Significant Microbial Growth Research Articles

Monitoring and characterisation of bacteria in corroding district heating systems using fluorescence in situ hybridisation and microautoradiography

Presence of biofilm and biocorrosion has been observed in Danish district heating (DH) systems despite very good water quality that was expected to prevent significant microbial growth. The microbiological water quality was investigated in order to identify the dominating bacterial groups on surfaces with corrosion problems. Water samples from 29 DH systems were investigated for the total number of bacteria and presence of sulphate reducing bacteria (SRBs). SRBs were found to be present in more than 80% of the DH systems. The microbial population in samples from 2 DH system (biofilm from a test coupon and an in situ sample from a heat exchanger) was investigated with fluorescence in situ hybridisation, and the results showed significant differences in population composition. Betaproteobacteria was the dominant population in both samples. SRBs were present in both samples but were most numerous in the biofilm from the test coupon. Examination of functional groups based on uptake of radiolabelled acetate (microautoradiography) showed presence of both aerobic and anaerobic bacteria despite the fact that oxygen is not anticipated in DH systems.

Prevalence of Asymptomatic Genital Infection among Pregnant Women in Benin City, Nigeria

The prevalence of asymptomatic genital infection among pregnant women and their susceptibility to antibacterial agents was investigated to provide baseline data on common asymptomatic genital microorganisms and identify potentials for development of clinical disease among this cohort of patients. High vaginal swabs were obtained from five hundred consecutive and consenting pregnant women attending the antenatal clinic of the University of Benin Teaching Hospital (UBTH) and the Central Hospital, both in Benin City, Nigeria. A total of three hundred specimens showed significant microbial growth, giving a prevalence rate of 60% for asymptomatic genital infections. Candida albicans (65%), Staphylococcus aureus (51.8%) and Enterobacteriacae (E. coli and Klebsiella species) were predominantly isolated, followed by Trichomonas vaginalis and Neisseria gonorrhoea. Most of the bacterial isolates were susceptible to ciprofloxacin, ceftazidime, cotrimoxazole, norfloxacin and augmentin. All the isolates except Streptococcus faecalis were resistant to ampicillin. These results show a high rate of asymptomatic genital tract infections among pregnant women in Benin City, which have implications for adverse maternal and neonatal outcomes.

Degradation and mineralization of high-molecular-weight polycyclic aromatic hydrocarbons by defined fungal-bacterial cocultures.

This study investigated the biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons (PAHs) in liquid media and soil by bacteria (Stenotrophomonas maltophilia VUN 10,010 and bacterial consortium VUN 10,009) and a fungus (Penicillium janthinellum VUO 10, 201) that were isolated from separate creosote- and manufactured-gas plant-contaminated soils. The bacteria could use pyrene as their sole carbon and energy source in a basal salts medium (BSM) and mineralized significant amounts of benzo[a]pyrene cometabolically when pyrene was also present in BSM. P. janthinellum VUO 10,201 could not utilize any high-molecular-weight PAH as sole carbon and energy source but could partially degrade these if cultured in a nutrient broth. Although small amounts of chrysene, benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene were degraded by axenic cultures of these isolates in BSM containing a single PAH, such conditions did not support significant microbial growth or PAH mineralization. However, significant degradation of, and microbial growth on, pyrene, chrysene, benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene, each as a single PAH in BSM, occurred when P. janthinellum VUO 10,201 and either bacterial consortium VUN 10,009 or S. maltophilia VUN 10,010 were combined in the one culture, i.e., fungal-bacterial cocultures: 25% of the benzo[a]pyrene was mineralized to CO(2) by these cocultures over 49 days, accompanied by transient accumulation and disappearance of intermediates detected by high-pressure liquid chromatography. Inoculation of fungal-bacterial cocultures into PAH-contaminated soil resulted in significantly improved degradation of high-molecular-weight PAHs, benzo[a]pyrene mineralization (53% of added [(14)C]benzo[a]pyrene was recovered as (14)CO(2) in 100 days), and reduction in the mutagenicity of organic soil extracts, compared with the indigenous microbes and soil amended with only axenic inocula.

A biogeochemical assessment of the Tono site, Japan

When designing investigations of microbial populations in the subsurface, it is extremely valuable to undertake scoping calculations to estimate the likely microbial abundances and evaluate the effects of contamination during sampling. A biogeochemical assessment of the groundwater and lithologies of the Tono mine, Japan, has been made using the BGS/NAGRA computer code BGSE (Bacterial Growth in Subsurface Environments). This code enables an assessment to be made of the maximum microbial growth rates that may be achieved in ideal circumstances, based on availability of nutrients and energy calculated from mineralogical and groundwater analyses. The effect of drilling fluid/groundwater mixing on biomass was assessed using a hypothetical drilling fluid composition. The results of modelling the mixing between groundwater and drilling fluid shows that the addition of only small concentrations of drilling fluid (<1% (v/v)) to the groundwater gives rise to significant microbial growth rates for the systems studied. Maximum growth rates were observed at ratios of 50:50 (v/v) (groundwater: drilling fluid) for the Akeyo and Toki lower groundwaters, and ratios of 90:10 (v/v) (groundwater:drilling fluid) for the Toki upper and Granite groundwaters. At low ratios of drilling fluid (<1% (v/v)) the limiting factor in each system was the availability of an energy source. This reflects the fact that the system is approaching pristine conditions. However, there was sufficient energy to permit a significant growth rate to be observed.

Effect of irradiation and chilled storage on the microbiological and sensory quality of a ready meal

SummaryThe sensory and microbiological quality of both non‐irradiated and irradiated cook‐chill ready meals consisting of roast beef and gravy, cauliflower and sauce together with roast and mashed potatoes were assessed at intervals during 15 d storage at 2–3°C.Growth of Pseudomonas spp. caused obvious spoilage of the non‐irradiated meals after storage, whereas spoilage was not apparent in the irradiated meals. Irradiation (2 and 3 kGy) reduced the number of microorganisms in the meal to &lt;100 g−1 initially and significant microbial growth did not occur during storage.Using sensory profiling techniques a trained panel found that the effects of irradiation and chilled storage were most apparent in the cauliflower and potato components and occurred most often in the colour, appearance and textural attributes.The combination of low dose irradiation and chilled storage effectively controlled microbial growth but changes in the sensory characteristics may limit the potential of irradiation to extend the shelf‐life and enhance the safety of this ready meal.

Rapid quantification of bacterial and fungal growth in burn wounds: biopsy homogenate Gram stain versus microbial culture results

A prospective analysis of 370 burn wound biopsies was done to correlate Gram-stain results from biopsy homogenates with quantitative culture results. The number of bacteria seen in a total of 10 oil immersion microscope fields of Gram-stained homogenates was correlated with significant microbial growth (1×10 5 organisms/gram of tissue) of the same biopsy homogenate plated on trypticase soy agar. Of the biopsies examined, Gram-negative rods were present in 36·8 per cent, Gram-positive cocci in 49·7 per cent and yeast in 15·9 per cent. Mixtures of organisms were present in 24·3 per cent. When Gram stains showed one or more organisms per oil immersion microscope field, the correlation with significant microbial growth was 94·5 per cent or more. When five or more organisms were seen per field, the correlation with significant growth became 97 per cent or greater. When no organism was seen on Gram stain, the cultures grew significant numbers of organisms 19·1 per cent of the time or less. This false-negative rate was considered to be high. It is believed, however, that this method of early detection of significant burn wound microbial growth may prove to be valuable in the management of severely burned patients.