Methicillin-sensitive Isolates Research Articles

Determination of Biofilm Formation Properties of Methicillin Sensitive and Resistant Staphylococcus aureus Isolates by Conventional and Molecular Methods

Biofilm-related infections are considered as among the foremost causes of treatment failure nowadays. One of the most common causes of biofilm-related infections is Staphylococcus aureus. It becomes extremely difficult to determine the appropriate treatment protocol while biofilm-related infections are coexisting with bacterial methicillin resistance. The aim of this study was to observe the potential of biofilm formation of methicillin-sensitive and -resistant S.aureus strains isolated from different clinical specimens and to determine reliable and effective methods for biofilm detection. A total of 200 S.aureus strains (100 methicillin-resistant and 100 methicillin-susceptible) isolated from 107 wound, 93 blood and catheter specimens, which were accepted as causative agents, included in the study. In order to determine the methicillin sensitivity, oxacillin minimal inhibitory concentration value obtained by an automated system and cefoxitin disc diffusion method were evaluated together. Biofilm formation was investigated by modified Christensen (MC), MTT, BioTimer and Congo Red Agar (CRA) methods, and the presence of ica operon responsible for biofilm formation was also observed by polymerase chain reaction. It has been shown that methicillin-resistant isolates produce biofilms in a shorter time and higher rate, and their biofilm structure is denser than methicillin-sensitive isolates in all MC, MTT and BioTimer methods. There was no difference between blood and wound isolates in biofilm formation. The most sensitive and specific conventional methods were MTT and BioTimer methods respectively. There was no significant difference between the isolates containing a gene region of icaADBC operon and the biofilm forming isolates according to MC, MTT, BioTimer and CCA methods. There was a high correlation between the presence of biofilm and ica positivity, and the tendency to form biofilm augmented as the number of ica genes increased. It has been emphasized that more virulent strains such as methicillin-resistant S.aureus have a higher tendency to form biofilm, and these two resistance mechanisms have been shown to support each other as cascade. ica detection may be an important reagent in itself for the detection of virulent strains, thus detection of the ica presence may be an early marker of treatment decisions, determination of protection strategies, and struggle with biofilm-related infections. In cases where molecular methods are not available, the existence of quick, easy-to-apply and reliable conventional methods to detect biofilm formation is extremely important. All conventional methods used in this study seem to be sufficient in this respect. MC and MTT methods stand out in terms of biofilm quantitation. BioTimer method is a very new and remarkable test used to detect biofilm formation. In conclusion, determining the potential of biofilm formation of colonizing or causative agents and taking essential precautions before interventional procedures will decrease biofilm related infections and related morbidity and mortality.

Staphylococcus aureus from ocular and otolaryngology infections are frequently resistant to clinically important antibiotics and are associated with lineages of community and hospital origins.

Staphylococcus aureus is an important human pathogen that causes serious antibiotic-resistant infections. Its population structure is marked by the appearance and dissemination of successful lineages across different settings. To begin understanding the population structure of S. aureus causing ocular and otolaryngology infections, we characterized 262 isolates by antimicrobial sensitivity testing and multilocus sequence typing (MLST). Methicillin-resistant S. aureus were subjected to SCCmec typing and Panton-Valentine leukocidin (PVL) screening. Although we detected a high level of genetic diversity among methicillin-sensitive (MSSA) isolates, (63 sequence types—STs), the population was dominated by five lineages: ST30, ST5, ST8, ST15 and ST97. Resistance to penicillin, erythromycin and clindamycin was common among the major MSSA lineages, with fluctuations markedly impacted by genetic background. Isolates belonging to the predominant lineage, ST30, displayed high rates of resistance to penicillin (100%), erythromycin (71%), and clindamycin (63%). Overall, 21% of the isolates were methicillin-resistant (MRSA), with an apparent enrichment among otitis and orbital cellulitis isolates (>40%). MRSA isolates belonged to 14 STs grouped in 5 clonal complexes (CC), however, CC5 (56.1%) and CC8 (38.6%) dominated the population. Most CC5 strains were SCCmec type II, and resembled the hospital-adapted USA100 clone. CC8 strains were SCCmec type IV, and 86% were positive for the PVL toxin, common features of the community-acquired clone USA300. CC5 strains harboring a SCCmec type IV, typical for the USA800 clone, comprised 15.5% of the population. USA100 strains were highly resistant to clindamycin, erythromycin and levofloxacin (100%), while USA300 strains were frequently resistant to erythromycin (89%) but displayed lower rates of resistance to levofloxacin (39%) and clindamycin (17%). Our data demonstrate that the ocular and otolaryngology S. aureus populations are composed of strains that are commonly resistant to clinically relevant antibiotics, and are associated with the major epidemic clonal complexes of both community and hospital origins.

A molecular epidemiological study of methicillin-resistant and methicillin-susceptible Staphylococcus aureus contamination in the airport environment.

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) causes a wide variety of serious infections worldwide. There are few studies on the prevalence, antimicrobial susceptibility, and molecular characteristics of MRSA contamination in the environment of airports.Materials and methodsA cross-sectional survey was conducted in Guangzhou Baiyun Airport. Environmental surface sampling was conducted in frequently touched locations for S. aureus analysis. All isolates were characterized by multilocus sequence typing (MLST) and tested for antimicrobial susceptibility, resistance genes, and virulence genes. Data were analyzed by chi-squared test and correspondence analysis.ResultsOf the 1,054 surface samples, the contamination rate was 7.2% (76/1,054) for S. aureus and 2.2% (23/1,054) for MRSA. There were 62.9% (56/89) S. aureus isolates classified as multidrug resistant (MDR), with six linezolid-resistant isolates and two cfr-carrying isolates. The most prevalent S. aureus genotypes were CC6 (ST6), CC59 (ST59), and CC188 (ST188), with ST59-MRSA-IV (pvl–) as the predominant MRSA. There were significant differences between methicillin-resistant and methicillin-sensitive isolates in rates of resistance to tetracycline (P<0.001) and sek carriage (P=0.029). The correspondence analyses revealed significant corresponding relationships between genotypes and phenotype–genotype characteristics of S. aureus isolates.ConclusionOur findings revealed a potential risk of cross-transmission of MRSA between human beings and environments, suggesting more stringent contamination control measures. In addition, this study revealed significant corresponding relationships between genotypes and phenotype–genotype characteristics of S. aureus isolates, which may provide new ideas for monitoring the latest epidemiological trends.

Antimicrobial and anti-biofilm activity of hexadentated macrocyclic complex of copper (II) derived from thiosemicarbazide against Staphylococcus aureus

Multidrug-resistant pathogens causing nosocomial and community acquired infections delineate a significant threat to public health. It had urged to identify new antimicrobials and thus, generated interest in studying macrocyclic metal complex, which has been studied in the past for their antimicrobial activity. Hence, in the present study, we have evaluated the antimicrobial activity of the hexadentated macrocyclic complex of copper (II) (Cu Complex) derived from thiosemicarbazide against Gram-positive and Gram-negative bacteria. We observed increased susceptibility against standard isolates of Staphylococcus aureus with a minimum inhibitory concentration (MIC) range of 6.25 to 12.5 μg/mL. Similar activity was also observed towards methicillin resistant and sensitive clinical isolates of S. aureus from human (n = 20) and animal (n = 20) infections. The compound has rapid bactericidal activity, and we did not observe any resistant mutant of S. aureus. The compound also exhibited antibiofilm activity and was able to disrupt pre-formed biofilms. Cu complex showed increased susceptibility towards intracellular S. aureus and was able to reduce more than 95% of the bacterial load at 10 μg/mL. Overall, our results suggest that Cu complex with its potent anti-microbial and anti-biofilm activity can be used to treat MRSA infections and evaluated further clinically.

Spectrum of constitutive and inducible clindamycin resistance in Staphylococcus spp isolated from clinical samples and its relation with methicillin resistance.

Backgound: Increasing Staphylococcal infections with changing patterns of antimicrobial resistance has led to renewed interest in macrolide-lincosamide-streptogramin group B (MLS B ) antibiotic. Misuse of MLS B antibiotics has increased resistance of Staphylococcusspp. to these drugs. Failure to detect inducible clindamycin resistance leads to therapeutic failure. Determine the prevalence of constitutive and inducible clindamycin resistance in clinical isolates of Staphylococcus spp. Ascertain the relationship between methicillin-resistance in Staphylococcus spp with constitutive and inducible clindamycin resistance. Methods: Prospective study was carried over a period of six months with 722 clinical specimens. A total of 184 Staphylococcal isolates were identified. Staphylococcal isolates were speciated as S aureus, S epidermidis and S saprophyticus. Antibiotic susceptibility testing was done by Kirby-Bauer’s disc diffusion method using cefoxitin, erythromycin, and clindamycin. A disc approximation test was performed for detection of inducible clindamycin resistance for all strains resistant to erythromycin but sensitive to clindamycin. Results: Out of 184 staphylococcal isolates, 128 (69.5%) S aureus and 56 (30.4%) Coagulase negative Staphylococcus spp were identified. 114 (61.9%) of the isolates were susceptible to both clindamycin and erythromycin. Overall 70 (38.04%) isolates were resistant to erythromycin. Out of these,38 (54.2%%) of strains depicted cMLS B phenotype being resistant to both erythromycin and clindamycin.20 (28.5%) isolates showed inducible clindamycin resistance while 12(17.1%) isolates indicated MS phenotype. Percentage of both constitutive and inducible clindamycin resistance was found to be higher in methicillin resistant staphylococcal isolates than methicillin sensitive isolates. Conclusions: We recommend that the clinical microbiology laboratories should test the isolates for inducible clindamycin resistance by D test, for all isolates that appear erythromycin resistant and clindamycin susceptible in vitro.

Inducible clindamycin resistance among Staphylococcal clinical isolates from Tripoli Central Hospital, Libya

Abstract Background: The resistance to antimicrobial agents among Staphylococci is an increasing problem. This has led to a renewed interest in the usage of macrolide-lincosamide-streptogramin B (MLSB) antibiotics to treat staphylococcal infections. Clinical failure has been reported due to multiple mechanisms that confer resistance to clindamycin antibiotics. The present study was to investigate the inducible clindamycin resistance among isolates of methicillin resistant Staphylococci by the D-test method. MATERIALS &amp; METHODS: This study was conducted on 218 staphylococcal isolates obtained from different clinical specimens of outpatients and inpatients admitted to Tripoli Central Hospital (TCH), Libya. Methicillin resistance was detected by oxacillin, cefoxitin disc diffusion test (Kirby Bauer method) and confirmed by other biochemical tests. Detection of inducible clindamycin resistance was performed by D-test using erythromycin and clindamycin. Results: Eighty-six out of 218 staphylococcal isolates were resistant to erythromycin,26 (11.9%) isolates were D-test positive indicating inducible (iMLSB) phenotype, 24 (11%) isolates exhibited constitutive (cMLSB) phenotype, while 36 (16.5%) showed true sensitivity to clindamycin indicating (MS) phenotype. The distribution of isolates showing iMLSB phenotype was 12 (19.4%) for methicillin-resistant Staphylococcus aureus (MRSA), 8 (17.0%) for methicillin-resistant coagulase-negative Staphylococci (MRCNS), 6 (6.4%) for methicillin-sensitive Staphylococcus aureus (MSSA) and 0 (0%) for methicillin-sensitive coagulase-negative Staphylococci (MSCNS). Conclusion: Higher prevalence of iMLSB phenotype was mainly associated with methicillin-resistant than methicillin-sensitive isolates. We recommend that D-test should be performed to facilitate the appropriate treatment of patients infected with Staphylococci.

Clonal diversity and epidemiological characteristics of Staphylococcus aureus: high prevalence of oxacillin-susceptible mecA-positive Staphylococcus aureus (OS-MRSA) associated with clinical isolates in Brazil.

BackgroundStaphylococcus aureus is the major cause of global and nosocomial infections with a significant impact in hospitals worldwide. Our objective was to investigate clinical and molecular characteristics of S. aureus isolates causing infections in patients admitted to hospitals from Recife city, Brazil, and investigate the prevalence of oxacillin-susceptible mecA-positive S. aureus (OS-MRSA) in the region, as well as genetically characterize the isolates and compare with epidemic clones.ResultsWe characterized 89 isolates in total, 31 clinical methicillin-resistant S. aureus (MRSA) and 58 methicillin-sensitive (MSSA) isolates by PFGE, MLST, spa typing and SCCmec genotyping. Isolates belonging to international MRSA clones were present: Brazilian epidemic clone (BEC) (61 % of MRSA isolates), Paediatric (36 %), New York/Japan (3 %). Some MSSA isolates were related to MRSA clones: USA400-related (10 % of MSSA isolates), Berlin clone (2 %), Paediatric (14 %), New York/Japan (2 %) and Southwest Pacific clone (17 %). MLST revealed new sequence types (ST’s): ST2381, ST2382, and ST2383 and new spa types: 10548 and 10550. Among isolates phenotypically identified as MSSA by antimicrobial susceptibility assays, we verified 30 oxacillin-susceptible isolates, which exhibited the mecA gene, without mec complex amplification and were thus classified as OS-MRSA. We observed clonal spread of MRSA and MSSA, including OS-MRSA, within several areas of the main hospital investigated and closely related isolates between hospitals analyzed.ConclusionsThe results of this study suggest a possible spread of the strains in hospital environment that could be responsible for nosocomial infections. We documented the presence of several MRSA clones, as well as new MLST and spa types, that were responsible for severe infections in hospitalized patients. The finding of OS-MRSA isolates could have implications for therapy, because testing for mecA and PBP2a is not a routine procedure performed by clinical microbiology laboratories in Brazil and, as consequence, these isolates could be misclassified as MSSA. Our data alert to the necessity to develop more effective strategies for epidemiological control of S. aureus in order to avoid an increase of hospital infections provoked by this pathogen. We reinforce the use of genetic methods, in addition to phenotypic tests, for a precise identification of MRSA.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0733-4) contains supplementary material, which is available to authorized users.

High frequency of Panton-Valentine leukocidin in Staphylococcus aureus causing pediatric infections in the city of Cartagena-Colombia.

Panton-Valentine leucocidin (PVL) is a pore-forming toxin that has been epidemiologically associated with CA-MRSA infections. However, its role in the pathogenicity of Staphylococcus aureus is still unclear. We evaluated the prevalence of PVL-coding genes in methicillin-resistant (MRSA) and methicillin-sensitive (MSSA) isolates that cause infections in pediatric patients in the city of Cartagena, Colombia. We obtained S. aureus isolates from patients at the Napoleon Franco Pareja Children's Hospital in Cartagena. Then, we evaluated the presence of the nuc, mecA, and PVL genes in these isolates by multiplex PCR and determined the antibiotic susceptibility profiles using CLSI standards. We further correlated methicillin susceptibility and the presence of PVL genes with clinical variables. Overall PVL prevalence in S. aureus isolates was 73.91%, with a frequency of 80.92% among MRSA isolates and 67.59% among MSSA. We found a correlation between erythromycin resistance and lack of PVL and found that PVL+ cases were more common in older patients. We found a high PVL prevalence in both MRSA and MSSA isolates, in concordance with previous regional reports.

Determination of Vancomycin, Teicoplanin and Linezolid resistance among Staphylococcal isolates from a tertiary care hospital

Background and Objectives: Increasing reports of Vancomycin creep have been observed in both Methicillin sensitive and Methicillin resistant staphylococcal isolates. The objective of this study was to determine the sensitivity pattern among clinical isolates of Methicillin sensitive and Methicillin resistant Staphylococcus aureus (MRSA), S. epidermidis, S. haemolyticus, to Vancomycin, Teicoplanin and Linezolid. Materials and Methods: A total of 82 S. aureus, 34 S. epidermidis and 26 S. haemolyticus isolated during Jan 2011 to Dec 2011 were included in the study. None of the S. aureus isolates were resistant to Vancomycin and Linezolid. Only one MRSA isolate was resistant to Teicoplanin. Vancomycin resistant strains among Methicillin resistant S. epidermidis was one (4.3%) and among S. haemolyticus was two (8.3%) respectively. Teicoplanin resistant strains among Methicillin resistant S. epidermidis was six (26.1%) and among S. haemolyticus was two (8.3%). Linezolid resistant strains among Methicillin resistant S. epidermidis was two (8.7%) and among S. haemolyticus was one (4.2%). Conclusion: Emergence of Vancomycin, Teicoplanin and Linezolid resistance among Methicillin resistant coagulase negative staphylococci (CoNS) is alarming limiting the therapeutic options.

A scabies mite serpin interferes with complement-mediated neutrophil functions and promotes staphylococcal growth.

BackgroundScabies is a contagious skin disease caused by the parasitic mite Sarcoptes scabiei. The disease is highly prevalent worldwide and known to predispose to secondary bacterial infections, in particular by Streptococcus pyogenes and Staphylococcus aureus. Reports of scabies patients co-infected with methicillin resistant S. aureus (MRSA) pose a major concern for serious down-stream complications. We previously reported that a range of complement inhibitors secreted by the mites promoted the growth of S. pyogenes. Here, we show that a recently characterized mite serine protease inhibitor (SMSB4) inhibits the complement-mediated blood killing of S. aureus.Methodology/Principal FindingsBlood killing of S. aureus was measured in whole blood bactericidal assays, counting viable bacteria recovered after treatment in fresh blood containing active complement and phagocytes, treated with recombinant SMSB4. SMSB4 inhibited the blood killing of various strains of S. aureus including methicillin-resistant and methicillin-sensitive isolates. Staphylococcal growth was promoted in a dose-dependent manner. We investigated the effect of SMSB4 on the complement-mediated neutrophil functions, namely phagocytosis, opsonization and anaphylatoxin release, by flow cytometry and in enzyme linked immuno sorbent assays (ELISA). SMSB4 reduced phagocytosis of S. aureus by neutrophils. It inhibited the deposition of C3b, C4b and properdin on the bacteria surface, but did not affect the depositions of C1q and MBL. SMSB4 also inhibited C5 cleavage as indicated by a reduced C5b-9 deposition.Conclusions/SignificanceWe postulate that SMSB4 interferes with the activation of all three complement pathways by reducing the amount of C3 convertase formed. We conclude that SMSB4 interferes with the complement-dependent killing function of neutrophils, thereby reducing opsonization, phagocytosis and further recruitment of neutrophils to the site of infection. As a consequence secreted scabies mites complement inhibitors, such as SMSB4, provide favorable conditions for the onset of S. aureus co-infection in the scabies-infected microenvironment by suppressing the immediate host immune response.

Detection of genes for superantigen toxins in methicillin-resistant Staphylococcus aureus clinical isolates in Karachi.

To detect genes for enterotoxins, exfoliative and toxic shock syndrome toxins in Staphylococcus aureus (S. aureus) strains isolated from clinical specimens. Cross-sectional observational study. Department of Molecular Genetics, Dr. Ziauddin Hospital, Karachi, from January to December 2010. Two hundred and ninety eight S. aureus clinical isolates were obtained from various clinical samples received at Dr. Ziauddin Hospital, Karachi. Out of these, 115 were detected as methicillin resistant (MRSA) by cefoxitin disk diffusion test showing a prevalence rate of 38.6%. Detection of individual toxin genes was performed by Polymerase Chain Reaction (PCR) by using only one primer pair for each tube. Uniplex primers were preferred as multiplex primers are longer in base pairs and have the potential for cross reaction due to non-specific binding and increase in optimization time. The possession of a single gene or more than a single gene in MRSA isolates was found in 61.73% of clinical samples; the highest number was found in pus swab, followed by sputum, blood, urethral swab, and urine. The prevalence of toxin genes was higher in MRSA as compared to methicillin sensitive (MSSA) isolates (19.12%). PCR detects strains possessing toxin genes independent of their expression. The possession of genes for super-antigens seems to be a frequent and habitual trait of S. aureus more so in MRSA.

Surface Water-Borne Multidrug and Heavy Metal-Resistant Staphylococcus Isolates Characterized by 16S rDNA Sequencing

Four Staphylococcus isolates having both multidrug- and multimetal-resistant ability were isolated from surface water. Further identification of the isolates was obtained through biochemical tests and 16S rDNA gene sequencing. One methicillin-resistant and two methicillin-sensitive isolates were determined as Staphylococcus aureus. The other isolate was identified as Staphylococcus warneri. The antibiotic and heavy metal resistance profiles of the Staphylococcus isolates were determined by using 26 antibiotics and 17 heavy metals. S. aureus isolates displayed resistance to most of the β-lactam antibiotics tested. All Staphylococcus isolates were resistant to heavy metals including silver, lithium, and barium. Due to a possible health risk of these pathogenic bacteria, a need exists for an accurate assessment of their acquired resistance to multiple drugs and metals.

Pharmacokinetics and protein binding of cefazolin in morbidly obese patients

The aim of this study was to assess the pharmacokinetics and protein binding of cefazolin in morbidly obese patients undergoing bariatric surgery, to study the influence of bodyweight measures and age on pharmacokinetic parameters and to evaluate unbound cefazolin concentrations over time in this population. Twenty morbidly obese patients (bodyweight 112-260 kg, body mass index 38-79 kg m(-2)) were studied following the administration of cefazolin 2 g at induction of anaesthesia. Blood samples were collected up to 4 h post-dosing to determine total and unbound plasma cefazolin concentrations. Non-compartmental pharmacokinetic data analysis was performed. Cefazolin clearance was 4.2 ± 1.0 L h(-1) (mean ± standard deviation) and showed a negative correlation with age (p = 0.003) but not with bodyweight measures (p > 0.05). Volume of distribution was 13.0 ± 3.1 L and correlated positively with bodyweight measures (p ≤ 0.001). Saturable protein binding was observed with a median protein binding of 79% (interquartile range 74-82), which proved similar to reported protein binding in non-obese patients. In all patients, unbound cefazolin concentrations remained above 1 mg L(-1) (minimal inhibitory concentration for 90% (MIC(90)) of methicillin-sensitive isolates of Staphylococcus aureus in Europe) until 4 h post-dosing. Younger age--and not bodyweight--was significantly associated with higher cefazolin clearance. However, as in all patients with bodyweights up to 260 kg, unbound plasma cefazolin concentrations remained above 1 mg L(-1) until 4 h after the intravenous administration of a 2-g dose. As such, re-dosing within 4 h or dosing with another antibiotic class should only be considered in the case of a higher MIC(90) of the local isolates.

Incidence of methicillin resistant Staphylococcus aureus (MRSA) from septicemia suspected children

The objective of the present study is to determine the incidence, clinical features, bacteriological pattern and antibiotic sensitivity profile of septicemia suspected children in Tamil nadu, India. This study was undertaken in SBS Hospital Pvt. Ltd., Hosur and SRM Medical College and Hospital, Chennai. All children (Age 1-5 yr) admitted with clinical features and risk factors, suspected with septicemia were selected and the blood samples were collected. The study identified 54 septicemia or bacteremia children out of 298 suspected children screened (18.12 %). The isolated organisms from the blood sample were characterized by primary, biochemical and selective media identification methods. From the identified isolates, Staphylococcus aureus was found to be prominent organism (48.14 %). Then the screening of MRSA was carried out using standard method (38.46%). The antibiotic sensitivity pattern of S. aureus differs widely between methicillin resistant and sensitive isolates. The present study reveals that in case of MRSA isolates resistant to nearly all antibiotics, they were sensitive to oxacillin and vancomycin.

Incidence of Methicillin Resistant Staphylococcus Aureus (MRSA) from Septicemia Suspected Children

The objective of the present study is to determine the incidence, clinical features, bacteriological pattern and antibiotic sensitivity profile of septicemia suspected children in Tamil nadu, India. This study was undertaken in SBS Hospital Pvt. Ltd., Hosur and SRM Medical College and Hospital, Chennai. All children (Age 1-5 yr) admitted with clinical features and risk factors, suspected with septicemia were selected and the blood samples were collected. The study identified 54 septicemia or bacteremia children out of 298 suspected children screened (18.12 %). The isolated organisms from the blood sample were characterized by primary, biochemical and selective media identification methods. From the identified isolates, Staphylococcus aureus was found to be prominent organism (48.14 %). Then the screening of MRSA was carried out using standard method (38.46%). The antibiotic sensitivity pattern of S. aureus differs widely between methicillin resistant and sensitive isolates. The present study reveals that in case of MRSA isolates resistant to nearly all antibiotics, they were sensitive to oxacillin and vancomycin.

Social bacteria and asocial eukaryotes

The end of 2007 brought us draft genome sequences of two eukaryotic microorganisms, Babesia bovis and Malassezia globosa, as well as complete genomes of the ammonia-oxidizing archaeal chemoautotroph Nitrosopumilus maritimus, and several environmental bacteria (Table 1). In terms of genome size, this list covers both sides of the spectrum: the 245 kb genome of an obligate insect symbiont Sulcia muelleri is the second smallest microbial genome sequenced so far, whereas the 13 033 kb chromosome of the social myxobacterium Sorangium cellulosum breaks the record as the largest bacterial genome – and the largest DNA molecule in the prokaryotic world.

Prevalence and antimicrobial susceptibility pattern of methicillin resistant Staphylococcus aureus isolates from Trinidad & Tobago

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) has become increasingly prevalent worldwide since it was first reported in a British hospital. The prevalence however, varies markedly in hospitals in the same country, and from one country to another. We therefore sought to document comprehensively the prevalence and antimicrobial susceptibility pattern of MRSA isolates in Trinidad and Tobago.MethodsAll Staphylococcus aureus isolates encountered in routine clinical specimens received at major hospitals in the country between 2000 and 2001 were identified morphologically and biochemically by standard laboratory procedures including latex agglutination test (Staphaurex Plus; Murex Diagnostics Ltd; Dartford, England); tube coagulase test with rabbit plasma (Becton, Dickinson & Co; Sparks, MD, USA), and DNase test using DNase agar (Oxoid Ltd; Basingstoke, Hampshire, England). MRSA screening was performed using Mueller-Hinton agar containing 6 μg oxacillin and 4% NaCl, latex agglutination test (Denka Seiken Co. Ltd, Tokyo, Japan) and E-test system (AB Biodisk, Solna, Sweden). Susceptibility to antimicrobial agents was determined by the modified Kirby Bauer disc diffusion method while methicillin MICs were determined with E-test system.ResultsOf 1,912 S. aureus isolates received, 12.8% were methicillin (oxacillin) resistant. Majority of the isolates were recovered from wound swabs (86.9%) and the least in urine (0.4%) specimens. Highest number of isolates was encountered in the surgical (62.3%) and the least from obstetrics and gynaecology (1.6%) facilities respectively. Large proportions of methicillin sensitive isolates are >85% sensitive to commonly used and available antimicrobials in the country. All MRSA isolates were resistant to ceftriaxone, erythromycin, gentamicin and penicillin but were 100% sensitive to vancomycin, rifampin and chloramphenicol.ConclusionThere is a progressive increase in MRSA prevalence in the country but the present rate is still low in comparison to values in some other countries. Vancomycin is still the drug of choice for treating multidrug resistant MRSA infections. Further use of molecular studies to monitor the epidemiology of MRSA in these hospitals in the country is highly recommended too.

Comparison of genotypes of methicillin-resistant and methicillin-sensitive Staphylococcus aureus in Finland

The frequency of horizontal transfer of the staphylococcal cassette chromosome mec to methicillin-susceptible Staphylococcus aureus is unknown. In order to gain more information regarding this frequency in Finland, the genotypes of 299 clinical methicillin-sensitive Staphylococcus aureus isolates were compared to representatives of 24 epidemic methicillin-resistant Staphylococcus aureus genotypes. Sixty-eight percent of the methicillin-sensitive isolates had a genotype similar to eight of the epidemic methicillin-resistant strains. The remaining isolates (32%) showed 22 different genotypes. The results indicate that, in Finland, several methicillin-sensitive Staphylococcus aureus genotypes may have acquired the staphylococcal cassette chromosome mec.

Prevalence of methicillin-resistant, coagulase-negative staphylococci in neonatal intensive care units: findings from a tertiary care hospital in India.

This study was undertaken to determine the antimicrobial resistance pattern and species of coagulase-negative staphylococci (CNS) isolated from the blood and skin of neonates with clinical suspicion of late-onset septicaemia (>72 h post-delivery) admitted to neonatal intensive care units, with particular reference to the phenotypic and genotypic expression of methicillin resistance. Blood culture specimens were collected by venipuncture from 660 such neonates in brain heart infusion broth. Skin swabs from axillae were obtained from 60 neonates and inoculated on mannitol salt agar. All CNS thus obtained were further identified and antibiotic sensitivity was performed according to NCCLS recommendations. PCR for the mecA gene was carried out on 54 randomly selected isolates. Staphylococcus haemolyticus was the commonest species (34 %) followed by Staphylococcus epidermidis (24 %) amongst blood isolates. All blood isolates were sensitive to glycopeptides. Resistance to penicillin and methicillin was 94 and 66 %, respectively. Similar biotypes and antimicrobial resistance patterns were observed in skin isolates. All phenotypically methicillin-resistant isolates had the mecA gene and two of the phenotypically methicillin-sensitive isolates were also positive for mecA. A PCR assay for detection of the mecA gene in CNS may be a beneficial adjunct to standard susceptibility testing for timely and reliable detection of methicillin resistance. Given the large number of methicillin-resistant CNS, inclusion of vancomycin in empiric therapy for neonates with late-onset septicaemia may be justified.

Ciprofloxacin and levofloxacin resistance among methicillin-sensitive staphylococcus aureus isolates from keratitis and conjunctivitis

PurposeThe majority of Staphylococcusaureus isolated from ocular infections are methicillin sensitive (MSSA). Fluoroquinolone resistance among methicillin- resistant Staphylococcusaureus is well known but not among MSSA. In this study we investigate the emergence of fluoroquinolone (ciprofloxacin, levofloxacin) resistance among methicillin-sensitive Staphylococcusaureus isolates from keratitis and conjunctivitis. DesignCross-sectional study. MethodsMinimal inhibitory concentration susceptibility profiles for 1230 S. aureus isolates from keratitis and conjunctivitis were analyzed. Historical and current rates of emerging fluoroquinolone resistance for methicillin-resistant (MRSA) and methicillin-sensitive isolates (MSSA) were evaluated. Sensitivity patterns for vancomycin and gentamicin were also documented. ResultsCiprofloxacin resistance among corneal and conjunctival S. aureus isolates during the first 6 years after its introduction (baseline) (1990–1995) was 8% and ranged from 3% to 11%. The rate for the most recent 6 years (current) (1996–2001) was 20.7%. Baseline ciprofloxacin resistance for MSSA isolates was 2% vs 55.8% for MRSA. The current resistance rate for MSSA is 5% vs 83.7% for MRSA. The general resistance rate from January 2000 to December 2001 for levofloxacin was 25.5% vs 33.2% for ciprofloxacin (P = .13). The levofloxacin-resistance rate for MSSA was 4.7% vs 11.9% for ciprofloxacin (P = .05). In MRSA isolates, a higher resistance rate was found for ciprofloxacin (95.7%) vs levofloxacin (82.1%) (P = .04). No resistance for vancomycin was documented for any of the S. aureus isolates. Gentamicin susceptibility for MSSA was 99% and MRSA was 86%. ConclusionsCiprofloxacin and levofloxacin resistance among methicillin-sensitive S. aureus corneal and conjunctival isolates is increasing. This is of concern because it narrows treatment choices for the management of these common ocular infections.