Toxigenic characterization, spoilage potential, and antimicrobial susceptibility of coagulase-positive Staphylococcus species isolated from Minas Frescal cheese

This study aimed to identify coagulase-positive staphylococci (CPS) species from 21 samples of clandestine Minas Frescal cheese, investigate the potential for deterioration in psychrotrophic and mesophilic conditions, verify the toxigenic potential of Staphylococcus aureus, and determine the antimicrobial susceptibility profile of toxigenic S. aureus. Species determination was performed based on the detection of β-hemolysis in 5% ovine blood agar; fermentation of mannitol, maltose, and trehalose sugars; and production of acetoin. After species determination, DNA extraction and analysis was performed for S. aureus colonies for genes encoding staphylococcal toxins (eta, etb, tst, sea, seb, sec, sed, and see) using 2 multiplex PCR assays. Isolates identified as toxigenic S. aureus were tested for antimicrobial susceptibility to tetracycline, erythromycin, clindamycin, gentamicin, ciprofloxacin, sulfazotrim, trimethoprim, streptomycin, cefoxitin, vancomycin and enrofloxacin. Elevated CPS counts were observed with an average of >6 log cfu/g. Of the 355 isolates, 177 (49.86%) were identified as S. aureus. Staphylococcus hyicus, Staphylococcus intermedius, Staphylococcus delphini, and Staphylococcus coagulans were identified in 3 (0.84%), 2 (0.56%), 2 (0.56%), and 1 (0.28%) isolates, respectively. Of the total number of S. aureus, 25 (52.08%) were positive for the gene that encodes for toxic shock toxin (TSST-1). Another 16 (33.33%) were positive for the sea gene, and 4 isolates (8.33%) were positive for see and one isolate each was positive for seb (2.08%), sec (2.08%), and etb (2.08%) genes. All isolates demonstrated lipolytic activity under mesophilic and psychrotrophic conditions. S. intermedius and S. hyicus had the most prominent proteolytic potential. Multidrug resistance was observed in most of the potentially toxigenic isolates, with clindamycin having the lowest efficiency (40%), whereas the aminoglycosides (gentamicin and streptomycin) had the highest effectiveness demonstrating inhibition in all evaluated isolates. Methicillin-resistant S. aureus (MRSA) was detected. Minas Frescal cheeses, marketed in the north of Tocantins in the Brazilian Amazon region, do not comply with legal quality standards and pose a public health risk due to the enterotoxigenic potential of multiresistant isolates, in addition to low shelf life of the samples given the high spoilage potential of this microbiota.

Characterization of coagulase-negative staphylococci and macrococci isolated from cheese in Germany

Cheese, especially ripened varieties, harbor a very complex and heterogeneous microbiota. In addition to the desired microorganisms (starter cultures) added during cheese production, potentially harmful bacteria may also enter the production chain. Regarding the latter, the focus of this study was on coagulase-negative staphylococci (CNS) and Macrococcus caseolyticus. Both are known to harbor a variety of genes coding for antibiotic resistance, including mecA, mecB, mecC, and mecD. Coagulase-negative staphylococci or macrococci carrying such genes or other virulence factors should not be present in cheese. Cheese samples (101 in total) were collected from retail sources. Coagulase-negative staphylococci and M. caseolyticus were isolated utilizing selective agars, and species were identified by phenotypical tests and partial sequencing of the sodA gene. The results allowed identification of 53 CNS strains and 19 M. caseolyticus strains. Among the CNS, 11 isolates of Staphylococcus saprophyticus and one Staphylococcus epidermidis isolate were obtained. Both species are potential human pathogens and may thus adversely affect the safety of these food products. Screening for antimicrobial resistance was performed by application of disc diffusion tests, a gradient strip-test, and 14 different PCR tests. Evidence for methicillin resistance (by either positive disc diffusion assay for cefoxitin or by mec PCR) was found in CNS isolates and M. caseolyticus (9 isolates each). Regarding other virulence factors, no genetic determinants for coagulase or the most common staphylococcal enterotoxins sea, seb, sec, sed, and see were detected in any of the CNS or M. caseolyticus isolates by PCR testing. In conclusion, the presence of facultatively pathogenic CNS and carriers of genes for antibiotic resistance in both groups of microorganisms, especially mec genes, and the respective food safety issues need further evaluation and surveillance.

Antibiotic resistance profiles of Staphylococcus spp. from white button mushrooms and handlers

The presence of Staphylococcus spp. has increasingly been reported in food products and poses a public health threat. The aim of this study was to determine the diversity of Staphylococcus spp. and the antibiotic resistance profiles of isolates obtained from freshly harvested and packed ready-to-eat mushrooms (n=432) and handlers’ hands (n=150). A total of 56 Staphylococcus isolates [46.4% (n=26) from hands and 53.6% (n=30) from mushrooms] were recovered belonging to 10 species. Staphylococcus succinus isolates (n=21) were the most prevalent, of which 52.4% came from mushrooms and 47.6% from hands. This was followed by S. equorum isolates [n=12; 91.7% (n=11) from mushrooms and 8.3% (n=1) from hands] and S. saprophyticus [n=9; 66.7% (n=6) from mushrooms and 33.3% (n=3) from hands]. Six isolates that were characterised as multidrug resistant were isolated from hands of handlers. Most (83.9%; n=47) of the 56 isolates were resistant to penicillin [53.2% (n=25) from mushrooms and 46.8% (n=22) from hands] and 14.3% (n=8) were resistant to cephalosporin classes [25% (n=2) from mushrooms and 75% (n=6) from hands], both of which are used to treat staphylococcal infections. Antibiotic resistance genes blaZ [25.0% (n=14) of all isolates of which 71.4% (n=10) were from hands and 28.57% (n=4) from mushrooms], tetL and tetK [both 1.8% (n=1) from hands], mecA [5.4% (n=3) from hands] and ermA [1.8% (n=1) from mushrooms] were detected from the 56 isolates. Only two (25.0%) of the eight methicillin-resistant staphylococci harboured the mecA gene, while only 11 (23%) of the 47 penicillin-resistant isolates harboured the blaZ gene [36.4% (n=4) from mushrooms and 63.6% (n=7) from hands]. Our results demonstrate that food handlers and harvested and packed ready-to-eat mushrooms could be a source of diverse Staphylococcus spp. that exhibit antimicrobial resistance. Clinically relevant S. aureus was only detected on one handler’s hand; however, the isolate was not multidrug resistant. The presence of diverse Staphylococcus spp. on mushrooms and the hands of handlers is a potential public health concern due to their potential to cause opportunistic infections.

Presence and growth prediction of Staphylococcus spp. and Staphylococcus aureus in Minas Frescal cheese, a soft fresh cheese produced in Brazil

Physical-chemical characteristics of Minas Frescal cheese (MFC) favor the growth of Staphylococcus spp. and allow the production of enterotoxins by specific strains. Here, we aimed to characterize the physical-chemical aspects (pH, storage temperature, and salt content) and the presence of Staphylococcus spp. in MFC samples (n = 50) to support a modeling study for the growth by this microorganism. Coagulase-positive staphylococci isolates were obtained and subjected to PCR assays to identify them as Staphylococcus aureus (nuc) and to detect staphylococcal enterotoxin-related genes (sea, seb, sec, sed, see). Staphylococcus aureus growth kinetics (maximum growth rate, Grmax, and lag time) were predicted based on ComBase model and MFC physical-chemical aspects. Mean counts of Staphylococcus spp. ranged from 3.3 to 6.7 log cfu/g, indicating poor hygiene practices during production. Selected isolates (n = 10) were identified as S. aureus, but none presented classical enterotoxin-related genes. pH, temperature, and salt content ranged from 5.80 to 6.62, 5°C to 12°C, and 0.85% to 1.70%, respectively. The Grmax values ranged from 0.012 to 0.419 log cfu/g per h. Independent of the storage temperature, the lowest Grmax values (0.012 to 0.372 log cfu/h) were obtained at pH 5.80 associated with salt content of 1.7%; independent of the pH and salt content, the best temperature to avoid staphylococcal growth was 7.5°C. Hygienic conditions during MFC production must be adopted to avoid staphylococcal contamination, and storage at temperatures lower than 7.5°C can prevent staphylococcal growth and the potential production of enterotoxins.

Photodynamic Inactivation Using Natural Bioactive Compound Prevents and Disrupts the Biofilm Produced by Staphylococcus saprophyticus

Staphylococcus saprophyticus, the food-borne bacteria present in dairy products, ready-to-eat food and environmental sources, has been reported with antibiotic resistance, raising concerns about food microbial safety. The antimicrobial resistance of S. saprophyticus requires the development of new strategies. Light- and photosensitizer-based antimicrobial photodynamic inactivation (PDI) is a promising approach to control microbial contamination, whereas there is limited information regarding the effectiveness of PDI on S. saprophyticus biofilm control. In this study, PDI mediated by natural bioactive compound (curcumin) associated with LED was evaluated for its potential to prevent and disrupt S. saprophyticus biofilms. Biofilms were treated with curcumin (50, 100, 200 µM) and LED fluence (4.32 J/cm², 8.64 J/cm², 17.28 J/cm²). Control groups included samples treated only with curcumin or light, and samples received neither curcumin nor light. The action was examined on biofilm mass, viability, cellular metabolic activity and cytoplasmic membrane integrity. PDI using curcumin associated with LED exhibited significant antibiofilm activities, inducing biofilm prevention and removal, metabolic inactivation, intracellular membrane damage and cell death. Likewise, scanning electronic microscopy observations demonstrated obvious structural injury and morphological alteration of S. saprophyticus biofilm after PDI application. In conclusion, curcumin is an effective photosensitizer for the photodynamic control of S. saprophyticus biofilm.

Non-aureus Staphylococci and Bovine Udder Health: Current Understanding and Knowledge Gaps

Despite considerable efforts to control bovine mastitis and explain its causes, it remains the most costly and common disease of dairy cattle worldwide. The role and impact of non-aureus staphylococci (NAS) in udder health are not entirely understood. These Gram-positive bacteria have become the most frequently isolated group of bacteria in milk samples of dairy cows and are associated with (mild) clinical and subclinical mastitis. Different species and strains of NAS differ in their epidemiology, pathogenicity, virulence, ecology and host adaptation, and antimicrobial resistance profiles. They have distinct relationships with the microbiome composition of the udder and may also have protective effects against other mastitis pathogens. Some appear to persist on the skin and in the teat canal and udder, while others seem to be transient residents of the udder from the environment. Analyzing genotypic and phenotypic differences in individual species may also hold clues to why some appear more successful than others in colonizing the udder. Understanding species-level interactions within the microbiome and its interactions with host genetics will clarify the role of NAS in bovine mastitis and udder health.

Virulence Factors in Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) have emerged as major pathogens in healthcare-associated facilities, being S. epidermidis, S. haemolyticus and, more recently, S. lugdunensis, the most clinically relevant species. Despite being less virulent than the well-studied pathogen S. aureus, the number of CoNS strains sequenced is constantly increasing and, with that, the number of virulence factors identified in those strains. In this regard, biofilm formation is considered the most important. Besides virulence factors, the presence of several antibiotic-resistance genes identified in CoNS is worrisome and makes treatment very challenging. In this review, we analyzed the different aspects involved in CoNS virulence and their impact on health and food.

Antimicrobial resistance of Staphylococcus spp. isolated from organic and conventional Minas Frescal cheese producers in São Paulo, Brazil

The genus Staphylococcus is recognized worldwide as a cause of bacterial infections in humans and animals. Antibiotics used in dairy cattle combined with ineffective control can increase antimicrobial resistance. The objective of this study was to characterize 95 Staphylococcus strains isolated from organic and conventional Minas Frescal cheese production regarding antibiotic resistance (phenotype and genotype), presence of sanitizer-resistant genes and biofilm-formation genes, and SCCmec typing. Most strains (25.3%) showed higher resistance to penicillin, followed by oxacillin (21.1%) and clindamycin (11.6%). Among antibiotic resistance genes, the most prevalent were blaZ (25.3%), mecA (13.7%), lsaB (6.3%), msrA (4.2%), ant4 (3.2%), and tetM (2.1%); among sanitizer-resistance genes they were qacA/B (5.3%) and qacC (6.3%); and among biofilm, bap (4.2%), icaA (29.5%), icaD (41.1%). However, there was no statistically significant difference between organic and conventional dairy products, possibly due to the lack of synthetic antibiotic use on conventional farms during the sample collection period. Methicillin-resistant Staphylococcus aureus (MRSA) had their SCCmec identified as types I and IVc, and the methicillin-resistant coagulase-negative staphylococci had nontypeable SCCmec. These results suggest that there are antibiotic-resistant strains in both organic and conventional Minas Frescal cheese production in the state of São Paulo, Brazil. This supports the idea that improved quality control is needed from the milking stage up to the final product.

Microbiological quality and safety of Brazilian artisanal cheeses

The establishment of norms that regulates the production and trade of Brazilian Artisanal Cheeses (BAC) has been stimulating many small farmers for this activity. The predominance of lactic acid bacteria (LAB) is a typical characteristic of BAC, which confers desirable attributes to artisanal cheeses. However, these products can be contaminated by other microbial groups, including those that indicate hygienic failures during production and may cause spoilage, or even microorganisms that pose risks to consumers' health. A systematic review of the literature published from January 1996 to November 2020 was carried out to identify scientific data about production characteristics and microbiological aspects of BAC, with a major focus on quality and safety status of these traditional products. Studies that fulfilled the inclusion criteria indicated that artisanal chesses produced in Brazil still do not satisfactorily meet the microbiological criteria established by the national laws, mainly due to the high counts of coagulase-positive Staphylococcus and coliforms. Despite low prevalence, pathogens such as Salmonella and Listeria monocytogenes were isolated in some BAC. This review contributed to better understanding microbiological aspects of BAC, the data compiled by the authors highlight the need to improve hygiene practices along the production chain of these traditional cheeses.

Prevalence and distribution of resistance and enterotoxins/enterotoxin-like genes in different clinical isolates of coagulase-negative Staphylococcus

Background

Coagulase-negative staphylococcus (CoNS) is considered to be the major reservoirs for genes facilitating the evolution of S. aureus as a successful pathogen. The present study aimed to determine the occurrence of genes conferring resistance to fluoroquinolone, determining of the prevalence of insertion sequence elements IS256, IS257 and different superantigens (SAgs) among CoNS isolates obtained from various clinical sources.

Materials and methods

The current study conducted on a total of the 91 CoNS species recovered from clinical specimens in Hamadan hospitals in western Iran in 2017–2019. The antimicrobial susceptibility testing was performed using disk diffusion method and the presence of the IS256 and IS257, genes conferring resistance to fluoroquinolone and enterotoxins/enterotoxin-like encoding genes were investigated by polymerase chain reaction (PCR) method.

Results

Among genes encoding classic enterotoxins, sec was the most frequent which was carried by 48.4% of the 91 isolates, followed by seb in 27.5% of the isolates. None of the CoNS isolates was found to be positive to enterotoxin-like encoding genes. In 11(12%) of all isolates that were phenotypically resistant to levofloxacin, 9 isolates (81.8%) were positive for gyrB, 8 isolates (72.7%) were positive for gyrA, 8 isolates (72.7%) harbored grlB and 7 isolates (63.6%) were found to carry grlA. The IS256 and IS257 were identified in 31.8% and 74.7% of the isolates, respectively. The results of statistical analysis showed a significant association between the occurrence of staphylococcal enterotoxins (SEs) encoding genes and antimicrobial resistance.

Conclusion

Antimicrobial resistant determinants and SEs are co-present in clinical CoNS isolates that confer selective advantage for colonization and survival in hospital settings. The coexistence of insertion elements and antibiotic resistance indicate their role in pathogenesis and infectious diseases.

Farming Practices Influence Antibiotic Resistance and Biogenic Amine Capacity of Staphylococci from Bulk Tank Ewe's Milk

Staphylococci are one of the main microorganisms responsible for intramammary infections in sheep, causing important economic losses for farmers and eventually health problems in humans, especially by the consumption of dairy products made with raw milk containing toxic compounds, such as biogenic amines or antibiotic resistant bacteria. This study aimed to check the presence and safety of staphylococci in bulk tank ewe's milk from different farms, and to determine the relationship between the presence of these staphylococci and farming practices, by applying nonlinear canonical correlation models (OVERALS). Two-hundred and fifty-nine staphylococci from milk samples from eighteen farms were genotyped and representative isolates of the major clusters were identified as belonging to Staphylococcus (S.) aureus, S. epidermidis, S. arlettae, S. lentus, S. simulans, and S. chromogenes species. Identified isolates were assayed in terms of their safety, by evaluating resistance to antimicrobial drugs and the aminobiogenic capacity, using both phenotypic and genetic assays. Antibiotic resistance phenotypic assay revealed that 82.9% were resistant to some antibiotics, although in the genotypic assay only the genes tetM, ermB, ermC, and grlA were detected. Fifty-three percent were high biogenic amine (BA) producers, being putrescine the most produced amine. A lowered risk of finding antibiotic-resistant and BA-producing staphylococci is related to some farming methods such as enrolling in a breeding program, use of good farming practices, postdipping teat disinfection, hygienic livestock housing, or periodic check of the milking machine.

[Profile of antimicrobial resistance in isolates of Staphylococcus spp. obtained from bovine milk in Colombia]

Staphylococcus spp. is one of the pathogens that cause bovine mastitis and may present multiple resistance to different antimicrobial groups. The aim of this study was to phenotypically identify Staphylococcus spp. isolates obtained from bovine milk and to characterize their antimicrobial resistance profile. The 101 strains were classified by phenotypic tests, their resistance to oxacillin, cefoxitin, penicillin, ampicillin, tetracycline, kanamycin, sulfamethoxazole / trimethoprim, clindamycin and erythromycin was determined by the Kirby-Bauer technique and the presence of resistance genes by PCR. A total of 65 strains was S. aureus and 36 strains were coagulase-negative staphylococci (CoNS). We found different patterns of resistance to antibiotics evaluated in strains of S. aureus and CoNS, only the resistance to ampicillin was found associated with the species (p<0.005). In the 101 strains, the mecA gene was detected in 27%, aph(3')-IIIa in 75.2%, aac(6')/aph(2")-3 in 47.4%, ant(4')-Ia in 32.7%, tetM in 63% and tetK in 43.6%; however, no association was found with the resistance to penicillin, ampicillin, cefoxitin, kanamycin and tetracycline, respectively (p>0.05). On the other hand, the blaZ gene was found in 59.4% of the 101 strains and the ermCgene in 62.3%, which was associated with resistance to β-lactams and macrolides, respectively (p<0.001). In this study, antimicrobial multiresistance was found in S. aureus and CoNS strains. This finding impacts on the dairy industry, representing a risk to public health.

Characterization of coagulase-negative staphylococci from brining baths in Germany

Brining is an important step in cheese making, and using brine baths for this purpose is common practice in German dairies. Time of brining, brine concentration, and composition of the complex and heterogeneous microbiota, including coagulase-negative staphylococci (CNS), contribute to the ripening and taste of cheese. As well as producing staphylococcal enterotoxins, some CNS show antibiotic resistance; therefore, we isolated 52 strains of presumptive CNS from cheese brines from 13 factories in Germany. Species identification by sodA gene sequencing revealed that 50 isolates were CNS: 31 Staphylococcus saprophyticus, 4 Staphylococcus carnosus, 4 Staphylococcus equorum, 3 Staphylococcus sciuri, 2 Staphylococcus hominis, and 2 Staphylococcus warneri. One isolate each was identified as Staphylococcus epidermidis, Staphylococcus pasteurii, Staphylococcus succinus, and Staphylococcus xylosus. Further subtyping of the Staph. saprophyticus isolates to the subspecies level revealed the presence of 6 Staph. saprophyticus ssp. saprophyticus. Using pulsed-field gel electrophoresis with the identified Staph. saprophyticus strains, 12 independent clones were identified, resulting in the exclusion of 18 strains from further testing. In 19 of the remaining 32 CNS isolates, resistance to antibiotics was observed. Resistance was found against oxacillin (17), penicillin (5), and cefoxitin (1). Four isolates expressed resistance to both oxacillin and penicillin. No resistance was found to enrofloxacin, tetracycline, gentamicin, or erythromycin. Then, PCR analysis for antibiotic resistance genes was performed for 22 different genes. Only genes blaZ and bla_TEM were found in 7 isolates. These isolates were selected for challenge tests with different concentrations of lactic acid and NaCl to examine whether expression of antibiotic resistance was influenced by these stressors. An increase in the minimal inhibitory concentration from 0 to 2.0 µg/mL was seen for trimethoprim/sulfamethoxazole only in one isolate of Staph. saprophyticus at an increased lactic acid concentration. Finally, all isolates were tested for genetic determinants (entA, entB, entC, entD, and entE) of the most common staphylococcal enterotoxins; none of these genes were detected. We found no indication for unacceptable risks originating from the isolated CNS.

Study of the effectiveness of staphylococcins in biopreservation of Minas fresh (Frescal) cheese with a reduced sodium content

Reducing salt content in foods such as cheeses, while limiting the growth of spoilage microorganisms and foodborne pathogens, is a difficult challenge. One method that may prove useful is use of staphylococcins, which are bacteriocins produced by staphylococci. Therefore, staphylococcin antimicrobial activity against six strains of S. aureus isolated from cheese was tested aiming at their industrial application in biopreservation of Minas fresh (Frescal) cheese with reduced sodium content. Three staphylococcins were selected for these tests: Pep 5, aureocin A53 and lysostaphin. All three staphylococcins proved to be bacteriolytic against all six strains of S. aureus. The antimicrobial activity of the partially purified staphylococcins was subsequently investigated against strains S. aureus Q1 and QJ3 in cheese matrices (6.0 log CFU/g) with different NaCl contents (control, a 25% reduction, and a 50% reduction), kept under refrigeration at 4 °C, for 21 days. Both strains were shown to be of concern for food industry as they carry the SEA, SEB and SEH enterotoxin genes, and are resistant to β-lactam drugs and moderate biofilm formers when grown in TSB. When used singly, Pep5, aureocin A53 and lysostaphin reduced approximately 95%, 99% and 99.99% of the viable cell counts, respectively, irrespective of the sodium content of the cheese matrix. The combined action of aureocin A53 and Pep5 resulted in an additional and significant reduction (p < 0.05) of ~1.0 log CFU/g when compared with the reduction caused by the use of either one singly. The combined action of lysostaphin and aureocin A53 or lysostaphin and Pep5 resulted in a reduction similar to or slightly smaller (p > 0.05) than that observed when lysostaphin was employed singly. Lysostaphin also proved to reduce the number of the staphylococcal viable cells to a level (~ 2.0 log CFU/g) at which enterotoxin production should not reach a sufficient quantity to cause food poisoning. Therefore, lysostaphin may have a practical application in the food industry to control staphylococcal contamination of Minas fresh cheese with a sodium content reduced up to 50%, providing consumers with more safe options to reduce their intake of sodium.

Recovery of Antimicrobials and Bioaccessible Isoflavones and Phenolics from Soybean (Glycine max) Meal by Aqueous Extraction

Soybeans display strategic potential in food security as a source of protein and functional bioactives for human consumption. Polyphenols and other bioactive compounds can be recovered after an aqueous extraction from soybean meal, a byproduct of soy oil refining. The objective of the present study was to compile and quantify compounds from soybean oil refinery by-products, providing information about valuable bioactive phytochemicals, their bioaccessibility and potential bioactivities. Genistin, daidzin, glycitin and malonylgenistin were the predominant isoflavones, and the overall bioaccessibility of their glycosidic forms was of nearly 75%. Sixteen phenolics were identified and caffeic acid, 5-caffeoylquinic chlorogenic acid and hesperidin were the most predominant. Approximately 30% of gallic acid, syringic acid, vanillic acid and myricetin were released and the antioxidant capacity of aqueous extract was enhanced after simulated in vitro gastro intestinal digestion. The ability of aqueous soybean meal extract to inhibit lipid peroxidation was higher than natural and synthetic food antioxidants. Antimicrobial activity against several foodborne pathogens and antitumoral activity towards human glioblastoma cell line were also observed, but the aqueous extract showed no cytotoxicity to healthy murine cells. Compounds derived from the aqueous soybean meal extract have the potential to be used as health promoting agents.

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.

Comparative genome analysis of 24 bovine-associated Staphylococcus isolates with special focus on the putative virulence genes

Non-aureus staphylococci (NAS) are most commonly isolated from subclinical mastitis. Different NAS species may, however, have diverse effects on the inflammatory response in the udder. We determined the genome sequences of 20 staphylococcal isolates from clinical or subclinical bovine mastitis, belonging to the NAS species Staphylococcus agnetis, S. chromogenes, and S. simulans, and focused on the putative virulence factor genes present in the genomes. For comparison we used our previously published genome sequences of four S. aureus isolates from bovine mastitis. The pan-genome and core genomes of the non-aureus isolates were characterized. After that, putative virulence factor orthologues were searched in silico. We compared the presence of putative virulence factors in the NAS species and S. aureus and evaluated the potential association between bacterial genotype and type of mastitis (clinical vs. subclinical). The NAS isolates had much less virulence gene orthologues than the S. aureus isolates. One third of the virulence genes were detected only in S. aureus. About 100 virulence genes were present in all S. aureus isolates, compared to about 40 to 50 in each NAS isolate. S. simulans differed the most. Several of the virulence genes detected among NAS were harbored only by S. simulans, but it also lacked a number of genes present both in S. agnetis and S. chromogenes. The type of mastitis was not associated with any specific virulence gene profile. It seems that the virulence gene profiles or cumulative number of different virulence genes are not directly associated with the type of mastitis (clinical or subclinical), indicating that host derived factors such as the immune status play a pivotal role in the manifestation of mastitis.

Antibiotic Resistance Genetic Markers and Integrons in White Soft Cheese: Aspects of Clinical Resistome and Potentiality of Horizontal Gene Transfer

Antibiotic resistance poses an important threat to global public health and has become a challenge to modern medicine. The occurrence of antibiotic-resistant bacteria in a broad range of foods has led to a growing concern about the impact that food may have as a reservoir of antibiotic resistance genes. Considering Minas Frescal Cheese (MFC)-a typical Brazilian white soft cheese-and its economic and cultural values, in this study, medically relevant antimicrobial-resistance genetic markers (AR genes) were screened, and the occurrence of integrons were evaluated in manufactured MFC using culture-independent approaches. Through a fingerprinting analysis, the tested MFCs were brand-clustered, indicating reproducibility along the production chain. A common core of resistance markers in all brands evaluated and related antimicrobials such as β-lactams, tetracyclines, quinolones, and sulfonamide was detected. Several other markers, including efflux pumps and aminoglycosides-resistance were distributed among brands. Class 1 and 2 integrons were observed, respectively, in 77% and 97% of the samples. The presence of AR genes is of special interest due to their clinical relevance. Taken together, the data may suggest that the production chain of MFC might contribute to the spread of putative drug-resistant bacteria, which could greatly impact human health. Furthermore, detection of class 1 and class 2 integrons in MFC has led to discussions about resistance gene spread in this traditional cheese, providing evidence of potential horizontal transfer of AR genes to human gut microbiota.

Enterotoxin production and antimicrobial susceptibility in Staphylococci isolated from traditional raw milk cheeses in Serbia

This study was undertaken to determine the prevalence of coagulase positive staphylococci (CPS) by examining a total of 71 raw milk cheeses. Additionally, enterotoxigenicity, antimicrobial susceptibility and the presence of mecA and mecC genes in the staphylococcal isolates were investigated. The isolation and enumeration procedure of CPS followed the International Organization for Standardization (ISO) standard. The presumptive staphylococci were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) using the VITEK MS system. VIDAS® Staph enterotoxin II assay was used for the detection of classical enterotoxins. Antimicrobial susceptibility testing (AST) was accomplished performing the disk diffusion method. All suspected methicillin resistant staphylococci were investigated for the presence of mecA and mecC genes by PCR assay. A high prevalence (87.32%) of CPS was detected in the cheeses at contamination levels up to 5.58 log CFU g^-1. Among 47 staphylococcal isolates screened for enterotoxin production, only one isolate, identified as S. hyicus, was confirmed as being enterotoxigenic. Resistance to penicillin (63.70%) was the most common resistance among the tested Staphylococcus aureus isolates. The dominant phenotypic resistance patterns in coagulase negative staphylococci (CNS) were resistance to ofloxacin and fusidic acid. All CNS isolates were susceptible to the clinically important antibiotics clindamycin, chloramphenicol, gentamicin, linezolid, rifampicin and trimethoprim-sulfamethoxazole. The mecA and mecC genes were not detected. To the best of our knowledge, this is the first study concerning evaluation of the presence of methicillin resistant staphylococci (MRS) in dairy products in Serbia.

Plectranthus amboinicus essential oil and carvacrol bioactive against planktonic and biofilm of oxacillin- and vancomycin-resistant Staphylococcus aureus

Background

The emergence of multidrug-resistant bacteria is a worldwide concern and in order to find an alternative to this problem, the occurrence of antimicrobial compounds in Plectranthus amboinicus essential oil was investigated. Thus, this study aims to determine susceptibility of Staphylococcus aureus isolated from food to antibiotics, P. amboinicus essential oil (PAEO) and carvacrol.

Methods

Leaves and stem of P. amboinicus were used for extraction of essential oil (PAEO) by hydrodistillation technique and EO chemical analysis was performed by gas chromatography coupled to a mass spectrometer. S. aureus strains (n = 35) isolated from food and S. aureus ATCC 6538 were used to evaluate the antimicrobial and antibiofilm activity of PAEO and carvacrol. All strains (n = 35) were submitted to antimicrobial susceptibility profile by disk diffusion method. Determination of MIC and MBC was performed by microdilution technique and antibiofilm activity was determined by microtiter-plate technique with crystal violet assay and counting viable cells in Colony Forming Units (CFU).

Results

Carvacrol (88.17%) was the major component in the PAEO. Antibiotic resistance was detected in 28 S. aureus strains (80%) and 12 strains (34.3%) were oxacillin and vancomycin-resistant (OVRSA). From the 28 resistant strains, 7 (25%) showed resistance plasmid of 12,000 bp. All strains (n = 35) were sensitive to PAEO and carvacrol, with inhibition zones ranging from 16 to 38 mm and 23 to 42 mm, respectively. The lowest MIC (0.25 mg mL⁻¹) and MBC (0.5 mg mL⁻¹) values were observed when carvacrol was used against OVRSA. When a 0.5 mg mL⁻¹ concentration of PAEO and carvacrol was used, no viable cells were found on S. aureus biofilm.

Conclusion

The antibacterial effect of carvacrol and PAEO proves to be a possible alternative against planktonic forms and staphylococcal biofilm.