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SCC mec is a large mobile genetic element that includes the mecA gene and confers resistance to β-lactam antibiotics in methicillin-resistant Staphylococcus aureus (MRSA). There is evidence that SCC mec disseminates among staphylococci, but the transfer mechanisms are unclear. Here, we show that two-component systems mediate the upregulation of natural competence genes in S. aureus under biofilm growth conditions, and this enhances the efficiency of natural transformation. We observe SCC mec transfer via natural transformation from MRSA, and from methicillin-resistant coagulase-negative staphylococci, to methicillin-sensitive S. aureus . The process requires the SCC mec recombinase genes ccrAB , and the stability of the transferred SCC mec varies depending on SCC mec types and recipients. Our results suggest that natural transformation plays a role in the transfer of SCC mec and possibly other mobile genetic elements in S. aureus biofilms. SCC mec is a large mobile genetic element that confers resistance to β-lactam antibiotics in methicillin-resistant Staphylococcus aureus . Here, the authors show that biofilm growth conditions enhance the efficiency of natural transformation in S. aureus and allow the transfer of SCC mec to methicillin-sensitive strains.

Background: The incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections is increasing in the United States, and it is possible that municipal wastewater could be a reservoir of this microorganism. To date, no U.S. studies have evaluated the occurrence of MRSA in wastewater. Objective: We examined the occurrence of MRSA and methicillin-susceptible S. aureus (MSSA) at U.S. wastewater treatment plants. Methods: We collected wastewater samples from two Mid-Atlantic and two Midwest wastewater treatment plants between October 2009 and October 2010. Samples were analyzed for MRSA and MSSA using membrane filtration. Isolates were confirmed using biochemical tests and PCR (polymerase chain reaction). Antimicrobial susceptibility testing was performed by Sensititre® microbroth dilution. Staphylococcal cassette chromosome mec (SCCmec) typing, Panton-Valentine leucocidin (PVL) screening, and pulsed field gel electrophoresis (PFGE) were performed to further characterize the strains. Data were analyzed by two-sample proportion tests and analysis of variance. Results: We detected MRSA (n = 240) and MSSA (n = 119) in 22 of 44 (50%) and 24 of 44 (55%) wastewater samples, respectively. The odds of samples being MRSA-positive decreased as treatment progressed: 10 of 12 (83%) influent samples were MRSA-positive, while only one of 12 (8%) effluent samples was MRSA-positive. Ninety-three percent and 29% of unique MRSA and MSSA isolates, respectively, were multidrug resistant. SCCmec types II and IV, the pvl gene, and USA types 100, 300, and 700 (PFGE strain types commonly found in the United States) were identified among the MRSA isolates. Conclusions: Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater. Because of increasing use of reclaimed wastewater, further study is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater.

Triple combinations of carbapenem, penicillin and β-lactamase inhibitor antibiotic classes are synergistic against MRSA through a mechanism involving allostery-based synergy and collateral sensitivity and can thus be applied at doses that lead to less resistance. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent multidrug-resistant pathogens worldwide, exhibiting increasing resistance to the latest antibiotic therapies. Here we show that the triple β-lactam combination meropenem-piperacillin-tazobactam (ME/PI/TZ) acts synergistically and is bactericidal against MRSA subspecies N315 and 72 other clinical MRSA isolates in vitro and clears MRSA N315 infection in a mouse model. ME/PI/TZ suppresses evolution of resistance in MRSA via reciprocal collateral sensitivity of its constituents. We demonstrate that these activities also extend to other carbapenem-penicillin–β-lactamase inhibitor combinations. ME/PI/TZ circumvents the tight regulation of the mec and bla operons in MRSA, the basis for inducible resistance to β-lactam antibiotics. Furthermore, ME/PI/TZ subverts the function of penicillin-binding protein-2a (PBP2a) via allostery, which we propose as the mechanism for both synergy and collateral sensitivity. Showing in vivo activity similar to that of linezolid, ME/PI/TZ demonstrates that combinations of older β-lactam antibiotics could be effective against MRSA infections in humans.

Clinical isolates of Staphylococcus aureus can express biofilm phenotypes promoted by the major cell wall autolysin and the fibronectin-binding proteins or the icaADBC-encoded polysaccharide intercellular adhesin/poly-N-acetylglucosamine (PIA/PNAG). Biofilm production in methicillin-susceptible S. aureus (MSSA) strains is typically dependent on PIA/PNAG whereas methicillin-resistant isolates express an Atl/FnBP-mediated biofilm phenotype suggesting a relationship between susceptibility to β-lactam antibiotics and biofilm. By introducing the methicillin resistance gene mecA into the PNAG-producing laboratory strain 8325-4 we generated a heterogeneously resistant (HeR) strain, from which a homogeneous, high-level resistant (HoR) derivative was isolated following exposure to oxacillin. The HoR phenotype was associated with a R₆₀₂H substitution in the DHHA1 domain of GdpP, a recently identified c-di-AMP phosphodiesterase with roles in resistance/tolerance to β-lactam antibiotics and cell envelope stress. Transcription of icaADBC and PNAG production were impaired in the 8325-4 HoR derivative, which instead produced a proteinaceous biofilm that was significantly inhibited by antibodies against the mecA-encoded penicillin binding protein 2a (PBP2a). Conversely excision of the SCCmec element in the MRSA strain BH1CC resulted in oxacillin susceptibility and reduced biofilm production, both of which were complemented by mecA alone. Transcriptional activity of the accessory gene regulator locus was also repressed in the 8325-4 HoR strain, which in turn was accompanied by reduced protease production and significantly reduced virulence in a mouse model of device infection. Thus, homogeneous methicillin resistance has the potential to affect agr- and icaADBC-mediated phenotypes, including altered biofilm expression and virulence, which together are consistent with the adaptation of healthcare-associated MRSA strains to the antibiotic-rich hospital environment in which they are frequently responsible for device-related infections in immuno-compromised patients.

Staphylococcus aureus is a major pathogen in humans and causes serious problems due to antibiotic resistance. We investigated the antimicrobial effect of glycyrrhetinic acid (GRA) and its derivatives against 50 clinical S. aureus strains, including 18 methicillin-resistant strains. The minimum inhibitory concentrations (MICs) of GRA, dipotassium glycyrrhizate, disodium succinoyl glycyrrhetinate (GR-SU), stearyl glycyrrhetinate and glycyrrhetinyl stearate were evaluated against various S. aureus strains. Additionally, we investigated the bactericidal effects of GRA and GR-SU against two specific S. aureus strains. DNA microarray analysis was also performed to clarify the mechanism underlying the antibacterial activity of GR-SU. We detected the antimicrobial activities of five agents against S. aureus strains. GRA and GR-SU showed strong antibacterial activities compared to the other three agents tested. At a higher concentration (above 2x MIC), GRA and GR-SU showed bactericidal activity, whereas at a concentration of 1x MIC, they showed a bacteriostatic effect. Additionally, GRA and GR-SU exhibited a synergistic effect with gentamicin. The expression of a large number of genes (including transporters) and metabolic factors (carbohydrates and amino acids) was altered by the addition of GR-SU, suggesting that the inhibition of these metabolic processes may influence the degree of the requirement for carbohydrates or amino acids. In fact, the requirement for carbohydrates or amino acids was increased in the presence of either GRA or GR-SU. GRA and GR-SU exhibited strong antibacterial activity against several S. aureus strains, including MRSA. This activity may be partly due to the inhibition of several pathways involved in carbohydrate and amino acid metabolism.

Staphylococcus aureus is an opportunistic bacterium that can infect humans and animals. We previously reported that Staphylococcus aureus as one of the most frequent Gram-positive bacteria found in the infection in juvenile green turtles ( Chelonia mydas ) from the Sea Turtle Conservation Center of Thailand (STCCT), Sattahip, Chonburi Province. It was also the most detected Gram-positive bacteria in rearing seawater. In this study, we investigated the presence of S. aureus in coastal seawater used as supply water to rearing containers, rearing water, fish fillet used as feed, and juvenile green turtle carcasses at STCCT. From the results, S. aureus can be isolated from rearing water, fish fillet, and juvenile turtle carcasses but not from incoming coastal seawater. The determination of antibiotic resistance against 11 drugs demonstrated that more S. aureus from juvenile turtles were antibiotic resistant than the isolates from rearing water and fish fillet. Furthermore, a higher isolate number of methicillin-resistant S. aureus (MRSA) was found in juvenile turtle carcasses. We also detected penicillin-susceptible MRSA and mecA -positive methicillin-susceptible S. aureus from juvenile turtles and fish fillet, respectively. Differences in the antibiotic resistance profiles were observed in this study compared with our previous observation. A change in the antibiotic resistance properties possibly continued in S. aureus . This finding suggests that the status of animal health is at high risk and emphasizes the need for a surveillance plan and treatment strategies to confront this serious threat.

Community-acquired (CA) methicillin-resistant Staphylococcus aureus (MRSA) infection among individuals without healthcare-associated (HA) risk factors was first recognized about a decade ago. It has now emerged as an epidemic that is responsible for rapidly progressive, fatal diseases including necrotizing pneumonia, severe sepsis and necrotizing fasciitis. Unlike HA-MRSA, CA-MRSA are usually pan-susceptible to non-β-lactam antimicrobials. In addition to novel methicillin resistance genetic cassettes, many CA-MRSA harbor a phage harboring Panton–Valentine Leukocidin (PVL) genes and some data support the idea that PVL is responsible at least in part for the increased virulence of CA-MRSA. The tight association between the novel methicillin resistance cassettes and PVL phage cannot be explained, as they integrate into distinct sites on the S. aureus chromosome. This paper presents the evidence that CA-MRSA isolates are distinct strains emerging de novo from CA-methicillin susceptible isolates rather than from HA-MRSA isolates that have escaped from the hospital setting and that these novel CA-MRSA isolates may be more virulent than HA-MRSA. The second aim is to outline the progress in understanding the role of PVL in CA-MRSA pathogenesis.

Staphylococcus pseudintermedius is an important opportunistic pathogen of companion animals, mainly associated with skin and mucous membrane colonization among pets. We aimed to characterize the S. pseudintermedius isolates collected from dogs and cats nationwide in South Korea. A total of 1,071 S. pseudintermedius isolates were recovered from mostly dogs ( n  = 1037) and cats ( n  = 34) in four different infection sites: skin/ear ( n  = 887), urine ( n  = 28), respiratory tract ( n  = 49), and genital organs ( n  = 107). S. pseudintermedius isolates exhibited high resistance (> 50%) to penicillin, erythromycin, clindamycin, trimethoprim/sulfamethoxazole, and chloramphenicol. Antimicrobial resistance rates were significantly higher in non-skin isolates than in skin isolates from dogs ( p  < 0.05). In addition, the isolates demonstrated higher resistance to most antimicrobials in dogs of older ages. Multidrug resistance was detected in more than 70% of isolates. The methicillin resistance was detected in 35.1% of S. pseudintermedius. Furthermore, the methicillin-resistant S. pseudintermedius (MRSP) isolates showed significantly higher resistance to non-beta-lactam antimicrobials than the methicillin-sensitive S. pseudintermedius (MSSP) isolates ( p  < 0.05). Multi-locus sequence typing revealed the presence of 48 sequence types (STs) in 100 MRSPs, of which 24 types were identified newly in this study. The most frequently detected STs were ST121, ST794, ST1328, ST71, and ST496, comprising 33.3%. pRE25-like elements, including rec , IS 1252 , and IS 1216 , were identified in 62% of MRSP, commonly showing resistance to chloramphenicol. Moreover, the pRE25-like elements were associated with STs, with five predominantly detected STs carrying pRE25-like elements, except for ST71. The occurrence of methicillin resistance among S. pseudintermedius with predominant STs and pRE25-like elements in dogs and cats potentially poses health hazards to humans.

Objectives Molecular typing such as spa typing is used to control and prevent Staphylococcus aureus widespread in hospitals and communities. Hence, the aim of this study was to find the most common types of S. aureus strain circulating in Shiraz via spa and SCCmec typing methods. Results Total of 159 S. aureus isolates were collected from two tertiary hospitals in Shiraz. Isolates were identified by biochemical tests. Antimicrobial susceptibility tests were performed by standard disk diffusion method and then genetic analysis of bacteria was performed using SCCmec and spa typing. In this study 31.4% of the isolates were methicillin-resistant S. aureus . The majority of isolates were SSCmec type III. Spa type t030 was the most prominent type among MRSA strains. For the first time in Iran, spa003, t386, t1877, t314, t186, t1816, t304, t325, t345 were reported in this study. It was shown that there is a possibility that these spa types are native to this region. Our findings showed that SCCmec II, III and IV disseminate from hospital to community and vice versa. Thus, effective monitoring of MRSA in hospital and community is necessary.

Coagulase-negative staphylococci (CoNS) represent a diverse group of opportunistic pathogens associated with human and animal infections. The burden of infectious diseases attributed to antibiotic-resistant CoNS, particularly methicillin-resistant CoNS (MR-CoNS), is a global public health concern. However, there is limited data on the epidemiology of MR-CoNS in Africa. This systematic review provides insights on MR-CoNS from human and non-human sources in Africa, the methicillin-resistance gene determinants and the associated mobile genetic elements. The review retrieved articles from four electronic databases: PubMed, Scopus, Web of Science, and Google Scholar, using specific keywords. This study was carried out until 20 November 2024. Articles were screened and data was extracted and analyzed following the PRISMA guidelines. The meta-analysis used the binary random effects model with a 95% confidence interval. Overall, 65 articles from 16 African countries were included in the study. The pooled prevalence rates for CoNS and MR-CoNS in Africa were 27% and 36%, respectively. The review identified 36 species of CoNS from human and non-human sources. In addition, 20 (31%) studies each reported CoNS and MR-CoNS from human and animal infections. The most prevalent species of MR-CoNS included Staphylococcus epidermidis , Staphylococcus haemolyticus , and Mammaliicoccus sciuri . The African MR-CoNS harboured different staphylococcal chromosome cassette mec (SCC mec ) elements (types I, II, III, IV, V, VI, VIII, and a SCC mec - mecC (hybrid), and the most common SCC mec element was the SCC mec type IV. The findings highlight the paucity of data on the epidemiology of MR-CoNS in Africa. The identification of MR-CoNS from human and animal infections indicates the need for a detailed characterization using molecular methods. This strategy will provide data to healthcare practitioners and policymakers to develop effective measures to combat antimicrobial resistance in Africa.