Prevalence and characterization of Staphylococcus aureus isolated from goat milk powder processing plants

Rapid detection of major enterotoxin genes and antibiotic resistance of Staphylococcus aureus isolated from raw milk in the Yazd province, Iran

INTRODUCTION

Raw milk is a nutrient-rich food, but it may harbour harmful bacteria, such as enterotoxigenic Staphylococcus aureus (S. aureus), which can cause staphylococcal food poisoning. Antibiotic resistance of S. aureus in raw milk can increase the risk of such infections, particularly among susceptible individuals.

OBJECTIVE

This study aimed to investigate the prevalence of enterotoxin genes a, d, g, i and j and the antibiotic resistance of S. aureus isolated from raw milk samples.

METHODS

During a 6-month sampling period, 60 raw milk specimens were obtained from diverse locations in Yazd province, Iran. Antibiogram profiling was conducted via the disc diffusion method. In addition, staphylococcal enterotoxin (SE) genes a, d, g, i, and j were detected through real-time PCR analysis.

RESULTS

Bacteriological assays confirmed the presence of S. aureus in 11 samples (18.3%). All isolates demonstrated 100% resistance to penicillin G but exhibited sensitivity to vancomycin, while resistance to other antibiotics ranged from 36.4% to 45.5%. The prevalence of enterotoxin genes in these strains showed variable distribution, with sea being the predominant SE (45.5%), followed by sed (36.4%), seg (18.2), sej and sei (9.1% each).

CONCLUSIONS

This study discovered the presence of multiple enterotoxins in S. aureus strains obtained from raw milk samples. These strains also demonstrated resistance to a variety of antibiotics. Since enterotoxigenic S. aureus is known to cause human food poisoning, monitoring food hygiene practices, especially during raw milk production, is critical.

Genotypic diversity of staphylococcal enterotoxin B gene (seb) and its association with molecular characterization and antimicrobial resistance of Staphylococcus aureus from retail food

To investigate the expression pattern of staphylococcal enterotoxin B (SEB) in food and the genotypic diversity of SEB-encoding gene in association with molecular characteristics and antimicrobial resistance of S. aureus, 498 isolates from retail food were screened for seb gene and detected for SEB production in S. aureus. In addition, the seb nucleotide sequences, virulence genes, resistance genes, antimicrobial susceptibility and molecular characteristics of S. aureus were examined. A total of 45 (9.0 %) seb-positive S. aureus strains were identified, all of which expressed SEB. The detection rate of SEB-production strains was significantly higher from dairy-related sources than those from other sources (P < 0.05). In vitro simulations showed that S. aureus could grow and express SEB in both milk and pork, with SEB expression exceeding 20 ng/g after 1 day of storage at room temperature. There were 2 distinct SEB genotyping (SEB1 and SEB2) in the SEB amino acid sequences of the 45 isolates, including 4 amino acid differences (Ala-13Val, Ser14Ala, Asn192Ser, and Met222Leu). There was no significant difference (P > 0.05) in SEB production between SEB1 and SEB2 genotyping strains. Based on MLST clustering analysis, the same molecular type strains were found to have the same SEB genotyping, virulence gene profile, resistance gene profile and drug resistance profile. Among them, the dominant molecular types of SEB1 and SEB2 strains were CC1-ST188-t189 and CC59-ST59-t437, respectively. Compared to the CC1-ST188-t189 clonal strain, the CC59-ST59-t437 clonal strain carried a higher number of virulence and resistance genes and exhibited a broader resistance profile. Therefore, understanding the characteristics of the strains and their expression patterns in food can be effective in preventing food poisoning incidents.

Lebanese fermented goat milk products: From tradition to meta-omics

Ambriss, Serdaleh and Labneh El Darff are traditional Lebanese products made from fermented goat's milk. A questionnaire completed by 50 producers of these products showed that they are prepared by periodic percolation either by milk or by Laban in amphora or goat skins during the lactation season. Production is carried out on a small scale and in a limited number of production units, often by elderly people, resulting in a real risk of disappearance of these products and loss of the corresponding microbial resources. In this study, 34 samples from 18 producers were characterized by culture-dependent and -independent analyses. The results obtained from these two methods were radically different, the latter revealing in Ambriss and Serdaleh the co-dominance of Lactobacillus kefiranofaciens, a fastidious-growing species, and Lactococcus lactis in a viable but not culturable state. Overall, their composition is reminiscent of kefir grains. Phylogenomic and functional analyses of the genomes of the key species Lb. kefiranofaciens have revealed differences from those found in kefir, particularly in their polysaccharide genes, which may explain the absence of grains. However, Labneh El Darff displayed a dominance of Lactobacillus delbrueckii, probably due to the addition of Laban. In addition, the study identified several zoonotic pathogens, including Streptococcus parasuis, which dominated in one sample. Metagenome-Assembled Genome (MAG) analysis indicated that this pathogen acquired lactose utilization genes through horizontal gene transfer. The contamination of the herd with Mycoplasmopsis agalactiae in the Chouf region was also revealed by MAG analysis of the Serdaleh samples. Antibiotic resistance genes were detected in most of the samples, particularly in the Serdaleh ones, where the dominant L. lactis strains possessed a plasmid with a multi-resistance island. Finally, this study paves the way for further analyses to shed light on the resilience of these ecosystems established in amphora or in goatskins and to improve hygiene practices for milk production.

Antibiotics Resistance and Virulence of Staphylococcus aureus Isolates Isolated from Raw Milk from Handmade Dairy Retail Stores in Hefei City, China

Handmade dairy products, which retain the nutrients in milk to the greatest extent, have become popular in China recently. However, no investigation regarding the characteristics of Staphylococcus aureus (S. aureus) in raw milk of handmade dairy retail stores has been reported. Here, we investigated the antimicrobial susceptibility, virulence, biofilm formation, and genetic diversity of S. aureus in raw milk from handmade dairy retail stores in Hefei, China. After 10 months of long-term monitoring, 50 S. aureus strains were isolated from 69 different raw milk samples, of which 6 were positive for methicillin-resistant S. aureus (MRSA). The resistance rates of these isolates to ampicillin, erythromycin, kanamycin, tetracycline, sulfamethoxazole-trimethoprim, gentamicin, ofloxacin, oxacillin, chloramphenicol, and doxycycline were 56, 54, 40, 24, 22, 22, 18, 14, 8 and 6%, respectively. All 50 isolates were susceptible to vancomycin and 29 strains (58%) showed multidrug resistance phenotype. For enterotoxins genes, selp (14%) was detected the most frequently, followed by sea (6%), sec (4%), sei (4%), ser (4%), selj (4%), and seh (2%). By microplate assay, 32 and 68% of the strains showed moderate and strong biofilm formation ability, respectively. Fifty isolates were discriminated into nine spa types, and the most common spa typing was t034 (42%). The results of this study indicate that S. aureus from raw milk may constitute a risk concerning food poisoning, and more attention must be given to awareness and hygienic measures in the food industry.

Hazard of Staphylococcal Enterotoxins in Food and Promising Strategies for Natural Products against Virulence

Staphylococcal enterotoxins (SEs) secreted by Staphylococcus aureus frequently contaminate food and cause serious foodborne diseases but are ignored during food processing and even cold-chain storage. Notably, SEs are stable and resistant to harsh sterilization environments, which can induce more serious hazards to public health than the bacterium itself. Therefore, it is necessary to develop promising strategies to control SE contamination in food and improve food safety. Natural products not only have various pharmaceutical properties, such as antimicrobial and antitoxin activities, but they are also eco-friendly, safe, nutritive, and barely drug-resistant. Here, the hazards of SEs and the promising natural compounds with different inhibitory mechanisms are summarized and classified. The key points of future research and applications for natural products against bacterial toxin contamination in food are also prospected. Overall, this review may provide enlightening insights for screening effective natural compounds to prevent foodborne diseases caused by bacterial toxins.

Recent Insights Into Processing Approaches and Potential Health Benefits of Goat Milk and Its Products: A Review

Goat milk is considered to be a potential source of various macro- and micro-nutrients. It contains a good proportion of protein, fat, carbohydrates, and other nutritional components which help in promoting nutritional and desirable health benefits. Goat milk is considered to be superior in terms of numerous health benefits, and lower risk of allergy, when compared to the milk of other species. Several processing techniques such as pasteurization, ultrafiltration, microfiltration, and ultrasound have been employed to enhance the quality and shelf life of goat milk and its products. The diverse range of goat milk-based products such as yogurt, cheese, fermented milk, goat milk powder, and others are available in the market and are prepared by the intervention of advanced processing technologies. Goats raised in pasture-based feeding systems are shown to have a better milk nutritional composition than its counterpart. Goat milk contains potential bioactive components, which aids in the maintenance of the proper metabolism and functioning of the human body. This review gives insight into the key nutritional ingredients and bioactive constituents present in goat milk and their potential role in the development of various functional foods using different processing technologies. Goat milk could be considered as a significant option for milk consumption in infants, as compared to other milk available.

Isolation and Genetic Characterization of Vancomycin-resistant and mecC+ Methicillin-resistant Staphylococcus aureus Strains in Clinical Samples of Bojnurd, Northeastern Iran

Background: The emergence of antibiotic-resistant Staphylococcus aureus strains is one of the major concerns about the various staphylococcal infections. Vancomycin is one the most important effective antibiotics on staphylococcal lethal infections. To date, vancomycin-resistant strains are increasingly isolated in different parts of the world, and it is alerting. Objectives: The current study was designed to evaluate the prevalence, and antibiotic susceptibility pattern of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) isolates in the main tertiary hospital of Bojnurd, Iran. Methods: Staphylococcus aureus isolates were collected from different clinical samples in Imam Reza Hospital of Bojnurd. After identification of isolates through using conventional methods, they were evaluated by agar screening, disk diffusion, and minimum inhibitory concentration (MIC) methods to determine resistance to vancomycin and methicillin. We also performed polymerase chain reaction (PCR) for the detection of mecA, mecC, vanA, and vanB genes. After confirmation of vancomycin resistance, genetic analysis was performed using SCCmec, agr, and spa typing, and multilocus sequence typing (MLST) methods on VRSA isolates. Results: We found four vancomycin-resistant isolates (1.29%). Also, 75% of isolates were resistant to cefoxitin. Using the PCR method, mecA was found in 73%, mecC in 0.64%, and vanA in 1.29% of isolates. Interestingly, we found two mecC positive isolates in MRSA isolates. The alpha-hemolysin (81.81%) and enterotoxin C (27%) had the highest and lowest toxins percentage, respectively. Among mecA positive isolates, SCCmec IV (37%), SCCmec III (31.27%), SCCmec I (14%), SCCmec II (11%), and SCCmec V (5.7%) were the most prevalent SCCmec types, respectively. It should be noted that the two mecC positive isolates belonged to SCCmec XI. Agr I (76.29%) was the highest agr type. We recognized t037 as the dominant spa type, and ST239, ST6, ST97, and ST8 were found in VRSA isolates. Conclusions: In our study, the frequency of mecA genes in MRSA isolates was very high. It seems that the resistant isolates belonged to endemic clones of Iran.

Prevalence, Drug Resistance, and Virulence Genes of Potential Pathogenic Bacteria in Pasteurized Milk of Chinese Fresh Milk Bar

Fresh Milk Bar (FMB), an emerging dairy retail franchise, is used to instantly produce and sell pasteurized milk and other dairy products in China. However, the quality and safety of pasteurized milk in FMB have received little attention. The objective of this study was to investigate the prevalence, antimicrobial resistance, and virulence genes of Escherichia coli, Staphylococcus aureus, and Streptococcus in 205 pasteurized milk samples collected from FMBs in China. Four (2.0%) isolates of E. coli, seven (3.4%) isolates of S. aureus, and three (1.5%) isolates of Streptococcus agalactiae were isolated and identified. The E. coli isolates were resistant to amikacin (100%), streptomycin (50%), and tetracycline (50%). Their detected resistance genes include aac(3)-III (75%), blaTEM (25%), aadA (25%), aac(3)-II (25%), catI (25%), and qnrB (25%). The S. aureus isolates were mainly resistant to penicillin G (71.4%), trimethoprim-sulfamethoxazole (71.4%), kanamycin (57.1%), gentamicin (57.1%), amikacin (57.1%), and clindamycin (57.1%). blaZ (42.9%), mecA (28.6%), ermB (14.3%), and ermC (14.3%) were detected as their resistance genes. The Streptococcus strains were mainly resistant to tetracycline (66.7%) and contained the resistance genes pbp2b (33.3%) and tetM (33.3%). The virulence genes eae and stx2 were only found in one E. coli strain (25%), sec was detected in two S. aureus strains (28.6%), and bca was detected in one S. agalactiae strain (33.3%). The results of this study indicate that bacteria with drug resistance and virulence genes isolated from the pasteurized milk of FMB are a potential risk to consumers' health.

Prevalence and Characteristics of Staphylococcus aureus Isolated From Retail Raw Milk in Northern Xinjiang, China

Staphylococcus aureus is one of the main pathogens causing mastitis in dairy animals worldwide. It is an important opportunistic pathogen of raw milk, and the enterotoxin causes significant food poisoning. Monitoring the antibiotic resistance of S. aureus in raw milk is helpful for a risk assessment of S. aureus. In this study, 62 strains (43.1%) of S. aureus were isolated from 144 retail raw milk samples of different varieties from four regions in northern Xinjiang, China. Among them, the isolation rates at Shihezi, Hami, Altay, and Tacheng were 58.1% (54/93), 12.9% (4/31), 18.2% (2/11), and 22.2% (2/9), respectively. The isolation rate of positive strains in cow milk samples was the highest (61.7%, 37/60), followed by camel milk (35.9%, 23/64), and horse milk (10.0%, 2/20). The results of the classical virulence genes test showed that 12.9% (8/62) of the isolates carried at least one virulence gene. The main genotype was see (6.5%, 4/62), followed by sea+sec (3.2%, 2/62), sea (1.6%, 1/62), and sec (1.6%, 1/62). The analysis of 13 resistance genes and the susceptibility to 12 different antibiotics of 62 isolates showed that 80.6% (50/62) of the strains were resistant to at least one antibiotic, and 46.8% (29/62) were resistant to three or more antibiotics. The isolated strains had the highest resistance rate to penicillin (72.6%, 45/62), and 25.8% (16/62) of the isolates carried the blaZ resistance gene. In addition, 32 strains (51.6%, 32/62) of methicillin-resistant S. aureus were detected. All isolates had the ability to form biofilms. The pulsed-field gel electrophoresis results showed that the 47 isolates revealed 13 major pulsotypes (P1–P13) and 26 subtypes with 80% similarity, indicating the overall genetic diversity in the distribution area and sources of the samples. These findings indicate that S. aureus causes serious pollution of raw milk in northern Xinjiang, which has a negative effect on public health. Therefore, control measures and continuous monitoring should be undertaken to ensure the quality and safety of raw milk.

Prevalence and characterization of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus isolated from retail yak butter in Tibet, China

This study aimed to investigate the prevalence, molecular characteristics and antibiotic resistance of Staphylococcus aureus isolates from yak butter in Tibet, China. A total of 218 yak butter samples were collected from retail stores in Tibet and screened for Staph. aureus. Furthermore, the virulence genes, resistance genes, antimicrobial susceptibility, and molecular typing [pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, and staphylococcal protein A (spa) typing] of Staph. aureus isolates were detected. The results showed that 12.4% of yak butter samples were contaminated with Staph. aureus, including 5 samples positive for methicillin-resistant Staph. aureus (MRSA). Among all isolates, 96.3% harbored one or more virulence genes, including classical (sea and sec), novel enterotoxin-encoding genes (seh, sek, sel, and seq), and hemolysin genes (hla and hld). All isolates were resistant to at least 2 different antibiotic classes, and the isolates were most commonly resistant to sulfonamides, β-lactams, and erythromycin. For resistance genes, blaZ (74.1%) was most frequently detected, followed by dfrG (51.9%), erm(B) (22.2%), mecA (18.5%), tet(K) (14.8%), aph(2″)-Ia, aph(3')-III, and ant(6)-Ia (11.1% for each), and erm(C) (7.4%). We detected 8 spa types, 6 sequence types (ST), and 5 clonal complex (CC) types. In addition, 1 isolate of Staph. aureus was nontypeable. We found that CC1-ST1-t559 (55.6%) was the most predominant clone, followed by CC59-ST59-t437 (11.1%), CC5-ST5-t002 (7.4%), CC1-ST1, CC1-ST1-t114, CC1-ST573-t4938, CC1-ST573-t8915, CC30-ST30-t021, and CC25-ST25-t167 (3.7% for each). For PFGE typing, a total of 5 clusters and 15 pulsotypes were generated, and some isolates from different samples showed indistinguishable pulsotypes. Our findings suggest that yak butter produced in Tibet, China, could be contaminated by Staph. aureus strains, including MRSA strains, carrying various virulence and resistance genes, representing multiple antimicrobial resistance phenotypes. The presence of potentially virulent and antibiotic-resistant Staph. aureus strains in yak butter poses a potential threat to consumers, and appropriate measures need to be taken in the production chain to reduce the occurrence of Staph. aureus in yak butter.

Malonyl-proteome profiles of Staphylococcus aureus reveal lysine malonylation modification in enzymes involved in energy metabolism

BACKGROUND

Protein lysine malonylation, a novel post-translational modification (PTM), has been recently linked with energy metabolism in bacteria. Staphylococcus aureus is the third most important foodborne pathogen worldwide. Nonetheless, substrates and biological roles of malonylation are still poorly understood in this pathogen.

RESULTS

Using anti-malonyl-lysine antibody enrichment and high-resolution LC-MS/MS analysis, 440 lysine-malonylated sites were identified in 281 proteins of S. aureus strain. The frequency of valine in position - 1 and alanine at + 2 and + 4 positions was high. KEGG pathway analysis showed that six categories were highly enriched, including ribosome, glycolysis/gluconeogenesis, pentose phosphate pathway (PPP), tricarboxylic acid cycle (TCA), valine, leucine, isoleucine degradation, and aminoacyl-tRNA biosynthesis. In total, 31 malonylated sites in S. aureus shared homology with lysine-malonylated sites previously identified in E. coli, indicating malonylated proteins are highly conserved among bacteria. Key rate-limiting enzymes in central carbon metabolic pathways were also found to be malonylated in S. aureus, namely pyruvate kinase (PYK), 6-phosphofructokinase, phosphoglycerate kinase, dihydrolipoyl dehydrogenase, and F1F0-ATP synthase. Notably, malonylation sites were found at or near protein active sites, including KH domain protein, thioredoxin, alanine dehydrogenase (ALD), dihydrolipoyl dehydrogenase (LpdA), pyruvate oxidase CidC, and catabolite control protein A (CcpA), thus suggesting that lysine malonylation may affect the activity of such enzymes.

CONCLUSIONS

Data presented herein expand the current knowledge on lysine malonylation in prokaryotes and indicate the potential roles of protein malonylation in bacterial physiology and metabolism.

Occurrence, Antimicrobial Resistance Patterns, and Genetic Characterization of Staphylococcus aureus Isolated from Raw Milk in the Dairy Farms over Two Seasons in China

This study investigated the occurrence and resistance rates of Staphylococcus aureus strains isolated from raw milk in the dairy farms over two seasons (spring and autumn) and across four regions that included 11 provinces in China. In total, 750 raw milk samples from the 405 dairy farms were collected. Fifteen antimicrobial agents were tested for antimicrobial resistance via disk diffusion tests, and PCR tests were performed to identify drug resistance genes of S. aureus isolates. Out of 750 samples, 276 (36.8%) were positive for S. aureus, with 150 (41.1%) being positive in spring and 126 (32.7%) being positive in autumn. The occurrence rate of S. aureus in northeastern China (45%) was higher than that in western China (33%) and southern China (31.9%), respectively, and the rate significantly (p < 0.05) differed from those of western China and southern China. Of 276 isolates, 261 (94.6%) strains were resistant to more than 1 antimicrobial drug, and 193 (69.9%) strains were multidrug resistant. The blaZ (46.3%), dfrG (35.5%), and tetM (27.2%) genes were detected at a high frequency in the S. aureus strains. Our data revealed a variation (p < 0.05) in the resistance patterns in the different regions and across the two seasons. The occurrence and drug resistance rates of S. aureus isolated from raw milk obtained from dairy farms may still cause severe problems in China.

Recombinase polymerase amplification with polymer flocculation sedimentation for rapid detection of Staphylococcus aureus in food samples

Currently, rapid, sensitive, and convenient visual detection methods for Staphylococcus aureus (S. aureus) are scarce. In this study, a novel detection method based on recombinase polymerase amplification (RPA) and polymer flocculation sedimentation (PFS) was developed. Twelve effective primer combinations derived from four forward primers F1, F2, F3, F4, and three reverse primers R1, R2, R3 targeting the nuc gene of S. aureus were designed and screened by a polymerase chain reaction and RPA methods. RPA reaction conditions, including temperature, time, and volume as well as PEG8000 and NaCl concentrations range, were optimized. Moreover, the specificity and sensitivity of the RPA-PFS assay were further analyzed. Finally, the potential use of the RPA-PFS assay was evaluated using artificially S. aureus contaminated food samples, including pork, beef, shrimp, fish, cheese, cabbage, leftover rice, egg, milk, and orange juice. Results showed that the SA5 (F2/R2) combination was the optimal primer candidate. The optimal temperature range, the shortest time and the minimal volume of RPA reaction were 40-42 °C, 10 min and 10 μL, respectively and the optimal PEG8000/NaCl concentrations were 0.2 g/mL and 2.5 M, respectively, for the adsorption between magnetic beads and RPA products. The RPA-PFS method could detect as little as 13 fg genomic DNA of S. aureus and was also specific for five target S. aureus as well as twenty-seven non-target foodborne bacteria. The limit of detection of RPA-PFS for S. aureus in artificially contaminated food samples was 38 CFU/mL (g). Besides, RPA-PFS has directly been judged by the naked eye and has totally taken less than 20 min. In short, the assay RPA-PFS developed in this study is a rapid, sensitive, and specific visual detection method for S. aureus.

Avaliação da contaminação por Staphylococcus aureus em queijo coalho artesanal elaborado com leite de cabra produzido no estado de Pernambuco

RESUMO A fabricação de queijo coalho artesanal elaborado com leite de cabra é composta pelas etapas de obtenção do leite, refrigeração, manipulação e armazenamento, que aumentam o risco de contaminação do produto. Objetivou-se neste estudo avaliar o nível de contaminação por Staphylococcus aureus em amostras de queijo coalho artesanal produzido com leite de cabra cru no estado de Pernambuco, Brasil, bem como avaliar a concordância entre a técnica oficial da Instrução Normativa nº62/2003 (Mapa) e a técnica molecular (gene nuc) para identificar S. aureus no queijo. Houve crescimento de colônias típicas de Staphylococcus aureus em 100% das amostras, e a contagem variou de 7,0×103 a 8,6×106 UFC/g. Das 30 amostras analisadas, 18 (60,0%) apresentaram valores superiores ou iguais a 105UFC/g, e 21 (70,0%) estavam contaminadas por S. aureus. A concordância entre os métodos de diagnóstico de S. aureus em queijo coalho caprino foi moderada. O nível de contaminação dos queijos revela a necessidade de ações de melhoria das condições de elaboração do produto, a fim de garantir um produto seguro aos consumidores.

Epidemiological Characteristics of Staphylococcus Aureus in Raw Goat Milk in Shaanxi Province, China

Goat milk has been frequently implicated in staphylococcal food poisoning. The potential risk of raw goat milk contaminated by Staphylococcus aureus (S. aureus) in Shaanxi province of China is still not well documented. This study investigated the prevalence, antibiotic resistance, as well as virulence-related genes of S. aureus from raw goat milk samples in Shaanxi, China. A total of 68 S. aureus isolates were cultured from 289 raw goat milk. Most of the isolates were resistant to penicillin and oxacillin, although 41.18%, 33.82%, and 29.41% of the isolates expressed resistance to piperacillin, trimethoprim-sulfamethoxazole, and ciprofloxacin, respectively. Our data demonstrated that 91.18% of the isolates produced biofilm, of which 54.41% isolates belonged to high-biofilm producers. In addition, genotypic analysis of biofilm related genes (fnbA, clfB, fnbB, cna) revealed that 91.18% of the isolates harbored at least one of the genes, in which the most prevalent genes were fnbA (66. 17%), clfB (48.53%), and fnbB (26.47%). 94.8% of the isolates contained at least one toxin-related gene, of which seb (76.47%), tsst (36.76%), and sea (23.53%) genes were the more frequently detected. Further analysis revealed a positive association between fnbA, clfB, fnbB, seb, tsst, and sea genes and certain antibiotic resistance. The results indicated that raw goat milk samples contaminated by S. aureus can be a potential risk to public health.

Short communication: High frequency of β-lactam-resistant Staphylococcus aureus in artisanal coalho cheese made from goat milk produced in northeastern Brazil

Reports of β-lactam-resistant Staphylococcus aureus in artisanal goat cheese are increasing, and this phenomenon is relevant to public health. The objective of the present study was to determine the prevalence of S. aureus strains carrying the blaZ and mecA resistance genes, as well as the genes encoding the staphylococcal enterotoxins SEA, SEB, SEC, SED, SEE, and TSST-1 in artisanal coalho cheese made from goat milk produced in northeastern Brazil. We used biochemical and molecular tests to characterize 54 S. aureus isolates found in artisanal coalho cheese collected from commercial establishments producing animal products in 11 municipalities of Pernambuco State, Brazil. A PCR analysis revealed that 42.6% (23/54) of the isolates were positive for the blaZ gene, and 7.4% (4/54) were resistant to methicillin by phenotypic testing. We did not detect mecA or any genes encoding enterotoxins. The presence of S. aureus carriers of the blaZ gene and the identification of methicillin-resistant S. aureus strains are of concern for the health of consumers of this type of cheese.

Prevalence, resistance pattern, and molecular characterization of Staphylococcus aureus isolates from healthy animals and sick populations in Henan Province, China

Background

Staphylococcus aureus is one of the most prevalent pathogens and a causative agent of a variety of infections in humans and animals. A total of 640 samples were collected from healthy animals and patients from 2013 to 2014 in Henan Province, China, to investigate the prevalence and perform molecular characterization of S. aureus. Antimicrobial resistance and virulence genes were determined and pulsed-field gel electrophoresis (PFGE) and staphylococcal cassette chromosome mec (SCCmec) typing were performed.

Results

Overall, 22.3% (n = 143) of the samples were positive for S. aureus. The prevalence of methicillin-resistant S. aureus (MRSA) was 5.59%. Capsular polysaccharide locus type 5 (Cap5; 56.64%) was the dominant serotype. S. aureus strains showed high resistance to penicillin (96.50%), ciprofloxacin (52.45%), amikacin (67.83%), erythromycin (96.50%), lincomycin (97.20%), and tetracycline (68.53%) and 109 (76.2%) isolates harbored six or more tested resistance genes. The most predominant resistance genes were aphA (52.45%), ermC (53.15%), and tetM (52.45%). Eighty-seven (60.8%) isolates harbored six or more tested virulence genes. The most predominant enterotoxin genes were sed (20.28%), sej (20.98%), sep (14.69%), and set (37.76%). The prevalence of lukED gene was (57.34%), and a small number of isolates carried pvl (5.59%) and TSST-1 (2.80%). A total of 130 (82.52%) isolates could be typed by PFGE with SmaI digestion. PFGE demonstrated that 45 different patterns (P) that were grouped into 17 pulsotypes and 28 separate pulsotypes using a 90% cut-off value. A total of 118 (82.52%) isolates were successfully typed by spa, and 26 spa types were identified, t15075 (14.00%) and t189 (12.59%) were the most common types. SCCmec types were detected from eight MRSA isolates, with the most prevalent type being SCCmec IVa. MRSA-SCCmec Iva-t437 was observed in human isolates.

Conclusion

This study revealed a high prevalence of S. aureus in healthy animals and patients from Henan Province, China. Resistant S. aureus exhibited varying degrees of multidrug resistance. The presence of antibiotic resistance and virulence genes may facilitate the spread of S. aureus strains and pose a potential threat to public health, highlighting the need for vigilant monitoring of these isolates at the human–animal interface.

Electronic supplementary material

The online version of this article (10.1186/s13099-018-0254-9) contains supplementary material, which is available to authorized users.

Presence of Classical Enterotoxin Genes, agr Typing, Antimicrobial Resistance, and Genetic Diversity of Staphylococcus aureus from Milk of Cows with Mastitis in Southern Brazil

Staphylococcus aureus is a common causative agent of bovine mastitis in dairy cows and commonly associated with foodborne disease outbreaks. The aim of this study was to evaluate the presence of enterotoxin genes, agr typing, antimicrobial resistance, and genetic diversity of S. aureus isolated from milk of cows with mastitis in dairy farms from southern Brazil. Results showed that 7 (22.6%) of 31 S. aureus isolates were positive for enterotoxin genes. Specifically, the genes encoding for enterotoxins A ( n = 4), C ( n = 2), and B ( n = 1) were detected. Isolates belonging to the agr group III (10 of 31, 32.2%) and agr group I (7 of 31, 22.5%) were the most common. To our knowledge, this is the first report of both agr I and III in the same S. aureus isolate from milk of cows with bovine mastitis. The antimicrobial resistance test showed that 54% of the isolates were multiresistant to antimicrobial agents. The macrorestriction analysis produced 16 different major SmaI pulsed-field gel electrophoresis patterns, with up to two subpatterns. Moreover, the presence of some S. aureus clones in a distinct area was observed. Although this study characterized a limited number of S. aureus isolates, the presence of classical enterotoxin genes and resistance to multiple antimicrobial agents reinforces the importance of this microorganism to animal and human health. In addition, similar genetic profiles have been identified in distinct geographic areas, suggesting clonal dissemination of S. aureus in dairy herds from southern Brazil.

Genetic Characterization, Antimicrobial Resistance Patterns and Virulence Determinants of Staphylococcus aureus Isolated form Bovine Mastitis

BACKGROUND AND OBJECTIVE

Staphylococcus aureus is commonly associated with mastitis in dairy herds with potential public health implications. This study was conducted to investigate the existence of S. aureus in mastitic milk and to determine the antimicrobial resistance profiles of the isolated strains as well as the resistance and virulence associated genes.

MATERIALS AND METHODS

Two hundred quarter milk samples were collected from 3 dairy farms at Dakahliya (n = 2) and Damietta (n = 1) Governorates, Egypt from September to December 2016. Conventional culturing and Polymerase Chain Reaction (PCR) assays targeting nuc (thermonuclease) and coa (coagulase) genes were performed. Isolates were tested for its susceptibility against 14 antimicrobial agents using disk diffusion method. All the isolates were screened for the presence of β-lactamases (blaZ, mecA) and virulence associated (pvl and tst) genes by PCR.

RESULTS

The S. aureus was detected in 42% (84/200) of the total examined milk samples. Regarding the antibiogram results, S. aureus revealed a high resistance against ampicillin (95.2%) and penicillin (83.3%) and a lower resistance was observed against gentamicin (23.8%), amikacin (16.7%) and ciprofloxacin (14.3%). Multidrug resistances were detected in 83.3% of the isolated S. aureus. Of the 70 penicillin-resistant S. aureus isolates, blaZ gene was identified in 67 (95.7%) isolates. Fifty percent of S. aureus isolates harbored the specific amplicon of mecA gene. Markedly, all mecA positive strains displayed multidrug resistance and were also positive for blaZ gene. The virulence determinants pvl and tst were detected in 7.1 and 11.9% of the isolated S. aureus, respectively.

CONCLUSION

Presence of multidrug resistant and toxin producing S. aureus in dairy farms pose a major risk to public health. Therefore, this study highlighted the importance of developing an efficient control program to inhibit the transmission of S. aureus, particularly multidrug resistant strains to humans.

Prevalence and molecular characterization of Staphylococcus aureus isolated from goats in Chongqing, China

BACKGROUND

Staphylococcus aureus is an important zoonotic pathogen which not only causes significant economic loss in livestock production but also poses a potential threat to public health. Compared with bovine and swine, the information on the colonization of S. aureus in goats is very limited. To understand the prevalence and characteristics of S. aureus in goats, we used the nasal swabs collected from apparently healthy goats to isolate S. aureus, and tested their antimicrobial susceptibility, virulence gene carrying levels, and multilocus sequence typing (MLST).

RESULTS

In 74 nasal swabs of apparently healthy goats, 32 (43.24%) S. aureus strains were isolated and identified, most of which were susceptible to many antibiotics, except for trimethoprim, furazolidone, amoxicillin, lincomycin and roxithromycin, and the resistance incidence of which were 50%, 40.63%, 37.5%, 28.13%, and 21.88% respectively. All the isolates were methicillin-susceptible S. aureus (MSSA) and mecA-negative. Enterotoxin genes were found in 53.13% of the strains. Of which, sej was the most prevalent (21.88%), followed by seb, sec, and see with the same level (18.75%). The most prevalent combination were seb + see and seb + tst. None of the S. aureus isolates harbored sea, sed, seh, eta and etb. Multilocus sequence typing (MLST) revealed 6 new alleles (aroe-552, aroe-553, glpf-500, pta-440, yqil-482 and yqil-496) and 5 new sequence types (STs) (3431,3440,3444,3445 and 3461). Using eBURST, the 5 STs were assigned to clonal complex 522 (CC522) and a further CC with no predicted ancestor. Phylogenetic analysis of seven concatenated MLST alleles revealed that the 5 STs were grouped into cluster I composed of S. aureus mainly from goats and sheep.

CONCLUSION

We provide the data for prevalence of S. aureus in goats in Chongqing municipality and their characterization which will help in tracking evolution of epidemic strains and their control methods.

Prevalence, antimicrobial susceptibility, and molecular characterization of Staphylococcus aureus isolated from dairy herds in northern China

Staphylococcus aureus is one of the main pathogens involved in dairy cow mastitis. Monitoring of antibiotic use would prove useful to assess the risk of Staph. aureus in raw milk. The objective of this work was to investigate the prevalence of Staph. aureus strais isolated from raw milk in northern China, and to characterize antimicrobial susceptibility of these strains and their key virulence genes. In total, 195 raw milk samples were collected from 195 dairy farms located in 4 cities of northern China from May to September 2015. Out of 195 samples, 54 (27.7%) were positive for Staph. aureus. Among these 54 samples, 54 strains of Staph. aureus were isolated, and 16 strains were identified as methicillin-resistant Staph. aureus. The strains exhibited high percentages of resistance to penicillin G (85.2%), ampicillin (79.6%), and erythromycin (46.3%). Moreover, 72% of the strains showed resistance to more than one antimicrobial agent. Overall, 63% of penicillin-resistant strains possessed the blaZ gene, and 60% of the erythromycin-resistant strains possessed erm(A), erm(B), erm(C), msr(A), or msr(B) genes with 8 different gene patterns. All isolates resistant to gentamicin, kanamycin, and oxacillin carried the aac6'-aph2", ant(4')-Ia, and mecA genes, respectively. Two tet(M)-positive isolates carried specific genes of the Tn916-Tn1545 transposon. The most predominant virulence genes were sec, sea, and pvl, which encode staphylococcal enterotoxins (sec and sea) and Panton-Valentine leukocidin, respectively. Thirty-two isolates (59.2%) harbored one or more virulence genes. The majority of Staph. aureus strains were multidrug resistant and carried multiple virulence genes, which may pose a risk to public health. Our data indicated that antimicrobial resistance of Staph. aureus was prevalent in dairy herds in northern China, and that antibiotics, especially penicillin G and ampicillin, to treat mastitis caused by Staph. aureus should be used with caution in northern China.

Molecular characterization and antibiotic resistance of Staphylococcus spp. isolated from cheese processing plants

The aim of this research paper was to characterize coagulase-positive and coagulase-negative staphylococci from raw milk, Minas cheese, and production lines of Minas cheese processing. One hundred isolates from 3 different cheese producers were characterized using molecular approaches, such as PCR, molecular typing, and DNA sequencing. Staphylococcus aureus (88% of the isolates) was the most abundant followed by Staphylococcus epidermidis, Staphylococcus hyicus, and Staphylococcus warneri. Among the 22 enterotoxin genes tested, the most frequent was seh (62% of the isolates), followed by selx and ser. Hemolysin genes were widely distributed across isolates, and Panton-Valentine leukocidin and toxic shock syndrome toxin genes were also identified. Methicillin-resistant S. aureus were staphylococcal cassette chromosome mec III, IVa, IVd, and others nontypeable. In the phenotypic antibiotic resistance, multiresistant isolates were detected and resistance to penicillin was the most observed. Using spa typing, we identified several types and described a new one, t14969, isolated from cheese. These findings suggest that antibiotic resistance and potentially virulent strains from different sources can be found in the Brazilian dairy processing environment. Further research should be conducted with collaboration from regulatory agencies to develop programs of prevention of virulent and resistant strain dissemination in dairy products and the processing environment.

Quality preservation of deliberately contaminated milk using thyme free and nanoemulsified essential oils

The objective of this study is to evaluate the effect of either a solution of Thymus capitatus essential oil or its nanoemulsion on the quality of milk contaminated by bacteria. After 24h of S. aureus inoculation, bacterial growth reached 202×10(3)CFU/ml in the presence of the essential oil while it was limited to 132×10(3)CFU/ml when treated with nanoemulsion. The reduction of antioxidant capacity of milk treated with essential oil was higher when treated with nanoemulsion. Moreover, free essential oil was more efficient in protecting proteins from degradation than the nanoemulsion. For instance, after 24h of E. hirae contamination, 26% of the total proteins were consumed in the presence of nano-encapsulated essential oil, while only 14% of the initial content was consumed when free essential oil was added. Concerning milk acidity increase and the inhibition of peroxide production, no statistical differences have been recorded between the use of free essential oil or its nano-emulsion. In conclusion, bulk or nano-encapsulated T. capitatus essential oil preserve milk quality and can extend its shelf life.

Prevalence, Molecular Characterization, and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus Isolated from Milk and Dairy Products

The present work was undertaken to study the prevalence, molecular characterization, virulence factors, and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) in raw milk and dairy products in Mansoura City, Egypt. MRSA was detected in 53% (106/200) among all milk and dairy products with prevalence rates of 75%, 65%, 40%, 50%, and 35% in raw milk, Damietta cheese, Kareish cheese, ice cream, and yogurt samples, respectively. The mean S. aureus counts were 3.49, 3.71, 2.93, 3.40, and 3.23 log10 colony-forming units (CFU)/g among tested raw milk, Damietta cheese, Kareish cheese, ice cream and yogurt, respectively, with an overall count of 3.41 log10 CFU/g. Interestingly, all recovered S. aureus isolates were genetically verified as MRSA strains by molecular detection of the mecA gene. Furthermore, genes encoding α-hemolysin (hla) and staphylococcal enterotoxins (sea, seb, sec) were detected in all isolates. The antimicrobial susceptibility pattern of recovered MRSA isolates against 13 tested antimicrobials revealed that the least effective drugs were penicillin G, cloxacillin, tetracycline, and amoxicillin with bacterial resistance percentages of 87.9%, 75.9%, 65.2%, and 55.6%, respectively. These findings suggested that milk and dairy products represent a potential infection risk threat of multidrug-resistant and toxigenic S. aureus in Egypt due to neglected hygienic practices during production, retail, or storage stages. These findings highlighted the crucial importance of applying more restrictive hygienic measures in dairy production in Egypt for food safety.