Oxacillin Agar Screen Research Articles

Methicillin Resistant Staphylococcus aureus Carriage, Antibiotic Resistance and Molecular Pathogenicity among Healthy Individuals Exposed and Not Exposed to Hospital Environment.

Healthcare workers as well as healthy community-dwelling individuals may be colonised by methicillin-resistant Staphylococcus aureus (MRSA). Healthcare workers who carry MRSA may transmit it to patients, causing various nosocomial infections. Literature shows that the differences between MRSA isolated from healthcare settings and from community settings, with regard to multi-drug resistance (traditionally exhibited by the former) and possession of pvl genes (traditionally exhibited by the latter), is diminishing due to a large community reservoir and increasing influx of community harboured strains into the hospital. However, there is no literature on the current scenario in India. This study examines the influence of exposure to hospital environment on MRSA carriage, antimicrobial resistance patterns of MRSA, and the presence of genes encoding five extracellular pathogenicity determinants (pvl, sea, seb, tsst-1 and hly a). Nasal, throat and palmar swabs were collected from 119 nursing students of the age group 18-23 years (exposed group) and 100 age matched pharmacy students (non-exposed group). S. aureus was identified and antibiogram obtained as per Clinical and Laboratory Standards Institute (CLSI) guidelines. MRSA was detected by cefoxitin disc diffusion test and by growth on oxacillin screen agar as per CLSI guidelines. Conventional PCR was performed for mecA, pvl, sea, seb, tsst-1 and hly a. The differences in carrier rates, antibiotic resistance patterns and expression of extracellular pathogenicity determinants between MRSA isolates from the two study groups were not significant, and pvl was found in all the MRSA isolates. The nursing students carried MRSA strains similar to those carried by the non-exposed group. Our results suggest that healthcare workers could act as a link and transmit MRSA acquired from the community to patients.

English

The emergence of heterogeneous populations of methicillin-resistant Staphylococcus aureus (MRSA) causes major problems in routine screening for MRSA. Cefoxitin is a potent inducer of the mecA regulatory system and can be use for detection of heterogeneous populations of MRSA. Detection of the mecA gene by PCR was considered to be the “gold standard”. In this study we determined the sensitivity and specificity of the oxacillin disk diffusion test, cefoxitin disk diffusion test and oxacillin agar screening for detection of MRSA. A total of 124 non-duplicate isolates of S. aureus were included in the study. Methicillin resistance was measured using oxacillin (1μg) and cefoxitin(30μg) disc diffusion method and oxacillin agar screening test (6 mg/ml oxacillin) according to CLSI guideline and PCR for the mecA gene. Compared with the molecular detection of methicillin resistance the overall sensitivities and specificities of the phenotypic tests for cefoxitin disc diffusion were 100%, for oxacillin disc diffusion were 91.7 and 92.8% and for oxacillin agar screening were 95 and 95.5%, respectively. We concluded that in the absence of availability of molecular biology techniques, the cefoxitin disc was the best detector of methicillin resistance in S. aureus related to the other phenotypic tests.   Key words: Methicillin-resistant Staphylococcus aureus, mecA, Cefoxitin, polymerized chain reaction

Incidence of constitutive and inducible clindamycin resistance among hospital-associated Staphylococcus aureus.

Clindamycin is one of the important alternative antibiotics in the therapy of Staphylococcus aureus infections. Clinical failure of clindamycin therapy has been reported due to multiple mechanisms that confer resistance to macrolides, lincosamides and Streptogramin B (MLSB) antibiotics. In vitro routine tests for clindamycin susceptibility may fail to detect inducible clindamycin resistance due to erm genes, resulting in the treatment failure. Although data from the developed countries have shown to be enormity of the problem, data from the developing countries are lacking. The aim of the study was to distinguish different resistance phenotypes in erythromycin-resistant S. aureus by a simple double-disc diffusion test (D test). A total of 153 S. aureus isolates were subjected to routine antibiotic susceptibility testing, including cefoxitin disc (30 μg) and by oxacillin screen agar. Inducible clindamycin resistance was tested by ‘D test’ as per CLSI guidelines. Odds ratios (OR) and 95 % confidence intervals (95 % CI) were calculated. P values were calculated using SPSS (version 18). Among 153 S. aureus isolates, 42 (27.45 %) were resistant to methicillin, whereas 111 (72.54 %) were methicillin susceptible. Out of the 63 (41.17 %) erythromycin-resistant S. aureus isolates, 14 (9.15 %) showed inducible resistance [P = 0.0002, odds ratio (OR) 18.30; 95 % confidence interval (CI) 8.72–25.77), 20 (13.07 %)] showed constitutive resistance (P = 0.002, OR 14.38, 95 % CI 5.33–21.49), while the remaining 29 (18.95 %) showed inducible phenotype. Inducible and constitutive resistance was found to be higher in MSSA when compared with MRSA. Clinical laboratories should perform D test routinely to guide the clinicians about the inducible clindamycin resistance and to prevent misuse of antibiotics.

English

BACKGROUND: Methicillin Resistant Staphylococcus aureus (MRSA) has emerged as one of the most important nosocomial pathogen. Its remarkable ability to develop resistance to a variety of antibiotics makes it a major threat to public health. OBJECTIVES: - To detect the prevalence and in vitro antimicrobial susceptibility pattern of the MRSA isolates. MATERIALS & METHODS: - 202 Staphylococcus aureus strains isolated from clinical samples like blood, pus, sputum & body fluids were screened for Methicillin resistance by standard disk diffusion method and then confirmed with Oxacillin Screening agar. Antibiotic susceptibility of both the MRSA and Methicillin sensitive Staphylococcus aureus (MSSA) for other antibiotics was subsequently carried out by standard disc diffusion method. RESULTS: Methicillin resistance was detected in 114 strains of Staphylococcus aureus giving a prevalence rate of 56.44%. More than 80% of the MRSA isolates were resistant to antibiotics such as Penicillins, Cephalosporins, Aminoglycosides, Macrolides and Quinolones. All strains were uniformly sensitive to Vancomycin & Linezolid. Coexisting resistance to most of the antibiotics was significantly higher in the MRSA isolates as compared to the MSSA (Methicillin sensitive Staphylococcus aureus) isolates (p < 0.001). INTERPRETATION & CONCLUSIONS: Multi drug resistance among the MRSA isolates poses a major hurdle in treating systemic infections. Monitoring antibiotic sensitivity pattern, implementing aggressive surveillance measures & good infection control practices would be helpful in reducing the prevalence of MRSA and its multi drug resistance.

Prevalence and Antimicrobial Susceptibility Pattern of Methicillin-Resistant Staphylococcus aureus and Coagulase-Negative Staphylococci in Rawalpindi, Pakistan

Methicillin resistant Staphylococcus aureus(MRSA) and methicillin resistant coagulase negative staphylococci (MRCoNS) are the important nosocomial infectious agents. There is a growing concern about the rapid rise in the resistance of Staphylococcus aureusto presently available antimicrobial agents. The aim of this study was to evaluate the prevalence rate of MRSA and MRCoNS and their rate of resistance to different antistaphylococcal antibiotics used broadly for treatment. Out of the total 350 staphylococcal isolates from different clinical specimens 148 isolates (60.40%) were identified as MRSA by oxacillin screen agar method, and 46 isolates (43.80%) were screened as MRCoNS. All the MRSA and MRCoNS isolates were tested for antibiotic resistance pattern by disc diffusion method for 16 different antibiotics. All the isolates of

Changing Trends in Resistance Pattern of Methicillin Resistant Staphylococcus aureus

Methicillin resistance in Staphylococcus aureus is associated with multidrug resistance, an aggressive course, increased mortality and morbidity in both community and health care facilities. Monitoring of newly emerging and prevalent Methicillin Resistant Staphylococcus aureus (MRSA) strains for their resistance patterns to conventional as well as novel drugs, are essential for infection control. To study the changing trends in resistance patterns of MRSA at our hospital. This cross sectional study was carried out in a 750 bed tertiary care hospital in south India. One hundred and two clinical isolates of MRSA which were obtained in 2004-2011 were identified by using oxacillin, cefoxitin disc diffusion test and oxacillin screening agar test. Antibiotic susceptibility test was done for commonly used non beta lactam anti-Staphylococcal drugs, as well as for anti-MRSA drugs like vancomycin, linezolid, mupirocin and rifampicin. Minimum inhibitory concentration (MIC) of vancomycin was determined by using Vancomycin HiComb strip (Himedia, Mumbai, India). Statistical Analysis which was done: Chi-square test and proportions were used to compare the two groups. MRSA isolates showed high resistance to co-trimoxazole (82.3%), ciprofloxacin (76.4%), gentamicin (64.7%) and tetracycline (49%) as compared to other drugs. High prevalence of ciprofloxacin resistance was detected, particularly among outpatients. Multi resistant MRSA with a ≥ 3 non-beta lactam agent resistance was 79%. All MRSA isolates were sensitive to vancomycin, linezolid, mupirocin and rifampicin. MRSA had displayed increase in resistance to most antibiotics except tetracycline in recent years. Taking into consideration the prevalence of multidrug resistance in MRSA, resistance patterns should be evaluated periodically and antibiotic therapy should be guided by susceptibility testing.

Antimicrobial resistance profile of Staphylococcus aureus isolates obtained from skin and soft tissue infections of outpatients from a university hospital in Recife -PE, Brazil

BACKGROUNDStaphylococcus aureus has a notable ability to acquire resistance to antibiotics, and methicillin resistance represents a growing public health problem. Methicillin-resistant S. aureus (MRSA) has also become important outside the hospital environment, particularly in the United States. In Brazil, since 2005, cases of community skin infections caused by MRSA have been reported, but resistance studies involving outpatients are scarce.OBJECTIVETo know the resistance profile of S. aureus involved in skin and soft tissue infections of patients seen at the Dermatology outpatient clinic of a university hospital in Recife, Pernambuco State, northeastern Brazil. METHODSProspective study involving 30 patients with skin and soft tissue infections, seen at the Dermatology outpatient clinic from May until November 2011. To evaluate the susceptibility of S. aureus to antibiotics, the disk diffusion method and oxacillin screening agar were used. RESULTSFrom a total of 30 samples of skin lesions, 19 (63%) had positive culture for S. aureus. The following resistance patterns of S. aureus were observed: penicillin, 95%; tetracycline, 32%; erythromycin, 21%; gentamicin, 16%; cefoxitin, 11%; oxacillin, 11%; trimethoprim-sulfamethoxazole, 11%; chloramphenicol, 11%; clindamycin, 5% ; and ciprofloxacin, 0%. One of the identified MRSA was obtained from a patient without risk factors for its acquisition, and was resistant, beyond to the beta-lactams, only to tetracycline. CONCLUSIONSWith regard to the resistance patterns of S. aureus, resistances to tetracycline, erythromycin and gentamicin were the highest. It was documented, for the first time in Pernambuco, a case of skin infection caused by community-associated MRSA.

Comparison of five methods for oxacillin susceptibility testing of Staphylococcus aureus isolates from cystic fibrosis patients

Methicillin-resistant Staphylococcus aureus (MRSA) are now a worldwide problem. Cystic fibrosis (CF) patients are commonly colonized and infected by MRSA. Accurate oxacillin susceptibility testing is mandatory for the adequate management of these patients. We performed a comparison of the accuracy of different tests in CF isolates, including methicillin-susceptible S. aureus and MRSA with different SCCmec types, and using the mecA gene as the gold-standard. The sensitivity and specificity of oxacillin disc, Etest, and oxacillin agar screening plate were 100%. Sensitivity of the cefoxitin disc was 85% and specificity was 100%. For clinically relevant isolates, laboratories may consider the use of a combination of two phenotypic methods.

Incidence and antibiotic susceptibility of methicillin resistant Staphylococcus aureus in pus samples of patients of Bastar region, Central India

Increasing prevalence of methicillin resistant S. aureus (MRSA) and resistanceto multiple antibiotic classes is a global issue. Regional surveillance of antibiotic susceptibility of the organism is a necessary step to overcome the issues of antimicrobial resistance and treatment failure in MRSA infections. The study was conducted to find the pattern of antibiotic susceptibility in MRSA isolated from the pus samples of patients attending a tertiary care hospital in Bastar tribal region in Central India. The study was performed on 215 MRSA isolates cultured from pus samples of patients over a period of two years and five months. In the methicillin resistant organisms selected by oxacillin screen agar test and cefoxitin disk diffusion test, antibiotic susceptibility was determined by Kirby Baur disk diffusion test with CLSI guide lines. Of the total S. aureus isolates, the incidence of MRSA was 34.1% of which 82.8% were resistant to co‐trimoxazole, 77.2% to tetracycline, 68.8% to gentamycin, 66% to erythromycin, 64.2% to ciprofloxacin, 1.4% to vancomycin, and 0.9% to linezolid. All these isolates were resistant to the ß‐lactam antibiotics tested. Emergence of linezolid resistance and relatively higher vancomycin resistance in the MRSA isolates is a worrisome finding of this study. The antibiotic prescribing must rely on both initial empirical therapy and microbiological antibiotic susceptibility result.

Comparison of Agar screen and duplex-PCR methods in determination of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from nasal carriage

Methicillin-resistant Staphylococcus aureus strains (MRSA) have become a serious health issue in engendering nosocomial infections. Due to the heterogeneity of this type of resistance, the conventional antibiotic susceptibility tests may fail to detect MRSA strains. The purpose of this research was to compare the phenotypic agar screen method with polymerase chain reaction (PCR) for detection of MRSA strains isolated from the nasal samples of hospital personnel. Totally, 52 coagulase positive S. aureus strains were isolated from nasal samples of 204 hospital personnel of Hajar Hospital affiliated to Shahrekord University of Medical Sciences. Susceptibility to oxacillin in the strains was evaluated by the phenotypic agar screen method. The presence of the methicillin resistance gene, mec A, was studied through duplex PCR method. The results of both methods were compared and the sensitivity and specificity of the methods were determined. Totally, 23 out of the 52 isolated S. aureus (44%) were phenotypically resistant to oxacillin, but 27 (52%) carried mecA gene. The sensitivity and specificity of the phenotypic agar screen method for determination of MRSA strains were found to be 81.5 and 96%, respectively. As compared to duplex PCR, oxacillin agar screen method is a simple, inexpensive, and practical phenotypic method with relatively low false positive results and thus may be suitable for verification of suspicious MRSA strains. However, for the relatively high false negative results, it may not be recommended for the primary screening of MRSA strains from the nasal samples of healthy carriers working at hospitals. Key words: Nosocomial infections, methicillin resistance Staphylococcus aureus(MRSA), polymerase chain reaction (PCR)

Methicillin-resistant Staphylococcus aureus bloodstream infection: risk factors and clinical outcome in non-intensive-care units

Methicillin-resistant Staphylococcus aureus (MRSA) is spread out in hospitals across different regions of the world and is regarded as the major agent of nosocomial infections, causing infections such as skin and soft tissue pneumonia and sepsis. The aim of this study was to identify risk factors for methicillin-resistance in Staphylococcus aureus bloodstream infection (BSI) and the predictive factors for death. A retrospective cohort of fifty-one patients presenting bacteraemia due to S. aureus between September 2006 and September 2008 was analysed. Staphylococcu aureus samples were obtained from blood cultures performed by clinical hospital microbiology laboratory from the Uberlândia Federal University. Methicillinresistance was determined by growth on oxacillin screen agar and antimicrobial susceptibility by means of the disk diffusion method. We found similar numbers of MRSA (56.8%) and methicillin-susceptible Staphylococcus aureus (MSSA) (43.2%) infections, and the overall hospital mortality ratio was 47%, predominantly in MRSA group (70.8% vs. 29.2%) (p=0.05). Age (p=0.02) was significantly higher in MRSA patients as also was the use of central venous catheter (p=0.02). The use of two or more antimicrobial agents (p=0.03) and the length of hospital stay prior to bacteraemia superior to seven days (p=0.006) were associated with mortality. High odds ratio value was observed in cardiopathy as comorbidity. Despite several risk factors associated with MRSA and MSSA infection, the use of two or more antimicrobial agents was the unique independent variable associated with mortality.

Research Article: Prevalence of MRSA on meat products in central Kentucky

Abstract. Methicillin-resistant Staphylococcus aureus (MRSA) was isolated from 10 (18.5%) of 54 meat samples collected in central Kentucky. Meat specimens were collected from six local markets in the central Kentucky region. MRSA found in meat samples may be a possible source for community-associated infections of MRSA. There were nine samples obtained from each location (18 pork, 18 beef, and 18 processed meats). The specimens were placed on ice for transport to the lab where they were individually processed using an aseptic technique. Meat samples were streaked for isolation on mannitol salt agar plates (MSA) and placed in 7% salt enrichment broth upon arrival in the laboratory. MSA isolates that fermented mannitol were tested for the presence of Staphylococcus aureus (S. aureus) with the coagulase and d-trehalose fermentation test. S. aureus isolates were placed on the oxacillin agar screen test (Mueller Hinton Agar with 6 μg/mL oxacillin and 4 % NaCl) to determine if MRSA was present. The positive spe...

Comparison of an automated system with four phenotypic methods for the detection of methicillin-resistant Staphylococcus aureus

Correct and rapid detection of methicillin resistance in Staphylococcus aureus is very important for treatment of infected patients. Detection of the mecA gene or PBP2a by polymerase chain reaction (PCR) is considered the gold standard for determination of methicillin resistance in staphylococci. In most clinical laboratories, phenotypic methods are used for the detection of methicillin resistance in S. aureus because PCR is not suitable for routine usage. In this study, we aimed to compare different phenotypic methods: disk diffusion, agar screening, latex agglutination and an automated system employed to establish the presence of methicillin-resistant S. aureus (MRSA). Presence of the mecA gene via PCR was used as the marker for MRSA positivity. Afterward, 214 samples were analyzed for methicillin resistance via oxacillin or cefoxitin disk diffusions, oxacillin agar screening, MRSA latex agglutination and the automated BD Phoenix system. Sensitivity, specificity, negative and positive predictive values of these phenotypic methods were evaluated. In the detection of MRSA, the cefoxitin disk-diffusion method was found to be more useful than oxacillin disk diffusion. The automated MRSA strain-detection system was found to be more successful than the other phenotypic methods. These results showed that the automated system could be used safely for routine MRSA detection. Key words: Phoenix, cefoxitin disk diffusion, mecA, oxacillin, methicillin-resistantStaphylococcus aureus, latex agglutination.

Evaluation of various methods for the detection of meticillin-resistant Staphylococcus aureus strains and susceptibility patterns

Meticillin-resistant Staphylococcus aureus (MRSA) has been recognized as one of the major pathogens in hospital as well as community settings. In India, the mean isolation rate of MRSA is 20-40 % and many studies have suggested an escalating rate of infections caused by this organism. Despite pharmaceutical and technological advancement, infections caused by MRSA still remain difficult to diagnose. The present study was undertaken to compare five phenotypic methods for the detection of MRSA. This involved examining 200 isolates of S. aureus by oxacillin disc diffusion, cefoxitin disc diffusion, oxacillin screen agar test, the latex agglutination test and growth on CHROMagar. PCR for mecA gene detection was taken as the gold standard. It was found that 35 % of all S. aureus infections were caused by MRSA. The cefoxitin disc diffusion method, as recommended by the Clinical and Laboratory Standards Institute, was found to be a reliable method for MRSA detection but it should be supplemented with some other method like latex agglutination, CHROMagar or oxacillin screen agar testing so that no MRSA is missed. We recommend that along with cefoxitin disc diffusion, another method, preferably latex agglutination, should be routinely used in all hospitals to detect MRSA.

Biochemical characters and antibiotic susceptibility of Staphylococcus aureus isolates

Objective To observe the biochemical characters and antibiotic susceptibility of isolated Staphylococcus aureus (S. auerus) strains against some conventional and traditional antibiotics. Methods Thirty post operative pathogenic isolated S. aureus strains were used in this study. Bacterial culture was done in Mueller-Hinton broth at 37 °C. Characters of these strains were determined by traditional biochemical tests such as hydrolysis test of gelatin, urea, galactose, starch and protein, and fermentation of lactose and sucrose. Antibiotic susceptibility were carried out by minimum inhibitory concentration test, minium bactericidal concentration test, disc agar diffusion test and brain heart infusion oxacillin screening agar. Results From this study, it was observed that 100% S. aureus isolates showed positive results in gelatin, urea and galactose hydrolysis test, 50% isolates were positive in starch hydrolysis test, 35% in protein hydrolysis test, 100% isolates in lactose fermenting test, but no isolate was positive in sucrose fermenting test. Antibiotic susceptibility testing suggested that 20% of isolates were resistant to kanamycin and 46.67% were resistant to oxacillin. Conclusions These findings show that all these isolates have gelatin, urea, galactose hydrolysis and lactose fermenting activity. 20% of these isolates were resistant to kanamycin and 46.67% were resistant to oxacillin.

Genotypic and Phenotypic Characterization of Methicillin-Susceptible Staphylococcus aureus Isolates Misidentified as Methicillin-Resistant Staphylococcus aureus by the BD GeneOhm MRSA Assay

Twenty-three nasal swab samples that tested positive for methicillin-resistant Staphylococcus aureus (MRSA) on initial testing by the BD GeneOhm MRSA assay (BD-MRSA PCR; BD GeneOhm, San Diego, CA) were culture positive only for methicillin-susceptible S. aureus (MSSA) from an enrichment broth. The 23 recovered isolates were confirmed as MSSA by a variety of phenotypic methods, including the BD Phoenix automated microbiology system (BD Diagnostics, Sparks, MD), oxacillin screening agar (BD Diagnostics), BBL CHROMagar MRSA (BD Diagnostics), and a PBP2' assay (Denka Seiken Co., Tokyo, Japan); susceptibilities were determined by using Mueller-Hinton agar with oxacillin. All were positive by nuc PCR, specific for S. aureus, but negative for mecA with one exception. Isolates were characterized by using multiplex PCR methodology to determine structural types and variants (SCCmec typing); additional PCRs were performed for the detection of the ccr and mec complexes, the junkyard regions as well as the Panton-Valentine leukocidin. Pulsed-field gel electrophoresis was used to determine clonality. One phenotypic MSSA isolate contained an intact SCCmec. Twelve MSSA isolates tested positive for MRSA by the BD-MRSA PCR because of amplification of the mec priming site flanking the SCC insertion point, although these isolates lacked mecA. The 10 remaining isolates were not MRSA and tested as MSSA by phenotypic and genotypic assays. In our patient population, diagnostic and surveillance testing and subsequent infection control practices may be impacted by the frequency of these excision events when using the BD-MRSA PCR for MRSA detection.

Accuracy of phenotypic methicillin susceptibility methods in the detection of Staphylococcus aureus isolates carrying different SCCmec types

A total of 138 isolates, 118 methicillin-resistant Staphylococcus aureus (MRSA) isolates (staphylococcal cassette chromosome type II, 20 isolates, type III, 39 isolates and type IV, 59 isolates) and 20 methicillin-sensitive S. aureus isolates were evaluated by phenotypic methods: cefoxitin and oxacillin disk diffusion (DD), agar dilution (AD), latex agglutination (LA), oxacillin agar screening (OAS) and chromogenic agar detection. All methods showed 100% specificity, but only the DD tests presented 100% sensitivity. The sensitivity of the other tests ranged from 82.2% (OAS)-98.3% (AD). The LA test showed the second lowest sensitivity (86.4%). The DD test showed high accuracy in the detection of MRSA isolates, but there was low precision in the detection of type IV isolates by the other tests, indicating that the genotypic characteristics of the isolates should be considered.

Phenotypic methods of greater accuracy to detect the mecA gene product for the recognition of MRSA in resource constraint settings

Objective To evaluate the detection of methicillin resistant Staphylococcus aureus (MRSA) and analyze the performance of Mastalex MRSA (Mast, UK). Methods Two hundred and ten Staphylococcus aureus (S. aureus) strains were isolated from different clinical samples and were tested for methicillin resistance by Oxacillin (1 μg) and Cefoxitin (30 μg) disc diffusion, oxacillin agar screen, and minimum inhibitory concentration of oxacillin and cefoxitin. S. aureus isolates were grown on the blood agar and mannitol salt agar with (2 mg/L) and without oxacillin for the analysis of Mastalex MRSA. Results Out of 210 S. aureus strains tested, 103 strains were detected as methicillin resistant by Cefoxitin disk diffusion, Cefoxitin minimal inhibitory concentration (MIC) and Mastalex MRSA test. Whereas oxacillin disc diffusion and oxacillin agar screen detected 91 and 97 MRSA respectively. The Cefoxitin MIC test performance was equivalent to Cefoxitin disc diffusion. 103 (100%) strains grown on blood agar without and with oxacillin, and 76 (74%) and 93 (91%) strains grown on mannitol salt agar without and with oxacillin shown positive agglutination with Mastalex MRSA test respectively. Conclusions The cefoxitin disk diffusion/Mastalex MRSA is very suitable for detection of MRSA and the tests can be an alternative to PCR for detection of MRSA in resource constraint settings. Mastalex test would be particularly useful when confirmation of resistance is urgently required.

Prevalence of Methicillin-resistant Staphylococcus Aureus (MRSA) in a Tertiary Care Hospital in Northern India

Aim:The emergence of Methicillin-resistant Staphylococcus aureus (MRSA) has posed a serious therapeutic challenge. We report the prevalence and antibiotic susceptibility pattern of MRSA in the hospitals attached to GMC, Amritsar, Punjab.Materials and Methods:The study comprised of 250 coagulase-positive staphylococci (COPS) isolated from a total of 6743 clinical specimens (like pus, blood, urine, high vaginal swab, sputum, etc.) of patients admitted in hospitals attached to Government Medical College, Amritsar from January 2008–February 2009. Routine antibiotic susceptibility testing was performed and interpreted as per standard guidelines. Methicillin resistance was detected using oxacillin and cefoxitin disc diffusion method, oxacillin screen agar method, and minimum inhibitory concentration using broth macrodilution method.Results:A total of 115 (46%) strains were found to be methicillin resistant. Multidrug resistance was observed in 73% MRSA strains. However, no strain was resistant to vancomycin.Conclusion:Regular surveillance of hospital-associated infection and monitoring of antibiotic sensitivity pattern is required to reduce MRSA prevalence.

Avaliação de métodos comumente usados em laboratórios para a determinação da suscetibilidade à oxacilina entre amostras de Staphylococcus sp, isoladas de um hospital de Vitória, Estado do Espírito Santo

The genus Staphylococcus is of great importance because of its high prevalence in hospital infections and because it presents high rates of resistance to oxacillin and other antimicrobials. Thus, evaluation of the accuracy of the phenotypic methods that are used to determine the profile of antimicrobial resistance is essential to ensure that the most appropriate therapy is chosen. One hundred and fourteen strains of Staphylococcus sp (53 S. aureus and 61 CNS) were used to evaluate the accuracy of the methods of disk diffusion, agar microdilution, oxacillin screening agar and automated systems, in comparison with PCR for investigating resistance to oxacillin. The mecA gene was detected in 48 strains (42.1%), and 27 strains (23.7%) showed discrepant results in at least one of the methods (74.1% of CNS, 25.9% of S. aureus). For S. aureus, with the exception of the Microscan Walkaway, all the methods showed 100% specificity and sensitivity. In relation to CNS, the automated system and cefoxitin disk had lower accuracy. Use of two methods should be the best option for improved accuracy, especially when the diagnostic laboratory only uses an automated system or oxacillin disk diffusion test. Combination of these methods with others presented almost 100% sensitivity and specificity in our study.