An in vitro study assessing the infection risk of low-cost polyethylene mosquito net compared with commercial hernia prosthetics.

BACKGROUND: The innovative use of sterilized mosquito net as a cheaper alternative to commercial mesh for hernia repair has gained increasing recognition. Developing health care systems have inherently higher surgical site infection rates, and concerns regarding the introduction of untested prosthetic hernia meshes have been raised. This in vitro study assesses the infection risk of polyethylene (PE) mosquito net mesh compared with commercial hernia prosthetics by assessing the essential (first) step in the pathogenesis of mesh infections. MATERIALS AND METHODS: Individual meshes were inoculated with Staphylococcusepidermidis and Staphylococcusaureus with a bacterial inoculum of 10(2) bacteria. Inoculated meshes were incubated for 18 h in tryptone soy broth and then analyzed using scanning electron microcopy. The final fraction of the bacteria adherent to each of the meshes was compared. One-way analysis of variance was performed on the bacterial counts. The Tukey test was used to determine the difference between the different biomaterials in the event the one-way analysis of variance was significant. RESULTS: There was no significant difference in the mean number of adherent bacteria to PE mosquito net compared with the monofilament polypropylene-based meshes (Prolene and Bard Soft Mesh). Multifilament Vypro mesh had significantly greater mean bacterial adherence compared with PE mosquito net (P < 0.001 with S aureus and P = 0.003 with S epidermidis). CONCLUSIONS: In vitro infection risk of PE mosquito net is not significantly different from commonly used monofilament polypropylene commercial prosthetics and is in fact lower than a commonly used commercial multifilament mesh. This study adds to the growing body of evidence that indicates that these meshes can be safely deployed.

An experimental study exploring the relationship between the size of bacterial inoculum and bacterial adherence to prosthetic mesh.

BACKGROUND: Infection is a major concern with medical implants. Surgical meshes used for the repair of abdominal wall hernias are associated with wound infection rates ranging from 7 to 18 %. Although mesh infection is relatively rare, once a patient shows clinical signs of mesh infection, the surgeon may be required to remove the mesh, resulting in additional surgery, morbidity, and cost. The usual causative organisms associated with cases of mesh infection are Staphylococcus species. The first stage of implant infection is bacterial adherence to the biomaterial. An accurate assessment of adherent bacteria to medical prosthetics is therefore important in order to determine the infection risk associated with surgical implants. METHODS: This experimental study evaluated the relationship between the size of the bacterial inoculum and bacterial adherence to three commonly used hernia prosthetics (polypropylene, polyester, and ePTFE). Tenfold dilutions of S. epidermidis (Evans-ATCC 12228) and S. aureus (Rosenbach-ATCC 25923), created with phosphate-buffered saline, were used to inoculate each of the meshes in 3 ml of tryptone soya broth for 18 h at 37 °C, 95 % air/5 % CO(2). The number of viable bacteria in each dilution was calculated using a spot plate technique. The number of adherent bacteria to the meshes was counted using direct imaging analysis with scanning electron microscopy and expressed as a mean. RESULTS: One hundred eight mesh samples were analysed. The size of the bacterial inoculum of S. epidermidis significantly influenced the number of adherent bacteria to the mesh, and lower rates of adhesion were observed with smaller inoculums for all three meshes (polypropylene, p = 0.02; ePTFE p = 0.03; polyester p = 0.02). A similar, albeit less profound, pattern of results was observed with S. aureus. Bacterial adherence was observed with inoculum sizes as small as <10 bacteria. CONCLUSIONS: The results demonstrate that even a very low number of bacterial inoculums can result in adherence to hernia biomaterials and that the level of adherence is directly related to the size of the inoculum. These in vitro results provide evidence that the size of the inoculum is important in the colonization of hernia biomaterials and demonstrate the importance of minimising the bacterial inoculum in the clinical setting.

Design and validation of a novel quantitative method for rapid bacterial enumeration using programmed stage movement scanning electron microscopy.

The adhesion of bacteria to surgical implants is the first stage of implant infection. The method for detecting bound bacteria is an important consideration in the study of bacterial adherence and colonisation. Enumeration of bacteria by direct visualisation techniques is labour intensive and time consuming. We have developed and validated a method for enumerating bacteria on porous material surfaces using programmed stage movement scanning electron microscopy and compared cumulative counts after 1-10 stage movements with absolute bacterial counts. We describe this method with three commercially sourced meshes used for abdominal wall hernia repair and with three different inoculums of Staphylococcus epidermidis. The results demonstrate significant correlation to the absolute count after five cumulative counts for all meshes analysed. The mean time saved by the cumulative counting method was 1h and 9 min per mesh. We conclude that advances in scanning electron microscopy and the advent of precise automated stage control have facilitated rapid data acquisition for bacterial counting purposes and that five cumulative counts at 1000× or 2500× magnification are a valid quantitative method for enumerating S. epidermidis bacteria on porous surfaces (with a pore size of up to 1.3 mm).

Guidelines for prevention and control of group A streptococcal infection in acute healthcare and maternity settings in the UK.

Hospital outbreaks of group A streptococcal (GAS) infection can be devastating and occasionally result in the death of previously well patients. Approximately one in ten cases of severe GAS infection is healthcare-associated. This guidance, produced by a multidisciplinary working group, provides an evidence-based systematic approach to the investigation of single cases or outbreaks of healthcare-associated GAS infection in acute care or maternity settings. The guideline recommends that all cases of GAS infection potentially acquired in hospital or through contact with healthcare or maternity services should be investigated. Healthcare workers, the environment, and other patients are possible sources of transmission. Screening of epidemiologically linked healthcare workers should be considered for healthcare-associated cases of GAS infection where no alternative source is readily identified. Communal facilities, such as baths, bidets and showers, should be cleaned and decontaminated between all patients especially on delivery suites, post-natal wards and other high risk areas. Continuous surveillance is required to identify outbreaks which arise over long periods of time. GAS isolates from in-patients, peri-partum patients, neonates, and post-operative wounds should be saved for six months to facilitate outbreak investigation. These guidelines do not cover diagnosis and treatment of GAS infection which should be discussed with an infection specialist.

A novel hemotropic Mycoplasma (hemoplasma) in a patient with hemolytic anemia and pyrexia.

A patient with chronic moderate neutropenia, acute hemolysis, and pyrexia was found to be infected with a novel hemoplasma species. A clinical response to doxycyline was noted, and moxifloxacin was added subsequently to aid infection clearance. This represents the first report of hemolysis in association with confirmed hemoplasma infection in a human.

Comparison of BD Phoenix, Vitek 2, and MicroScan automated systems for detection and inference of mechanisms responsible for carbapenem resistance in Enterobacteriaceae.

We assessed the ability of three commercial systems to infer carbapenem resistance mechanisms in 39 carbapenemase-producing and 16 other carbapenem-resistant Enterobacteriaceae. The sensitivity/specificity values for "flagging" a likely carbapenemase were 100%/0% (BD Phoenix), 82 to 85%/6 to 19% (MicroScan), and 74%/38% (Vitek 2), respectively. OXA-48 producers were poorly detected, but all systems reliably detected isolates with KPC and most with metallo-carbapenemases.