MSSA Isolates Research Articles

Investigating the potential use of an Antarctic variant of Janthinobacterium lividum for tackling antimicrobial resistance in a One Health approach

The aim of this paper is to describe a new variant of Janthinobacterium lividum - ROICE173, isolated from Antarctic snow, and to investigate the antimicrobial effect of the crude bacterial extract against 200 multi-drug resistant (MDR) bacteria of both clinical and environmental origin, displaying various antibiotic resistance patterns. ROICE173 is extremotolerant, grows at high pH (5.5–9.5), in high salinity (3%) and in the presence of different xenobiotic compounds and various antibiotics. The best violacein yield (4.59 ± 0.78 mg·g−1 wet biomass) was obtained at 22 °C, on R2 broth supplemented with 1% glycerol. When the crude extract was tested for antimicrobial activity, a clear bactericidal effect was observed on 79 strains (40%), a bacteriostatic effect on 25 strains (12%) and no effect in the case of 96 strains (48%). A very good inhibitory effect was noticed against numerous MRSA, MSSA, Enterococci, and Enterobacteriaceae isolates. For several environmental E. coli strains, the bactericidal effect was encountered at a violacein concentration below of what was previously reported. A different effect (bacteriostatic vs. bactericidal) was observed in the case of Enterobacteriaceae isolated from raw vs. treated wastewater, suggesting that the wastewater treatment process may influence the susceptibility of MDR bacteria to violacein containing bacterial extracts.

Synthesis and antibacterial activity evaluation of novel biaryloxazolidinone analogues containing a hydrazone moiety as promising antibacterial agents

A series of linezolid analogues containing a hydrazone moiety were designed, synthesized and evaluated for their antibacterial activity. Most compounds exhibited more potent antibacterial activity against S.aureus, MRSA, MSSA, LREF and VRE pathogens as compared with linezolid and radezolid. Compounds 9a, 9c, 9f, 9g, 10m and 10t were more potent against tested clinical isolates of MRSA, MSSA, VRE and LREF as compared to linezolid. Compound 9a exhibited comparable activity with linezolid against human MAO-A for safety evaluation and showed moderate metabolism in human liver microsome. The most promising compound 9a showed remarkable antibacterial activity against S.aureus, MRSA, MSSA, LREF and VRE pathogens with MIC value of 0.0675 mg/mL, respectively, which was 15- to 30-fold more potent than linezolid.

Investigation of coa Gene Polymorphism in Clinical Isolates of Staphylococcus aureus in North of Iran

Staphylococcus aureus is a common pathogen potentially able to cause a wide range of infectious diseases in human and animals and coagulase enzyme is one of the important virulence factors of this bacterium. Polymorphism of the coagulase encoding gene (coa) is one of the molecular-based typing methods of S. aureus isolates. In this study, the polymorphism of the coagulase gene among MRSA and MSSA isolates were investigated using PCR-RFLP analysis. To perform coagulase gene typing, the repeated units encoding hypervariable regions of coagulase gene of 30 clinical isolates of S. aureus were amplified by the PCR technique; this was followed by AluI restriction enzyme digestion and analysis of restriction fragment length polymorphism (RFLP) patterns. In total two amplicons (680 bp and 750 bp) and four distinct RFLP banding patterns (280+400, 340+340, 280+470, and no digested amplicon of 750 bp) were observed. Genotype with PCR-RFLP patterns of 280+400 bp was predominated. The results indicated polymorphism in the investigated regions of coagulase gene. This polymorphism can be used for identification of S. aureus isolates and showing the epidemiological relationship among them.

Genomic epidemiology of meticillin-resistant Staphylococcus aureus ST22 widespread in communities of the Gaza Strip, 2009.

BackgroundRemarkably high carriage prevalence of a community-associated meticillin-resistant Staphylococcus aureus (MRSA) strain of sequence type (ST) 22 in the Gaza strip was reported in 2012. This strain is linked to the pandemic hospital-associated EMRSA-15. The origin and evolutionary history of ST22 in Gaza communities and the genomic elements contributing to its widespread predominance are unknown. Methods: We generated high-quality draft genomes of 61 ST22 isolates from Gaza communities and, along with 175 ST22 genomes from global sources, reconstructed the ST22 phylogeny and examined genotypes unique to the Gaza isolates. Results: The Gaza isolates do not exhibit a close relationship with hospital-associated ST22 isolates, but rather with a basal population from which EMRSA-15 emerged. There were two separate resistance acquisitions by the same MSSA lineage, followed by diversification of other genetic determinants. Nearly all isolates in the two distinct clades, one characterised by staphylococcal cassette chromosome mec (SCCmec) IVa and the other by SCCmec V and MSSA isolates, contain the toxic shock syndrome toxin-1 gene. Discussion: The genomic diversity of Gaza ST22 isolates is not consistent with recent emergence in the region. The results indicate that two divergent Gaza clones evolved separately from susceptible isolates. Researchers should not assume that isolates identified as ST22 in the community are examples of EMRSA-15 that have escaped their healthcare roots. Future surveillance of MRSA is essential to the understanding of ST22 evolutionary dynamics and to aid efforts to slow the further spread of this lineage.

GW779439X and Its Pyrazolopyridazine Derivatives Inhibit the Serine/Threonine Kinase Stk1 and Act As Antibiotic Adjuvants against β-Lactam-Resistant Staphylococcus aureus.

As antibiotic resistance rises, there is a need for strategies such as antibiotic adjuvants to conserve already-established antibiotics. A family of bacterial kinases known as the penicillin-binding-protein and serine/threonine kinase-associated (PASTA) kinases has attracted attention as targets for antibiotic adjuvants for β-lactams. Here, we report that the pyrazolopyridazine GW779439X sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to various β-lactams through inhibition of the PASTA kinase Stk1. GW779439X potentiates β-lactam activity against multiple MRSA and MSSA isolates, including the sensitization of a ceftaroline-resistant isolate to ceftaroline. In silico modeling was used to guide the synthesis of GW779439X derivatives. The presence and orientation of GW779439X's methylpiperazine moiety was crucial for robust biochemical and microbiologic activity. Taken together, our data provide a proof of concept for developing the pyrazolopyridazines as selective Stk1 inhibitors which act across S. aureus isolates.

Determination of antimicrobial resistance pattern and molecular characteristics of methicillin-resistant Staphylococcus aureus strains isolated from patients in a teaching hospital of Isfahan, Iran

BackgroundS. aureus seems to play a significant role in the pathogenesis of infection in hospitals setting. This study aimed to the investigation of the prevalence of S. aureus isolates and the determination of antibiotic susceptibility pattern and the different types of SCCmec in MRSA isolates obtained from a clinical sample in Isfahan, Iran. MethodsThis study was performed during January 2013 to March 2014 at tertiary care hospitals. S. aureus isolates were collected from the clinical samples. Determination of antibiotic susceptibility pattern was done by the disc diffusion method. Also, SCCmec typing was performed by PCR method. ResultsA total of 150 S. aureus isolates were collected from the different clinical sample. Among them, 41.3% (62/150) isolates were MRSA. The most sensitivity for MRSA isolates was to vancomycin with 90% sensitivity and the high rate of resistance was toward tetracycline in MRSA and MSSA isolates. All of MRSA isolates were MDR. The rate of SCCmec types IV, III, I and II among MRSA isolates were 44.4%, 40.7%, 11.1% and 3.7, respectively. ConclusionsThe results of the current study showed that S. aureus especially MRSA isolates with a high rate of resistance still remains an important healthcare problem. Majority of the isolates were community-acquired and belonged to Sccmec type.

Prevalence and Characterization of Staphylococcus aureus Isolated From Retail Vegetables in China.

Staphylococcus aureus is a pathogen associated with serious community and hospital-acquired diseases. The aim of this study was to investigate the prevalence of S. aureus from retail vegetables in China and then characterized S. aureus isolates by antibiotic resistance, staphylococcal enterotoxin genes, spa-typing and multi-locus sequence typing. Of 419 retail vegetable samples from 39 cities in China during 2011–2016, 24 (5.73%) samples were positive for S. aureus and the geometric mean was 3.85 MPN/g. The prevalence of S. aureus was highest in lettuce (13/84, 15.48%) followed by tomato (7/110, 6.36%), caraway (2/87, 2.30%), and cucumber (2/128, 1.56%), whereas other vegetables were free of S. aureus. A total of 30 isolates were analyzed. For antibiotics susceptibility test, most isolates (93.3%) were resistant to ampicillin and penicillin, whereas all isolates were susceptible to linezolid, trimethoprim/sulphamethoxazole 1:19, nitrofurantoin, rifampicin, and teicoplanin. All isolates (30/30, 100%) were resistant or intermediate resistant to more than three tested antibiotics, including 9 isolates (30%) were resisted more than 10 antibiotics. Five isolates were resistant to cefoxitin and carried mecA genes which confirmed as MRSA. Of the 18 investigated SE genes, the sem gene was the most frequently detected (86.7%) followed by the sec (83.3%), sep (70.0%), seg (56.7%), sel (53.3%), seh (50.0%), seq (50.0%), sej (46.7%), seb (36.7%), sen (36.7%), and ser (33.3%) genes were harbored by more than one third of the isolates, whereas the seo and seu were detected in only 6.75% of the isolates. MLST and spa typing observed high genetic diversity in S. aureus isolated from retail vegetable in China. ST59-t437 was the predominant types (3/5, 60%) of MRSA isolates, whereas ST188-t189 was the predominant types (7/25, 28%) of MSSA isolates. Our study reflects that the retail vegetable in China could be contaminated with S. aureus but the levels of S. aureus were not very excessive. In addition, these isolates had virulence potential, most of them were enterotoxigenic and multiple antimicrobial resistance, should be draw public attention. These data have signification implications for epidemiological and public health studies of this pathogen.

Genotyping of Staphylococcus aureus associated with nasal colonization among healthcare workers using DNA microarray.

Healthcare workers (HCWs) colonized with Staphylococcus aureus may serve as a reservoir of infection. This study was carried to determine the genetic make-up of S. aureus nasal colonizers in HCWs. Nasal swabs were obtained from 93 HCWs and molecular characterization of identified S. aureus isolates was carried out using the StaphyType DNA microarray (Alere Technologies GmbH, Jena, Germany). Twenty-nine HCWs (31%) were colonized with S. aureus (MSSA = 23; MRSA = 6). Thus the overall MRSA carriage rate was 6.5% (n/N = 6/93) and 20.7% (n/N = 6/29) of those colonized with S. aureus harboured MRSA. The S. aureus isolates belonged to 16 clonal complexes (CC). MSSA isolates included three each for CC15, CC188, ST2867; two each for CC5, CC97, CC367 as well as one each for CC1, CC8, CC30, CC45, CC101, CC121, ST291/813 and CC1153. The staphylococcal cassette chromosome recombinase genes ccrA-1; ccrB-1 and the fusidic acid resistance gene (fusC) were present in two MSSA isolates (CC1 and CC8). The six MRSA isolates included CC5-MRSA-[VI+fusC] (n = 2); one each of CC5-MRSA-V; CC22-MRSA-IV (tst1+); CC80-MRSA-IV [pvl+] ("European CA-MRSA Clone") and CC97-MRSA-[V+fusC]. There is wide clonal diversity of S. aureus colonizers with associated high MRSA carriage among the HCWs. The presence of genetically stable MSSA isolates with the capability to transform into MRSA isolates is of concern.

Association of Vancomycin MIC and Molecular Characteristics with Clinical Outcomes in Methicillin-Susceptible Staphylococcus aureus Acute Hematogenous Osteoarticular Infections in Children.

Strains of methicillin-resistant Staphylococcus aureus (MRSA), particularly those belonging to the USA300 pulsotype, have been well described to cause severe osteoarticular infections (OAIs). A vancomycin MIC of ≥1.5 μg/ml has been demonstrated to contribute to disease severity in adults with MRSA and even methicillin-susceptible S. aureus (MSSA) bacteremia. Little data exist describing the outcomes of MSSA OAIs in terms of molecular characteristics and vancomycin MIC. All patients/isolates were chosen from a surveillance study at Texas Children's Hospital (TCH). S. aureus OAI isolates were identified from 2011 to 2016 and subjected to vancomycin Etests, pulsed-field gel electrophoresis (PFGE), and PCR to determine Panton-Valentine leucocidin (PVL) production and agr group. Two hundred fifty-two cases of S. aureus OAI were identified; 183 cases were MSSA (72.6%). During the study period, a decrease in the proportion of cases secondary to MRSA was observed, declining from 37.8% to 15.9% (P = 0.02). Of the MSSA isolates, 26.2% and 23.5% were USA300 and PVL positive, respectively. An increase in the proportion of MSSA isolates with a vancomycin MIC of ≥1.5 μg/ml occurred in the study period (P = 0.004). In MSSA, an elevated vancomycin MIC was associated with multiple surgical procedures and venous thromboses, even when adjusting for empirical β-lactam use. An increase in vancomycin MIC was noted among isolates belonging to agr group 4 during the study period. Methicillin resistance is declining among S. aureus OAI isolates at TCH. Simultaneously, vancomycin Etest MICs are increasing among MSSA isolates. Vancomycin MICs of ≥2 μg/ml are associated with adverse clinical outcomes in MSSA irrespective of antibiotic choice, suggesting that this may be a surrogate for organism virulence.

Limitations of ceftriaxone compared with cefazolin against MSSA: an integrated pharmacodynamic analysis

Despite the convenience of once-daily dosing, the use of ceftriaxone for Staphylococcus aureus infections has significant limitations, including scarce clinical evidence and increasingly questionable pharmacodynamic activity. Our goal was to conduct an integrated pharmacokinetic-pharmacodynamic analysis of the appropriateness of ceftriaxone compared with cefazolin for treating serious MSSA infections. Ceftriaxone and cefazolin activity against five clinical MSSA isolates was characterized in an in vitro pharmacodynamic model. Monte Carlo simulations were then used to evaluate various dosing regimens of ceftriaxone and cefazolin based on relevant patient pharmacokinetic data, significant pharmacodynamic targets derived from the in vitro studies (55%ƒT>MIC for bacteriostasis, 75%ƒT>MIC for 1 log10 bacterial kill, 100%ƒT>MIC for ≥3 log10 bacterial kill) and MIC distributions for MSSA from national surveillance data. Ceftriaxone at 1 g once daily had poor activity against MSSA with net bacterial growth predicted in 76% of simulated subjects. The standard 2 g of ceftriaxone once daily had predicted bacterial growth or bacteriostasis in 54% of cases with bactericidal effects in only 17%. Cefazolin at 2 g once daily was notably similar to ceftriaxone in expected target attainments. Cefazolin at 2 g twice daily demonstrated maximal pharmacodynamic activity with bactericidal effects in 97% of simulated subjects. Given the limited activity of ceftriaxone against S. aureus, particularly for serious infections when bacterial kill is desired, the convenience of once-daily dosing should be weighed against the risks of using an overly broad, suboptimal therapy. Cefazolin warrants further consideration, particularly as optimal pharmacodynamics against MSSA may be achieved with twice-daily dosing in most patients.

Spa type distribution in MRSA and MSSA bacteremias and association of spa clonal complexes with the clinical characteristics of bacteremia

The genetic distribution of invasive methicillin-susceptible (MSSA) and resistant S. aureus (MRSA) strains has to be addressed in order to target infection control strategies. A large MRSA epidemic caused by a certain MRSA strain (spa type 067) broke out in 2001 in our health district. We wanted to investigate the current spa type distribution in MRSA and MSSA bacteremias and assess the potential association of spa clonal complexes (spaCC) with the clinical characteristics of S. aureus bacteremia. One hundred nine invasive MRSA isolates and 353 invasive MSSA isolates were spa typed and grouped into clonal complexes (spaCC). Spa type distribution was compared to that of colonizing MRSA strains. Spa type and spaCC data linked to clinical information on the course of bacteremic cases was used to search for differences in virulence between strains. Spa type distribution in MRSA is less heterogenic than in MSSA. t067 dominates both in MRSA colonisations and in invasive findings. Among MSSA, no such dominating strains were found. Of spaCCs, mortality was the highest in spaCC 067 (25.6%). SpaCC 008 was more often associated with endocarditis than other CCs (22.7 vs 5.8%, p= 0.013), spaCC 2133 with skin infections (68.4 vs 36.4%, p= 0.007), and spaCC 012 with foreign body infections (25.0 vs 9.3%, p= 0.029) than other clonal complexes. A single successful strain can explain the major proportion of MRSA among S. aureus bacteremias. Certain spaCCs showed association with certain clinical characteristics. These findings suggest that S. aureus strains differ in their virulence and invasiveness.

Molecular analysis of immune evasion cluster (IEC) genes and intercellular adhesion gene cluster (ICA) among methicillin-resistant and methicillin-sensitive isolates of Staphylococcus aureus.

SummaryIntroductionResistance to antibiotics and presence of virulence factors play an important role in increased mortality associated with infection due to Staphylococcus aureus. In this study, we determine antibiotic resistance pattern, presence of the icaADBC locus as well as biofilm formation and distribution and diversity the immune evasion cluster (IEC) genes in clinical isolate of S. aureus from Kerman, Iran.Materials and methodsDuring 15 months, 100 clinical isolates S. aureus recovered from different patients were admitted to Kerman University affiliated hospitals. Resistance to different antibiotic agents was determined by disk diffusion method. Phenotypic method was used to the determination of biofilm formation ability and methicillin-resistance S. aureus (MRSA). Polymerase chain reaction technique (PCR) was used to the detection of nuc, mecA, icaA, icaD, icaB, icaC, scn, sea, sak, sep and chp genes.ResultsForty-four isolates were considered as MRSA and all of isolates were sensitive to vancomycin and linezolid. Our results showed, 77.2% (34/44) of MRSA and 8.9 % (5/56) of MSSA isolates were multidrug resistant. The predominant IEC variant was type B and our results displayed that 77.7% of the MRSA isolates harbor loci icaD and mecA. There was no significant difference in production biofilm between MSSA and MRSA isolates (P ≥ 0.05). There was significant difference in presence IEC types between MSSA and MRSA isolates (P = 0.000).ConclusionsThe presence of icaADBC locus may not be a determining factor for biofilm formation in Staphtlocooci and other mechanisms might be involved in this process.The high prevalence IEC types in MSSA isolates can indicate that the presence of these genes can be an advantage for pathogenesis of these isolates in different infections.

Bacteria induce autophagy in a human ocular surface cell line

Autophagy protects cells from intracellular pathogens, but can be exploited by some infectious agents to their benefit. Currently it is not known if bacteria induce autohpagy in cells of the cornea. The goal of this study was to develop an ocular surface autophagy reporter cell line and determine whether ocular bacterial pathogens influence host responses through autophagy induction. The cell line was made using lentivirus transduction of an LC3-GFP fusion protein in human corneal limbal epithelial (HCLE) cells. LC3-GFP puncta in HCLEs were induced by rapamycin and ammonium chloride treatments, and prevented by the autophagy inhibitors 3-methyladenine (3′MA) and bafilomycin. Importantly, secretomes from Escherichia coli, Serratia marcescens, Staphylococcus aureus, methicillin sensitive (MSSA) and resistant (MRSA), were found to induce autophagy, whereas other bacteria, including Acinetobacter baumannii, Achromobacter xylosoxidans, Enterococcus faecalis, Klebsiella pneumoniae, Moraxella sp., and Stenotrophomonas maltophilia, did not. Our data indicates differences between tested ocular isolates of MRSA and MSSA in the activation of autophagy. HCLEs treated with 3′MA were slightly more susceptible to cytotoxic factors produced by S. marcescens and MRSA keratitis isolates, by contrast, bafilomycin A1 treatment caused no difference. This work demonstrates the successful development and validation of an autophagy reporter corneal cell line and indicates differences between ocular bacterial isolates in the activation of autophagy.

Antibiograms, toxin profiling and molecular typing of Staphylococcus aureus isolates from two tertiary hospitals in Jordan.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital-associated infections. This study was undertaken to investigate toxin profiles as well as antibiotic resistance patterns of S. aureus isolates form two tertiary hospitals in Jordan. A total of 250 S. aureus isolates from clinical samples of two tertiary hospitals were analyzed for the presence of the mecA, vanA, vanB, and 16 Staphylococcus toxin encoding genes using PCR. The isolates were further tested for antimicrobial sensitivities using the disc diffusion method. DNA from all the isolates were fingerprinted by coa gene Restriction Fragment Length Polymorphism (RFLP) to study relationships between isolates from the two hospitals. 73.2% of the isolates contained the mecA gene and thus were designated MRSA. All MRSA isolates showed high levels of resistance to many of the antibiotics compared to those of MSSA. All MRSA isolates were susceptible to vancomycin and teicoplanin while all MSSA isolates were susceptible to nitrofurantoin, teicoplanin, vancomycin, cefoxitin, clindamycin, erythromycin and gentamycin. The isolates exhibited high prevalence of the toxin genes and none of the isolates contained less than 4 genes with one isolate contained 14 genes with no apparent differences in gene profiles among MRSA and MSSA. About 60% of the isolates contained 12 to 13 toxin genes and were isolated either from pus or blood. Antibiograms of the MRSA isolates were significantly different from MSSA antibiograms while there were no apparent differences in the toxin genes profiles. Further, coagulase gene RFLP of the isolates showed that the isolates are very heterogenic.

Outbreak of gentamicin-resistant, meticillin-susceptible Staphlococcus aureus on a neonatal unit

This report describes an outbreak of gentamicin-resistant, meticillin-resistant Staphylococcus aureus (GR MSSA) which occurred on a 21-bed neonatal unit (NNU) in Ninewells Hospital, Dundee, UK. An outbreak investigation was triggered by two new GR MSSA isolates from babies admitted directly to the NNU who had acquired this organism during their stay. Data on MSSA cases and antibiograms of patient isolates were flagged as an alert, and microbiology records were trawled to detect previous cases. Eight babies were affected by the outbreak strain over six months. Typing of all isolates by pulsed-field gel electrophoresis and spa typing showed that all were clonal complex 30, spa type t012. None of the outbreak strains were associated with bacteraemia, apart from one baby who was born at 24 weeks of gestation with a birth weight of 500g. Observation of practice and environmental swabbing of an incubator suggested that this was the most likely source of spread of the outbreak strain. Three of 11 surfaces sampled were positive for the outbreak strain. On inspection, it was found that the impeller was not removed routinely during cleaning, and debris was seen in the housing. Swabs that were taken from the impeller and housing yielded the outbreak strain. GR MSSA isolates from the NNU have been set up as an alert organism on the infection control system. No further cases were detected over one year of follow-up after full compliance with the new guidelines for cleaning and disinfection of incubators was implemented.

Antibiotic Resistance Patterns and Virulence Determinants of Different SCCmec and Pulsotypes of Staphylococcus Aureus Isolated from a Major Hospital in Ilam, Iran.

Aims & Objectives:The aim of this study is to evaluate genetic relatedness, antibiotic resistance pattern, and virulence characteristics of different types of S. aureus isolated from air, surfaces, staff, and patients in a Public hospital in Ilam.Methods & Materials:A total of 88 of 140 staphylococci identified as S. aureus by conventional and molecular methods were used in this study. Isolate samples were obtained from surfaces, staff, patients, and hospital indoor air. The sampling from staff and surfaces was done through using swab and air by standard pump. Antimicrobial susceptibility testing and presence different resistant and virulence determinants was assessed. Isolates were then typed by pulsed-field gel electrophoresis (PFGE) and SCCmec typing methods.Results:Out of 88isolates, 36 of them (40.9%) were MRSA. Among MRSA isolates, the range of resistance to antibiotic was 0% in vancomycin to 83.3% in gentamycin. The most prevalent resistant genes among gentamicin resistant S. aureus were acc (6')/aph (2”)Ia and aph(3”)IIIa. The most common erythromycin resistant gene was ermC. Surprisingly, SCCmec types I (30.5%), II (25%)were highly distributed. PFGE analysis showed 33 different pulsotypes.Conclusion:This study confirms that different isolates of MSSA and MRSA circulate in Ilam which differ in antimicrobial susceptibility, content of resistance, and virulence determinants.

Activity of Antistaphylococcal Lysin CF-301 against Contemporary Staphylococcus aureus Clinical Isolates from the USA and Europe

BackgroundCF-301 is a novel, recombinantly-produced bacteriophage-derived lysin (cell wall hydrolase) and is the first agent of this class in the US to enter into clinical development for the treatment of bacteremia including endocarditis due to S. aureus. Hallmark features of CF-301 include rapid and pathogen-specific bacteriolytic activity, synergy with antibiotics, biofilm-disrupting activity, a low propensity for resistance, and the capacity to suppress antibiotic resistance. This is the first report of an international surveillance study for CF-301.Methods349 methicillin-sensitive and –resistant S. aureus (MSSA and MRSA, respectively) isolates were collected from various infection sources at multiple hospitals from 2015–2017 throughout the US, Greece, Hungary and Italy. In addition to the contemporary isolates, a set of 149 MSSA and MRSA clinical isolates from 2011 were also obtained from US hospital sources. MICs for CF-301 were determined using a new antimicrobial susceptibility testing (AST) medium for broth microdilution recently endorsed by Clinical and Laboratory Standards Institute (CLSI) for use with CF-301. The testing medium consists of cation-adjusted Muller Hinton Broth supplemented with 25% horse serum and 0.5 mM DTT (CAMHB-HSD). Susceptibility to conventional antibiotics was also examined in this study using standard methodology (CLSI document M07-A10) and included: vancomycin, trimethoprim-sulfamethoxazole, daptomycin, oxacillin, linezolid, clindamycin, and cefazolin.ResultsCF-301 had MIC50, MIC90, and MIC100 values of 0.5, 1, and 2 μg/mL, respectively, against each set of contemporary MSSA (n = 176) and MRSA (n = 173) clinical isolates. There were no differences noted with respect to the geographic source (in the US and Europe) of isolates. Furthermore, the CF-301 MICs reported here for 2015–2017 isolates were identical to that observed for MSSA and MRSA isolates from 2011.ConclusionCF-301 demonstrated potent in vitro activity against a total of 498 clinical S. aureus isolates from a range of human infections (including bacteremia) and different geographies. Contemporary clinical isolates did not demonstrate reduced susceptibility to CF-301 compared with the 2011 isolates.Disclosures J. Oh, ContraFect Corp: Employee, Salary; R. Schuch, ContraFect Corp: Employee, Salary

The Association of Molecular Characteristics, Vancomycin MIC and Clinical Outcomes in Methicillin-susceptible Staphylococcus aureus Osteoarticular Infections in Children

BackgroundMethicillin-resistant Staphylococcus aureus, particularly those belonging to the USA300 pulsotype and bearing Panton–Valentine leucocidin (pvl), have been well described to cause severe osteoarticular infection (OAI). Vancomycin minimum inhibitory concentration (MIC) ≥ 1.5 µg/ml has been demonstrated to contribute to disease severity in MRSA bacteremia. Little data exist to describe the spectrum of outcomes in MSSA OAI in terms of molecular characteristics and vancomycin MIC.MethodsOAI isolates were identified from 2011 to 2016 and subjected to vancomycin E-tests. MSSA isolates underwent PFGE, PCR for pvl, and a stepwise assay to determine accessory gene regulator (agr) group. A review of the medical record was performed. Orthopedic complications included chronic osteomyelitis, pathologic fracture, and growth arrest.ResultsDuring the study period, 167 cases of S. aureus OAI were identified; 115 were MSSA (68.9%). 29.1 and 26.1% of MSSA isolates were USA300 and pvl positive, respectively. USA300 isolates were more likely to be pvl-positive (66.7 vs. 13.6%, P < 0.001) and agr I (80% vs. 57.5%, P = 0.001). The presence of pvl was associated with agr I (P = 0.03), larger abscesses (6 vs. 2cm, P = 0.04), ICU admission (16.7 vs. 3.5%, P = 0.03) and a longer length of stay (11 vs. 6 days, P = 0.05). agr III and IV were associated with a higher rate of orthopedic complications (36.4 vs. 13.9%, P = 0.03) and surgical procedures (90.1 vs. 64.5%, P = 0.02) than other agr groups. An increase in the proportion of MSSA isolates with a vancomycin MIC ≥ 1.5 µg/ml occurred in the study period (P = 0.007, Figure 1). In MSSA, vancomycin MIC ≥ 2 µg/ml was associated with agr III (p = 0.07) and higher rates of orthopedic complications (P = 0.08) and venous thrombosis (P = 0.06, Figure 2).ConclusionMSSA accounts for 70% of S. aureus isolates causing OAI at TCH. While pvl-positive strains are associated with worse short-term outcomes, agr III and IV are associated with long-term morbidity. Vancomycin E-test MICs appear to be increasing among MSSA; vancomycin MIC ≥ 2 µg/ml are associated with agr-III and adverse clinical outcomes suggesting that this may be a surrogate for disease severity. Further work is needed to understand the contribution of these factors to invasive MSSA disease.Disclosures J. McNeil, NIAID, NIH: Grant Investigator, Grant recipient. S. L. Kaplan, Pfizer: Grant Investigator and Speaker at PCV13 Launch Meeting in China, Research grant and Speaker honorarium

Genomic epidemiology of methicillin-susceptible Staphylococcus aureus across colonisation and skin and soft tissue infection

Staphylococcus aureus skin and soft tissue infection (Sa-SSTI) places a significant burden on healthcare systems. New Zealand has a high incidence of Sa-SSTI, and here most morbidity is caused by a polyclonal methicillin-susceptible (MSSA) bacterial population. However, MSSA also colonise asymptomatically the cornified epithelia of approximately 20% of the population, and their divide between commensalism and pathogenicity is poorly understood. We aimed to see whether MSSA are genetically differentiated across colonisation and SSTI; and given the close interactions between people and pets, whether strains isolated from pets differ from human strains. We compared the genomes of contemporaneous colonisation and clinical MSSA isolates obtained in New Zealand from humans and pets. Core and accessory genome comparisons revealed a homogeneous bacterial population across colonisation, disease, humans, and pets. The rate of MSSA colonisation in dogs was comparatively low (5.4%). In New Zealand, most Sa-SSTI morbidity is caused by a random sample of the colonising MSSA population, consistent with the opportunistic infection model rather than the paradigm distinguishing strains according to their pathogenicity. Thus, studies of the factors determining colonisation and immune-escape may be more beneficial than comparative virulence studies. Contact with house-hold pets may pose low zoonotic risk.

Characterization of Heterogeneous MRSA and MSSA with Reduced Susceptibility to Chlorhexidine in Kuwaiti Hospitals.

The objective of this investigation was to identify the lineages of MRSA and MSSA with reduced susceptibility to chlorhexidine in Kuwaiti hospitals. 121 clinical MRSA and 56 MSSA isolates were included in this study. Antimicrobial susceptibility testing was performed for a selection of agents including chlorhexidine and resistance genes were amplified and sequenced. PFGE, spa typing, and MLST were completed for a selection of isolates. The results showed SCCmec II, III, IV, and V were present in 0.8, 21.5, 69.4, and 8.3% of the MRSA isolates. agr-1Sa was the most prevalent type in both MSSA (48%) and MRSA (54%). Forty-five percentage of MRSA contained pvl and 39% contained lukE-lukD, however, as many as 86% of MSSA contained pvl and 96.4% contained lukE-lukD. qac A-C genes were identified in 12.3% of MRSA, norA was present in 82.6% and blaZ in 94.2%. Among MSSA only 5.4% harbored qacA, 83% contained norA, and 91% blaZ. Multi-drug resistant ST239/t945 lineage containing a qac gene was the most identified S. aureus. However, other lineages, including ST772-MRSA-V/t4867/pvl(+)qacC/smr and non-qac harboring lineages of ST217-MRSAIV/t3244/pvl(–), ST34-MSSA/t161/pvl(+), ST5-MSSA/t688/pvl(+), ST5-MSSA/t4867/norA(+), and ST672-MSSA/t003/pvl(–), also showed reduced susceptibility to chlorhexidine. The observed reduced susceptibility of non-qac dependent MSSA isolates to chlorhexidine suggests the involvement of other elements in promoting higher MBC (≥30 mg/L). Our results confirm that monitoring MSSA is essential as they may have the potential to survive low level biocide exposure.