SpA, ClfA, and FnbA genetic variations lead to Staphaurex test-negative phenotypes in bovine mastitis Staphylococcus aureus isolates

Rapid detection of Staphylococcus aureus in blood culture samples using human IgG-based lateral flow assay

Staphylococcus aureus is one of the most common pathogens. The conventional workflow for identifying this organism is time-consuming and takes up to several days. Therefore, we developed a colloidal gold-based lateral flow immunoassay (LFIA) using human IgG as a conjugated antibody to detect S. aureus. One hundred and thirty-eight clinical isolates, including 79 S. aureus and 59 non-S. aureus were spiked in blood samples, and incubated at 37°C for 24 h. The bacterial antigens were simply extracted before being tested by the developed LFIA strips. The results were read by the naked eye within 15 min. Conventional PCR was used as a reference method. The sensitivity and specificity of the developed LFIA were 100% (95% CI: 94.2%-100.0% and 92.4%-100.0%, respectively) in spiked blood culture samples. The detection limits of the LFIA for the purified protein A and bacterial colonies were 10-3 µg/mL and 107 CFU/mL, respectively. The performance of the LFIA testing in 221 bacterial colony isolates and 118 positive blood culture bottles from three hospitals by their medical technologists showed 98.1% (95% CI: 94.1%-99.5%) and 89.7% (95% CI: 79.3%-95.4%) sensitivity, respectively. The LFIA is a quick, easy, and sensitive method for detecting S. aureus without expensive equipment. It might have the potential for early diagnosis of routine service in low-resource laboratories, leading to a rapid and effective treatment.IMPORTANCEIn this study, we modified our previously developed lateral flow immunoassay (LFIA) test for the detection of Staphylococcus aureus by using an in-house human IgG as a conjugated antibody instead of the specific commercial antibody. It gave comparable results to the former developed-LFIA test and helped cost reduction.

Effect of Salicylic Acid on the gene expression of FnbA and FnbB genes in Staphylococcus hominis

BACKGROUND

Staphylococcus hominis is an opportunistic pathogen that expresses surface proteins, which are adhesive proteins that play a major role in biofilm formation. Biofilm is a protective layer that provides S. hominis bacteria with greater antibiotic resistance and promotes its adherence to biomedical surfaces, facilitating its entry into the bloodstream.

OBJECTIVE

This research aimed to investigate the activity of Salicylic Acid (SA) and its effect on the gene expression of biofilm genes (FnbA and FnbB genes).

METHODS

A total of 150 blood specimens were collected from patients. The specimens were cultured in broth media of the BacT/ALERT® system and subcultured on blood and chocolate agar. Bacteria were detected using the VITEK2 system. FnbA and FnbB genes were detected using PCR. The broth microdilution method performed the minimum inhibitory concentration (MIC) of Salicylic acid (SA) on S. hominis isolates with both genes. Detection of the gene expression levels of FnbA and FnbB genes was assessed using Real-Time PCR(RT-PCR).

RESULTS

The results showed that out of the 150 specimens collected, 35 were S. hominis. The detection of S. hominis bacteria was performed by PCR amplification of two genes FnbA and FnbB and showed 100% and 17.14% of isolates were positive for genes FnbA and FnbB, respectively. The expression of FnbA and FnbB genes was decreased in samples treated with SA compared with untreated ones.

CONCLUSION

In conclusion, there is a significant impact of SA on the prevention of biofilm formation of S. hominis through the suppression of gene expression, specifically FnbA and FnbB. This could enhance susceptibility to antimicrobial treatments. However, more research is required to determine whether SA leads to the selection of resistant bacteria.

Antimicrobial resistance and virulence profiles of staphylococci isolated from clinical bovine mastitis

Staphylococci, mainly including Staphylococcus aureus and coagulase-negative staphylococci (CNS), are one of the most common pathogens causing bovine mastitis worldwide. In this study, we investigated the antimicrobial resistance and virulence profiles of staphylococci from clinical bovine mastitis in Ningxia Hui Autonomous Region of China. Antimicrobial resistance was determined by disc diffusion combined with E-test method. Genes of antimicrobial resistance and virulence factors were determined by PCR. A total of 332 staphylococcal isolates were confirmed from 1,519 mastitic milk samples, including 172 S. aureus and 160 CNS isolates. Fifteen CNS species were identified, with S. chromogenes being the most frequent found (49.4%), followed by S. equorum (13.8%). Noticeably, 2 S. agnetis isolates were found among the CNS isolates. To our knowledge, this is the first report documenting the presence of S. agnetis from bovine mastitis in China. The S. aureus and CNS isolates showed high resistance against penicillin, followed by erythromycin and tetracycline. Multidrug resistance was found in 11.6 and 16.3% of the S. aureus and CNS isolates, respectively. Resistance to penicillin was attributed to the presence of blaZ, erythromycin resistance to ermC (alone or combined with ermB) and tetracycline resistance to tetK (alone or combined with tetM). Notably, one S. equorum isolate and one S. saprophyticus isolate were both methicillin-resistant and mecA positive. Additionally, all S. aureus isolates carried the adhesin genes fnbpA, clfA, clfB, and sdrC, and most of them contained cna and sdrE. Conversely, only a few of the CNS isolates carried clfA, cna, and fnbA. Regarding toxin genes, all S. aureus isolates harbored hlb, and most of them were hlg positive. The lukE-lukD, lukM, sec, sed, sei, sen, seo, tst, seg, seh, and sej were also detected with low frequencies. However, no toxin genes were observed in CNS isolates. This study reveals high species diversity of staphylococci from clinical bovine mastitis in Ningxia Hui Autonomous Region of China. The findings for the genetic determinants of antimicrobial resistance and virulence factor provide valuable information for control and prevention of staphylococcal bovine mastitis.

Characterization of Staphylococcus aureus Isolates from Bovine Mastitis and Bulk Tank Milk: First Isolation of Methicillin-Susceptible Staphylococcus aureus in Japan

Staphylococcus aureus is one of the most important pathogens in humans as well as in livestock. Particularly, bovine mastitis caused by S. aureus is a serious issue in dairy farms due to disease recurrence. Here, cases of S. aureus-mediated intramammary infection occurring in the Miyagi Prefecture in Japan were monitored from May 2015 to August 2019; a total of 59 strains (49 from bovine milk and 10 from bulk milk) were obtained from 15 dairy farms and analyzed via sequence-based typing methods and antibiotic susceptibility tests. Two pairs of isolates were determined as recurrence cases from the same cows in distinct farms. The sequence type (ST), spa type, and coa type of each pair were the same: one pair showed ST705, t529, and VIb and the other showed ST352, t267, and VIc. In addition, the possession of toxin genes analyzed of each pair was exactly the same. Furthermore, seven oxacillin-sensitive clonal complex 398 isolates were obtained from a single farm. This is the first confirmed case of a Methicillin-Sensitive SA (MSSA) ST398 strain isolated from mastitis-containing cows in Japan. Our findings suggest that nationwide surveillance of the distribution of ST398 strains in dairy farms is important for managing human and animal health.

Biofilms as a microbial hazard in the food industry: A scoping review

Biofilms pose a serious public health hazard with a significant economic impact on the food industry. The present scoping review is designed to analyze the literature published during 2001-2020 on biofilm formation of microbes, their detection methods, and association with antimicrobial resistance (if any). The peer-reviewed articles retrieved from 04 electronic databases were assessed using PRISMA-ScR guidelines. From the 978 preliminary search results, a total of 88 publications were included in the study. On analysis, the commonly isolated pathogens were Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli, Bacillus spp., Vibrio spp., Campylobacter jejuni and Clostridium perfringens. The biofilm-forming ability of microbes was found to be influenced by various factors such as attachment surfaces, temperature, presence of other species, nutrient availability etc. A total of 18 studies characterized the biofilm-forming genes, particularly for S. aureus, Salmonella spp., and E. coli. In most studies, polystyrene plate and/or stainless-steel coupons were used for biofilm formation, and the detection was carried out by crystal violet assays and/or by plate counting method. The strain-specific significant differences in biofilm formation were observed in many studies, and few studies carried out analysis of multi-species biofilms. The association between biofilm formation and antimicrobial resistance wasn't clearly defined. Further, viable but non-culturable (VBNC) form of the foodborne pathogens is posing an unseen (by conventional cultivation techniques) but potent threat food safety. The present review recommends the need for carrying out systematic surveys and risk analysis of biofilms in food chain to highlight the evidence-based public health concerns, especially in regions where microbiological food hazards are quite prevalent.

Detection of Antibiotic Resistance, Virulence Gene, and Drug Resistance Gene of Staphylococcus aureus Isolates from Bovine Mastitis

Antimicrobial therapy plays an important role in mastitis control caused by Staphylococcus aureus but has become less effective due to widespread drug resistance. The purpose of this study was to detect antibiotic resistance, drug resistance gene, and virulence gene of S. aureus strains. In this study, 2,962 milk samples were collected from 43 dairy farms located in 16 provinces of China and cultured for isolation of S. aureus. Antibiotic resistance, capsular polysaccharide, spa typing, virulence genes, and drug resistance genes of the strains were analyzed. Of 2,962 samples, 298 strains were isolated and identified as S. aureus. The strains exhibited high percentages of resistance to penicillin G (91.95%). Moreover, all strains showed resistance to more than one antimicrobial agent but were sensitive to nitrofurantoin and sulfamethoxazole/trimethoprim. The results indicate that type 8 was the dominant capsular polysaccharide serotype and t459 was the dominant spa type. The most prevalent virulence gene was clfA (98%). The resistance genes of several antibiotics were detected, among which the blaZ gene (92.95%) was the highest. In conclusion, we present the antimicrobial resistance and virulence genes of S. aureus in this study which are of importance for mastitis control. IMPORTANCE Bovine mastitis is a serious disease associated with both high incidence and economic loss, posing a major challenge to the dairy industry worldwide. Staphylococcus aureus is one of the most common pathogens to cause bovine mastitis, and antimicrobial therapy plays an important role in mastitis control caused by S. aureus but has become less effective due to widespread drug resistance. The purpose of this study was to detect antibiotic resistance, drug resistance gene, and virulence gene of S. aureus strains, which would be helpful to mastitis control.

Feline Otitis Externa Caused by Methicillin-Resistant Staphylococcus aureus with Mixed Hemolytic Phenotype and Overview of Possible Genetic Backgrounds

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infections in humans, but its importance in small animal practice is increasing. Here, we present a case of feline otitis externa (OE) caused by MRSA; both hemolytic and nonhemolytic variants with a stable phenotype were recovered from the external auditory canal after infection was detected by routine otoscopy. One isolate per variant underwent antimicrobial susceptibility testing (AST) by broth microdilution method, conventional spa typing and whole-genome sequencing (WGS). The results showed that both variants were genetically related and were of sequence type (ST) 1327, SCCmec type IV and spa type t005. AST and WGS showed that both isolates were resistant to β-lactams and sensitive to all tested non-β-lactam antibiotics. Both isolates were pvl-negative, but encoded several other virulence genes (aur, hlgABC, sak, scn, seg, sei, sem, sen, seo and seu). Genetic background of the mixed hemolytic phenotype was not identified; no differences in the agr locus or other regulatory regions were detected. Three single-nucleotide polymorphisms were identified but could not be associated with hemolysis. This well-documented case of MRSA infection in companion animals adds to the reports of MRSA infections with a mixed hemolytic phenotype.

Characterization of Staphylococcus aureus Isolates From Cases of Clinical Bovine Mastitis on Large-Scale Chinese Dairy Farms

Bovine mastitis is a prevalent disease that causes serious economic problems globally in the dairy industry. Staphylococcus aureus is an important pathogen of bovine mastitis. This study was conducted to characterize S. aureus isolates from clinical bovine mastitis cases in large-scale dairy herds in China. S. aureus was isolated from 624 clinical mastitis cases and confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). In total, 62 S. aureus isolates were obtained. Cluster analysis, genetic diversity, quantification of biofilm formation, antimicrobial resistance, and detection of virulence genes were performed on these isolates of S. aureus. Eight isolates harbored the mecA gene and were sensitive to oxacillin. MALDI-TOF MS cluster analysis revealed that the 62 isolates were divided into three major clusters (I, II, III) and eight main groups (A–H) at the distance level of 700. The agr II was the most prevalent (56.5%). The 62 S. aureus isolates were assigned to seven spa types. The most common spa type was t529(58.1%), followed by t2196 (14.5%), t518 (14.5%), t571(6.5%), t034 (3.2%), t2734 (1.6%), and t730 (1.6%). Five STs were identified from seven representative isolates as follows: ST630/CC8, ST97/CC97, ST50, ST398, and ST705. All isolates had the ability to form biofilm. Antimicrobial resistance was most frequently observed to ciprofloxacin (29%), followed by penicillin (24.2%), and streptomycin (9.6%). All isolates harbored the fnbA, clfB (100%), icaA, and icaD genes. This study provides the basis for the development of bovine mastitis prevention program on large-scale dairy farms.

Microarray based genetic profiling of Staphylococcus aureus isolated from abattoir byproducts of pork origin

Many parts of pork meat processing are currently not used for human consumption in Switzerland, although they are of great nutritional value. Therefore, data on the occurrence of pathogenic organisms on byproducts is extremely scarce and the prevalence and population structure of Staphylococcus aureus on meat processing sidestreams is unknown. Hence, abattoir byproducts of pork origin including ear, forefoot, heart, intestine, liver, rib bone, sternum, bladder, stomach, hind foot and tongue originating from six abattoirs were screened for S. aureus. The obtained isolates were investigated by spa typing and DNA microarray analysis to reveal their genomic profile and population structure. The prevalence of S. aureus was generally low with a mean of 8%. In total, 40 S. aureus strains were detected and assigned to 12 spa types (t015, t1491, t1778, t091, t337, t899, t2922, t7439, t1333, t208, t4049, t034) and seven clonal complexes (CC1, CC7, CC9, CC30, CC45, CC49, CC398). Detected enterotoxin genes included sea, seb, sec, seh, sel and egc encoded toxin genes seg, sei, sem, sen, seo, and seu. None of the isolates harbored genes conferring methicillin resistance, but blaZ/I/R genes causing penicillin resistance were frequently found. In addition, strains from CC398 exhibited tetM and tetK, conferring tetracycline resistance. Similarity calculations based on microarray profiles revealed no association of clonal complexes with particular body parts, but revealed a certain correspondence of clonal complex and originating abattoir.

Role of staphylococci in mastitis in sheep

Staphylococci have been isolated from various sites of the body of healthy sheep, as well as from many infections of those animals, the main one being mastitis. The objective of this review is to appraise the importance and significance of staphylococci in causing mastitis in ewes. The review includes a brief classification and taxonomy of staphylococci and describes the procedures for their isolation and identification, as well as their virulence determinants and the mechanisms of resistance to antibacterial agents. Various staphylococcal species have been implicated in staphylococcal mastitis and the characteristics of isolates are discussed with regards to potential virulence factors. Staphylococcal mastitis is explicitly described, with reference to sources of infection, the course of the disease and the relevant control measures. Finally, the potential significance of staphylococci present in ewes' milk for public health is discussed briefly.

Identification of staphylococci causing mastitis in dairy cattle from Algeria and characterization of Staphylococcus aureus

AIMS

This study was conducted to determine the occurrence of staphylococci from cows with subclinical mastitis from independent herds in Algeria, and to characterize Staphylococcus aureus isolates.

METHODS AND RESULTS

Quarter milk samples were collected separately, somatic cells were counted and samples with more than 200 000 somatic cells per ml were cultured on blood agar. Staphylococci isolates were identified by routine diagnostics, and S. aureus isolates were tested for antibiotic susceptibility by disk diffusion and microdilution. Congo red agar was used to detect biofilm formation and capsule synthesis was detected on serum soft agar (SSA). The S. aureus isolates were characterized by spa typing. DNA microarray analysis was performed to detect resistance and virulence genes. Overall, 40·0% (167/418) of the cows suffered from mastitis. In 63·5% (106/167) of the cows staphylococci were identified. Nine of the 106 Staphylococcus isolates (8·5%) were S. aureus. The coagulase-negative staphylococci belonged to 14 species. All S. aureus isolates were multiresistant and biofilm forming, with 66·67% of them showing diffuse colonies on SSA and belonged to CC97-agrI-cap5. Biofilm genes (icaA/C/D), 13 genes encoding for adhesion, six genes encoding proteases, 11 genes encoding superantigen like toxins were found. Genes conferring resistance to tetracycline (tet(K)), penicillin (blaZ/I/R) and macrolide-lincosamide-streptogramin B (erm(B), erm(A)) were also detected in the S. aureus from this study.

CONCLUSIONS

The current investigation provides a detailed molecular and biofilm formation ability of S. aureus involved in subclinical mastitis in Algeria and shows the wide distribution of adhesion and enterotoxin(-like) genes among S. aureus responsible for causing subclinical bovine mastitis.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings are valuable in tracking the evolution and genomic variation of S. aureus from bovine origin.

Comparative genomics of Staphylococcus aureus associated with subclinical and clinical bovine mastitis

Many efforts have been made to understand the pathogenesis of bovine mastitis to reduce losses and promote animal welfare. Staphylococcus aureus may cause bovine clinical mastitis, but it is mainly associated with subclinical infection, which is usually persistent and can easily reoccur. Here, we conducted a comparative genomic analysis between strains of S. aureus causing subclinical infection (Sau170, 302, 1269, 1364), previously sequenced by our group, and two well-characterized strains causing clinical mastitis (N305 and RF122) to find differences that could be linked to mastitis outcome. A total of 146 virulence-associated genes were compared and no appreciable differences were found between the bacteria. However, several nonsynonymous single nucleotide polymorphisms (SNPs) were identified in genes present in the subclinical strains when compared to RF122 and N305, especially in genes encoding host immune evasion and surface proteins. The secreted and surface proteins predicted by in silico tools were compared through multidimensional scaling analysis (MDS), revealing a high degree of similarity among the strains. The comparison of orthologous genes by OrthoMCL identified a membrane transporter and a lipoprotein as exclusive of bacteria belonging to the subclinical and clinical groups, respectively. No hit was found in RF122 and N305 for the membrane transporter using BLAST algorithm. For the lipoprotein, sequences of Sau170, 302, 1269, and 1364 with identities between 68–73% were found in the MDS dataset. A conserved region found only in the lipoprotein genes of RF122 and N305 was used for primer design. Although the polymerase chain reaction (PCR) on field isolates of S. aureus did not validate the findings for the transporter, the lipoprotein was able to separate the clinical from the subclinical isolates. These results show that sequence variation among bovine S. aureus, and not only the presence/absence of virulence factors, is an important aspect to consider when comparing isolates causing different mastitis outcomes.

Characterisation of mecA gene negative Staphylococcus aureus isolated from bovine mastitis milk from Northern Germany

Staphylococcus aureus (S. aureus) is an important causative agent of contagious intermammary infections in dairy cattle. S. aureus is also considered as an important foodborne pathogen and cause of food poisoning cases and outbreaks worldwide. In order to understand the molecular ecology of S. aureus, the present study compared phenotypic and genotypic characteristics of 70 S. aureus isolates from bovine mastitis milk samples collected during the period from August 2001 to March 2014 in different regions of Northern Germany. The S. aureus isolates were characterised phenotypically, as well as genotypically for their genetic diversity using multi-locus sequence typing (MLST), spa typing and the presence of virulence genes encoding 16 staphylococcal enterotoxins (sea-selu), toxic shock syndrome toxin (tst), thermonuclease (nuc), clumping factor (clfA and clfB), coagulase (coa) and the methicillin resistance gene mecA. A total of 16 sequence types were grouped into eight clonal complexes (CCs), and 17 spa types were identified. These included six novel sequence types and one novel spa type. The majority of bovine mastitis milk-associated sequence types belonged to the clonal complex CC5, CC97, CC133, and CC151 and showed closely related genotypes or lineages with sequence types of human origin. The genotype CC133 (ST133-t1403) was predominant, constituting 27.1% of the isolates. In addition, the S. aureus isolates displayed nine different enterotoxigenic profiles. All S. aureus were methicillin-susceptible (MSSA). The current study provides new information on phenotypic and genotypic traits of S. aureus isolates from bovine mastitis. The comparison of characteristics of isolates from the present study originating from mastitis milk showed similarities with human isolates. This might help to better understand the distribution of S. aureus in the one health context.

Symposium review: Intramammary infections-Major pathogens and strain-associated complexity

Intramammary infection (IMI) is one of the most costly diseases to the dairy industry. It is primarily due to bacterial infection and the major intramammary pathogens include Escherichia coli, Streptococcus uberis, and Staphylococcus aureus. The severity and outcome of IMI is dependent on several host factors including innate host resistance, energy balance, immune status, parity, and stage of lactation. Additionally, the infecting organism can influence the host immune response and progression of disease. It is increasingly recognized that not only the infecting pathogen species, but also the strain, can affect the transmission, severity, and outcome of IMI. For each of 3 major IMI-associated pathogens, S. aureus, Strep. uberis, and E. coli, specific strains have been identified that are adapted to the intramammary environment. Strain-dependent variation in the host immune response to infection has also been reported. The diversity of strains associated with IMI must be considered if vaccines effective against the full repertoire of mammary pathogenic strains are to be developed. Although important advances have been made recently in understanding the molecular mechanism underpinning strain-specific virulence, further research is required to fully elucidate the cellular and molecular pathogenesis of mammary adapted strains and the role of the strain in influencing the pathophysiology of infection. Improved understanding of molecular pathogenesis of strains associated with bovine IMI will contribute to the development of new control strategies, therapies, and vaccines. The development of enabling technologies such as pathogenomics, transcriptomics, and proteomics can facilitate system-level studies of strain-specific molecular pathogenesis and the identification of key mediators of host-pathogen interactions.

Distinct phenotypic traits of Staphylococcus aureus are associated with persistent, contagious bovine intramammary infections

Staphylococcus aureus causing persistent, recurrent bovine intramammary infections are still a major challenge to dairy farming. Generally, one or a few clonal lineages are predominant in dairy herds, indicating animal-to-animal transfers and the existence of distinct pathotypic traits. The aim of this study was to determine if long term persistence and spreading of S. aureus are associated with specific phenotypic traits, including cellular invasion, cytotoxicity and biofilm formation. Mastitis isolates were collected over a 3-years period from a single dairy herd, resulting in two persistent subtypes, the high within-herd prevalent subtype ST9 (CC9)-methicillin-susceptible S. aureus (MSSA), designated HP/ST9, and the low within-herd prevalent subtype ST504 (CC705)-MSSA, designated LP/ST504. Characterization of the two different coexisting persistent subtypes showed that the following phenotypic traits are particularly associated with high within-herd prevalence: lack of capsular polysaccharide expression, high cellular invasiveness, low cytotoxicity and high biofilm/ poly-N-acetylglucosamine (PNAG) production, which may concomitantly contribute to the spreading of HP/ST9 within the herd. By contrast to HP/ST9, LP/ST504 is characterized by the formation of colony dendrites, which may help the bacteria to access deeper tissues as niches for persistence in single animals. Thus, within a single herd, two different types of persistence can be found in parallel, allowing longtime persistence of S. aureus in dairy cattle. Furthermore, this study indicates that ST9 (CC9)-MSSA strains, which are currently thought to have their primary reservoir in swine and humans, can also successfully spread to new hosts and persist in dairy herds for years.

New host shift from human to cows within Staphylococcus aureus involved in bovine mastitis and nasal carriage of animal's caretakers

Staphylococcus aureus is a commensal and pathogen of both humans and bovines. While the epidemiology of both groups has been extensively studied individually, little is known about the potential zoonotic transfer from animal strains to human being and vice versa. To determine the S. aureus prevalence of bovine mastitis in Algeria and the zoonotic transfer of strains to human beings, mastitis milk samples were collected, and professionals in a close contact with bovines were nasal swabbed. S. aureus isolates were all characterized by methicillin resistance and spa-typing. DNA microarrays analysis was performed on a subset of strains in order to detect other virulence factors, including toxins, and to assign the isolates to theirs MLST clonal complexes. Overall, 116/222 (52.3%) cows suffered from mastitis, whose 38.8% (45/116) infected with S. aureus. Human nasal carriage was of 38% (49/129), with only 4 MRSA carriers (3.1%). A higher diversity of spa-types was observed in human (35/50) than in bovine (18/67) isolates, with a predominance of clonal complexes CC97 and CC22 in bovines. The typical animal clone CC97 was occasionally detected in human beings. Conversely, the CC22 S. aureus clone largely switched from humans to bovines. Our study highlights the potential dynamics of animal and human S. aureus strains in the farm environment in Algeria, which may represent a health threat in both populations.

Gentisaldehyde and Its Derivative 2,3-Dihydroxybenzaldehyde Show Antimicrobial Activities Against Bovine Mastitis Staphylococcus aureus

Bovine mastitis is a worldwide disease of dairy cattle associated with significant economic losses for the dairy industry. One of the most common pathogens responsible for mastitis is Staphylococcus (S.) aureus. Due to the development and spreading of antibiotic resistance, the search for novel antimicrobial substances against S. aureus is of great importance. The aim of this study was to evaluate two dihydroxybenzaldehydes for the prevention of bovine mastitis. Therefore we determined the minimal inhibitory concentration (MICs) of gentisaldehyde (2,5-dihydroxybenzaldehyde) and 2,3-dihydroxybenzaldehyde of a diverse set of 172 bovine mastitis S. aureus isolates using an automated robot-based microdilution method. To characterize the bovine isolates we determined the genotype by spa-typing, the antimicrobial resistance to eight antibiotic classes using the disk diffusion method and the MICs of three commonly used antiseptics (benzalkonium chloride, chlorhexidine, and iodine). Further we investigated the cytotoxicity of gentisaldehyde and 2,3-dihydroxybenzaldehyde in bovine mammary epithelial MAC-T cells using the XTT assay. The S. aureus strains showed a high genetic diversity with 52 different spa-types, including five novel types. Antibiotic susceptibility testing revealed that 24% of isolates were resistant to one antimicrobial agent and 3% of isolates were multi-resistant. The occurrence of antibiotic resistance strongly correlated with the spa-type. Both dihydroxybenzaldehydes showed antimicrobial activities with a MIC50 of 500 mg/L. The MIC of gentisaldehyde significantly correlated with that of 2,3-dihydroxybenzaldehyde, whereas no correlation was observed with the MIC of the three antiseptics. Cytotoxicity testing using bovine mammary epithelial MAC-T cells revealed that gentisaldehyde and 2,3-dihydroxybenzaldehyde show low toxicity at MIC50 and MIC90 concentrations. In conclusion, gentisaldehyde and 2,3-dihydroxybenzaldehyde exhibited antimicrobial activities against a diverse range of bovine mastitis S. aureus strains at low-cytotoxic concentrations. Therefore, both compounds are potential candidates as antiseptics to prevent bovine mastitis and to reduce the use of antibiotics in dairy cows.

Some coagulase negative Staphylococcus spp. isolated from buffalo can be misidentified as Staphylococcus aureus by phenotypic and Sa442 PCR methods

Objective

Staphylococcus aureus is a commonly reported cause of buffalo mastitis. However, its prevalence may be overestimated. The aim of this study was to compare S. aureus identification by conventional phenotypic and genotypic assays versus Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) and novel real-time quantitative PCR tests for the cytochrome oxidase subunit D II (cydB) and staphylocoagulase (coa) genes.

Results

From 408 samples obtained from buffalo milk/milking environment, 32 putative S. aureus strains were identified based on characteristic growth on Baird Parker agar, positive catalase reaction, ability to clot rabbit plasma, and positive Sa442 PCR assay. However, in further testing, only 10 of these strains were positive in latex agglutination tests and by MALDI-TOF MS, only eight of the 32 strains were S. aureus while the rest were S. chromogenes (19), S. agnetis (3), S. cohnii (1), or S. xylosus (1). All eight strains identified as S. aureus by MALDI-TOF analysis and confirmed by 16S RNA gene sequencing were positive in a S. aureus-specific cydB PCR test. As well, 7/8 S. aureus strains were PCR positive in a real-time coa PCR test as were 2/69 S. chromogenes and the lone S. xylosus strain tested.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3449-8) contains supplementary material, which is available to authorized users.

Identification of a novel mechanism of action of bovine IgG antibodies specific for Staphylococcus aureus

Staphylococcus aureus is a major pathogen that causes subclinical mastitis associated with huge economic losses to the dairy industry. A few vaccines for bovine mastitis are available, and they are expected to induce the production of S. aureus-specific antibodies that prevent bacterial adherence to host cells or promote opsonization by phagocytes. However, the efficacy of such vaccines are still under debate; therefore, further research focusing on improving the current vaccines by seeking additional mechanisms of action is required to reduce economic losses due to mastitis in the dairy industry. Here, we generated S. aureus-specific bovine IgG antibodies (anti-S. aureus) that directly inhibited bacterial growth in vitro. Inhibition depended on specificity for anti-S. aureus, not the interaction between Protein A and the fragment crystallizable region of the IgG antibodies or bacterial agglutination. An in vitro culture study using S. aureus strain JE2 and its deletion mutant JE2ΔSrtA, which lacks the gene encoding sortase A, revealed that the effect of anti-S. aureus was sortase-A-independent. Sortase A is involved in the synthesis of cell-wall-associated proteins. Thus, other surface molecules, such as membrane proteins, cell surface polysaccharides, or both, may trigger the inhibition of bacterial growth by anti-S. aureus. Together, our findings contribute insights into developing new strategies to further improve the available mastitis vaccine by designing a novel antigen on the surface of S. aureus to induce inhibitory signals that prevent bacterial growth.

Molecular Characterization of Staphylococcus aureus Isolated from Bovine Mastitis and Close Human Contacts in South African Dairy Herds: Genetic Diversity and Inter-Species Host Transmission

Staphylococcus aureus is one of the most common etiological agents of contagious bovine mastitis worldwide. The purpose of this study was to genetically characterize a collection of S. aureus isolates (bovine = 146, human = 12) recovered from cases of bovine mastitis and nasal swabs of close human contacts in the dairy environment. Isolates were screened for a combination of clinically significant antimicrobial and virulence gene markers whilst the molecular epidemiology of these isolates and possible inter-species host transmission was investigated using a combination of genotyping techniques. None of the isolates under evaluation tested positive for methicillin or vancomycin resistance encoding genes. Twenty seven percent of the bovine S. aureus isolates tested positive for one or more of the pyrogenic toxin superantigen (PTSAg) genes with the sec and sell genes predominating. Comparatively, 83% of the human S. aureus isolates tested positive for one or more PTSAg genes with a greater variety of genes being detected. Genomic DNA macrorestriction followed by pulsed-field gel electrophoresis (PFGE) of the bovine isolates generated 58 electrophoretic patterns which grouped into 10 pulsotypes at an 80% similarity level. The majority of the bovine isolates, 93.2% (136/146), clustered into four major pulsotypes. Seven sequence types (ST) were identified among the representative bovine S. aureus isolates genotyped, including: ST8 (CC8), ST97 (CC97), ST351 (CC705), ST352 (CC97), ST508 (CC45), ST2992 (CC97) and a novel sequence type, ST3538 (CC97). Based on PFGE analysis, greater genetic diversity was observed among the human S. aureus isolates. Bovine and human isolates from three sampling sites clustered together and were genotypically indistinguishable. Two of the isolates, ST97 and ST352 belong to the common bovine lineage CC97, and their isolation from close human contacts suggests zoonotic transfer. In the context of this study, the third isolate, ST8 (CC8), is believed to be a human clone which has transferred to a dairy cow and has subsequently caused mastitis. The detection of indistinguishable S. aureus isolates from bovine and human hosts at three of the sampling sites is suggestive of bacterial transmission and supports the need for vigilant monitoring of staphylococcal populations at the human-animal interface.

Diversity of Virulence Factors Associated with West Australian Methicillin-Sensitive Staphylococcus aureus Isolates of Human Origin

An extensive array of virulence factors associated with S. aureus has contributed significantly to its success as a major nosocomial pathogen in hospitals and community causing variety of infections in affected patients. Virulence factors include immune evading capsular polysaccharides, poly-N-acetyl glucosamine, and teichoic acid in addition to damaging toxins including hemolytic toxins, enterotoxins, cytotoxins, exfoliative toxin, and microbial surface components recognizing adhesive matrix molecules (MSCRAMM). In this investigation, 31 West Australian S. aureus isolates of human origin and 6 controls were analyzed for relative distribution of virulence-associated genes using PCR and/or an immunoassay kit and MSCRAMM by PCR-based typing. Genes encoding MSCRAMM, namely, Spa, ClfA, ClfB, SdrE, SdrD, IsdA, and IsdB, were detected in >90% of isolates. Gene encoding α-toxin was detected in >90% of isolates whereas genes encoding β-toxin and SEG were detectable in 50–60% of isolates. Genes encoding toxin proteins, namely, SEA, SEB, SEC, SED, SEE, SEH, SEI, SEJ, TSST, PVL, ETA, and ETB, were detectable in >50% of isolates. Use of RAPD-PCR for determining the virulence factor-based genetic relatedness among the isolates revealed five cluster groups confirming genetic diversity among the MSSA isolates, with the greatest majority of the clinical S. aureus (84%) isolates clustering in group IIIa.

Lineage associated expression of virulence traits in bovine-adapted Staphylococcus aureus

Bovine mastitis is the most costly disease to the dairy industry worldwide with Staphylococcus aureus commonly associated with intramammary infections that are persistent and refractory to treatment. The strains of S. aureus that cause mastitis predominantly belong to a number of well-described bovine-adapted lineages. The objective of this study was to determine if a variety of potential virulence traits were associated with lineage. Bovine-adapted S. aureus isolates (n=120), belonging to lineages CC97, CC151 and ST136, were tested for their ability to adhere to and internalise within cultured bovine mammary epithelial cells (bMEC), to bind bovine fibronectin, to form a biofilm in TSB, TSB+1% glucose and TSB+4% NaCl, and to induce an immune response from bMEC. There were no significant differences between the lineages in ability to adhere to or internalise within bMEC although there were significant differences between individual isolates. For lineages CC97 and ST136, mammalian cell adherence was correlated with the ability to bind bovine fibronectin, however isolates from CC151 could not bind bovine fibronectin in vitro, but adhered to bMEC in a fibronectin-independent manner. There were significant differences between the lineages in ability to form a biofilm in all three growth media with ST136 forming the strongest biofilm while CC151 formed the weakest biofilm. Lineages also differed in their ability to elicit an immune response from bMEC with CC97 eliciting a stronger immune response than CC151 and ST136. These data indicate the potential for both lineage and strain-specific virulence and a strain-specific response to infection in vivo and caution against extrapolating an effect from a single strain of S. aureus to draw conclusions regarding virulence or the host response to infection in unrelated lineages.

Staphylococcus aureus Isolates from Goat and Sheep Milk Seem to Be Closely Related and Differ from Isolates Detected from Bovine Milk

Dairy goat and sheep farms suffer severe economic losses due to intramammary infections, with Staphylococcus aureus representing the main cause of clinical mastitis in small ruminants. In addition, S. aureus contamination of goat and sheep milk may cause staphylococcal food poisoning, as many traditional caprine and ovine milk products are not subjected to pasteurization. Data on virulence and antimicrobial resistance genes, as well as on the clonality of S. aureus detected in goat and sheep milk is scarce. Therefore, it was the aim of this study to determine (i) spa types and clonal complexes (CC) and (ii) virulence and resistance gene profiles of S. aureus isolated from goat and sheep milk. A total of 162 milk samples from sheep and goats presenting signs of an intramammary infection and 104 bulk milk samples were collected. While low prevalence rates of S. aureus was detected on single animal level, 46% of the bulk tank milk samples from small ruminants were positive for S. aureus. All isolates were spa typed and CC and virulence and resistance gene patterns were determined using a DNA microarray. Data from 49 S. aureus isolates was included in the statistical analysis and the construction of a SplitsTree. The analyzed isolates could be assigned to eleven CC, with the large majority of goat and sheep isolates being assigned to CC130 and CC133. The findings of this study suggest that S. aureus shows pronounced adaptation to small ruminants in general, but not to sheep or goats in particular. Although some common characteristics among S. aureus from caprine, ovine, and bovine milk samples were observed, S. aureus from small ruminants seem to form a distinct population. As 67% of the detected S. aureus strains exhibited at least one enterotoxin gene, many caprine, or ovine raw milk products may be contaminated with low levels of enterotoxigenic S. aureus, stressing the importance of strict maintenance of the cold chain.

Staphylococcus aureus nasal carriage could be a risk for development of clinical infections in rabbits

<p>Although nasal carriage has been described as a risk factor for <em>Staphylococcus aureus</em> infections in humans, there is a scarcity of studies about <em>S. aureus</em> nasal carriers in animals. In rabbits, <em>S. aureus</em> is one of the most important pathogens responsible for a number of different types of infections. This study was designed to determine the extent of staphylococcal nasal carriage and to establish whether a relationship exists between nasal carriage and development of lesions. One hundred and sixteen rabbits with and without chronic signs of staphylococcosis from 6 industrial rabbitries were monitored. Nasal swabs for microbiological assessments were obtained from all animals. Microbiological results showed that 56% of the animals carried <em>S. aureus</em> in their nasal cavities with significantly higher incidence in animals with staphylococcal-related lesions (84.2%) compared to apparently healthy animals (28.8%). Additionally, the <em>S. aureus</em> strains isolated from the nasal cavity and lesions were clonally related in 91.7% of animals. This suggests that nasal carriage of <em>S. aureus</em> in rabbits could be a risk for development of clinical infections.</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.

Prevalence, molecular characterization of Staphylococcus aureus isolated from cheese and in vitro antibacterial activity of silver nanoparticles against such strains

AIM

The aim was to investigate cheese samples for the prevalence of Staphylococcus aureus, evaluate multiplex polymerase chain reaction (PCR) methods for S. aureus identification, as well as to determine the antibacterial activity of silver nanoparticles against such strains.

MATERIALS AND METHODS

Total of 100 random locally manufactured cheese samples were collected from Qena dairy markets, Egypt, and examined conventionally for the prevalence of S. aureus then, confirmation of these isolates were done using multiplex PCR. The antibacterial activity of silver nanoparticles against such isolates was also checked.

RESULTS

Lower prevalence of S. aureus in Damietta cheese (54%) than in Kareish cheese (62%) was recorded. As well lower frequency distribution for both S. aureus (36%) and CNS (8%) was also reported for Damietta cheese. Using of multiplex PCR method for S. aureus identification have been confirmed all 58 S. aureus stains that were identified conventionally by detection of two PCR products on agarose gel: The 791 bp and the 638 bp. The correlation coefficient between conventional and multiplex PCR method was 0.91 and was significant at p≤0.001. Regarding antibacterial activity of silver nanoparticles using disk diffusion method on Baird Parker agar it was found that inhibition zone of silver nanoparticles against S. aureus, was 19.2±0.91 mm and it was higher than that produced by gentamicin (400 units/ml) 15.2±0.89 mm.

CONCLUSIONS

The present study illustrated the higher prevalence of S. aureus in cheese samples that may constitute a public health hazard to consumers. According to the results, it can be concluded that silver nanoparticles can be used as an effective antibacterial against S. aureus. Thereby, there is a need for an appropriate study for using silver nanoparticles in cleaning and disinfection of equipment and in food packaging.

Staphylococcal Immune Evasion Proteins: Structure, Function, and Host Adaptation

Staphylococcus aureus is a successful human and animal pathogen. Its pathogenicity is linked to its ability to secrete a large amount of virulence factors. These secreted proteins interfere with many critical components of the immune system, both innate and adaptive, and hamper proper immune functioning. In recent years, numerous studies have been conducted in order to understand the molecular mechanism underlying the interaction of evasion molecules with the host immune system. Structural studies have fundamentally contributed to our understanding of the mechanisms of action of the individual factors. Furthermore, such studies revealed one of the most striking characteristics of the secreted immune evasion molecules: their conserved structure. Despite high-sequence variability, most immune evasion molecules belong to a small number of structural categories. Another remarkable characteristic is that S. aureus carries most of these virulence factors on mobile genetic elements (MGE) or ex-MGE in its accessory genome. Coevolution of pathogen and host has resulted in immune evasion molecules with a highly host-specific function and prevalence. In this review, we explore how these shared structures and genomic locations relate to function and host specificity. This is discussed in the context of therapeutic options for these immune evasion molecules in infectious as well as in inflammatory diseases.

Moving towards the immunodiagnosis of staphylococcal intramammary infections

Bovine mastitis is the primary disease of dairy cattle that has a great impact on the dairy industry. It is estimated that worldwide economic losses due to mastitis range between US$82 and US$131 per cow/year. A fast and efficient diagnosis of the disease remains a major bottleneck that directly influences the speed with which treatment decisions and management are undertaken. Microbiological culture remains the gold standard in the identification of bacteria that cause mastitis, but the method has inherent limitations, such as a delay in obtaining results and cost, and requires special care during the collection and processing of the sample. For this reason, multiple groups have devoted efforts to develop alternative methods that, preferably, can be easily accomplished in the field. The specificity of the antigen-antibody reaction has enabled the emergence of major diagnostic methods used in clinical practice, such as immunoassays, which have significant advantages in terms of speed, sensitivity, specificity, and portability. Commercially, immunodiagnostics have been used in the detection of various diseases in cattle. However, in several cases, only a presumptive diagnosis can be made, which requires confirmation using culture-based methods. This review discusses the immunological-based assays developed since the 1990s for the detection of Staphylococcus aureus, which is considered the primary pathogen of contagious bovine mastitis. Although no ideal antigens ensure the accurate performance of tests and the costs need to be reduced to allow for good market competitiveness, immunoassays, particularly lateral flow immunoassay and immunoagglutination, have emerged as promising tests to be used in the field.

Validation of reference genes for normalization of qPCR mRNA expression levels in Staphylococcus aureus exposed to osmotic and lactic acid stress conditions encountered during food production and preservation

Staphylococcus aureus represents the most prevalent cause of food-borne intoxications worldwide. While being repressed by competing bacteria in most matrices, this pathogen exhibits crucial competitive advantages during growth at high salt concentrations or low pH, conditions frequently encountered in food production and preservation. We aimed to identify reference genes that could be used to normalize qPCR mRNA expression levels during growth of S. aureus in food-related osmotic (NaCl) and acidic (lactic acid) stress adaptation models. Expression stability of nine housekeeping genes was evaluated in full (LB) and nutrient-deficient (CYGP w/o glucose) medium under conditions of osmotic (4.5% NaCl) and acidic stress (lactic acid, pH 6.0) after 2-h exposure. Among the set of candidate reference genes investigated, rplD, rpoB,gyrB, and rho were most stably expressed in LB and thus represent the most suitable reference genes for normalization of qPCR data in osmotic or lactic acid stress models in a rich medium. Under nutrient-deficient conditions, expression of rho and rpoB was highly stable across all tested conditions. The presented comprehensive data on changes in expression of various S. aureus housekeeping genes under conditions of osmotic and lactic acid stress facilitate selection of reference genes for qPCR-based stress response models.

Short communication: Staphylococcus aureus isolated from colostrum of dairy heifers represent a closely related group exhibiting highly homogeneous genomic and antimicrobial resistance features

In heifers, intramammary infections caused by Staphylococcus aureus affect milk production and udder health in the first and subsequent lactations, and can lead to premature culling. Not much is known about Staph. aureus isolated from heifers and it is also unclear whether or not these strains are readily transmitted between heifers and lactating herd mates. In this study, we compared phenotypic characteristics, spa types, and DNA microarray virulence and resistance gene profiles of Staph. aureus isolates obtained from colostrum samples of dairy heifers with isolates obtained from lactating cows. Our objective was to (1) characterize Staph. aureus strains associated with mastitis in heifers and (2) determine relatedness of Staph. aureus strains from heifers and lactating cows to provide data on transmission. We analyzed colostrum samples of 501 heifers and milk samples of 68 lactating cows within the same herd, isolating 48 and 9 Staph. aureus isolates, respectively. Staphylococcus aureus strains from heifers, lactating herd mates, and an unrelated collection of 78 strains from bovine mastitis milk of mature cows were compared. With 1 exception each, characterization of all strains from heifers and lactating cows in the same herd yielded highly similar phenotypic and genotypic results. The strains were Staphaurex latex agglutination test negative (Oxoid AG, Basel, Switzerland) and belonged to agr type II, CC705, and spa types tbl 2645 and t12926. They were susceptible to all antimicrobial agents tested. In contrast, the strains from mature cows in other herds were spread across different clonal complexes, spa types, and SplitsTree clusters (http://www.splitstree.org/), thus displaying a far higher degree of heterogeneity. We conclude that strains isolated from colostrum of heifers and mastitis milk of lactating cows in the same herd feature highly similar phenotypic and genomic characteristics, suggesting persistence of the organism during the first and potentially subsequent lactations or transmission between heifers and mature herd mates.

Prevalence of Staphylococcus aureus protein A (spa) mutants in the community and hospitals in Oxfordshire

Background

Staphylococcal protein A (spa) is an important virulence factor which enables Staphylococcus aureus to evade host immune responses. Genotypes known as “spa-types”, based on highly variable Xr region sequences of the spa-gene, are frequently used to classify strains. A weakness of current spa-typing primers is that rearrangements in the IgG-binding region of the gene cause 1-2% of strains to be designated as “non-typeable”.

Results

We developed an improved primer which enabled sequencing of all strains, containing any type of genetic rearrangement, in a large study among community carriers and hospital inpatients in Oxfordshire, UK (6110 isolates). We identified eight novel spa-gene variants, plus one previously described. Three of these rearrangements would be designated “non-typeable” using current spa-typing methods; they occurred in 1.8% (72/3905) asymptomatically carried and 0.6% (14/2205) inpatient S. aureus strains. Some individuals were simultaneously colonized by both formerly non-typeable and typeable strains; previously such patients would have been identified as carrying only currently typeable strains, underestimating mixed carriage prevalence and diversity. Formerly non-typeable strains were found in more spa-types associated with multilocus sequence type ST398 (35%), common among livestock, compared to other groups with any non-typeable strains (1-4%), suggesting particular spa-types may have been under-represented in previous human studies.

Conclusions

This improved method allows us to spa-type previously non-typeable strains with rearrangements in the spa-gene and to resolve cases of mixed colonization with deletions in one or more strains, thus accounting for hidden diversity of S. aureus in both community and hospital environments.

The inflammatory response of primary bovine mammary epithelial cells to Staphylococcus aureus strains is linked to the bacterial phenotype

Staphylococcus aureus is a major mastitis-causing pathogen in dairy cows. The latex agglutination-based Staphaurex test allows bovine S. aureus strains to be grouped into Staphaurex latex agglutination test (SLAT)-negative [SLAT(−)] and SLAT-positive [SLAT(+)] isolates. Virulence and resistance gene profiles within SLAT(−) isolates are highly similar, but differ largely from those of SLAT(+) isolates. Notably, specific genetic changes in important virulence factors were detected in SLAT(−) isolates. Based on the molecular data, it is assumed that SLAT(+) strains are more virulent than SLAT(−) strains. The objective of this study was to investigate if SLAT(−) and SLAT(+) strains can differentially induce an immune response with regard to their adhesive capacity to epithelial cells in the mammary gland and in turn, could play a role in the course of mastitis. Primary bovine mammary epithelial cells (bMEC) were challenged with suspensions of heat inactivated SLAT(+) (n = 3) and SLAT(−) (n = 3) strains isolated from clinical bovine mastitis cases. After 1, 6, and 24 h, cells were harvested and mRNA expression of inflammatory mediators (TNF-α, IL-1β, IL-8, RANTES, SAA, lactoferrin, GM-CSF, COX-2, and TLR-2) was evaluated by reverse transcription and quantitative PCR. Transcription (ΔΔCT) of most measured factors was induced in challenged bMEC for 6 and 24 h. Interestingly, relative mRNA levels were higher (P<0.05) in response to SLAT(+) compared to SLAT(−) strains. In addition, adhesion assays on bMEC also showed significant differences between SLAT(+) and SLAT(−) strains.

The present study clearly shows that these two S. aureus strain types cause a differential immune response of bMEC and exhibit differences in their adhesion capacity in vitro. This could reflect differences in the severity of mastitis that the different strain types may induce.

Short repeats in the spa gene of Staphylococcus aureus are prone to nonsense mutations: stop codons can be found in strains isolated from patients with generalized infection

Fifteen sequences with stop codons have been obtained in the course of standard methicillin-resistant Staphylococcus aureus (MRSA) spa typing. In nine of those sequences, stop codons occurred due to nonsense G-T and A-T transversions. G-T transversions would appear to be frequent in the spa gene, mostly due to symmetric mutational AT-pressure in the whole S. aureus genome and due to replication-associated mutational pressure characteristic of lagging strands of the "chromosome". A-T transversions would appear to be frequent in the spa gene mostly due to transcription-associated mutational pressure. Relative to other S. aureus genes, short repeats in spa are enriched by nonsense sites for G-T and A-T transversions; the probability of being nonsense for A-T transversion is high in that part of spa coding region. 13 out of 15 (87%) of the sequences with stop codons were obtained from strains isolated from patients with generalized S. aureus infection. Truncation of spa at its C-terminus is predicted to result in a protein that possesses functional IgG binding domains unable to be linked to the cell wall. This is discussed in light of the known fact that extracellular spa is a strong virulence factor involved in immune evasion.

Performance of culture media for the isolation and identification of Staphylococcus aureus from bovine mastitis

Rapid isolation and identification of pathogens is a major goal of diagnostic microbiology. In order to isolate and identify Staphylococcus aureus, a number of authors have used a variety of selective and/or differential culture media. However, to date, there are no reports comparing the efficacy of selective and differential culture media for S. aureus isolation from bovine mastitis cases using the 16S rRNA (rrs) gene sequence as a gold standard test. In the present study, we evaluated the efficacy of four selective and/or differential culture media for the isolation of S. aureus from milk samples collected from cows suffering from bovine mastitis. Four hundred and forty isolates were obtained using salt-mannitol agar (SMA, Bioxon), Staphylococcus-110 agar (S110, Bioxon), CHROMAgar Staph aureus (CSA, BD-BBL) and sheep's blood agar (SBA, BD-BBL). All bacterial isolates were identified by their typical colony morphology in the respective media, by secondary tests (for coagulase and β-haemolysis) and by partial 16S rRNA (rrs) gene sequencing as a gold standard test. Sensitivity, positive predictive and negative predictive values were higher for SMA (86.96, 52.63 and 95.95%, respectively) compared with S110 (70.00, 23.73 and 90.91%, respectively), CSA (69.23, 28.13 and 95.74%, respectively) and SBA (68.75, 37.93 and 89.58%, respectively) while specificity values were similar for all media. Data indicated that the use of culture media for S. aureus isolation combined with determination of coagulase activity and haemolysis as secondary tests improved accuracy of the identification and was in accordance with rrs gene sequence-analysis compared with the use of the culture media alone.

Comparison of genomic and antimicrobial resistance features of latex agglutination test-positive and latex agglutination test-negative Staphylococcus aureus isolates causing bovine mastitis

The dairy industry suffers massive economic losses due to staphylococcal mastitis in cattle. The Staphaureux latex agglutination test (Oxoid, Basel, Switzerland) was reported to lead to negative results in 54% of bovine Staphylococcus aureus strains, and latex-negative strains are thought to be less virulent than Staphaurex latex-positive strains. However, comparative information on virulence and resistance profiles of these 2 groups of Staph. aureus is scarce. Our objective was to associate the latex agglutination phenotype of Staph. aureus strains isolated from bovine mastitis milk with data on clonal complexes, virulence genes, and antibiotic resistance to (1) determine the virulence profiles of the Staphaureux test positive and Staphaurex test negative groups, and (2) provide data needed to improve treatment of bovine mastitis and to identify potential vaccine targets. Seventy-eight Staph. aureus strains isolated from 78 cows on 57 Swiss farms were characterized. Latex agglutination was tested by Staphaureux kit, and resistance profiles were generated by disk diffusion. A DNA microarray was used to assign clonal complexes (CC) and to determine virulence and resistance gene profiles. By the Staphaureux test, 49% of the isolates were latex-positive and 51% were latex-negative. All latex-negative strains were assigned to CC151, whereas latex-positive strains were assigned to various clonal complexes, including CC97 (n=16), CC8 (n=10), CC479 (n=5), CC20 (n=4), CC7 (n=1), CC9 (n=1), and CC45 (n=1). Although the latex-negative isolates were susceptible to all antimicrobial agents tested, 24% of latex-positive isolates were classified as intermediate with regard to cefalexin-kanamycin and 13% were resistant to both ampicillin and penicillin. Microarray profiles of latex-negative isolates were highly similar, but differed largely from those of latex-positive isolates. Although the latex-negative group lacked several enterotoxin genes and sak, it exhibited significantly higher prevalence rates of genes encoding enterotoxin C, toxic shock syndrome toxin, and leukocidins (lukM/lukF-P83, lukD). Our findings suggest that latex-negative isolates represent a group of closely related strains with specific resistance and virulence gene patterns.

A real-time PCR antibiogram for drug-resistant sepsis

Current molecular diagnostic techniques for susceptibility testing of septicemia rely on genotyping for the presence of known resistance cassettes. This technique is intrinsically vulnerable due to the inability to detect newly emergent resistance genes. Traditional phenotypic susceptibility testing has always been a superior method to assay for resistance; however, relying on the multi-day growth period to determine which antimicrobial to administer jeopardizes patient survival. These factors have resulted in the widespread and deleterious use of broad-spectrum antimicrobials. The real-time PCR antibiogram, described herein, combines universal phenotypic susceptibility testing with the rapid diagnostic capabilities of PCR. We have developed a procedure that determines susceptibility by monitoring pathogenic load with the highly conserved 16S rRNA gene in blood samples exposed to different antimicrobial drugs. The optimized protocol removes heme and human background DNA from blood, which allows standard real-time PCR detection systems to be employed with high sensitivity (<100 CFU/mL). Three strains of E. coli, two of which were antimicrobial resistant, were spiked into whole blood and exposed to three different antibiotics. After real-time PCR-based determination of pathogenic load, a ΔC_t<3.0 between untreated and treated samples was found to indicate antimicrobial resistance (P<0.01). Minimum inhibitory concentration was determined for susceptible bacteria and pan-bacterial detection was demonstrated with 3 Gram-negative and 2 Gram-positive bacteria. Species identification was performed via analysis of the hypervariable amplicons. In summary, we have developed a universal diagnostic phenotyping technique that assays for the susceptibility of drug-resistant septicemia with the speed of PCR. The real-time PCR antibiogram achieves detection, susceptibility testing, minimum inhibitory concentration determination, and identification in less than 24 hours.