Oxoid Medium Research Articles

Sensitivity and Selectivity of Two Commercially Available Media for Legionella spp. Recovery from Environmental Water Samples.

The quality control of culture media used for Legionella spp. isolation and enumeration is paramount to achieve a satisfactory degree of comparability among water testing results from different laboratories. Here, we report on a comparative assessment of the sensitivity and selectivity of MWY and BCYEα media supplied by two different manufacturers (i.e., Xebios Diagnostics GmbH and Oxoid Ltd) for the detection of Legionella spp. from environmental water samples. Even though our analysis showed an excellent agreement between the recovery rates of the four media tested (90.5%), the quantitative recovery of Legionella spp. colonies using Xebios media was significantly greater than that achieved by Oxoid media (P = 0.0054). Furthermore, the sensitivity of detection was significantly higher when samples were plated on MWY Xebios agar (P = 0.0442), while the selectivity of MWY appeared to be the same regardless of the manufacturer. Furthermore, MWYXebios agar favored the growth of much larger colonies compared to those observed on MWYOxoid agar. Finally, MWYXebios medium enhanced the recovery of non-pneumophila Legionella species. Collectively, our findings demonstrate that quality control is crucial to ensure high selectivity and sensitivity of the culture media used for the detection and enumeration of Legionella spp. from environmental water resources. As water remediation measures strictly depend on Legionella spp. recovery, culture protocol standardization, as well as quality control of the culture media, is essential to achieve intra- and interlaboratory reproducibility and accuracy.

Influence of Media and Testing Methodology on Susceptibility to Tigecycline of Enterobacteriaceae with Reported High Tigecycline MIC

The tigecycline susceptibility of six different Enterobacteriaceae strains with reported high tigecycline MICs was determined in quintuplicate by four methodologies using Mueller-Hinton agar and broth from six manufacturers. The MICs determined by Etest were a >or=1-fold dilution lower than those determined by broth microdilution and agar dilution, with the highest modal values given by agar dilution. The highest modal MICs were obtained using Oxoid medium, and the lowest inhibition zone values (disc diffusion) were obtained using Oxoid and bioMérieux media. The lowest MICs were obtained by Etest using Difco or Merck media.

Preliminary Evaluation of a Laboratory-Prepared Voges-Proskauer Medium

The performance of a Voges-Proskauer (VP) medium prepared from basic chemical reagents in the laboratory was compared with that of a commercial VP medium, obtained from Oxoid (Basingstoke, UK), using 64 coded laboratory cultures. The sensitivity of the laboratory-prepared VP medium was 100% and the specify was 96%. The percentage accuracy of the laboratory medium was 98.4% and colour development on which the result of the VP reaction depends was more intense in the laboratory-prepared medium than in the Oxoid medium. This blind study indicates that reasonable accuracy can be achieved when VP reaction is determined using a medium prepared in the laboratory with basic chemical reagents. It is suggested that the laboratory prepared medium can conveniently replace the commercial VP medium in the determination of VP reaction in laboratories with limited resources. Key words: Voges-Proskauer medium, evaluation, cost, Enterobacteriaceae Journal of Medical Laboratory Sciences Vol.12(1) 2003: 15-24

Interaction of an Acanthamoeba human isolate harboring bacteria with murine peritoneal macrophages.

Acanthamoeba spp. are the causative agents of granulomatous amebic encephalitis (GAE), a chronic progressive fatal infection of the central nervous system. These free-living amebae have been associated, also with cutaneous acanthamoebiasis and sinusitis in immunocompromised patients [8,10,13]. Studies on the biological properties of these amebae have been performed using strains cultured axenically for long periods of time. Virulence in the ameba declines after prolonged culture in vitro [11]. Therefore, a recent clinical isolate obtained from an immune suppressed patient who had undergone a renal transplant was subjected to immediate analysis. The patient was diagnosed post mortem with disseminated acanthamoebiasis based on the presence of trophozoites and cysts in hematoxylin and eosin stained tissue sections [13]. Amebae were isolated from cutaneous lesions at the time of autopsy and cultured axenically in Oxoid medium. The clinical isolate was identified as Acanthamoeba and was shown to harbor bacteria both within trophozoites and cysts. Furthermore, co-culture of these amebae with murine peritoneal macrophages resulted in a robust induction of the pro-inflammatory cytokine tumor necrosis factor alpha (TNFa) at levels, which approximated those elicited by the potent immunomodulator bacterial lipopolysaccharide (LPS).

Media for the detection of sulphide-producing bacteria in industrial water systems

The importance of sulphate-reducing bacteria (SRB) in microbiological induced corrosion (MIC) has been widely recognized for many years [1]. There are many formulations of culture media used for enumerating SRB [2,3]. Previous studies indicated that viable count procedures underestimated the in situ population by a factor of approximately 1000 compared to in situ sulphate reduction activity [1,4]. The aim of this study was to evaluate different isolation media and carbon sources for the isolation and detection of SRB in South African industrial water systems. Modified iron sulphite (IS) medium yielded the highest numbers when used to enumerate SRB from pure cultures and industrial water samples. When comparing API, SABS, IS, Oxoid and modified synthetic medium using pure cultures of Desulfovibrio desulfuricans IS-medium gave a 12.1%, 40%, 53.3% and 60.3% higher recovery than SABS-, Postgate-, API- and synthetic medium, respectively ( p < 0.05). IS-medium gave a 20.1%, 61.8% and 100% higher recovery than SABS-, API- and Oxoid medium, respectively, when using pure cultures of Desulfotomaculum orientis ( p < 0.05). The dominant sulphide-producing bacteria isolated from the industry using IS-medium were facultative aerobic gram-negative rods that were able to produce sulphide from sulphite under strictly anaerobic conditions. IS-medium was therefore not selective for SRB only. H 2S-producing bacteria that utilized lactate, acetate, formate or palmitic acid as different carbon sources were also isolated from industrial water samples when using synthetic medium.

Mutagenicity of dichloroacetylene and its degradation products trichloroacetyl chloride, trichloroacryloyl chloride and hexachlorobutadiene

Dichloroacetylene (DCA) is a highly reactive compound that decomposes rapidly in contact with air into a series of chlorinated aliphatic hydrocarbons (e.g., phosgene, trichloroacetyl chloride, trichloroacryloyl chloride and hexachlorobutadiene). Experiments were performed to compare the mutagenic properties of DCA and its degradation products on the histidine-dependent tester strains TA98 and TA100 of Salmonella typhimurium. In these experiments, DCA vapour was streamed under analytical control through the bacterial suspensions. DCA is soluble in aqueous solution and was stable under the experimental steady-state conditions of the bacterial exposure. There is a linear correlation between the supply of DCA vapour and solubilized DCA in the range of 1000 and 16 000 ppm. Mutagenic response was observed with strain TA100 if the bacteria were suspended in Oxoid medium. No mutagenicity could be detected with strain TA98. DCA mixtures with acetylene, as used as stabilizer for animal experiments, were not mutagenic in either bacterial strain, irrespective of the presence or absence of S9 mix in the cell suspension. One of the degradation products of DCA, trichloroacryloyl chloride, showed pronounced mutagenic properties with and without drug-metabolizing enzymes. Other degradation products of DCA, such as trichloroacetyl chloride and hexachlorobutadiene, were not mutagenic, either in the presence or absence of liver homogenate.