Methicillin-resistant Staphylococcus Aureus Agar Research Articles

Surveillance of Staphylococci Presence in and Around Neonate Isolette Beds in a Neonatal Intensive Care Unit of a Children's Hospital

Background Neonates in a neonatal intensive care unit (NICU) represent patients vulnerable to many pathogens due to their immunocompromised status. An earlier study of Staphylococci in this NICU suggested widespread environmental contamination, including Methicillin Resistant Staphylococcus aureus (MRSA). This study focused on Staphylococci associated with occupied isolette beds in the unit. Methods Two phases of this study were conducted. Initially, sterile transport swabs were used to collect samples from 10 different locations in 7 different pods of a NICU on 9 dates, focusing on areas surrounding neonate isolette beds. The second phase involved collection of swabs from 10 different locations in and on occupied neonate isolette beds, on 5 dates. For both phases swabs were used to inoculate Hardy CHROM MRSA agar plates (to detect MRSA), and mannitol salt agar (to detect S. aureus). Incubation was at 37°C for 48 hours. Descriptive statistics and Mann Whitney Utest was used for analysis. Results Results of phase one indicated that the floors by the pod sinks were most contaminated (p < .05) by MRSA and S. aureus (% positive swabs, MRSA = 76.2%; S. aureus = 87.3%). Looking more closely at the isolettes in phase two, we found MRSA present at the foot of the bed (11.4%), in ports at the foot of the beds (5.7%), and on suction tips (25.7%). Conclusions These data suggest that after efforts to reduce bacterial contamination in this NICU, focused on care-giver:patient contacts, several key environments near isolettes remain contaminated by Staphylococci. The floors in the unit may serve as a reservoir for MRSA and S. aureus. More concerning are the high levels of MRSA contamination found in the suction devices often found adjacent to or inside isolettes. Additional measures to target Staphylococci reduction in this NICU are now underway. Neonates in a neonatal intensive care unit (NICU) represent patients vulnerable to many pathogens due to their immunocompromised status. An earlier study of Staphylococci in this NICU suggested widespread environmental contamination, including Methicillin Resistant Staphylococcus aureus (MRSA). This study focused on Staphylococci associated with occupied isolette beds in the unit. Two phases of this study were conducted. Initially, sterile transport swabs were used to collect samples from 10 different locations in 7 different pods of a NICU on 9 dates, focusing on areas surrounding neonate isolette beds. The second phase involved collection of swabs from 10 different locations in and on occupied neonate isolette beds, on 5 dates. For both phases swabs were used to inoculate Hardy CHROM MRSA agar plates (to detect MRSA), and mannitol salt agar (to detect S. aureus). Incubation was at 37°C for 48 hours. Descriptive statistics and Mann Whitney Utest was used for analysis. Results of phase one indicated that the floors by the pod sinks were most contaminated (p < .05) by MRSA and S. aureus (% positive swabs, MRSA = 76.2%; S. aureus = 87.3%). Looking more closely at the isolettes in phase two, we found MRSA present at the foot of the bed (11.4%), in ports at the foot of the beds (5.7%), and on suction tips (25.7%). These data suggest that after efforts to reduce bacterial contamination in this NICU, focused on care-giver:patient contacts, several key environments near isolettes remain contaminated by Staphylococci. The floors in the unit may serve as a reservoir for MRSA and S. aureus. More concerning are the high levels of MRSA contamination found in the suction devices often found adjacent to or inside isolettes. Additional measures to target Staphylococci reduction in this NICU are now underway.

Bacterial Contamination of Floors in a Hematology/Oncology Unit in a Children's Hospital

Background Healthcare associated infections (HAIs) continue to be prevalent in hospitals, including pediatric Hematology/Oncology (HO) Units. Contamination of floors in HO units may pose a unique problem for the immunocompromised patients treated there. The objective of this study was to determine whether Clostridium difficile (Cdiff) or Methicillin Resistant Staphylococcus aureus (MRSA) were present on floors in a Hematology/Oncology unit of a Children's Hospital, potentially serving as a reservoir for these pathogens. Methods Two locations in four rooms (floor at room entry and room bathroom floor), and two floor locations (main sink and the adjoining hallway) were swabbed weekly for seven weeks with sterile transport swabs. Swabs were used to inoculate Hardy CHROM MRSA agar plates (to detect MRSA), and to inoculate Hardy Cdiff Banana Broth tubes (to detect Cdiff). Incubation was at 37°C for 48 hours. Data was analyzed with SPSS 26 and used descriptive statistics and odds-ratios to compare contamination by site. Results Results of the cultures indicated the following: the percent positive swabs for the room sites for Cdiff were 29.2% and 25.0% (floor by door, and bathroom), and for the hallways were 19.0% and 33.3% (by the main sink, and main door). For MRSA presence the percent positive for the room sites were 42.3% and 26.9% (floor by door, and bathroom), and for the hallways 42.9% and 33.3% (by the main sink, and main door). Odds-ratios were highest (1.99) for room entry doors. Conclusions The data presented suggests that Cdiff is fairly uniformly distributed throughout the floors of the rooms, possibly serving as the source of this contamination in the hallway. MRSA in the rooms appears to represent a possible reservoir for this pathogen, leading to contamination of the hallway floors. Our data suggests that the floors in HemOnc patient rooms present a potential hazard for HAIs in these patients. Healthcare associated infections (HAIs) continue to be prevalent in hospitals, including pediatric Hematology/Oncology (HO) Units. Contamination of floors in HO units may pose a unique problem for the immunocompromised patients treated there. The objective of this study was to determine whether Clostridium difficile (Cdiff) or Methicillin Resistant Staphylococcus aureus (MRSA) were present on floors in a Hematology/Oncology unit of a Children's Hospital, potentially serving as a reservoir for these pathogens. Two locations in four rooms (floor at room entry and room bathroom floor), and two floor locations (main sink and the adjoining hallway) were swabbed weekly for seven weeks with sterile transport swabs. Swabs were used to inoculate Hardy CHROM MRSA agar plates (to detect MRSA), and to inoculate Hardy Cdiff Banana Broth tubes (to detect Cdiff). Incubation was at 37°C for 48 hours. Data was analyzed with SPSS 26 and used descriptive statistics and odds-ratios to compare contamination by site. Results of the cultures indicated the following: the percent positive swabs for the room sites for Cdiff were 29.2% and 25.0% (floor by door, and bathroom), and for the hallways were 19.0% and 33.3% (by the main sink, and main door). For MRSA presence the percent positive for the room sites were 42.3% and 26.9% (floor by door, and bathroom), and for the hallways 42.9% and 33.3% (by the main sink, and main door). Odds-ratios were highest (1.99) for room entry doors. The data presented suggests that Cdiff is fairly uniformly distributed throughout the floors of the rooms, possibly serving as the source of this contamination in the hallway. MRSA in the rooms appears to represent a possible reservoir for this pathogen, leading to contamination of the hallway floors. Our data suggests that the floors in HemOnc patient rooms present a potential hazard for HAIs in these patients.

Methicillin-Resistant Staphylococcus aureus Prevalence Among Healthcare Workers in Contact Tracings in a Dutch Hospital

Background: In The Netherlands, the national guidelines on Methicillin-Resistant Staphylococcus aureus (MRSA) prevention and control advocate screening of healthcare workers (HCWs) after unprotected exposure to MRSA carriers. Although this strategy is largely successful, contact tracing of staff is a time-consuming and costly component. We evaluated our contact tracing policy for HCWs over the years 2010–2018. Methods: A retrospective, observational study was performed in a Dutch teaching hospital. All HCWs who had unprotected contact with an MRSA carrier were included in contact tracing. When there had been a long period of unprotected admission prior to an MRSA finding, or when the index case was an HCW, the entire (nursing) team was tested. All samples of HCWs who were tested for MRSA carriage as part of contact tracing from 2010 until 2018 were included. A pooled nose, throat, and perineum swab was collected using the eSwab medium (Copan) and inoculated on chromID MRSA agar plates (bioMérieux) after enrichment in a broth. Molecular typing was performed using multiple-locus variable number of tandem repeat analysis (MLVA). Results: In total, we included 8,849 samples (range, 677–1,448 samples per year) from 287 contact tracings (range, 26–55 contact tracings per year). Overall, 32 HCWs were colonized with MRSA (0.36%; 95% CI, 0.26%–0.51%). None of them developed a clinical infection. Moreover, 8 HCWs (0.10%; 95% CI, 0.05%–0.19%) were colonized with the same MLVA type as the index case and were detected in 6 of 287 contact tracings (2%). In 4 of 8 of these cases, a positive HCW was the index for undertaking contact tracing. In 3 of 8 cases, it was clear that the HCW who was identified in the contact tracing was the source of the outbreak and was the cause of invasive MRSA infections in patients. Notably, a different MLVA type as the index case was found in 24 HCWs (0.27%; 95% CI, 0.18%–0.40%) of whom 7 of 24 HCWs (29.2%) were intermittent carriers. Conclusions: This study revealed a sustained low MRSA prevalence among samples in contact tracing of HCWs over 9 years. Furthermore, it shows that when MRSA contact tracing is performed according to the national guideline, only 1 of 1,000 samples results in a secondary case. This is similar to the population carriage rate of MRSA in The Netherlands. More frequently, an unrelated strain is found. These findings raise questions regarding the efficacy of the current strategy to perform contact tracing after unprotected exposure.Funding: NoneDisclosures: None

Influence of Broth Enrichment as well as Storage and Transport Time on the Sensitivity of MRSA Surveillance in the Tropics.

Direct growth on blood and screening agar for methicillin-resistant Staphylococcus aureus (MRSA) at a tropical surveillance site was compared with broth enrichment and subsequent growth on selective MRSA agar after international sample transport.In Madagascar, 1548 swabs from an MRSA surveillance study were assessed for growth on Columbia blood agar enriched with 5% sheep blood and MRSA screening agar at the surveillance site with subsequent cold storage of the samples and shipment to Germany. In Germany, 1541 shipped samples were analyzed by non-selective broth enrichment with subsequent culture on MRSA selective agar.A total of 28 MRSA isolates were detected. Of these, 20 strains were isolated from direct culture on blood and MRSA screening agars at the surveillance site, 24 MRSA strains were isolated using the broth enrichment method in Germany, and 16 MRSA strains were identified by both approaches.In spite of the observed die-off of individual strains due to long-term storage and transport, broth enrichment with subsequent screening on MRSA selective agar after international sample shipment led to comparable sensitivity of MRSA detection like streaking on blood and MRSA agar at the tropical surveillance site.

Is there a relationship between rectal colonization and nosocomial infection of patients in intensive care unit?

Nosocomial infections caused by multidrug-resistant (MDR) microorganisms are a major problem in intensive care units (ICUs) with high mortality and morbidity rates and the prior colonization is an important risk factor for these infections. The aim of this study was to investigate the prevalence of rectal colonization of MDR microorganisms and the association between the microorganisms that caused colonization and infection in the patients with nosocomial infections in ICUs. Rectal swabs were obtained on the day of 0, 3, 7, 14, 21 and weekly thereafter from 80 patients over 18 years of age hospitalized in ICU for more than 48 hours, and cultured for vancomycin-resistant enterococcus (VRE), methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum β-lactamase (ESBL)- producing gram-negative bacilli (GNB) and carbapenem-resistant enteric and nonenteric bacilli. Patients whose rectal swabs were not obtained on admission (on the day of 0), were excluded even they were hospitalized more than 48 hours. Bile esculin agar containing 64 μg/mL ceftazidime and 6 μg/mL vancomycin, chromogenic MRSA agar and blood agar media, MacConkey agar containing 1 mg/L ceftazidime and ceftriaxone, and 5 mL tryptic soy broth media containing 10 µg imipenem and meropenem discs were used for identification. Identification of GNB was determined by conventional methods and ESBL production was determined by double-disc synergy test. Patients have been followed up for nosocomial infections. Bacterial identification and antibiotic susceptibility tests were performed with standard microbiological methods. In 37 (46%) of the 80 patients, at least one MDR microorganism was isolated in rectal swab cultures on the day of 0. The most common microorganisms were ESBL-positive E.coli (19%), followed by ESBL-positive K.pneumoniae (13%), carbapenem-resistant P.aeruginosa (10%), ESBL-positive K.oxytoca (3%), MRSA (1%), VRE (1%), carbapenem-resistant Acinetobacter sp. (1%) and carbapenem-resistant K.pneumoniae (1%), respectively. The number of microorganisms isolated from rectal swab cultures on the following days have increased, and on the 7th day, the rate of the patients with rectal colonization ascended to 72%. Out of 80 patients, 52 (65%) had nosocomial infections in the follow-up and the mean duration of infection development was 11.8±9.9 days in these patients. Patients with and without rectal colonization were compared in terms of subsequent nosocomial infection rates. While no statistically significant difference has been detected between two groups on the day of 0, patients with rectal colonization detected on the day of 3 and 7, had a significantly higher incidence of nosocomial infections (p=0.02, p=0.01). Among the patients with ESBL-positive GNB, carbapenem-resistant K.pneumoniae, carbapenem-resistant P.aeruginosa and VRE infections, the same microorganisms have been isolated in the rectal swab cultures taken before the development of infection. This result was statistically significant for each of these microorganisms (p=0.00-0.03). However, such a correlation was not observed for Acinetobacter infections. Since MRSA infections developed in only two patients, no istatistical analysis has been done for this microorganism. In conclusion, our data suggest that MDR microorganisms that cause nosocomial infections, initially colonize the gastrointestinal tract, and early detection of colonized patients in ICUs may help an effective infection control by preventing the spread of these resistant microorganisms.

Hastanede Yatan Hastalar, Poliklinik Hastaları ve Hastane Personelinde Metisiline Dirençli Staphylococcus aureus Nazal Taşıyıcılık Oranları ve Risk Faktörleri

Introduction: The aim of this study was to determine the ratio of nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) and the risk factors among 1500 subjects including 689 hospital staff, 609 inpatients, and 202 outpatients in Ankara Training and Research Hospital. Materials and Methods: Nasal swabs were obtained from hospital staff, inpatients and outpatients, which were then inoculatedinto mannitol-salt agar, oxacillin resistance screening agar base (ORSAB), and chromogenic MRSA agar media, respectively. Methicillin resistance was confirmed with cefoxitin disk by the disk-diffusion test. In statistical analyses, the Chi-square and the Kruskal Wall is tests were used, considering p< 0.05 value statistically significant. Results: MRSA nasal carriage rate was determined 3.03%, 9.03% and 3.96% in hospital staff, inpatients and outpatients, respectively. The rate of nasal carriage of MRSA amongst doctors, nurses and auxiliary health personnel was 1.36%, 1.735% and 5.06% respectively.

Laboratory evaluation of phenotypic detection methods of methicillin-resistant Staphylococcus aureus.

Although conventional antibiotic susceptibility tests are most commonly performed for methicillin-resistant Staphylococcus aureus (MRSA), the results of these phenotypic tests are dependent on the standardization of the culture conditions. The aim of the study was to evaluate the conventional phenotypic screening tests in comparison to the mecA gene polymerase chain reaction (PCR). One hundred and two clinical isolates of MRSA identified by the oxacillin disk diffusion were subjected to PCR for the mecA gene and by the cefoxitin disk diffusion test and culture on oxacillin screen agar, mannitol salt agar, and methicillin-resistant Staphylococcus aureus Agar (MeReSA) selective medium, for MRSA. Although all 102 isolates were resistant in oxacillin and cefoxitin disk diffusion, 92 (90.1%) isolates were positive for the mecA gene. The sensitivities of the mannitol salt agar, MeReSA agar, and oxacillin screen agar were 89.13, 97.82, and 98.91%, respectively. The oxacillin screen agar may be recommended for confirming methicillin resistance in the disk diffusion test in resource-poor settings, where molecular methods are not available.

English

This study was based on the comparison of revised guidelines of Clinical and Laboratory Standard Institute (CLSI), British Society for Antimicrobial Chemotherapy (BSAC) and BrillianceTM&nbsp;MRSA agar (Oxoid) for the phenotypic identification of methicillin resistantStaphylococcus aureus&nbsp;(MRSA).&nbsp;A total of 133 clinical isolates of&nbsp;S. aureus&nbsp;were tested using new CLSI, BSAC guidelines and BrillianceTM&nbsp;MRSA Agar. All the strains were tested according to prescribed guidelines of CLSI (M100-S20, 2010) and BSAC (10.2, 2011). The 30&nbsp;&micro;g and 10&nbsp;&micro;g cefoxitin (FOX) performed best for the detection of MRSA and gave 100% sensitivity and specificity. While 1&nbsp;&micro;g oxacillin (OX) showed less effective results showing sensitivity and specificity of 96.8% and 100% respectively.&nbsp;The cefoxitin disc diffusion method appears to be a good option for the identification of MRSA.&nbsp;BrillianceTM&nbsp;MRSA agar when used for the detection of MRSA, showed sensitivity and specificity of 98.4% and 100% respectively. In conclusion the efficiency of&nbsp;FOX is very high and FOX disc diffusion method is the most efficient method for the identification of MRSA phenotypicallyand&nbsp;could be a second choice for the detection of MRSA. &nbsp; Key words:&nbsp;Staphylococcus aureus,&nbsp;CLSI, BSAC, Chromogenic media, MRSA.

Evaluation of the LightCycler Methicillin-Resistant Staphylococcus aureus (MRSA) Advanced Test for Detection of MRSA Nasal Colonization

Rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization is crucial for the prevention and control of MRSA infections in health care settings. The LightCycler MRSA Advanced Test (Roche Diagnostics) is a commercially available real-time PCR assay for direct detection of MRSA nasal colonization by targeting of the staphylococcal cassette chromosome mec (SCCmec)-orfX junction. The diagnostic performance of the assay was compared with that of ChromID MRSA agar (bioMérieux) culture and an in-house duplex real-time PCR assay. Among 1,246 nasal swab specimens collected from 2 general hospitals in Hong Kong, 174 (14%) were considered true positive for MRSA. Chromogenic culture and the in-house real-time PCR assay identified 147 (84.5%) and 133 (76.4%) true-positive cases with specificities of 100% and 98.6%, respectively. Based on the target melting temperature (Tm) values (57.0 to 62.0 °C) defined by the manufacturer, the LightCycler MRSA Advanced Test identified only 85 (48.9%) true-positive specimens. Interestingly, an additional 60 (34.5%) true-positive specimens were detected despite atypical Tm values of 55 °C, providing overall sensitivity and specificity values of 83.3% and 99%, respectively. Among isolates with Tm values of 55 °C, most were typed as clonal complex 45 (CC45). By sequence analysis of the SCCmec-orfX junction, characteristic single-nucleotide polymorphisms (SNPs) were identified only in isolates with Tm values of 55°C and not in those with typical Tm values. It is conceivable that those SNPs were located inside the target region of the proprietary hybridization probes, which resulted in a Tm shift in the melting curve analysis. Our study highlights the importance of a global evaluation of commercial kits so that the interpretation algorithm covers different lineages of MRSA clones prevalent in various geographical regions.

Rapid confirmation of suspected methicillin-resistant Staphylococcus aureus colonies on chromogenic agars by a new commercial PCR assay, the GenomEra MRSA/SA Diagnose

A new automated closed tube PCR assay, the GenomEra(™) MRSA/SA Diagnose (Abacus Diagnostica Oy, Finland) was evaluated for rapid confirmation of methicillin-resistant Staphylococcus aureus (MRSA) from cultured screening specimens. The ability of the assay to detect genotypically different MRSA strains was studied with a collection of 304 MRSA isolates covering 68 spa types. The specificity was investigated with a collection of 146 non-MRSA staphylococcus isolates. The usefulness of the assay for clinical purposes was assessed by a sequential combination of MRSA screening culture and confirmation of the colonies with the GenomEra MRSA/SA Diagnose assay. A total of 145 suspected MRSA colonies on chromogenic plates were analyzed this way. All MRSA isolates from the culture collection and from the clinical screening specimens were confirmed as MRSA with the GenomEra MRSA/SA Diagnose assay and none of the non-MRSA staphylococci caused false-positive results, which indicates both sensitivity and specificity of 100%. The combination of GenomEra MRSA/SA Diagnose with preceding culture on selective MRSA agar permitted MRSA confirmation within 24 h. This practice offers a reliable and quick detection of MRSA that is also suitable in areas where several strain types cause epidemics.

Study of methicillin resistant Staphylococcus aureus (MRSA) in Danish pigs at slaughter and in imported retail meat reveals a novel MRSA type in slaughter pigs

Methicillin-resistant Staphylococcus aureus (MRSA), especially CC398, have emerged in livestock worldwide. We investigated the occurrence of MRSA in pigs at slaughter and in retail meat. During 2009, nasal swabs (n=789) were taken from pigs at slaughter. Moreover, 866 meat samples [Danish: pork (153), broiler meat (121), beef (142) and; imported: pork (173), broiler meat (193), and beef (84)] were randomly collected in retail stores and outlets. MRSA was isolated from nasal swabs or from meat samples after preenrichment (Mueller Hinton broth with 6.5% NaCl), selective enrichment (tryptone soya broth with 4mg/L cefoxitine and 75mg/L aztreonam) and selective plating on Brilliance Chromogenic MRSA agar. The presence of mecA was confirmed by PCR and the MRSA isolates were spa typed. Novel MRSA spa types were characterized by MLST, PFGE and SCCmec typing. Thirteen percent (101/789) of the pigs had MRSA. Based on spa types 93% corresponded to CC398 (spa t011, t034, t1451, t2876, t2974), 4% to CC30 (t1333) and one isolate to CC1 (t0127). The spa type t1333 (CC30), which is common among methicillin susceptible S. aureus (MSSA) from pigs in Denmark, contained a SCCmec cassette type V and czrC zinc resistance gene. Imported broiler meat had the highest occurrence (18%) of MRSA, followed by imported pork (7.5%) and Danish pork (4.6%). MRSA ST398 was found for the first time in Danish beef (1.4%). The finding of MRSA CC30 (spa t1333) suggest possible spread of the SCCmec cassette normally associated with ST398 into another S. aureus lineage common in pigs.

The presence of methicillin-resistant Staphylococcus aureus on large pig breeding farms in Croatia

Methicillin-resistant Staphylococcus aureus (MRSA) have emerged worldwide and have become resistant to a variety of antibiotics. MRSA colonisation in pigs was first reported from the Netherlands in 2005, where pigs were implicated as a source of human MRSA infections (Voss et al., 2005). This paper presents the first report on the presence of MRSA on large pig breeding farms in Croatia, together with the determination of the mecA gene, the results of spa typing and susceptibility to commonly used antimicrobials. Dust samples (7-11 per farm) were collected from eight large pig farms in Croatia. Of the total 68 swabs, the mecA gene was detected in 24 isolates growing on the MRSA agar. All isolates were resistant to oxacillin, tetracycline and streptomycin, and susceptible only to vancomycin, while 92% of the strains were susceptible to ciprofloxacin. Genotyping of the MRSA strains was performed by spa typing, and revealed t011 (n = 17), t034 (n = 5) and t1451 (n = 2). The results presented here predict that MRSA is present on a large number of pig farms in Croatia.

Detection of methicillin-resistant Staphylococcus pseudintermedius with commercially available selective media

Commercially available selective media for methicillin-resistant Staphylococcus aureus (MRSA) were tested for the detection and isolation of methicillin-resistant Staphylococcus pseudintermedius (MRSP). Five different screening agars [mannitol salt agar with oxacillin and BD BBL™ Chromagar™ MRSA (BD Diagnostics); chromID™ MRSA agar (bioMérieux); Oxacillin resistance screening agar base (ORSAB); and Brilliance MRSA agar (Oxoid)] were analysed for the detection of MRSP. Bacteria that may be isolated together with MRSP and may grow on the screening agars were included in the study to determine possible interference with the growth of MRSP. MRSP grew well on all selective media except on BD BBL™ Chromagar™ MRSA (BD Diagnostics) and chromID™ MRSA agar (bioMérieux), on which a low to moderate growth rate was noted. ORSAB (Oxoid) and Brilliance MRSA agar (Oxoid) are most suitable for the detection and isolation of MRSP from clinical material. The importance of MRSP in veterinary medicine is increasing. Diagnostic systems are needed to detect MRSP carrier as soon as possible. This study provides information about selected MRSA screening agars for the detection of MRSP to the clinical microbiologists.

Rapid diagnostic testing of methicillin-resistant Staphylococcus aureus carriage at different anatomical sites: costs and benefits of less extensive screening regimens

Multiple body site screening and pre-emptive isolation of patients at risk for methicillin-resistant Staphylococcus aureus (MRSA) carriage are considered essential for control of nosocomial spread. The relative importance of extranasal screening when using rapid diagnostic testing (RDT) is unknown. Using data from a multicentre study evaluating BD GeneOhm™ MRSA PCR (IDI), Xpert MRSA (GeneXpert) and chromogenic agar, added to conventional cultures, we determined cost-effectiveness assuming isolation measures would have been based on RDT results of different hypothetical screening regimes. Costs per isolation day avoided were calculated for regimes with single or less extensive multiple site RDT, regimes without conventional back-up cultures and when PCR would have been performed with pooling of swabs. Among 1764 patients at risk, MRSA prevalence was 3.3% (n = 59). In all scenarios the negative predictive value is above 98.4%. With back-up cultures of all sites as a reference, the costs per isolation day avoided were £15.19, £30.83 and £45.37 with ‘nares only’ screening using chromogenic agar, IDI and GeneXpert, respectively, as compared with £19.95, £95.77 and £125.43 per isolation day avoided when all body sites had been screened. Without back-up cultures costs per isolation day avoided using chromogenic agar would range from £9.24 to £76.18 when costs per false-negative RDT range from £5000 up to £50 000; costs for molecular screening methods would be higher in all scenarios evaluated. In conclusion, in a low endemic setting chromogenic agar screening added to multiple site conventional cultures is the most cost-effective MRSA screening strategy.

Effects of tetracycline and zinc on selection of methicillin-resistant Staphylococcus aureus (MRSA) sequence type 398 in pigs

An in vivo experiment was conducted to evaluate the effects of tetracycline and zinc on pig colonization and transmission of methicillin-resistant Staphylococcus aureus (MRSA) sequence type (ST) 398. Eight piglets naturally colonized with MRSA ST398 and 8 MRSA-negative piglets of the same age and breed were assigned to three groups treated with tetracycline and zinc (Group 1), zinc (Group 2) or tetracycline alone (Group 3) and one non-treated group (Group 4), each containing two MRSA-positive and two MRSA-negative animals. Two additional non-treated control groups composed of only MRSA-positive (Group 5) and MRSA-negative (Group 6) animals were used to check for stability of MRSA carriage status. Nasal swabs and environmental wipes were collected on Days 0, 7, 14, and 21, and the occurrence of MRSA in each sample was quantified by bacteriological counts on Brilliance™ MRSA agar. Significantly higher nasal MRSA counts were observed in the zinc-treated (p=0.015) and tetracycline-treated (p=0.008) animals compared to the non-treated animals. Environmental MRSA counts appeared to increase over time in Groups 1 and 2 but such an increase was not statistically significant. MRSA-negative animals housed with MRSA-positive animals became positive in all groups, whereas the carriage status of the animals in Groups 5 and 6 did not change. This study demonstrates that feed supplemented with tetracycline or zinc increases the numbers of MRSA ST398 in the nasal cavity of pigs. Transmission of MRSA from positive to negative animals housed within the same pen was not influenced by exposure to these agents.

Performance evaluation of a modified chromogenic medium, ChromID MRSA New, for the detection of methicillin-resistant Staphylococcus aureus from clinical specimens

A novel chromogenic medium for the detection of methicillin-resistant Staphylococcus aureus (MRSA), ChromID MRSA New, was evaluated and compared with the original ChromID MRSA agar, using 355 consecutive screening specimens from nose (120), throat (121) and perineum (114). The specimens were collected with an E-swab and inoculated within 24 hours onto both ChromID MRSA New and on ChromID MRSA. ChromID MRSA New was more sensitive than ChromID MRSA in detecting MRSA after 24 hours of incubation (94.3% versus 81.4%; p<0.05). With the ChromID MRSA New, processing time is reduced from 48h to 24h and confirmation of the resistance to methicillin is redundant.

Alternative Use for Spectra MRSA Chromogenic Agar in Detection of Methicillin-Resistant Staphylococcus aureus from Positive Blood Cultures

Spectra MRSA agar (Remel, Lenexa, KS), a novel chromogenic medium originally developed to detect methicillin-resistant Staphylococcus aureus (MRSA) from nasal swabs, was evaluated in this multicenter study for the detection of MRSA from positive blood cultures exhibiting Gram-positive cocci upon initial Gram staining.

Semi-selective broth improves screening for methicillin-resistant Staphylococcus aureus

To evaluate two enrichment broths for methicillin-resistant Staphylococcus aureus (MRSA) detection and compare results with direct plating. Swabs from 1224 patients were re-analysed for MRSA in a central laboratory (Münster) using six methods. Swabs were suspended in 0.5 mL of non-selective enrichment broth (NB) and vortexed. Aliquots of 100 microL were inoculated on/into: (I) ChromID MRSA agar; (II) Columbia sheep blood (5%) agar (BA) and ChromID MRSA; (III, IV) NB incubated overnight followed by plating on BA and ChromID MRSA; and (V, VI) a semi-selective broth containing cefoxitin and aztreonam (TSB-SSI) incubated overnight followed by plating on BA and ChromID MRSA. In III-VI, 100 microL of the enriched broth was plated on each agar. The combined MRSA-positive rate was 21.5%. MRSA isolates detected by each method were: TSB-SSI, n = 223; NB, n = 205; BA and ChromID MRSA, n = 203; ChromID MRSA alone, n = 183. TSB-SSI detected more positive throat samples than the comparators and significantly reduced methicillin-susceptible S. aureus (MSSA) growth. The maximum sensitivity obtained was only 85%, possibly due to the study design using pre-used swabs and dilution of swab material. For 997 samples, results from Münster were compared with initial results. Peripheral laboratories identified 172 MRSA compared with Münster where 186, 186 and 204 MRSA were found for direct plating, NB and TSB-SSI broth, respectively. TSB-SSI was superior to both NB and direct plating on ChromID MRSA and BA. Despite re-using swabs for the study, we showed that routine diagnostic screening could be significantly improved, using a semi-selective enrichment broth.

Comparative Evaluation of Five Culture Media with Triplex PCR Assay for Detection of Methicillin-Resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) is responsible for nosocomial and community-acquired infections. Hence, rapid and accurate laboratory diagnosis of MRSA is a vital constituent of control measures. The present study evaluated five different methods for the identification of MRSA. A total of 207 S. aureus clinical isolates that consisted of 89 MRSA and 118 methicillin-susceptible S. aureus (MSSA) strains confirmed by PCR were tested. MRSA strains were evaluated by five different methods: chromogenic MRSA agar (CMRSA), oxacillin resistance screening agar base (ORSAB), mannitol salt oxacillin agar (MSO), mannitol salt cefoxitin agar with two different concentrations of cefoxitin [4 microg/ml (MSC-4) and 6 microg/ml (MSC-6)]. The results of the different methods were compared to mecA PCR as the gold standard. MSC-6 showed only six false-positive MRSA in comparison with PCR. The sensitivities and specificities of MSC-6, MSC-4, MSO-4, ORSAB, and CMRSA were as follows: 98.9/94.9%, 100/83.1%, 89.9/87.3%, 97.8/96.6%, and 95.5/94.9%, respectively. In comparison with PCR, it was found that both MSC-6 and ORSAB were relatively the least expensive screening tests ($0.70 and $1.00, respectively). In conclusion, all methods were comparable, but MSC-6 was the least expensive medium for MRSA screening.