Gastrointestinal colonization by methicillin-resistant Staphylococcus aureus in immunosuppressed mice

Evaluación in vitro del potencial probiótico de bacterias ácido lácticas aisladas de suero costeño

Un grupo de 53 bacterias ácido lácticas (BAL) aisladas del suero costeño, fueron sometidas a estudios preliminares in vitro simulando las condiciones del tracto digestivo, para determinar sus características como potenciales probióticos: se evaluó la tolerancia a pH ácido (MRS pH: 2,0) y sales biliares (MRS con sales biliares al 0,3%) y posteriormente se determinó la población sobreviviente como log UFC/ml. A las cepas tolerantes a las condiciones mencionadas, se les determinó la resistencia a 14 antibióticos de uso comercial, se evaluó la adhesión a mucus intestinal y la producción de ácido láctico por cromatografía líquida de alta precisión (HPLC). Se encontró que 54,7% de las BAL evaluadas son tolerantes a las condiciones de pH ácido y 49,1 a 0,3% de sales biliares con una población de 106 log UFC/ml en promedio. Siete cepas fueron seleccionadas por presentar sensibilidad a vancomicina antibiótico de importancia epidemiológica y se adhirieron a mucus intestinal, reuniendo las condiciones requeridas para considerarse como potencialmente probióticas. Adicionalmente la cuantificación de ácido láctico para las cepas seleccionadas presentó un rango entre 0,13 ± 0,05 y 1,0 ± 0,08 g/l.

Outbreak of Neonatal Diarrhea in Farmed Mink Kits (Mustella vison) Associated With Enterotoxigenic Staphylococcus delphini

An outbreak of diarrhea on a large commercial mink farm affected 5,000 of 36,000 neonatal mink kits, with 2,000 dying within a 2-week period. Affected kits were severely dehydrated, and their furcoats and paws were covered with yellow- to green-tinged mucoid feces. On necropsy, the small intestines of examined animals were markedly distended by serous to mucoid fluid. Microscopically, there was prominent colonization of the intestinal villar epithelium by gram-positive bacterial cocci in the absence of inflammation and morphologic changes in villous enterocytes. The colonizing bacteria were phenotypically identified as belonging to the Staphylococcus intermedius group of bacteria. This was confirmed by nucleic acid sequence analysis of the 16S ribosomal RNA gene. Further nucleic acid sequencing of polymerase chain reaction (PCR) amplicons from the superoxide dismutase gene and the heat shock protein 60 gene differentiated the isolate as Staphylococcus delphini. Production of staphylococcal enterotoxins A and E was demonstrated with a commercial ELISA-based immunoassay. Sequencing of PCR amplicons confirmed the presence of the enterotoxin E gene, but PCR amplification of the enterotoxin A, B, C, or D genes was not successful. Although direct causation was not confirmed in this study, the authors postulate that the observed hypersecretory diarrhea in these mink kits was the result of colonization of the small intestine by S delphini and subsequent production of enterotoxin.

Methicillin-resistant Staphylococcus non-aureus infection in an irradiated rhesus macaque (Macaca mulatta)

We describe a case of methicillin-resistant Staphylococcus non-aureus infection in a rhesus macaque (Macaca mulatta). The nonhuman primate described was part of a research project that involved whole-body gamma irradiation and subsequently developed acute generalized dermatitis with skin dryness, peeling, and erythema around the eyes. After initial evaluation, which included microbiologic culture and 6 d of medical treatment, the animal was euthanized due to concern regarding a possible outbreak of infectious or zoonotic disease. On the basis of skin culture, diagnosis of methicillin-resistant Staphylococcus non-aureus was confirmed. This report underscores the importance of the occupational risk of methicillin-resistant Staphylococcus non-aureus to research and animal care staff in a research animal facility setting.

Relationship between immunosuppression and intensive care unit-acquired multidrug-resistant bacteria: a case-control study

OBJECTIVE

To determine the relationship between immunosuppression and intensive care unit (ICU)-acquired multidrug-resistant (MDR) bacteria.

DESIGN

Retrospective case-control study based on prospectively collected data.

SETTING

A 30-bed medical and surgical ICU.

PATIENTS

All patients hospitalized >48 hrs in the ICU were eligible during a 2-yr period.

INTERVENTIONS

Immunosuppression was defined as active solid or hematologic malignancy, leucopenia, or chronic immunosuppressive treatment. MDR bacteria were defined as methicillin-resistant Staphylococcus aureus, ceftazidime- or imipenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia, and extending spectrum beta-lactamase producing Gram-negative bacilli. MDR bacteria screening (nasal, anal, and axilla swabs and tracheal aspirate in intubated patients) was performed at ICU admission and weekly. Only MDR bacteria isolated >48 hrs after ICU admission were taken into account; duplicates were excluded. Isolation measures were applied in all patients at ICU admission, in patients with MDR bacteria, and in patients with immunosuppression. Immunosuppressed patients (cases) were matched (1:1) with immunocompetent patients (controls) according to all the following criteria: age +/-5 yrs, Simplified Acute Physiology Score II +/-5, duration of ICU stay +/-3 days, and category of admission (medical/surgical). Risk factors for ICU-acquired MDR bacteria were determined using univariate and multivariate analyses.

MEASUREMENTS AND MAIN RESULTS

Of 1,065 eligible patients, nine patients were excluded for absence of MDR bacteria screening at ICU admission. One hundred thirty-three (12%) patients were immunosuppressed, and 128 (96%) of them were successfully matched. Mean time between ICU admission and first ICU-acquired MDR bacteria was 12 +/- 9 days. Incidence of MDR bacteria was significantly higher in cases than in controls (22 vs. 12 MDR bacteria/1000 ICU days, p = .004). However, immunosuppression was not independently associated with ICU-acquired MDR bacteria.Multivariate analysis identified prior antibiotic treatment and antibiotic treatment in the ICU as risk factors for ICU-acquired MDR bacteria (odds ratio [95% confidence interval] = 1.9 [1-3.6], p = .003; 11 [1.4-83], p = .02; respectively).

CONCLUSIONS

Immunosuppression is not independently associated with ICU-acquired MDR bacteria. However, infection control measures used in our ICU may have influenced this result.

Inhibition of methicillin-resistantStaphylococcus aureusby an in vitro continuous-flow culture containing human stool microflora

We used an in vitro continuous-flow culture model of human stool microflora to examine the ability of human stool microflora to inhibit growth of two methicillin-resistant S. aureus (MRSA) strains. Continuous-flow cultures consistently eliminated MRSA inocula of 10(6) cfu/mL within 4 days, and addition of continuous-flow culture resulted in elimination of a pre-established MRSA culture ( approximately 10(8) cfu/mL) within 6-8 days. Anaerobic or "aerobic" (i.e., continuous bubbling of room air to eliminate obligate anaerobes) cultures eliminated MRSA at similar rates. The MRSA strains were unable to replicate under anaerobic conditions in sterile filtrates produced from the continuous-flow culture, but rapid growth occurred when glucose was added. These data demonstrate that indigenous stool microflora efficiently eliminate MRSA colonization and obligate anaerobes are not essential for inhibition. Our findings also suggest that inhibition of MRSA in continuous-flow cultures is due to depletion of nutrients rather than production of inhibitory conditions.

Role of macrophages in a mouse model of postoperative MRSA enteritis

BACKGROUND

We have established a mouse model for fatal postoperative enteritis due to Staphylococcus aureus to analyze mechanisms of bacterial translocation and determine reasons for the lethality of this infection. In the present study the role of macrophages was ascertained in protection against S. aureus induced enteritis.

MATERIALS AND METHODS

Mice were pretreated with cyclophosphamide (CY), an immunosuppressant, and then infected directly into the jejunum with methicillin-resistant S. aureus (MRSA) isolated from a patient. In other groups of mice liposome-encapsulated dichloromethylene diphosphate (Cl2MDP) was administered to deplete macrophages in vivo. Other experimental groups received lipoteichoic acid (LTA), which was used to inhibit the ability of macrophages to bind MRSA, and additionally, to analyze dependence of bacterial clearance on the macrophage scavenger receptor. The ability of macrophages to bind MRSA was compared with survival rates in this mouse model of fatal postoperative enteritis.

RESULTS

Injection of liposome-encapsulated Cl2MDP decreased survival rate of mice infected intraintestinally with MRSA in a dose-dependent manner. Cyclophosphamide also decreased survival rate of MRSA-infected mice and was found to correlate with its ability to decrease the number of macrophages in the spleen. Intravenous LTA administration did not affect total splenocyte numbers or the number of splenic macrophages but decreased the ability of macrophages to bind MRSA and adversely affected survival of mice infected with MRSA.

CONCLUSIONS

Macrophages play a critical role in protection against MRSA administered directly into the jejunum. LTA recognition sites (probably type A scavenger receptors) on macrophages are required for binding and phagocytosing MRSA.

Coexistence of vancomycin-resistant enterococci and Staphylococcus aureus in the intestinal tracts of hospitalized patients

The potential for transfer of vancomycin-resistance genes from enterococci to Staphylococcus aureus exists when these organisms share an ecologic niche. We performed an 8-month prospective study to determine the frequency at which S. aureus and vancomycin-resistant enterococci (VRE) coexist in the intestinal tracts of VRE-colonized patients and evaluated whether antianaerobic antibiotic therapy promoted increased density of S. aureus colonization. Of 37 patients colonized with vancomycin-resistant Enterococcus faecium, 23 (62%) had S. aureus recovered from stool specimens and 20 (87%) had methicillin-resistant strains. There was no significant difference in the mean density (+/- standard deviation) of S. aureus during versus > or =1 month after discontinuation of antianaerobic antibiotic therapy (5.1+/-1.5 vs. 4.7+/-1.6 log10 colony-forming units per gram of stool; P=.34). No S. aureus isolates were resistant to vancomycin. S. aureus and VRE often coexist in the intestinal tract, providing a potential reservoir for the emergence of vancomycin-resistant S. aureus isolates.

Enterocolitis caused by methicillin-resistant Staphylococcus aureus: molecular characterization of respiratory and digestive tract isolates

We investigated the mechanism of outbreak of enterocolitis caused by methicillin-resistant Staphylococcus aureus (MRSA). Five epidemiological markers [coagulase type, enterotoxin type, toxic shock syndrome toxin-1 (TSST-1) production, beta-lactamase production and pulsed-field gel electrophoresis (PFGE)] of 45 strains of MRSA isolated simultaneously from the respiratory tract (nasal cavity and/or pharynx and/or sputum) and stool (plus one sample of gastric juice) in 13 patients (8 males and 5 females, mean age, 77.1 years) were compared retrospectively. Forty-four of the 45 isolates of MRSA were positive for enterotoxin C and TSST-1 production, and the remaining isolate was positive for enterotoxin A and negative for TSST-1 production. All isolates were coagulase type II, and 27 showed beta-lactamase production. The patterns of coagulase type, enterotoxin type, TSST-1 and beta-lactamase production of MRSA isolated from the respiratory tract were similar to those of MRSA isolated from the intestine in 12 of 13 patients. Molecular typing by PFGE demonstrated that the pattern of respiratory tract isolates was identical to those of stool isolates in 9 (69.2%), similar in 3 (23.1 %), and different in 1 (7.7%). The data suggested that enterocolitis might be caused by the MRSA colonized in the respiratory tract and incorporated into the digestive tracts. Therefore, we propose that early eradication of MRSA in the respiratory tract is important for protection of patients against the development of enterocolitis, particularly in susceptible patients, e.g., immunocompromised or pre-operated patients with digestive diseases, especially malignant disease.

A mouse model for postoperative fatal enteritis due to Staphylococcus infection

BACKGROUND

Postoperative infection of intestine with methicillin-resistant Staphylococcus aureus (MRSA) is fatal in some cases. The object of this study was to establish a mouse model for the infection, providing a useful tool for investigating mechanisms in the progression of infection.

METHODS

Mice were pretreated with cyclophosphamide, injected orally or directly into jejunum with MRSA prepared from a postoperative patient, and then given 5 daily doses of antibiotics. Forty-eight hours after the injection, bacterial translocation and serum endotoxin levels were examined. Macrophage depletion was carried out by the administration of liposome-encapsulated dichloromethylene diphosphate (Cl(2)MDP), 4 days before MRSA injection.

RESULTS

Injection into the jejunum but not oral administration of MRSA induced enteritis with diarrhea and resulted in death in most cyclophosphamide-treated mice. Translocation of MRSA in mesenteric lymph nodes and liver was observed, concomitantly with E. coli infection. Endotoxin-resistant C3H/HeJ mice infected with MRSA survived longer than endotoxin-sensitive C3H/He mice, but also died within a week after MRSA injection. Selective depletion of macrophages induced infection in mice that were not pretreated with cyclophosphamide.

CONCLUSION

We established a mouse model for the fatal MRSA infection which induced enteritis with diarrhea, that will be a useful tool for investigating the mechanisms for sometimes fatal MRSA infection of the intestine in postoperative patients. The presence of E. coli or endotoxin seemed to play a major role in the mortality of mice in the early days of MRSA-induced enteritis, but other factors, probably from MRSA, in the later days. Phagocytes were quite important for protection against the MRSA infection.