Staphylococcus aureus causes a wide range of hospital infections. Often, these infections involve epidemic methicillin-resistant S. aureus (MRSA) strains that are transferred by health care workers to patients. In order to detect outbreaks that are caused by epidemic strains, the clinical isolates have to be typed. Multilocus sequence typing (MLST) relies on the sequence analysis of housekeeping genes and is used to allocate the strains to sequence types (ST), which can be grouped into clonal complexes (CC). This method has provided a detailed insight into the population structure of MRSA and methicillin-susceptible S. aureus (MSSA) strains (1). Finer discrimination is achieved by pulsed-field gel electrophoresis (PFGE) and spa typing (2). All of these methods need additional experimentation.In matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), different spectra or signatures of cell extracts (3, 4, 5, 6) or whole cells (7,8,9,10,11,12) could be identified for different strains or groups of strains. An increasing number of laboratories use MALDI-TOF MS for the identification of S. aureus. However, the differences in the signatures of the strains have not been evaluated so far, because the discriminatory threshold of the software used in clinical settings is set up to assign the isolate to a species. To this end, more subtle differences are ignored. Another reason is that, so far, MALDI-TOF MS of whole bacterial cells has been employed in a heuristic manner, and for most species, the identities of the compounds that are detected in the measurements are unknown. Thus, the spectra are not well understood, and the variations in the signatures cannot be interpreted.In principle, two spectra might differ by signal intensity, loss of a signal, or by the shift of a signal. Variations in signal intensity are probably caused by expression differences, which might be directly correlated with culture conditions and, therefore, do not give unambiguous information about a genotype of the strain. The loss of a signal is caused by the total failure to express a protein or peptide, which in turn might indicate a mutation causing a frameshift or stop codon, but might also depend on culture conditions, mutations of regulatory factors, or sample preparation. Thus, there is no clear-cut correlation between the loss of a signal and a genotype. In contrast, peak shifts (i.e., loss of a signal coupled to the appearance of a new signal, both of which are correlated to the same peptide) correspond to point mutations in the genes of the peptides detected in the analysis; the mutation leads to an amino acid exchange that alters the molecular weight of the corresponding gene product.In order to characterize the clonal lineages of S. aureus in the MALDI-TOF MS, this work was aimed at the identification of the peptides that are detected in the spectra and that show mass variations between the clonal complexes of S. aureus. To this end, we analyzed the spectra of 401 S. aureus strains, concentrating on...

No abstract

Livestock-associated bacteria with resistance to two or more antibiotic drug classes have heightened our awareness for the consequences of antibiotic consumption and spread of resistant bacterial strains in the veterinary field. In this study we assessed the prevalence of concomitant colonization with livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) and enterobacteriaceae expressing extended-spectrum betalactamases (ESBL-E) in farms at the German-Dutch border region. Nasal colonization of pigs with MRSA (113/547 (20.7%)) was less frequent than rectal colonization with ESBL-E (163/540 (30.2%)). On the individual farm level MRSA correlated with ESBL-E recovery. The data further provide information on prevalence at different stages of pig production, including abattoirs, as well as in air samples and humans living and working on the farms. Notably, MRSA was detected in stable air samples of 34 out of 35 pig farms, highlighting air as an important MRSA transmission reservoir. The majority of MRSA isolates, including those from humans, displayed tetracycline resistance and spa types t011 and t034 characteristic for LA-MRSA, demonstrating transmission from pigs to humans. ESBL-E positive air samples were detected on 6 out of 35 farms but no pig-to-human transmission was found. Detection of ESBL-E, e.g. mostly Escherichia coli with CTX-M-type ESBL, was limited to these six farms. Molecular typing revealed transmission of ESBL-E within the pig compartments; however, related strains were also found on unrelated farms. Although our data suggest that acquisition of MRSA and ESBL-E might occur among pigs in the abattoirs, MRSA and ESBL-E were not detected on the carcasses. Altogether, our data define stable air (MRSA), pig compartments (ESBL-E) and abattoir waiting areas (MRSA and ESBL-E) as major hot spots for transmission of MRSA and/or ESBL-E along the pig production chain.

The species Staphylococcus argenteus was separated recently from Staphylococcus aureus (Tong S.Y., F. Schaumburg, M.J. Ellington, J. Corander, B. Pichon, F. Leendertz, S.D. Bentley, J. Parkhill, D.C. Holt, G. Peters, and P.M. Giffard, 2015). The objective of this work was to characterise the genome of a non-human S. argenteus strain, which had been isolated from the faeces of a wild-living western lowland gorilla in Gabon, and analyse the spectrum of this species in matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The full genome sequence revealed a scarcity of virulence genes and absence of resistance genes, indicating a decreased virulence potential compared to S. aureus and the human methicillin-resistant S. argenteus isolate MSHR1132. Spectra obtained by MALDI-TOF MS and the analysis of available sequences in the genome databases identified several MALDI-TOF MS signals that clearly differentiate S. argenteus, the closely related Staphylococcus schweitzeri and S. aureus. In conclusion, in the absence of biochemical tests that identify the three species, mass spectrometry should be employed as method of choice.

g Colonization of livestock with bacteria resistant to antibiotics is considered a risk for the entry of drug-resistant pathogens into the food chain. For this reason, there is a need for novel concepts to address the eradication of drug-resistant commensals on farms. In the present report, we evaluated the decontamination measures taken on a farm contaminated with methicillin-resistant Staphylococcus aureus (MRSA) and Enterobacteriaceae expressing extended-spectrum ␤-lactamases (ESBL-E). The decontamination process preceded the conversion from piglet breeding to gilt production. Microbiological surveillance showed that the decontamination measures eliminated the MRSA and ESBL-E strains that were detected on the farm before the complete removal of pigs, cleaning and disinfection of the stable, and construction of an additional stable meeting high-quality standards. After pig production was restarted, ESBL-E remained undetectable over 12 months, but MRSA was recovered from pigs and the environment within the first 2 days. However, spa (Staphylococcus aureus protein A gene) typing revealed acquisition of an MRSA strain (type t034) that had not been detected before decontamination. Interestingly, we observed that a farmworker who had been colonized with the prior MRSA strain (t2011) acquired the new strain (t034) after 2 months. In summary, this report demonstrates that decontamination protocols similar to those used here can lead to successful elimination of contaminating MRSA and ESBL-E in pigs and the stable environment. Nevertheless, decontamination protocols do not prevent the acquisition of new MRSA strains. N umerous studies have highlighted the emergence of methicillin-resistant Staphylococcus aureus (MRSA) (1-4) and Enterobacteriaceae expressing extended-spectrum ␤-lactamases (ESBL-E) (5-7) in livestock production, particularly in pigs. Hence, there is an ongoing debate whether the use of antibiotics in food animal production represents an important source of continuous spread of MRSA and ESBL-E to humans (8-10). Farmers are confronted with two different consequences of this problem: the potential danger of animal colonization with drug-resistant bacteria for (i) humans living on or in the vicinity of farms (11-13) and for (ii) consumers of animal products (14-18). Indeed, livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) have been found in humans living and working in close contact with pigs and also in hospitals in rural areas (11,(19)(20)(21)(22)(23)(24)(25). In contrast, ESBL-E could possibly be transferred from animals to humans via meat products (16,(26)(27)(28). As a consequence, control points to limit transmission of resistant pathogens "from stable to table" have been demanded (29).Notably, bacteria not only persist on/in the living animal but also on surfaces that are in contact with the animals, such as barn walls and equipment (30, 31). LA-MRSA isolates were detected in dust samples from the investigated breeding farms in Germany as part of the EFSA (European Food Safe...