Staphylococcal Enterotoxin Genes in Coagulase-Negative Staphylococci-Stability, Expression, and Genomic Context

Staphylococcus haemolyticus: An updated review on nosocomial infections, antimicrobial resistance, virulence, genetic traits, and strategies for combating this emerging opportunistic pathogen

Staphylococcus haemolyticus, a key species of the Staphylococcus genus, holds significant importance in healthcare-associated infections, due to its notable resistance to antimicrobials, like methicillin, and proficient biofilms-forming capabilities. This coagulase-negative bacterium poses a substantial challenge in the battle against nosocomial infections. Recent research has shed light on Staph. haemolyticus genomic plasticity, unveiling genetic elements responsible for antibiotic resistance and their widespread dissemination within the genus. This review presents an updated and comprehensive overview of the clinical significance and prevalence of Staph. haemolyticus, underscores its zoonotic potential and relevance in the one health framework, explores crucial virulence factors, and examines genetics features contributing to its success in causing emergent and challenging infections. Additionally, we scrutinize ongoing studies aimed at controlling spread and alternative approaches for combating it.

Characterization of Staphylococcus Species Isolates from Sheep Milk with Subclinical Mastitis: Antibiotic Resistance, Enterotoxins, and Biofilm Production

Subclinical mastitis represents one of the most contagious diseases affecting animals involved in dairy production systems. Although coagulase-negative staphylococci (CoNSs) have been considered minor pathogens for many years, they have recently emerged as opportunistic pathogens in mastitis disorders. The objectives of this work were to assess the antimicrobial resistance profile and the ability to produce a biofilm in comparison with a reference strain and to search for genes related to biofilm production, antimicrobial resistance, and enterotoxins in 18 isolates of Staphylococcus species from the milk of sheep with subclinical mastitis, collected from different Sicilian farms. This knowledge is essential to provide basic information on the pathogenicity and virulence of staphylococcal species and their impact on animal health. All isolates were resistant to ampicillin, 88.8% to streptomycin, 77.7% to gentamicin, 44.4% to chloramphenicol, 27.7% to erythromycin, and 11.1% to tetracycline, and two isolates were strong biofilm producers. Antibiotic resistance gene profiling showed that 16.6% of isolates possess the blaZ gene, whereas the search of biofilm-associated genes revealed the occurrence of the sasC gene in 33.3% of isolates, the ica gene in 27.7%, and bap and agr (accessory gene regulator) genes in 16.6% of isolates. Altogether, the results of this study indicate that CoNSs can acquire virulence genes and could have a role as pathogens in subclinical mastitis.

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.

Coagulase-Negative Staphylococci as an Etiologic Agent of Ovine Mastitis, with a Focus on Subclinical Forms

The objective of this review is to investigate the distribution and the characteristics of coagulase-negative Staphylococci (CoNS) implicated in ovine mastitis, and especially in subclinical cases, in order to provide a global perspective of the current research data and analyze specific critical aspects of the issue. PRISMA guidelines were implemented in the search of the last 20 years of the related literature in two databases. In total, 139 studies were included in this review. Relevant data were tracked down, assembled, and compared. Regarding the geographical distribution, most studies originated from Europe (68), followed by South America (33). Lacaune was the most examined breed, while S. epidermidis was the predominantly identified species, representing approximately 39% of the obtained isolates. Antibiotic resistance in the relevant bacteria was documented mostly for Penicillin (32.8%) and Amoxicillin (32.1%), while biofilm- and toxin-associated genes were encountered in variable rates because significant inequalities were observed between different articles. Significantly higher rates of antimicrobial resistance were detected in Asia and South America compared to Europe. Finally, the diagnostic procedures carried out in the respective studies were evaluated. Conventional culture and biochemical tests were mostly performed for simple strain identification; therefore, further molecular investigation of isolates should be pursued in future studies, as this will provide important data regarding specific aspects of the implication of CoNS in ovine mastitis.

spa Types and Staphylococcal Enterotoxin Production of Staphylococcus aureus Isolated from Wild Boar

Little is known about the structure of S. aureus population and the enterotoxin gene content in wild boar. In 1025 nasal swabs from wild boars, 121 S. aureus isolates were identified. Staphylococcal enterotoxin (SE) genes were identified in 18 isolates (14.9%). The seb gene was found in 2 S. aureus isolates, sec in 2 isolates, the see and seh genes were found in 4 and 11 isolates, respectively. The production of SEs was evaluated in bacteria grown in microbial broth. Concentration of SEB reached 2.70 µg/ml after 24 h and 4.46 µg/ml at 48 h. SEC was produced at 952.6 ng/ml after 24 h and 7.2 µg/ml at 48 h. SEE reached 124.1 ng/ml after 24 h and 191.6 ng/ml at 48 h of culture. SEH production reached 4.36 µg/ml at 24 h and 5.42 µg/ml at 48 h of culture. Thirty-nine spa types were identified among S. aureus isolates. The most prevalent spa types were t091 and t1181, followed by t4735 and t742, t3380 and t127. Twelve new spa types, i.e., t20572‒t20583 were identified. The wild boar S. aureus population was shown to contain previously identified animal/human-associated spa types and spa types not identified in humans or animals. We also indicate that wildlife animals can be a significant reservoir of see-positive S. aureus.

Staphylococcus xylosus and Staphylococcus aureus as commensals and pathogens on murine skin

Skin ulcers, skin dermatitis and skin infections are common phenomena in colonies of laboratory mice and are often found at increased prevalence in certain immunocompromised strains. While in many cases these skin conditions are mild, in other cases they can be severe and lead to animal morbidity. Furthermore, the presence of skin infections and ulcerations can complicate the interpretation of experimental protocols, including those examining immune cell activation. Bacterial species in the genus Staphylococcus are the most common pathogens recovered from skin lesions in mice. In particular, Staphylococcus aureus and Staphylococcus xylosus have both been implicated as pathogens on murine skin. Staphylococcus aureus is a well-known pathogen of human skin, but S. xylosus skin infections in humans have not been described, indicating that there is a species-specific difference in the ability of S. xylosus to serve as a skin pathogen. The aim of this review is to summarize studies that link S. aureus and S. xylosus to skin infections of mice and to describe factors involved in their adherence to tissue and their virulence. We discuss potential differences in mouse and human skin that might underlie the ability of S. xylosus to act as a pathogen on murine skin, but not human skin. Finally, we also describe mouse mutants that have shown increased susceptibility to skin infections with staphylococcal bacteria. These mutants point to pathways that are important in the control of commensal staphylococcal bacteria. The information here may be useful to researchers who are working with mouse strains that are prone to skin infections with staphylococcal bacteria.

Stability and Resistance to Proteolysis of Enterotoxins SEC and SEL Produced by Staphylococcus epidermidis and Staphylococcus aureus

The only staphylococcal enterotoxins produced by Staphylococcus epidermidis include SEC_epi and SEL_epi, whereas Staphylococcus aureus produces orthologous SECs and SEL having different sequences. We compared S. epidermidis and S. aureus SECs and SELs in terms of resistance to proteolysis and both, thermal and chemical stability. We show that SEC_epi and SEL_epi produced by S. epidermidis have similar resistance to proteolysis if compared with their respective orthologues produced by S. aureus. Studied S. epidermidis and S. aureus SEC variants incubated with pepsin at pH 2.0 were found to be more resistant to proteolysis than SELs. SELs turned out to be more resistant than SECs to proteolysis with trypsin at pH 8.0. SEC_epi was found to be more resistant to thermal denaturation if compared with its S. aureus orthologues. The S. epidermidis and S. aureus SEC variants were found to have higher thermal stability than SELs. Our data indicate that, due to their high stability, the enterotoxins SEC_epi and SEL_epi produced in food by S. epidermidis may pose a food safety risk comparable with that posed by S. aureus enterotoxins.

Detection of Resistant and Enterotoxigenic Strains of Staphylococcus warneri Isolated from Food of Animal Origin

The topic of this work is the detection of antimicrobial resistance to Staphylococcus warneri strains and the genes encoding staphylococcal enterotoxins. It is considered a potential pathogen that can cause various—mostly inflammatory—diseases in immunosuppressed patients. The experimental part of the paper deals with the isolation of individual isolates from meat samples of Oryctolagus cuniculus, Oncorhynchus mykiss, Scomber scombrus, chicken thigh, beef thigh muscle, pork thigh muscle, and bryndza cheese. In total, 45 isolates were obtained and subjected to phenotypic (plasma coagulase activity, nuclease, pigment, hemolysis, lecithinase, and lipase production) and genotypic analyses to confirm the presence of the S. warneri species. The presence of genes encoding staphylococcal enterotoxins A (three isolates) and D (six isolates) was determined by PCR. Using the Miditech system, the minimum inhibitory concentration for various antibiotics or antibiotics combinations was determined, namely for ampicillin; ampicillin + sulbactam; oxacillin; cefoxitin; piperacillin + tazobactam; erythromycin; clindamycin; linezolid; rifampicin; gentamicin; teicoplanin; vancomycin; trimethoprim; chloramphenicol; tigecycline; moxifloxacin; ciprofloxacin; tetracycline; trimethoprim + sulfonamide; and nitrofurantoin. Resistance to ciprofloxacin and tetracycline was most common (73%). At the same time, out of a total of 45 isolates, 22% of the isolates were confirmed as multi-resistant. Isolates that showed phenotypic resistance to β-lactam antibiotics were subjected to mecA gene detection by PCR.