profiles was observed in environmental isolates, in particular from farm B. These results demonstrate the possibility of a dynamic sharing and exchange of MRSA lineages or genotypes between different species and farm compartments in mixed-species farms. The risk of transmission between swine and related dairy cattle herds should be considered. Our findings also confirm the zoonotic potential of livestock-associated MRSA and underline the importance of applying biosecurity measures and good hygiene practices to prevent MRSA spread at the farm level and throughout the food production chain.

Unusual presence of the immune evasion gene cluster in livestock-associated MRSA of lineage CC398 causing peridural and psoas abscesses in a poultry farmer

OBJECTIVE

To characterize a methicillin-resistant Staphylococcus aureus (MRSA) isolate responsible for an aggressive infection (peridural and psoas abscess secondary to haematogenous septic arthritis) in a poultry farmer.

METHODS

Molecular characterization was performed, including spa- and multilocus sequence typing of the isolate, assessment of its resistance phenotype and detection of tetracycline resistance and of virulence and immune evasion cluster (IEC) genes were performed.

RESULTS

The MRSA isolate was tetracycline- and fluorquinolone-resistant, and was ascribed to CC398, spa-t1451. The isolate harboured tet(M) (distinctive of livestock-associated (LA) MRSA-CC398 clade) and IEC-type B system (characteristic of the methicillin-susceptible human lineage, but typically absent in LA-MRSA-CC398 strains), and lacked toxin-coding genes lukF/lukS-PV, tsst-1, eta and etb.

CONCLUSION

IEC re-acquisition by LA-MRSA-CC398-LA strains is an unusual finding, but could constitute an emerging public health problem. It would represent an evolutionary step towards LA-MRSA-CC398's adaptation to human hosts, and might enhance its invasiveness and ability to be transmitted to humans.

New Synthesis of Gold- and Silver-Based Nano-Tetracycline Composites

A new synthetic methodology of water-soluble gold and silver nanoparticles (AuNPs@TC and AgNPs@TC), using the antibiotic tetracycline (TC) as co-reducing and stabilizing agent, is reported. Both colloids exhibit high water stability. The average sizes obtained were 25±10 and 15±5 nm, respectively. Both composites were tested against TC-resistant bacteria, presenting an increasing antibacterial effect in the case of AgNPs@TC. The sensing towards metal ions was also explored. An interesting and reversible affinity of AuNPs@TC towards AlIII cations in an aqueous system was also observed.

Individual predisposition to Staphylococcus aureus colonization in pigs on the basis of quantification, carriage dynamics, and serological profiles

Previous research on Staphylococcus aureus in pigs focused on livestock-associated methicillin-resistant S. aureus (MRSA) and had a qualitative cross-sectional design. This study aimed to elucidate the frequency, load, and stability of S. aureus nasal carriage in pigs over time and investigated possible associations between carriage and immune response. Nasal swabs were collected three times weekly from 480 tagged adult pigs in 20 Danish production farms. S. aureus and MRSA were quantified on selective media by the most-probable-number method. The levels of IgG against 10 S. aureus antigens in serum were quantified in selected pigs by a Luminex assay. All the farms were positive for S. aureus and 15 for MRSA, leading to overall prevalences of persistent and intermittent carriers and noncarriers of 24, 52, and 23%, respectively. Carriage frequency and nasal loads were significantly higher on MRSA-positive farms. Logistic-regression modeling revealed the presence of individual pigs characterized by high nasal loads (>10,000 CFU per swab) and stable carriage regardless of farm- and pen-associated factors. On the other hand, the humoral response was strongly influenced by these environmental factors. The existence of a minority of shedders contributing to maintenance of S. aureus within farms opens up new perspectives on the control of MRSA in pig farming.

MRSA colonization and infection among persons with occupational livestock exposure in Europe: Prevalence, preventive options and evidence

Colonization with livestock-associated Methicillin-resistant Staphylococcusaureus (LA-MRSA) among persons occupationally exposed to pigs, cattle or poultry is very frequent. In Europe, LA-MRSA mostly belong to the clonal lineage CC398. Since colonized persons have an increased risk of developing MRSA infections, defining the burden of work-related infection caused by LA-MRSA CC398 is of interest to exposed personnel, insurance companies and infection control staff. This review summarizes data on the types of occupation-related infections caused by LA-MRSA CC398, the incidence of such infections as well as potential preventive strategies. We identified twelve case reports on infections among livestock-exposed persons. Overall, there is a lack of data describing the incidence of occupation-related infections due to MRSA CC398. Currently, no specific guidance towards the prevention of LA-MRSA CC398 colonization of persons with routine exposure exists. In vitro, MRSA CC398 strains are susceptible (>95%) to mupirocin. Single reports have described effective decolonization of persons carrying LA-MRSA CC398, but long-term success rates are low in case of continuous livestock contact. Overall, the occupational health risk due to LA-MRSA CC398 is not well understood. Currently, prevention of human LA-MRSA CC398 infection is mostly based on the recommendation to perform screening and decolonization therapies prior to elective medical interventions in order to avoid nosocomial infections, but there is no conclusive evidence to perform specific measures aiming to forestall community-acquired infections.

Surfaceome and exoproteome of a clinical sequence type 398 methicillin resistant Staphylococcus aureus strain

For many years Staphylococcus aureus has been recognized as an important human pathogen. In this study, the surfacome and exoproteome of a clinical sample of MRSA was analyzed. The C2355 strain, previously typed as ST398 and spa-t011 and showing a phenotype of multiresistance to antibiotics, has several resistance genes. Using shotgun proteomics and bioinformatics tools, 236 proteins were identified in the surfaceome and 99 proteins in the exoproteome. Although many of these proteins are related to basic cell functions, some are related to virulence and pathogenicity like catalase and isdA, main actors in S. aureus infection, and others are related to antibiotic action or eventually resistance like penicillin binding protein, a cell-wall protein. Studying the proteomes of different subcellular compartments should improve our understanding of this pathogen, a microorganism with several mechanisms of resistance and pathogenicity, and provide valuable data for bioinformatics databases.

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We examine the surface proteome and exoproteome of multiresistant strains.

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We identify bacterial infection proteins in the extracellular proteome.

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Confirmation that moonlighting proteins will extend the localization data.

Economic features of antibiotic resistance: the case of methicillin-resistant Staphylococcus aureus

This paper analyses and updates the economic information regarding methicillin-resistant Staphylococcus aureus (MRSA), including information that has been previously reviewed by other authors, and new information, for the purpose of facilitating health management and clinical decisions. The analysed articles reveal great disparity in the economic burden on MRSA patients; this is mainly due to the diversity of the designs of the studies, as well as the variability of the patients and the differences in health care systems. Regarding prophylactic strategies, the studies do not provide conclusive results that could unambiguously orientate health management. The studies addressing treatments noted that linezolid seems to be a cost-effective treatment for MRSA, mostly because it is associated with a shorter length of stay (LOS) in hospital. However, important variables such as antimicrobial susceptibility, infection type and resistance emergence should be included in these analyses before a conclusion is reached regarding which treatment is the best (most efficient). The reviewed studies found that rapid MRSA detection, using molecular techniques, is an efficient technique to control MRSA. As a general conclusion, the management of MRSA infections implicates important economic costs for hospitals, as they result in higher direct costs and longer LOS than those related to methicillin-susceptible S. aureus (MSSA) patients or MRSA-free patients; there is wide variability in those increased costs, depending on different variables. Moreover, the research reveals a lack of studies on other related topics, such as the economic implications of changes in MRSA epidemiology (community patients and lineages associated with farm animals).

Nasal carriage of coagulase positive staphylococci in patients of a Primary-Healthcare-Center: genetic lineages and resistance and virulence genes

INTRODUCTION

Staphylococcus aureus and Staphylococcus pseudintermedius are highly important due to their capacity for producing diseases in humans and animals, respectively. The aim of the study was to investigate and characterize the coagulase positive Staphylococcus (CoPS) carriage in a Primary Healthcare Center population.

METHODS

Nasal swabs were obtained from 281 non-infectious patients. The CoPS isolates recovered were typed, and their resistance phenotype and genotype, as well as their virulence profiles, were analyzed.

RESULTS

CoPS isolates were recovered from 56/281 patients (19.9%). Fifty-five were S. aureus (19.6%), 54 were methicillin susceptible (MSSA) and one was methicillin resistant (MRSA). The remaining isolate was S. pseudintermedius (0.4%). A high diversity of spa-types (n=40) was detected, with 6 of them being new ones. The multi-locus-sequence-typing of 13 MSSA and one MRSA selected isolates was performed and the STs detected were: ST8, ST15, ST30, ST34, ST121, ST146, ST398, ST554, ST942, ST2499, and ST2500 (the last two STs being new). One MSSA isolate was typed as t1197-ST398-(Clonal complex)CC398. The MRSA isolate was typed as t002-ST146-CC5-SCCmec-IVc, and exhibited a multiresistance phenotype. The detected resistances were: penicillin (76%), macrolides (7%), tetracycline (7%), trimethoprim-sulfamethoxazole (7%), quinolones (7%), and lincosamides (5%). Five isolates contained lukF/lukS-PV genes, 17 tst gene, one eta gene, and two etb gene. The S. pseudintermedius isolate presented a new spa-type (t57) (belonging to a new ST180) and the genes lukS/F-I, siet, se-int, and expB.

CONCLUSIONS

A high genetic diversity of S. aureus was detected. Mention must be made of the identification of MSSA CC398 and S. pseudintermedius isolates in two patients, one of them with animal contact. The detection of the genes lukF/lukS-PV and tst should be noted.

Mini-review: Epidemiology and zoonotic potential of multiresistant bacteria and Clostridium difficile in livestock and food

AIM

Information on the epidemiology of multiresistant bacteria (MRB) with zoonotic potential is growing but still remains quite incomplete. This narrative mini-review provides a general overview of the epidemiology of the most important zoonotic MRB in cattle, swine and poultry in Europe.

METHODS

A literature search was conducted mainly on the PubMed website including articles published until April 2012.

RESULTS

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) especially poses a zoonotic risk to people working in close contact with livestock. These people may become carriers themselves and the hazard of transmission into health-care facilities needs surveillance. Extended-spectrum beta-lactamases (ESBL) producing bacteria are widely spread in both humans and livestock, sharing similar genotypes, especially of the CTX-M-group, which makes a zoonotic transfer very likely. Identical strains of vancomycin-resistant enterococci (VRE) were found both in humans and animals, after ingestion of animal strains transient colonization of the human gut may be possible. Only a few data are available on the transmission of methicillin-resistant coagulase-negative staphylococci (MR-CoNS) between humans and animals. Direct contact to colonized animals may be a risk factor as well as the exchange of resistance genes between human and animal staphylococci. Clostridium difficile (C. difficile) ribotype 078 emerges in livestock and humans and a zoonotic transmission seems probable as genotypes and diseases resemble each other.

CONCLUSION

All discussed MRB and C. difficile are important nosocomial agents which also occur in livestock and were found in foods of animal origin. Further analysis is needed to reveal the exact transmission routes and to perform a reliable risk assessment.

Quantitative assessment of human MRSA risks from swine

The public health community, news media, and members of the general public have expressed significant concern that methicillin-resistant Staphylococcus aureus (MRSA) transmitted from pigs to humans may harm human health. Studies of the prevalence and dynamics of swine-associated (ST398) MRSA have sampled MRSA at discrete points in the presumed causative chain leading from swine to human patients, including sampling bacteria from live pigs, retail meats, farm workers, and hospital patients. Nonzero prevalence is generally interpreted as indicating a potential human health hazard from MRSA infections, but quantitative assessments of resulting risks are not usually provided. This article integrates available data from several sources to construct a conservative (plausible upper bound) probability estimate for the actual human health harm (MRSA infections and fatalities) arising from ST398-MRSA from pigs. The model provides plausible upper bounds of approximately one excess human infection per year among all U.S. pig farm workers, and one human infection per 31 years among the remaining total population of the United States. These results assume the possibility of transmission events not yet observed, so additional data collection may reduce these estimates further.

Phenotypes and genotypes of old and contemporary porcine strains indicate a temporal change in the S. aureus population structure in pigs

INTRODUCTION

Staphylococcus aureus sequence type ST398 has recently gained attention due to the spread of methicillin-resistant strains among people exposed to livestock. The aim of this study was to explore temporal changes in the population structure of S. aureus in pigs over the last 40 years with particular reference to the occurrence of ST398.

METHODS

We analysed a unique collection of 91 porcine strains isolated in six countries between 1973 and 2009 using a biotyping scheme described in the 1970's in combination with spa typing and multi-locus sequence typing (MLST). The collection comprised 32 historical isolates from 1973-1974 (n = 19) and from 1991-2003 (n = 13), and 59 contemporary isolates from 2004-2009. The latter isolates represented the most common MLST types (ST1, ST9, ST97 and ST433) and spa types isolated from pigs in Europe.

RESULTS AND DISCUSSION

S. aureus sequence type ST398 was not found among old isolates from the 1970's or from 1991-2003, suggesting that this lineage was absent or present at low frequencies in pigs in the past. This hypothesis is supported by the observed association of ST398 with the ovine ecovar, which was not described in pigs by studies carried out in the 1970's. In addition, various phenotypic and genotypic differences were observed between old and contemporary isolates. Some biotypes commonly reported in pigs in the 1970's were either absent (human ecovar) or rare (biotype A) among contemporary isolates. Nine clonal lineages found among old porcine isolates are occasionally reported in pigs today (ST8, ST30, ST97, ST387, ST1092, ST2468) or have never been described in this animal host (ST12, ST133, ST1343). These results indicate that the population structure of porcine S. aureus has changed over the last 40 years and confirm the current theory that S. aureus ST398 does not originate from pigs.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) isolates of swine origin form robust biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) colonization of livestock animals is common and prevalence rates for pigs have been reported to be as high as 49%. Mechanisms contributing to the persistent carriage and high prevalence rates of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) strains in swine herds and production facilities have not been investigated. One explanation for the high prevalence of MRSA in swine herds is the ability of these organisms to exist as biofilms. In this report, the ability of swine LA-MRSA strains, including ST398, ST9, and ST5, to form biofilms was quantified and compared to several swine and human isolates. The contribution of known biofilm matrix components, polysaccharides, proteins and extracellular DNA (eDNA), was tested in all strains as well. All MRSA swine isolates formed robust biofilms similar to human clinical isolates. The addition of Dispersin B had no inhibitory effect on swine MRSA isolates when added at the initiation of biofilm growth or after pre-established mature biofilms formed. In contrast, the addition of proteinase K inhibited biofilm formation in all strains when added at the initiation of biofilm growth and was able to disperse pre-established mature biofilms. Of the LA-MRSA strains tested, we found ST398 strains to be the most sensitive to both inhibition of biofilm formation and dispersal of pre-formed biofilms by DNaseI. Collectively, these findings provide a critical first step in designing strategies to control or eliminate MRSA in swine herds.

From pig to pork: methicillin-resistant Staphylococcus aureus in the pork production chain

Methicillin-resistant Staphylococcus aureus (MRSA) is a major global public health concern and could be a food safety issue. Recurrent reports have documented that pig herds are an important reservoir for MRSA, specifically the livestock-associated sequence type 398. The high prevalence of MRSA in pig primary production facilities and the frequent detection of MRSA of the same types in pork and pig meat products raise the question of underlying mechanisms behind the introduction and transmission of MRSA along the pork production chain. A comprehensive review of current literature on the worldwide presence of livestock-associated MRSA in various steps of the pork production chain revealed that the slaughter process plays a decisive role in MRSA transmission from farm to fork. Superficial heat treatments such as scalding and flaming during the slaughter process can significantly reduce the burden of MRSA on the carcasses. However, recontamination with MRSA might occur via surface treating machinery, as a result of fecal contamination at evisceration, or via increased human handling during meat processing. By optimizing processes for carcass decontamination and avoiding recontamination by effective cleaning and personal hygiene management, transmission of MRSA from pig to pork can be minimized.

Isolation and characterization of Staphylococcus aureus strains from a Paso del Norte dairy

The primary purpose of this study was to determine if methicillin-resistant Staphylococcus aureus (MRSA) strains could be identified in the milk of dairy cattle in a Paso del Norte region dairy of the United States. Using physiological and PCR-based identification schemes, a total of 40 Staph. aureus strains were isolated from 29 raw milk samples of 133 total samples analyzed. Pulsed-field gel electrophoresis after digestion with the SmaI enzyme revealed that the 40 confirmed strains were represented by 5 pulsed-field types, which each contained 3 or more strains. Of 7 hospital strains isolated from cows undergoing antibiotic therapy, 3 demonstrated resistance to 3 or more antimicrobial classes and displayed similar pulsed-field gel electrophoresis patterns. A secondary purpose of this study was to elucidate the evolutionary relationships of strains isolated in this study to genomically characterized Staph. aureus strains. Therefore, Roche 454 GS (Roche Diagnostics Corp., Dallas, TX) pyrosequencing was used to produce draft genome sequences of an MRSA raw milk isolate (H29) and a methicillin-susceptible Staph. aureus (PB32). Analysis using the BLASTn database (http://blast.ncbi.nlm.nih.gov/) demonstrated that the H29 draft genome was highly homologous to the human MRSA strain JH1, yet the β-lactamase plasmid carried by H29 was different from that carried by JH1. Genomic analysis of H29 also clearly explained the multidrug resistance phenotype of this raw milk isolate. Analysis of the PB32 draft genome (using BLASTn) demonstrated that this raw milk isolate was most related to human MRSA strain 04-02981. Although PB32 is not a MRSA, the PB32 draft genome did reveal the presence of a unique staphylococcal cassette mec (SCCmec) remnant. In addition, the PB32 draft genome revealed the presence of a novel bovine staphylococcal pathogenicity island, SaPIbovPB32. This study demonstrates the presence of clones closely related to human and (or) bovine Staph. aureus strains circulating in a dairy herd.

Expansion of a plasmid classification system for Gram-positive bacteria and determination of the diversity of plasmids in Staphylococcus aureus strains of human, animal, and food origins

An expansion of a previously described plasmid classification was performed and used to reveal the plasmid content of a collection of 92 Staphylococcus aureus strains of different origins. rep genes of other genera were detected in Staphylococcus. S1 pulsed-field gel electrophoresis (PFGE) hybridizations were performed with 18 representative S. aureus strains, and a high number of plasmids of different sizes and organizations were detected.

Characterization of a cfr-positive methicillin-resistant Staphylococcus epidermidis strain of the lineage ST22 implicated in a life-threatening human infection

The cfr gene was identified in 3 methicillin-resistant Staphylococcus epidermidis (MRSE) isolates of lineage ST22 implicated in a fatal human infection. MRSE isolates displayed an indistinguishable pulsed-field gel electrophoresis profile and SCCmec type III, and showed a multiresistance phenotype. The presence of cfr, fexA, aac(6')-aph(2″), and dfrS1 genes was confirmed by polymerase chain reaction and sequencing. A mutation in 23S rRNA gene (C2534T) and amino acid changes and/or insertions in L3 and L4 proteins were detected. The cfr and fexA genes were located in a conjugative plasmid of approximately 45 kb and in the chromosome.

Prevalence, antibiotic resistance and molecular characterisation of Staphylococcus aureus in pigs at agricultural fairs in the USA

Fairs and petting zoos have been associated with outbreaks of zoonotic disease. Previously, the presence of meticillin-resistant Staphylococcus aureus (MRSA) was documented in commercial pigs; therefore, it was hypothesised that antibiotic-resistant S aureus may also occur in pigs exhibited at agricultural fairs. To test this hypothesis, 157 pigs were swabbed at two state fairs in 2008 to 2009. Both nares were sampled and cultures were grown in enrichment broth, then plated onto selective MRSA plates and blood plates. S aureus was confirmed using phenotypic and molecular methods, and was analysed using spa typing, gene-specific polymerase chain reaction and antibiotic susceptibility testing. The presence of S aureus was confirmed in samples collected from pigs exhibited at USA pig shows. Twenty-five of 157 (15.9 per cent) samples were positive for S aureus. Two isolates (8 per cent) were resistant to meticillin; 23/25 (92 per cent), 14/25 (56 per cent) and 15/25 (60 per cent) were resistant to tetracycline, erythromycin and clindamycin, respectively. spa typing revealed multiple isolates of spa type t034 (9/25, 36 per cent) and t337 (7/25, 28 per cent) and singletons of t002, t209, t526, t1236, t1334, t1683, t3075, t5784 and t5883. These results verify the presence of antibiotic-resistant S aureus in pigs exhibited at USA fairs, suggesting that pigs are a potential reservoir for S aureus within this environment.

MRSA in conventional and alternative retail pork products

In order to examine the prevalence of Staphylococcus aureus on retail pork, three hundred ninety-five pork samples were collected from a total of 36 stores in Iowa, Minnesota, and New Jersey. S. aureus was isolated from 256 samples (64.8%, 95% confidence interval [CI] 59.9%–69.5%). S. aureus was isolated from 67.3% (202/300) of conventional pork samples and from 56.8% (54/95) of alternative pork samples (labeled “raised without antibiotics” or “raised without antibiotic growth promotants”). Two hundred and thirty samples (58.2%, 95% CI 53.2%–63.1%) were found to carry methicillin-sensitive S. aureus (MSSA). MSSA was isolated from 61.0% (183/300) of conventional samples and from 49.5% (47/95) of alternative samples. Twenty-six pork samples (6.6%, 95% CI 4.3%–9.5%) carried methicillin-resistant S. aureus (MRSA). No statistically significant differences were observed for the prevalence of S. aureus in general, or MSSA or MRSA specifically, when comparing pork products from conventionally raised swine and swine raised without antibiotics, a finding that contrasts with a prior study from the Netherlands examining both conventional and “biologic” meat products. In our study spa types associated with “livestock-associated” ST398 (t034, t011) were found in 26.9% of the MRSA isolates, while 46.2% were spa types t002 and t008—common human types of MRSA that also have been found in live swine. The study represents the largest sampling of raw meat products for MRSA contamination to date in the U.S. MRSA prevalence on pork products was higher than in previous U.S.-conducted studies, although similar to that in Canadian studies.

Proteome of a methicillin-resistant Staphylococcus aureus clinical strain of sequence type ST398

Proteomics is a powerful tool to analyze the differences in gene expression of bacterial strains. Staphylococcus aureus has long been recognized as an important pathogen in human disease. In order to investigate this pathogen, the proteome of a clinical methicillin-resistant S. aureus (MRSA) strain of the sequence type ST398 was determined using 2-DE. Using 2-DE we obtained a total of 105 spots the MRSA strain. Furthermore in correlation with bioinformatic databases, they allowed accurate identification and characterization of proteins, resulting in 227 identified proteins. There were found proteins related to basic function of the cell, but also proteins related to virulence like catalase, specific of S. aureus species, and proteins related to antibiotic resistance. Proteins associated with antibiotic resistance or virulence factors are related to genomic databases. The most abundant classes identified involved glycolysis, energy production, one-carbon metabolism, and oxidation-reduction process, all of which reflect an active metabolism. These results highlight the importance of proteomics to deepen in the knowledge of protein expression of MRSA strain of the lineage ST398, microorganism with diverse and important resistance mechanisms. With this proteome map we have an essential tool for a better understanding of this pathogen and providing new data for protein databases. This article is part of a Special Issue entitled: Proteomics: The clinical link.

Skin lesion by methicillin-resistant Staphylococcus aureus ST398-t1451 in a Spanish pig farmer: possible transmission from animals to humans

Skin lesions by methicillin-resistant Staphylococcus aureus (MRSA) of the lineage ST398-t1451 were detected in a pig-farmer in Spain in 2010. Similar MRSA ST398-t1451 strains were also detected in nasal samples from the patient, his brother, and nine pigs from his farm. All human and animal strains were ascribed to the SCCmec type V and the agr type I, showed tetracycline-erythromycin-clindamycin resistances, and harbored the tetK, tetM, and ermC resistance genes. They were negative for all tested toxin genes (lukS/lukF, tst, eta, etb, and etd). All human and animal strains showed closely related pulsed-field gel electrophoresis-ApaI patterns. Possible MRSA transmission from animals to humans is suggested.

Methicillin-resistant Staphylococcus aureus (MRSA) ST398 in a farmer with skin lesions and in pigs of his farm: clonal relationship and detection of lnu(A) gene

Skin infection associated with methicillin-resistant Staphylococcus aureus (MRSA)-ST398 was detected in a pig-farmer, and MRSA-ST398 isolates were also detected in nasal samples of the patient and of 11/12 pigs on his farm. Twelve MRSA isolates were obtained from skin lesions (n = 6) and nasal samples (n = 6) of the patient in two sampling moments and 11 MRSA isolates from nasal samples of pigs. They were typed as t011-SCCmecIVa-agrI and t108-SCCmecV-agrI (patient and pigs) and t588-SCCmecV-agrI (patient). The following resistance genes were detected (number isolates): tet(K) (1), tet(L) (23), tet(M) (13), erm(A) (13), erm(C) (13), msr(A) (11), lnu(A) (21), aph(2'')-acc(6') (3), ant(4') (13), aph(3') (12), dfrS1 (15) and dfrK (22). Seventeen human and animal MRSA-ST398 isolates showed indistinguishable PFGE patterns (A1-spa-t011 or B2-spa-t108) and similar phenotypic-genotypic characteristics, including the presence of the lnu(A) gene, associated with lincomycin resistance. Potential pig-to-human transference of ST398 is suggested in this study. The first detection of the lnu(A) gene in MRSA-ST398 is reported.