Risk factors for bacterial catheter colonization in regional anaesthesia

BACKGROUND: Although several potential risk factors have been discussed, risk factors associated with bacterial colonization or even infection of catheters used for regional anaesthesia are not very well investigated. METHODS: In this prospective observational trial, 198 catheters at several anatomical sites where placed using a standardized technique. The site of insertion was then monitored daily for signs of infection (secretion at the insertion site, redness, swelling, or local pain). The catheters were removed when clinically indicated (no or moderate postoperative pain) or when signs of potential infection occurred. After sterile removal they were prospectively analyzed for colonization, defined as > 15 colony forming units. RESULTS: 33 (16.7%) of all catheters were colonized, and 18 (9.1%) of these with additional signs of local inflammation. Two of these patients required antibiotic treatment due to superficial infections. Stepwise logistic regression analysis was used to identify factors associated with catheter colonization. Out of 26 potential factors, three came out as statistically significant. Catheter placement in the groin (odds-ratio and 95%-confidence interval: 3.4; 1.5-7.8), and repeated changing of the catheter dressing (odds-ratio: 2.1; 1.4-3.3 per removal) increased the risk for colonization, whereas systemic antibiotics administered postoperatively decreased it (odds ratio: 0.41; 0.12-1.0). CONCLUSION: Colonization of peripheral and epidural nerve catheter can only in part be predicted at the time of catheter insertion since two out of three relevant variables that significantly influence the risk can only be recorded postoperatively. Catheter localisation in the groin, removal of the dressing and omission of postoperative antibiotics were associated with, but were not necessarily causal for bacterial colonization. These factors might help to identify patients who are at increased risk for catheter colonization.     

Evaluation of the Adherence of Candida Species to Urinary Catheters

Catheter-associated urinary tract infections (CAUTIs) are the most common kind of nosocomial infection. Recent years have seen a significant increase in numbers of infections caused by yeasts of the genus Candida. The adherence of a microorganism to the host surface is a decisive factor in the success of colonization and the pathogenesis of infection. The objective of this work was to evaluate the adherence of species of the genus Candida to urinary catheters. In vitro adherence to the sections of latex and silicon catheters of Candida albicans and Candida parapsilosis were studied. Adherence was measured by counting the number of adhering viable cells and the results were expressed as Colonies Forming Units per mL. The results demonstrated that the latex catheter facilitated adherence more than the silicon catheter (p < 0.01). The adherence of the C. albicans was significantly greater than C. parapsilosis on latex, but it was similar on silicon.     

Bacterial strains colonizing subcutaneous catheters of personal insulin pumps

Continuous subcutaneous insulin infusion (CSII) is a commonly used, safe intensive insulin therapy method effective in maintaining normoglycaemia. The disadvantage of CSII are skin infections of the catheter injection site. The aim of the study was to gain insight on the colonization of subcutaneous insulin pump catheters by skin flora and to investigate the correlation between Staphylococcus aureus carrier state (presence in the nose), its presence on the skin and catheter. 141 catheters obtained from 94 children with T1DM and CSII were examined using the semi quantitative culture technique of Maki. The result was positive in 34 examinations (24.1%) in 30 children (31.9%). Most often coagulase negative staphylococci were isolated (30), mainly Staphylococcus epidermidis, 1/3 of the staphylococci were methicillin resistant. S. aureus was detected in 7 examinations in 6 children. S. aureus carrier state was proved in 31.9% of all examined patients, more often in children with a positive catheter culture (41.4%), there were no MRSA. No correlation between S. aureus carrier state and catheter colonization was shown. Statistically significant correlations between: coagulase negative staphylococci presence, including the methicillin resistant strains, on the skin and on the catheter surface (p< 0.0001); glycosylated hemoglobin (HbA1c) and bacteria catheter colonization (p = 0.0335) were observed. Subcutaneous catheter colonization by microorganisms often occurs in CSII. Microorganisms found on the skin are the most frequent cause of the subcutaneous catheter infection.     

Virulence factors in Proteus bacteria from biofilm communities of catheter-associated urinary tract infections

More than 40% of nosocomial infections are those of the urinary tract, most of these occurring in catheterized patients. Bacterial colonization of the urinary tract and catheters results not only in infection, but also various complications, such as blockage of catheters with crystalline deposits of bacterial origin, generation of gravels and pyelonephritis. The diversity of the biofilm microbial community increases with duration of catheter emplacement. One of the most important pathogens in this regard is Proteus mirabilis. The aims of this study were to identify and assess particular virulence factors present in catheter-associated urinary tract infection (CAUTI) isolates, their correlation and linkages: three types of motility (swarming, swimming and twitching), the ability to swarm over urinary catheters, biofilm production in two types of media, urease production and adherence of bacterial cells to various types of urinary tract catheters. We examined 102 CAUTI isolates and 50 isolates taken from stool samples of healthy people. Among the microorganisms isolated from urinary catheters, significant differences were found in biofilm-forming ability and the swarming motility. In comparison with the control group, the microorganisms isolated from urinary catheters showed a wider spectrum of virulence factors. The virulence factors (twitching motility, swimming motility, swarming over various types of catheters and biofilm formation) were also more intensively expressed.     

Improving our ability to diagnose infections associated with central venous catheters: value of Gram's staining and culture of entry site swabs.

We prospectively studied 45 central venous catheters to determine whether Gram''s staining and culture of skin swabs from the entry site could be used to predict catheter-related infection. Data were collected from insertion site swabs, intracutaneous and intravascular catheter segments, and blood cultures. Surveillance site cultures at the time of dressing changes showed that bacterial growth, once established, persisted until removal of the catheter but that the time of onset of infection was not predictable. Gram''s staining alone and Gram''s staining combined with culture were tested for their ability to predict catheter colonization and catheter-related infection. Bacteria seen with Gram''s staining invariably denoted catheter colonization. When bacteria were not seen with Gram''s staining, positive results of culture did not change the pretest probabilities of colonization or infection; however, negative results of culture reduced the probability of colonization to low levels (likelihood ratio less than 0.06). We conclude that Gram''s staining and culture of skin swabs from the entry site provide, without line removal, a simple, inexpensive and practical test for the diagnosis of catheter-related infection.     

左氧氟沙星浸涂导管对铜绿假单胞菌生物膜的影响

目的评估左氧氟沙星（levofloxacin,LFX）浸涂导管抑制铜绿假单胞菌粘附、定植,防止生物膜形成的能力。方法体外部分：制备LFX浸涂导管。LFX浸涂导管、PVC导管分别浸没在5 mL 50%LB培养液中（含PAO1 108CFU/mL）,37℃孵育6、12、24和48 h,在各时间点,予导管表面和导管培养液进行细菌计数。体内部分：小鼠皮下植入LFX浸涂导管或PVC导管,沿着导管注射PAO1菌液50μL（107CFU）。第1、5天,对植入导管及导管周围组织进行细菌计数及扫描电镜（SEM）观察。结果 （1）LFX浸涂导管显示药物的快速释放。（2）在各孵育时间点,LFX浸涂导管及导管培养液的细菌数较PVC导管均明显减少（P〈0.05）。（3）小鼠感染第1、5天,LFX浸涂植入导管表面没有或很少细菌;LFX浸涂导管较PVC导管能明显减少植入导管周围组织的细菌量（P〈0.05）。（4）SEM观察：感染第1、5天,LFX浸涂导管表面散在单个细菌或者没有细菌;而第1天,PVC导管表面大量细菌分散存在。第5天,导管表面＂珊瑚状＂生物膜形成。结论 LFX浸涂导管能抑制铜绿假单胞菌粘附、定植,防止生物膜形成,从而有效降低导管生物膜相关感染的发生。     

Characteristics of Biofilms from Urinary Tract Catheters and Presence of Biofilm-Related Components in Escherichia coli

Long term catheterization of the urinary tract leads to bacterial colonization of the urine, whereby adherence to the catheter surface is a major determinative factor for colonization. Collection of bacterial isolates from urine and urinary catheters of 45 patients showed multi-species catheter-colonization, while Escherichia coli isolates were frequently found in the urine in high numbers. Biofilm formation of catheter and urine-derived E. coli isolates was associated with the presence of the fluA gene, loss of O-antigen, and expression of type 1 fimbriae. The second messenger cyclic di-GMP (cdiGMP), a major regulator of biofilm formation, regulated adherence to the catheter surface in a selected clinical isolate suggesting that the cdiGMP second messenger pathway may be a target for anti-biofilm therapeutic approaches.     

Síndrome de la bolsa de orina púrpura en dos pacientes institucionalizados

Purple urine bag syndrome (PUBS) is an uncommon but particularly striking phenomenon characterised by a chemical reaction involving the urine, plastic and certain enzymes from some sulphatase- and phosphatase-producing bacteria, including Proteus mirabilis, Escherichia coli and Morganella morganii, amongst others. Following this reaction, the catheter and the bag may be stained red, blue or purple. This phenomenon tends to occur in patients with multiple pathology and with urinary catheters, as part of a urinary tract infection. We describe two clinical cases of PUBS in institutionalised patients with permanent urinary catheters.     

Prevention of catheter-related infections by a new, catheter-restricted antibiotic filling technique

Catheter-related infections pose a hazard to both humans and laboratory animals. The aim of this study was to develop a technique preventing bacterial colonization of intravascular catheters. In 27 dogs a total of 70 catheters were implanted. On an average catheters were used for 207 days. Three protocols were compared: (1) flushing the catheters with a heparinized solution; (2) filling only the catheter lumen with alpha-chymotrypsin solution (225 units/ml); (3) filling only the catheter lumen with a solution containing a mixture of the aminoglycoside antibiotic gentamicin (20 mg/ml) and chymotrypsin (225 units/ml). Catheter fillings were always withdrawn before catheter use. Catheter exit sites were all treated with povidone iodine ointment once a day. Body temperatures and weights were recorded, bacteriological and electron microscopical examinations of catheters performed. Without gentamicin filling all catheters were colonized after a few weeks. The dogs showed clinical signs of chronic bacteraemia. Gentamicin filling eradicated colonization. No further bacteraemia was observed. We conclude that filling only the catheter lumen with a concentrated solution of chymotrypsin and gentamicin, combined with measures to prevent infections via the subcutaneous catheter tunnel, is an effective and safe technique to prevent catheter-related infections.     

The effect of chlorhexidine and gentian violet on the adherence of <Emphasis Type="Italic">Candida</Emphasis> spp. to urinary catheters

Urinary tract infection associated with catheters is the most common infection in the hospital environment. The adherence of microorganisms to the surface is a determining factor in colonization and infection. Antiseptics such as chlorhexidine and gentian violet have been shown to be effective against yeasts, as well as having low toxicity and being low-cost. The objective of the present study was to evaluate whether prior treatment of siliconized latex urinary catheters with antiseptics reduces the adherence of yeasts. Two reference strains of C. albicans (ATCC 645448 and ATCC 90028) and six strains isolated from catheter, two each of C. albicans, C. tropicalis, and C. parapsilosis, were used. An in␣vitro study of adherence was carried out with previously treated catheters, in separate experiments of 1 h and 24 h of incubation under continued shaking. The relative hydrophobicity of the cell surface of the yeasts before and after 1 h of exposure to chlorhexidine was determined. The results demonstrated that both treatments were effective in controlling the adherence of yeast to the catheter (P < 0.0001), and that the hydrophobicity of the eight strains significantly increased after contact with chlorhexidine (P < 0.0001). These results suggest that the antimicrobial activity of chlorhexidine and gentian violet reduces the adherence of the microorganisms to the catheter.     

Use of Pistacia lentiscus mastic for sustained-release system of chlorocresol and benzoic acid for in vitro prevention of bacterial colonization of silicon urinary catheter

Urinary tract infections (UTI) are among the most common types of nosocomial infections. Patients with indwelling urinary catheters are at the highest risk of getting infections. A sustained-release method of chlorocresol and benzoic acid using a varnish of Pistacia lentiscus mastic was developed to prevent catheter colonization by Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Pseudomonas aeruginosa. Coatings of both antiseptics significantly reduced the number of colonizing bacteria on silicon urinary catheters for 72 h. Chlorocresol-coated catheters were significantly (P ≤ 0·05) more effective than benzoic acid. Except for the Pr. mirabilis, chlorocresol completely inhibited the colonization of catheters by the tested bacteria for 48 h. Nonetheless, the colonization of catheters by Pr. mirabilis was significantly reduced after 48 and 72 h by more than 3·5 logs. Although benzoic acid failed to completely inhibit bacterial growth, it significantly reduced the colonization of the catheters by all the tested bacteria by more than two logs for 72 h. The inhibition of colonization of catheters was confirmed by examining the tested catheters by scanning electron microscopy. The obtained results indicate the potential benefits of using mastic as a varnish for sustaining the release of chlorocresol and benzoic acid to prevent and reduce the colonization of urinary catheters by bacteria.     

Application of poly ethylene glycol hydrogel to overcome latex urinary catheter related problems

Urinary catheterization is a routine procedure in an intensive care unit (ICU) for monitoring the urine output of critically ill patients. The catheters which are most often used to help with urinary incontinence and retention also face problems like blockage, leakage and infection. These problems are due to proteins that adhere to the catheter surface and quickly build up on each other forming a protein layer. As the layers build up they can crystallize, providing the major source of blockage and leakage. Current strategies to avoid these problems include coating a catheter with silver alloy to reduce bacteria on the catheter surface. However, silver alloy coatings can lead to increased silver resistance for bacteria. Since silver is already used as an antibacterial agent in many places in a hospital, it is even more possible that resistance can develop. An alternative solution is presented involving coating latex, a common urinary catheter material with a micro layer (5-100 microns) of polyethylene glycol. This hydrogel is applied using an interfacial photopolymerization process with ethyl eosin as the photoinitiator. A 25 ppm concentration of ethyl eosin provided the strongest gel to surface adhesion and significantly lowered protein adhesion when compared to an uncoated latex substrate.     

Susceptibility of antibiotic-resistant gram-negative bacteria to biocides: a perspective from the study of catheter biofilms

Bacteria resistant to both the agents deployed to prevent infections and those used to treat infections would be formidable nosocomial pathogens. The aim of this paper is to review the evidence that gram-negative bacteria resistant to antibiotics and biocides have emerged and been responsible for catheter-associated urinary tract infection. A study of patients undergoing intermittent bladder catheterization revealed that the frequent application of the antiseptic chlorhexidine to the perineal skin prior to the insertion of the catheter was effective against the normal gram-positive skin flora but not against the gram-negative organisms that subsequently colonized this site. Organisms such as Providencia stuartii, Pseudomonas aeruginosa and Proteus mirabilis were repeatedly isolated from the skin of these patients and inevitably went on to cause urinary infections. The minimum inhibitory concentration (MIC) of chlorhexidine for many of these strains proved to be 200-800 microg ml(-1) compared with the 10-50 microg ml(-1) recorded for reference strains of gram-negative species. A subsequent survey of over 800 gram-negative isolates from urinary tract infections in patients from both hospitals and the community revealed that chlorhexidine resistance was not a widespread phenomenon, but was restricted to these species and to units where the care of catheterized patients involved the extensive use of chlorhexidine. Analysis of the antibiotic resistance patterns revealed that the chlorhexidine-resistant strains were also multidrug resistant. Other clinical studies also reported catheter-associated infections with chlorhexidine- and multidrug-resistant strains of Pr. mirabilis when chlorhexidine was being used extensively. This species poses particular problems to the catheterized patient. Chlorhexidine thus proved counterproductive in the care of catheters and its use in this context has been largely abandoned. Suggestions of reintroducing this agent in the form of biocide-impregnated catheters should be resisted.     

Effects of Hydrogel/Silver Coatings on In Vitro Adhesion to Catheters of Bacteria Associated with Urinary Tract Infections

Sections of sterile all-silicone-, hydrogel/silver-all-silicone-, and hydrogel/silver-latex-Foley urinary catheters were exposed to suspensions of bacteria and Candida albicans associated with urinary tract infections. The adhesion of these microorganisms to the catheters was determined with a radiolabel–cell procedure and scanning electron microscopy. Anomalous data with the radiolabel procedure were produced with the hydrogel/silver-latex catheters for certain species. These aberrant data were related to adhesion on the untreated cut ends of the latex catheter. Radiolabel-cell-adhesion procedures that involve sections of coated materials may need to be supplemented with additional procedures such as scanning electron microscopy for valid interpretations of the data. Adhesion to the hydrogel/silver catheters by both Gram-positive- and Gram-negative bacteria most commonly associated with nosocomial urinary tract infections, including a strain of Pseudomonas aeruginosa noted for its superior adhesion capacity, was significantly lower than the adhesion to the control all-silicone catheter. Received: 21 January 2000 / Accepted: 26 February 2000     

Mouse models of short- and long-term foreign body in the urinary bladder: analogies to the bladder segment of urinary catheters.

Catheter-associated bacteriuria is the most common infection occurring in hospitals, where urethral catheters are generally in place for a few days, and in nursing homes, where catheters may be in place for months or years. We developed murine models with intrabladder urinary catheters for studying complications of bacteriuria in short- and long-term catheterization. In the short-term model, a catheter segment was inserted transurethrally and lay free within the bladder lumen. Half of the animals expelled segments during a 2-to-7-day period, durations similar to catheterizations in hospitalized patients. For studies of long-term catheter use, the catheter segment was secured within the bladder by a single suture for up to 12 months. Antibiotics administered for 7 days after catheter placement and housing mice in cages with wire screen floors reduced spontaneous bacteriuria to an acceptably low incidence rate of only 7%. Proteus mirabilis bacteriuria of high concentration provoked the same complications that are common in patients with long-term catheters: acute pyelonephritis, chronic renal inflammation, and struvite stone formation. These models allow inoculation of the bacteria of interest and are suitable for studies of short- and long-term foreign body-associated bacteriuria and its complications.     

Type 1 Fimbriae Contribute to Catheter-Associated Urinary Tract Infections Caused by Escherichia coli

Biofilm formation on catheters is thought to contribute to persistence of catheter-associated urinary tract infections (CAUTI), which represent the most frequent nosocomial infections. Knowledge of genetic factors for catheter colonization is limited, since their role has not been assessed using physicochemical conditions prevailing in a catheterized human bladder. The current study aimed to combine data from a dynamic catheterized bladder model in vitro with in vivo expression analysis for understanding molecular factors relevant for CAUTI caused by Escherichia coli. By application of the in vitro model that mirrors the physicochemical environment during human infection, we found that an E. coli K-12 mutant defective in type 1 fimbriae, but not isogenic mutants lacking flagella or antigen 43, was outcompeted by the wild-type strain during prolonged catheter colonization. The importance of type 1 fimbriae for catheter colonization was verified using a fimA mutant of uropathogenic E. coli strain CFT073 with human and artificial urine. Orientation of the invertible element (IE) controlling type 1 fimbrial expression in bacterial populations harvested from the colonized catheterized bladder in vitro suggested that the vast majority of catheter-colonizing cells (up to 88%) express type 1 fimbriae. Analysis of IE orientation in E. coli populations harvested from patient catheters revealed that a median level of ∼73% of cells from nine samples have switched on type 1 fimbrial expression. This study supports the utility of the dynamic catheterized bladder model for analyzing catheter colonization factors and highlights a role for type 1 fimbriae during CAUTI.     

内毒素和降钙素原在妇科术后尿路感染中的鉴别诊断价值

目的评价中段尿内毒素和血清降钙素原在妇科术后不同种类细菌尿路感染中的鉴别诊断价值。方法收集临床1205例妇科术后患者中段尿进行细菌培养及内毒素检测,同时对患者进行血清降钙素原检测,比较结果对尿路感染的鉴别诊断价值。结果1205份标本中尿培养出阳性350例,感染率为29．04％,其中298例为均存在留置导尿管,而在剩余400例尿培养阴性的患者中仅仅120例留置导尿管。两组之间差异有统计学意义（χ2=26．78,P〈0．05）。其中革兰阴性杆菌189例（54％）,革兰阳性菌112例（32％）,真菌49例（14％）。在三组患者中,中段尿内毒素在革兰阴性菌引起的术后尿路感染较革兰阳性菌和真菌的患者中明显升高,差异均有统计学意义（P〈0．05）。而对于血清降钙素原在革兰阴性菌和革兰阳性菌感染的患者明显高于真菌尿路感染的患者,差异均有统计学意义（P〈0．05）。而在革兰阴性菌和革兰阳性菌感染的患者中差异无统计学意义（P〉0．05）。结论妇科术后尿路感染与留置导尿管密切相关,革兰阴性菌是引起妇科术后尿路感染的主要致病菌,中段尿内毒素有助于鉴别诊断出革兰阴性菌引起尿路感染,而血清PCT升高时则有助于排除真菌尿路感染。     

Biofilm formation of Klebsiella pneumoniae on urethral catheters requires either type 1 or type 3 fimbriae

Urinary catheters are standard medical devices utilized in both hospital and nursing home settings, but are associated with a high frequency of catheter-associated urinary tract infections (CAUTI). In particular, biofilm formation on the catheter surface by uropathogens such as Klebsiella pneumoniae causes severe problems. Here we demonstrate that type 1 and type 3 fimbriae expressed by K.?pneumoniae enhance biofilm formation on urinary catheters in a catheterized bladder model that mirrors the physico-chemical conditions present in catheterized patients. Furthermore, we show that both fimbrial types are able to functionally compensate for each other during biofilm formation on urinary catheters. In situ monitoring of fimbrial expression revealed that neither of the two fimbrial types is expressed when cells are grown planktonically. Interestingly, during biofilm formation on catheters, both fimbrial types are expressed, suggesting that they are both important in promoting biofilm formation on catheters. Additionally, transformed into and expressed by a nonfimbriated Escherichia coli strain, both fimbrial types significantly increased biofilm formation on catheters compared with the wild-type E.?coli strain. The widespread occurrence of the two fimbrial types in different species of pathogenic bacteria stresses the need for further assessment of their role during urinary tract infections.     

Catheter-associated urinary tract infections in intensive care units

The purpose of this review is to analyze literature concerning the diagnosis, prevention, and management of catheter-associated urinary tract infection (CAUTI) occurring in patients hospitalized in the intensive care unit (ICU). Analysis was performed from personal and "Pubmed" data, crossing the following keywords: "urinary tract infection", "catheter', and "intensive care unit". Few clinical trials including ICU patients were found despite the abundance of expert opinions. There is no consensus on the use of urinary reagent tests for diagnosis. The prevention of CAUTI in ICU patients does not require expensive devices. Neither complex closed drainage systems nor silver-coated urinary catheters have demonstrated efficacy in comparative randomized clinical trials. Bladder irrigation should not be used, except when an obstruction of the catheter is highly likely. The administration of prophylactic antimicrobial therapy, although effective in reducing the incidence of urinary bacteria, cannot be recommended in ICU patients. The management of CAUTI in ICU patients has not been evaluated in clinical trials. The level of evidence provided in this field is weak, and underlines the need for randomized studies to improve management of patients.     

Catheter colonization and abscess formation due to Staphylococcus epidermidis with normal and small-colony-variant phenotype is mouse strain dependent

Coagulase-negative staphylococci (CoNS) form a thick, multilayered biofilm on foreign bodies and are a major cause of nosocomial implant-associated infections. Although foreign body infection models are well-established, limited in vivo data are available for CoNS with small-colony-variant (SCV) phenotype described as causative agents in implant-associated infections. Therefore, we investigated the impact of the Staphylococcus epidermidis phenotype on colonization of implanted PVC catheters and abscess formation in three different mouse strains. Following introduction of a catheter subcutaneously in each flank of 8- to 12-week-old inbred C57BL/6JCrl (B6J), outbred Crl:CD1(ICR) (CD-1), and inbred BALB/cAnNCrl (BALB/c) male mice, doses of S. epidermidis O-47 wild type, its hemB mutant with stable SCV phenotype, or its complemented mutant at concentrations of 10(6) to 10(9) colony forming units (CFUs) were gently spread onto each catheter. On day 7, mice were sacrificed and the size of the abscesses as well as bacterial colonization was determined. A total of 11,500 CFUs of the complemented mutant adhered to the catheter in BALB/c followed by 9,960 CFUs and 9,900 CFUs from S. epidermidis wild type in BALB/c and CD-1, respectively. SCV colonization was highest in CD-1 with 9,500 CFUs, whereas SCVs were not detected in B6J. The minimum dose that led to colonization or abscess formation in all mouse strains was 10(7) or 10(8) CFUs of the normal phenotype, respectively. A minimum dose of 10(8) or 10(9) CFU of the hemB mutant with stable SCV phenotype led to colonization only or abscess formation, respectively. The largest abscesses were detected in BALB/c inoculated with wild type bacteria or SCV (64 mm(2) vs. 28 mm(2)). Our results indicate that colonization and abscess formation by different phenotypes of S. epidermidis in a foreign body infection model is most effective in inbred BALB/c followed by outbred CD-1 and inbred B6J mice.