Comparison of enterotoxins and haemolysins produced by methicillin-resistant (MRSA) and sensitive (MSSA) Staphylococcus aureus

Increased Risk of Thrombocytopenia and Death in Patients with Bacteremia Caused by High Alpha Toxin-Producing Methicillin-Resistant Staphylococcus aureus

Alpha toxin (Hla) is a major virulence factor of Staphylococcus aureus that targets platelets but clinical data on Hla pathogenesis in bacteremia (SAB) is limited. We examined the link between in vitro Hla activity and outcome. Study isolates obtained from 100 patients with SAB (50 survivors; 50 non-survivors) were assessed for in vitro Hla production by Western immunoblotting in a subset of isolates and Hla activity by hemolysis assay in all isolates. Relevant demographics, laboratory and clinical data were extracted from patients' medical records to correlate Hla activity of the infecting isolates with outcome. Hla production strongly correlated with hemolytic activity (r_s = 0.93) in vitro. A trend towards higher hemolytic activity was observed for MRSA compared to MSSA and with high-risk source infection. Significantly higher hemolytic activity was noted for MRSA strains isolated from patients who developed thrombocytopenia (median 52.48 vs. 16.55 HU/mL in normal platelet count, p = 0.012) and from non survivors (median 30.96 vs. 14.87 HU/mL in survivors, p = 0.014) but hemolytic activity of MSSA strains did not differ between patient groups. In vitro Hla activity of MRSA strains obtained from patients with bacteremia is significantly associated with increased risk for thrombocytopenia and death which supports future studies to evaluate feasibility of bedside phenotyping and therapeutic targeting.

Characteristics of Staphylococcus aureus Isolated from a Case of Foodborne Outbreak in Bulgaria

This paper presents an outbreak provoked by methicillin-resistant strains of coagulase-positive S. aureus (CPS), produced staphylococcal enterotoxins (se) in pig meatballs and potato salad consumed from 70 people in the village Mamarchevo, Bulgaria. Eighteen women aged 50 to 70 years, and two children aged 4 and 5 years have demonstrated a severe malaise with vomiting and indigestion. Two food samples and isolates of CPS were received in the laboratory of Bulgarian Food Safety Agency. Both samples were found to have a high level of CPS. The level of S. aureus contamination in the potato salad was 8.3 logs CFU/g and 7.7 logs CFU/g in roasted meatballs, which was a significant reason to doubt the production of the toxin. The samples were analyzed according to the European Screening Method v5 using mini VIDAS SET2. The results showed a presence of staphylococcal enterotoxin (TV 2.67 for meatballs and TV 3.27 for potato salad), which was the reason for the ensuing food intoxication. EURL CPS applying quantitative indirect sandwich-type ELISA confirmed the presence of sea, sec and sed in the potato salad and sea and sed in the roasted meatballs. Two CPS isolates were confirmed as S. aureus by a species-specific 23S rRNA targeted PCR test. Real-time PCR method detected sea, sed, seg, sei, sej, and ser genes in S. aureus strains, found in both matrixes. Multiplex PCR method proved the existence of the mecA gene in both S. aureus strains. Resistance to cefoxitin (>16 mg/L), penicillin (>2 mg/L), kanamycin (64 mg/L) and sulfamethoxazole (>512 mg/L) was found.

A Pyrrhic Victory: The PMN Response to Ocular Bacterial Infections

Some tissues of the eye are susceptible to damage due to their exposure to the outside environment and inability to regenerate. Immune privilege, although beneficial to the eye in terms of homeostasis and protection, can be harmful when breached or when an aberrant response occurs in the face of challenge. In this review, we highlight the role of the PMN (polymorphonuclear leukocyte) in different bacterial ocular infections that invade the immune privileged eye at the anterior and posterior segments: keratitis, conjunctivitis, uveitis, and endophthalmitis. Interestingly, the PMN response from the host seems to be necessary for pathogen clearance in ocular disease, but the inflammatory response can also be detrimental to vision retention. This “Pyrrhic Victory” scenario is explored in each type of ocular infection, with details on PMN recruitment and response at the site of ocular infection. In addition, we emphasize the differences in PMN responses between each ocular disease and its most common corresponding bacterial pathogen. The in vitro and animal models used to identify PMN responses, such as recruitment, phagocytosis, degranulation, and NETosis, are also outlined in each ocular infection. This detailed study of the ocular acute immune response to infection could provide novel therapeutic strategies for blinding diseases, provide more general information on ocular PMN responses, and reveal areas of bacterial ocular infection research that lack PMN response studies.

Strain Discrimination of Staphylococcus aureus Using Superantigen Profiles

Staphylococcus aureus is one of the major bacterial species that may cause clinical infection and food-poisoning cases. Strains of this species may produce a series of superantigens (SAgs). Due to the importance of staphylococcal infections, reliable methods for the discrimination of strains of this species are important. Such data may allow us to trace the infection origins and be used for epidemiological study. For strain discrimination, genotyping methods, such as pulsed-field gel electrophoresis (PFGE), random amplified polymorphic DNA (RAPD), and multi-locus sequence typing (MLST), etc., could be used. Recently, toxin gene profiles, which can be used for the elucidation of the genetic and pathogenic relatedness between strains, also have been used to improve the strain discrimination. For S. aureus, as more SAg genes were discovered, the SAg profiles become more useful for the strain discrimination of S. aureus. In this chapter, a method for the discrimination of S. aureus strains using superantigen profiles will be described in detail.

Improvement of strain discrimination by combination of superantigen profiles, PFGE, and RAPD for Staphylococcus aureus isolates from clinical samples and food-poisoning cases

Staphylococcus aureus is one of the major bacterial species that may cause clinical infection and food-poisoning cases. Strains of this bacterial species may produce a series of superantigens (SAgs) (i.e., staphylococcal enterotoxins [SEs], staphylococcal enterotoxin-like toxins, and toxic shock syndrome toxin). In this study, S. aureus strains from clinical samples and food-poisoning cases in Taiwan were collected; their SAg profiles, and SmaI digestion patterns determined by pulsed-field gel electrophoresis (PFGE), were then analyzed. Results showed that their SAg gene profiles and SmaI digestion patterns of chromosomal DNA were highly diverse. Although PFGE has been used as a criterion standard for typing of S. aureus strains, and the SAg profiles have been used in combination with PFGE for typing of S. aureus strains, we found that strains grouped in these combined patterns could be further discriminated by the random amplified polymorphic DNA (RAPD) method. Thus, the combined use of SAg profiles, PFGE, and RAPD patterns permits high discrimination for typing of S. aureus strains from not only the clinical samples but also the food-poisoning cases. Such a combined method may be used as a highly accurate approach for epidemiological study and tracing of the contamination origin of staphylococcal infections either in hospitals or food-poisoning cases.

The interface between antibiotic resistance and virulence in Staphylococcus aureus and its impact upon clinical outcomes

The ability of Staphylococcus aureus to rapidly acquire antibiotic resistance in the face of antimicrobial challenge has enabled it to remain an ongoing, significant human pathogen. Mechanisms behind the evolution of resistance in S. aureus are well documented, but the effects of these phenotypes upon virulence are less clear. By exploring available clinical and experimental data, we have shown that a number of the major steps in the evolution of antibacterial resistance in S. aureus have been accompanied by alterations in virulence. This review also highlights that further experimentation is required to fully elucidate the mechanisms involved in the interface between virulence and antibiotic resistance, with the intention of identifying novel preventative or therapeutic strategies for this important human pathogen.

Is MRSA more virulent than MSSA?

Numerous clinical studies have indicated, based on mortality rates, that methicillin-resistant Staphylococcus aureus (MRSA) strains are more virulent than methicillin-susceptible S. aureus (MSSA) strains. In contrast, quantitative laboratory examinations of the presence and magnitude of pathogenic mechanisms and virulence factors in strains of MRSA and MSSA have generated conflicting data. The most important reason for these conflicting results is probably the heterogeneic nature of the resistant population. A comparison of selected and congenic MRSA and MSSA sub-populations of the same strain is required to resolve this issue.

Is Methicillin Resistance Associated with a Worse Prognosis in Staphylococcus aureus Ventilator-Associated Pneumonia?

BACKGROUND

Excess mortality associated with methicillin resistance in patients with Staphylococcus aureus ventilator-associated pneumonia (SA-VAP), taking into account such confounders as treatment adequacy and time in the intensive care unit (ICU), have not been adequately estimated.

METHODS

One hundred thirty-four episodes of SA-VAP entered in the Outcomerea database were studied. Patients from whom methicillin-resistant S. aureus (MRSA) was recovered were compared with those from whom methicillin-susceptible S. aureus (MSSA) was recovered, stratified for duration of stay in the ICU at the time of VAP diagnosis and adjusted for confounders (severity at admission, characteristics at VAP diagnosis, and treatment adequacy).

RESULTS

Treatment was adequate within 24 h after VAP diagnosis for 86% of the 65 MSSA-infected patients and 77% of the 69 MRSA-infected patients (P = .2). Polymicrobial VAP was more commonly associated with MSSA than with MRSA (49.2% vs. 25.7%; P = .01). MRSA infection was associated with a lower prevalence of coma at hospital admission and a higher rate of use of central venous lines and fluoroquinolones during the first 48 h of the ICU stay. The rates of shock, recurrence, and superinfection were similar in both groups. The crude hospital mortality rate was higher for MRSA-infected patients than for MSSA-infected patients (59.4% vs. 40%; P = .024). This difference disappeared after controlling for time in the ICU before VAP and parameters imbalanced at ICU admission (odds ratio [OR], 1.23; 95% confidence interval [CI], 0.49-3.12; P = .7) and remained unchanged after further adjustments for initial treatment adequacy and polymicrobial VAP (OR, 0.98; 95% CI, 0.36-2.66).

CONCLUSIONS

Differences in patient characteristics, initial ICU treatment, and time in the ICU confounded estimates of excess death due to MRSA VAP. After careful adjustment, methicillin resistance did not affect ICU or hospital mortality rates.

Immunology of Staphylococcal biofilm infections in the eye: new tools to study biofilm endophthalmitis

Endophthalmitis is an important disease of the eye that is most frequently caused by postoperative and post-traumatic introduction of bacteria into the posterior segment of the eye. In the case of severe infections, visual acuity is greatly damaged or completely lost. Much work has focused on the ability of planktonic bacteria to cause infection and ocular damage while little work has focused on chronic infections in endophthalmitis mediated by the formation of bacterial biofilms on the surface of the lens. This review focuses on the interaction of Staphylococcus aureus and Staphylococcus epidermidis lens-associated biofilms in endophthalmitis. Additionally, this review highlights some relevant biofilm-immune system interactions and outlines a new in vivo mouse model to explore biofilm-related infections in endophthalmitis.

Corneal virulence of Staphylococcus aureus in an experimental model of keratitis

The aim of this study was to determine the pathogenic role of alpha-, beta-, and gamma-toxins in a rabbit model of Staphylococcus aureus keratitis. S. aureus strains 8325-4, Newman, and their isogenic mutants were intrastromally injected into rabbit corneas. Eyes were scored for pathology by slit lamp examination (SLE), histologic examination, and bacterial colony-forming units (CFU) per cornea were determined. Rabbits were immunized against alpha-toxin and subsequently challenged with S. aureus strain 8325-4 or Newman. All strains grew equivalently to approximately 7 log CFU/cornea at 25 h postinfection. SLE scores at 15, 20, and 25 h postinfection revealed that alpha-toxin - producing strains caused greater corneal pathology than strains deficient in alpha-toxin. A beta-toxin - deficient mutant produced significantly less ocular edema than its parent or rescued strains. The gamma-toxin-deficient mutant, relative to its parent strain or genetically rescued strain, had reduced virulence. These results demonstrate that the virulence of S. aureus involves mainly alpha-toxin and to a lesser extent gamma-toxin, with beta-toxin mediating minimal corneal pathology.

Immunization with alpha-toxin toxoid protects the cornea against tissue damage during experimental Staphylococcus aureus keratitis

Alpha-toxin is a major virulence factor in Staphylococcus aureus keratitis. Active or passive immunization with alpha-toxin toxoid could protect against corneal damage. Results show that either form of immunization did not kill bacteria but did significantly protect against corneal pathology, especially epithelial erosion.

[Methicillin-resistant Staphylococcus aureus: factors responsible for its incidence]

INTRODUCTION

How can we explain that the proportion of methicillin-resistant Staphylococcus aureus (MRSA) varies between the European countries, ranging from < 1% in Scandinavia to > 30% in Spain, France and Italy? This paper is aimed at attempting to determine factors at the origin of the spreading of endemic MRSA strains as of the early 1980s. Those strains are characterized by their ability to develop resistance to current antibiotics and make treatment of severe and deep infections more complex.

CURRENT KNOWLEDGE AND KEY POINTS

Differences in the virulence of MRSA strains and that of susceptible strains appear unlikely. MRSA prevalence seems to be a growing problem, especially in Southern Europe where rates of resistance to other anti-staphylococcal antibiotics are high. General policies for antibiotic therapy as well as the implementation of strategies for prevention and control of MRSA might be responsible for such rates. Indeed, once MRSA is introduced into a facility without control program, this multiresistant bacteria rapidly spreads within the hospital and becomes endemic, expanding its reservoir. FUTURE PROSPECTS ET PROJECTS: Due to the introduction of new methods in microbiology and communication, infection control measures including procedures for isolation and identification of MRSA reservoirs are still feasible; however, their implementation requires human and material resources. Areas requiring improvement in the detection of MRSA outbreaks are identified in this paper, with particular emphasis on the need for national surveillance of MRSA prevalence and reappraisal of MRSA control strategies in French hospitals.

Methicillin-resistant Staphylococcus aureus in human milk

We collected and analyzed 500 samples of human milk, from five Brazilian cities (100 from each) to detect methicillin-resistant strains of Staphylococcus aureus (MRSA) producing enterotoxins. We found 57 strains of MRSA, and the mecA gene, responsible for resistance, was detected in all of them using a specific molecular probe. We examined 40 strains for the presence of four enterotoxins, after selecting a subset that included all strains from each region, except for the largest sample, from which 10 were randomly selected. Among these two presented enterotoxin B, and growth in human colostrum and trypicase soy broth. After 5 h of incubation at 37 degrees C, population sizes were already higher than 9.4 x 10(5) UFC/ml and enterotoxin was released into culture medium and colostrum. Our results stress the importance of hygiene, sanitary measures, and appropriate preservation conditions to avoid the proliferation of S. aureus in human milk.

Predominant Staphylococcus aureus isolated from antibiotic-associated diarrhea is clinically relevant and produces enterotoxin A and the bicomponent toxin LukE-lukD

Staphylococcus aureus was isolated as the predominant or only isolate from cultures of stools of 60 patients over 2 years in a university hospital, leading to the collection of 114 isolates. Diarrhea was observed in 90% of the patients. Ninety-eight percent of the patients had received antibiotics in the month before the diarrhea. Ninety-two percent of the S. aureus isolates were methicillin resistant. S. aureus was encountered with antibiotic-associated diarrhea among 47 quite elderly patients affected or not affected by a gastrointestinal disease. Among the antimicrobial treatments, cessation of the previous therapy when possible or rapid application of oral vancomycin therapy was the most appropriate. Analysis of total DNA by pulsed-field gel electrophoresis revealed 27 different SmaI pulsotypes distributed in 15 clusters. The pulsotypes never differed for related isolates from a single patient, even if they originated from patients with bacteremia. S. aureus was not isolated as the predominant isolate in cultures of stools of 57 patients who received an antimicrobial treatment for more than 5 days without diarrhea. Occurence of production of both enterotoxin A and the bicomponent leucotoxin LukE-LukD by the S. aureus isolates was significantly different from that by random isolates. The results strongly suggest that when predominant in stool samples, S. aureus should be considered a possible etiologic agent for some cases of antibiotic-associated diarrhea.

Pathogenicity of microbes associated with cystic fibrosis

Cystic fibrosis patients are exceptionally prone to colonisation by a narrow spectrum of pathogenic bacteria. Since pulmonary infection presently, and for the foreseeable future, plays such a major role in CF lung disease, we review the microbes that are classically associated with CF and the virulence, inflammatory potential and resistance mechanisms which contribute to the reduction in life expectancy for colonised CF patients.

Clonal heterogeneity, distribution, and pathogenicity of methicillin-resistant Staphylococcus aureus

Four thousand eighty-eight Staphylococcus aureus isolates obtained from patients hospitalised in a university clinic and four community hospitals over a period of one year were screened for methicillin resistance. A resistance rate of 5% was detected among initial isolates. Distribution of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus showed an increased prevalence of MRSA in clinically significant specimens such as blood, central venous catheter tips, bronchial secretions, and wound secretions. Typing of 110 MRSA strains (initial isolates) by macrorestriction analysis of chromosomal DNA revealed 26 different genotypes that could be divided into five epidemic and 21 sporadic strains. More than 50% of all isolates belonged to one type that was confirmed to be closely related to the "southern-German" epidemic strain. Production of virulence factors such as enterotoxin A-D and toxic shock syndrome-toxin 1 among MRSA strains (initial isolates) occurred in ten of 26 different MRSA types. A strong correlation between genotype and toxin production was demonstrated.

Enterotoxin and toxic shock syndrome toxin-1 production of methicillin resistant and methicillin sensitive Staphylococcus aureus strains

In this study the production of enterotoxin A-D and toxic shock syndrome toxin-1 (TSST-1) of 181 methicillin resistant (MRSA) and 100 methicillin sensitive (MSSA) Staphylococcus aureus first isolates from different patients was investigated. All the MRSA- and MSSA isolates in the study were collected in a period between 1993 and 1995 from specimens sent from 11 different acute care hospitals in the greater Düsseldorf area. As far as possible the isolates were matched according to ward and hospital. The isolates were collected in the same time period and matched for specimen from which isolated. Furthermore, only first isolates were analysed in both groups. No significant difference in the production of toxin of any type between MRSA and MSSA could be detected (51 and 40% respectively). When the individual toxins were analysed, again no significant difference between MRSA and MSSA was demonstrable (enterotoxin production by MRSA 40% and MSSA 36%, and TSST-1 16% and 8% respectively). Despite this, a slight tendency for MRSA to produce enterotoxin A and B and for MSSA to produce enterotoxin C was observed. In addition, generation of TSST-1 by both groups was independent of enterotoxin A-D production. Interestingly, no increase in the proportion of TSST-1- or enterotoxin-producing MRSA and MSSA isolates was observed in strains isolated from blood cultures from patients with a clinical diagnosis of sepsis. Genotypical pulsed-field-gel-electrophoresis (PFGE) and phenotypical (bacteriophage typing, lysotyping) characterization of the 181 MRSA isolates resulted in 28 different PFGE patterns (of which 19 were toxin producers) and 22 lysotyping groups (18 of which produced toxin). In summary, the investigated clinical S. aureus isolates showed no difference in their ability to produce toxin and this was independent of their sensitivity to methicillin.

Staphylococcal accessory regulator (sar) in conjunction with agr contributes to Staphylococcus aureus virulence in endophthalmitis

Previous studies showed that an agr mutant strain of Staphylococcus aureus was partially attenuated in virulence compared to a parental strain in experimental endophthalmitis. The purpose of this study was to determine whether the sar locus, either alone or through interactions with agr, contributes to the regulation of virulence in S. aureus endophthalmitis. Experimental endophthalmitis was established by the midvitreous injection of approximately 30 CFU of S. aureus RN6390 or the isogenic attenuated strains RN6911 (agr mutant), ALC136 (sar mutant), and ALC135 (agr sar double mutant). Unexpectedly, the rate of reduction in electroretinographic B-wave amplitude in eyes infected with strain ALC136 (sar mutant) was not significantly different from the parental strain on postinfection day (PID) 5 (10% retention). In contrast, ALC135 (agr sar double mutant)-infected eyes retained 73% of preoperative B-wave amplitude on PID 5. Therefore, unlike agr, a mutation in the sar locus alone does not alter the overall virulence of wild-type S. aureus in experimental endophthalmitis. However, the combined effect of insertional mutations in both the sar and agr global regulators leads to near-complete attenuation of virulence.

Nosocomial propagation of multiresistant Staphylococcus aureus: an analysis using biotyping and drug sensitivity

We performed an epidemiologic study of multi-resistant Staphylococcus aureus in our hospital. We combined bacteriologic biotyping and sensitivity to 19 drugs to conduct an environmental investigation. We assumed that complete matching in two or more strains denoted nosocomial propagation. A total of 667 isolates were recovered from a total of 144 patients. In a general surgical ward, 19 (52.8%) out of 36 patients developed an infection. The number of strains for every biotype and the combined susceptibility tended to show negative correlation (r = -0.376) before and after 1990, when an isolation policy was initiated. A similar regression analysis disclosed that between the general surgical ward and other wards the number of strains tended to show a positive association (r = 0.349). Thus, the isolation system employed in the general surgical ward may have arrested the persistence of intraward strains but permitted the interward travel of strains. In conclusion, an analysis of the propagation of multiresistant S. aureus using biotyping and drug sensitivity was found to be an effective method for evaluating the most appropriate measures to counter the endemic spread of this microbe.

High prevalence of Helicobacter pylori metronidazole resistance in migrants to east London: relation with previous nitroimidazole exposure and gastroduodenal disease

A high prevalence of metronidazole resistance in Helicobacter pylori is reported in developing countries. This study examined whether migrants referred for diagnostic gastroscopy at a United Kingdom centre (n = 54), had a higher prevalence of metronidazole resistance than subjects born in the United Kingdom attending endoscopy (n = 46). Records of nitroimidazole treatment prescribed in the United Kingdom was obtained in 83 patients to find out if there was an association between H pylori metronidazole resistance and previous ingestion of either metronidazole or tinidazole. The prevalence of metronidazole resistant isolates varied according to country of birth: Bangladesh (90%, 27 of 30), other countries (67%, 16 of 24), and United Kingdom (37%, 17 of 46) (p < 0.001). Among those born in the United Kingdom, women were more likely to harbour resistant H pylori than men (54% v 18% respectively, p = 0.01) and more likely to have a history of previous nitroimidazole ingestion (41% v 11% respectively, p = 0.02). Patients previously exposed to either metronidazole or tinidazole were more likely to harbour resistant strains (84% (27 of 32) v 41% (21 or 51), p < 0.0001). The distribution of gastroduodenal disease, assessed endoscopically, was not affected by metronidazole resistance status.

Comparative study of the cellular fatty acids of methicillin-resistant and -susceptible Staphylococcus aureus

The cellular fatty acid compositions of 26 strains of methicillin-resistant Staphylococcus aureus (MRSA) and 17 strains of methicillin-susceptible S. aureus (MSSA) were analyzed by gas-liquid chromatography. The fatty acid compositions of the two groups were very similar with 16 identified components. The major fatty acids were Ci14 = 0, Ci15 = 0, C18 = 0 and C20 = 0. Among these fatty acids, the percentage of the Ci15 = 0 fatty acid component of MRSA strains (11.4 +/- 3.9%) was statistically higher than that of MSSA strains (6.2 +/- 2.4%) (p < 0.001). On the other hand, the percentage of the C20 = 0 fatty acid components of MRSA strains (20.2 +/- 8.8%) was statistically lower than that of MSSA strains (30.7 +/- 10.4%) (p < 0.001). The production of beta-lactamase and beta-hemolysin in both groups' strain was also unrelated to the relative amounts of the fatty acid components. These results indicated a statistical tendency for the percentage fatty acid compositions of the MRSA strains to be quantitatively different from those of the MSSA for both the Ci15 = 0 and C20 = 0 fatty acid components. Analysis of the fatty acid compositions may have an application in the differentiation of MRSA and MSSA strains.