Calibrated Dichotomous Sensitivity Research Articles

Keratitis antimicrobial resistance surveillance program, Sydney, Australia: 2016 Annual Report.

Antimicrobial resistance data from bacterial keratitis in Australia are lacking. Antimicrobial resistance is a global health threat. Bacterial keratitis is an ophthalmic emergency requiring immediate and effective treatment. Retrospective cohort study of bacterial isolates and antibiotic susceptibility profiles at a quaternary hospital in Sydney, Australia. Two hundred and twenty-four corneal scrapes from patients from January 1 to December 31, 2016. Matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry identified bacteria. The Calibrated Dichotomous Sensitivity (CDS) method determined antibiotic susceptibilities. Isolated organisms and antibiotic susceptibilities. One hundred and sixty-eight scrapes of 224 (75%) were culture positive. One hundred and thirty-one patients had a single organism isolated and 21 had mixed bacterial growth. Of the 157 organisms isolated, 131 (83%) were Gram-positive and 27 (17%) Gram-negative. Of the Gram-positive organisms, 75 (57%) were coagulase-negative Staphylococci (CoNS), 15 (11%) Staphylococcus aureus (including one methicillin-resistant Staphylococcus aureus [MRSA]) and 8 (6%) Corynebacterium spp. Of the Gram-negative organisms, 15 (58%) were Pseudomonas aeruginosa. With methicillin-sensitive Staphylococcus aureus (MSSA) resistance to chloramphenicol was 21%, ciprofloxacin 7% and gentamicin 7%. With CoNS resistance to cefalotin was 9%, gentamicin 9% and ciprofloxacin 9%. With Corynebacterium spp. resistance was 40% to cefalotin, chloramphenicol 25% and ciprofloxacin 14%. Staphyloccocus spp. and Pseudomonas spp. were the most common microorganisms isolated. There was low resistance to cefalotin and ciprofloxacin for these isolates. More than 90% of these would be covered by current therapeutic recommendations for empiric therapy in Australia.

A comparison of agar dilution with the Calibrated Dichotomous Sensitivity (CDS) and Etest methods for determining the minimum inhibitory concentration of ceftriaxone against Neisseria gonorrhoeae

ObjectivesThe objective of this study was to compare the Calibrated Dichotomous Sensitivity (CDS) based agar dilution (CDS AD) method with the Etest (bioMérieux SA) methods using 2 method protocols for determining the minimum inhibitory concentration (MIC) of ceftriaxone against Neisseria gonorrhoeae. The two method protocols were the manufacturer’s protocol for which the Clinical and Laboratory Standards Institute (CLSI) interpretative criteria for Neisseria gonorrhoeae could be applied, and the CDS-adapted protocol. Comparability of MIC data is critical for situation analysis and monitoring trends in global antimicrobial analysis. MethodsTwo hundred and forty eight clinical isolates of N. gonorrhoeae and the World Health Organisation (WHO) N. gonorrhoeae reference strains were tested using the three methods. ResultsWhen compared, CDS AD and CDS Etest gave a regression R2 value of 94%, the Pearson’s correlation coefficient was 97% and a paired comparison within one log2 dilution was 98%. The CDS AD and the Etest (CLSI) comparison gave a regression R2 value of 90%, a Pearson’s correlation coefficient of 95% and a paired comparison within one log2 dilution was 98%. The comparison of the CDS Etest and CLSI Etest gave a regression R2 value of 91%, a Pearson’s correlation coefficient of 95% and a paired comparison within one log2 dilution of 99%. Importantly, there was robust agreement between all three methods for the categorization of susceptibility of Neisseria gonorrhoeae isolates using the WHO nominated breakpoint for decreased susceptibility to ceftriaxone (≥0.125 μg/mL). ConclusionsThe CDS Etest method is comparable to agar dilution and the Etest methods for determining the MIC of ceftriaxone against N. gonorrhoeae.

Gentamicin in vitro activity and tentative gentamicin interpretation criteria for the CLSI and calibrated dichotomous sensitivity disc diffusion methods for Neisseria gonorrhoeae.

XDR Neisseria gonorrhoeae imposes the threat of untreatable gonorrhoea. Gentamicin is considered for future treatment; however, no interpretation criteria for the CLSI and calibrated dichotomous sensitivity (CDS) disc diffusion (DD) techniques are available for N. gonorrhoeae. We investigated the in vitro gentamicin activity by MIC and DD methods, proposed DD breakpoints and determined DD ranges for 10 international quality control (QC) strains. Gentamicin susceptibility of 333 N. gonorrhoeae isolates, including 323 clinical isolates and 10 QC strains, was determined. MIC determination (Etest) and DD methods (CLSI and CDS) were performed. The relationship between MIC, inhibition zone diameter and annular radius was determined by linear regression analysis and the correlation coefficient (r) was calculated. Gentamicin MICs for the QC strains were within published ranges. Of the 323 clinical isolates, according to published breakpoints 75.9%, 23.5% and 0.6% were susceptible, intermediately susceptible and resistant, respectively. Based on error minimization with MICs of ≤4, 8-16 and ≥32 mg/L, breakpoints proposed are susceptible ≥16 mm, intermediately susceptible 13-15 mm and resistant ≤12 mm for the CLSI method and susceptible ≥6 mm, less susceptible 3-5 mm and resistant ≤2 mm for the CDS technique. Low resistance to gentamicin was identified and gentamicin might be a future treatment option for gonorrhoea. Tentative gentamicin zone breakpoints were defined for two DD methods and QC ranges for 10 international reference strains were established. Our findings suggest that in resource-poor settings where MIC testing is not a feasible option, the DD methods can be used to indicate gentamicin resistance.

Extended spectrum beta-lactamase testing of community Enterobacteriaceae in the west of Australia: poor performance of phenotypic methods

Expanded spectrum β-lactamase (ESBL) producing organisms have long been recognised in institutions worldwide. Recently, community isolates producing ESBL have been reported overseas and in eastern Australia. We tested 571 consecutive Enterobacteriaceae urinary isolates from Western Australia and the Northern Territory phenotypically by calibrated dichotomous sensitivity (CDS) methods in two periods (2007 and 2012). Eleven ESBL-producing isolates from 2012 and 39 banked strains were genotyped by PCR. Twenty-six (4.6%) strains produced ESBL by CDS. Only 57.7% of CDS-confirmed ESBL strains had an initial reduced cephalosporin zone. Vitek 2 identified only nine (34.6%) CDS-ESBL strains. There was no significant change in ESBL strain prevalence over the two periods by CDS, but our laboratory information system showed a steady increase from 2007-2012 in ESBL strain prevalence (identified by multiple methods) at a rate of 0.02% per month to reach 2% by 2012. Genotyping of 50 CDS-confirmed isolates demonstrated ESBL genes in 44 (88%), mainly CTX-M genes. Twenty-five ESBL strains contained more than one β-lactamase gene, up to a maximum of three genes. There is a rising prevalence of ESBL strains in our communities. CDS and Vitek-2 testing is neither sensitive nor specific in detecting ESBL enzymes. Routine laboratories need access to genotyping to identify and monitor ESBLs in the community.

Monitoring antimicrobial resistance in Neisseria gonorrhoeae in selected countries of the WHO South-East Asia Region between 2009 and 2012: a retrospective analysis

ObjectiveThe aim of the present study was to retrospectively analyse the data reported on antimicrobial resistance (AMR) in Neisseria gonorrhoeae in six South-East Asia Region countries from 2009 to 2012...

A disc test of antifungal susceptibility

Diagnostic laboratories are frequently requested to perform antifungal susceptibility tests on isolates recovered from systemic infections. A standard reference procedure of broth dilution was proposed by the Clinical and Laboratory Standards Institute (CLSI), but it is too labour-intensive for most clinical laboratories. CLSI also suggested a disc diffusion method, which is a cost-effective alternative method and simple to use in diagnostic microbiology laboratories. However, the method does not deal satisfactorily with the difficulty in interpretation of inhibitory zones on disc testing of those strains that show a ?trailing effect? on minimum inhibitory concentration (MIC) determination of the azole group of antifungals. Although disconcerting, trailing is regarded as an in vitro phenomenon and these strains are generally regarded as susceptible. We present a disc diffusion test for use with available antifungals, based on the Calibrated Dichotomous Sensitivity (CDS) method, used in antibiotic susceptibility testing of bacteria. The disc testing was done under predetermined optimal condition of growth, that overcame the problem of the ill-defined inhibitory zones of the azoles.

Evaluation of direct disc diffusion susceptibility testing for bacteriuria using diluted urine against standard cds method

Consecutive urine specimens with > or = 10(9) organisms/L on microscopy were diluted 1:100 and direct disc diffusion susceptibility tests performed. Subsequently, the standard Calibrated Dichotomous Sensitivity (CDS) test was performed on all isolates. Urines with > 2 Isolates or where growth was < 10(8) colony forming units (CFU)/L were excluded. Only Gram negative organisms were considered. 361 urines were evaluated, 324 with one and 37 with 2 isolates, comprising 255 Escherichia coli, 49 klebsiella, 41 proteus, 29 either citrobacter, enterobacter, providencia, serratia or alcaligenes, and 14 Pseudomonas aeruginosa. There were 2272 organism/antimicrobial test comparisons. A concordance of 98.5% was obtained. The results are considered acceptable for routine clinical use.

Biological screening of selected traditional medicinal plants species utilized by local people of Manokwari, West Papua Province

Abstract. Lense O. 2011. Biological screening of selected traditional medicinal plants species utilized by local people of Manokwari, West Papua Province. Nusantara Bioscience 3: 145-150. The aim of the research was to determine the presence of alkaloids and anti-microbial activity in extracts from selected medicinal plants from Manokwari District, West Papua, Indonesia. The method of alkaloid testing followed the standard phytochemical methods. The procedure of the Calibrated Dichotomous Sensitivity (CDS) test was used for the antimicrobial bioassays. Results of biological screening suggested that all but one of the 56 species tested contained different levels of alkaloids. Eleven species showed anti-microbial activity using bioassays of responses to two bacteria, Salmonella typhi and Klebsiella pneumoniae, and two fungi Candida albicans, and Cryptococcus neoformans; none of the plant extracts showed an antimicrobial effect against the bacteria Escherichia coli. Extract of Planconella sp. was the most active one as it showed activity against three different organisms (C. albicans, C. neoformans, and S. typhi).