Μg Disc Research Articles

Inducible Clindamycin Resistance in Clinical Isolates of Staphylococcus aureus

Background: Staphylococcus aureus is one of the most important agents causing nosocomial infections. Inducible clindamycin resistance is an important concern, because common laboratory tests could not detect it. Objectives: The aim of this study was to detect the inducible clindamycin resistance by D-test method. Materials and Methods: A total of 209 clinical S. aureus isolates were collected and identified by conventional phenotypic tests. Antibiotic susceptibility pattern was detected by disc diffusion method. D-test was done using clindamycin (2 μg) and erythromycin (15 μg) discs according to the protocols of Clinical and Laboratory Standards Institute (CLSI). To detect methicillin resistant Staphylococcus aureus (MRSA), oxacillin disc was used and the results were confirmed by detection of mecA gene. Results: Of all 209 clinical S. aureus isolates, 207 (99%) were resistant to amoxicillin. All isolates were susceptible to vancomycin and linezolid. The rate of clindamycin inducible resistance was 4% (n = 8). This phenotype was not observed in MRSA strains. There was no significant difference between methicillin resistant and susceptible strains. Resistance to clindamycin and erythromycin was higher in MRSA strains. D+ phenotype was detected in 1 (1%) of all isolates. Methicillin resistance was detected in 66 (32%) isolates by oxacillin disc and mecA gene was detected by PCR. Conclusions: In our study, inducible clindamycin resistance rate was 4%; so it is necessary to conduct D-test regularly by disc diffusion for this bacterium. Resistance to erythromycin, clindamycin, ciprofloxacin and gentamicin was significantly higher in MRSA isolates than methicillin susceptible Staphylococcus aureus (MSSA), although the methicillin resistance prevalence was low.

Mupirocin resistant staphylococcus aureus nasal colonization among healthcare workers.

Mupirocin resistant staphylococcus aureus nasal colonization among healthcare workers.

Prevalence of Multidrug Resistant Enterococci in a Tertiary Care Hospital in India: A Growing Threat

Introduction: Enterococci are members of the healthy human intestinal flora, but are also leading causes of highly antibiotic-resistant infections. Serious enterococcal infections are often difficult to treat since the organisms have a tremendous capacity to acquire resistance to penicillin, high concentration of aminoglycoside & vancomycin. Careful review of in vitro susceptibility data is required to treat infections caused by MDR Enterococci. Therefore we conducted the study to find out prevalence of MDR Enterococci. Aims & Objectives: To study the prevalence of Vancomycin resistance, High Level Streptomycin Resistance (HLSR) & High Level Gentamicin Resistance (HLGR) in different enterococcal isolates. Materials & Methods: Total 180 enterococcal isolates were studied. Identification was done by conventional biochemical methods. Antibiotic susceptibility testing was done by Kirby-Bauer disc diffusion method on Mueller–Hinton agar and results were interpreted as per CLSI guidelines. HLSR & HLGR was determined by disc diffusion method using high level Gentamicin disc (120 μg) & Streptomycin (300 μg) discs. Minimum inhibitory concentration (MIC) determination for Vancomycin was done by vancomycin E test strips. Results: Total 180 entetococcal isolates were studied. E. faecalis was 60%, E. faecium was 32.2%, E. durans and E. raffinosus were 4.4% & 3.3% respectively. Enterococcus fecium showed resistance in high percentage as compared to E. faecalis. 15 isolates were found to be vancomycin resistant. Conclusion: Resistance to aminoglycoside is of great concern. Regular screening of enterococcal isolates for vancomycin resistance detection should be implemented. It is very important to implement infection control measures, screening of health care workers, surveillance cultures in intensive care units which can control spread of multidrug resistant enterococci.

Changing Trends of Vulvovaginal Candidiasis

Introduction:Vulvovaginal candidiasis is one of the most common infections seen in women.Materials and Methods:A total of 300 symptomatic women were studied. High vaginal swabs collected from each patient were processed by Gram stain, culture on Sabourauds dextrose agar and CHROM agar plates. Isolates were identified and speciated using conventional methods and by the color of the colonies on the CHROM agar. Antifungal susceptibility was performed by disc diffusion method for fluconazole (25 μg) and voriconazole (1 μg) discs as per Clinical and Laboratory Standards Institute (CLSI) guidelines.Results:Vulvovaginal candidiasis was found in 53 (17.7%) of cases. Gram stain was positive in 22 (41.41%) of culture positives. Speciation of isolates by conventional and CHROM agar methods showed similar results. C. albicans 35 (66.0%) was the most common species isolated followed by C. tropicalis 14 (26.4%), C. krusei 2 (3.8%), C. parapsilosis and C. glabrata in 1 (1.9%) case each. Sensitivity to fluconazole was found in 91.4% of C. albicans, 57.1% of C. tropicalis and 50.0% of C. krusei. Sensitivity to voriconazole was seen in 91.4% of C. albicans, 85.7% of C. tropicalis and 50.0% of C. krusei. C. parapsilosis and C. glabrata were found sensitive only to voriconazole.Conclusion:CHROM agar has the advantage of being rapid, simple and cost effective method as compared to conventional methods in speciation of Candida. Routine susceptibility testing of Candida isolates help in selecting the most appropriate antifungal agent for vulvovaginal candidiasis.

Antimicrobial Susceptibility Patterns of Methicillin-Resistant Staphylococcus aureus Isolates Collected from Healthcare and Community Facilities in Libya Show a High Level of Resistance to Fusidic Acid

Staphylococcus aureus is an important human pathogen and is implicated in a wide variety of infections in the healthcare and community settings. The organism is often subcategorized as community-associated MRSA (CAMRSA) or health care-associated MRSA (HA-MRSA). Five hundred and eleven S. aureus strains were isolated from clinical specimens submitted to the microbiology laboratories at Tripoli Central Hospital, Tripoli Trauma/ Accident Hospital, Tripoli Medical Centre and Tripoli Burn Hospital between October 2009 and November 2010. MRSA was detected using cefoxitin (30 μg) disc and antibiotic susceptibility pattern was determined using the Kirby and Bauer disc diffusion susceptibility testing method and confirmed for fusidic acid and vancomycin by determination of minimum inhibitory concentration The prevalence of Inpatient Healthcare Associated MRSA (IP-MRSA), outpatient-Healthcare Associated MRSA (OP-MRSA) and community carried MRSA (CC-MRSA) was 43%, 37% and 34% respectively. The isolates of MRSA displayed resistance to fusidic acid and multiple drug resistance (MDR) to 2-9 antibiotics for IP-MRSA, 2-7 antibiotics for OP-MRSA and 2-6 antibiotics for CC-MRSA. The most frequent MDR was resistance to fusidic acid, ciprofloxacin, streptomycin and clindamycin. This study has shown that MRSA is prevalent with similar rates for IP-MRSA, OP-MRSA and CC-MRSA strains. Lack of controls on supply of antibiotics may be responsible for the fusidic acid resistance.

Prevalence of extended spectrum beta lactamase producing Escherichia coli and Klebsiella pneumoniae urinary isolates in a tertiary care hospital in Kathmandu, Nepal

BackgroundEscherichia coli and Klebsiella pneumoniae are the major bacterial pathogens being isolated and reported from mid stream urine (MSU) specimens, globally. These uropathogens are mostly implicated as the major extended spectrum beta-lactamase (ESBL) producers, severely limiting the therapeutic management in cases of urinary tract infections. Limited studies had been reported from Nepal investigating the ESBL producers among uropathogens. This study was designed to assess the prevalence of ESBL producing E.coli and K. pneumoniae in urinary isolates at a centrally located major tertiary care hospital in Kathmandu valley, Nepal.MethodsBetween September 2011 and May 2012, during the nine months period, 6308 MSU specimens were collected aseptically from the same number of clinically suspected patients of urinary tract infections. The samples were cultured on MacConkey agar and blood agar. The isolates with significant bacteriuria (105 CFU / ml) were identified based on standard laboratory procedures. Antimicrobial susceptibility tests were carried out using various antimicrobial discs alongwith ceftriaxone on E.coli and K. pneumoniae isolates by Kirby Bauer disc diffusion method as per the recommendations of CLSI. On initial screening with ceftriaxone (30 μg) disc showing resistance was then confirmed for ESBL production by phenotypic confirmatory disc diffusion test (PCDDT) using ceftazidime (30 ug) and ceftazidime + clavulanic acid (30 μg + 10ug) disc as per guidelines of CLSI (2011).ResultsOut of a total of 6308 MSU specimens investigated for significant bacteriuria, E.coli isolates were 444 (7.04%) and K.pneuminiae were 145 (2.3%) making a total of 589 (9.34%). Initial screening with ceftriaxone disc revealed 155 isolates of E.coli and 70 isolates of K.pneumoniae to be resistant. Further testing by PCDDT method showed 60/444 (=13.51%) of E. coli and 24/145 (=16.55%) of K. pneumoniae isolates to be confirmed ESBL producers. These ESBL – producer uropathogens showed high degree of resistance to ceftriaxone (100.0%), amoxycillin, fluoroquinolones and co-trimoxazole.ConclusionAn emerging and moderately high prevalence of ESBL-producing E. coli and K. pneumoniae was observed and confirmed in the urinary isolates investigated. It is essential to have a regular and routine monitoring of ESBL producing clinical isolates in laboratory practice.

Tigecycline activity against metallo-β-lactamase-producing bacteria

Backgound:Treatment of serious life-threatening multi-drug-resistant organisms poses a serious problem due to the limited therapeutic options. Tigecycline has been recently marketed as a broad-spectrum antibiotic with activity against both gram-positive and gram-negative bacteria. Even though many studies have demonstrated the activity of tigecycline against ESBL-producing Enterobacteriaceae, its activity is not well-defined against micro-organisms producing metallo-β-lactamases (MBLs), as there are only a few reports and the number of isolates tested is limited.Aims:The aim of the present study was to evaluate the activity of tigecycline against MBL-producing bacterial isolates.Materials and Methods:The isolates were tested for MBL production by (i) combined-disk test, (ii) double disc synergy test (DDST), (iii) susceptibility to aztreonam (30 μg) disk. Minimum inhibitory concentration to tigecycline was determined according to agar dilution method as per Clinical Laboratory Standards Institute (CLSI) guidelines. Disc diffusion susceptibility testing was also performed for all these isolates using tigecycline (15 μg) discs.Results:Among the total 308 isolates included in the study, 99 were found to be MBL producers. MBL production was observed mostly in isolates from pus samples (40.47%) followed by urine (27.4%) and blood (13.09%). MBL production was observed in E. coli (41.48%), K. pneumoniae (26.67%), Proteus mirabilis (27.78%), Citrobacter spp. (41.67%), Enterobacter spp. (25.08%), and Acinetobacter spp. (27.27%). The result showed that tigecycline activity was unaffected by MBL production and it was showed almost 100% activity against all MBL-producing isolates, with most of the isolates exhibiting an MIC ranging from 0.25-8 μg/ml, except 2 MBL-producing E. coli isolates who had an MIC of 8 μg/ml.Conclusion:To conclude, tigecycline was found to be highly effective against MBL-producing Enterobacteriaceae and acinetobacter isolates, but the presence of resistance among organisms, even before the mass usage of the drug, warrants the need of its usage as a reserve drug. The study also found that the interpretative criteria for the disc diffusion method, recommended by the FDA, correlates well with the MIC detection methods. So, the microbiology laboratories might use the relatively easier method of disc diffusion, as compared to the comparatively tedious method of MIC determination.

In vitro susceptibility of chloramphenicol against methicillin-resistant Staphylococcus aureus.

To determine the in vitro susceptibility of chloramphenicol against methicillin-resistant Staphylococcus aureus. Cross-sectional study. Department of Microbiology, Armed Forces Institute of Pathology, Rawalpindi, from January to June 2012. One hundred and seventy four isolates of methicillin-resistant Staphylococcus aureus were included in this study using cefoxitin (30 μg) disc for detection. Minimum inhibitory concentration (MIC) of chloramphenicol against MRSA was determined by using E-strip (AB BIO DISK). The susceptibility was determined by swabbing the Mueller-Hinton agar (MHA) plates with the resultant saline suspension of MRSA and applying E-strip of chloramphenicol from AB Biodisk Sweden and determining the MIC of chloramphenicol (in μg/ml). Clinical and Laboratory Standards Institute (CLSI) recommendations of ≤ 8 μg/ml being sensitive, 16 μg/ml as intermediate and ≥32 μg/ml as resistant were followed in interpreting the results. Out of the 174 MRSA isolates, 132 (75.86%) isolates were susceptible to chloramphenicol with MICs of ≤ 8 μg/ml, 38 (21.84%) were resistant ≥32 μg/ml while 4 (2.30%) were in intermediate range with MIC of 16μg/ml. Chloramphenicol has shown good in vitro activity against MRSA and is likely to have a key role in the treatment of MRSA infections providing us a good alternative to newer expensive antimicrobials in resource limited countries.

Quality control ranges for tylosin 30 μg and 15 μg discs applicable to Staphylococcus aureus ATCC® 25923

Quality control ranges for tylosin 30 μg and 15 μg discs applicable to Staphylococcus aureus ATCC® 25923

Phenotypic and molecular characteristics of methicillin-resistant Staphylococcus aureus isolates from Ekiti State, Nigeria

IntroductionThe characteristics and antimicrobial resistance profiles of Staphylococcus aureus differs according to geographical regions and in relation to antibiotic usage. The aim of this study was to determine the biochemical characteristics of the prevalent S. aureus from Ekiti State, Nigeria, and to evaluate three commonly used disk diffusion methods (cefoxitin, oxacillin, and methicillin) for the detection of methicillin resistance in comparison with mecA gene detection by polymerase chain reaction.Materials and methodsA total of 208 isolates of S. aureus recovered from clinical specimens were included in this study. Standard microbiological procedures were employed in isolating the strains. Susceptibility of each isolate to methicillin (5 μg), oxacillin (1 μg), and cefoxitin (30 μg) was carried out using the modified Kirby–Bauer/Clinical and Laboratory Standard Institute disk diffusion technique. They were also tested against panels of antibiotics including vancomycin. The conventional polymerase chain reaction method was used to detect the presence of the mecA gene.ResultsPhenotypic resistance to methicillin, oxacillin, and cefoxitin were 32.7%, 40.3%, and 46.5%, respectively. The mecA gene was detected in 40 isolates, giving a methicillin-resistant S. aureus (MRSA) prevalence of 19.2%. The S. aureus isolates were resistant to penicillin (82.7%) and tetracycline (65.4%), but largely susceptible to erythromycin (78.8% sensitive), pefloxacin (82.7%), and gentamicin (88.5%). When compared to the mecA gene as the gold standard for MRSA detection, methicillin, oxacillin, and cefoxitin gave sensitivity rates of 70%, 80%, and 100%, and specificity rates of 76.2%, 69.1%, and 78.5% respectively.ConclusionWhen compared with previous studies employing mecA polymerase chain reaction for MRSA detection, the prevalence of 19.2% reported in Ekiti State, Nigeria in this study is an indication of gradual rise in the prevalence of MRSA in Nigeria. A cefoxitin (30 μg) disk diffusion test is recommended above methicillin and oxacillin for the phenotypic detection of MRSA in clinical laboratories.

Antibacterial mode of action of seed essential oil of Eleutherococcus senticosus against foodborne pathogens

SummaryThis study investigated the antibacterial mechanism of action of the seed essential oil of Eleutherococcus senticosus (ESEO) against foodborne pathogenic bacteria. Preliminarily, the ESEO (1000 μg disc−1) showed potential antibacterial effect as diameter of inhibition zones (12.0 ± 0.2–37.0 ± 2.0 mm) against the tested foodborne pathogens. The MIC and MBC values of ESEO against the tested bacteria were found in the range of 125–500 and 500–1000 μg mL−1, respectively. At MIC concentration, the ESEO had potential inhibitory effect on the cell viability of the tested pathogens. In addition, SEM analysis showed the inhibitory effect of ESEO as confirmed by considerable morphological alterations on the cell wall of B. cereus ATCC 13061 and E. coli O157:H7 ATCC 43889. Moreover, the ESEO revealed its mode of action against foodborne pathogens on membrane integrity as confirmed by release of extracellular ATP, 260‐nm absorbing materials and leakage of potassium ions. These findings confirm that the ESEO can be used as a potential antibacterial agent in food industry to inhibit the growth of various foodborne pathogens.

Exploitation of Rhizobacteria for Functional Traits in Mungbean

The enrichment of plant rhizosphere with beneficial bacteria is a strategy that favours the production of more vigorous seedlings, which is essential for the success of legume cultivation. The aim of this study was to select rhizobacteria that are able to act as plant growth-promoting rhizobacteria (PGPR). A total of 17 rhizobacteria belonging to genera Bacillus (8), Pseudomonas (5) and Azotobacter (4) from mungbean rhizosphere were selected on the basis of their ability to solubilize phosphate. These selected rhizobacteria were further characterized for Plant Growth Promoting (PGP) traits for quantitative phosphate solubilisation, Indole Acetic Acid (IAA), organic acid production and Intrinsic antibiotic spectra (IAR), control of phytopathogen via siderophore and cellulase production and stress tolerant management by 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Significantly high phosphate was solubilized by strain of Bacillus sp. B2 (9.77 mg ml−100) followed by strain of Pseudomonas sp. P10 (9.14 mg ml−100) and strain of Azotobacter sp. A3 (8.98 mg ml−100). In the presence of L-trptophan P10, A3 and B2 were also able to produce significant high amount of IAA i.e. 55.6 μg ml−1, 52.6 μg ml−1 and 50.3 μg ml−1 respectively and they also produced organic acid, siderophore and cellulase. Of 17 rhizobacterial isolates, 11 were found compatible with Rhizobium sp. vigna (LSMR1) in-vitro. IAR pattern revealed 52.9% of rhizobacteria resistant to ampicillin (10 μg disc−1) and chloramphenicol (25 μg disc−1). ACC deaminase activity was measured by their growth in DF medium supplemented with ACC (OD 600 ranged from 0.117 to 0.432) as nitrogen (N) source. In the present investigation, rhizobacterial isolates viz, B2, P10 and A3 were found most promising for multiple activities (PGP traits, biocontrol and stress tolerant activities) and can be evaluated in-vivo for their possible role in mungbean growth and development.

Analysis of Different Fractions of Swertia Chirata Against Gram Positive and Gram Negative Bacteria

Complementary and alternative medicine (CAM) is becoming increasingly popular and experienced a high growth all over the world. A medicinal plant, Swertia chirata, has been widely use as herbal medicine in Asian countries and some parts of the world. The aim of this study was to evaluate the antibacterial property of Swertia chirata. Plants were extracted using ethanol. Disc diffusion technique was used to determine antimicrobial activity. Crude extraction of whole plant showed significant antimicrobial activities against some gram positive and gram negative bacteria. Test materials at a concentration of 100 µg disc -1 were used to evaluate the antimicrobial activity and 30 µg disc -1 concentration of Chloramphenicol was used as positive control. Zone of inhibition against Staphylococcus aureus, Bacillus cereus, Escherichia coli and Salmonella arizonae were 10mm, 6mm, 9mm and 7mm respectively. Minimum Inhibitory Concentration of the crude extract was determined by serial dilution technique which showed 128 µg/ml, 64 µg/ml, 128 µg/ml and 128 µg/ml respectively . Although the results obtained revealed inhibition against some gram positive and gram negative bacteria, a further study need to be carried out to detect the active compounds of this highly potent plant. Moreover, problems of drug resistance leading to recurrent infections highlight a need to search for new compounds for treatment of microbial infections. Hence, Swertia chirata which possesses antimicrobial activity, hope will complement if not replace a standard antimicrobial drug that will be of benefits to the health of the mankind.

Comparison of Cefoxitin and Oxacillin disc diffusion test for the detection of mecA mediated methicillin resistance in Staphylococcus aureus

The study was designed to evaluate the efficacy of cefoxitin disc diffusion test to detect methicillin resistance in Staphylococcus aureus and compare it with oxacillin disc diffusion test and detection of mecA gene by PCR. A total 116 S. aureus were isolated from clinical samples, collected from SSMC&MH, BIRDEM and NMC hospital, and was isolated by culture and identified by standard laboratory procedure. Antibiotic susceptibility testing was performed by oxacillin (1µg) and cefoxitin (30 µg) discs. PCR for amplification of mecA gene was performed as a gold standard method. Out of 116 isolates, 28 were PCR positive, 33 and 31 were oxacillin and cefoxitin resistant respectively. The sensitivity and specificity for the detection of MRSA was 100% and 94.31%inoxacillin disc diffusion test, and 96.42% and 95.45%in cefoxitin disc diffusion test respectively. Specificity is higher (95.45%) in cefoxitin disc diffusion test than oxacillin disc diffusion test in the detection of MRSA. Use of disc diffusion tests for both oxacillin and cefoxitin can help in more accurate prediction of methicillin resistance than single test, especially in centers which are not equipped to carry out more sophisticated tests for the detection of MRSA.DOI: http://dx.doi.org/10.3329/bjmm.v7i1.19314 Bangladesh J Med Microbiol 2013; 07(01): 7-10

Nasal methicillin-resistant Staphylococcus aureus colonization in HIV-infected patients from eastern India

Background: Human immunodeficiency virus (HIV)-infected patients are now recognized as one of the higher risk groups for increased rates of both methicillin-resistant Staphylococcus aureus (MRSA) colonization and infections over the past decade. Staphylococcus aureus are known to colonize the anterior nares of HIV-infected patients with greater frequency than that of the general population, leading authors to postulate that this higher colonization burden might translate into a higher incidence of infections. Settings and Design: The study was a prospective study, including HIV-infected patients. Exclusion criteria: Patients having diabetes or any other immunodeficient conditions besides HIV. Materials and Methods: One hundred and forty two non-duplicate patients with HIV infection, attending the anti-retroviral therapy (ART) center at a tertiary care hospital were studied for nasal carriage of MRSA and associated factors affecting nasal colonization. Nasal swabs were used for isolation of S. aureus. MRSA were detected by using cefoxitin (30 μg) disc as per the Clinical Laboratory Standards Institute (CLSI) guidelines. Careful examination for dermatoses was carried out. Statistical Analysis: Descriptive statistics and testing of hypothesis were used for the analysis using SPSS 16 software. Results and Conclusions: Seventy two (50.70%) of the 142 patients were colonized with S. aureus in the anterior nares. Significant number of S. aureus carriers were in the 31-40 year age group. Methicillin resistance was found in 26 (36.11%) isolates. Cotrimoxazole prophylaxis was found to be a risk factor for MRSA colonization (P < 0.0001). Decreased CD4 counts was found to be a significant risk factor for MRSA colonization (P < 0.0001).

Prevalence of extended-spectrum beta-lactamases, AmpC beta-lactamase, and metallo-beta-lactamase producing Pseudomonas aeruginosa and Acinetobacter baumannii in an intensive care unit in a tertiary care hospital

Background: Resistance to broad-spectrum beta-lactams, mediated by extended-spectrum beta-lactamases (ESBL), AmpC beta-lactamase, and metallo-beta-lactamase (MBL) enzymes, is an increasing problem worldwide. Aim of the study: This study was undertaken to detect ESBL, AmpC beta-lactamase and metallo-beta-lactamase producing Pseudomonas aeruginosa and Acinetobacter species from the endotracheal aspirates. Materials and Methods: A prospective study was performed over a period of 15 month in a tertiary care hospital. A total of 26 clinical isolates of P.aeruginosa and 40 of Acinetobacter species were tested for the presence of ESBL, AmpC beta-lactamase, and metallo-beta-lactamase enzyme. Detection of ESBL was done by the combined disk diffusion method as per Clinical and Laboratory Standards Institute (CLSI) guidelines, and MBL was detected by imipenem-Ethylenediaminetetraacetic acid (EDTA) combined disk method. Isolates showing reduced susceptibility to cefoxitin (30 μg) disk were considered 'screen positive' for AmpC beta-lactamases and selected for detection of plasmid-mediated AmpC by the AmpC disk test. Results : 42.30% isolates of P.aeruginosa were positive for ESBL while 53.85% were MBL producers. Among 39 isolates of Acinetobacter baumannii, 43.59% were AmpC producers while 48.72% were MBL-producing strains. Conclusion: The study emphasizes the high prevalence of multidrug-resistant P.aeruginosa and A.baumannii producing beta-lactamase enzymes of diverse mechanisms. Thus, proper antibiotic policy and measures to restrict the indiscriminative use of cephalosporins and carbapenems should be taken to minimize the emergence of this multiple beta-lactamase-producing pathogens.

Nosocomial Infections and Drug Susceptibility Patterns in Methicillin Sensitive and Methicillin Resistant Staphylococcus aureus

Staphylococcus aureus is one of the leading causes of nosocomial infections and is known for its ability to develop resistance to antibiotics. The drug susceptibility pattern of Methicillin Sensitive S. aureus (MSSA) and Methicillin Resistant S. aureus (MRSA) may vary. AIMs and Objectives: This study was carried out to determine and compare the drug susceptibility patterns in nosocomial MSSA and MRSA. The study was conducted between September 2009 and August 2011. Standard conventional methods were used for the isolation and identification of S. aureus. MRSA was identified by the cefoxitin (30 μg) disk method. Antibiotic susceptibility test was done using Kirby-Bauer disk diffusion method and the interpretation of the results was done using CLSI guidelines. Out of 685 strains of S. aureus studied, 173(25.25%) were MRSA and 512 (74.25%) were MSSA. Out of 173 MRSA strains, 114(65.89%) were isolated from pus, 22(12.71%) from vaginal swab, 18(10.40%) from central catheter tip and the remaining from other specimens. All isolates were susceptible to vancomycin and least number of isolates were susceptible to penicillin. MRSA displayed significantly higher resistance to other antibiotics. 45.7% of MRSA strains were resistant to clindamycin, 64.7% to ciprofloxacin, 87.3% to cotrimoxazole, 54.3% to erythromycin, 17.3% to gentamicin, 16.8% to netilmycin, and 58.38% to tetracycline. Inducible clindamycin resistance was detected in 37 (21.38%) strains of MRSA. Nosocomial infections caused by MRSA is a significant problem. MRSA and MSSA differ with their susceptibility to antibiotics. All MRSA isolates in our hospitals were susceptible to vancomycin. Proper selection of the antibiotics based on antibiotic susceptibility test results is needed for effective treatment and prevention of emergence of resistance in MRSA and MSSA.

The prevalence of Inducible and Constitutive Clindamycin Resistance Among the Nasal Isolates of Staphylococci

One of the important sources of Staphylococci which causes nosocomial infections, is the nasal carriage of Staphylococci among Health Care Workers (HCWs). The commonest antibiotic which is preferred for the treatment of the methicillin and multi drug resistant Staphylococcal infections is clindamycin. The inducible clindamycin resistance in Staphylococci is not detected by the routine antibiotic susceptibility testing and it results in treatment failures. The present study was undertaken to know the prevalence of constitutive and inducible clindamycin resistance and its correlation with the methicillin resistance among the nasal isolates of Staphylococci which were obtained from different HCWs. Nasal swabs were collected from 206 HCWs and they were processed. The Staphylococci which were isolated were tested for methicillin resistance by using cefoxitin (30 μg) discs. The inducible clindamycin resistance was tested by using erythromycin (15 μg) and clindamycin (2μg) discs and the D test according to the CLSI guidelines. Inducible clindamycin resistance was seen in 21(16.40%) of the S.aureus and 14 (7.56%) of the coagulase negative Staphylococcal isolates. Constitutive clindamycin resistance was seen in 23(17.96%) of the S.aureus and 43(23.24%) of the coagulase negative Staphylococcal isolates. The inducible and constitutive clindamycin resistance was more common among the methicillin resistant Staphylococcal isolates. The prevalence of inducible and constitutive clindamycin resistance in the nasal Staphylococcal isolates which were obtained from the HCWs was high, especially among the methicillin resistant Staphylococci. The D test which is recommended by the CLSI should be routinely done to detect inducible clindamycin resistance, to prevent treatment failures.

Prevalence of High and Low Level Mupirocin Resistance among Staphylococcal Isolates from Skin Infection in a Tertiary Care Hospital.

Mupirocin has been used for the treatment of skin infections and for the eradication of the nasal carriage of Methicillin -resistant Staphylococcus aureus (MRSA). The increased use of this antibiotic has been accompanied by its resistance, resulting in treatment failures. This study was aimed at determining the prevalences of low and high level Mupirocin resistance among the clinical isolates of Staphylococcus species which were obtained from pyogenic infections. Clinical samples such as wound swabs, tissues and pus which were submitted to the microbiology laboratory during a period of six months were screened for the growth of Staphylococcus species, which were identified as Staphylococcus aureus and Coagulase negative Staphylococcus species by the routine microbiological procedures. All the isolates were tested for their Mupirocin susceptibilities by using 5 and 200 μg discs and their resistance was confirmed from their Minimum Inhibitory Concentrations (MICs). Out of 400 samples, 150 samples grew Staphylococcus species, of which 113 were Staphylococcus aureus and 37 were Coagulase negative Staphylococcus (CoNS). Only 5(3.3%) mupirocin resistant Staphylococcus species: three high level and two low level strains were detected. The MICs for the two low level and three high level Mupirocin resistant strains were 256 mg/L and ≥512mg/L each respectively. We conclude that the screening for mupirocin resistance, in terms of high-level and low-level resistance among the Staphylococcus species from patients with skin and soft tissue infections is warranted and that it is important for the clinicians in selecting the appropriate, empirical, topical, antimicrobial therapy. It also provides useful information about the prevalence of these resistant pathogens.

Evaluation of the EUCAST disc diffusion susceptibility testing method for Haemophilus influenzae based on the resistance mechanism to -lactam antibiotics

EUCAST developed an antibiotic susceptibility testing method for Haemophilus influenzae. We assessed the EUCAST testing method and EUCAST clinical breakpoints and newly proposed epidemiological cut-off values against H. influenzae clinical isolates with known molecular mechanisms of resistance to β-lactam antibiotics. In total, 89 clinical isolates were used: 30 were β-lactamase negative with PBP3 mutations (gBLNAR), 20 were β-lactamase positive without PBP3 mutations (gBLPAR), 15 were β-lactamase positive with PBP3 mutations (gBLPACR), and 24 were β-lactamase negative without resistance mechanism (gBLNAS). Twelve different β-lactam antibiotics and disc charges were tested. None of the discs tested fully separated between gBLNAS and gBLNAR populations. According to EUCAST clinical zone diameter breakpoints, overall the best values of sensitivity and specificity were obtained with cefuroxime 30 μg and amoxicillin/clavulanic acid 2/1 μg discs for detection of gBLNAR and gBLPACR populations, although a previous β-lactamase test was needed. Other antibiotic discs could be suitable for epidemiological purposes, such us penicillin 10 U for separating gBLNAR isolates and cefoxitin 30 μg for detection of gBLPACR isolates. By Etest using the EUCAST method, the EUCAST MIC clinical breakpoints for ampicillin and amoxicillin/clavulanic acid showed high specificity, but low sensitivity, for the detection of genotypes with mutations in PBP3. The main genotypes of β-lactam-resistant H. influenzae can be separated by using the EUCAST disc diffusion method, although it should be noted that overlapping between populations with and without PBP3 mutations is common.