The role of virulence factors in the outcome of staphylococcal peritonitis in CAPD patients

Pasqual Barretti 1 Augusto C Montelli 1 Jackson EN Batalha 1 Jacqueline CT Caramori 1 Maria de Lourdes RS Cunha 0 0 Department of Microbiology and Immunology, Biosciences Institute , UNESP, Botucatu, Sao Paulo , Brazil 1 Department of Internal Medicine, Botucatu School of Medicine , UNESP, Botucatu, Sao Paulo , Brazil Background: Peritonitis continues to be the most frequent cause of peritoneal dialysis (PD) failure, with an important impact on patient mortality. Gram-positive cocci such as Staphylococcus epidermidis, other coagulase-negative staphylococci (CoNS), and Staphylococcus aureus are the most frequent etiological agents of PD-associated peritonitis worldwide. The objective of the present study was to compare peritonitis caused by S. aureus and CoNS and to evaluate the factors influencing outcome. Methods: Records of 86 new episodes of staphylococcal peritonitis that occurred between 1996 and 2000 in the Dialysis unit of a single university hospital were studied (35 due to S. aureus, 24 to S. epidermidis and 27 to other CoNS). The production of slime, lipase, lecithinase, nuclease (DNAse), thermonuclease (TNAse), - and -hemolysin, enterotoxins (SEA, SEB, SEC, SED) and toxic shock syndrome toxin-1 (TSST-1) was studied in S. aureus and CoNS. Antimicrobial susceptibility was evaluated based on the minimal inhibitory concentration determined by the Etest. Outcome predictors were evaluated by two logistic regression models. Results: The oxacillin susceptibility rate was 85.7% for S. aureus, 41.6% for S. epidermidis, and 51.8% for other CoNS (p = 0.001). Production of toxins and enzymes, except for enterotoxin A and hemolysin, was associated with S. aureus episodes (p < 0.001), whereas slime production was positive in 23.5% of CoNS and 8.6% of S. aureus strains (p = 0.0047). The first model did not include enzymes and toxins due to their association with S. aureus. The odds of resolution were 9.5 times higher for S. epidermidis than for S. aureus (p = 0.02) episodes, and were similar for S. epidermidis and other CoNS (p = 0.8). The resolution odds were 68 times higher for non-slime producers (p = 0.001) and were not influenced by oxacillin resistance among vancomycin-treated cases (p = 0.89). In the second model, the resolution rate was similar for S. aureus and S. epidermidis (p = 0.70), and slime (p = 0.001) and -hemolysin (p = 0.04) production were independent predictors of nonresolution. Conclusion: Bacterial species and virulence factors rather than antibiotic resistance influence the outcome of staphylococcal peritonitis. - Background Peritonitis continues to be the most frequent cause of peritoneal dialysis (PD) failure [1], and has an important impact on patient mortality [2]. Gram-positive cocci such as Staphylococcus epidermidis, other coagulase-negative staphylococci (CoNS), and Staphylococcus aureus are the most frequent etiological agents of PD-associated peritonitis worldwide [3]. Previous studies comparing the outcome of peritonitis caused by S. aureus and CoNS have shown a lower resolution rate and a higher frequency of complications in the former [4-8]. Perez-Fontan et al [2] observed a mortality rate of 15.2% for S. aureus episodes and of only 0.5% for CoNS episodes. These findings are in contrast to the susceptibility profile observed for CoNS. According to Kim et al [9], the frequency of methicillin-resistance among CoNS increased from 18.4% in 1992-1993 to 41.7% in 2000-2001. Similar results have been reported by other investigators [10]. Previous data from our group showed that oxacillin resistance does not influence the outcome of staphylococcal peritonitis [8]. In addition to species and antibiotic resistance, other factors related to the causal agent may influence the prognosis of peritonitis. Recurrence of CoNS infections is frequently observed and has been suggested to be associated with the presence of a biofilm in the peritoneal catheter [11]. Biofilm formation is related to the production of an extracellular mucoid polysaccharide, called slime, which permits microorganisms to adhere to plastic surfaces [12]. Kristinsson et al [13] reported a higher recurrence rate of peritonitis for slime-positive strains compared to slime-negative ones, whereas Alexander and Rimland [14] did not observe a relationship between slime production and peritonitis outcome. In our unit, slime production was found to be an independent risk factor for the non-resolution of CoNS peritonitis [15]. The production of enzymes and toxins is a well-known fact in Staphylococcus species, particularly S. aureus. Proteases, lipases, nucleases, and collagenases convert tissue components into nutrients, facilitating bacterial growth and invasion [16], while toxic shock syndrome toxin (TSST-1) and enterotoxins have effects such as superantigenicity, pyrogenicity, toxicity and direct damage to endothelial [6]. Although these products are potential virulence factors in staphylococcal PD-associated peritonitis, their influence on the clinical outcome of these infections is unknown. The objective of the present study was to compare the capacity of traditional clinical and bacteriologic and selected virulence factors such as production of slime, enzymes and toxins to predict the outcome of new perito Methods Data collection and definitions The present study was approved by the institutional Ethics Committee. All episodes of continuous ambulatory peritoneal dialysis (CAPD)-associated peritonitis caused by staphylococcal species between January 1996 and December 2000 were reviewed. This period was chosen because a single antibiotic protocol based on the 1996 Update of the International Society for Peritoneal Dialysis [17] was used. After this period, new guidelines were proposed [18] and adopted in our unit. The diagnosis of peritonitis was made when at least two of the following criteria were present: (a) presence of a cloudy peritoneal effluent, (b) abdominal pain, (c) dialysate white cell count higher than 100/L, with at least 50% polymorphonuclear cells, and (d) positive culture of peritoneal effluent [17]. Only cases considered to be new episodes, i.e., a patient's first peritonitis or an episode diagnosed at least 28 days after completion of the last peritonitis treatment, were included in the study [17]. Thus, 86 of 122 diagnosed staphylococcal peritonitis episodes were analyzed. Exclusion criteria were staphylococcal peritonitis within 28 days prior to presentation, presence of concomitant exit site or tunnel infections, incomplete clinical data, concomitant antibiotic use for other indications, and use of an empirical antibiotic protocol other than the combination of cefazolin and amikacin. Resolution was defined as the disappearance of signs and symptoms within 96 h after the beginning of antibiotic therapy and a negative peritoneal fluid culture at least 28 days after treatment completion [7]. Relapse was defined as an episode with the same organism or a neg (...truncated)