Host- and tissue-specific pathogenic traits of Staphylococcus aureus

Identification of the Enterotoxigenic Potential of Staphylococcus spp. from Raw Milk and Raw Milk Cheeses

This study aimed to genotypic and phenotypic analyses of the enterotoxigenic potential of Staphylococcus spp. isolated from raw milk and raw milk cheeses. The presence of genes encoding staphylococcal enterotoxins (SEs), including the classical enterotoxins (sea-see), non-classical enterotoxins (seg-seu), exfoliative toxins (eta-etd) and toxic shock syndrome toxin-1 (tst-1) were investigated. Isolates positive for classical enterotoxin genes were then tested by SET-RPLA methods for toxin expression. Out of 75 Staphylococcus spp. (19 Staphylococcus aureus and 56 CoNS) isolates from raw milk (49/65.3%) and raw milk cheese samples (26/34.7%), the presence of enterotoxin genes was confirmed in 73 (97.3%) of them. Only one isolate from cheese sample (1.3%) was able to produce enterotoxin (SED). The presence of up to eight different genes encoding enterotoxins was determined simultaneously in the staphylococcal genome. The most common toxin gene combination was sek, eta present in fourteen isolates (18.7%). The tst-1 gene was present in each of the analyzed isolates from cheese samples (26/34.7%). Non-classical enterotoxins were much more frequently identified in the genome of staphylococcal isolates than classical SEs. The current research also showed that genes tagged in S. aureus were also identified in CoNS, and the total number of different genes detected in CoNS was seven times higher than in S. aureus. The obtained results indicate that, in many cases, the presence of a gene in Staphylococcus spp. is not synonymous with the ability of enterotoxins production. The differences in the number of isolates with genes encoding SEs and enterotoxin production may be mainly due to the limit of detection of the toxin production method used. This indicates the need to use high specificity and sensitivity methods for detecting enterotoxin in future studies.

Community-Acquired Methicillin-Resistant Staphylococcus aureus in Hospitals: Age-Specificity and Potential Zoonotic-Zooanthroponotic Transmission Dynamics

Methicillin-resistant Staphylococcus aureus (MRSA) lineages are a devastating clinical and public health issue. Data on local lineage profiles are limited. We report on the frequency of community-acquired and hospital-acquired cases (CA-MRSA, HA-MRSA). We studied 147 isolates from King Khalid tertiary care hospitals (KKH), each from a case in a patient and including 33 patients at the Maternity and Children's Hospital (MCH). Of the 147 isolates, 87 males (59%) and 60 females (41%) were in KKH. The overwhelming majority (80%; n = 119/147) were CA-MRSA in KKH. Intriguingly, despite significant differences between males (70%) and females (53%), lineage-acquisition remained age-specific around 58-60 years in both genders. However, while CA-MRSA dominated early in life (0-20, 70% MCH), it increased with age in KKH adults; 21-50 (28%), >50 (59%) until the overall 80% (n = 144/180). Major specimens included skin-wounds, surgeries (70.3%), blood (13.5%), sputum (8.8%), very rarely urine (4.1%), and nasal (3.4%), albeit most patients showed severe enteritis and necrotizing pneumonia. Antibiograms showed high beta lactam resistances, including amoxicillin-clavulanate (83%), oxacillin (84%), cefoxitin FOX (100%), penicillin and ampicillin (~100%), as well as high resistance (82%) to carbapenem. Fortunately, high susceptibility was seen to non-beta lactams and, to a lesser extent, gentamicin, erythromycin, and fusidic acid; 33%, 34%, and 38%, respectively, in KKH. A similar pattern was seen in MCH except for a low resistance pattern to gentamicin CN, clindamycin CD, erythromycin E, and tobramycin TOB; 34%, 31%, 39%, and 41%, respectively, except for fusidic acid. These findings have significant clinical implications for MRSA patient management strategies. Clinical- and lineage-profiles imply host-selection and zoonotic-zooanthroponotic transmission dynamics. Future molecular typing, sequencing, and characterization of dominant clone(s) is imperative.

Molecular and Source-Specific Profiling of Hospital Staphylococcus aureus Reveal Dominance of Skin Infection and Age-Specific Selections in Pediatrics and Geriatrics

Staphylococcus aureus is a major human-associated pathogen that causes a wide range of clinical infections. However, the increased human dynamics and the changing epidemiology of the species have made it imperative to understand the population structure of local ecotypes, their transmission dynamics, and the emergence of new strains. Since the previous methicillin-resistant S. aureus (MRSA) pandemic, there has been a steady increase in global healthcare-associated infections involving cutaneous and soft tissue and resulting in high morbidities and mortalities. Limited data and paucity of high-quality evidence exist for many key clinical questions about the pattern of S. aureus infections. Using clinical, molecular, and epidemiological characterizations of isolates, hospital data on age and infection sites, as well as antibiograms, we have investigated profiles of circulating S. aureus types and infection patterns. We showed that age-specific profiling in both intensive care unit (ICU) and non-ICU revealed highest infection rates (94.7%) in senior-patients > 50 years; most of which were MRSA (81.99%). However, specific distributions of geriatric MRSA and MSSA rates were 46.5% and 4.6% in ICU and 35.48% and 8.065% in non-ICU, respectively. Intriguingly, the age groups 0−20 years showed uniquely similar MRSA patterns in ICU and non-ICU patients (13.9% and 9.7%, respectively) and MSSA in ICU (11.6%). The similar frequencies of both lineages in youth at both settings is consistent with their increased socializations and gathering strongly implying carriage and potential evolutionary replacement of MSSA by MRSA. However, in age groups 20−50 years, MRSA was two-fold higher in non-ICU (35%) than ICU (18.6%). Interestingly, a highly significant association was found between infection-site and age-groups (p-value 0.000). Skin infections remained higher in all ages; pediatrics 32.14%, adults 56%, and seniors 25% while respiratory infections were lower in pediatrics (14.3%) and adults (17%) while it was highest in seniors (38%). Blood and “other” sites in pediatrics were recorded (28.6%; 25%, respectively), and were slightly lower in adults (18.6%; 8.6%) and seniors (14%; 22.8%), respectively. Furthermore, a significant association existed between infection-site and MRSA (Chi-Square Test, p-value 0.002). Thus, the common cutaneous infections across all age-groups imply that skin is a significant reservoir for endogenous infections; particularly, for geriatrics MRSA. These findings have important clinical implications and in understanding S. aureus profiles and transmission dynamics across different age groups that is necessary for strategic planning in patient management and infection control.

Molecular characterization of virulence factors in Staphylococcus aureus isolated from bovine subclinical mastitis in central Ethiopia

Purpose

Staphylococcus aureus (S. aureus) is the most important pathogen involved in bovine mastitis in dairy production. S. aureus produces a spectrum of extracellular protein toxins and virulence factors which are thought to contribute to the pathogenicity of the organism. The aim of this work was to isolate and molecular characterize S. aureus associated with bovine subclinical mastitis in the central part of Ethiopia.

Methods

A total of 265 lactating dairy cows from various dairy farms in four different geographical locations were screened by the California mastitis test (CMT) for bovine subclinical mastitis. One hundred thirty CMT-positive milk samples were collected and transported to the laboratory. Different biochemical tests and polymerase chain reaction (PCR) were used for the identification of S. aureus isolates. Finally, PCR was performed for molecular detection of virulence genes.

Results

From a total of 265 lactating dairy cows screened, 49% (n = 130) were positive for bovine subclinical mastitis. One hundred thirty mastitic milk samples were subjected to bacterial culturing, and one hundred (76%) S. aureus isolates were identified based on phenotypic characters. Sixty-eight confirmed S. aureus isolates were obtained using PCR. The confirmed S. aureus isolates were tested for six virulence genes (tsst-1, hlb, eta, sea, clfA, and icaD) using PCR. Of the six virulence genes screened from all the isolates, only two (clfA and eta) were detected in the isolates. Out of 68 isolates, 25% and 22% were possessed the eta and clfA genes, respectively.

Conclusion

The presence of Staphylococcus aureus having virulence genes (eta and clfA) revealed that mastitis is a major concern nowadays affecting animal health, milk quality, and yield. Further genomic study of these isolates will provide broad new insights on virulence.

Staphylococcus aureus Isolated from Ruminants with Mastitis in Northern Greece Dairy Herds: Genetic Relatedness and Phenotypic and Genotypic Characterization

Staphylococcus aureus is the most common mastitis-related pathogen in dairy cattle, goats, and sheep worldwide. However, the population structure and genomic characteristics of mastitis-associated S. aureus in small ruminants are limited. Furthermore, the genotypic and phenotypic characteristics involved in the pathogenicity of S. aureus have been thoroughly defined, yet their association with the severity of mastitis is not fully established. Here, we performed genotyping by pulsed-field gel electrophoresis (PFGE) and spa analyses to assess the genetic diversity and relatedness of 162 S. aureus strains recovered from clinical mastitis (CM) and subclinical mastitis (SCM) cases from goats, sheep, and bovines. PFGE analysis revealed 108 distinguishable pulsotypes and 3 main clusters that comprised isolates from the three host species, while according to spa typing, 32 different spa types were identified. Genotypic analysis revealed a spreading of genetically related or indistinguishable S. aureus strains among ovine, caprine, and bovine farms of distant geographical regions. In total, 28 different staphylococcal enterotoxin (SE) gene profiles were observed, revealing a diverse range of SE genes among isolates. By evaluating the antimicrobial resistance, we found low phenotypic antimicrobial resistance among all ruminant isolates. We also performed multiple correspondence analysis, which indicated that the presence of the sec gene, biofilm production, and high autoaggregation ability are associated with CM cases.

Genetic diversity and virulence characteristics of Staphylococcus aureus isolates from cases of bovine mastitis

Staphylococcus aureus is one of the major bacterial mastitis pathogens with significant effects on animal and human health. Some studies showed that S. aureus strains that infect different host species are genetically distinct, although most strains can infect a wide range of host species. However, there are no clearly defined clonal patterns of S. aureus strains that are known to infect a specific host. The objectives of this study were to evaluate the clonal diversity and virulence characteristics of S. aureus isolates from cases of bovine mastitis. Bacteriological tests were conducted on milk samples from cases of bovine mastitis from 11 dairy farms including some milk samples from unknown farms in Eastern Tennessee. Overall, a total of 111 S. aureus were isolated and identified, and further evaluated for their genetic diversity by pulsed-field gel electrophoresis (PFGE) and virulence characteristics by PCR. Genotypic virulence factors including staphylococcal enterotoxins, and toxic shock syndrome toxin 1 (tsst-1) were tested by PCR. In addition, the association among several known virulence factors of these isolates based on our current and previous studies in our lab were evaluated. Previously generated data that were included in the analysis of association among virulence factors were the presence of biofilm production associated genes in the ica operon such as icaA, icaD and icaAB, and phenotypic virulence characteristics such as hemolysis on blood agar, slime production and resistance or susceptibility to ten commonly used antimicrobials in dairy farms. The PFGE results showed the presence of 16 PFGE types (designated A - P) throughout farms, of which three pulsotypes, I, M and O were the most frequently isolated PFGE types from most farms. The PFGE type M was the most prevalent of all 16 PFGE types, with 64 isolates being present among nine farms. The PCR results of enterotoxin genes showed that out of the total 111 tested 84 (75.7%) were negative whereas 13 (11.7%), 2 (1.8%), 3 (2.7%), 1 (0.9%) and 8 (7.2%) were positive for seb, seb and sec, sec, see, and tsst-1, respectively. All 111 isolates were negative for sea and sej. Results of the evaluation of I, M and O strains adhesion to and invasion into mammary epithelial cells showed that the total count of each strain of bacteria adhered to and invaded into mammary epithelial cell line (MAC-T cells) was not significantly different (P > 0.05). This may be an indication that there is no significant difference in their ability to establish early host-pathogen interaction and colonization of the host. There were no statistically significant associations among PFGE types and other known virulence factors of these strains. However, PFGE types O and M tend to cluster with β-hemolysin, absence of enterotoxins and susceptibility to antimicrobials. In conclusion, there was not any association between pulsotype and genotypic and phenotypic virulence factors. S. aureus isolates from cases of bovine mastitis had diverse genotypes that possessed variable virulence factors.

Virulence Factors and Phylogeny of Staphylococcus aureus Associated With Bovine Mastitis in Russia Based on Genome Sequences

Staphylococcus aureus is a causative agent of different infectious processes, food poisoning, and autoimmune disorders. The horizontal transfer of pathogenic strains can occur from animal to human under both house and farm conditions, and the spread of strains with antibiotic resistance is an existing problem. In addition to the spread of antibiotic-resistant strains in clinics, this problem also exists in veterinary medicine. It is especially important to monitor antibiotic resistance on farms where antibiotics are the standard treatment of animals, which may trigger the spread of antibiotic-resistant strains among animals and to the human population, and these strains can also be distributed in milk products produced by these farms (milk, cheese, and butter). In this work, we investigated 21 S. aureus isolates using whole-genome sequence analysis and tried to establish a relationship between these isolates with the development of bovine mastitis in seven regions of Western Russia. An S. aureus virulence profile was identified. We identified two groups of S. aureus associated with subclinical mastitis, namely, the enterotoxin-positive and enterotoxin-negative groups. The most prevalent factor associated with bovine mastitis in Russia was cytotoxins, including hemolysins and leukocidins. Multidrug resistance strains were investigated, and antibiotic resistance genes were identified. We identified S. aureus ST 97 type as the most common type in the regions in Western Russia. To the best of our knowledge, this is the first in-depth study of a range S. aureus isolates originating from cattle infections in Russia.

Molecular Characterization of Methicillin-Resistant Enterotoxin-Producing Staphylococcus aureus Isolated From Samosa and Falafel in Iran

Objective: This study aimed to determine the contamination rate of Staphylococcus aureus in Samosa and falafel as most popular snacks, detect the classic enterotoxins, mecA, and tst genes and investigate antimicrobial resistance in the isolates. Materials and Methods: The samples were examined using bacterial culture and the suspected isolates were characterized by biochemical tests. The identity of S. aureus isolates and the presence of enterotoxin-encoding genes were assessed using a multiplex polymerase chain reaction (PCR) assay and antibiotic resistance of the isolates was determined. Results: The results revealed that 56 (46.67%) samples were contaminated with S. aureus, among which 45 isolates (80.35%) were characterized as enterotoxigenic S. aureus. The highest prevalence rate belonged to sea encoding gene as 20 isolates (35.71%) were positive for this gene followed by sed gene which was detected in 14 S. aureus isolates (25%). Most isolates (75%) were resistant to cefoxitin. Moreover, the results of PCR assays indicated that 10 (17.58%) and 7 (12.5%) isolates were positive for mecA and tst genes, respectively. Conclusion: The results of the present study demonstrated that staphylococcal contamination of Samosa and falafel should be considered as a potential health risk for consumers.

Molecular characterization and susceptibility screening for methicillin-resistant Staphylococcus aureus reveals the dominant clones in a tertiary care hospital in Al Qassim, Saudi Arabia

OBJECTIVE

Staphylococcus aureus has become an important pathogen in hospitals worldwide. Despite its differentiation into human and animal lineages, common methods are used for genotyping. While these methods are useful, they are based on the stable genome, and hence, are insensitive to host-specific subtyping. The objectives of this study were to investigate the repeat-domain of the Clumping-Factor A gene (clfA- R) as an objective and adaptation-sensitive approach.

METHODOLOGY

We have used 113 isolates for susceptibility testing and genotyping by polymerase chain reaction amplification of the clfA- R regions. Of these, 105 were from King Fahad Specialist Hospital, Buraidah and eight were published sequences used as references. Isolates were further confirmed as S. aureus by the commercial Kits. Amplicon sizes were measured and the number of the 18-bp-repeating-units in each isolate was determined against that of methicillin-resistant S. aureus COL (MRSA) sequence.

RESULTS

Results showed that all 42 nasal screening isolates (100%) and all but six isolates from clinical specimens were MRSA with 37% of the former and 50% of the latter isolates showing community-acquired-MRSA susceptibility patterns. clfA-R analysis grouped 113 isolates into 14 repeat-genotypes. The two dominant types, D and X, represented the long- and short clfA-R types found in humans and animals, respectively. Linezolid, rifampicin, and vancomycin were the drugs of choice.

CONCLUSIONS

clfA-R was useful in rapid genotyping and implied host-specific phenotypic properties of the ClfA. It has been recommended that the approach used in regional laboratories for uniform strain-profiling. Future work will show more insights into the gene content and origins of clones .

Characterization of Staphylococcus aureus isolates from mastitic milk, udder surfaces and milkers' hands from arid and semi arid regions of India for capsular (cap5K and cap8K) and collagen adhesin (cna) genes

Staphylococcus aureus (S. aureus) is an important cause of bovine mastitis. The antiphagocytic capsule of bacteria promotes colonization and persistence on mucosal surfaces while the presence of collagen adhesin (cna gene) is associated with bacterial adhesion in mammary tissues; hence both are regarded as important determinants of virulence. In the present study, 197 samples consisting of mastitic milk, milkers' hand swabs and udder surface swabs were collected which yielded 107 S. aureus isolates. These S. aureus isolates (107) from different sources of sampling were characterized for their capsular types targeting cap5K and cap8K genes in a duplex PCR along with amplification of cna gene. Majority of the isolates (67.6%) possessed cap5K gene with a lower percentage (22.9%) of isolates carrying cap8K gene and 9.5% carrying both the genes. Moreover, cap5K gene was predominant in isolates from milkers’ hands (85.7%) while cap8K gene was more common in bovine udder isolates (41.2%). cna gene was observed in 27.6% isolates with highest occurrence in milk isolates (44.8%) compared to udder (37.9%) and milkers' hand (17.2%). cna positive isolates carried cap8K gene (66.7%) and were significantly associated with both cap5k and cap8k genes. In conclusion, the majority of the S. aureus isolates of mastitis obtained from arid and semi arid zones of India possessed the genes for capsule production, and cap5K was the predominant gene. The cna gene for collagen adhesion was observed in fewer isolates with significant association with cap8K gene.

Genotyping and antimicrobial resistance of Staphylococcus aureus isolates from dairy ruminants: differences in the distribution of clonal types between cattle and small ruminants

Staphylococcus aureus is part of the normal flora of animals, and represents one of the leading causes of contagious mastitis in dairy herds worldwide. Sixty-seven epidemiologically unrelated S. aureus isolates from nasal and mastitis milk samples of dairy-producing animals (32 cows, 25 sheep, and 10 goats) were characterized by antimicrobial susceptibility testing and spa typing followed by multilocus sequence typing (MLST) on representative isolates and SCCmec-typing on methicillin-resistant S. aureus (MRSA) isolates. The highest resistance was observed to penicillin (64.2%, 43/67), followed by tetracycline (23.9%, 16/67), erythromycin (22.4%, 15/67), and streptomycin (17.9%, 12/67). In general, 18 spa types (including newly identified t16958) and 13 sequence types (STs) belonging to 8 clonal complexes (CCs) were detected. The cow-associated isolates were mainly assigned to CC5 (n = 18, related to t267-ST97, t521-ST352, t527-ST97, t304-ST6, and t084-ST15), followed by CC398 (n = 6, t937-ST291), CC45 (n = 3, t230-ST45), CC88 (n = 2, t2526-ST88), CC22 (n = 2, t3680-ST22), and CC522 (n = 1, t3576-ST522). Small ruminant isolates were mostly clustered into CC522 (n = 29, related to t3576, t1534, t16958, t7308, t7311, t7305 [ST522], t1534-ST2057, and t5428-ST2079). Two isolates from cows with mastitis were found to be MRSA, exhibited a composite profile of t937-ST291-SCCmecIV. No isolates carried the PVL and mecC genes. A significant difference in clonal types of S. aureus isolates from cows in comparison with those from small ruminants was found. This study demonstrated the circulation of diverse clones of S. aureus among dairy animals in Iran, with a different clonal composition between cows and small ruminants. The current study also reports MRSA-related mastitis in dairy cows, emphasizing the need for comprehensive surveillance.

Isoenzymatic genotyping of Staphylococcus aureus from dairy cattle and human clinical environments reveal evolutionary divergences

Background

The genetic variability of 610 S. aureus isolates from the hands of professional dentists (A), dental clinic environment air (B), bovine milk from cows with and without mastitis (C), an insufflator for milking equipment (D) and milking environment air (E) was studied by isoenzyme genotyping and genetic and cluster analysis.

Results

Monoclonal and polyclonal patterns of S. aureus were detected in every bacterial population; however, isolates belonging to the same strain were not found among the populations, suggesting the genetic heterogeneity and the intrapopulation spread of strains. Genetic relationship analysis revealed the co-existence of highly related strains at low frequency among populations.

Conclusion

The data suggest that some strains can adapt and colonize new epidemiologically unrelated habitats. Consequently, the occurrence of an epidemiological genotypic identity can assume a dynamic character (spread to new habitats), however infrequently. A tendency of microevolutionary and genetic divergences among populations of S. aureus from human sources (AB) and bovine milk (DE), and especially the mammary quarter (C), is also suggested. This research can contribute to the knowledge on the distribution and dissemination of strains and the implementation of control measures and eradication of S. aureus in important dental clinic environments, as well as animal environments and dairy production.

Characterization of Staphylococcus aureus isolated from milk samples of dairy cows in small holder farms of North-Western Ethiopia

Background

Staphylococcus aureus is a contagious, opportunistic pathogen that causes clinical or subclinical mastitis in dairy cattle. The genetic background and antimicrobial resistance of isolates from Ethiopian dairy farms has not been studied. Therefore, the aim of this study was to characterize S. aureus from Ethiopian hand milked dairy cows, by spa, MLST and virulence factor typing, and by assessment of antimicrobial susceptibility. A total of 79 S. aureus isolates from intramammary infections was studied. A PCR was used to detect lukM-lukF’ and pvl genes encoding the bovine and human associated bi-component leukocidins, and the toxic shock syndrome toxin gene-1 (tst). Antimicrobial susceptibility was determined using the broth microdilution method.

Results

Twenty different spa types were identified, most isolates were t042 (58%), and the closely related t15786 (11%). The proportion of isolates positive for lukM-lukF’, tst and pvl was low at 0.04, 0.10 and 0.09 respectively, with lukM-lukF’ often co-occurring with tst, but not with pvl. Methicillin-resistance was not found, but resistance to penicillin/ampicillin (86%) and tetracycline (54%) was very common.

Conclusions

We found a high degree of relatedness among bovine S. aureus isolates in North-Western Ethiopia, suggesting contagious within and between farm transmission of strains that are often resistant to commonly used antimicrobials. This highlights the need for effective preventive measures that aim at limiting transmission of bacteria rather than using antimicrobials to control S. aureus mastitis in Ethiopia.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1558-1) contains supplementary material, which is available to authorized users.

Initial adhesion of methicillin-sensitive and methicillin-resistant Staphylococcus aureus strains to untreated and electropolished surgical steel drill bits

Electropolishing of stainless steel has been thoroughly investigated as a prophylactic measure to prevent bacterial colonization of orthopaedic implants and infection. Initial bacterial adhesion onto surgical drill bits as a possible factor for orthopaedic surgical site infections has not yet been documented. The present study investigated the influence of electropolishing on initial staphylococcal adhesion onto AISI 440A stainless steel drill bits. Specifically, one methicillin-susceptible standard laboratory Staphylococcus aureus type strain (DSM 20231^T), one methicillin-resistant S. aureus reference strain (DSM 46320) and one methicillin-resistant clinical isolate from an infected orthopaedic implant were used. After standard sterilization, drill bits were immersed in the respective bacterial suspension; bacteria adherent to surface were harvested by vortexing the drill bits in phosphate-buffered saline and viable counts of bacteria transferred from the suspension were made (transferred to log10 for further analysis). Electropolishing significantly reduced adhesion of the clinical S. aureus strain and the S. aureus DSM 20231^T. However, electropolishing significantly increased adhesion of the S. aureus DSM 46320. These results show that electropolishing significantly influences initial adhesion of S. aureus strains to surgical drill bits and that the nature of this influence depends on the S. aureus strain examined. For a general recommendation of electropolishing drill bits and guidelines for their handling during surgery, further studies with more strains isolated from infected wounds are suggested.

Prevalence of Subclinical Mastitis and Distribution of Pathogens in Dairy Farms of Rubavu and Nyabihu Districts, Rwanda

A cross-sectional study was conducted from May 2016 to January 2017 in Rubavu and Nyabihu districts, Western Rwanda, aiming at estimating the prevalence of subclinical mastitis (SCM) and identifying its causative bacteria. Management practices and milking procedures were recorded through a questionnaire. 123 crossbreed milking cows from 13 dairy farms were randomly selected and screened for SCM using California Mastitis Test (CMT). Composite CMT positive milk samples were processed for bacterial isolation and identification. The overall SCM prevalence at cow level was 50.4%. 68 bacterial isolates were identified by morphological and biochemical characteristics. They included, Coagulase Negative Staphylococci (51.5%), Staphylococcus aureus (20.6%), Streptococcus species (10.3%), Bacillus species (10.3%), Streptococcus agalactiae (5.8%), and Escherichia coli (1.5%). About 67.1% of the farmers checked for mastitis; of these, 58.9% relied on clinical signs and only 6.8% screened with CMT. Only 5.5% and 2.7% of the farmers tried to control mastitis using dry cow therapy and teat dips, respectively. Thus, to reduce the prevalence of SCM, farmers in the study area need to be trained on good milking practices, including regular use of teat dips, application of dry cow therapy, and SCM screening. This will improve their sales and their financial status.

Molecular Epidemiology of Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus in the Ovine Dairy Chain and in Farm-Related Humans

Staphylococcus aureus is a major cause of clinical infections in humans and its enterotoxins cause foodborne disease. In the present study, we tested a total of 51 isolates of S. aureus from small-ruminant dairy farms with artisan dairy facilities, all located in Latium, Italy. The farms have a known history of a high prevalence of methicillin-resistant S. aureus (MRSA). Most of the MRSA isolates (27 of 51) belonged to spa-type t127 (43.1%), followed by t2678 (3.9%), t044 (2%), t1166 (2%), and t1773 (2%). PFGE performed on mecA positive strains identified one cluster (≥ 80% of similarity), comprising 22 MRSA. Nine of twenty-two MRSA isolates were assigned human host origin, and 13 isolates did not belong to a specific host. During the characterization study, one strain isolated from bulk tank milk samples harbored the pvl gene; the strain was not enterotoxigenic with a non-specific host according to the biotyping scheme, highlighting the possible emerging risk of transmission of bacterial virulence factors by foods, the environment, and foodhandlers. These findings stress the importance of hygienic measures at all processing steps of the food production chain and underline that monitoring for the presence of MRSA throughout the food chain is essential for public health.

Virulence gene profiles in Staphylococcus aureus isolated from cows with subclinical mastitis in eastern Poland

Staphylococcus aureus is arguably the most important pathogen involved in bovine mastitis. The aim of this study was to determine the virulence gene profiles of 124 Staph. aureus isolates from subclinical mastitis in cows in eastern Poland. The presence of 30 virulence genes encoding adhesins, proteases and superantigenic toxins was investigated by PCR. The 17 different combinations of adhesin genes were identified. Occurrence of eno (91·1%) and fib (82·3%) genes was found to be common. The frequency of other adhesion genes fnbA, fnbB, ebps were 14·5, 50, 25%, respectively, and for cna and bbp were 1·6%. The etA and etD genes, encoding exfoliative toxins, were present in genomes of 5·6 and 8·9% isolates, respectively. The splA and sspA, encoding serine protease, were detected in above 90% isolates. The most frequent enterotoxin genes were sei (21%), sem (19·4%), sen (19·4%), seg (18·5%) and seo (13·7%). The tst gene was harboured by 2·4% isolates. The 19 combinations of the superantigenic toxin genes were obtained and found in 35·5% of isolates. Three of them (seg, sei, sem, sen, seo; sec, seg, sei, sem, sen, seo and seg, sei, sem, sen) were the most frequent and found in 16·1% of the isolates. The most common virulotype, present in 17·7% of the isolates, was fib, eno, fnbB, splA, splE, sspA. The results indicate the variation in the presence of virulence genes in Staph. aureus isolates and considerable diversity of isolates that are able to cause mastitis in cows.

Recombination-mediated remodelling of host-pathogen interactions during Staphylococcus aureus niche adaptation

Large-scale recombination events have led to the emergence of epidemic clones of several major bacterial pathogens. However, the functional impact of the recombination on clonal success is not understood. Here, we identified a novel widespread hybrid clone (ST71) of livestock-associated Staphylococcus aureus that evolved from an ancestor belonging to the major bovine lineage CC97, through multiple large-scale recombination events with other S. aureus lineages occupying the same ruminant niche. The recombination events, affecting a 329 kb region of the chromosome spanning the origin of replication, resulted in allele replacement and loss or gain of an array of genes influencing host–pathogen interactions. Of note, molecular functional analyses revealed that the ST71 hybrid clone has acquired multiple novel pathogenic traits associated with acquired and innate immune evasion and bovine extracellular matrix adherence. These findings provide a paradigm for the impact of large-scale recombination events on the rapid evolution of bacterial pathogens within defined ecological niches.

Screening of virulence genes in Staphylococcus aureus isolates from rabbits

<p><em>Staphylococcus aureus</em> is a versatile pathogen able to cause disease in both humans and animals. In rabbits, this bacterium infects animals of different ages, producing several purulent lesions. The ability of <em>S. aureus</em> to cause disease depends on a combination of virulence factors. The aim of this study was therefore to investigate the distribution of bacterial virulence determinants in 69 <em>S. aureus</em> isolates from rabbits. Some virulence factors (7 adhesins, 1 toxin and 1 protease) were positive in all rabbit <em>S. aureus</em> isolates analysed, while others (1 adhesin and 10 toxins) were always negative. The remaining virulence factors were more variable among isolates. An association between genotype and the different profiles of virulence factors was observed, but not with the type of lesion (P&lt;0.05). One strain of each genotype was further analysed by multilocus sequence typing, generating ST121, ST96 and ST2951, determining a greater number of enterotoxins in ST121 isolates compared to ST96 and ST2951 isolates, which could justify the different pathogenicity between strains. </p>

Genomic characteristics of Staphylococcus aureus strains associated with high within-herd prevalence of intramammary infections in dairy cows

Staphylococcus aureus is one of the most important causes of mastitis in dairy cattle. Based on previous research, Staph. aureus genotypes with different pathogenic and contagious properties can cause intramammary infection (IMI) and coexist in the same herd. Our study aimed to compare Staph. aureus strains from herds that differed in IMI prevalence using different molecular approaches such as ribosomal spacer (RS)-PCR, multilocus sequence typing (MLST), spa typing, ribotyping, pulsed-field gel electrophoresis (PFGE), and multiplex PCR. For this purpose, 31 dairy herds with Staph. aureus IMI were selected, and 16 of these were chosen for a comparison study: the 8 high-prevalence (HP) herds had Staph. aureus IMI prevalence >28% and the 8 low-prevalence (LP) herds had an IMI prevalence <4%. A total of 650 isolates of Staph. aureus from mammary quarters of all positive cows were genotyped with RS-PCR, a technique based on amplification of a portion of the intergenic spacer 16S-23S rRNA, and a subset of 54 strains was also analyzed by multiplex PCR, ribotyping, PFGE, MLST, and spa typing. The RS-PCR analysis revealed 12 different profiles. Staphylococcus aureus strains isolated from 5 out of 8 HP herds showed a profile identical to the genotype B (GTB), described in previous studies as being strongly associated with high within-herd prevalence of Staph. aureus mastitis and the presence of the genes coding for enterotoxins sea, sed, and sej, a long x-region of spa gene, and 3 lukE fragments. Moreover, all strains isolated in the HP herds possessed genes coding for staphylococcal enterotoxins. In LP herds, a limited number of strains of 6 genotypes, different from those isolated in HP herds, were identified and GTB was not found. Within these genotypes, 4 strains were positive for the mecA gene. Preliminary results and comparison with other genotyping methods confirmed that genotyping by RS-PCR is an accurate, rapid, and inexpensive tool for future field studies on Staph. aureus mastitis strains and generates clinically relevant results.

Preterm infant gut colonization in the neonatal ICU and complete restoration 2 years later

Preterm infants in a neonatal intensive care unit (NICU) are exposed to multidrug-resistant bacteria previously adapted to the hospital environment. The aim of the present study was to characterize the bacterial antibiotic-resistant high-risk lineages colonizing preterm infants during their NICU stay and their persistence in faeces after 2 years. A total of 26 preterm neonates were recruited between October 2009 and June 2010 and provided 144 faecal samples. Milk samples (86 mother's milk, 35 human donor milk and 15 formula milk) were collected at the same time as faecal samples. An additional faecal sample was recovered in 16 infants at the age of 2 years. Samples were plated onto different selective media, and one colony per morphology was selected. Isolates were identified by 16S rDNA nucleotide sequence and MALDI-TOF. Antibiotic susceptibility (agar dilution), genetic diversity (RAPD, PFGE and MLST) and virulence factors (only in enterococcal and staphylococcal isolates) were determined by PCR. A high proportion of antibiotic-resistant high-risk clones was detected in both faecal and milk samples during the NICU admittance. Almost all infants were colonized by Enterococcus faecalis ST64 and Enterococcus faecium ST18 clones, while a wider genetic diversity was observed for the Gram-negative isolates. Multidrug-resistant high-risk clones were not recovered from the faecal samples of the 2-year-olds. In conclusion, the gut of preterm infants admitted to the NICU might be initially colonized by antibiotic-resistant and virulent high-risk lineages, which are later replaced by antibiotic-susceptible community ones.

Staphylococcal enterotoxin H induced apoptosis of bovine mammary epithelial cells in vitro

Staphylococcal enterotoxins (SEs) are powerful superantigenic toxins produced by Staphylococcus aureus (S. aureus). They can cause food poisoning and toxic shock. However, their impact on bovine mammary epithelial cells (bMECs) is still unknown. In this study, the distribution of SE genes was evaluated in 116 S. aureus isolates from bovine mastitis, and the most prevalent genes were seh (36.2%), followed by sei (12.1%), seg (11.2%), ser (4.3%), sec (3.4%), sea (2.6%) and sed (1.7%). To better understand the effect of staphylococcal enterotoxin H (SEH) on bMECs, the seh gene was cloned and inserted into the prokaryotic expression vector, pET28a, and transformed into Escherichia coli BL21 (DE3). The recombinant staphylococcal enterotoxin H (rSEH) was expressed and purified as soluble protein. Bioactivity analysis showed that rSEH possessed the activity of stimulating lymphocytes proliferation. The XTT assay showed that 100 μg/mL of rSEH produced the cytotoxic effect on bMECs, and fluorescence microscopy and flow cytometry analysis revealed that a certain dose of rSEH is effective at inducing bMECs apoptosis in vitro. This indicates that SEs can directly lead to cellular apoptosis of bMECs in bovine mastitis associated with S. aureus.

Staphylococcus aureus from 152 cases of bovine, ovine and caprine mastitis investigated by Multiple-locus variable number of tandem repeat analysis (MLVA)

Staphylococcus aureus is one of the main etiological agents of mastitis in ruminants. In the present retrospective study, we evaluated the potential interest of a previously described automated multiple loci Variable Number of Tandem Repeats (VNTR) Assay (MLVA) comprising 16 loci as a first line tool to investigate the population structure of S. aureus from mastitis. We determined the genetic diversity of S. aureus strains from cases of clinical and subclinical mastitis in dairy cattle (n = 118, of which 16 were methicillin-resistant), sheep (n = 18) and goats (n = 16). The 152 strains could be subdivided into 115 MLVA genotypes (including 14 genotypes for the ovine strains and 15 genotypes for the caprine strains). This corresponds to a discriminatory index (D) value of 0.9936. Comparison with published MLVA data obtained using the same protocol applied to strains from diverse human and animal origins revealed a low number (8.5%) of human-related MLVA genotypes among the present collection. Eighteen percent of the S. aureus mastitis collection belonged to clonal complexes apparently not associated with other pathological conditions. Some of them displayed a relatively low level of diversity in agreement with a restricted ecological niche. These findings provide arguments suggesting that specific S. aureus lineages particularly adapted to ruminant mammary glands have emerged and that MLVA is a convenient tool to provide a broad overview of the population, owing to the availability via internet of databases compiling published MLVA genotypes.

Proteomics in farm animals models of human diseases

The need to provide in vivo complex environments to understand human diseases strongly relies on the use of animal models, which traditionally include small rodents and rabbits. It is becoming increasingly evident that the few species utilised to date cannot be regarded as universal. There is a great need for new animal species that are naturally endowed with specific features relevant to human diseases. Farm animals, including pigs, cows, sheep and horses, represent a valid alternative to commonly utilised rodent models. There is an ample scope for the application of proteomic techniques in farm animals, and the establishment of several proteomic maps of plasma and tissue has clearly demonstrated that farm animals provide a disease environment that closely resembles that of human diseases. The present review offers a snapshot of how proteomic techniques have been applied to farm animals to improve their use as biomedical models. Focus will be on specific topics of biomedical research in which farm animal models have been characterised through the application of proteomic techniques.

Staphylococcus aureus in veterinary medicine

Staphylococcus aureus is a major opportunistic pathogen in humans and one of the most important pathogenic Staphylococcus species in veterinary medicine. S. aureus is dangerous because of its deleterious effects on animal health and its potential for transmission from animals to humans and vice-versa. It thus has a huge impact on animal health and welfare and causes major economic losses in livestock production. Increasing attention is therefore being paid to both livestock and companion animals in terms of this pathogen. In this review, we summarise the current knowledge on the animal host adaptation of S. aureus. Different types of S. aureus infections in animals are also presented, with particular emphasis on mastitis in dairy herds, which is probably the costliest and therefore the best documented S. aureus infection seen in animals.

Staphylococcus aureus Efb protein expression in Nicotiana tabacum and immune response to oral administration

Staphylococcus aureus (S. aureus) is one of the most widespread agent of diseases in humans and animals. In dairy cows, S. aureus is the most frequently isolated contagious pathogens in mastitis cases and vaccines are one of the potential tools to control the infections, thus decreasing the use of antibiotics. Among all the virulence factors produced by S. aureus, extra cellular fibrinogen binding protein (Efb) is an important one in the pathogenesis of mastitis. Plants are useful bioreactors to produce antigens and the aim of the study was the production of Efb in two cultivars of Nicotiana tabacum as a mean to produce vaccine against S. aureus in plants. A matrix attachment region (MAR) sequence was inserted near the two borders of transfer-DNA in the transformation vector in the two possible orientations. The presence of MAR elements in the transformation system significantly improved transformation efficiency and Efb protein yield up to a 2% level on total soluble protein (TSP). Mice orally immunized with transgenic lyophilized leaves produced an antigen-specific immune response.

Population structure of Staphylococcus aureus isolated from bulk tank goat's milk

The presence of Staphylococcus aureus in raw milk can represent a potential threat to human health, due to the introduction of pathogenic strains into dairy food supply chain. The present study was performed to investigate the genetic variation among S. aureus strains isolated from bulk tank goat's milk. The virulence profiles were also assessed to link the isolates with the potential source of milk contamination. A population study was performed on 60 strains using distance-based methods such as pulsed-field gel electrophoresis (PFGE), and the output was analyzed using Structure statistical software (University of Chicago; http://pritch.bsd.uchicago.edu/structure.html ). This Bayesian clustering model tool allows one to assign individuals into a population with no predefined structure. In order to assess partition of genetic variability among isolates, groups obtained by Structure were also investigated using analysis of molecular variance. S. aureus was recovered in 60 out of 78 samples (76.9%) collected from 26 farms. According to PFGE analysis, the strains were divided into 25 different pulsotypes and grouped into two main clusters. Restriction profiles, analyzed by Structure, allowed us to identify two distinct S. aureus genetic groups. Within each group, the strains showed a high coefficient of membership. A great part of genetic variability was attributable to within-groups variation. On the basis of the virulence profile, 45% of the isolates were linked to "animal" biovar, while 6.7% could be assigned to "human" biovar. Out of 60 strains, 27 were characterized by in vitro production of either enterotoxins A (5.0%), C (38.3%), or D (1.7%). The present study showed a high prevalence of bulk tank goat's milk contamination with S. aureus of animal origin. The presence in goat's milk of S. aureus strains able to produce enterotoxins and their potential introduction into dairy chain may represent a serious threat to human health.

Molecular analysis of human and canine Staphylococcus aureus strains reveals distinct extended-host-spectrum genotypes independent of their methicillin resistance

Staphylococcus aureus causes a wide range of infectious diseases in humans and various animal species. Although presumptive host-specific factors have been reported, certain genetic lineages seem to lack specific host tropism, infecting a broad range of hosts. Such Extended-Host-Spectrum Genotypes (EHSGs) have been described in canine infections, caused by common regional human methicillin-resistant S. aureus (MRSA) lineages. However, information is scarce about the occurrence of methicillin-susceptible S. aureus (MSSA) EHSGs. To gain deeper insight into EHSG MSSA and EHSG MRSA of human and canine origin, a comparative molecular study was carried out, including a convenience sample of 120 current S. aureus (70 MRSA and 50 MSSA) isolates obtained from infected dogs. spa typing revealed 48 different spa types belonging to 16 different multilocus sequence typing clonal complexes (MLST-CCs). Based on these results, we further compared a subset of canine (n = 48) and human (n = 14) strains, including isolates of clonal complexes CC5, CC22, CC8, CC398, CC15, CC45, and CC30 by macrorestriction (pulsed-field gel electrophoresis [PFGE]) and DNA-microarray analysis. None of the methods employed was able to differentiate between clusters of human and canine strains independently of their methicillin resistance. In contrast, DNA-microarray analysis revealed 79% of the 48 canine isolates as carriers of the bacteriophage-encoded human-specific immune evasion cluster (IEC). In conclusion, the high degree of similarity between human and canine S. aureus strains regardless of whether they are MRSA or MSSA envisions the existence of common genetic traits that enable these strains as EHSGs, challenging the concept of resistance-driven spillover of MRSA.

Comparative host specificity of human- and pig- associated Staphylococcus aureus clonal lineages

Bacterial adhesion is a crucial step in colonization of the skin. In this study, we investigated the differential adherence to human and pig corneocytes of six Staphylococcus aureus strains belonging to three human-associated [ST8 (CC8), ST22 (CC22) and ST36(CC30)] and two pig-associated [ST398 (CC398) and ST433(CC30)] clonal lineages, and their colonization potential in the pig host was assessed by in vivo competition experiments. Corneocytes were collected from 11 humans and 21 pigs using D-squame® adhesive discs, and bacterial adherence to corneocytes was quantified by a standardized light microscopy assay. A previously described porcine colonization model was used to assess the potential of the six strains to colonize the pig host. Three pregnant, S. aureus-free sows were inoculated intravaginally shortly before farrowing with different strain mixes [mix 1) human and porcine ST398; mix 2) human ST36 and porcine ST433; and mix 3) human ST8, ST22, ST36 and porcine ST398] and the ability of individual strains to colonize the nasal cavity of newborn piglets was evaluated for 28 days after birth by strain-specific antibiotic selective culture. In the corneocyte assay, the pig-associated ST433 strain and the human-associated ST22 and ST36 strains showed significantly greater adhesion to porcine and human corneocytes, respectively (p<0.0001). In contrast, ST8 and ST398 did not display preferential host binding patterns. In the in vivo competition experiment, ST8 was a better colonizer compared to ST22, ST36, and ST433 prevailed over ST36 in colonizing the newborn piglets. These results are partly in agreement with previous genetic and epidemiological studies indicating the host specificity of ST22, ST36 and ST433 and the broad-host range of ST398. However, our in vitro and in vivo experiments revealed an unexpected ability of ST8 to adhere to porcine corneocytes and persist in the nasal cavity of pigs.

Mapping the genetic diversity within major clonal complexes of meticillin-resistant Staphylococcus aureus utilizing genome-wide fluorescent amplified fragment length polymorphism markers

The genetic diversity between major meticillin-resistant Staphylococcus aureus (MRSA) lineages was probed using fluorescent amplified fragment length polymorphism (FAFLP) as a random genome sampling tool. Genomic DNA was digested with endonucleases BglII and Csp6I and a subset of the restricted fragments were amplified using the primer pair BglII+A and Csp6I+0. Sixty-seven FAFLP profiles consisting of 46-68 amplified fragments ranging in size from 50 to 600 bp were exhibited amongst the 71 isolates analysed. Cluster analysis of FAFLP data revealed concordance with spa typing and MLST clonal complexes (CC), with isolates of each CC grouping in the same FAFLP cluster. Furthermore, FAFLP could differentiate subtypes within the homogeneous CC22 isolates and also between MLST sequence types 8 and 239. The discriminatory power of FAFLP was 0.998 compared to values of 0.975 and 0.909 for spa typing and MLST, respectively. Thus, FAFLP analysis proved to be a rapid, reproducible and high-resolution tool that displayed the microheterogeneity within MRSA lineages. Using FAFLP data, lineage-specific fragments were identified and sequenced; these encoded toxins, antibiotic resistance determinants and bacteriophage resistance factors. Lineage-specific sequence variations were observed, which may provide insights into the evolution and fitness of successful lineages. This will also aid in the development of rapid and high-throughput diagnostic PCR-based assays for the identification of MRSA lineages in resource-poor settings.

Detection of the enterotoxigenic genes (sei,sej) in Staphylococcus aureus isolates from bovine mastitis milk in the West Azerbaijan of Iran

Staphylococcus aureus is a major causative pathogen of clinical and subclinical mastitis of dairy domestic ruminants. This organism produces a variety of extracellular toxins and virulence factors such as enterotoxin SEI and SEJ that contribute to its pathogenic potential. In this study 25 S. aureus isolates obtained from four dairy herds of Urmia region which is located in West Azerbaijan province in Iran. The tested isolates were identified on the basis of the cultural and biochemical properties, as well as amplification of the aroA gene which is specific for S. aureus. All isolates were also analyzed for the presence of the SEI (sei) and SEJ (sej) encoding genes using polymerase chain reaction (PCR). Seven positive isolates were detected for sei, but sej gene was not detected in any of the total number of 25 isolates. The present study revealed that the PCR amplification of the aroA gene could be used as a powerful tool for identification of S. aureus from the cases of bovine mastitis. Results of the present study also showed that the strains of S. aureus which cause mastitis can potentially produce enterotoxin SEI. Overall, our results suggest that it is of special importance to follow the presence of enterotoxin-producing S. aureus in other dairy products, especially for protecting the consumers from staphylococcal food poisoning.

HLA molecules and nasal carriage of Staphylococcus aureus isolated from dialysis and kidney transplant patients at a hospital in Southern Brazil

Background

Healthy individuals can host Staphylococcus aureus in the nasopharynx, body surface and vagina. Most invasive infections by this bacterium are endogenous, caused by strains spread from the nasopharynx of carriers. S. aureus is a pathogen involved in the etiology of hospital- and community-acquired infections. Transplant and dialysis patients are at risk of colonization or infection by multi-resistant S. aureus. Infection is directly linked to individual immunity, and the major histocompatibility complex (MHC) plays a crucial role in determining susceptibility to diseases. Different MHC specificities have been shown to be more frequent in individuals suffering from certain diseases. This study aimed to investigate the association between HLA class I (HLA-A and -B) and class II (HLA-DRB1) molecules and nasal carriage of S. aureus in dialysis and kidney transplant patients at a hospital in Southern Brazil.

Results

The sample consisted of 70 dialysis and 46 kidney transplant patients, totaling 116 patients. All subjects were typed for HLA molecules using LABType^® SSO (One Lambda). Nasal swab samples of S. aureus were isolated from the nasal cavity (both nostrils) of patients undergoing dialysis or kidney transplantation.

In renal dialysis patients, HLA-A*02 was the most frequent allele in both carriers (25.5%) and non-carriers (21.2%) of S. aureus. Allele A*68 was not observed in the carrier group, but the allele was observed six times in the non-carrier group (p = 0.0097). Regarding HLA-B and HLA-DRB1, no allele was shown to be involved in protection against or susceptibility to carriage of S. aureus. In kidney transplant patients, allele A*03 was more frequent in the non-carrier (20.83%) than in the carrier (5.88%) group (p = 0.0486). HLA-B*15 was present in carriers (5.88%) and non-carriers (25%) (p = 0.0179). Regarding class II alleles, DRB1*03 appeared to be related to susceptibility to carriage of S. aureus (p = 0.0319).

Conclusions

Our findings suggest that HLA-DRB1*03 may be involved in susceptibility to nasal carriage of S. aureus in transplant patients. In addition, HLA-A*68 (dialysis patients) and HLA-A*03 and HLA-B*15 (transplant patients) appear to be associated with increased resistance to S. aureus nasal carriage.

Use of 5-Enolpyruvylshikmate-3-Phosphate Synthase Encoding Gene for Typing of Staphylococcus aureus Isolated from Skin and Urinary Tract Infections of Human

OBJECTIVE(S)

Staphylococcus aureus is both a successful human commensal and a major pathogen. In this study we investigated the genetic diversity of 26 S. aureus isolates recovered from human skin and urinary tract infections.

MATERIALS AND METHODS

Typing procedure for the studied S. aureus isolates was performed based on PCR amplification of the aroA gene, which encodes the enzyme 5-enolpyruvylshikmate-3-phosphate synthase (EPSPS) that involves in aromatic amino acid biosynthesis, and restriction fragment length polymorphism (RFLP) analysis of the product.

RESULTS

All S. aureus isolates produced a single PCR amplification product of 1,153 bp. Digestion of the PCR products with the TaqI endonuclease revealed four different aroA gene patterns designated as A, B, N and H according to the nomenclature system of previous studies. In general, 80.77% of the studied isolates displayed type N, 7.69% were type B, 7.69% were type H and 3.85% displayed type A.

CONCLUSION

Divergent aroA types were detected among S. aureus isolates from skin and urinary tract infections. The results showed that urinary tract infections were contaminated by S. aureus isolates with identical banding patterns (A), while isolates recovered from skin infections had different aroA types. This study also indicates that aroA genotypes vary not only from region to region, but also in individual hosts within a region.

Mastitis: comparative etiology and epidemiology

Mastitis is broadly defined as the inflammation of the mammary gland; however, the concept of mastitis is customized to address its social and clinical impact in the case of humans and the health, welfare, and economic consequences for other mammals. There are many microbial, host, and environmental factors that influence the development of mastitis. Some are common to all mammals as well as inherent to each species. Together these factors influence the most prevalent etiological agents for each species and might determine the possibility of interspecies transmission with its consequences to public health. The present review will summarize and compare reports on mastitis etiology and its epidemiology in humans and food animal species.

Genotypic Characterization of Staphylococcus aureus Obtained from Humans and Bovine Mastitis Samples in India

AIM AND BACKGROUND

Staphylococcus aureus is a major human pathogen that also causes important infections in cattle and sheep. The present study aimed to test genetic diversity among strains of S. aureus isolated from cattle (n=34) and humans (n=22) by DNA typing.

MATERIALS AND METHODS

Fluorescent amplified fragment length polymorphism (FAFLP) is the genotyping tool used in the study. The presence of the mecA and Panton-Valentine leukocidin (PVL) genes among these strain groups was also checked.

RESULTS

A dendrogram deduced from FAFLP showed that all the strains clustered into 10 groups (A-J) with a relative genetic divergence of less than 8%. Sixty-seven percent of the isolates from bovine sources clustered together in two clades (A and H), while another major cluster with 13 isolates (59%) (Cluster G) had all strains from a human host. The remaining strains from both the hosts clustered independently into smaller clusters with the exception of two strains of human origin, which clustered along with a bovine cluster. Thirteen strains belonging to cluster G were highly clonal. About 77% of strains obtained from human infections were methicillin-resistant S. aureus (MRSA), whereas only 29% of strains from bovine origin were MRSA. Only three strains from human origin showed PVL positive, while no strain from cattle had PVL genes. The complete absence of PVL genes in all the bovine strains in the study appears to be significant.

CONCLUSIONS

FAFLP can be successfully applied to assess the genetic relationship of S. aureus isolates from different hosts. The study also provided the valuable epidemiological data on S. aureus from bovine sources in India, which is lacking.

Genotypic characterization by polymerase chain reaction of Staphylococcus aureus isolates associated with bovine mastitis

Staphylococcus aureus is recognized worldwide as a pathogen causing many serious diseases in humans and animals, and is the most common aetiological agent of clinical and subclinical bovine mastitis. The importance of evaluating the combination of S. aureus virulence factors has been emphasized both in human and veterinary medicine, and knowledge about the genetic variability within different S. aureus populations would help in the design of efficient treatments. The aim of the present study was to determine the genetic profiles of S. aureus strains isolated from milk of cows suffering from clinical and subclinical mastitis in Belgium. The presence of about forty virulence-associated genes was investigated by specific polymerase chain reaction (PCR) amplification. A high number of genotypic subtypes were observed, demonstrating further the large variation in the presence of virulence genes in S. aureus isolates and the considerable diversity of strains populations that are able to cause mastitis in cows. In accordance with other studies, we showed that some genes are associated with mastitis-causing S. aureus isolates, whereas others are absent or rarely present. We also further highlighted the presence of conserved gene combinations, namely the enterotoxigenic egc-cluster and the bovine pathogenicity island SaPIbov. Importantly, the presence of isolates carrying genes coding for toxins involved in important human infections makes the milk of cows with mastitis a potential reservoir for these toxins, and therefore a potential danger in human health, which strengthens the importance to consider raw milk consumption and its processing very carefully.

Screening of Staphylococcus aureus nasal strains isolated from medical students for toxin genes

Three hundred twenty-one students (156 students with no clinical exposure and 165 students with clinical exposure) were screened for nasal colonization by Staphylococcus aureus; 20.9% of students were S. aureus nasal carriers, and 40.3% of S. aureus isolates harbored toxin genes. The most prevalent genes were tst (15.0 %) and sec (13.4 %). Isolates with multiple genes were only found among clinical students (p = 0.045). Six of 11 PFGE clones were positive for toxin genes. Methicillin-resistant (MRSA) isolates were only detected in the clinical students (4.5 %). The exposure of students to the hospital environment neither radically increased S. aureus nasal carriage, nor the frequency of clinically important toxin gene presence, but it could have influenced the positive selection of toxigenic MRSA strains.

Immune evasion cluster-positive bacteriophages are highly prevalent among human Staphylococcus aureus strains, but they are not essential in the first stages of nasal colonization

The Staphylococcus aureus immune evasion cluster (IEC), located on β-haemolysin-converting bacteriophages (βC-Φs), encodes the immune-modulating proteins chemotaxis inhibitory protein, staphylococcal complement inhibitor (SCIN), staphylococcal enterotoxin A and staphylokinase. Its precise role in S. aureus colonization is unclear. We studied the presence of the IEC-carrying bacteriophages in human and animal S. aureus isolates, using PCR for the gene encoding SCIN (scn). Human isolates were obtained by collecting serial nasal swabs from 21 persistent carriers. S. aureus strains from 19 (90%) persistent carriers contained an IEC that was present and indistinguishable in 95% of cases at all five sampling moments over a 3-month period. Of the 77 infectious animal strains included in the study, only 26 strains (34%) were IEC-positive. Integration of these IEC-positive strains into an amplified fragment length polymorphism genotype database showed that 24 of 53 (45%) strains were human-associated and only two of 24 (8%) were 'true' animal isolates (p < 0.001). The high prevalence and stability of IEC-carrying βC-Φs in human strains suggested a role for these βC-Φs in human nasal colonization. To test this hypothesis, 23 volunteers were colonized artificially with S. aureus strain NCTC 8325-4 with or without the IEC type B-carrying βC-Φ13. Intranasal survival was monitored for 28 days after inoculation. The strain harbouring βC-Φ13 was eliminated significantly faster (median 4 days; range 1-14 days) than the strain without βC-Φ13 (median 14 days; range 2-28 days; p 0.011). In conclusion, although IEC-carrying βC-Φs are highly prevalent among human colonizing S. aureus strains, they are not essential in the first stages of S. aureus nasal colonization.

Novel Technology to study co-evolution of humans and Staphylococcus aureus: consequences for interpreting the biology of colonisation and infection

Human nasal carriage of Staphylococcus aureus is a textbook example of an apparently neutral interaction between humans and a bacterial species that can still lead to (severe) opportunistic infections. The co-evolutionary aspects of this interaction are slowly surfacing, facilitated by the emergence of a diversity of diagnostic, epidemiological and molecular research tools. Basic microbiology has helped define persistent vs. non-carriage and the genotype of both host and guest has been explored in search of genetic markers for bacterial persistence. This chapter summarises the current state of affairs relating to artificial human colonisation studies with S. aureus, large-scale human cohort studies and innovative assessment of the humoral immune status of (non-)nasal carriers. These experimental approaches have recently assisted in identifying bacterial and human determinants and risk factors for staphylococcal carriage. Further refinement of the model by describing the interactions between S. aureus and its human host in molecular detail is important since it may pinpoint novel anti-infectious strategies.

Relationship between S. aureus gene pattern and dairy herd mastitis prevalence

The importance to evaluate Staphylococcus aureus virulence analysing the combination of virulence genes is largely recognised, and the recent availability of simplified microarray tools allows performing these analyses also in the dairy field. The combined availability of herd-specific S. aureus mastitis prevalence data, isolates from these herds, and microarray technology offered the opportunity to investigate the relationship between S. aureus genetic pattern and their prevalence among dairy herds. Eleven commercial dairy herds following a S. aureus control programme were enrolled in the study, and 33 S. aureus isolates were collected from these herds. Diagnostic DNA microarrays based on the array-tube platform were used for genotyping of staphylococcal DNA. The genetic analysis of the 157-genes microarray showed as only 19 genes were present in all the isolates considered, and among them the genes coding for the leukocidin subunits (LukF, LukS and LukY), haemolysins (hla, hld and an unnamed haemolysin) and enterotoxin X. Several genes considered in the arrays were absent in all the isolates, including the ones encoding the resistance to most of the antimicrobials, except for tetracycline. In our isolates, some agr alleles were never identified (B-III, C-III, D-III, C-IV and D-IV). The comparison of epidemiological data with the genetic pattern suggests that agr type II is associated to the most diffusive isolates, being recovered from the largest number of herds and with the highest frequency. Microarray technique showed to be a useful method to assess the characteristics of virulence of S. aureus isolated in dairy herds and to investigate the relationship with the prevalence of the microorganism. These results support previous evidence that specific gene patterns could be associated to S. aureus mastitis.

Heterogeneity of the humoral immune response following Staphylococcus aureus bacteremia

Expanding knowledge on the humoral immune response in Staphylococcus aureus-infected patients is a mandatory step in the development of vaccines and immunotherapies. Here, we present novel insights into the antibody responses following S. aureus bacteremia. Fifteen bacteremic patients were followed extensively from diagnosis onwards (median 29 days, range 9–74). S. aureus strains (median 3, range 1–6) and serial serum samples (median 16, range 6–27) were collected. Strains were genotyped by pulsed-field gel electrophoresis (PFGE) and genes encoding 19 staphylococcal proteins were detected by polymerase chain reaction (PCR). The levels of IgG, IgA, and IgM directed to these proteins were determined using bead-based flow cytometry. All strains isolated from individual patients were PFGE-identical. The genes encoding clumping factor (Clf) A, ClfB, and iron-responsive surface-determinant (Isd) A were detected in all isolates. Antigen-specific IgG levels increased more frequently than IgA or IgM levels. In individual patients, different proteins induced an immune response and the dynamics clearly differed. Anti-ClfB, anti-IsdH, and anti-fibronectin-binding protein A IgG levels increased in 7 of 13 adult patients (p < 0.05). The anti-IsdA IgG level increased in 12 patients (initial to peak level: 1.13–10.72 fold; p < 0.01). Peak level was reached 7–37 days after diagnosis. In a bacteremic 5-day-old newborn, antistaphylococcal IgG levels declined from diagnosis onwards. In conclusion, each bacteremic patient develops a unique immune response directed to different staphylococcal proteins. Therefore, vaccines should be based on multiple components. IsdA is immunogenic and, therefore, produced in nearly all bacteremic patients. This suggests that IsdA might be a useful component of a multivalent staphylococcal vaccine.

Regional profiling for determination of genotype diversity of mastitis-specific Staphylococcus aureus lineage in Canada by use of clumping factor A, pulsed-field gel electrophoresis, and spa typing

One of the major concerns in global public health and the dairy industry is the emergence of host-specific virulent Staphylococcus aureus strains. The high degree of stability of the species genome renders detection of genetic microvariations difficult. Thus, approaches for the rapid tracking of specialized lineages are urgently needed. We used clumping factor A (clfA) to profile 87 bovine mastitis isolates from four regions in Canada and compared the results to those obtained by pulsed-field gel electrophoresis (PFGE) and spa typing. Twenty-five pulsotypes were obtained by PFGE with an index of discrimination of 0.91. These were assigned to six PFGE lineage groups A to F and seven spa types, including two novel ones. Group A had 48.3% of the isolates and group D had 43.7% of the isolates, while only 8% of the isolates were variable. The results of antimicrobial susceptibility testing indicated that all isolates were sensitive to methicillin and the non-beta-lactam antibiotics, while three isolates were resistant to penicillin and one isolate was resistant to tetracycline. All isolates had the clfA gene and belonged to 20 clfA repeat types with an index of discrimination of 0.90. The dominant clfA types, types X, Q, C, and Z, formed 82% and 43% of PFGE groups A and D, respectively, and had copy numbers that varied only within a narrow range of between 46 and 52 copies, implying clonal selection. The rest were variable and region specific. Furthermore, the dominant groups contained subpopulations in different regions across Canada. Sequence information confirmed the relatedness obtained by the use of clfA repeat copy numbers and other methods and further revealed the occurrence of full-repeat deletions and conserved host-specific codon-triplet position biases at 18-bp units. Thus, concordant with the results of PFGE and spa typing, clfA typing proved useful for revealing the clonal nature of the mastitis isolate lineage and for the rapid profiling of subpopulations with comparable discriminatory powers.