Evaluation of mannitol salt agar for detection of oxacillin resistance in Staphylococcus aureus by disk diffusion and agar screening

Comparison of Phenotypic and Genotypic Characterization Methods for the Detection of Methicillin-Resistant Staphylococcus Aureus

Introduction Methicillin-resistant Staphylococcus aureus (MRSA) is associated with high morbidity and mortality due to the development of antimicrobial resistance secondary to irrational use of antibiotics, nonadherence to infection control practices, and increased use of intravascular devices in healthcare systems. Detection of MRSA is critical in clinical microbiology laboratories as it helps identify MRSA carriers and avoid treatment failure in patients. Hence, this study compared various phenotypic methods with the standard genotyping method to determine a method that permits rapid and accurate detection of MRSA. Materials & Methods Staphylococcus aureus (S. aureus) was initially identified based on colony morphology, Gram staining, standard biochemical tests, and antibiotic susceptibility using disk diffusion. MRSA was identified based on the detection of the mecA gene by polymerase chain reaction (PCR) and subsequent gel electrophoresis. Disk diffusion using cefoxitin or oxacillin and mannitol salt agar with 6-µg/ml oxacillin were used for phenotypic detection of MRSA. The D test was used to detect inducible clindamycin resistance in S. aureus isolates. Results Of the 100 S. aureus isolates analyzed, 37% were identified as MRSA by PCR and the cefoxitin disk diffusion method; however, only 31% were detected by the oxacillin disk diffusion method and 29% by the mannitol salt agar method. The sensitivity of the cefoxitin disk diffusion test, oxacillin disk diffusion, and mannitol salt agar methods was 86.05%, 83.78%, and 70.73%, respectively. Specificity was 100% for all the three phenotypic methods (p < 0.001). Notably, inducible clindamycin resistance was found in 37.2% of the MRSA isolates, indicating potential challenges in treatment. Conclusion Among the three phenotypic methods tested, the cefoxitin disk diffusion method had 100% sensitivity and specificity, which is similar to that of PCR-based MRSA detection. Hence, the cefoxitin disk diffusion method is recommended for use in clinical laboratories, where molecular methods are not available as it is both cost-effective and easy to perform.

Current pathogens infecting open fracture tibia and their antibiotic susceptibility at a tertiary care teaching hospital in South East Asia

Background

Methods

Results

Conclusion

Staphylococcus aureus and community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in and around therapeutic whirlpools in college athletic training rooms

CONTEXT

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has become a leading cause of skin and soft tissue infection in the nonhospitalized community. Care of the athletes in athletic training rooms is specifically designed with equipment tailored to the health care needs of the athletes, yet recent studies indicate that CA-MRSA is still prevalent in athletic facilities and that cleaning methods may not be optimal.

OBJECTIVE

To investigate the prevalence of Staphylococcus aureus and CA-MRSA in and around whirlpools in the athletic training room.

DESIGN

Cross-sectional study.

SETTING

National Collegiate Athletic Association Division I university.

PATIENTS OR OTHER PARTICIPANTS

Student-athletes (n = 109) consisting of 46 men (42%) and 63 women (58%) representing 6 sports.

MAIN OUTCOME MEASURE(S)

Presence of MRSA and Staphylococcus aureus in and around the whirlpool structures relative to sport and number of athletes using the whirlpools.

RESULTS

We identified Staphylococcus aureus in 22% (n = 52/240) of the samples and MRSA in 0.8% (n = 2/240). A statistically significant difference existed between the number of athletes using the whirlpool and the presence of Staphylococcus aureus in and around the whirlpools (F(2,238) = 2.445, P = .007). However, Staphylococcus aureus was identified regardless of whether multiple athletes used a whirlpool or no athletes used a whirlpool. We did not identify a relationship between the number of athletes who used a whirlpool and Staphylococcus aureus or MRSA density (P = .134).

CONCLUSIONS

Staphylococcus aureus and MRSA were identified in and around the whirlpools. Transmission of the bacteria can be reduced by following the cleaning and disinfecting protocols recommended by the Centers for Disease Control and Prevention. Athletic trainers should use disinfectants registered by the Environmental Protection Agency to sanitize all whirlpools between uses.

Prevalence of nosocomial infections and anti-infective therapy in Benin: results of the first nationwide survey in 2012

Background

Data on nosocomial infections in hospitals in low-income countries are scarce and often inconsistent. The objectives of this study were to estimate the prevalence of nosocomial infections and antimicrobial drug use in Benin hospitals.

Methods

All hospitals were invited to participate in the first national point prevalence study conducted between 10–26 October 2012 using the protocol developed by the “Hospitals in Europe Link for Infection Control through Surveillance” (HELICS) project. Infection prevalence rates and the proportion of infected patients and exposure to antimicrobials were assessed.

Results

Overall, 87% (39/45) of hospitals participated. Of 3130 inpatients surveyed, 972 nosocomial infections were identified among 597 patients, representing an overall prevalence of infected patients of 19.1%. The most frequent infections were related to the urinary tract (48.2%), vascular catheter use (34.7%), and surgical site (24.7%). 64.6% of patients surveyed were treated with antibiotics, including a significant proportion (30%) of non-infected patients and a high proportion of self-medication (40.8%). Resistance of leading nosocomial pathogens to antimicrobials included methicillin-resistance (52.5%) among Staphylococcus aureus, vancomycin resistance among enterococci (67.5%), cefotaxime resistance among Escherichia coli (67.6%), and ceftazidime resistance among Acinetobacter baumannii (100%) and Pseudomonas aeruginosa (68.2%).

Conclusions

Benin has high nosocomial infection rates and calls for the implementation of new national infection control policies. Patient safety education and training of all individuals involved in healthcare delivery will be critical to highlight awareness of the burden of disease. The high use of antimicrobials needs to be addressed, particularly their indiscriminate use in non-infected patients.

Development and evaluation of a novel combinatorial selective enrichment and multiplex PCR technique for molecular detection of major virulence-associated genes of enterotoxigenic Staphylococcus aureus in food samples

AIMS

To develop a multiplex PCR assay coupled with selective enrichment step to detect major virulence-associated genes of enterotoxigenic Staphylococcus aureus and evaluate the same directly on contaminated food samples.

METHODS AND RESULTS

The most important virulence-associated genes of Staph. aureus, which are commonly related to food safety issues, are targeted in this study. They include five major enterotoxigenic genes-sea, seb, sec, seg and sei, tst-which encodes TSST-1, mecA-which confer methicillin resistance and coa-for the enzyme coagulase along with an internal amplification control (IAC) to rule out false-negative result. A modified mannitol salt broth (MSB) supplemented with sodium pyruvate was used for selective enrichment of Staph. aureus from food samples prior to PCR. Evaluation of efficiency of different media revealed that enrichment of samples in modified MSB followed by PCR resulted in specific, sensitive and effective amplification of the targeted genes in comparison with other enrichment media. Incorporation of bovine serum albumin (BSA) as PCR enhancer improved the intensity of amplicons. The standardized multiplex PCR (mPCR) format was able to detect all the target genes at a bacterial load of 10(6) CFU ml(-1) in any sample. The PCR results were unequivocally correlated with the conventional methods when the mPCR format was assessed on a total of 91 Staph. aureus isolates. The entire assay was found to be effectual when evaluated on naturally contaminated food samples.

CONCLUSIONS

The combinatorial approach involving selective enrichment followed by mPCR developed in this study was found to be effective for the detection of toxigenic Staph. aureus directly from various food sources.

SIGNIFICANCE AND IMPACT OF THE STUDY

The developed format would find a promising application in early detection of food contaminations as well as in the diagnosis of food poisoning due to Staph. aureus.

Strategies of adaptation of Staphylococcus epidermidis to hospital and community: amplification and diversification of SCCmec

OBJECTIVES

Staphylococcus epidermidis is a harmless commensal, but it can become a human pathogen, mainly in the hospital environment. In order to clarify strategies used by these bacteria to adapt to the hospital environment, we compared the population structure and staphylococcal cassette chromosome mec (SCCmec) content of S. epidermidis from the community and hospital.

METHODS

S. epidermidis were collected from nasal swabs of both healthy military draftees (192 isolates) and patients (94 isolates) recovered in the same time period and geographical region. S. epidermidis were characterized by PFGE, multilocus sequence typing and SCCmec typing.

RESULTS

Clonal complex 5 was predominant in the hospital (100%) and the community (58%), but some clonal types were specific to each environment and others were found in both (C/H clones). The methicillin-resistant S. epidermidis (MRSE) colonization rate in the community was very low (7%) when compared with the hospital (30%; P < 0.05). Community-associated MRSE carried mostly SCCmec IV and V [Simpson's index of diversity (SID) = 57.52%; 95% CI 38.35-76.69], whereas hospital-associated MRSE carried 17 SCCmec structures (SID = 82.67%; 95% CI 77.38-87.96). Isolates of the same PFGE type had a much higher number of different SCCmec types when collected in the hospital than in the community.

CONCLUSIONS

Our data suggest that the S. epidermidis population is composed of hospital-associated clonal types, community-associated clonal types and types that are able to survive in both environments. Moreover, adaptation to the hospital environment in S. epidermidis appears to promote an increase in the frequency and diversification of SCCmec.

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.

Molecular identification and characterization of mannitol-negative methicillin-resistant Staphylococcus aureus

We report on the isolation, molecular identification, and characterization of 5 mannitol-negative methicillin-resistant Staphylococcus aureus (MRSA) from clinical samples in KwaZulu-Natal (KZN) province, South Africa. Identification based on phenotypic testing and polymerase chain reaction detection of the S. aureus species-specific nuc gene and the coagulase gene indicated that the mannitol-negative isolates were S. aureus. Furthermore, they were mecA positive, and SCCmec typing demonstrated that all the isolates harbored type IV SCCmec. API STAPH (Biomerieux, Marcy-l'Etoile, France) misidentified 2 mannitol-negative MRSA that belonged to the major clone in KZN province, as Staphylococcus lugdunensis. Although the prevalence and mechanism of mannitol-negative MRSA is unknown, laboratories are encouraged to investigate S. aureus with atypical characteristics.

Staphylococcus aureus ampicillin-resistant from the odontological clinic environment

The aim of this research was to evaluate the prevalence of Sthaphylococcus spp. and S. aureus in the odontological clinic environment (air), their production of beta-lactamase and antibacterial susceptibility to the major antibiotics utilized in medical particle. During 12 months of samples collect were isolated 9775 CFU by MSA medium suggesting a high amount of Staphylococcus spp. in the clinic environment which can appear through aerosols. A total of 3149 colonies (32.2%) were suggestive of pathogenic staphylococci. Gram coloration, catalase test, colony-mallow growing on chromogenic medium, and coagulase test confirmed the identity of 44 (0.45%) S. aureus isolates. Of these, 35 isolates (79.5%) showed production of beta-lactamase by CefinaseTM discs and resistance to ampicillin, erythromycin (7 isolates) and tetracycline (1 isolate) suggesting the existence of multiresistant isolates. The evaluation of the oxacillin MIC by Etest® assays showed susceptibility patterns suggesting the inexistence of the mecA gene in chromosomal DNA. These results point out to the need of a larger knowledge on the contamination means and propagation of this microorganism into the odontological clinic.

Eradication of methicillin-resistant Staphylococcus aureus with an antiseptic soap and nasal mupirocin among colonized patients--an open uncontrolled clinical trial

BACKGROUND

Aim of the study was to determine the clinical efficacy of a new antiseptic liquid soap (Stellisept scrub), based on the combination of undecylenamidopropyltrimonium methosulphate (4%) and phenoxyethanol (2%), for eradication of MRSA among colonized patients who do not receive antibiotic therapy.

METHODS

Over two years 50 MRSA patients in 6 hospitals were observed. Treatment was defined as the daily application of Stellisept scrub for the antiseptic body and hair wash (at least 60 s) in combination with nasal mupirocin. A treatment cycle was a minimum of 5 days treatment. Screening was carried out at least 48 h after the treatment cycle was finished, with 24 h between each of the requested three or more samplings, which included the nasopharynx, groin, axilla, perineum and other MRSA-positive skin areas.

RESULTS

Fifteen cases were retrospectively excluded (lack of outcome documentation, concomitant antibiotic therapy, open wounds). All 35 patients had colonization with MRSA before antiseptic treatment on the skin, in the groin (80%), the axilla (25.7%), the perineum (20%) or other skin areas (14.3%). Colonization at more than one skin sites was found in 34.3%. Nasal colonization was found in 21 of 28 patients (75%), 7 patients were without nasal screening prior to the antiseptic treatment. After one treatment cycle MRSA was eradicated in 25 patients (71.4%), after a second cycle the total eradication rate was 91.4%, after a third cycle the rate increased to 94.2%. No patient discontinued the antiseptic treatment due to dermal intolerance of the product.

CONCLUSIONS

Progressive eradication of MRSA carriage was observed with the antiseptic soap and mupirocin. The eradication rate was not biased by concomitant antibiotic treatment, screening during treatment or lack of evidence for colonization in contrast to other studies with other preparations.

Inducibility and potential role of MecA-gene-positive oxacillin-susceptible Staphylococcus aureus from colonized healthcare workers as a source for nosocomial infections

To determine the carrier rate of methicillin-susceptible mecA-positive Staphylococcus aureus (dormant MRSA) among healthcare workers (HCWs), 447 nurses and physicians from 13 general wards and intensive care units were investigated for nasal or oropharyngeal S. aureus carriage during one year whenever an MRSA patient was treated. Induction of phenotypic resistance in all mecA-positive oxacillin-susceptible aureus was attempted by 24 h exposure to oxacillin and cefotaxime. Organisms from the broth tube with the highest antibiotic concentration and visible growth after incubation were re-exposed for a total of seven repetitive exposures. Two mecA-negative oxacillin-susceptible S. aureus served as negative control. A population analysis before and after antibiotic exposure was performed. A third of the HCWs were found to be S. aureus carriers. Only three nurses were MRSA positive (0.7%). Seven isolates of dormant MRSA were isolated in six nurses and one doctor (1.6%). After four days of repetitive antibiotic exposure six of seven dormant MRSA were highly resistant to oxacillin. Resistance of the two control S. aureus without the mecA gene was not changed by repetitive antibiotic exposure. Two of the seven dormant MRSA were clonally related as shown by pulsed-field gel electrophoresis (PFGE). The PFGE pattern of one dormant MRSA (HCW) was identical to an MRSA (HCW). The pattern of another dormant MRSA was indistinguishable from an MRSA isolated from a patient who was treated at the same time on the same ward suggesting transmission from the HCW to the patient. Dormant MRSA may be isolated twice as often as MRSA from HCWs. Transmission to patients is possible, which may lead to clinical infections. It might be useful to screen methicillin-susceptible S. aureus isolates from HCWs for the mecA gene when recurrent infections with MRSA occur on a ward and a source cannot be found.

Cost-effectiveness of different MRSA screening methods

We describe a model to examine the cost-effectiveness of various laboratory-screening approaches to detect methicillin-resistant Staphylococcus aureus (MRSA). A critical literature review was used to derive relevant data on the sensitivity (X), specificity (S) and time to result (T) of different tests. Additional cost information was provided by a hospital. Tests were considered in four interactive groups based on a hierarchy of procedures used in laboratories. X, S and Ts of screening tests were then used in formulae to calculate effectiveness for the various tests. The model was developed to explore the effects on MRSA infection acquisition of differing X, S and T for the different tests in detecting MRSA colonized patients admitted to a high-risk unit such as an intensive care unit. It was concluded that taking a sample from the nose alone and inoculating directly on to Ciprofloxacin Baird-Parker agar without broth incubation and confirmation by a Pastorex Staph-Plus test without any methicillin resistance confirmation test was the most cost-effective approach. The complexity of designing this apparently simple scenario is apparent, and we describe many other factors that would need to be considered to refine this model further. However, this and other models should aid the debate and development of more cost-effective screening strategies given the lack of standardization or agreement concerning so many of the variables within the UK and elsewhere.

Agar diffusion, agar dilution, Etest, and agar screening test in the detection of methicillin resistance in staphylococci

Methicillin resistant Staphylococcus is an important worldwide problem. Resistance is verified in strains harboring the mecA gene and laboratory methods used to detect resistance are object of constant investigation. In the present study, 99 clinical isolates of staphylococci (41 S. aureus, 33 S. epidermidis, 12 S. saprophyticus and 13 members of other species) were submitted to different phenotypic methods and conditions. Detection of the mecA gene by PCR was used as the reference method and detected 14/41, 10/33, and 10/25 isolates of S. aureus, S. epidermidis and other species, respectively. Results showed that, for S. aureus and S. epidermidis, agar diffusion, agar dilution, and the E test incubated during 24h at 35 degrees C correctly discriminated mecA positive from mecA negative isolates. For other species, all methods and conditions presented low specificity (ranging from 20% to 66.7%) and, particularly S. saprophyticus, may need molecular methods to correctly assess methicillin resistance.

Evaluation of a latex agglutination assay for rapid detection of oxacillin resistant Staphylococcus aureus

Oxacillin resistance in Staphylococcus aureus is mediated by the mecA gene, resulting in production of penicillin-binding protein 2a (PBP2a), which is not present in the oxacillin susceptible strains. We evaluated the ability of a 30-min latex agglutination (LA) test (Seiken, Tokyo, Japan) to detect production of PBP2a in 315 clinical isolates of S. aureus. The LA results were compared with results of susceptibility testing using the Vitek GPS-SV test card. The latex test was positive for all 206 isolates determined to be methicillin resistant by Vitek (sensitivity 100%), the latex test was negative for 108 of 109 isolates determined to be oxacillin susceptible by Vitek, and the latex test was positive for 1 isolate determined to be susceptible by Vitek (specificity 99.1%). The discrepant isolate was negative for the mecA gene by polymerase chain reaction (PCR). The LA test is a rapid and reliable method for detecting oxacillin resistant S. aureus.

Comparison of susceptibility testing methods with mecA gene analysis for determining oxacillin (methicillin) resistance in clinical isolates of Staphylococcus aureus and coagulase-negative Staphylococcus spp

Ninety-nine clinical staphylococcal isolates (58 coagulase-negative Staphylococcus spp. [CoNS] and 41 Staphylococcus aureus isolates) were evaluated for susceptibility to oxacillin. The following susceptibility testing methods, media, and incubation conditions were studied: agar dilution by using Mueller-Hinton (MH) medium (Difco) supplemented with either 0, 2, or 4% NaCl and incubation at 30 or 35 degrees C in ambient air for 24 or 48 h; disk diffusion by using commercially prepared MH medium (Difco) and MH II agar (BBL) and incubation at 35 degrees C in ambient air for 24 or 48 h; and agar screen (spot or swab inoculation) by using commercially prepared agar (Remel) or MH agar (Difco) prepared in-house, each containing 4% NaCl and 6 microg of oxacillin/ml (0.6-microg/ml oxacillin was also studied with MH agar prepared in-house for the agar swab method and CoNS isolates) and incubation at 35 degrees C in ambient air for 24 or 48 h for swab inoculation and at 30 or 35 degrees C in ambient air for 24 or 48 h for spot inoculation. The results for these methods were compared to the results for mecA gene detection by a PCR method. Given the ability to support growth and the results for susceptibility testing (the breakpoint for susceptible isolates was </=2 microg/ml), the best methods for CoNS isolates were (i) agar dilution by using MH medium supplemented with 4% NaCl and incubation at 35 degrees C for 48 h (no growth failures were noted, and sensitivity was 97.6%) and (ii) agar screen (swab inoculation) by using MH medium prepared in-house supplemented with 4% NaCl and containing 0.6 microg oxacillin/ml and incubation at 35 degrees C for 48 h (one isolate that did not carry the mecA gene did not grow, and the sensitivity was 100%). All but one (agar dilution without added NaCl and incubation at 30 degrees C for 48 h) of the methods tested revealed all oxacillin-resistant S. aureus isolates, and no growth failures occurred with any method. If the breakpoint for susceptibility was lowered to </=1 microg/ml for agar dilution methods, more CoNS isolates with oxacillin resistance related to the mecA gene were detected when 0 or 2% NaCl agar supplementation was used. Only one CoNS isolate with mecA gene-associated resistance was not detected by using agar dilution and MH medium supplemented with 4% NaCl with incubation for 48 h. When the breakpoint for susceptibility was decreased 10-fold (from 6.0 to 0.6 microg of oxacillin per ml) for the agar swab screen method, fully 100% of the CoNS isolates that carried the mecA gene were identified.

Methicillin-resistant Staphylococcus aureus infections in 11 dogs

Methicillin-resistant Staphylococcus aureus infection was identified in 11 dogs. The infection was associated with surgical treatment especially orthopaedic surgery. Infection after traumatic wounding, and recurrent pyoderma was also seen. Oral antibiotic treatment improved or resolved the infection in nine of the 11 dogs, although the methicillin-resistant isolates were susceptible to relatively few antibiotics.