Staphylococcal Cassette Chromosome Mec Element Research Articles

A Look into the Melting Pot: The mecC-Harboring Region Is a Recombination Hot Spot in Staphylococcus stepanovicii.

IntroductionHorizontal gene transfer (HGT) is an important driver for resistance- and virulence factor accumulation in pathogenic bacteria such as Staphylococcus aureus.MethodsHere, we have investigated the downstream region of the bacterial chromosomal attachment site (attB) for the staphylococcal cassette chromosome mec (SCCmec) element of a commensal mecC-positive Staphylococcus stepanovicii strain (IMT28705; ODD4) with respect to genetic composition and indications of HGT. S. stepanovicii IMT28705 was isolated from a fecal sample of a trapped wild bank vole (Myodes glareolus) during a screening study (National Network on “Rodent-Borne Pathogens”) in Germany. Whole genome sequencing (WGS) of IMT28705 together with the mecC-negative type strain CM7717 was conducted in order to comparatively investigate the genomic region downstream of attB (GenBank accession no. KR732654 and KR732653).ResultsThe bank vole isolate (IMT28705) harbors a mecC gene which shares 99.2% nucleotide (and 98.5% amino acid) sequence identity with mecC of MRSA_LGA251. In addition, the mecC-encoding region harbors the typical blaZ-mecC-mecR1-mecI structure, corresponding with the class E mec complex. While the sequences downstream of attB in both S. stepanovicii isolates (IMT28705 and CM7717) are partitioned by 15 bp direct repeats, further comparison revealed a remarkable low concordance of gene content, indicating a chromosomal “hot spot” for foreign DNA integration and exchange.ConclusionOur data highlight the necessity for further research on transmission routes of resistance encoding factors from the environmental and wildlife resistome.

Characterization of Staphylococcal Cassette Chromosome mec (SCCmec) in Methicillin-Resistant Staphylococcus epidermidis Strains Isolated from Biomaterial-Associated Infections and their Antibiotic Resistance Patterns.

This work aims to provide an insight into staphylococcal cassette chromosome mec elements and antibiotic resistance in clinical isolates of Staphylococcus epidermidis. The dominating type was SCCmec - IV. Fifteen isolates were assigned to SCCmec type III, two isolates to SCCmec type II. Most isolates were resistant to at least three of the non-β-lactam antibiotics tested. None of the strains exhibited resistance to new generation antibiotics, such as daptomycin and linezolid. Also, none of these strains showed resistance to tigecycline and only four strains were resistant to rifampin i.e. antibiotics which are very efficient in treating biofilm-associated infections.

Can Panton Valentine Leukocidin Gene And Clindamycin Susceptibility Serve As Predictors of Community Origin of MRSA From Skin and Soft Tissue Infections?

Community associated Methicillin-resistant Staphylococcus aureus (CA-MRSA) strains have begun to replace Hospital Associated MRSA (HA-MRSA) strains in hospital settings all over the world. With the epidemiological distinctions between these strains beginning to become ill-defined, the categorisation of a strain as CA-MRSA or HA-MRSA is dependent on molecular methods to detect the presence of SCCmec (Staphylococcal Cassette Chromosome mec) elements. However other markers like the presence of Panton Valentine Leukocidin toxin (pvl) genes or Clindamycin susceptibility may also be associated with community origin of MRSA. To determine the prevalence of CA-MRSA among MRSA strains isolated from skin and soft tissue infections and to evaluate the usefulness of Panton Valentine Leukocidin and Clindamycin susceptibility as markers of community origin of MRSA. One hundred isolates of MRSA from skin and soft tissue were studied for the presence of SCCmec IV and V genes and Panton valentine leukocidin gene by Polymerase chain reaction. Inducible clindamycin resistance was screened for using the D-test. Fischer's exact test. A p-value <0.05 was considered significant. Eighteen out of 100 MRSA strains were found to be CA-MRSA based on presence of SCCmecV. The proportion of Panton Valentine Leukocidin gene carriage among CA- MRSA as compared to HA-MRSA was found to be statistically significant (p<0.0001). Among the CA-MRSA strains, 94.4% were found to be susceptible to Clindamycin as against only 13.4% of the HA-MRSA strains (p<0.0001). The odds of an MRSA strain being CA-MRSA if it was both Clindamycin susceptible and PVL gene positive was calculated to be 68.25 (p<0.0001). Both Clindamycin susceptibility and pvl gene carriage were found to be independent predictors of community origin of MRSA, but taken together the association was highly significant.

A Novel Staphylococcal Cassette Chromosome mec Type XI Primer for Detection of mecC-Harboring Methicillin-Resistant Staphylococcus aureus Directly from Screening Specimens.

Methicillin-resistant Staphylococcus aureus (MRSA) screening using real-time PCR has decreased in sensitivity due to the emergence of variant staphylococcal cassette chromosome mec element (SCCmec) types. We have designed and validated a novel SCCmec XI primer, which enables for the first time the rapid detection of mecC-harboring MRSA directly from nasopharyngeal swabs without prior cultivation.

Prevalence of vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA among methicillin-resistant S. aureus with high vancomycin minimal inhibitory concentrations in Taiwan: A multicenter surveillance study, 2012–2013

Intermediate-resistance and heteroresistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) is reported worldwide. A surveillance study in 2003 showed that the prevalence rates of vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) in Taiwan were 0.2% and 0.7%, respectively. This study aimed to investigate the updated prevalence of VISA and hVISA in Taiwan. MRSA isolates from sterile sites with minimal inhibitory concentrations (MICs) of 1μg/mL or more to vancomycin were collected from 15 participating hospitals in Taiwan. Enrolled MRSA isolates were submitted to antimicrobial susceptibility testing, staphylococcal cassette chromosome mec (SCCmec) element typing, and multilocus sequence typing. Isolates with vancomycin MIC of 1μg/mL or 2μg/mL were screened for vancomycin heterogeneous resistance by Etest glycopeptide-resistance detection (GRD). Those with positive GRD screening results were then analyzed by modified population analysis profiling-area under the curve method for confirmation of vancomycin heteroresistance. Between 2012 and 2013, a total of 622 MRSA isolates from sterile sites with vancomycin MIC of 1μg/mL or more were studied. The prevalence rates of hVISA and VISA among these isolates were 10.0% and 2.7%, respectively. The hVISA prevalence increased significantly compared to that in 2003. Compared with vancomycin-susceptible S. aureus, hVISA and VISA isolates were less susceptible to ciprofloxacin, clindamycin, daptomycin, gentamicin, rifampin, and trimethoprim/sulfamethoxazole, and are thus, more likely to have SCCmec II or III element. A twofold increase in either vancomycin or teicoplanin MIC doubled the probability of being hVISA. Growing hVISA prevalence was highly suspected. Longitudinal surveillance of this phenomenon and monitoring of its clinical impact are necessary.

MRSAspat1081, a Highly Transmissible Strain Endemic to Hong Kong, China, in the Netherlands

MRSA<i>spa</i>t1081, a Highly Transmissible Strain Endemic to Hong Kong, China, in the Netherlands

Dissemination of the same cfr-carrying plasmid among methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococcal isolates in China.

Six cfr-harboring methicillin-resistant Staphylococcus aureus (MRSA) isolates, which belonged to the same clone of sequence type 5 (ST5)-staphylococcal cassette chromosome mec element II (SCCmec II)-spa t311, were investigated in this study. Complete sequencing of a cfr-carrying plasmid, pLRSA417, revealed an 8,487-bp fragment containing a Tn4001-like transposon, cfr, orf1, and ISEnfa4. This segment, first identified in an animal plasmid, pSS-01, was observed in several plasmids from clinical coagulase-negative staphylococci in China, suggesting that the cfr gene, which might originate from livestock, was located in the same mobile element and disseminated among different clinical staphylococcal species.

Agr dysfunction affects staphylococcal cassette chromosome mec type-dependent clinical outcomes in methicillin-resistant Staphylococcus aureus bacteremia.

Staphylococcal cassette chromosome mec element (SCCmec) type-dependent clinical outcomes may vary due to geographical variation in the presence of virulence determinants. We compared the microbiological factors and mortality attributed to methicillin-resistant Staphylococcus aureus (MRSA) bacteremia between SCCmec types II/III and type IV. All episodes of MRSA bacteremia in a tertiary-care hospital (South Korea) over a 4.5-year period were reviewed. We studied the microbiological factors associated with all blood MRSA isolates, including spa type, agr type, agr dysfunction, and the genes for Panton-Valentine leukocidin (PVL) and phenol-soluble modulin (PSM)-mec, in addition to SCCmec type. Of 195 cases, 137 involved SCCmec types II/III, and 58 involved type IV. The mortality attributed to MRSA bacteremia was less frequent among the SCCmec type IV (5/58) than that among types II/III (39/137, P = 0.002). This difference remained significant when adjusted for clinical factors (adjusted odds ratio [aOR], 0.14; 95% confidence interval [CI], 0.04 to 0.49; P = 0.002). Of the microbiological factors tested, agr dysfunction was the only significant factor that showed different positivity between the SCCmec types, and it was independently associated with MRSA bacteremia-attributed mortality (aOR, 4.71; 95% CI, 1.72 to 12.92; P = 0.003). SCCmec type IV is associated with lower MRSA bacteremia-attributed mortality than are types II/III, which might be explained by the high rate of agr dysfunction in SCCmec types II/III in South Korea.

Genomic insights into the rapid emergence and evolution of MDR in Staphylococcus pseudintermedius.

MDR methicillin-resistant Staphylococcus pseudintermedius (MRSP) strains have emerged rapidly as major canine pathogens and present serious treatment issues and concerns to public health due to their, albeit low, zoonotic potential. A further understanding of the genetics of resistance arising from a broadly susceptible background of S. pseudintermedius is needed. We sequenced the genomes of 12 S. pseudintermedius isolates of varied STs and resistance phenotypes. Nine distinct clonal lineages had acquired either staphylococcal cassette chromosome (SCC) mec elements and/or Tn5405-like elements carrying up to five resistance genes [aphA3, sat, aadE, erm(B), dfrG] to generate MRSP, MDR methicillin-susceptible S. pseudintermedius and MDR MRSP populations. The most successful and clinically problematic MDR MRSP clones, ST68 SCCmecV(T) and ST71 SCCmecII-III, have further accumulated mutations in gyrA and grlA conferring resistance to fluoroquinolones. The carriage of additional mobile genetic elements (MGEs) was highly variable, suggesting that horizontal gene transfer is frequent in S. pseudintermedius populations. Importantly, the data suggest that MDR MRSP evolved rapidly by the acquisition of a very limited number of MGEs and mutations, and that the use of many classes of antimicrobials may co-select for the spread and emergence of MDR and XDR strains. Antimicrobial stewardship will need to be comprehensive, encompassing human medicine and veterinary disciplines to successfully preserve antimicrobial efficacy.

Descriptive epidemiology of nasal carriage of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus among patients admitted to two healthcare facilities in Algeria.

To evaluate nasal carriage rate and variables associated with Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) in patients admitted in two healthcare facilities. S. aureus was isolated from 159 (26%) of the enrolled patients. Methicillin-susceptible S. aureus was isolated from 150 (24.5%) patients, and MRSA was isolated from 9 (1.5%). Cancer and previous hospitalization were associated with a significantly higher frequency of nasal S. aureus carriage among the patients admitted to the general hospital and the nephrology department, respectively. MRSA isolates were heterogeneous with respect to their staphylococcal cassette chromosome mec element (SCCmec) type, sequence type (ST), and toxin genes (pvl and tst1) content. Four isolates were attributed with the ST80-MRSA-IV clone, which is known to be predominant in Algeria. This is the first assessment of S. aureus and MRSA nasal carriage and associated variables in Algeria. Our findings provide also a picture of the MRSA strains circulating in the community in this geographic area. They can be useful as a guide for implementing screening and control procedures against S. aureus/MRSA in the Algerian healthcare facilities.

Draft Genome Sequences of Vancomycin-Susceptible Staphylococcus aureus Related to Heterogeneous Vancomycin-Intermediate S.aureus.

We report the draft genome sequences of three vancomycin-susceptible methicillin-resistant Staphylococcus aureus strains. S. aureus strain MV8 is a sequence type 8 (ST-8) staphylococcal cassette chromosome mec element type IV (SCCmec IV) derivative, while the other two strains (S. aureus MM25 and MM61) are ST-5 SCCmec II strains. MM61 is also closely related to the heterogeneous vancomycin-intermediate S. aureus strain MM66.

Molecular epidemiology of nasal isolates of methicillin-resistant Staphylococcus aureus from Jordan.

Asymptomatic carriage of methicillin-resistant Staphylococcus aureus (MRSA) can predispose the host to a wide range of infections. To inform public health strategies, this study sought to determine the prevalence and the phenotypic and genotypic characteristics of MRSA from nasal swabs of health care workers (HCWs) and other healthy individuals in Jordan. Overall, 716 nasal swabs were collected from 297 HCWs, 141 adults and 278 children in the community. MRSA was recovered from 56 (7.8%) nasal swabs, which represented carriage rates of 10.1%, 4.3% and 7.2% among HCWs, adults and children, respectively. The MRSA isolates were resistant to oxacillin (100%), erythromycin (42.8%), tetracycline (37.5%), clindamycin (5.3%), fucidin (5.3%), and ciprofloxacin (3.5%). A total of 17 different spa types belonging to eight different clonal complexes (CCs) were identified. All isolates were mecA positive, and mecC-MRSA was not detected. Analysis of the staphylococcal cassette chromosome mec (SCCmec) elements revealed that the majority (54; 96.4%) of the samples harbored the smaller type IV and V elements (the most common were SCCmec IVa or IVc, and there were two each of the IVg and V elements), and two were nontypable. The genes for Panton-Valentine leukocidin (luk-PV) were detected in 5.4% of the study isolates. A tst-positive, CC22-MRSA-SCCmecIVa clone (spa type t223) was identified as the dominant MRSA lineage among the nasal carriage isolates from both HCWs and other individuals (adults and children) in the community. These findings provide important information for public health personnel for the formulation of effective infection prevention and control strategies. Studies to further our understanding of the distribution, pathogenicity, transmissibility and fitness of this lineage would be prudent.

Evaluation of vancomycin population susceptibility analysis profile as a predictor of outcomes for patients with infective endocarditis due to methicillin-resistant Staphylococcus aureus.

Infective endocarditis due to methicillin-resistant Staphylococcus aureus (MRSA IE) is associated with high morbidity and mortality. Vancomycin continues to be the primary treatment for this disease. The emergence of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA), defined as a modified population analysis profile (PAP) of ≥ 0.9, may affect patient outcomes. The objective of this study was to evaluate the relationship of vancomycin subpopulation susceptibility and the clinical outcomes of MRSA IE. We conducted a retrospective cohort study of patients treated with vancomycin for MRSA IE from 2002 to 2013 at the Detroit Medical Center. A modified PAP was used to measure the vancomycin PAP MIC and the PAP-to-area under the curve (AUC) ratio. Treatment failure was defined as bacteremia for ≥ 7 days or death attributed to MRSA. Classification and regression tree (CART) analysis was used to select a failure breakpoint between the PAP-AUC ratios and the PAP MIC. A total of 202 patients were included in the study. Twenty-seven percent of the patients had left-sided IE, 19% of the strains were hVISA, and 70% of the strains were staphylococcal cassette chromosome mec element (SCCmec) type IV. Overall treatment failure was observed in 64%; 59% had persistent bacteremia, and the 30-day attributable mortality rate was 21%. The CART breakpoint between failure and success in terms of the PAP-AUC ratio was 0.9035. On logistic regression analysis, intensive care unit (ICU) admission (adjusted odds ratio [aOR], 2.8; 95% confidence interval [CI], 1.5 to 5.2) and a PAP MIC of ≥ 4 mg/liter (aOR, 3.2; 95% CI, 1.3 to 8.4) were associated with failure (P = 0.001 and 0.015, respectively). A PAP MIC of ≥ 4 mg/liter and ICU admission were significant for treatment failure for patients with MRSA IE. The PAP-AUC ratio of ≥ 0.9035 predicted failure consistent with the hVISA definition. The role of population MIC analysis in predicting outcome with MRSA infections warrants further investigation.

Characteristics of hospital- and community-acquired meticillin-resistant Staphylococcus aureus in Tehran, Iran

Staphylococcus aureus is a leading cause of hospital-acquired (HA) and community-acquired (CA) infections worldwide. Recently, S. aureus strains resistant to meticillin (MRSA) have become established within both communities. We isolated 314 isolates of MRSA from hospitalized patients in a referral hospital (HA isolates) and 268 isolates from its outpatient clinic (CA isolates) in Tehran, Iran, between February 2008 and December 2010. These isolates were tested for their susceptibility to 17 antibiotics and typed using the PhPlate system. The diversity in the structures of staphylococcal cassette chromosome mec (SCCmec) elements and ccr types was also detected using a multiplex-PCR assay and isolates were examined for the presence of different classes of prophages. Whilst all isolates were resistant to penicillin, the HA isolates were significantly more resistant to all other antibiotics tested than the CA isolates. Isolates carrying only SCCmec type III and ccr type 3 were dominant (91 %), but 20 % of the CA isolates belonging to less prevalent types carried only SCCmec types IVa, c and ccr type 2. These isolates also carried pvl genes and contained SGA prophage type. Our results indicate that whilst the dominant clonal groups of HA- and CA-MRSA belong to SCCmec type III and carry ccr type 3 genes, several distinct but less prevalent types of CA-MRSA carrying SCCmec type IVa, c and type 2 ccr are also found in Tehran. These strains carry pvl genes and the SGA prophage type, a characteristic that might be used as a marker for detection of CA-MRSA in this country.

Molecular epidemiological characteristics and clonal genetic diversity of Staphylococcus aureus with different origins in China.

To understand the intrinsic links and epidemic features of Staphylococcus aureus, isolates of this bacterium were collected from different origins in China. A total of 503 isolates from different sources were tested for the presence of methicillin-resistant Staphylococcus aureus (MRSA) and types of staphylococcal cassette chromosome mec (SCCmec) elements. Of these isolates, 250 were analyzed by multilocus sequence typing (MLST). Results showed that MRSA isolates account for 21.67% and have five types. SCCmec type I, II, and III isolates were all from humans, while SCCmec type IV, V, and untypeable MRSA isolates were from clinical origin, pigs, raw milk, or environments. The results by MLST showed considerable molecular heterogeneity in 52 different sequence types (STs) including 16 novel STs, which yielded 7 clonal complexes (CCs) and 5 doublets (Ds). The results from these analyses showed that hospital-acquired MRSA (HA-MRSA), rather than community-associated MRSA (CA-MRSA), remained the major pathogenic bacterium in the clinical setting. CA-MRSA infections have been increasing and forming new pandemic clones. CC630, CC239, D9, and D398 were important clones in this study. CC630 was a new epidemic CA clone circulating among humans, environments, and animals. CC239 was a HA-MRSA-III pandemic clone of clinical origin. The D9 clone was a livestock-associated (LA) clone, which up to now, has spread only in livestock and has not been found in humans that live in Jiangsu province. In Europe and America, there are many reports of the ST398-LA-clone in pigs and in humans who are in contact with pigs. However, various studies in China, including this one, indicate that the ST398 clone could be a CA clone rather than an LA clone. This clone also has been infecting humans for about 2 decades.

Diversity of antibiotic resistance genes and staphylococcal cassette chromosome mec elements in faecal isolates of coagulase-negative staphylococci from Nigeria.

BackgroundCoagulase-negative staphylococci (CoNS) are opportunistic pathogens found as colonisers of the human gut. This study was carried out to examine the genetic resistance mechanisms in faecal isolates of CoNS. The study investigated 53 non-duplicate CoNS isolates obtained from the fresh stool samples of apparently healthy subjects in the community of Ile-Ife, South-Western Nigeria. Antibiotic susceptibility testing was assessed by the disc diffusion test while antibiotic resistance genes were analysed by PCR. mecA positive isolates were analysed by Staphylococcal Chromosome Cassette mec (SCCmec) and cassette chromosome recombinase (ccr) complex typing methods.ResultsResistance genes were detected only in isolates that showed resistance by phenotypic screening. The aac(6′)–aph(2″) gene was detected in all the three isolates resistant to gentamicin. Four of the five erythromycin resistant isolates were positive for the ermC gene, the remaining isolate carried the msrA gene. The tetK gene was detected in 6 of the 7 tetracycline resistant isolates while 4 possessed the tetM gene. Three of the isolates (S. haemolyticus, S. xylosus and S. capitis) had both genes. Several SCCmec types were found: SCCmec I- ccrABβ2-α2 (4 isolates: 3 S. epidermidis, 1 S. warneri), SCCmecIVb- ccrABβ2-α3 (1 isolate: S. epidermidis), SCCmecIVd- ccrABβ2-α3 (8 isolates: 3 S. epidermidis, 2 S. xylosus, 1 S. saprophyticus, 1 S. warneri, 1 S. capitis), and untypable (2 isolates: S. epidermidis).ConclusionThis genetic background could be a reservoir for interspecies gene transfer among CoNS and S. aureus in the intestinal tract.

Draft Genome Sequence of Methicillin-Resistant Staphylococcus aureus KT/Y21, a Sequence Type 772 (ST772) Strain Isolated from a Pediatric Blood Sample in Terengganu, Malaysia.

Here, we report the draft genome sequence of a methicillin-resistant Staphylococcus aureus (MRSA) strain, KT/Y21, isolated from a blood sample of a pediatric patient. This strain belongs to sequence type 772 (ST772), harbors the staphylococcal cassette chromosome mec element (SCCmec) type V, and is positive for the Panton-Valentine leukocidin (PVL) pathogenic determinant.

Ceftaroline-Heteroresistant Staphylococcus aureus

Heteroresistance refers to the presence, within a large population of antimicrobial-susceptible microorganisms, of subpopulations with lesser susceptibilities. Ceftaroline is a novel cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA). The aim of this study was to detect the prevalence of ceftaroline heteroresistance in vitro in a select group of S. aureus strains. There were 57 isolates selected for evaluation, 20 MRSA, 20 vancomycin-intermediate S. aureus (VISA), 7 daptomycin-nonsusceptible S. aureus (DNSSA), 6 linezolid-nonsusceptible S. aureus (LNSSA), and 4 heteroresistant VISA (hVISA) isolates. MICs and minimal bactericidal concentrations were determined using the broth microdilution method according to CLSI guidelines. All of the isolates were analyzed by pulsed-field gel electrophoresis. The staphylococcal cassette chromosome mec element (SCCmec) types were determined by a multiplex PCR. Population analysis profiles (PAPs) were performed to determine heteroresistance for all of the isolates using plates made by adding various amounts of ceftaroline to brain heart infusion agar. The frequencies of resistant subpopulations were 1 in 10(4) to 10(5) organisms. We determined that 12 of the 57 (21%) isolates tested were ceftaroline-heteroresistant S. aureus (CHSA). CHSA occurred among strains with reduced susceptibilities to vancomycin, daptomycin, and linezolid but occurred in none of the USA-300 isolates tested. Evaluation of the heteroresistant strains demonstrated that the phenotype was unstable. Further studies are needed to determine whether CHSA has a role in clinical failures and to determine the implications of our study findings.

MRSA clones identified in outpatient dermatology clinics

To know the characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains disseminating through the Japanese community, we have determined types of Staphylococcal cassette chromosome mec (SCCmec) elements, Multi-Locus Sequence Typing (MLST), and carriages of four exotoxin genes (toxic-shock syndrome toxin, Panton-Valentine Leukocidine, and exfoliative toxins a and b) using 54 MRSA strains isolated from outpatients attending dermatology clinics at the four university hospitals of Juntendo University. Ten clonal complexes and 12 SCCmec types have been identified. As a result, more than 15 MRSA clones that were defined by the combination of genotype and SCCmec type, were identified. Among them, Clonal Complex (CC) 5-type IIa SCCmec strains were the most major (16 strains). In contrast to the fact that CC5- type IIa SCCmec strains known as a hospital-associated MRSA clone in Japan carried toxic-shock syndrome toxin gene (tst), only 2 of 16 strains have been shown to carry tst. Thirty-eight (70.4%) of isolates belonged to the clones distinct from the CC5-type IIa SCCmec strains. Among them, CC8 strains were major (12 strains), which contained 9 tst-positive CC8-type IVl SCCmec clones and a CC8-type IVa SCCmec strain carrying the Panton Valentine Leukocidin gene (lukS, F-PV). Clones related to impetigo were also identified: 7 exfoliative toxin b (etb) -positive clones, CC89-type IIa SCCmec and CC89-type V SCCmec strains; and 2 exfoliative toxin a (eta) -positive CC121-type V SCCmec strains. Other clones were as follows: CC1-type IVa SCCmec, CC8-type I SCCmec, CC81-type IVg SCCmec, CC97-type IVc SCCmec, CC91-type IVa SCCmec, CC59-type IVg SCCmec, CC45-type IIn SCCmec, CC89-SCCmec nontypeable, and CC8-type IVm, novel subtype of type IV SCCmec were identified in this study. Our data showed that many novel MRSA clones have emerged in the community.

Combination of Alpha-Melanocyte Stimulating Hormone with Conventional Antibiotics against Methicillin Resistant Staphylococcus aureus

Our previous studies revealed that alpha-melanocyte stimulating hormone (α-MSH) is strongly active against Staphylococcus aureus (S. aureus) including methicillin resistant S. aureus (MRSA). Killing due to α-MSH occurred by perturbation of the bacterial membrane. In the present study, we investigated the in vitro synergistic potential of α-MSH with five selected conventional antibiotics viz., oxacillin (OX), ciprofloxacin (CF), tetracycline (TC), gentamicin (GM) and rifampicin (RF) against a clinical MRSA strain which carried a type III staphylococcal cassette chromosome mec (SCCmec) element and belonged to the sequence type (ST) 239. The strain was found to be highly resistant to OX (minimum inhibitory concentration (MIC) = 1024 µg/ml) as well as to other selected antimicrobial agents including α-MSH. The possibility of the existence of intracellular target sites of α-MSH was evaluated by examining the DNA, RNA and protein synthesis pathways. We observed a synergistic potential of α-MSH with GM, CF and TC. Remarkably, the supplementation of α-MSH with GM, CF and TC resulted in ≥64-, 8- and 4-fold reductions in their minimum bactericidal concentrations (MBCs), respectively. Apart from membrane perturbation, in this study we found that α-MSH inhibited ∼53% and ∼47% DNA and protein synthesis, respectively, but not RNA synthesis. Thus, the mechanistic analogy between α-MSH and CF or GM or TC appears to be the reason for the observed synergy between them. In contrast, α-MSH did not act synergistically with RF which may be due to its inability to inhibit RNA synthesis (<10%). Nevertheless, the combination of α-MSH with RF and OX showed an enhanced killing by ∼45% and ∼70%, respectively, perhaps due to the membrane disrupting properties of α-MSH. The synergistic activity of α-MSH with antibiotics is encouraging, and promises to restore the lost potency of discarded antibiotics.