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The aim of this study was to investigate the reliability of disc diffusion testing with penicillin, erythromycin and ciprofloxacin within the viridans group streptococci (VGS). In total, the antibiotic susceptibilities of 167 VGS isolates were compared by standard disc diffusion and broth microdilution methods, and these phenotypic data were compared to the carriage of the respective gene resistance determinants [ermB and mefA/E (macrolides); QRDR, gyrA, gyrB, parC and parE (quinolones)]. Overall, there were 35 discrepancies [resistant by MIC and susceptible by zone diameter (21.0%)] between MIC and disc diameter when penicillin susceptibility was interpreted by Clinical and Laboratory Standards Institute criteria. Scattergrams showed a bimodal distribution between non-susceptible and susceptible strains when erythromycin susceptibility was tested by both methods. Thirty-four (20.4%) isolates were categorized as resistant by MIC breakpoints, while disc diameter defined these as having intermediate resistance. With ciprofloxacin, three isolates (1.8%) showed minor discrepancies between MIC breakpoints and disc diameter. Isolates non-susceptible to all three antimicrobial agents tested were reliably distinguished from susceptible isolates by disc diffusion testing, except for the detection of low-level resistance to penicillin, where broth microdilution or an alternative quantitative MIC method should be used. Otherwise, we conclude that disc diffusion testing is a reliable method to detect strains of VGS non-susceptible to penicillin, erythromycin and ciprofloxacin, as demonstrated with their concordance to their gene resistance characteristics., (© 2011 SGM)

Current methods for the detection of Cryptosporidium oocysts in water samples are both time-consuming and subject to variation in sensitivity. A genus-specific PCR assay was designed for the specific amplification of a 552-bp region of the 18S rRNA gene. Postamplification endonuclease restriction generated unique digest patterns that enabled differentiation between the three species, C. muris, C. baileyi and C. parvum, the major human pathogen. Theoretical restriction profiles for other Cryptosporidium species were also predicted. The assay routinely detected 10 oocysts in 10-ml purified oocyst preparations, but sensitivity was found to be 10(3)-10(4) -fold lower in environmental water samples. The use of Chelex resin and an immunomagnetic separation procedure overcame this inhibition. This provided detection levels of 10(1)-10(3) oocysts, depending on water turbidity. Rapid and sensitive pathogen detection methods are essential for the water industry. The results of this study demonstrate that PCR has the potential to improve current detection capabilities greatly by differentiating the major human pathogens from non-pathogenic species. This will greatly facilitate a closer examination of the epidemiology of this important pathogen.