Comparative genomics study of Staphylococcus aureus isolated from cattle and humans reveals virulence patterns exclusively associated with bovine clinical mastitis strains

Staphylococcus aureus causes nosocomial and intramammary infections in humans and cattle, respectively. A large number of virulence factors are thought to play important roles in the pathogenesis of this bacterium. Currently, genome-wide and data-analysis studies are being used to better understand its epidemiology. In this study, we conducted a genome wide comparison and phylogenomic analyses of S. aureus to find specific virulence patterns associated with clinical and subclinical mastitis strains in cattle and compare them with those of human origin. The presence/absence of key virulence factors such as adhesin, biofilm, antimicrobial resistance, and toxin genes, as well as the phylogeny and sequence type of the isolates were evaluated. A total of 248 genomes (27 clinical mastitis, 43 subclinical mastitis, 21 milk, 53 skin-related abscesses, 49 skin infections, and 55 pus from cellulitis) isolated from 32 countries were evaluated. We found that the cflA, fnbA, ebpS, spa, sdrC, coa, emp, vWF, atl, sasH, sasA, and sasF adhesion genes, as well as the aur, hglA, hglB, and hglC toxin genes were highly associated in clinical mastitis strains. The strains had diverse genetic origins (72 protein A and 48 sequence types with ST97, ST8 and ST152 being frequent in isolates from clinical mastitis, abscess, and skin infection, respectively). Further, our phylogenomic analyses suggested that zoonotic and/or zooanthroponotic transmission may have occurred. These findings contribute to a better understanding of S. aureus epidemiology and the relationships between adhesion mechanisms, biofilm formation, antimicrobial resistance, and toxins and could aid in the development of improved vaccines and strain genotyping methods.

Comparison of superantigens and attachment factors genes of Staphylococcus aureus in clinical isolates and nasal colonizers in the same patients

BACKGROUND

Staphylococcus aureus (S. aureus) is a bacterial pathogen can cause a wide range of nosocomial infections. Nasal colonization by S.aureus plays important role both in the epidemiology and pathogenesis of infection.

OBJECTIVES

The purpose of this study was to investigate the association of clinical isolates and nasal colonizers of S. aureus in the same patients by molecular methods, and their antibiotic susceptibility pattern.

METHODS

A total of 181 S. aureus isolates were collected from 100 patients admitted that including 100 clinical isolates and 81 nasal swabs from the same patients (19 cases were found as noncarriers). Superantigens and adhesion genes were identified by PCR. Molecular typing of the isolates was performed by repetitive element polymerase chain reaction (Rep-PCR). Antimicrobial susceptibility pattern of the isolates was conducted by disk diffusion. MIC of the isolates to vancomycin was determined by microbroth dilution. The ability of S. aureus isolates to form biofilm was determined by microtiter plate assay.

RESULTS

The most frequent adhesion gene in both clinical isolates and nasal colonizer was clfA with 93% and 76%, respectively. Staphylococcal enterotoxin A (SEA) was the most commonly superantigen (68%) in both nasal colonizers (71.6%) and clinical isolates (65%). The highest resistance rate was to erythromycin (45.3%) with 36% and 56.8% in clinical and nasal colonizer isolates, respectively. All S. aureus isolates were susceptible to linezolid and vancomycin. Multiple drug resistance (MDR) was detected in 36% (n = 65) of the isolates. Biofilm formation was identified in 160 (88.4%) isolates with 87% and 90% in clinical isolates and nasal colonizers, respectively. Repetitive element polymerase chain reaction (Rep-PCR) typing divided 181 S. aureus isolates into six clusters. Twelve isolates from clinical isolates and nasal carriers were closely related.

CONCLUSION

There is a high concordance rate between colonizing and clinical isolates of S. aureus in terms of adhesion factors and superantigen genes. It is suggested that nasal decolonization could be effective in the preventing of S. aureus infections.

Prevalence of Genes Encoding Aminoglycoside-Modifying Enzymes in Clinical Isolates of Gram-Positive Cocci in Iran: A Systematic Review and Meta-Analysis

Introduction: Several studies have investigated the genes encoding aminoglycoside-modifying enzymes (AMEs) among gram-positive cocci (GPC) such as Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), coagulase-negative staphylococci (CoNS), and Enterococcus spp. in Iran; however, a comprehensive analysis has not yet been performed. Thus, the present systematic review and meta-analysis was conducted to determine the prevalence of genes encoding AMEs among GPC in Iran. Methods: A systematic review of the data published in the English and Persian languages from January 2000 to October 2018 was performed by searching different electronic databases (Medline, Embase, Web of Science, and the Iranian Database). Meta-analysis was performed by using the Comprehensive Meta-Analysis (Biostat V2.2) software. Cochran's Q and I² statistics were used to test heterogeneity, and publication bias was assessed by using funnel plot and Begg's and Egger's tests. Results: Out of 117 studies, 28 were considered eligible for inclusion in the current meta-analysis. The most prevalent AMEs gene among GPC was aac(6')-Ie-aph(2'')-Ia, with a prevalence of 97.7% (95% CI; 94.4-99) in high-level gentamicin-resistant enterococci and 67.7% (95% CI; 59.2-75.2) in MRSA. The second most common gene was ant(4')Ia, with a prevalence of 45.3% (95% CI; 23.9-68.6) in MRSA. Conclusions: It was ultimately determined that the prevalence of AMEs genes among GPC had reached alarming levels in Iran; therefore, aminoglycosides should be prescribed with caution by clinicians. The implementation of a regional and nationwide surveillance system to monitor antimicrobial resistance, especially aminoglycosides, and increasing the awareness of AMEs genes among clinicians are essential to guiding empirical and pathogen-specific therapy.

Molecular Study of Enterotoxins Genes of Staphylococcus aureus Isolated from Patients in Intensive Care Units

Introduction:

Staphylococcus aureusis responsible for healthcare-associated sepsis. Various virulence genes may be responsible for the severity of the outcome of this infection.

Aims & objectives:

Therefore, the aim of the present study was to investigate the prevalence of enterotoxin genes inS .aureusassociated with HCA sepsis affecting adult's patients in Intensive Care Units (ICU).

Materials & Methods:

The study is a cross-sectional observational study included 432 patients admitted to intensive care units with Healthcare-Associated Infections (HCAIs). The patients were subjected to blood culture and identification of the isolated bacteria according to the standard microbiological method. Isolates identified asS. aureuswere subjected to molecular studies for the detection of meca gene and enterotoxins genes by multiplex Polymerase Chain Reaction (PCR).

Results & Discussion:

Blood culture was positive in 170 of the patients (39.3%). 47 of the blood culture yieldS. aureu.Regarding studies of virulence genes in isolatedS. aureus, the most frequent genes were seg (61.7%), mecA (46.8%) and sea (42.6%). The less frequent genes were tst and eta 6.4% for each. Analysis of demographic, clinical and virulence genes of isolatedS. aureusto HAIs outcome reveals that the virulence genes namely mec, sei and tst ofS. aureuswere the only significant factors associated with death The distribution of enterotoxigenic genes among MRSA and MSSA shows a significant association between seg and sei genes in MRSA isolates.

Conclusion:

The present study highlights the prevalence of enterotoxin genes in isolated S.aureus from patients with hospital-acquired infections in intensive care units in a tertiary hospital. There was high prevalence as about two-thirds of the isolates harbor seg and sea genes in addition to methicillin resistance gene mecA. The fatal outcome of sepsis in those patients was associated with the presence of enterotoxin genes sei and tst. There is a need for screening patients admitted to intensive care units forS. aureusharboring these genes for proper management and application of isolation and contact guidelines of infection control