Molecular characterization of resistance to Rifampicin in an emerging hospital-associated Methicillin-resistant Staphylococcus aureus clone ST228, Spain

Virulence determinants and antibiotic resistance in staphylococci isolated from the skin of captive bred reptiles

Knowledge of the composition and properties of skin microbiota in healthy reptiles is essential for preservation strategies and thus the prevention of skin dysbiosis leading to dermatological diseases. Despite the greatly increasing popularity of reptiles as pets, only a few studies have dealt with this topic. Therefore, the aim of this work was to analyse species composition of bacteria isolated from skin swabs of 40 reptiles (17 species) using MALDI-TOF spectrometry and to characterise the virulence properties of identified staphylococci (n = 51). The most common species were Staphylococcus xylosus and S. sciuri. Bacilli, enterococci, Escherichia coli, Salmonella sp. and Acinetobacter sp. were also common. The most frequent antimicrobial resistance in staphylococcal isolates was observed for ampicillin (100.0%) and cefoxitin (98.0%) with the blaZ gene being most prevalent (58.8%). In contrast, all staphylococci were susceptible to gentamicin, kanamycin and imipenem. Slime and biofilm production was observed in 86.3% and 76.5% of isolates, respectively. Gelatinase, DNase, protease and lipase activity was found more rarely (41.2%; 25.5%; 27.5% and 21.6%). Since reptiles are a reservoir of bacteria for their owners, common multi-drug resistance (84.3%, MAR index average 0.29 ± 0.09) and biofilm formation must be kept in mind, especially in the case of injury when handling reptiles.

Molecular Characteristics and Prevalence of Rifampin Resistance in Staphylococcus aureus Isolates from Patients with Bacteremia in South Korea

Rifampin resistance (RIF-R) in Staphylococcus aureus (S. aureus) with rpoB mutations as one of its resistance mechanisms has raised concern about clinical treatment and infection prevention strategies. Data on the prevalence and molecular epidemiology of RIF-R S. aureus blood isolates in South Korea are scarce. We used broth microdilution to investigate RIF-R prevalence and analyzed the rpoB gene mutation in 1615 S. aureus blood isolates (772 methicillin-susceptible and 843 methicillin-resistant S. aureus (MRSA)) from patients with bacteremia, between 2008 and 2017. RIF-R prevalence and antimicrobial susceptibility were determined. Multilocus sequence typing was used to characterize the isolate's molecular epidemiology; Staphylococcus protein A (spa), staphylococcal cassette chromosome mec (SCCmec), and rpoB gene mutations were detected by PCR. Among 52 RIF-R MRSA isolates out of 57 RIF-R S. aureus blood isolates (57/1615, 0.4%; 5 methicillin-susceptible and 52 MRSA), ST5 (44/52, 84.6%), SCCmec IIb (40/52, 76.9%), and spa t2460 (27/52, 51.9%) were predominant. rpoB gene mutations with amino acid substitutions showed that A477D (17/48, 35.4%) frequently conferred high-level RIF resistance (MIC > 128 mg/L), followed by H481Y (4/48, 8.3%). RIF-R S. aureus blood isolates in South Korea have unique molecular characteristics and are closely associated with rpoB gene mutations. RIF-R surveillance through S. aureus-blood isolate epidemiology could enable effective therapeutic management.

Clinical and microbiological characteristics of rifampicin-resistant MRSA bacteraemia

OBJECTIVES

The clinical significance of rifampicin resistance in Staphylococcus aureus infections has not been demonstrated. Here, we evaluated the clinical characteristics of rifampicin-resistant S. aureus infection.

METHODS

Data were collected from adult patients who were hospitalized with MRSA bacteraemia between March 2007 and May 2020 at a tertiary hospital in South Korea. The clinical characteristics and treatment outcomes of patients infected with rifampicin-resistant MRSA were compared with those of rifampicin-susceptible isolates. All-cause death and recurrence of MRSA infection were assessed for 90 days.

RESULTS

Of the 961 patients with MRSA bacteraemia, 61 (6.3%) were infected by rifampicin-resistant isolates. The type of infection focus and duration of bacteraemia did not significantly differ between the two groups. Rifampicin-resistant MRSA isolates were more likely to have multidrug resistance and a higher vancomycin MIC relative to the rifampicin-susceptible isolates. The 90-day recurrence rate was higher in the patients infected with rifampicin-resistant MRSA compared with those with rifampicin-susceptible MRSA (18.0% versus 6.2%, P < 0.001), whereas the 90-day mortality was comparable between the two groups (27.9% versus 29.2%, P = 0.94). After adjusting for potential confounding factors, rifampicin resistance was significantly associated with 90-day recurrence (subdistributional HR: 2.31; 95% CI: 1.05-5.10; P = 0.04).

CONCLUSIONS

Rifampicin-resistant MRSA isolates showed distinct microbiological features in terms of multidrug resistance and a high vancomycin MIC. Although the management of MRSA bacteraemia was not significantly different between the two groups, recurrence was significantly more common in the rifampicin-resistant group. Rifampicin resistance may play a significant role in infection recurrence.

Molecular Epidemiology, Antimicrobial Susceptibility, and Clinical Features of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections over 30 Years in Barcelona, Spain (1990-2019)

Methicillin-resistant Staphylococcus aureus bloodstream infections (MRSA-BSI) are a significant cause of mortality. We analysed the evolution of the molecular and clinical epidemiology of MRSA-BSI (n = 784) in adult patients (Barcelona, 1990−2019). Isolates were tested for antimicrobial susceptibility and genotyped (PFGE), and a selection was sequenced (WGS) to characterise the pangenome and mechanisms underlying antimicrobial resistance. Increases in patient age (60 to 71 years), comorbidities (Charlson’s index > 2, 10% to 94%), community-onset healthcare-associated acquisition (9% to 60%), and 30-day mortality (28% to 36%) were observed during the 1990−1995 and 2014−2019 periods. The proportion of catheter-related BSIs fell from 57% to 20%. Current MRSA-BSIs are caused by CC5-IV and an upward trend of CC8-IV and CC22-IV clones. CC5 and CC8 had the lowest core genome proportions. Antimicrobial resistance rates fell, and only ciprofloxacin, tobramycin, and erythromycin remained high (>50%) due to GyrA/GrlA changes, the presence of aminoglycoside-modifying enzymes (AAC(6′)-Ie-APH(2″)-Ia and ANT(4′)-Ia), and mph(C)/msr(A) or erm (C) genes. Two CC22-IV strains showed daptomycin resistance (MprF substitutions). MRSA-BSI has become healthcare-associated, affecting elderly patients with comorbidities and causing high mortality rates. Clonal replacement with CC5-IV and CC8-IV clones resulted in lower antimicrobial resistance rates. The increased frequency of the successful CC22-IV, associated with daptomycin resistance, should be monitored.

Rifamycin resistance, rpoB gene mutation, and clinical outcomes of Staphylococcus species isolated from prosthetic joint infections in Korea

PURPOSE

We conducted an in vitro investigation of rifamycin activity against planktonic and biofilm states of Staphylococcus aureus and S. epidermidis isolated from patients with prosthetic join infection (PJIs), characterized their rpoB mutations, and analyzed the clinical outcomes of rifampin-resistant isolates.

METHODS

A total of 110 staphylococcal isolates were collected from patients with PJIs. Antimicrobials tested using the broth microdilution method included rifampin, rifabutin, rifapentine, and rifaximin. We evaluated rpoB gene mutations to identify rifampin resistance mechanisms. Clinical outcomes were assessed in rifampin-resistant isolates.

RESULTS

Among the 110 staphylococcal isolates, we detected 85 S. aureus (methicillin-resistant, 55%) and 25 S. epidermidis (methicillin-resistant, 100%) isolates. Seven S. aureus isolates and two S. epidermidis isolates were rifampin resistant (minimum inhibitory concentration [MIC], ≥ 2 μg/mL); these exhibited rpoB gene mutations. Among 78 rifampin-susceptible S. aureus isolates and 23 S. epidermidis isolates, 76 S. aureus isolates and all S. epidermidis isolates were highly susceptible (MIC ≤ 0.06 μg/mL) to other rifamycins. The rifampin, rifabutin, rifapentine, and rifaximin minimum biofilm bactericidal concentrations for ≥ 50% of isolates were 4, 1, 2, and 4 μg/mL for S. aureus and 1, 0.125, 0.25, and 0.5 μg/mL for S. epidermidis, respectively, among rifampin-susceptible isolates. Among nine patients bearing rifampin-resistant isolates, only three (33%) had successful outcomes.

CONCLUSIONS

Rifamycins other than rifampin show promising staphylococcal activity, including antibiofilm activity. Rifamycin-resistant staphylococci exhibit rpoB gene mutations.

Molecular Characterization of Rifampicin-Resistant Staphylococcus aureus Isolates from Retail Foods in China

This study investigated the molecular characteristics of rifampin-resistant (RIF-R) Staphylococcus aureus isolates recovered from 4300 retail food samples covering most provincial capitals in China, from 2011 to 2016. Of the 1463 S. aureus enrolled, 149 isolates (142 MSSA and 7 MRSA) were identified as rifampicin-resistant, including 20 high-level (MICs ≥ 8 μg/mL) and 129 low-level (MICs between 2 and 4 μg/mL) rifampicin-resistant strains. Most of the RIF-R S. aureus isolates were resistant to more than three antibiotics. The mutations in the rifampicin resistance-determining region of the rpoB gene were studied in all RIF-R strains. All of the strains presented the mutational change 481 His/Asn and five isolates presented an additional mutation, including 477 Asp/Tyr, 527 Ile/Met, and 466 Leu/Ser, respectively. Thirteen STs and twenty-one spa types were represented, in which five MRSA showed non-type SCCmec and the remaining MRSA belonged to SCCmec type IV-where, ST1-t127 was the predominant type from all of the isolates, while ST398-t034 was the predominant type for the MRSA isolates. In this study, we found that the food-related RIF-R S. aureus may have a unique genetic background selection. However, the scenario regarding the presence of RIF-R S. aureus, especially MRSA, in retail food in China is not favorable and warrants public attention.

Molecular Characteristics of Rifampin-Sensitive and -Resistant Isolates and Characteristics of rpoB Gene Mutations in Methicillin-Resistant Staphylococcus aureus

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) infections have become a leading cause of severe infections in both healthcare and community settings. Mutations in the rpoB gene cause resistance to rifampin (RIF^R), a critical antibiotic for the treatment of multidrug-resistant Staphylococcus aureus. The aim of this study was to detect the molecular characteristics of RIF^R MRSA and analyze the rpoB gene mutations involved in RIF resistance.

Methods

A total of 49 RIF^R MRSA and 38 RIF^S MRSA isolates collected from seven cities in China were analyzed by multilocus sequence typing, staphylococcus chromosomal cassette mec (SCCmec) typing, spa typing, and rpoB gene mutations.

Results

ST239-III-t030 (35/49, 71.4%), the major clone in RIF^R MRSA isolates; ST45-IV-t116 (16/38, 42.1%), the major clone in RIF^S MRSA isolates with rpoB mutations. RIF^R MRSA isolates were resistant to erythromycin, ciprofloxacin, tetracycline, gentamicin, and clindamycin. By contrast, RIF^S MRSA isolates with rpoB mutation were more susceptible to ciprofloxacin, tetracycline, and gentamicin. Forty-three (87.8%) isolates present the mutational change H481N and L466S, conferring 128–512 μg/mL RIF resistance. The four isolates with RIF MIC ≥ 1024 μg/mL had additional amino acid substitution: H481N, L466S, A473T (n=2); H481Y (n=2), associated with a high-level RIF resistance. Of 38 RIF^S MRSA isolates, two mutations were observed, including H481N (n=37) and A477D (n=1).

Conclusion

In conclusion, the predominant RIF^R MRSA clones in China were ST239-III-t030. Molecular characteristics, antibiotic-resistant profiles, and rpoB mutations between RIF^R MRSA and RIF^S MRSA were diverse. Antibiotics for treating patients with MRSA infections can be selected based on molecular characteristics.

Genetic profile mutation rpoB in clinical isolate of rifampicin-resistant Staphylococcus aureus

OBJECTIVES

Staphylococcus aureus is one of the bacteria which causes nosocomial infection. Methicillin-Resistant Staphylococcus Aureus eradication using antibiotics combined with rifampicin has shown good results, whereas, adjuvant rifampicin has long been hypothesized to improve the outcome of S. aureus infection treatment. Resistant-rifampicin S. aureus mutates in rpoB gene at some codons. This study was conducted to identify the mutation of rpoB gene in S. aureus which was resistant toward rifampicin.

METHODS

In this study, isolates collected in the Microbiology Laboratory of Dr. Seotomo Surabaya Hospital during May-September 2019. Then, the dilution method was carried out to determine the minimum inhibition concentration for resistant-rifampicin and dilution to determine the inhibition zone diameter. After that, DNA extraction was carried out from rifampicin-susceptible isolates as a control and resistant-rifampicin isolates followed by identification of rpoB gene mutations by Polymerase Chain Reaction (PCR) and sequencing.

RESULTS

There were nine isolates studied. They were four resistant-rifampicin isolates and four susceptible-rifampicin isolates. In four rifampicin-resistant isolates, the most frequent mutations that occurred was His-481 codon (75%) followed by the Ile-527 codon (25%). Rifampicin-susceptible isolates mutated in Pro-475 and Asn-474 codons. One rifampicin-resistant isolate had two mutations in codons Ile-527 and Asn-474.

CONCLUSIONS

The type of mutation that causes the most rifampicin resistance was a missense mutation. The susceptible-rifampicin isolate experienced silent mutations. There was a relation between the type of missense mutation of rpoB gene and rifampin resistance.

First report of mecC gene in clinical methicillin resistant S. aureus (MRSA) from tertiary care hospital Islamabad, Pakistan

BACKGROUND

Staphylococcus aureus (S. aureus) is one of the leading causes of community and hospital acquired infections globally. The objective of the study was to assess the prevalence, study the carriage of antibiotic resistance genes and evaluate the molecular typing of S. aureus isolates from a tertiary care hospital in Islamabad.

METHODS

A total of 1528 staphylococci isolates were included in this study. Standard microbiological procedures were applied to identify S. aureus. Antimicrobial susceptability was evaluated using the disk diffusion method and Minimum Inhibitory Concentrations (MICs) were determined using microbroth dilution method following Clinical and Laboratory Standards Institute (CLSI) guidelines. Multiplex PCR was used to detect antibiotic resistance genes, and molecular typing was performed using agr, SCCmec, spa, and Multi-Locus Sequence Typing (MLST) and clonal relatedness by Pulse Field Gel Electrophoresis (PFGE) methods.

RESULTS

Overall 65% were MRSA and 35% were methicillin sensitive Staphylococcus aureus (MSSA). Among MRSA isolates, 83% were multi-drug resistant and mecA was found in 54% isolates, mecC was in 3% while 1 MRSA carried both mecA and mecC genes. agrI (22%) was most prevalent group in MRSA, while agrIII (16%) was observed in MSSA. SCCmec types I, II, III, IV, and VI were detected, with high prevalence of type III while type V was absent. The prevelant spa type in MRSA was t657 with SCCmecIII elelments while in MSSA it was t021. One NEW spa type identified in MSSA isolates. In a subset of isolates, ST772 with SCCmecIV, ST1 carrying PVL marker, and ST1535 was reported first time from Pakistan.

CONCLUSIONS

The study presents a comprehensive analysis of prevalent S. aureus types and their antibiotic resistance profiles. It also reports for the first time SCCmec type VI and clinical MRSA isolates with mecC alone and in combination with mecA from Islamabad, Pakistan. This calls for further detailed investigations in other hospital settings in the region.

Propyl-5-hydroxy-3-methyl-1-phenyl-1H-pyrazole-4-carbodithioate (HMPC): a new bacteriostatic agent against methicillin-resistant Staphylococcus aureus

The emergence of Staphylococcus aureus strains resistant to ‘last resort’ antibiotics compels the development of new antimicrobials against this important human pathogen. We found that propyl 5-hydroxy-3-methyl-1-phenyl-1H-pyrazole-4-carbodithioate (HMPC) shows bacteriostatic activity against S. aureus (MIC = 4 μg/ml) and rescues Caenorhabditis elegans from S. aureus infection. Whole-genome sequencing of S. aureus mutants resistant to the compound, along with screening of a S. aureus promoter-lux reporter array, were used to explore possible mechanisms of action. All mutants resistant to HMPC acquired missense mutations at distinct codon positions in the global transcriptional regulator mgrA, followed by secondary mutations in the phosphatidylglycerol lysyltransferase fmtC/mprF. The S. aureus promoter-lux array treated with HMPC displayed a luminescence profile that was unique but showed similarity to DNA-damaging agents and/or DNA replication inhibitors. Overall, HMPC is a new anti-staphylococcal compound that appears to act via an unknown mechanism linked to the global transcriptional regulator MgrA.

Small mammals as sentinels of antimicrobial-resistant staphylococci

A total of 39 coagulase-negative staphylococci and seven Staphylococcus aureus strains were isolated from small mammal feces, i.e., the striped field mouse (Apodemus agrarius) and the yellow-necked mouse (A. flavicollis) in two sampling areas, deciduous forest and karst plains. MALDI-TOF analysis revealed five species of coagulase-negative staphylococci: S. sciuri, S. hominis, S. warneri, S. haemolyticus, and S. xylosus. All strains were susceptible to tetracycline, linezolid, vancomycin, and teicoplanin. Three MRSA strains with the mecA gene were detected. The beta-lactamase gene blaZ was detected in ampicillin-resistant staphylococci and in the high-level resistant strains (oxacillin over 2 mg/L) mecA gene. The mecC gene was not detected by PCR. Erythromycin-resistant staphylococci harbored the ermC gene and/or the efflux gene msrA. There were no detectable dfr genes in trimethoprim-resistant staphylococci and the rifampicin-resistant strains were without mutation in the rpoB gene. In summary, wild small mammals may serve as sentinels of mecA-positive S. aureus with erythromycin resistance genes ermC and efflux msrA. Small mammals appear to be useful indicators of antibiotic resistance.

Novel Mutation Sites in the Development of Vancomycin- Intermediate Resistance in Staphylococcus aureus

Increased use of vancomycin has led to the emergence of vancomycin-intermediate Staphylococcus aureus (VISA). To investigate the mechanism of VISA development, 39 methicillin-susceptible strains and 3 MRSA strains were treated with vancomycin to induce non-susceptibility, and mutations in six genes were analyzed. All the strains were treated with vancomycin in vitro for 60 days. MICs were determined by the agar dilution and E-test methods. Vancomycin was then removed to assess the stability of VISA strains and mutations. Following 60 days of vancomycin treatment in vitro, 29/42 VISA strains were generated. The complete sequences of rpoB, vraS, graR, graS, walK, and walR were compared with those in the parental strains. Seven missense mutations including four novel mutations (L466S in rpoB, R232K in graS, I594M in walk, and A111T in walR) were detected frequently in strains with vancomycin MIC ≥ 12 μg/mL. Jonckheere-Terpstra trend test indicated these mutations might play an important role during VISA evolution. After the vancomycin treatment, strains were passaged to vancomycin-free medium for another 60 days, and the MICs of all strains decreased. Our results suggest that rpoB, graS, walk, and walR are more important than vraS and graR in VISA development.

In vitro investigations into the use of antimicrobials in combination to maintain efficacy of fluoroquinolones in poultry

The aim of this study was to determine if apramycin, colistin or lincomycin-spectinomycin, in combination with enrofloxacin, was able prevent the emergence of mutants with reduced susceptibility to fluoroquinolone antibiotics in vitro. MICs were determined for enrofloxacin alone and in combination for panels of Campylobacter (n=37), Escherichia coli (n=52) and Salmonella (n=52) isolates. MIC results suggested that apramycin, colistin and lincomycin-spectinomycin worked in an additive/indifferent way when each was combined with enrofloxacin. Apramycin was considered the most promising antibiotic for combination-therapy in conjunction with enrofloxacin, and further evaluations (MBCs, MPCs and time-kill-curves) were performed for this combination for selected isolates. Results suggest combination-therapy of enrofloxacin with apramycin increases the efficacy, as well as decreasing the emergence and survival of bacteria with mutational resistance to fluoroquinolone antibiotics. Such combination-therapy, minimising the development of mutational resistance, may have relevance for Campylobacter, E. coli and Salmonella infections in poultry.

Pre-Use Susceptibility to Ceftaroline in Clinical Staphylococcus aureus Isolates from Germany: Is There a Non-Susceptible Pool to be Selected?

Ceftaroline is a new cephalosporin active against Methicillin-resistant Staphylococcus aureus (MRSA). Based on a representative collection of clinical S. aureus isolates from Germany, supplemented with isolates of clonal lineages ST228 and ST239, we demonstrate the in-vitro susceptibility towards ceftaroline prior to its introduction into clinical use for a total of 219 isolates. Susceptibility testing was performed by broth microdilution, disc diffusion and Etest, respectively. Results were interpreted according to EUCAST guidelines and showed considerable variance in dependence on clonal affiliation of the isolates tested. Among isolates of widespread hospital-associated lineages we found a high proportion of clinical isolates with MICs close to the EUCAST breakpoint (MIC50/90 1.0/1.5 mg/L); currently, interpretation of these "borderline" MICs is complicated by a lack of concordant susceptibility testing methods and reasonable breakpoint determination. Isolates of clonal lineages ST228 and ST239 demonstrated increased MIC50/90 values of 2.5/3.33 mg/L. Sequencing of mecA revealed no association of resistance to a specific mecA polymorphism, but rather reveals two regions in the non-penicillin-binding domain of PbP2a which displayed different combinations of mutations putatively involved in resistance development. This study provides national baseline data to (i) adjust susceptibility testing methods and current breakpoints to clinical and epidemiological requirements, (ii) evaluate current breakpoints with respect to therapeutic outcome and (iii) monitor further resistance evolution.

Dissecting vancomycin-intermediate resistance in staphylococcus aureus using genome-wide association

Vancomycin-intermediate Staphylococcus aureus (VISA) is currently defined as having minimal inhibitory concentration (MIC) of 4–8 µg/ml. VISA evolves through changes in multiple genetic loci with at least 16 candidate genes identified in clinical and in vitro-selected VISA strains. We report a whole-genome comparative analysis of 49 vancomycin-sensitive S. aureus and 26 VISA strains. Resistance to vancomycin was determined by broth microdilution, Etest, and population analysis profile-area under the curve (PAP-AUC). Genome-wide association studies (GWAS) of 55,977 single-nucleotide polymorphisms identified in one or more strains found one highly significant association (P = 8.78E-08) between a nonsynonymous mutation at codon 481 (H481) of the rpoB gene and increased vancomycin MIC. Additionally, we used a database of public S. aureus genome sequences to identify rare mutations in candidate genes associated with VISA. On the basis of these data, we proposed a preliminary model called ECM+RMCG for the VISA phenotype as a benchmark for future efforts. The model predicted VISA based on the presence of a rare mutation in a set of candidate genes (walKR, vraSR, graSR, and agrA) and/or three previously experimentally verified mutations (including the rpoB H481 locus) with an accuracy of 81% and a sensitivity of 73%. Further, the level of resistance measured by both Etest and PAP-AUC regressed positively with the number of mutations present in a strain. This study demonstrated 1) the power of GWAS for identifying common genetic variants associated with antibiotic resistance in bacteria and 2) that rare mutations in candidate gene, identified using large genomic data sets, can also be associated with resistance phenotypes.

Characterisation of clinical canine meticillin-resistant and meticillin-susceptible Staphylococcus pseudintermedius in France

Staphylococcus pseudintermedius is a frequent pathogen in dogs. The emergence of meticillin-resistant S. pseudintermedius (MRSP), which is concomitantly resistant to nearly all veterinary licensed antibiotics used for systemic treatment in dogs, is a major problem for veterinarians. In France, 16.9% (41/243) of the S. pseudintermedius collected in 2010 were MRSP. They mainly belonged to the multiresistant MLST sequence type ST71, spa type t02, SCCmec type II-III (ST71-t02-II-III) European clone. Moreover, we also report the emergence of multiresistant meticillin-susceptible S. pseudintermedius isolates presenting atypical and/or new spa types. This study highlights the need for surveillance, optimised treatment guidelines and new therapeutic alternatives.

Mini-review: Staphylococcus epidermidis as the most frequent cause of nosocomial infections: old and new fighting strategies

Staphylococcus epidermidis is nowadays regarded as the most frequent cause of nosocomial infections and indwelling medical device-associated infections. One of the features that contributes to the success of this microorganism and which is elemental to the onset of pathogenesis is its ability to form biofilms. Cells in this mode of growth are inherently more resistant to antimicrobials. Seeking to treat staphylococcal-related infections and to prevent their side effects, such as the significant morbidity and health care costs, many efforts are being made to develop of new and effective antistaphylococcal drugs. Indeed, due to its frequency and extreme resistance to treatment, staphylococcal-associated infections represent a serious burden for the public health system. This review will provide an overview of some conventional and emerging anti-biofilm approaches in the management of medical device-associated infections related to this important nosocomial pathogen.

Mutations in rpoB and fusA cause resistance to rifampicin and fusidic acid in methicillin-resistant Staphylococcus aureus strains from a tertiary hospital in Malaysia

BACKGROUND

The prevalence of resistance to rifampicin and fusidic acid among Malaysian strains of methicillin-resistant Staphylococcus aureus (MRSA) is increasing. This study aimed to determine the mechanisms of rifampicin and fusidic acid resistance and the genetic diversity of MRSA strains from a Malaysian tertiary hospital.

METHODS

Minimum inhibitory concentrations (MIC) for 21 MRSA strains were determined by agar dilution test and Etest. The resistance genes, staphylococcal chromosome cassette mec (SCCmec) types, multilocus-sequence typing (MLST) types and spa types, were determined by PCR and DNA sequencing.

RESULTS

MIC for rifampicin and fusidic acid resistance ranged from <1 to 8 µg/ml and from <1 to 256 µg/ml, respectively. A double mutation (484Arg/His and 517Glu/Gln) in rpoB causes high rifampicin resistance while a mutational change (461Leu/Lys) in fusA was observed in seven strains highly resistant to fusidic acid. Five of the seven were also resistant to rifampicin (MIC 8 µg/ml) and carried a mutated rpoB gene (484Arg/His). No other acquired fusidic acid resistance gene (fusB, fusC or fusD) was detected. Most (14/21) of the strains belonged to clone ST239-III-t037. Three belonged to ST22-IV-t1378 and the remaining four to ST239-III-t2029, ST239-III-t421, ST1178-IV-t1107 and ST241-III-t363, respectively.

CONCLUSIONS

The study showed that both rifampicin and fusidic acid resistance was associated with mutational change in rpoB and fusA, respectively. All rifampicin-resistant strains were from the same clone ST239-III-t037 whereas strains resistant to fusidic acid were genetically more diverse.

Molecular docking between the RNA polymerase of the Moniliophthora perniciosa mitochondrial plasmid and Rifampicin produces a highly stable complex

Background

Moniliophthora perniciosa (Stahel) Aime & Phillips-Mora is the causal agent of witches’ broom disease (WBD) in cacao (Theobroma cacao). When the mitochondrial genome of this fungus had been completely sequenced, an integrated linear-type plasmid that encodes viral-like RNA polymerases was found. The structure of this polymerase was previously constructed using a homology modeling approach.

Methods

Using a virtual screening process, accessing the Kegg, PubChem and ZINC databases, we selected the eight most probable macrocyclic polymerase inhibitors to test against M. perniciosa RNA polymerase (RPO). AutoDock Vina was used to perform docking calculations for each molecule. This software returned affinity energy values for several ligand conformations. Subsequently, we used PyMOL 1.4 and Ligand Scout 3.1 to check the stereochemistry of chiral carbons, substructure, superstructure, number of rotatable bonds, number of rings, number of donor groups, and hydrogen bond receptors.

Results

On the basis of this evidence we selected Rifampicin, a bacterial RNA polymerase inhibitor, and then AMBER 12 was used to simulate the behavior of the RPO-Rifampicin complex after a set of 5000 ps and up to 300 K in water. This calculation returned a graph of potential energy against simulation time and showed that the ligand remained inside the active site after the simulation was complete, with an average energy of -15 x 10² Kcal/Mol.

Conclusions

The results indicate that Rifampicin could be a good inhibitor for testing in vitro and in vivo against M. perniciosa.

Molecular characterization of rifampicin-resistant Staphylococcus aureus isolates in a Chinese teaching hospital from Anhui, China

BACKGROUND

Staphylococcus aureus (S. aureus) is a major nosocomial pathogen that causes a variety of infections and toxicoses. In recent years, the percentage of rifampicin-resistant S. aureus has increased rapidly in China. The aims of this study were to analyze 1) the level of rifampicin resistance in S. aureus and its correlation with mutations in the rpoB gene, and 2) the molecular characterization of rifampicin-resistant S. aureus isolates.

RESULTS

88 rifampicin-resistant S. aureus isolates were collected for this study. Of the 88 isolates, 83 (94.3%) were high-level rifampicin resistant (MIC≥8 mg/L) while the remaining 5 isolates (5.7%) had a low-level resistance to rifampicin (MIC, 2 to 4 mg/L). Four amino acid substitutions were found in the 88 isolates, which were 481His/Asn (95.5%), 466Leu/Ser (87.5%), 477Ala/Asp (6.8%) and 486Ser/Leu (4.5%) respectively. All mutations were found to be present in cluster I of the rpoB gene. The low-level resistant isolates were found to have only one mutation, while the high-level resistant isolates had at least two or more mutations. The most common multiple mutations were 481His/Asn+466Leu/Ser(92.8%,77/83). The other multiple mutations found were 481His/Asn+477Ala/Asp (6.0%,5/83), and 481His/Asn+466Leu/Ser+477Ala/Asp (1.2%,1/83). Out of 28 high-level rifampicin-resistant S. aureus isolates, three molecular types were found, namely, ST239-MRSA-III-spa t030 (25/28, 89.3%), ST239-MRSA-III-spa t021 (2/28, 7.1%), and ST239-MRSA-III-spa t045 (1/28, 3.6%).

CONCLUSIONS

Rifampicin resistance in S. aureus was closely associated with mutations in the rpoB gene. High-level rifampicin-resistant S. aureus is one of the most important features in Anhui Provincial Hospital, and high-level rifampicin resistance in S. aureus is associated with multiple mutations of rpoB gene. The prevalence of high-level rifampicin-resistant S. aureus in Anhui may be associated with the spread of the ST239-MRSA III-spa t030 clone.

Frequency, spectrum, and nonzero fitness costs of resistance to myxopyronin in Staphylococcus aureus

The antibiotic myxopyronin (Myx) functions by inhibiting bacterial RNA polymerase (RNAP). The binding site on RNAP for Myx-the RNAP "switch region SW1/SW2 subregion"-is different from the binding site on RNAP for the RNAP inhibitor currently used in broad-spectrum antibacterial therapy, rifampin (Rif). Here, we report the frequency, spectrum, and fitness costs of Myx resistance in Staphylococcus aureus. The resistance rate for Myx is 4 × 10(-8) to 7 × 10(-8) per generation, which is equal within error to the resistance rate for Rif (3 × 10(-8) to 10 × 10(-8) per generation). Substitutions conferring Myx resistance were obtained in the RNAP β subunit [six substitutions: V1080(1275)I, V1080(1275)L, E1084(1279)K, D1101(1296)E, S1127(1322)L, and S1127(1322)P] and the RNAP β' subunit [five substitutions: K334(345)N, T925(917)K, T925(917)R, G1172(1354)C, and G1172(1354)D] (residues numbered as in Staphylococcus aureus RNAP and, in parentheses, as in Escherichia coli RNAP). Sites of substitutions conferring Myx resistance map to the RNAP switch region SW1/SW2 subregion and do not overlap the binding site on RNAP for Rif, and, correspondingly, Myx-resistant mutants exhibit no cross-resistance to Rif. All substitutions conferring Myx resistance exhibit significant fitness costs (4 to 15% per generation). In contrast, at least three substitutions conferring Rif resistance exhibit no fitness costs (≤0% per generation). The observation that all Myx-resistant mutants have significant fitness costs whereas at least three Rif-resistant mutants have no fitness costs, together with the previously established inverse correlation between fitness cost and clinical prevalence, suggests that Myx resistance is likely to have lower clinical prevalence than Rif resistance.

Evaluation of antimicrobial activity of certain combinations of antibiotics against in vitro Staphylococcus epidermidis biofilms

BACKGROUND & OBJECTIVES

Staphylococcus epidermidis is the most common pathogen associated with infections of surgical implants and other prosthetic devices owing to its adhesion and biofilm-forming ability on biomaterials surfaces. The objective of this study was to compare susceptibilities of biofilm-grown cells to single antibiotic and in combination with others to identify those that were effective against S. epidermidis biofilms.

METHODS

Biofilms were grown in the MBEC™ assay system. The use of this methodology allowed a rapid testing of an array of antibiotics alone (eight) and in combination (25 double combinations). The antibacterial effect of all treatments tested was determined by colony forming units (cfu) enumeration method.

RESULTS

The MBEC™ assay system produced multiple and reproducible biofilms of S. epidermidis. Although none of the antibiotics tested have demonstrated an antimicrobial effect (log reduction >3) against all S. epidermidis isolates biofilms, but combinations containing rifampicin showed in general a broader spectrum namely rifampicin-gentamicin and rifampicin-clindamycin. Levofloxacin in combination with rifampicin showed a killing effect against three isolates but failed to attain a bactericidal action against the other two.

INTERPRETATION & CONCLUSIONS

Our findings showed that rifampicin should be a part of any antibiotic therapy directed against S. epidermidis biofilms. However, the efficient antibiotics combination might be dependent on S. epidermidis isolate being tested.

Genetic basis of rifampicin resistance in methicillin-resistant Staphylococcus aureus suggests clonal expansion in hospitals in Cape Town, South Africa

Background

Since 2001, several studies have reported high rifampicin resistance rates (45 - 100%) among methicillin-resistant Staphylococcus aureus (MRSA) isolates from South Africa. The authors previously characterised 100 MRSA isolates from hospitals in Cape Town, South Africa; forty-five percent of these isolates were rifampicin-resistant. The majority (44/45) corresponded to ST612-MRSA-IV, which is prevalent in South Africa, but has not been reported frequently elsewhere. The remaining rifampicin-resistant isolate corresponded to ST5-MRSA-I. The aim of this study was to investigate further the prevalence and genetic basis of rifampicin-resistance in MRSA isolates from hospitals in Cape Town.

Results

Between July 2007 and June 2011, the prevalence of rifampicin-resistant MRSA in hospitals in Cape Town ranged from 39.7% to 46.4%. Based on the results of the aforementioned study, nine ST612-MRSA-IV isolates, the rifampicin-resistant ST5-MRSA-I isolate, and two rifampicin-susceptible MRSA isolates were investigated. Four previously described ST612-MRSA-IV isolates, including two each from South Africa and Australia, were also included.

The ST5-MRSA-I isolate carried a single mutational change, H₄₈₁Y, commonly associated with high-level rifampicin resistance. All ST612-MRSA-IV isolates carried an uncommon double amino acid substitution in RpoB, H₄₈₁N, I₅₂₇M, whilst one of the Australian ST612-MRSA-IV isolates carried an additional mutation within rpoB, representing a novel rpoB genotype: H₄₈₁N, I₅₂₇M, K₅₇₉R. All ST612-MRSA-IV isolates also shared a unique silent single nucleotide polymorphism (SNP) within rpoB.

Conclusions

That local ST612-MRSA-IV isolates described here share an uncommon rpoB genotype and a unique silent SNP suggests this clone may have undergone clonal expansion in hospitals in Cape Town. Further, the data suggest that these isolates may be related to rifampicin-resistant ST612-MRSA-IV previously described in South Africa and Australia.