An evaluation of 2.0 McFarland Etest method for detection of heterogeneous vancomycin-intermediate Staphylococcus aureus

Background: Staphylococcus aureus with reduced susceptibility to vancomycin or heterogeneous vancomycinintermediate S. aureus (hVISA) have become increasingly reported from various parts of the world. hVISA cannot be detected by routine test for minimal inhibitory concentration (MIC) for vancomycin. The gold standard method for detection, population analysis profiles (PAP) method, is complicated, time-consuming, expensive, and needs well-trained microbiologists. Objective: Evaluate of 2.0 McFarland Etest method, in comparison with the PAP method, for detection of hVISA in clinical specimens. Methods: All methicillin-resistant S. aureus strains from clinical specimens isolated from consecutive patients attended at King Chulalongkorn Memorial Hospital and Siriraj Hospital, Bangkok between 2006 and 2007 were studied. 1 hundred nineteen specimens were obtained. The PAP method detected six hVISA strains 5 from blood and from cultures) from four patients at King Chulalongkorn Memorial Hospital, accounting for a prevalence of 6.35%. The MIC determined by agar dilution method was in the range of 2-3 μg/mL. Results: 2.0 McFarland Etest method detected no false positive and five false negatives (42%), and gave a sensitivity and a specificity of 16.7% and 100%, respectively. The one-point population analysis screening method detected two false positives and 1 false negative, and gave a sensitivity of 83.3% and a specificity and 98.2%. Conclusion: The 2.0 McFarland Etest method had a very good specificity but a poor sensitivity for detecting hVISA. It may be used as an alternative method to confirm detection of hVISA.

Genetic variations in Aeromonas hydrophila isolates from clinical and environmental sources in Thailand.

Aeromonas hydrophila, a widely distributed human pathogen causing a variety of diseases, can be isolated from clinical and environmental sources. Analysis in Thailand of 110 isolates of Aeromonas hydrophila by randomly amplified polymorphic DNA-PCR (RAPD-PCR) revealed one specific RAPD pattern group (G) that was associated only with strains from environmental sources. Cytotoxic activity, adhesion to epithelial cells and exoenzyme secretions of A. hydrophila were also investigated. A comparison of isolates with pattern group G with a set of isolates derived from human blood showed low induction of cytotoxicity from those with RAPD pattern group G suggesting low virulence of these strains.

Microbial killing activity of peracetic acid.

In vitro killing activity of peracetic acid (Perasafe) at a concentration of 0.26 per cent w/v was tested against Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi, Salmonella paratyphi A, Acinetobacter baumannii, Sternotrophomonas maltophilia, Enterococcus faecium, Enterococcus faecalis, methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis spore, Mycobacterium tuberculosis and human immuno-deficiency virus type I. Exposure to Peracetic acid (0.26% w/v) for 10 minutes resulted in massive killing of all the aforementioned organisms and spore.

Bacterial infections in hospitalized patients in Thailand in 1997 and 2000.

Two surveys to determine the patterns of bacterial infections and trends in resistance to antibiotics of bacteria causing infections in patients admitted to hospitals in Thailand were conducted in 36 and 37 hospitals throughout Thailand in June 1997 and February 2000. Approximately 50 per cent of infections in hospitalized patients in Thailand were hospital-acquired infections. Urinary tract and lower respiratory tract were the most common sites of infections. Eighty per cent of infections were caused by gram negative bacteria. Gram negative bacteria causing infections in 2000 were more resistant to most commonly used antibiotics when compared with those in 1997. The prevalence of gram positive bacteria causing hospital-acquired infections significantly increased during this period. The trend of increase in resistance in most gram positive bacteria in 2000 was not clearly observed.

Epidemiology of arabinose assimilation in burkholderia pseudomallei isolated from patients and soil in Thailand.

Burkholderia pseudomallei is an environmental saprophyte that has been isolated widely from soil in Southeast Asia and the relationship between environmental contamination and clinical melioidosis has been established. It has been shown that the arabinose assimilation property of B. pseudonrallei is probably one of the determinants indicating virulence of this organism. Therefore, the distribution of arabinose assimilation biotypes of B. pseudomallei collected from four geographic regions of Thailand was studied in order to determine an association between arabinose assimilation of B. pseudomallei and the uneven distribution of melioidosis found among these four areas. A total of 830 isolates of B. pseudomallei (412 patient isolates and 418 soil isolates) collected from the patients and soil in four regions of Thailand in 1997 were tested for an ability to grow on a minimal agar medium supplemented with L-arabinose. All patient isolates except one could not utilise arabinose (Ara-). For 418 soil isolates, 232 (55.5%) isolates were identified as Ara type. They comprised 180 (62.5%), 36 (46.8%), 6 (35.3%) and 10 (27.8%) isolates derived from northeastern, southern, northern and central regions respectively. The ratios of Ara- to Ara, were 1.7, 0.9. 0.5 and 0.4 among isolates collected from northeastern, southern, northern and central regions respectively. The prevalence of Ara- in soil isolates in northeast is significantly higher than those in other regions. This observation suggests that in addition to the presence of B. pseudomallei in soil which is one of the factors contributing to a burden of melioidosis in northeastern Thailand, the distribution of more virulent biotype (Ara-) soil isolates is a factor contributing to a high prevalence of melioidosis in northeastern Thailand as well.

Isolation rates of Burkholderia pseudomallei among the four regions in Thailand.

This study aimed to compare the isolation rates of Burkholderia pseudomallei among community-based hospitals located in the central, north, northeast, and south of Thailand. A questionnaire inquiring about the number of isolation of B. pseudomallei from various clinical specimens during 1994-95 were mailed to 141 community-based hospitals. Of these, 125 hospitals (88.6%) responded to the questionnaire. Microbiological laboratory was not available in thirty hospitals. Data from 95 remaining hospitals with capability to do bacterial culture showed that B. pseudomallei was never isolated in 49 hospitals. Eleven, 9, 19 and 7 hospitals where B. pseudomallei has been isolated, are located in the central, north, northeast and south of Thailand respectively. From these 46 hospitals, a total of 1,131 strains of B. pseudomallei were isolated from 407,263 specimens in 1994 and 1,165 strains from 440,541 specimens in 1995. However, the isolation was most frequent in northeastern hospitals, which accounted for 890 and 964 strains in 1994 and 1995 respectively while only 94, 76, 71 and 83, 75, 43 strains were simultaneously isolated during the 2-year period in those located in central, north and south respectively. The isolation rates of B. speudomallei in 1994 and 1995 were 4.2 and 4.1 per 1,000 clinical specimens in northeastern hospitals as compared to 1.1, 1.8, 1.1 and 1.1, 1.2, 0.7 in those located in central, north and south respectively. Ubon Ratchathani, Nakhon Ratchasima, Buri Ram, Khon Kaen and Udon Thani were the five provinces which exhibited the highest isolation rates as follows; 244, 150, 147, 127, 100 and 218, 128, 114, 119, 58, in 1994 and 1995, respectively. It was concluded that B.pseudomallei was most commonly isolated in the northeast of Thailand. Under-recognition of B. pseudomallei may prevail not only in other parts of Thailand but in some areas of the northeast as well.

Undetectable anti-bacterial activity of Andrographis paniculata (Burma) wall. ex ness.

Andrographis paniculata (Burma) Wall. ex Ness (AP) is a herbal medicine and has been used for therapy of upper respiratory tract infection (URI) as well as acute diarrhea with reported efficacy of 75-100 per cent. To investigate whether anti-bacterial activity was responsible for the reported therapeutic success of AP, we carried out a number of studies. The first study was a direct assay of anti-bacterial activity of AP suspended in water. The tested pathogens included Salmonella, Shigella, E.coli, gr. A Streptococci and S.aureus. Anti-bacterial activity was not demonstrable even in a solution containing 25,000 mg per litre of crude powder. The second was designed to detect serum bactericidal activity after oral intake of stem and leaves of AP. Ten healthy volunteers were enrolled in the study. They received a single oral dose of AP (1, 2, 3 and 6 g) in a randomized, cross-over manner. The washout period was one week. Blood samples were taken at 0, 1, 2, 4, 8 and 24 hours after ingestion. Serum bactericidal activity was assayed by agar diffusion technique using Bacillus spores and five strains of each pathogen (Shigella, Salmonella typhi, S.aureus and gr. A Streptococci) incubated for 24 hours. Again serum bactericidal activity was not detected in any of the sera tested. In a third study, ninety-six rats were daily fed with high doses of AP ranging 0.12-24 g per kg body wt. for six months before sacrifice. Antibacterial activity was still undetectable when lung parenchyma and liver tissue was placed on culture media containing bacteria tested. In conclusion, anti-bacterial activity of AP is undetectable in our study.

A model for testing antiseptic efficacy: a preliminary study on Betadine and Germidine.

Efficacy of povidone iodine antiseptic, betadine and germidine, was tested against normal skin flora and four pathogenic bacteria namely S. aureus, S. epidermidis, E. coli and Pseudomonas aeruginosa by a new model. The study was performed on the volar surface of forearms of ten patients. First of all, the skin flora was cultured then 10(8) cu/ml of the tested organisms was applied by a cotton swab and left to dry for 1 minute before the culture was repeated. Betadine or germidine was applied over the area previously painted with the organism. The culture was taken 1 to 2 minutes thereafter. The results showed that this model was feasible and convenient. Betadine and germidine are efficacious against normal skin flora and pathogenic bacteria.

Patients colonized by antibiotic resistant bacteria--a potential source of infections in the medical wards.

Bacterial colonization was studied in 12 non-infected female patients admitted into one medical ward, Siriraj hospital, Bangkok, from March to June 1988. Swabs were taken on the first day of admission, then every other day until discharge, from six sites; i.e. anterior nares, vault of axilla, hands, anterior chest, abdomen and toe web. The times and total number of swabbing were 52 and 312 respectively. All patients were colonized with bacteria. S. epidermidis was found in all patients. S. aureus was found in 9 patients, 48 times (15.4%). Methicillin-resistant S. aureus (M.R.S.A.) was identified in 4 patients on 10 occasions (3.2%). Gram-negative bacilli were isolated in 11 of 12 patients, and the number of positive samples was 60 (19.2%). All bacteria were highly resistant to the commonly used antimicrobials. The study failed to show that colonization increased with the duration of hospitalization. It is concluded that the majority of patients who had been colonized with pathogenic bacteria were important sources of infections in the medical ward.