Molecular Characteristics of Staphylococcus aureus Causing Bovine Mastitis between 2014 and 2015

Long non-coding RNA (CMR) involved in autoprotection in S. aureus mastitis in dairy cows by regulating miR-877/FOXM1

Long non-coding RNAs (LncRNAs) are dysregulated in a variety of human diseases and are highly involved in the development and progression of tumors. Studies on lncRNAs associated with cow mastitis have been lagging behind compared to humans or model animals, therefore, the aim of this study was to explore the mechanism of LncRNAs (CMR) involved in autoprotection against S. aureus mastitis in Bovine Mammary Epithelial Cells (BMECs). First, qRT-PCR was used to examine the relative expression of CMR in a S. aureus mastitis model of BMECs. Then, cell proliferation and apoptosis were detected by EdU and apoptosis assay. Finally, the targeting relationship between miRNAs and mRNA/LncRNAs was determined by dual luciferase reporter gene, qRT-PCR and western blotting techniques. The results showed that CMR was upregulated in the S. aureus mastitis model of BMECs and promoted the expression of inflammatory factors, and SiRNA-mediated CMR inhibited the proliferation of mammary epithelial cells and induced apoptosis. Mechanistically, CMR acts as a competitive endogenous RNA (ceRNA) sponge miR-877, leading to upregulation of FOXM1, a target of miR-877. Importantly, either miR-877 overexpression or FOXM1 inhibition abrogated CMR knockdown-induced apoptosis promoting cell proliferation and reducing inflammatory factor expression levels. In summary, CMR is involved in the regulation of autoprotection against S. aureus mastitis through the miR-877/FOXM1 axis in BMECs and induces immune responses in mammary tissues and cells of dairy cows, providing an important reference for subsequent prevention and control of cow mastitis and the development of targeted drugs.

Molecular and epidemiological characterization of Staphylococcus aureus causing bovine mastitis in China

BACKGROUND

Staphylococcus aureus is one of the most prevalent pathogens in bovine mastitis, which leads to substantial financial losses for the dairy industry.

RESULTS

In this study, S. aureus (n = 72) was isolated from 18 dairy farms in 15 provinces across China in 2021. The identification of these isolates at the species level was achieved by employing 16S rRNA sequencing. An isothermal amplification method for auxiliary detection of S. aureus was established, which can be employed not only for laboratory detection but also for point-of-care testing (POCT). Molecular characteristics of S. aureus mastitis in Chinese dairy cows were determined through MLST and spa typing. Finally, methicillin-resistant Staphylococcus aureus (MRSA) and MRSA resistance genes were detected using MIC and PCR amplification techniques. 72 isolates were identified as 12 sequence types (STs) and 7 clonal complexes (CC). ST1/CC1 was the dominant prevalent accounting for 33.3 % of the total, and exhibiting a wide distribution range. In terms of spa types, t114 was the dominant type, accounting for 31.9 % of the total, followed by t529 as the second major type. Four S. aureus strains were classified as MRSA according to their levels of oxacillin resistance (MIC ≥4 μg/mL). Among these four MRSA strains, one of them was found to be mecA positive. However, the presence of drug-resistance genes mecA and mecC was not detected in the remaining three MRSA strains, indicating the possible existence of new resistance genes.

CONCLUSIONS

Our study investigated the prevalence of S. aureus mastitis in dairy cows in China, while also examined the molecular characteristics and MRSA strains. This information will help with the clinical monitoring, prevention, and control of S. aureus mastitis in dairy cattle.

Occurrence of Methicillin-Resistant Staphylococcus aureus (MRSA) in Bovine Bulk Milk and Farm Workers in Smallholder Dairy Farming Systems in Northwestern Ethiopia

Background and Purpose

Staphylococcus aureus is a common pathogen responsible for causing various human and animal infections and is well known for its ability to develop resistance to multiple antibiotics. This study aimed to evaluate the occurrence of methicillin-resistant Staphylococcus aureus (MRSA) in bulk milk and dairy farms in northwestern Ethiopia and to determine their phenotypic and genotypic antimicrobial susceptibility patterns.

Methods

We collected 50 bulk milk samples from 50 dairy farms and 50 hand swabs from dairy milkers. The cefoxitin disk diffusion test and PCR-based assays were used to identify MRSA isolates. In addition, cefoxitin-resistant isolates were tested for susceptibility to other antibiotics using the Kirby-Bauer disk diffusion method.

Results

The results showed that MRSA was detected in 8 samples: 6 from bulk milk samples (12%) and 2 from hand swabs (4%). All MRSA isolates exhibited a high resistance rate to penicillin (100%), followed by tetracycline (75%), ciprofloxacin (25%), chloramphenicol (25%), erythromycin (25%), gentamycin (12.5%), and trimethoprim-sulfamethoxazole (12.5%). Moreover, 72% of the isolates showed resistance to three or more antibiotic classes and were classified as multidrug-resistant.

Conclusion

This study identified methicillin-resistant Staphylococcus aureus and multidrug-resistant MRSA in bulk milk and dairy farms in northwestern Ethiopia. These findings highlight the potential risk of transmission of these antibiotic-resistant bacteria to humans and the need for improved antibiotic stewardship in the dairy sector using the One Health approach.

An observational study demonstrates human-adapted Staphylococcus aureus strains have a higher frequency of antibiotic resistance compared to cattle-adapted strains isolated from dairy farms making farmstead cheese

BACKGROUND

Staphylococcus aureus is a multi-host zoonotic pathogen causing human and livestock diseases. Dairy farms that make artisan cheese have distinctive concerns for S. aureus control. Antimicrobial-resistant (AMR) S. aureus is a public and animal health concern. There is a need to study the population structure of AMR S. aureus at the human-animal interface and understand the path of zoonotic transmission. This cross-sectional observational study aimed to assess the genetic diversity and AMR patterns of S. aureus isolated from cattle and humans on conventional and organic Vermont dairy farms that produce and sell farmstead cheese.

RESULTS

A convenience sample of 19 dairy farms in Vermont was enrolled, and 160 S. aureus isolates were collected from cow quarter milk (CQM), bulk tank milk (BTM), human-hand and -nasal swabs. After deduplication, 89 isolates were used for the analysis. Sequence types (STs) were determined by multilocus sequence typing and cataloged to the PubMLST database. Nine defined and five novel STs were identified. For BTM and CQM samples, six STs were identified within cow-adapted CC97 and CC151. Two human-adapted STs were isolated from BTM and CQM. Seven human-adapted clonal complexes with eight STs were identified from human samples. One cow-adapted ST was isolated from a human. Antimicrobial susceptibility of the isolates was tested using disc diffusion and broth microdilution methods. Approximately 27% of the isolates were beta-lactam resistant and blaZ gene-positive. S. aureus isolates from human swabs were more likely to carry blaZ compared to isolates from CQM or BTM. S. aureus isolated from cows and humans on the same farm belonged to different STs.

CONCLUSION

Humans were more likely to carry beta-lactam-resistant S. aureus compared to cows, and on organic farms only human-adapted blaZ positive STs were isolated from BTM. Moreover, we identified potential spillover events of S. aureus sequence types between host species. The presence of penicillin-resistant-human-adapted S. aureus on both organic and conventional dairy farms highlights a "One Health" concern at the junction of public and animal health requiring further surveillance.

Detection of Staphylococcus Isolates and Their Antimicrobial Resistance Profiles and Virulence Genes from Subclinical Mastitis Cattle Milk Using MALDI-TOF MS, PCR and Sequencing in Free State Province, South Africa

Staphylococcus species are amongst the bacteria that cause bovine mastitis worldwide, whereby they produce a wide range of protein toxins, virulence factors, and antimicrobial-resistant properties which are enhancing the pathogenicity of these organisms. This study aimed to detect Staphylococcus spp. from the milk of cattle with subclinical mastitis using MALDI-TOF MS and 16S rRNA PCR as well as screening for antimicrobial resistance (AMR) and virulence genes. Our results uncovered that from 166 sampled cows, only 33.13% had subclinical mastitis after initial screening, while the quarter-level prevalence was 54%. Of the 50 cultured bacterial isolates, MALDI-TOF MS and 16S rRNA PCR assay and sequencing identified S. aureus as the dominant bacteria by 76%. Furthermore, an AMR susceptibility test showed that 86% of the isolates were resistant to penicillin, followed by ciprofloxacin (80%) and cefoxitin (52%). Antimicrobial resistance and virulence genes showed that 16% of the isolates carried the mecA gene, while 52% of the isolates carried the Lg G-binding region gene, followed by coa (42%), spa (40%), hla (38%), and hlb (38%), whereas sea and bap genes were detected in 10% and 2% of the isolates, respectively. The occurrence of virulence factors and antimicrobial resistance profiles highlights the need for appropriate strategies to control the spread of these pathogens.

Screening of antibiogram, virulence factors, and biofilm production of Staphylococcus aureus and the bio-control role of some probiotics as alternative antibiotics

Background

Food safety is a serious challenge in the face of increasing population and diminishing resources. Staphylococcus aureus is a critical foodborne pathogen characterized by its capability to secret a diverse range of heat-resistant enterotoxins. Antibiotic usage in dairy herds resulted in the occurrence of antimicrobial resistance (AMR) patterns among bacterial species, which were consequently transmitted to humans via dairy products. Lactic acid bacteria (LAB) produce bacteriocins, which provide an excellent source of natural antimicrobials with the further advantage of being environmentally friendly and safe.

Aim

Detection of multidrug resistance (MDR) S. aureus isolates in concerned samples, molecular characteristics, biofilm production, and the inhibitory role of LAB against it.

Methods

Random samples of raw milk and other dairy products were analyzed for S. aureus isolation. Phenotypic and genotypic assessment of AMR was performed, in addition to detection of classical enterotoxin genes of S. aureus. Finally, evaluation of the antimicrobial action of some Lactobacillus strains against S. aureus.

Results

Incidence rates of presumptive S. aureus in raw milk, Kariesh cheese, and yogurt samples were 50%, 40%, and 60%, respectively. The highest resistance of S. aureus was to Kanamycin (100%) and Nalidixic acid (89.3%), respectively. (78.66%) of S. aureus were MDR. 11.1% of S. aureus carried mecA gene. In concern with enterotoxins genes, PCR showed that examined isolates harbored sea with a percentage of (22.2%), while sed was found in (11.1%) of isolates. Regarding biofilm production, (88.88%) of S. aureus were biofilm producers. Finally, agar well diffusion showed that Lactobacillus acidophilus had the strongest antimicrobial action against S. aureus with inhibition zone diameter ranging from 18 to 22 mm.

Conclusion

There is a widespread prevalence of MDR S. aureus in raw milk and dairy products. Production of staphylococcal enterotoxins, as well as biofilm production are responsible for public health risks. Therefore, installing proper hygienic routines and harsh food safety policies at food chain levels is substantial.

Diabetes mellitus promotes the nasal colonization of high virulent Staphylococcus aureus through the regulation of SaeRS two-component system

Diabetic foot infections are a common complication of diabetes. Staphylococcus aureus is frequently isolated from diabetic foot infections and commonly colonizes human nares. According to the study, the nasal microbiome analysis revealed that diabetic patients had a significantly altered nasal microbial composition and diversity. Typically, the fasting blood glucose (FBG) level had an impact on the abundance and sequence type (ST) of S. aureus in diabetic patients. We observed that highly virulent S. aureus ST7 strains were more frequently colonized in diabetic patients, especially those with poorly controlled FBG, while ST59 was dominant in healthy individuals. S. aureus ST7 strains were more resistant to human antimicrobial peptides and formed stronger biofilms than ST59 strains. Critically, S. aureus ST7 strains displayed higher virulence compared to ST59 strains in vivo. The dominance of S. aureus ST7 strains in hyperglycemic environment is due to the higher activity of the SaeRS two-component system (TCS). S. aureus ST7 strains outcompeted ST59 both in vitro, and in nasal colonization model in diabetic mice, which was abolished by the deletion of the SaeRS TCS. Our data indicated that highly virulent S. aureus strains preferentially colonize diabetic patients with poorly controlled FBG through SaeRS TCS. Detection of S. aureus colonization and elimination of colonizing S. aureus are critical in the care of diabetic patients with high FBG.

Molecular characteristics of Staphylococcus aureus strains isolated from subclinical mastitis of water buffaloes in Guangdong Province, China

Intramammary infections (IMI) in animals reared for milk production can result in large economic losses and distress to the animals. Staphylococcus aureus is an important causative agent of IMI in dairy cows, but its prevalence in water buffaloes has not been determined. Therefore, the current study was conducted to investigate the prevalence of subclinical mastitis in water buffaloes and the antimicrobial susceptibility, virulence genes and biofilm formation abilities of Staphylococcus aureus isolates recovered from water buffaloes in Guangdong, China. Staphylococcus aureus strains were isolated from milk samples of water buffaloes with subclinical mastitis, and twofold microdilution, PCR and crystal violet staining methods were used to determine antimicrobial susceptibility, distributions of virulence and antimicrobial resistance genes and biofilm formation ability, respectively. Our results indicated that 29.44% of water buffaloes were diagnosed with subclinical mastitis, and the most prevalent pathogens were Escherichia coli (96.17%), coagulase-negative staphylococci (CoNS) (67.60%) and S. aureus (28.57%). Most S. aureus isolates showed resistance to bacitracin, doxycycline, penicillin, florfenicol, and tetracycline but were susceptible to ciprofloxacin, ceftizoxime, cefoquinoxime, and ofloxacin. Moreover, 63.72% of S. aureus isolates were positive for tetM, and the prevalence of msrB, blaZ, mecA, fexA, and tetK ranged from 21.24 to 6.19%. All S. aureus isolates harbored clfB and icaA genes, and the virulence genes hla (93.8%), hld (91.15%), clfA (90.27%), fnbA (86.73%), and hlb (83.19%), and tsst, icaD, sec, see, fnbB, and sea showed a varied prevalence ranging from 3.5 to 65.49%. All S. aureus isolates possessed the ability to form biofilms, and 30.09% of isolates showed strong biofilm formation abilities, while 19.47% of isolates were weak biofilm producers. Our results indicated that subclinical mastitis is prevalent in water buffaloes in Guangdong, China, and S. aureus is prevalent in samples from water buffaloes with subclinical mastitis. Most S. aureus isolates were susceptible to cephalosporins and fluoroquinolones; thus, ceftizoxime and cefoquinoxime can be used to treat subclinical mastitis in water buffaloes.

Antimicrobial Resistance Profiles of Staphylococcus Isolated from Cows with Subclinical Mastitis: Do Strains from the Environment and from Humans Contribute to the Dissemination of Resistance among Bacteria on Dairy Farms in Colombia?

Staphylococcus is a very prevalent etiologic agent of bovine mastitis, and antibiotic resistance contributes to the successful colonization and dissemination of these bacteria in different environments and hosts on dairy farms. This study aimed to identify the antimicrobial resistance (AMR) genotypes and phenotypes of Staphylococcus spp. isolates from different sources on dairy farms and their relationship with the use of antibiotics. An antimicrobial susceptibility test was performed on 349 Staphylococcus strains (S. aureus, n = 152; non-aureus staphylococci (NAS), n = 197) isolated from quarter milk samples (QMSs) from cows with subclinical mastitis (176), the teats of cows (116), the milking parlor environment (32), and the nasal cavities of milk workers (25). Resistance and multidrug resistance percentages found for S. aureus and NAS were (S. aureus = 63.2%, NAS = 55.8%) and (S. aureus = 4.6%, NAS = 11.7%), respectively. S. aureus and NAS isolates showed resistance mainly to penicillin (10 IU) (54.1% and 32.4%) and ampicillin (10 mg) (50.3% and 27.0%) drugs. The prevalence of AMR Staphylococcus was higher in environmental samples (81.3%) compared to other sources (52.6-76.0%). In S. aureus isolates, the identification of the blaZ (83.9%), aacAaphD (48.6%), ermC (23.5%), tetK (12.9%), and mecA (12.1%) genes did not entirely agree with the AMR phenotype. We conclude that the use of β-lactam antibiotics influences the expression of AMR in Staphylococcus circulating on dairy farms and that S. aureus isolates from the environment and humans may be reservoirs of AMR for other bacteria on dairy farms.

Prevalence and epidemiological characteristics of methicillin-resistant Staphylococcus aureus isolated from cattle in Bangalore India as a part of the One Health approach

In India, limited studies are available on the epidemiological aspects of methicillin-resistant Staphylococcus aureus (MRSA) infections in both animal and human settings. Herein, we investigated the prevalence, antimicrobial resistance profile and molecular characteristics of MRSA isolates recovered from cattle using the One Health approach. Out of 66 mecA-positive staphylococci, species-specific multiplex PCR detected 24 % (n=16) of isolates as MRSA. Maximum antibiotic resistance was seen against cloxacillin (94 %, n=15) and least for enrofloxacin and cephalothin (each 13 %, n=2). Overall, 13 % (n=2) of MRSA isolates were multidrug-resistant. Molecular characterization by SCCmec typing identified 88 % (n=14) of MRSA isolates as type V. Twelve isolates (75 %) belonged to novel spa-type t17242, of which 67 % (n=8) belonged to agr type I. MLST analysis revealed ST 1687 (50 %, n=8) as the most predominant sequence type. Circulation of different MRSA clones among the cattle populace offers a risk of transmission to humans through direct contact, food chain or environmental contamination. Thus, continuous monitoring of MRSA strains is imperative for early diagnosis and for establishing effective treatment strategies to restrain the disease burden caused by MRSA infections.

Integrated co-expression analysis of regulatory elements (miRNA, lncRNA, and TFs) in bovine monocytes induced by Str. uberis

Non-coding RNAs, including long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), together with transcription factors, are critical pre-, co-, and post-transcriptional regulators. In addition to their criteria as ideal biomarkers, they have great potential in disease prognosis, diagnosis, and treatment of complex diseases. Investigation of regulatory mechanisms in the context of bovine mastitis, as most common and economic disease in the dairy industry, to identify elements influencing the expression of candidate genes as key regulators of the mammary immune response is not yet fully understood. Transcriptome profiles (50 RNA-Seq and 50 miRNA-Seq samples) of bovine monocytes induced by Str. uberis were used for co-expression module detection and preservation analysis using the weighted gene co-expression network analysis (WGCNA) approach. Assigned mi-, lnc-, and m-modules used to construct the integrated regulatory networks and miRNA-lncRNA-mRNA regulatory sub-networks. Remarkably, we have identified 18 miRNAs, five lncRNAs, and seven TFs as key regulators of str. uberis-induced mastitis. Most of the genes introduced here, mainly involved in immune response, inflammation, and apoptosis, were new to mastitis. These findings may help to further elucidate the underlying mechanisms of bovine mastitis, and the discovered genes may serve as signatures for early diagnosis and treatment of the disease.

Comparative Genomic Analyses of Lactococcus garvieae Isolated from Bovine Mastitis in China

Lactococcus garvieae is an emerging zoonotic pathogen, but there are few reports regarding bovine mastitis. The prevalence of L. garvieae represents an increasing disease threat and global public health risk. Thirty-nine L. garvieae isolates were obtained from 2,899 bovine clinical mastitis milk samples in 6 provinces of China from 2017 to 2021. Five clonal complexes were determined from 32 multilocus sequence types (MLSTs) of L. garvieae: sequence type 46 (ST46) was the predominant sequence type, and 13 novel MLSTs were identified. All isolates were resistant to chloramphenicol and clindamycin, but susceptible to penicillin, ampicillin, amoxicillin-clavulanic acid, imipenem, ceftiofur, enrofloxacin, and marbofloxacin. Based on genomic analyses, L. garvieae had 6,310 genes, including 1,015 core, 3,641 accessory, and 1,654 unique genes. All isolates had virulence genes coding for collagenase, fibronectin-binding protein, glyceraldehyde-3-phosphate dehydrogenase, superoxide dismutase, and NADH oxidase. Most isolates had lsaD and mdtA antimicrobial resistance (AMR) genes. Based on COG (Clusters of Orthologous Genes database) results, the functions of defense, transcription and replication, and recombination and repair were enhanced in unique genes, whereas functions of translation, ribosomal structure, and biogenesis were enhanced in core genes. The KEGG functional categories enriched in unique genes included human disease and membrane transport, whereas COG functional categories enriched in core genes included energy metabolism, nucleotide metabolism, and translation. No gene was significantly associated with host specificity. In addition, analysis of core genome single nucleotide polymorphisms (SNPs) implied potential host adaptation of some isolates in several sequence types. In conclusion, this study characterized L. garvieae isolated from mastitis and detected potential adaptations of L. garvieae to various hosts. IMPORTANCE This study provides important genomic insights into a bovine mastitis pathogen, Lactococcus garvieae. Comprehensive genomic analyses of L. garvieae from dairy farms have not been reported. This study is a detailed and comprehensive report of novel features of isolates of L. garvieae, an important but poorly characterized bacterium, recovered in the past 5 years in 6 Chinese provinces. We documented diverse genetic features, including predominant sequence type ST46 and 13 novel MLSTs. Lactococcus garvieae had 6,310 genes, including 1,015 core, 3,641 accessory, and 1,654 unique genes. All isolates had virulence genes coding for collagenase, fibronectin-binding protein, glyceraldehyde-3-phosphate dehydrogenase, superoxide dismutase, and NADH oxidase and resistance to chloramphenicol and clindamycin. Most isolates had lsaD and mdtA antimicrobial resistance genes. However, no gene was significantly associated with host specificity. This is the first report that characterized L. garvieae isolates from bovine mastitis and revealed potential host adaptations of L. garvieae to various hosts.

Genetic diversity, antibiotic resistance, and virulence characteristics of Staphylococcus aureus from raw milk over 10 years in Shanghai

Staphylococcus aureus (S. aureus) is a major cause of foodborne infections and its persistence in raw milk is a multifaceted phenomenon that poses a considerable public health challenge. Our study investigated the prevalence, virulence genes, antibiotic resistance, and genetic characterization of S. aureus in raw milk in six Shanghai districts from 2013 to 2022. At 18 dairy farms, a total of 704 S. aureus strains were isolated from 1799 samples tested for drug sensitivity. The highest rates of antibiotic resistance were ampicillin (96.7 %), sulfamethoxazole (65 %), and erythromycin (21.6 %). Between 2018 and 2022, there was a significant decrease in the resistance rates of ceftiofur, ofloxacin, tilmicosin, erythromycin, clindamycin, amoxicillin-clavulanic acid, and sulfamethoxazole in comparison to the period from 2013 to 2017. There were 205 S. aureus strains chosen for whole genome sequencing (WGS), with no more than 2 strains of the same resistance phenotype from each farm per year. The prevalence of mecA-positive strains was 14.15 %, while other antibiotic resistance-associated genes were observed as follows: blaI (70.21 %), lnu(B) (5.85 %), lsa(E) (5.75 %), fexA (6.83 %), erm(C) (4.39 %), tet(L) (9.27 %), and dfrG (5.85 %). Isolates harboring the immune evasion cluster (IEC) genes (scn, chp, and sak) were predominantly categorized as sequence types (STs) 7, 188, 15, 59, and 398. The predominant cluster complexes were CC97, CC1, CC398, and CC1651. In 2017-2022, there was a transition in CC1 from the highly antibiotic-resistant ST9 strain that emerged between 2013 and 2018 to the low-resistant but highly virulent ST1 strain. Retrospective phylogenetic analysis elucidated the evolutionary history of the isolates and demonstrated that the human-animal host transition of S. aureus was linked to the genesis of MRSA CC398. The implementation of extended surveillance will aid in the development of innovative strategies to avoid the transmission of S. aureus along the dairy food chain and the occurrence of public health events.

The Economic Evaluation of Mastitis Control Strategies in Holstein-Friesian Dairy Herds

The economic evaluation of mastitis control is challenging. The objective of this study was to perform the economic evaluation of mastitis control, under different intervention scenarios, quantifying the total cost of mastitis caused by S. aureus in Holstein cows in Argentina. A model was set for a dairy herd of Holstein cows endemically infected with S. aureus. A basic mastitis control plan including proper milking procedures, milking machine test, dry cow therapy, and treatment for clinical mastitis, was compared against other more complex and costly interventions, such as segregation and culling of chronically infected cows. Sensitivity analysis was performed by modifying the intramammary infection transition probabilities, economic parameters, and efficacy of treatment strategies. The basic mastitis control plan showed a median total cost of USD88.6/cow per year, which was close to the infected cows culling scenarios outputs. However, the segregation scenario was the most efficient, in which the total cost was reduced by about 50%. Such cost was more sensitive to probabilities and efficacy than the economic parameters. The model is flexible and can be customized by producers and veterinarians according to different control and herd settings.

A food poisoning caused by ST7 Staphylococcal aureus harboring sea gene in Hainan province, China

ST7 Staphylococcus aureus is highly prevalent in humans, pigs, as well as food in China; however, staphylococcal food poisoning (SFP) caused by this ST type has rarely been reported. On May 13, 2017, an SFP outbreak caused by ST7 S. aureus strains occurred in two campuses of a kindergarten in Hainan Province, China. We investigated the genomic characteristics and phylogenetic analysis of ST7 SFP strains combined with the 91 ST7 food-borne strains from 12 provinces in China by performing whole-genome sequencing (WGS). There was clear phylogenetic clustering of seven SFP isolates. Six antibiotic genes including blaZ, ANT (4′)-Ib, tetK, lnuA, norA, and lmrS were present in all SFP strains and also showed a higher prevalence rate in 91 food-borne strains. A multiple resistance plasmid pDC53285 was present in SFP strain DC53285. Among 27 enterotoxin genes, only sea and selx were found in all SFP strains. A ФSa3int prophage containing type A immune evasion cluster (sea, scn, sak, and chp) was identified in SFP strain. In conclusion, we concluded that this SFP event was caused by the contamination of cakes with ST7 S. aureus. This study indicated the potential risk of new emergencing ST7 clone for SFP.

Immunological and Oxidative Biomarkers in Bovine Serum from Healthy, Clinical, and Sub-Clinical Mastitis Caused by Escherichia coli and Staphylococcus aureus Infection

The study aimed to investigate the mastitis' emerging causative agents and their antimicrobial sensitivity, in addition to the hematological, biochemical indicators, oxidative biomarkers, acute phase protein (APP), and inflammatory cytokine changes in dairy farms in Gamasa, Dakahlia Governorate, Egypt. One hundred Holstein Friesian dairy cattle with clinical and subclinical mastitis were investigated and were allocated into three groups based on a thorough clinical examination. Escherichia coli and Staphylococcus aureus were found responsible for the clinical and subclinical mastitis in dairy farms, respectively. Multiple drug resistance (MDR) was detected in 100%, and 94.74% of E. coli and S. aureus isolates, respectively. Significantly low RBCs count, Hb, and PCV values were detected in mastitic cows compared with both subclinical mastitic and control groups; moreover, WBCs, lymphocytes, and neutrophil counts were significantly diminished in mastitic cows compared to the controls. Significantly higher levels of AST, LDH, total protein, and globulin were noticed in both mastitic and subclinical mastitic cows. The haptoglobin, fibrinogen, amyloid A, ceruloplasmin, TNF-α, IL-1β, and IL-6 levels were statistically increased in mastitic cows compared to the controls. Higher MDA levels and reduction of TAC and catalase were identified in all the mastitic cases compared to the controls. Overall, the findings suggested potential public health hazards due to antimicrobial resistance emergence. Meanwhile, the APP and cytokines, along with antioxidant markers can be used as early indicators of mastitis.

Genetic polymorphisms in immune- and inflammation-associated genes and their association with bovine mastitis resistance/susceptibility

Bovine mastitis, the inflammation of the mammary gland, is a contagious disease characterized by chemical and physical changes in milk and pathological changes in udder tissues. Depressed immunity and higher expression of inflammatory cytokines with an elevated milk somatic cell count can be observed during mastitis in dairy cattle. The use of somatic cell count (SCC) and somatic cell score (SCS) as correlated traits in the indirect selection of animals against mastitis resistance is in progress globally. Traditional breeding for mastitis resistance seems difficult because of the low heritability (0.10-0.16) of SCC/SCS and clinical mastitis. Thus, genetic-marker-selective breeding to improve host genetics has attracted considerable attention worldwide. Moreover, genomic selection has been found to be an effective and fast method of screening for dairy cattle that are genetically resistant and susceptible to mastitis at a very early age. The current review discusses and summarizes the candidate gene approach using polymorphisms in immune- and inflammation-linked genes (CD4, CD14, CD46, TRAPPC9, JAK2, Tf, Lf, TLRs, CXCL8, CXCR1, CXCR2, C4A, C5, MASP2, MBL1, MBL2, LBP, NCF1, NCF4, MASP2, A2M, and CLU, etc.) and their related signaling pathways (Staphylococcus aureus infection signaling, Toll-like receptor signaling, NF-kappa B signaling pathway, Cytokine-cytokine receptor, and Complement and coagulation cascades, etc.) associated with mastitis resistance and susceptibility phenotypic traits (IL-6, interferon-gamma (IFN-γ), IL17, IL8, SCS, and SCC) in dairy cattle.

High genetic diversity and zoonotic potential of Staphylococcus aureus strains recovered from bovine intramammary infections in Colombians dairy herds

Genotyping of Staphylococcus aureus isolated from mastitis has become a fundamental tool to understand its complex epidemiology and to evaluate spillover events. The aim of this study was to describe the frequency of genotypes of the S. aureus strains isolated from intramammary infections by spa typing technique, and to evaluate the association between genotypes and the ability to form biofilm under in vitro conditions. Sixty-six strains of S. aureus recovered from bovines intramammary infections on 56 dairy herds located in 14 municipalities of the department of Antioquia were characterized. The majority of strains (65/66) were isolated from milk samples collected from dairy cows with subclinical intramammary infections. Nineteen different spa types were found in this study, t521 (19.70%), t267 (15.15%), and t605 (12.12%) being the most frequent. The strains from the t605 spa type showed the highest biofilm production. The high frequency of spa types with zoonotic potential found in this study, identified cattle as an important reservoir of theses clones for people in close proximity, such as milkers and consumers of unpasteurized dairy products.

Genome sequencing and comparative genomic analysis of bovine mastitis-associated Staphylococcus aureus strains from India

BACKGROUND

Bovine mastitis accounts for significant economic losses to the dairy industry worldwide. Staphylococcus aureus is the most common causative agent of bovine mastitis. Investigating the prevalence of virulence factors and antimicrobial resistance would provide insight into the molecular epidemiology of mastitis-associated S. aureus strains. The present study is focused on the whole genome sequencing and comparative genomic analysis of 41 mastitis-associated S. aureus strains isolated from India.

RESULTS

The results elucidate explicit knowledge of 15 diverse sequence types (STs) and five clonal complexes (CCs). The clonal complexes CC8 and CC97 were found to be the predominant genotypes comprising 21 and 10 isolates, respectively. The mean genome size was 2.7 Mbp with a 32.7% average GC content. The pan-genome of the Indian strains of mastitis-associated S. aureus is almost closed. The genome-wide SNP-based phylogenetic analysis differentiated 41 strains into six major clades. Sixteen different spa types were identified, and eight isolates were untypeable. The cgMLST analysis of all S. aureus genome sequences reported from India revealed that S. aureus strain MUF256, isolated from wound fluids of a diabetic patient, was the common ancestor. Further, we observed that all the Indian mastitis-associated S. aureus isolates belonging to the CC97 are mastitis-associated. We identified 17 different antimicrobial resistance (AMR) genes among these isolates, and all the isolates used in this study were susceptible to methicillin. We also identified 108 virulence-associated genes and discuss their associations with different genotypes.

CONCLUSION

This is the first study presenting a comprehensive whole genome analysis of bovine mastitis-associated S. aureus isolates from India. Comparative genomic analysis revealed the genome diversity, major genotypes, antimicrobial resistome, and virulome of clinical and subclinical mastitis-associated S. aureus strains.

Prevalence, antimicrobial resistance, and staphylococcal toxin genes of blaTEM-1a -producing Staphylococcus aureus isolated from animals in Chongqing, China

BACKGROUND

Staphylococcus aureus infection of livestock animals and humans is a major public health issue. There are reports of antimicrobial resistance and multiple staphylococcal superantigen genes in many countries and several provinces of China, but the status in Chongqing, China is uncertain.

OBJECTIVES

The aim of this study was to determine the prevalence, antimicrobial susceptibility, and other molecular characteristics of S. aureus isolates from livestock animals in Chongqing.

METHODS

Staphylococcus aureus was isolated and identified by selective enrichment and amplification of the nuc gene from 1371 samples collected at farms in Chongqing. The agar dilution method was used to determine the resistant phenotype, and extended spectrum β-lactamase genes were amplified by PCR. Methicillin-resistant S. aureus was verified by the presence of the mecA gene, and the presence or absence of SE, SEl, and TSST-1 genes was detected in the isolates.

RESULTS

We cultured 89 S. aureus isolates from 1371 samples between March 2014 and December 2017. These isolates were from pigs, cattle, goats, rabbits, and chickens. There were four methicillin-resistant S. aureus strains (three from pigs and one from a chicken). The 89 isolates had high resistance to penicillin (93.3%) and ampicillin (92.1%), but most were susceptible to amikacin and ofloxacin, with resistance rates below 10%. A total of 62.9% of the isolates had varying degrees of multidrug resistance. Almost all strains, except for three isolates from chickens, were positive for bla_TEM-1a . There were 19 of 20 tested staphylococcal SE/SEl/TSST-1 genes present (all except for seq), and the predominant genes were sei (58.4%), tst-1 (56.2%), and seg (51.7%).

CONCLUSIONS

The high antimicrobial resistance and prevalence of bla_TEM-1a reinforce the need to reduce the usage of antimicrobials in livestock. The universal existence of staphylococcal toxin genes implies a potential threat to public health by animal-to-human transmission via the food chain.

Evaluation of three Staphylococcus aureus proteins involved in the adhesion process as antigens for the detection of bovine intramammary infections

Introduction. Fast and accurate diagnosis is one of the key strategies in the successful control of intramammary infections caused by Staphylococcus aureus. Immunoassays are one of the diagnostic tools that have been proposed for the detection of S. aureus infection because they offer an advantage in terms of cost and are fast and easy to use compared to other diagnostic tests.Gap statement. The main challenge of the immunoassays is to identify antigens or serological markers that allow accurate discrimination between infected and uninfected cows with S. aureus, since this bacterium can naturally colonize different areas of the animal body.Aim. To evaluate three S. aureus proteins (IsdA, ClfA, SdrD) involved in the adhesion process as antigens to detect indicator antibodies of bovine intramammary infections.Methodology. Ninety-six cows in lactation and not vaccinated against S. aureus were included. Forty-eight of these cows were infected with S. aureus, while the rest (n=48 cows) were uninfected. Blood and milk samples were collected from each animal to recover serum and whey. IgG titres against the three proteins individually and combined (Mix) were measured in each sample using an enzyme-linked immunosorbent assay (ELISA) test.Results. Significant differences in the IgG response against the proteins evaluated were observed, highlighting the antigenic potential of IsdA and demonstrating that some antigens can detect specific antibodies of infection better than others. According to receiver operating characteristic (ROC) curve analysis, the combined proteins showed the most remarkable capacity (sensitivity of 79 % and specificity of 77 %) to differentiate between infected and uninfected cows when blood samples were used. In addition, the combined proteins also showed the highest specificity (94 %) when using milk samples.Conclusion. Our findings provide information on the usefulness of three adhesion-associated S. aureus proteins in detecting serological markers of intramammary infections in bovines.

Differential immune response to two Staphylococcus aureus strains with distinct adaptation genotypes after experimental intramammary infection of dairy cows

The aim of this study was to evaluate and compare the ability of two S. aureus strains with different adaptation genotypes (low and high) to the bovine mammary gland (MG) to establish an intramammary infection (IMI) and induce an immune response after an experimental challenge in lactating cows. Two isolates (designated 806 and 5011) from bovine IMI with different genotypic profiles, harboring genes involved in adherence and biofilm production, belonging to different capsular polysaccharide (CP) type, accessory gene regulator (agr) group, pulsotype (PT) and sequence type/clonal complex (ST/CC) were selected. Strains 806 and 5011 were associated with low (nonpersistent-NP) and high (persistent-P) adaptation to the MG, respectively. Strain 806 (NP) was characterized as agr group II, cap5 positive and ST350; strain 5011 (P) agr group I, cap8 positive and CC188. Three groups of clinically healthy cows, 4 cows/treatment group, were inoculated by the intramammary route with strain 806 (NP), strain 5011 (P) and pyrogen-free saline solution. All mammary quarters challenged with strain 806 (NP) developed mild clinical mastitis between 1 and 7 d post inoculation (pi). Quarters challenged with strain 5011 (P) developed a persistent IMI; bacteria were recovered from milk from d 7 pi and up to d 56 pi. In quarters inoculated with strain 806 (NP) the inflammatory response induced was greater and earlier than the one induced by strain 5011 (P), since a somatic cell count (SCC) peak was observed at d 2 pi, while in quarters inoculated with strain 5011 (P) no variations in SCC were observed until d 4 pi reaching the maximum values at d 14 pi; indicating a lower and delayed initial inflammatory response. The highest levels of nitric oxide (NO) and lactoferrin (Lf) detected in milk from quarters inoculated with both S. aureus strains coincided with the highest SCC at the same time periods, indicating an association with the magnitude of inflammation. The high levels of IL-1β induced by strain 806 (NP) were associated with the highest SCC detected (d 2 pi); while quarters inoculated with strain 5011 (P) showed similar IL-1β levels to those found in control quarters. In quarters inoculated with strain 806 (NP) two peaks of IL-6 levels on d 2 and 14 pi were observed; while in quarters inoculated with strain 5011 (P) IL-6 levels were similar to those found in control quarters. The strain 806 (NP) induced a higher total IgG and IgG₁ response; while strain 5011 (P) generated a higher IgG₂ response (even against the heterologous strain). The present study demonstrated that S. aureus strains with different genotype and adaptability to bovine MG influence the local host immune response and the course and severity of the infectious process.

Staphylococcus aureus and Enterococcus faecium isolated from pigeon droppings (Columba livia) in the external environment close to hospitals

Background:

Domestic pigeons carry pathogens in their droppings, posing a potential public health problem.

Methods:

The phenotypic and genotypic antimicrobial resistances of Staphylococcus aureus and Enterococcus faecium in the feces of urban pigeons near hospitals with intensive care units were measured.

Results:

Twenty-nine samples showed Enterococcus growth, whereas one was positive for S. aureus. The S. aureus isolate was sensitive to the antibiotics tested via antibiogram, however resistance genes were identified. E. faecium isolates showed phenotypic resistance to gentamicin, erythromycin, and ciprofloxacin.

Conclusions:

Antimicrobial profiles harmful to health were demonstrated in bacterial pathogens isolated from the external environment of hospitals.

Usefulness of molecular typing methods for epidemiological and evolutionary studies of Staphylococcus aureus isolated from bovine intramammary infections

In cattle, Staphylococcus aureus is a major pathogen of increasing importance due to its association with intramammary infections (IMIs), which are a primary cause of antibiotic use on farms and thus of the rise in antibiotic resistance. Methicillin-resistant S. aureus (MRSA), which are frequently isolated from cases of bovine mastitis, represent a public health problem worldwide. Understanding the epidemiology and the evolution of these strains relies on typing methods. Such methods were phenotypic at first, but more recently, molecular methods have been increasingly utilized. Multiple-locus variable number tandem repeat analysis (MLVA), a high-throughput molecular method for determining genetic diversity and the emergence of host- or udder-adapted clones, appears to be the most useful PCR-based method. Despite the difficulties present in reproducibility, interlaboratory reliability, and hard work, it is agreed that pulsed-field gel electrophoresis (PFGE) remains the gold standard, particularly for short-term surveillance. Multilocus sequence typing (MLST) is a good typing method for long-term and global epidemiological investigations, but it is not suitable for outbreak investigations. Staphylococcal protein A (spa) typing is the most widely used method today for first-line typing in the study of molecular evolution, and outbreaks investigations. Staphylococcal cassette chromosome mec (SCCmec) typing has gained popularity for the evolutionary analysis of MRSA strains. Whole-genome sequencing (WGS) and DNA microarrays that represent relatively new DNA-based technologies, provide more information for tracking antibioresistant and virulent outbreak strains. They offer a higher discriminatory power, but are not suitable for routine use in clinical veterinary medicine at this time. Descriptions of the evolution of these methods, their advantages, and limitations are given in this review.

Prevalence, antimicrobial susceptibilities and risk factors of Methicillin resistant Staphylococcus aureus (MRSA) in dairy bovines

Staphylococcus aureus is a common mastitis pathogen in dairy cows, and methicillin-resistant S. aureus (MRSA) has been found in dairy farms all over the world. The study carried out on bovines from three governorates in Egypt, with the goal of determining the prevalence of MRSA in positive milk samples of subclinical mastitis, performing an antibiotic susceptibility test against MRSA isolates and determining the risk factors associated with MRSA. A total of 350 quarter milk samples (n = 200 mixed breed cow; n = 150 water buffalo) were collected and examined for subclinical mastitis using the California mastitis test (CMT) before being exposed to standard microbiological procedures for S. aureus isolation. The disc diffusion method was used to phenotypically analyse the positive S. aureus isolates for MRSA, which was verified by a PCR assay targeting the mecA gene. According to the findings of the study, 41.4% (145/350) milk samples were positive based on CMT, while 35.7% (125/350) of positive samples identified as MRSA based on PCR assay. However, the obtained results revealed non-significant disparity between cattle and buffalo and all predicted risk factors were strongly associated with prevalence of subclinical mastitis. The in-vitro antibiotic susceptibility test revealed that cefoxitin was completely resistant, whereas linezolid, ciprofloxacin, and trimethoprim + sulphamethoxazole were sensitive against the MRSA isolates. The relevance of S. aureus to public health, as well as the development of resistance to antibiotics like methicillin, needs ongoing testing of antimicrobial medications against MRSA isolates.

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.

Antibiotic Resistance and Molecular Profiling of the Clinical Isolates of Staphylococcus aureus Causing Bovine Mastitis from India

Staphylococcus aureus is an opportunistic bacterium known to cause severe infections in humans and animals. It is one of the major bacteria causing subclinical and clinical mastitis, leading to significant economic losses in livestock industry. In this study, we have isolated and characterized 80 S. aureus clinical isolates from mastitis-infected animals. The analysis of antimicrobial susceptibility, molecular typing, biofilm production and genetic determinants was performed to understand molecular and phenotypic features of the prevalent pathogen. Our antibiotic susceptibility assays showed the majority (57.5%) of isolates to be multidrug-resistant (MDR), 38.75% resistant and 3.75% sensitive. We found 25% isolates to be methicillin-resistant S. aureus (MRSA) based on oxacillin susceptibility assays. In the MRSA group, maximum isolates (95%) were MDR compared to 45% in MSSA. Multilocus sequence typing (MLST) revealed 15 different STs; ST-97 was the most common ST, followed by ST-2459, ST-1, ST-9 and ST-72. The agr typing showed agr-I as the most common type, followed by type II and III. Most isolates developed biofilms, which ranged in intensity from strong to weak. The presence or absence of lukS, a virulence-related gene, was found to have a substantial relationship with the biofilm phenotype. However, no significant association was found between biofilm formation and antimicrobial resistance or other virulence genes. We also found four MRSA isolates that were mecA negative based on molecular assays. Our findings reveal the prevalence of multidrug-resistant S. aureus clinical isolates in India that are biofilm positive and have critical genetic factors for disease pathogenesis causing bovine mastitis. This study emphasizes the need for the comprehensive surveillance of S. aureus and other mastitis-causing pathogens to control the disease effectively.

Diversity and pathogenesis of Staphylococcus aureus from bovine mastitis: current understanding and future perspectives

Staphylococcus aureus is a leading cause of bovine mastitis worldwide. Despite some improved understanding of disease pathogenesis, progress towards new methods for the control of intramammary infections (IMI) has been limited, particularly in the field of vaccination. Although herd management programs have helped to reduce the number of clinical cases, S. aureus mastitis remains a major disease burden. This review summarizes the past 16 years of research on bovine S. aureus population genetics, and molecular pathogenesis that have been conducted worldwide. We describe the diversity of S. aureus associated with bovine mastitis and the geographical distribution of S. aureus clones in different continents. We also describe studies investigating the evolution of bovine S. aureus and the importance of host-adaptation in its emergence as a mastitis pathogen. The available information on the prevalence of virulence determinants and their functional relevance during the pathogenesis of bovine mastitis are also discussed. Although traits such as biofilm formation and innate immune evasion are critical for the persistence of bacteria, the current understanding of the key host-pathogen interactions that determine the outcome of S. aureus IMI is very limited. We suggest that greater investment in research into the genetic and molecular basis of bovine S. aureus pathogenesis is essential for the identification of novel therapeutic and vaccine targets.

Antimicrobial Resistance and Molecular Characterization of Staphylococcus aureus Recovered from Cows with Clinical Mastitis in Dairy Herds from Southeastern Brazil

Staphylococcus aureus is a contagious pathogen frequently associated with bovine mastitis in Brazil. Molecular characterization of Staph. aureus isolated from affected mammary quarters of cows with clinical mastitis (CM) can provide data on epidemiological behavior of this pathogen and antimicrobial susceptibility (AMS) assessment at the genotypic level. This study genotypically characterized Staph. aureus isolates recovered from cows with CM and determined the association of genotypes and AMS. A total of 84 Staph. aureus strains identified from affected mammary quarters of cows with CM in 13 dairy herds from Southeastern Brazil were submitted for susceptibility testing to 10 antimicrobials using the technique of minimal inhibitory concentration. The same isolates were also genotyped using the spa-typing methodology. Results showed a high genotypic similarity between the Staph. aureus isolates within and between herds, which were categorized as resistant to most antimicrobials, especially to β-lactam antibiotics. In addition, differences in AMS were observed among genotypic clusters, which may affect the efficacy of antimicrobials used to treat CM in different dairy herds.

Comparative Genomics of Borderline Oxacillin-Resistant Staphylococcus aureus Detected during a Pseudo-outbreak of Methicillin-Resistant S. aureus in a Neonatal Intensive Care Unit

Active surveillance for methicillin-resistant Staphylococcus aureus (MRSA) is a component of our neonatal intensive care unit (NICU) infection prevention efforts. Recent atypical trends prompted review of 42 suspected MRSA isolates. Species identification was confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and methicillin resistance was reevaluated by PBP2a lateral flow assay, cefoxitin/oxacillin susceptibility testing, mecA and mecC PCR, and six commercially available MRSA detection agars. All isolates were confirmed S. aureus, but only eight were MRSA (cefoxitin resistant, PBP2a positive, mecA positive, growth on all MRSA screening agars). One MRSA isolate was cefoxitin susceptible but PBP2a and mecA positive, and the remaining 33 were cefoxitin susceptible, PBP2a negative, and mecA negative; interestingly, these isolates grew inconsistently across MRSA screening agars and had susceptibility profiles consistent with that of borderline oxacillin-resistant S. aureus (BORSA). Comparative genomic analyses found these BORSA isolates to be phylogenetically diverse and not representative of clonal expansion or shared gene content, though clones of two NICU strains were infrequently observed over 8 months. We identified 6 features-substitutions and truncations in PBP2, PBP4, and GdpP and beta-lactamase hyperproduction-that were used to generate a random forest classifier to distinguish BORSA from methicillin-susceptible S. aureus (MSSA) in our cohort. Our model demonstrated a robust ability to predict the BORSA phenotype among isolates collected across two continents (validation area under the curve [AUC], 0.902). Taking these findings together, we observed an unexpected prevalence of BORSA in our NICU, BORSA misclassification by existing MRSA screening methods, and markers that are together discriminatory for BORSA and MSSA within our cohort. This work has implications for epidemiological reporting of MRSA rates for centers using different screening methods. IMPORTANCE In this study, we found a high prevalence of Staphylococcus aureus isolates exhibiting a borderline oxacillin resistance phenotype (BORSA) in our neonatal intensive care unit (NICU) serendipitously due to the type of MRSA screening agar used by our laboratory for active surveillance cultures. Subsequent phenotypic and molecular characterization highlighted an unexpected prevalence and variability of BORSA isolates. Through whole-genome sequencing, we interrogated core and accessory genome content and generated a random forest classification model to identify mutations and truncations in the PBP2, PBP4, and GdpP proteins and beta-lactamase hyperproduction, which correlated with BORSA and MSSA phenotypes among S. aureus clinical isolates collected across two continents. In consideration of these findings, this work will help clinical microbiology laboratories and clinicians identify MRSA screening shortfalls and draw attention to the non-mecA-mediated BORSA phenotype.

Characterization of Virulence Factors in Enterotoxin-Producing Staphylococcus aureus from Bulk Tank Milk

Simple Summary

Staphylococcus aureus, apathogen that causes bovine mastitis, produces various virulence factors, and human consumption of milk contaminated with the S. aureus enterotoxin may pose a public health risk. This study analyzed the genetic characteristics of bovine-mastitis-related virulence factors to evaluate the potential pathogenesis of S. aureus isolated from bulk tank milk. The results show that S. aureus isolated from bulk tank milk, not from mastitis, had a high prevalence of virulence factors and that the high presence of enterotoxins may be due to poor hygiene. Therefore, developing a strong monitoring and sanitation program for dairy factories is important to ensure hygienic milk production.

Abstract

Staphylococcus aureus, a persistent mastitis-causing pathogen, produces various virulence factors, including enterotoxins. This study analyzed the genetic characteristics of bovine-mastitis-related virulence factors to evaluate the potential pathogenesis of S. aureus isolated from bulk tank milk. Among 93 S. aureus isolates from 396 dairy farms operated by 3 dairy companies in Korea, 40 (43.0%) isolates carried one or more enterotoxin genes. Moreover, S. aureus carrying enterotoxin genes showed a higher prevalence in all virulence genes tested in this study except for pvl and lukM, which were not detected in any isolate, than in the isolates without enterotoxin genes. In particular, the prevalence of six genes (hla, hlb, lukED, fnbA, clfA, and clfB) was significantly higher in S. aureus carrying the enterotoxin genes than in the isolates without the enterotoxin genes (p < 0.05). The most common multilocus sequence type of enterotoxin-producing isolates was ST188, and all isolates of ST188 harbored the see gene. S. aureus isolated from bulk tank milk, not from mastitis, had a high prevalence of virulence factors, posing a public health threat. Moreover, a high presence of enterotoxins in bulk tank milk is probably because of poor hygiene; therefore, it is important to develop strong monitoring and sanitation programs for dairy factories.

Bacteriophages: Combating Antimicrobial Resistance in Food-Borne Bacteria Prevalent in Agriculture

Through recent decades, the subtherapeutic use of antibiotics within agriculture has led to the widespread development of antimicrobial resistance. This problem not only impacts the productivity and sustainability of current agriculture but also has the potential to transfer antimicrobial resistance to human pathogens via the food supply chain. An increasingly popular alternative to antibiotics is bacteriophages to control bacterial diseases. Their unique bactericidal properties make them an ideal alternative to antibiotics, as many countries begin to restrict the usage of antibiotics in agriculture. This review analyses recent evidence from within the past decade on the efficacy of phage therapy on common foodborne pathogens, namely, Escherica coli, Staphylococcus aureus, Salmonella spp., and Campylobacter jejuni. This paper highlights the benefits and challenges of phage therapy and reveals the potential for phages to control bacterial populations both in food processing and livestock and the possibility for phages to replace subtherapeutic usage of antibiotics in the agriculture sector.

Regulatory network of miRNA, lncRNA, transcription factor and target immune response genes in bovine mastitis

Pre- and post-transcriptional modifications of gene expression are emerging as foci of disease studies, with some studies revealing the importance of non-coding transcripts, like long non-coding RNAs (lncRNAs) and microRNAs (miRNAs). We hypothesize that transcription factors (TFs), lncRNAs and miRNAs modulate immune response in bovine mastitis and could potentially serve as disease biomarkers and/or drug targets. With computational analyses, we identified candidate genes potentially regulated by miRNAs and lncRNAs base pair complementation and thermodynamic stability of binding regions. Remarkably, we found six miRNAs, two being bta-miR-223 and bta-miR-24-3p, to bind to several targets. LncRNAs NONBTAT027932.1 and XR_003029725.1, were identified to target several genes. Functional and pathway analyses revealed lipopolysaccharide-mediated signaling pathway, regulation of chemokine (C-X-C motif) ligand 2 production and regulation of IL-23 production among others. The overarching interactome deserves further in vitro/in vivo explication for specific molecular regulatory mechanisms during bovine mastitis immune response and could lay the foundation for development of disease markers and therapeutic intervention.

Investigation of clonal diversity, virulence genes, and antibiotic resistance of Staphylococcus aureus recovered from raw cow milk in southern Xinjiang, China

Staphylococcus aureus is an important pathogen of humans and animals. The aim of this study was to characterize 71 of S. aureus isolates from raw cow milk in southern Xinjiang of China, including molecular typing, distribution of virulence genes, and antimicrobial susceptibility. The isolates belonged to 18 sequence types (STs) (including 11 novel STs) and 6 spa types which were divided into five different clonal complexes (CCs), including CC188, CC352, CC22, CC398, and CC5406. The majority of the strains was grouped into multilocus sequence typing (MLST) CC188 (n = 41), t189 (n = 40), and ST5796 (n = 17). Only 30.9, 12.7, 11.3, and 9.9% of the isolates were resistant to erythromycin, clindamycin/norfloxacin, tetracycline, and gentamicin, respectively. Nine of multidrug resistant (MDR) isolates were observed which was associated with CC398-t2876. The adhesion molecules clfa, clfb, and hlb were most frequently detected with the percentage rate of 98.6% (70/71), 98.6% (70/71), and 90.1% (64/71), respectively. The percentage rates of the staphylococcal enterotoxin genes sea, seb, sec, sed, seg, and sei in S. aureus isolates were 5.6, 19.8, 40.8, 1.4, 49.3, and 30.9%, respectively. The see, seh, and sej genes were not found. This study provides data about the occurrence of S. aureus in raw cow milk, revealing high carriage frequency, drug resistance, and population structure of S. aureus. Furthermore, this study suggests that effective hygienic measures be taken when handling dairy cows, in order to prevent spreading MDR strains to human through direct contact and/or consumption of contaminated food.

Antimicrobial resistance studies in staphylococci and streptococci isolated from cows with mastitis in Argentina

BACKGROUND

Staphylococcus aureus and Streptococcus agalactiae are the main cause of clinical mastitis in dairy cattle in Argentina, whereas coagulase-negative staphylococci (CNS) and environmental streptococci are the main cause of subclinical mastitis. Bacteria isolated from infected animals show increasing antimicrobial resistance.

OBJECTIVES

This study aims to determine the antimicrobial resistance of staphylococci and streptococci isolated from milk with mastitis, and to genotypically characterize the methicillin-resistant (MR) staphylococci.

METHODS

Isolation was performed on blood agar and identification was based on biochemical reactions. Antimicrobial susceptibility was according to the Clinical and Laboratory Standards Institute guidelines. The antimicrobial resistance genes, SCCmec type and spa type were detected by the polymerase chain reaction method.

RESULTS

We isolated a total of 185 staphylococci and 28 streptococci from 148 milk samples. Among the staphylococcal isolates, 154 were identified as CNS and 31 as S. aureus. Among the 154 CNS, 24.6% (n = 38) were resistant to penicillin, 14.9% (n = 23) to erythromycin, 17.5% (n = 27) to clindamycin, 6.5% (n = 10) to cefoxitin and oxacillin. Among the S. aureus isolates, 16.1% (n = 5) were resistant to penicillin, 3.2% (n = 1) to cefoxitin and oxacillin (MRSA). Six MR isolates (5 CNS and 1 MRSA) were positive to the mecA gene, and presented the SCCmec IVa. The MRSA strain presented the sequence type 83 and the spa type 002. Among the 28 streptococcal isolates, 14.3% (n = 4) were resistant to penicillin, 10.7% (n = 3) to erythromycin and 14.3% (n = 4) to clindamycin.

CONCLUSIONS

The present findings of this study indicate a development of antimicrobial resistance in main bacteria isolated from cows with mastitis in Argentina.

DNase I improves blood-milk barrier integrity and alleviates inflammation induced by Staphylococcus aureus during mastitis

Mastitis is an inflammation of mammary gland, which directly affects the milk production performance and causes huge economic losses in the dairy industry. During mastitis, the blood-milk barrier (BMB) loses its integrity and aggravates the severity of mastitis. Exogenous DNase I has been exerted protective effects in different model of tissue injury. Here, we designed a study to investigate the effects of DNase I on inflammation and BMB in a mice model of Staphylococcus aureus-induced mastitis. In the model, we found that DNase I treatment significantly alleviated the inflammatory response through decrease of inflammatory cells in mammary alveoli, MPO activity and cytokines in mammary gland. Furthermore, immunofluorescent staining and western blotting demonstrated that exogenous DNase I obviously reduced BMB permeability and changed the expression of tight junction proteins to support the re-establishment of the barrier integrity. Mechanismly, DNase I treatment inhibited NF-κB and enhanced AKT signaling pathways. Therefore, our results indicate that DNase I may be an effective treatment for attenuating mastitis.

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.

Multilocus sequence analysis reveals genetic diversity in Staphylococcus aureus isolate of goat with mastitis persistent after treatment with enrofloxacin

Staphylococcus aureus is one of the main bacterial agents responsible for cases of mastitis in ruminants, playing an important role in the persistence and chronicity of diseases treated with antimicrobials. Using the multilocus sequence typing technique, network approaches and study of the population diversity of microorganisms, we performed analyzes of S. aureus (ES-GPM) isolated from goats with persistent mastitis (GPM). The most strains of ES-GPM were categorically different phylogenetically from the others and could be divided into two lineages: one with a majority belonging to ES-GPM and the other to varied strains. These two lineages were separated by 27 nuclear polymorphisms. The 43 strains comprised 22 clonal complexes (CCs), of which the ES-GPM strains were present in CC133, CC5 and a new complex formed by the sequence type 4966. The genetic diversity of some alleles showed be greater diversity and polymorphism than others, such as of the aroE and yqiL genes less than glpF gene. In addition, the sequences ES-GPM to the arc gene and glpF alleles showed the greatest number of mutations for ES-GPM in relation to non-ES-GPM. Therefore, this study identified genetic polymorphisms characteristic of S. aureus isolated from milk of goats diagnosed with persistent mastitis after the failed treatment with the antibiotic enrofloxacin. This study may help in the future to identify and discriminate this agent in cases of mastitis, and with that, the most appropriate antibiotic treatment can be performed in advance of the appearance of persistent mastitis caused by the agent, reducing the chances of premature culling and animal suffering.

Molecular fingerprinting of bovine mastitis-associated Staphylococcus aureus isolates from India

Staphylococcus aureus is a major etiological agent of clinical and subclinical bovine mastitis. Owing to the mostly backyard dairy practices, we hypothesized that genetic diversity among mastitis-associated S. aureus from India would be high, and investigated 166 isolates obtained mostly from the Southern State of Karnataka, but also from a few other states. The results revealed (a) 8 to 13 fragments in pulsed-field gel electrophoresis (PFGE), forming 31 distinct patterns, and (b) 34 spa types, of which three (t17680, t18314, and t18320) were newly identified. Multi-locus sequencing typing (MLST) identified 39 sequence types (STs), with ST2454 (34.4%) and ST2459 (24%) being the most commonly represented, which clustered to clonal complexes (CC) CC9 and CC97, respectively; 12 STs were newly identified. Thirty-four (20.5%) of the 166 isolates displayed oxacillin resistance. On the other hand, whereas none were mecC⁺, 44 (26.5%) isolates were mecA⁺, with a predominance of SCCmecIVb (26/32 isolates, others being untypeable); 24 isolates (14.46%) were oxacillin-susceptible methicillin-resistant S. aureus (OS-MRSA; mecA⁺ but OS). Integrated analysis revealed that CC9-ST2454- and CC97-ST2459-SCCmecIVb were the predominant MRSA, although the distribution of CC9 and CC97 was similar between methicillin-resistant and -susceptible isolates. By PCR, 56.25%, 28.75% and 47.5% of the 166 isolates were positive for hlg, tsst and pvl genes, respectively. Our results, for the first time describe the application of a combination of various molecular methods to bovine mastitis-associated S. aureus isolates from India, corroborate the worldwide distribution of CC97 and CC9, and suggest pathogenic potential of the isolates.

Methicillin-resistant Staphylococcus aureus of the clonal lineage ST5-SCCmecII-t2460 was associated with high mortality in a Wuhan hospital

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen that can cause serious infectious diseases. An emerging MRSA strain, ST5-SCCmecII spa-type-t2460 (SMRSA), has spread rapidly since its recent emergence in China, but little information is available about this lineage. In this study, 91 MRSA isolates were collected from patients treated in the Zhongnan Hospital, Wuhan University, from 2018 to 2019, and investigated for their molecular characteristics, antibiotic resistance profiles, and clinical characteristics. The predominant lineage, SMRSA, accounted for 37.4% (34/91) of the isolates, followed by ST239-SCCmecIII-t030 (19.8%, 18/91) and ST59-SCCmecIV-t437 (8.8%, 8/91). In contrast to the latter two non-SMRSA (nSMRSA) lineages, which are among the main MRSA found in Chinese settings, SMRSA exhibited small colony variant (SCV) phenotype and had extremely high resistance rates to erythromycin (100.0%), clindamycin (100.0%), levofloxacin (100.0%), tetracycline (97.1%), moxifloxacin (97.1%), and ciprofloxacin (100%), but was more susceptible to rifampicin (resistance rate 3%). The levels of white blood cells (WBC) and procalcitonin (PCT) and the 30-day mortality in patients infected with SMRSA were (12.54 ± 6.61) × 10⁹/L, 0.66 ng/mL, and 52.9%, respectively, which were much higher than those in patients infected with nSMRSA. In addition, patients infected with SMRSA were more frequently admitted to the intensive care unit (ICU) and submitted to invasive procedures than those infected with nSMRSA. In conclusion, SMRSA showed SCV phenotype and exhibited multiple antibiotic-resistance profiles. In this study, SMRSA was associated with serious infections and poor prognosis. Compared with ST239, ST59, or other nSMRSA strains, patients infected with SMRSA strains have higher 30-day mortality, increased levels of inflammatory biomarkers, and more frequent ICU hospitalization and invasive procedures.

Molecular Characteristics of Staphylococcus aureus From Food Samples and Food Poisoning Outbreaks in Shijiazhuang, China

As an opportunistic pathogen worldwide, Staphylococcus aureus can cause food poisoning and human infections. This study investigated the sequence typing, the penicillin (blaZ) and methicillin (mec) resistance profiles of S. aureus from food samples and food poisoning outbreaks in Shijiazhuang City, and the staphylococcal enterotoxin (SE) types of the S. aureus isolates from food poisoning. A total of 138 foodborne S. aureus isolates were distributed into 8 clonal complexes (CCs) and 12 singletons. CC1, CC5, CC8, CC15, CC97, CC59, CC398, CC88, and CC7 were the predominant CCs of foodborne S. aureus isolates. Moreover, CC59, CC15, and CC5 were the most prevalent CCs in food poisoning outbreaks. SEE was the most commonly detected SE in food poisoning isolates. One hundred thirty-three S. aureus isolates harbored the penicillin-resistant gene blaZ, and nine isolates carried the mec gene. The present study further explained the relationship between S. aureus and foods and food poisoning and indicated the potential risk of S. aureus infection.

Update on molecular diversity and multipathogenicity of staphylococcal superantigen toxins

Staphylococcal superantigen (SAg) toxins are the most notable virulence factors associated with Staphylococcus aureus, which is a pathogen associated with serious community and hospital acquired infections in humans and various diseases in animals. Recently, SAg toxins have become a superfamily with 29 types, including staphylococcal enterotoxins (SEs) with emetic activity, SE-like toxins (SEls) that do not induce emesis in primate models or have yet not  been tested, and toxic shock syndrome toxin-1 (TSST-1). SEs and SEls can be subdivided into classical types (SEA to SEE) and novel types (SEG to SElY, SE01, SE02, SEl26 and SEl27). The genes of SAg toxins are located in diverse accessory genetic elements and share certain structural and biological properties. SAg toxins are heat-stable proteins that exhibit pyrogenicity, superantigenicity and capacity to induce lethal hypersensitivity to endotoxin in humans and animals. They have multiple pathogenicities that can interfere with normal immune function of host, increase the chances of survival and transmission of pathogenic bacteria in host, consequently contribute to the occurrence and development of various infections, persistent infections or food poisoning. This review focuses on the following aspects of SAg toxins: (1) superfamily members of classic and novelty discovered staphylococcal SAgs; (2) diversity of gene locations and molecular structural characteristics; (3) biological characteristics and activities; (4) multi-pathogenicity of SAgs in animal and human diseases, including bovine mastitis, swine sepsis, abscesses and skin edema in pig, arthritis and septicemia in poultry, and nosocomial infections and food-borne diseases in humans.

Identification and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus-associated subclinical mastitis isolated from dairy cows in Bogor, Indonesia

Background and Aim:

Subclinical mastitis is an udder infection devoid of clinical symptoms, and Staphylococcus aureus is one of the bacteria causing this disease. This study aimed to identify and determine the prevalence and antibiotic susceptibility of methicillin-resistant S. aureus (MRSA)-associated subclinical mastitis isolated from dairy cows in Bogor, Indonesia.

Materials and Methods:

S. aureus was isolated from subclinical mastitis milk specimens. All strains were confirmed by polymerase chain reaction-based detection of staphylococcal nuc, and MRSA was confirmed by the presence of mecA. Antibiotic susceptibility was determined using the disk diffusion method.

Results:

From 86 milk samples, 49 isolates (57%) were confirmed as S. aureus. All S. aureus isolates were susceptible to tetracycline, gentamicin, chloramphenicol, erythromycin, and trimethoprim/sulfamethoxazole. Nine isolates were identified as MRSA (10.5%).

Conclusion:

In this study, we reported MRSA-associated subclinical mastitis in Bogor, Indonesia.

Antimicrobial resistance and genotyping of Staphylococcus aureus obtained from food animals in Sichuan Province, China

Background

Staphylococcus aureus (S. aureus), especially methicillin-resistant Staphylococcus aureus (MRSA), is considered a common zoonotic pathogen, causing severe infections. The objective of this study was to investigate the antimicrobial susceptibility, resistance genes and molecular epidemiology among MRSA and methicillin-susceptible Staphylococcus aureus (MSSA) isolated from food animals in Sichuan Province, China.

Methods

This study was conducted on 236 S. aureus isolates. All isolates were subjected to antimicrobial susceptibility testing by using a standard microbroth dilution method. The Polymerase Chain Reaction (PCR) was performed to identify genes encoding the β-lactams resistance (blaZ, mecA), macrolides (ermA, ermB, ermC) and aminoglycosides (aacA-aphD). The molecular structures and genomic relatedness of MRSA isolates were determined by staphylococcal chromosome cassette mec (SCCmec) typing and pulsed-field gel electrophoresis (PFGE), respectively.

Results

Among 236 isolates, 24 (10.17 %) were recognized as MRSA. MRSA isolates showed different resistance rates to 11 antimicrobials ranging from 33.33 to 100 %, while for MSSA isolates the rates varied from 8.02 to 91.51 %. Multi-drug resistance phenotype was found in all MRSA isolates. The ermC gene encoding macrolides-lincosamides-streptogramin B was the most prevalent gene detected in 87.29 % of the S. aureus isolates, followed by ermB (83.05 %), blaZ (63.98 %), aacA-aphD (44.07 %), ermA (11.44 %) and mecA (11.02 %) genes. The prevalence of resistance genes in MRSA isolates was significantly higher than that of MSSA. Regarding the molecular morphology, SCCmec III (12/24, 50 %) was the most common SCCmec type. Furthermore, the PFGE typing showed that 24 MRSA were divided into 15 cluster groups (A to O), the major pulsotype J encompassed 25 % of MRSA isolates.

Conclusions

The S. aureus isolates from food animals in Sichuan province of China have severe antimicrobials resistance with various resistance genes, especially MRSA isolates. Additionally, the genetic pool of MRSA isolates is diverse and complex, and further investigation is necessary.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02884-z.

Characterisation of Staphylococcus aureus isolates from bovine mastitis in Ningxia, Western China

OBJECTIVES

The aim of this study was to explore the antimicrobial resistance, virulence genes and molecular characteristics of Staphylococcus aureus from bovine mastitis cases.

METHODS

A total of 125 non-duplicate S. aureus isolates from bovine mastitis cases in Ningxia, China, were characterised by antimicrobial susceptibility and molecular testing to determine the antimicrobial resistance, virulence genes and molecular characteristics.

RESULTS

All methicillin-resistant S. aureus (MRSA) isolates were resistant to ampicillin, oxacillin, ceftiofur, erythromycin, gentamicin and clindamycin, with resistance to nine different categories of antibiotics observed amongst the MRSA isolates. Of the methicillin-susceptible S. aureus (MSSA) isolates, 62.1% were resistant to ampicillin and sulfisoxazole. Nine clonal complexes (CCs) and 16 spa types were identified by multilocus sequence typing (MLST) and spa typing. The dominant CCs were CC97 (51.2%) and CC50 (30.4%), while t224 (30.4%), t518 (20.0%) and t359 (16.8%) were the most common spa types. A relatively high proportion (27.2%) of the S. aureus isolates belonged to ST4053, a novel sequence type identified in this study. In addition, two CC30 MSSA isolates and two CC59 MRSA isolates were positive for Panton-Valentine leukocidin, while one CC239 MRSA isolate and three CC5 MSSA isolates were positive for TSST-1. All MRSA isolates carried the immune evasion cluster (IEC) genes, including scn (100%; 9/9) and sak (100%; 9/9), which were classified into type E.

CONCLUSION

Our study indicates severe antibiotic resistance and complicated molecular characterisation of S. aureus causing bovine mastitis. Additional studies should be conducted to monitor infection and transmission of S. aureus.

Molecular epidemiology of Staphylococcus aureus in African children from rural and urban communities with atopic dermatitis

Background

Staphylococcus aureus has been associated with the exacerbation and severity of atopic dermatitis (AD). Studies have not investigated the colonisation dynamics of S. aureus lineages in African toddlers with AD. We determined the prevalence and population structure of S. aureus in toddlers with and without AD from rural and urban South African settings.

Methods

We conducted a study of AD-affected and non-atopic AmaXhosa toddlers from rural Umtata and urban Cape Town, South Africa. S. aureus was screened from skin and nasal specimens using established microbiological methods and clonal lineages were determined by spa typing. Logistic regression analyses were employed to assess risk factors associated with S. aureus colonisation.

Results

S. aureus colonisation was higher in cases compared to controls independent of geographic location (54% vs. 13%, p < 0.001 and 70% vs. 35%, p = 0.005 in Umtata [rural] and Cape Town [urban], respectively). Severe AD was associated with higher colonisation compared with moderate AD (86% vs. 52%, p = 0.015) among urban cases. Having AD was associated with colonisation in both rural (odds ratio [OR] 7.54, 95% CI 2.92–19.47) and urban (OR 4.2, 95% CI 1.57–11.2) toddlers. In rural toddlers, living in an electrified house that uses gas (OR 4.08, 95% CI 1.59–10.44) or utilises kerosene and paraffin (OR 2.88, 95% CI 1.22–6.77) for heating and cooking were associated with increased S. aureus colonisation. However, exposure to farm animals (OR 0.3, 95% CI 0.11–0.83) as well as living in a house that uses wood and coal (OR 0.14, 95% CI 0.04–0.49) or outdoor fire (OR 0.31, 95% CI 0.13–0.73) were protective. Spa types t174 and t1476, and t272 and t1476 were dominant among urban and rural cases, respectively, but no main spa type was observed among controls, independent of geographic location. In urban cases, spa type t002 and t442 isolates were only identified in severe AD, t174 was more frequent in moderate AD, and t1476 in severe AD.

Conclusion

The strain genotype of S. aureus differed by AD phenotypes and rural-urban settings. Continued surveillance of colonising S. aureus lineages is key in understanding alterations in skin microbial composition associated with AD pathogenesis and exacerbation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06044-4.