Investigation of a pseudo-outbreak of orthopedic infections caused by Pseudomonas aeruginosa

A rapid culture independent methodology to quantitatively detect and identify common human bacterial pathogens associated with contaminated high purity water

Background

Water and High Purity Water (HPW) distribution systems can be contaminated with human pathogenic microorganisms. This biocontamination may pose a risk to human health as HPW is commonly used in the industrial, pharmaceutical and clinical sectors. Currently, routine microbiological testing of HPW is performed using slow and labour intensive traditional microbiological based techniques. There is a need to develop a rapid culture independent methodology to quantitatively detect and identify biocontamination associated with HPW.

Results

A novel internally controlled 5-plex real-time PCR Nucleic Acid Diagnostics assay (NAD), was designed and optimised in accordance with Minimum Information for Publication of Quantitative Real-Time PCR Experiments guidelines, to rapidly detect, identify and quantify the human pathogenic bacteria Stenotrophomonas maltophilia, Burkholderia species, Pseudomonas aeruginosa and Serratia marcescens which are commonly associated with the biocontamination of water and water distribution systems. The specificity of the 5-plex assay was tested against genomic DNA isolated from a panel of 95 microorganisms with no cross reactivity observed. The analytical sensitivities of the S. maltophilia, B. cepacia, P. aeruginosa and the S. marcescens assays are 8.5, 5.7, 3.2 and 7.4 genome equivalents respectively.

Subsequently, an analysis of HPW supplied by a Millipore Elix 35 water purification unit performed using standard microbiological methods revealed high levels of naturally occurring microbiological contamination. Five litre water samples from this HPW delivery system were also filtered and genomic DNA was purified directly from these filters. These DNA samples were then tested using the developed multiplex real-time PCR NAD assay and despite the high background microbiological contamination observed, both S. maltophilia and Burkholderia species were quantitatively detected and identified. At both sampling points the levels of both S. maltophilia and Burkholderia species present was above the threshold of 10 cfu/100 ml recommended by both EU and US guidelines.

Conclusions

The novel culture independent methodology described in this study allows for rapid (<5 h), quantitative detection and identification of these four human pathogens from biocontaminated water and HPW distribution systems. We propose that the described NAD assay and associated methodology could be applied to routine testing of water and HPW distribution systems to assure microbiological safety and high water quality standards.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0124-1) contains supplementary material, which is available to authorized users.

Pseudo-outbreak of extremely drug-resistant pseudomonas aeruginosa urinary tract infections due to contamination of an automated urine analyzer

By the end of May 2010, an increase in the number of urine specimens that were culture positive for extremely drug-resistant (XDR) Pseudomonas aeruginosa was observed in our 800-bed university hospital. This led to an infection control alert. No epidemiological link between the patients and no increase in the frequency of XDR P. aeruginosa in non-urine samples were observed. Therefore, a pseudo-outbreak due to analytical contamination in the laboratory was rapidly suspected. A prospective and retrospective search of cases was initiated, and the sampling of the automated urine analyzers used in the laboratory was performed. Antibiotypes were determined by disc diffusion, and genotypes were determined by pulsed-field gel electrophoresis (PFGE). From February to July 2010, 17 patients admitted to 12 different departments and 6 outpatients were included. The mixing device of the cytometric analyzer used for the numeration of urinary particles (Sysmex UF1000i) proved to be heavily contaminated. Isolates recovered from 12 patients belonged to the same antibiotype and PFGE type as the isolate recovered from the analyzer. Extensive disinfection with a broad-spectrum disinfectant and the replacement of the entire tubing was necessary to achieve the complete negativity of culture samples taken from the analyzer. A pseudo-outbreak caused by an XDR P. aeruginosa clone was proven to be due to the contamination of the cytometric analyzer for urinary sediment. Users of such analyzers should be aware that contamination can occur and should always perform culture either before the processing of the urine sample on the analyzer or on a distinct sample tube.

Laboratory contamination affecting orthopedic surgical management

Bacterial contamination of pathology specimens can occur during collection, transport, or laboratory processing. Recognized sources of laboratory contamination include contamination of microscopy slides before use and contamination of reagents. We present 2 cases where contamination of glass beads used in the microbiology department as part of the tissue preparation process for urgent Gram stain led to unnecessary revision surgery. Contamination of the glass beads alone has not been cited elsewhere in the literature, and the authors feel that this needs to be brought to the attention of arthroplasty surgeons and microbiologists.

Delayed recognition of a pseudo-outbreak of Mycobacterium terrae

Pseudo-outbreaks of mycobacteria are difficult to recognize because of long incubation periods for growth and species identification. We report our experience with one clinical microbiology laboratory that isolated a species of nontuberculous mycobacteria from 14 patient specimens. These specimens came from 12 patients at 2 hospitals over a 6-day period and included 6 different fluids or tissues. Because of the delay between mycobacterial specimen submission and growth in culture, the outbreak was not noted until more than a month later. Initial species determination by a reference laboratory indicated that these isolates were Mycobacterium fortuitum. One patient received treatment for presumed M fortuitum brain infection, and it was not effective in changing her clinical course. The isolates were sent to the Centers for Disease Control and Prevention (CDC) for identification and typing by pulsed-field gel electrophoresis. The CDC determined that the isolates were an identical strain of M terrae, thus confirming a pseudo-outbreak. Combining pseudo-outbreak isolates with those correctly identified initially as M terrae during the 6-day period in question, there were 22 samples from 20 patients with M terrae. Since the pseudo-outbreak, the number of cultures of M terrae in the clinical laboratory has returned to baseline levels without any specific intervention.

[Epidemiology of nosocomial infections due to Pseudomonas aeruginosa, Burkholderia cepacia and Stenotrophomonas maltophilia]

Non-fermentative Gram negative rods are opportunistic pathogens responsible for nosocomial infections. Using phenotypic markers (serotypes for Pseudomonas aeruginosa and antibiotic susceptibility) allows a preliminary screening of epidemiologically-related strains. However, genotypic markers are necessary to better characterize nosocomial strains for the investigation of outbreaks or cross-transmissions in the hospital setting. Infections due to P. aeruginosa, Burkholderia. cepacia or Stenotrophomonas. maltophilia are usually hospital-acquired and responsible for a high mortality rate as illustrated by the lethality of nosocomial pneumonia due to P. aeruginosa. The severity of these infections is due to the virulence factors of the bacteria and to their occurrence in debilitated patients in whom invasives devices are used. The hospital environment can act as a reservoir with a rate of exogeneous transmission of these bacteria as high as 50% in some studies. To better prevent nosocomial infections related to Gram negative non fermentative rods, the control of the aqueous hospital environment, the strict application of hand disinfection and the investigation of potential cross-transmission in the hospital setting are needed.

Ralstonia paucula (Formerly CDC group IV c-2): unsuccessful strain differentiation with PCR-based methods, study of the 16S-23S spacer of the rRNA operon, and comparison with other Ralstonia species (R. eutropha, R. pickettii, R. gilardii, and R. solanacearum)

Ralstonia paucula (formerly CDC group IV c-2) can cause serious human infections. Confronted in 1995 with five cases of nosocomial bacteremia, we found that pulsed-field gel electrophoresis could not distinguish between the isolates and that randomly amplified polymorphic DNA analysis was poorly discriminatory. In this study, we used PCR-ribotyping and PCR-restriction fragment length polymorphism analysis of the spacer 16S-23S ribosomal DNA (rDNA); both methods were unable to differentiate R. paucula isolates. Eighteen strains belonging to other Ralstonia species (one R. eutropha strain, six R. pickettii strains, three R. solanacearum strains, and eight R. gilardii strains) were also tested by PCR-ribotyping, which failed to distinguish between the four species. The 16S-23S rDNA intergenic spacer of R. paucula contains the tRNA(Ile) and tRNA(Ala) genes, which are identical to genes described for R. pickettii and R. solanacearum.