Methicillin-resistant Staphylococcus aureus: a controversial food-borne pathogen

Prevalence, Molecular Characterization, and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus from Different Origins in Sichuan Province, China, 2007-2015

Methicillin-resistant Staphylococcus aureus (MRSA) is a major multidrug-resistant (MDR) opportunistic pathogen that is responsible for nosocomial infections worldwide. The emergence of MRSA in food-producing animals has heightened concerns regarding the presence of MRSA in foods having an animal origin. The objectives of this study were to determine the prevalence of MRSA in different sources, including retail food, food-producing animals, and food handlers in Sichuan province. During 2007-2015, S. aureus was isolated from samples having different origins. Susceptibilities of MRSA to a panel of 12 antimicrobial agents were determined according to Clinical and Laboratory Standards Institute (CSLI) procedures. Pulsed-field gel electrophoresis, spa typing, staphylococcal chromosomal cassette (SCC) mec typing, and multilocus sequence typing (MLST) were used to characterize the relationship between these isolates. A total of 756 S. aureus were isolated from 11,067 samples. Of these, 52 isolates were classified as MRSA based on the presence of mecA genes. An antimicrobial susceptibility assay indicated that CHL-CLI-ERY-FOX-OXA-PEN-TET (n = 10) and CHL-CIP-CLI-ERY-FOX-OXA-PEN-TET (n = 8) were the two predominant MDR profiles in the isolates. Using 60% genetic similarity as a cutoff, the 52 MRSA isolates were grouped into 6 clusters having 34 pulsotypes. MLST typing showed seven multilocus sequence types (STs) with ST59 and ST9 being the most common. Six SCCmec types were identified in all MRSA isolates. The MRSA isolates had relatively low prevalence in Sichuan province. Clonal expansion is not involved in the dissemination of MRSA from food origins. Considering the threat of MRSA to public health, further surveillance is required to monitor the prevalence of food-related MRSA.

Nonconventional starter cultures of coagulase-negative staphylococci to produce animal-derived fermented foods, a SWOT analysis

Coagulase-negative staphylococci (CNS) are ubiquitous micro-organisms that are commonly present on animal skin and animal-derived foods. They are members of the beneficial microbial consortia of several fermented food products where they contribute to quality. Currently, only a few CNS species are included in commercial starter cultures, although many other ones with promising properties have been isolated from diverse food ecosystems. In the present study, a Strengths-Weaknesses-Opportunities-Threats (SWOT) analysis of the potential use of unconventional CNS starter cultures for the fermentation of animal-derived foods is carried out. An overview of both their desirable and worrisome metabolic traits is given. In general, the application of innovative CNS-based starter cultures offers opportunities to modulate flavour, improve the safety and health aspects and develop novel colour development strategies for clean label products. Yet, their implementation is often not straightforward as nontrivial obstacles or threats are encountered, which relate to technological, food safety and legal concerns. As most of the desirable and undesirable characteristics of CNS species are strain dependent, a case-by-case evaluation is needed when evaluating specific strains for their potential use as novel starter cultures.

Methicillin-Resistant Staphylococcus aureus in Poultry and Poultry Meat: A Meta-Analysis

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that colonizes and infects various host species and has been found in the poultry production chain, raising concerns about possible transmission from farm to fork. The objective of this study was to use meta-analytical methods to estimate the pooled prevalence of MRSA in chickens, turkeys, chicken meat, and turkey meat. Three electronic databases (PubMed, LILACS, and SciELO) were searched to establish MRSA prevalence from 51 studies published from 2003 through May 2017. The heterogeneity was assessed, and the pooled MRSA prevalence was calculated by using the random effects model according to the method of DerSimonian and Laird. Pooled MRSA prevalence (95% confidence interval [CI]) in turkeys, turkey meat, broilers, and chicken meat was 36% (1 to 78%), 13% (1 to 28%), 5% (2 to 9%), and 5% (3 to 8%), respectively. South America had the highest MRSA prevalence (27%; 95% CI, 17 to 37%), and North America had the lowest (1%; 95% CI, 0 to 2%). Livestock-associated MRSA has been isolated from poultry and poultry meat, indicating that this variant can spread from farm to fork. The presence of MRSA in poultry and poultry meat poses risks to public health, and steps should be taken to mitigate the contamination and spread of this bacterium along the poultry production chain.

Manipulation of Innate and Adaptive Immunity by Staphylococcal Superantigens

Staphylococcal superantigens (SAgs) constitute a family of potent exotoxins secreted by Staphylococcus aureus and other select staphylococcal species. SAgs function to cross-link major histocompatibility complex (MHC) class II molecules with T cell receptors (TCRs) to stimulate the uncontrolled activation of T lymphocytes, potentially leading to severe human illnesses such as toxic shock syndrome. The ubiquity of SAgs in clinical S. aureus isolates suggests that they likely make an important contribution to the evolutionary fitness of S. aureus. Although the apparent redundancy of SAgs in S. aureus has not been explained, the high level of sequence diversity within this toxin family may allow for SAgs to recognize an assorted range of TCR and MHC class II molecules, as well as aid in the avoidance of humoral immunity. Herein, we outline the major diseases associated with the staphylococcal SAgs and how a dysregulated immune system may contribute to pathology. We then highlight recent research that considers the importance of SAgs in the pathogenesis of S. aureus infections, demonstrating that SAgs are more than simply an immunological diversion. We suggest that SAgs can act as targeted modulators that drive the immune response away from an effective response, and thus aid in S. aureus persistence.

Tomatidine Is a Lead Antibiotic Molecule That Targets Staphylococcus aureus ATP Synthase Subunit C

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of deadly hospital-acquired infections. The discovery of anti-Staphylococcus antibiotics and new classes of drugs not susceptible to the mechanisms of resistance shared among bacteria is imperative. We recently showed that tomatidine (TO), a steroidal alkaloid from solanaceous plants, possesses potent antibacterial activity against S. aureus small-colony variants (SCVs), the notoriously persistent form of this bacterium that has been associated with recurrence of infections. Here, using genomic analysis of in vitro-generated TO-resistant S. aureus strains to identify mutations in genes involved in resistance, we identified the bacterial ATP synthase as the cellular target. Sequence alignments were performed to highlight the modified sequences, and the structural consequences of the mutations were evaluated in structural models. Overexpression of the atpE gene in S. aureus SCVs or introducing the mutation found in the atpE gene of one of the high-level TO-resistant S. aureus mutants into the Bacillus subtilis atpE gene provided resistance to TO and further validated the identity of the cellular target. FC04-100, a TO derivative which also possesses activity against non-SCV strains, prevents high-level resistance development in prototypic strains and limits the level of resistance observed in SCVs. An ATP synthesis assay allowed the observation of a correlation between antibiotic potency and ATP synthase inhibition. The selectivity index (inhibition of ATP production by mitochondria versus that of bacterial ATP synthase) is estimated to be >10⁵-fold for FC04-100.

Basis of Virulence in Enterotoxin-Mediated Staphylococcal Food Poisoning

The Staphylococcus aureus enterotoxins are a superfamily of secreted virulence factors that share structural and functional similarities and possess potent superantigenic activity causing disruptions in adaptive immunity. The enterotoxins can be separated into two groups; the classical (SEA-SEE) and the newer (SEG-SElY and counting) enterotoxin groups. Many members from both these groups contribute to the pathogenesis of several serious human diseases, including toxic shock syndrome, pneumonia, and sepsis-related infections. Additionally, many members demonstrate emetic activity and are frequently responsible for food poisoning outbreaks. Due to their robust tolerance to denaturing, the enterotoxins retain activity in food contaminated previously with S. aureus. The genes encoding the enterotoxins are found mostly on a variety of different mobile genetic elements. Therefore, the presence of enterotoxins can vary widely among different S. aureus isolates. Additionally, the enterotoxins are regulated by multiple, and often overlapping, regulatory pathways, which are influenced by environmental factors. In this review, we also will focus on the newer enterotoxins (SEG-SElY), which matter for the role of S. aureus as an enteropathogen, and summarize our current knowledge on their prevalence in recent food poisoning outbreaks. Finally, we will review the current literature regarding the key elements that govern the complex regulation of enterotoxins, the molecular mechanisms underlying their enterotoxigenic, superantigenic, and immunomodulatory functions, and discuss how these activities may collectively contribute to the overall manifestation of staphylococcal food poisoning.

Antibiotic Resistance Profiling, Analysis of Virulence Aspects and Molecular Genotyping of Staphylococcus aureus Isolated in Sicily, Italy

Staphylococcus aureus is the major cause of foodborne diseases worldwide. In this retrospective study, 84 S. aureus strains were characterized. The collection comprises 78 strains isolated during 1998 and 2014 from dairy products and tissue samples from livestock bred for dairy production in Sicily. One isolate was obtained from a pet (dog), one from an exotic animal (a circus elephant), and four human isolates were obtained during a severe food poisoning outbreak that occurred in Sicily in 2015. All the strains were characterized by pulsed-field gel electrophoresis (PFGE), for antibiotic resistance and presence of toxin genes. PFGE results showed 10 different pulsotypes, with three relatively frequent and three unique. The antibiotic resistance profiling showed that penicillin G (35.7%) and tetracycline (20.2%) resistance is largely spread. Most isolates contained at least one toxin gene making them a potential threat for public health. Enterotoxin sec gene was observed in 28.6% and seg in 23.8% of the strains, respectively; the human isolates were the only ones to concurrently harbor both seg and sei genes. In addition, 24 isolates were randomly selected and analyzed by multilocus sequence typing. Interestingly, the analysis showed the presence of 12 sequence types (STs), of which 6 were novel. One of them, ST700, was detected in 29% of the isolates and was found to be spread throughout Sicily. ST700 has been present in the island for almost 16 years (1998–2014) and it shows no host preference since it was isolated from different ruminant species. Four human isolates shared both the pulsotype (PT10) and the sequence type (ST9), as well as the virulence genes (seg-sei); this observation suggests that the isolates originated from a single clone, although they were obtained from two different individuals.

Phenotypic and genotypic characterization of antibiotic resistance of methicillin-resistant Staphylococcus aureus isolated from hospital food

BACKGROUND

Pathogenic biotypes of the Methicillin-resistant Staphylococcus aureus (MRSA) strains are considered to be one of the major cause of food-borne diseases in hospitals. The present investigation was done to study the pattern of antibiotic resistance and prevalence of antibiotic resistance genes of different biotypes of the MRSA strains isolated from various types of hospital food samples.

METHODS

Four-hundred and eighty-five raw and cooked hospital food samples were cultured and MRSA strains were identified using the oxacillin and cefoxitin disk diffusion tests and mecA-based PCR amplification. Isolated strains were subjected to biotyping and their antibiotic resistance patterns were analyzed using the disk diffusion and PCR methods.

RESULTS

Prevalence of S. aureus and MRSA were 9.69 and 7.62%, respectively. Meat and chicken barbecues had the highest prevalence of MRSA. Prevalence of bovine, ovine, poultry and human-based biotypes in the MRSA strains were 8.10, 8.10, 32.43 and 48.64%, respectively. All of the MRSA strains recovered from soup, salad and rice samples were related to human-based biotypes. MRSA strains harbored the highest prevalence of resistance against penicillin (100%), ceftaroline (100%), tetracycline (100%), erythromycin (89.18%) and trimethoprim-sulfamethoxazole (83.78%). TetK (72.97%), ermA (72.97%), msrA (64.86%) and aacA-D (62.16%) were the most commonly detected antibiotic resistance genes.

CONCLUSIONS

Pattern of antibiotic resistance and also distribution of antibiotic resistance genes were related to the biotype of MRSA strains. Presence of multi-drug resistance and also simultaneous presence of several antibiotic resistance genes in some MRSA isolates showed an important public health issue Further researches are required to found additional epidemiological aspects of the MRSA strains in hospital food samples.

WITHDRAWN: Incidence of methicillin resistant Staphylococcus aureus (MRSA) in microbial community of cancer patients and evaluation of their resistant pattern

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