The presence of skin bacteria in the sternal wound and contamination of implantation materials during cardiac surgery.

BACKGROUND: Sternal wound infections (SWIs) and aortic graft infections (AGIs) are serious complications after cardiac surgery. Staphylococcus aureus and coagulase-negative staphylococci are the most common causes of SWIs, whereas AGIs are less studied. AGIs may occur from contamination during surgery or postoperative haematogenous spread. Skin commensals, such as Cutibacterium acnes, are present in the surgical wound; however, their ability to cause infection is debated. AIM: To investigate the presence of skin bacteria in the sternal wound and to evaluate their potential to contaminate surgical materials. METHODS: Fifty patients undergoing coronary artery bypass graft surgery and/or valve replacement surgery at Örebro University Hospital from 2020 to 2021 were included. Cultures were collected from skin and subcutaneous tissue at two timepoints during surgery, and from pieces of vascular graft and felt that were pressed against subcutaneous tissue. The most common bacterial isolates were tested for antibiotic susceptibility with disc diffusion and gradient tests. FINDINGS: Cultures from skin had bacterial growth in 48% of patients at surgery start and in 78% after 2 h, and cultures from subcutaneous tissue were positive in 72% and 76% of patients, respectively. The most common isolates were C. acnes and S. epidermidis. Cultures from surgical materials were positive in 80-88%. No difference in susceptibility was found for S. epidermidis isolates at surgery start compared with after 2 h. CONCLUSION: The results suggest that skin bacteria are present in the wound and may contaminate surgical graft material during cardiac surgery.

Time-dependent bacterial air contamination of sterile fields in a controlled operating room environment: an experimental intervention study.

BACKGROUND: Surgical site infections are a global patient safety concern. Due to lack of evidence on contamination, pre-set surgical goods are sometimes disposed of or re-sterilized, thus increasing costs, resource use, and environmental effects. AIM: To investigate time-dependent bacterial air contamination of covered and uncovered sterile goods in the operating room. METHODS: Blood agar plates (N = 1584) were used to detect bacterial air contamination of sterile fields on 48 occasions. Each time, three aerobe and three anaerobe plates were used as baseline to model the preparation time, and 60 (30 aerobe, 30 anaerobe) were used to model the time pending before operation; half of these were covered with sterile drapes and half remained uncovered. Plates were collected after 4, 8, 12, 16, and 24 h. FINDINGS: Mean time before contamination was 2.8 h (95% confidence interval: 2.1-3.4) in the uncovered group and 3.8 h (3.2-4.4) in the covered group (P = 0.005). The uncovered group had 98 colony-forming units (cfu) versus 20 in the covered group (P = 0.0001). Sixteen different micro-organisms were isolated, the most common being Cutibacterium acnes followed by Micrococcus luteus. Of 32 Staphylococcus cfu, 14 were antibiotic resistant, including one multidrug-resistant Staphylococcus epidermidis. CONCLUSION: Protecting sterile fields from bacterial air contamination with sterile covers enhances the durability of sterile goods up to 24 h. Prolonged durability of sterile goods might benefit patient safety, since surgical sterile material could be prepared in advance for acute surgery, thereby enhancing quality of care and reducing both climate impact and costs.

Clonal diversity of Cutibacterium acnes (formerly Propionibacterium acnes) in prosthetic joint infections.

Prosthetic joint infections (PJIs) are rare but feared complications following joint replacement surgery. Cutibacterium acnes is a skin commensal that is best known for its role in acne vulgaris but can also cause invasive infections such as PJIs. Some phylotypes might be associated with specific diseases, and recently, a plasmid was detected that might harbour important virulence genes. In this study, we characterized C. acnes isolates from 63 patients with PJIs (n = 140 isolates) and from the skin of 56 healthy individuals (n = 56 isolates), using molecular methods to determine the phylotype and investigate the presence of the plasmid. Single-locus sequence typing and a polymerase chain reaction designed to detect the plasmid were performed on all 196 isolates. No statistically significant differences in sequence types were seen between the two study groups indicating that the C. acnes that causes PJIs originates from the patients own normal skin microbiota. Of the 27 patients with multiple tissue samples, 19 displayed the same sequence types among all their samples. Single-locus sequence typing identified different genotypes among consecutive C. acnes isolates from four patients with recurrent infections. The plasmid was found among 17 isolates distributed in both groups, indicating that it might not be a marker for virulence regarding PJIs. Patients presenting multiple sequence types in tissue samples may represent contamination or a true polyclonal infection due to C. acnes.

Emergence of Multidrug- and Pandrug- Resistant Pseudomonas aeruginosa from Five Hospitals in Qatar.

BACKGROUND: A global rise in multidrug-resistant (MDR) nosocomial infections has led to a significant increase in morbidity and mortality. MDR Gram-negative bacteria (GNB) are recognised for rapidly developing drug resistance. Despite Pseudomonas aeruginosa being the second most common GNB isolated from healthcare associated infections, the magnitude of MDR P. aeruginosa (MDR-PA) has not been evaluated in Qatar. AIM: To assess the prevalence and antimicrobial susceptibility patterns of MDR-PA from 5 major hospitals in Qatar. METHODS: A total of 2533 P. aeruginosa clinical isolates were collected over a one-year period. MDR-PA was defined as resistance to at least one agent of ≥ 3 antibiotic classes. Clinical and demographic data were collected prospectively. FINDINGS: The overall prevalence of MDR-PA isolates was 8.1% (205/2533); the majority of isolates were from patients exposed to antibiotics during 90 days prior to isolation (85.4 %, 177/205), and the infections were mainly hospital-acquired (95.1%, 195/205) with only 4.9% from the community. The majority of MDR-PA isolates were resistant to cefepime (96.6%, 198/205), ciprofloxacin, piperacillin/tazobactam (91%, 186/205), and meropenem (90%, 184/205). Patient comorbidities with MDR-PA were diabetes mellitus (47.3%, n=97), malignancy (17.1%, n=35), end-stage renal disease (13.7%, n=28) and heart failure (10.7%, n=22). CONCLUSION: There was a significant prevalence of MDR-PA in Qatar, primarily from healthcare facilities and associated with prior antibiotic treatment. There was an alarming level of antimicrobial resistance to carbapenems. Our results are part of a national surveillance of MDR to establish effective containment plans.

In vitro activity of tedizolid and linezolid against Staphylococcus epidermidis isolated from prosthetic joint infections.

Prosthetic joint infections (PJIs) are rare but long-lasting and are serious complications without any spontaneous resolution, requiring additional surgery and long-term treatment with antibiotics. Staphylococci are the most important aetiological agents of PJIs, and among the coagulase-negative staphylococci Staphylococcus epidermidis is the most common. However, S. epidermidis often displays multidrug resistance (MDR), demanding additional treatment options. The objective was to examine the effectiveness of tedizolid and linezolid against S. epidermidis isolated from PJIs. The standard antibiotic susceptibility pattern of S. epidermidis (n = 183) obtained from PJIs was determined by disc diffusion test, and MIC was determined by Etest for tedizolid, linezolid, and vancomycin. Tedizolid displayed MIC values ranging from 0.094 to 0.5 mg/L (MIC50: 0.19 mg/L, MIC90: 0.38 mg/L), linezolid MIC values ranging from 0.25 to 2 mg/L (MIC50: 0.75 mg/L, MIC90: 1 mg/L), and vancomycin MIC values ranging from 0.5 to 3 mg/L (MIC50 and MIC90 both 2 mg/L). According to the disc diffusion test, 153/183 (84%) isolates were resistant to ≥3 antibiotic groups, indicating MDR. In conclusion, S. epidermidis isolates from PJIs were fully susceptible, and the MIC50 and MIC90 values for tedizolid were two- to four-fold dilution steps lower compared with linezolid. Tedizolid is not approved, and there are no reports of long-term treatment, but it may display better tolerability and fewer adverse effects than linezolid; it thus could be a possible treatment option for PJIs, alone or in combination with rifampicin.

Staphylococcus capitis isolated from prosthetic joint infections.

Further knowledge about the clinical and microbiological characteristics of prosthetic joint infections (PJIs) caused by different coagulase-negative staphylococci (CoNS) may facilitate interpretation of microbiological findings and improve treatment algorithms. Staphylococcus capitis is a CoNS with documented potential for both human disease and nosocomial spread. As data on orthopaedic infections are scarce, our aim was to describe the clinical and microbiological characteristics of PJIs caused by S. capitis. This retrospective cohort study included three centres and 21 patients with significant growth of S. capitis during revision surgery for PJI between 2005 and 2014. Clinical data were extracted and further microbiological characterisation of the S. capitis isolates was performed. Multidrug-resistant (≥3 antibiotic groups) S. capitis was detected in 28.6 % of isolates, methicillin resistance in 38.1 % and fluoroquinolone resistance in 14.3 %; no isolates were rifampin-resistant. Heterogeneous glycopeptide-intermediate resistance was detected in 38.1 %. Biofilm-forming ability was common. All episodes were either early post-interventional or chronic, and there were no haematogenous infections. Ten patients experienced monomicrobial infections. Among patients available for evaluation, 86 % of chronic infections and 70 % of early post-interventional infections achieved clinical cure; 90 % of monomicrobial infections remained infection-free. Genetic fingerprinting with repetitive sequence-based polymerase chain reaction (rep-PCR; DiversiLab®) displayed clustering of isolates, suggesting that nosocomial spread might be present. Staphylococcus capitis has the potential to cause PJIs, with infection most likely being contracted during surgery or in the early postoperative period. As S. capitis might be an emerging nosocomial pathogen, surveillance of the prevalence of PJIs caused by S. capitis could be recommended.

Bacterial growth and wound infection following saphenous vein harvesting in cardiac surgery: a randomized controlled trial of the impact of microbial skin sealant.

The aim of the present study was to compare microbial skin sealant versus bare skin on the leg regarding intraoperative bacterial presence in the surgical wound and time to recolonization of the adjacent skin at the saphenous vein harvesting site. A second aim was to evaluate the incidence of leg wound infection 2 months after surgery. In this randomized controlled trial, 140 patients undergoing coronary artery bypass grafting (CABG) between May 2010 and October 2011 were enrolled. Bacterial samples were taken preoperatively and intraoperatively at multiple time points and locations. OF the patients, 125 (92.6 %) were followed up 2 months postoperatively regarding wound infection. Intraoperative bacterial growth did not differ between the bare skin (n = 68) and the microbial skin sealant group (n = 67) at any time point. At 2 months postoperatively, 7/61 patients (11.5 %) in the skin sealant versus 14/64 (21.9 %) in the bare skin group (p = 0.120) had been treated with antibiotics for a verified or suspected surgical site infection (SSI) at the harvest site. We found almost no intraoperative bacterial presence on the skin or in the subcutaneous tissue, irrespective of microbial skin sealant use. In contrast, we observed a relatively high incidence of late wound infection, indicating that wound contamination occurred postoperatively. Further research is necessary to determine whether the use of microbial skin sealant reduces the incidence of leg wound infection at the saphenous vein harvest site.

Heterogeneous glycopeptide intermediate Staphylococcus epidermidis isolated from prosthetic joint infections.

Methicillin-resistant Staphylococcus epidermidis (MRSE) poses a major problem in prosthetic joint infections (PJIs). Vancomycin is often considered the drug of choice in the empirical treatment of staphylococcal PJIs. As recent decades have seen reports of heterogeneous glycopeptide intermediate S. aureus (hGISA), our aim was to examine the prevalence of heterogeneous glycopeptide intermediate S. epidermidis (hGISE) in PJIs. S. epidermidis isolates (n = 122) from 119 patients in three Swedish counties between 1993 and 2012 were included. All were isolated from perioperative tissue samples from revision surgery in clinically verified PJIs. Antimicrobial susceptibility testing against staphylococcal antibiotics was performed. The macromethod Etest (MME) and glycopeptide resistance detection (GRD) Etest were used to detect hGISE. Standard minimal inhibitory concentration (MIC) determination revealed no vancomycin-resistant isolates, while teicoplanin resistance was detected in 14 out of 122 isolates (11.5%). hGISE was found in 95 out of 122 isolates (77.9%), 64 out of 67 of isolates with teicoplanin MIC >2 mg/L (95.5%) and 31 out of 55 of isolates with teicoplanin MIC ≤2 mg/L (56.4%). Thus, the presence of hGISE cannot be ruled out by teicoplanin MIC ≤2 mg/L alone. Multidrug resistance was detected in 86 out of 95 hGISE isolates (90.5%) and in 16 out of 27 isolates (59.3%), where hGISE could not be detected. In conclusion, hGISE detected by MME or GRD was common in this material. However, hGISE is difficult to detect with standard laboratory diagnostic routines. Glycopeptide treatment may not be sufficient in many of these PJIs, even if standard MIC classifies the isolated S. epidermidis as susceptible.

Bacterial recolonization of the skin and wound contamination during cardiac surgery: a randomized controlled trial of the use of plastic adhesive drape compared with bare skin.

BACKGROUND: Sternal wound infection after cardiac surgery is a serious complication. Various perioperative strategies, including plastic adhesive drapes, are used to reduce bacterial contamination of surgical wounds. AIM: To compare plastic adhesive drape to bare skin regarding bacterial growth in wound and time to recolonization of the adjacent skin intraoperatively, in cardiac surgery patients. METHODS: This single-blinded randomized controlled trial (May 2010 to May 2011) included 140 patients scheduled for cardiac surgery via median sternotomy. The patients were randomly allocated to the adhesive drape (chest covered with plastic adhesive drape) or bare skin group. Bacterial samples were taken preoperatively and intraoperatively every hour during surgery until skin closure. RESULTS: Disinfection with 0.5% chlorhexidine solution in 70% alcohol decreased coagulase-negative staphylococci (CoNS), while the proportion colonized with Propionibacterium acnes was not significantly reduced and was still present in more than 50% of skin samples. P. acnes was significantly more common in men than in women. Progressive bacterial recolonization of the skin occurred within 2-3 h. At 120 min there were significantly more positive cultures in the adhesive drape group versus bare skin group for P. acnes (63% vs 44%; P = 0.034) and for CoNS (45% vs 24%; P = 0.013). The only statistically significant difference in bacterial growth in the surgical wound was higher proportion of CoNS at the end of surgery in the adhesive drape group (14.7% vs 4.4%; P = 0.044). CONCLUSION: Plastic adhesive drape does not reduce bacterial recolonization. P. acnes colonized men more frequently, and was not decreased by disinfection with chlorhexidine solution in alcohol.

Staphylococcal cassette chromosome mec (SCCmec) and arginine catabolic mobile element (ACME) in Staphylococcus epidermidis isolated from prosthetic joint infections.

The aim of the present study was to characterise the staphylococcal cassette chromosome mec (SCCmec) in Staphylococcus epidermidis isolated from prosthetic joint infections (PJIs) and, if possible, assign them to any of the presently known SCCmec types. In addition, the isolates were examined for the presence of the arginine catabolic mobile element (ACME). Sixty-one S. epidermidis isolates obtained from PJIs and 24 commensal S. epidermidis isolates were analysed. The mecA gene was detected in 49 of the 61 (80 %) PJI isolates and in four of the 24 (17 %) commensal isolates, and the composition of the SCCmec was further analysed. SCCmec types I and IV were the most common types among the PJI isolates. However, for over half (57 %) of the isolates, it was not possible to assign an SCCmec type. ACME was detected in eight (13 %) of the PJI isolates and in 14 (58 %) of the commensal isolates. The characterisation of the SCCmec elements revealed a large heterogeneity, with a high frequency of isolates carrying more than one type of the ccr gene complex. ACME was more common among the commensal isolates and may represent a survival benefit for S. epidermidis colonising healthy individuals in the community.

Alteration of the colonization pattern of coagulase-negative staphylococci in patients undergoing treatment for hematological malignancy.

The aim was to prospectively describe the colonization pattern of coagulase-negative staphylococci (CoNS) and the relationship between colonizing and invasive CoNS isolates among patients undergoing treatment for hematological malignancy. Fourteen newly diagnosed patients were included with either multiple myeloma or acute leukemia. Patients were repeatedly sampled from nares, throat, axillae, and perineum, and the CoNS isolates obtained were phenotypically characterized together with blood isolates of CoNS using the PhenePlate system (PhP). During the treatment a gradual reduction in the heterogeneity of colonizing CoNS was observed as well as an inter-patient accumulation of phenotypically related and multi-drug-resistant CoNS. These clusters of CoNS persisted for 2-3 months after the end of therapy. Ten positive blood cultures of CoNS were obtained and in the majority of these cases CoNS of the same PhP type were found in superficial cultures collected prior to the blood culture sampling. In conclusion, the study shows that therapy for hematological malignancy is associated with a homogenization of colonizing CoNS isolates and that this acquired flora of CoNS is persistent several months after the end of therapy. Furthermore, the results suggest that the source of bloodstream infections of CoNS in hematological patients is colonizing CoNS of the skin and mucosa.

In vitro activity of beta-lactam antibiotics to community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA).

Community-associated (CA) MRSA often display low MIC values against oxacillin. The in vitro activity of various beta-lactam antibiotics against heterogeneous CA-MRSA (n = 98) isolated in a low endemic area was determined by Etest, and Mueller-Hinton agar (MUHAP) was compared with Mueller-Hinton agar supplemented with 2% NaCl (MUHSP). In general, the CA-MRSA isolates showed higher MIC values for the various beta-lactam antibiotics on MUHSP compared with MUHAP. MIC values for oxacillin ranged from 1 to >256 mg/L on MUHSP. Cephalothin, representing the first generation of cephalosporins, showed MICs from 0.75 to 96 mg/L and the MIC(50) and MIC(90) for cefuroxime, cefotaxime and cefepime, representing the second, third and fourth generations, respectively, were rather high. However, the MIC(50) and MIC(90) for ceftobiprole (fifth generation) were 1.5 and 2 mg/L, respectively, on MUHSP. The MIC(50) and MIC(90) for imipenem were 0.75 and 2 mg/L, respectively, on MUHSP. Only 3/98 (3%) CA-MRSA isolates showed a MIC >4 mg/L. Consequently, low MIC values for imipenem, lower than those of the newly developed fifth generation cephalosporins, were found among CA-MRSA. These findings may be considered for further studies including clinical trials in order to evaluate carbapenems as a potential treatment option for infections caused by CA-MRSA.

Glycopeptide resistance in coagulase-negative staphylococci isolated in blood cultures from patients with hematological malignancies during three decades.

The aim of this study was to determine if there was a long-term increase in glycopeptide minimum inhibitory concentration (MIC) values, MIC creep, among bloodstream isolates of Staphylococcus epidermidis and S. haemolyticus isolated from patients with hematological malignancies. We conducted a retrospective single-center study where all positive blood cultures of S. epidermidis (n = 387) and S. haemolyticus (n = 19) isolated from patients with hematological malignancies during three decades, 1980 to 2009, were re-evaluated for the presence of reduced susceptibility to vancomycin and teicoplanin. Three different methods for the detection of reduced susceptibility to glycopeptides were used; standard Etest, macromethod Etest, and glycopeptide resistance detection (GRD) Etest. The median MIC value for vancomycin was 2 mg/L. MIC values for vancomycin and teicoplanin did not show any statistically significant increase during the study period. The presence of heterogeneously glycopeptide-intermediate staphylococci (hGIS) was analyzed among 405 coagulase-negative staphylococci (CoNS) isolates. hGIS were found in 31-45% of the CoNS isolates by the macromethod Etest and in 53-67% by the GRD Etest during the three decades. In conclusion, we did not observe any long-term glycopeptide MIC creep determined by the standard Etest, although a high and increasing proportion of heterogeneous vancomycin resistance was observed.

Colonization pattern of coagulase-negative staphylococci in preterm neonates and the relation to bacteremia.

Coagulase-negative staphylococci (CoNS) are the major cause of sepsis in extreme preterm (EPT) newborns, but data on the CoNS colonization in EPT newborns prior to invasive infection are limited. Our aim was to describe the early establishment of the CoNS microflora in EPT newborns and to compare the colonization pattern in neonates with and without positive CoNS blood cultures. From a cohort of 46 EPT neonates, newborns with positive CoNS blood culture were identified (n = 10) and compared with matched controls. Samples for bacterial cultures were obtained repetitively from nares, perineum, and umbilicus. All CoNS isolates were characterized using the PhenePlate system for biochemical fingerprinting. Persistent CoNS strains were found on day 2-3 after delivery in 7/20 newborns, and there was a tendency for earlier colonization in nares than in the perineum or umbilicus. The CoNS blood strains were prevalent in superficial sites prior to positive blood culture (11/14 blood strains), but no single invasive pathway was identified. Most CoNS blood strains (9/14) persisted on superficial sites after antibiotic treatment. We hypothesize that the invasive pathways in neonatal CoNS sepsis are complex and that the colonization of mucosal membranes and umbilical catheters might be of equal importance.

Rapid typing of neonatal Staphylococcus epidermidis isolates using polymerase chain reaction for repeat regions in surface protein genes.

Staphylococcus epidermidis is a significant pathogen in neonatal sepsis and other nosocomial infections. For further investigations of the colonisation patterns and invasive pathways, typing methods that are applicable on large populations of bacterial isolates are warranted. In the present study, a genotyping method based on polymerase chain reaction (PCR) for the repeat regions of four genes (sdrG, sdrF, aap and sesE) that encode for bacterial surface proteins was developed and applied to a sample of well-characterised neonatal blood isolates of S. epidermidis (n = 49). The PCR products were visualised on agarose gel (sdrG, sdrF and sesE) or by fragment analysis (aap). The discriminatory index (D-index) for genotyping of the different genes was compared to genotyping by pulsed-field gel electrophoresis (PFGE). The highest D-index for the PCR-based typing methods was found for the combination of sdrF, sdrG and aap (D-index 0.94), whereas the optimal two-gene combination (sdrF and aap) resulted in a D-index of 0.92. We conclude that the described method can be used for the genotyping of large populations of S. epidermidis isolates with a sufficient discriminatory capacity, and we suggest that the combination of sdrF and aap is the most suitable to use.

In vitro antimicrobial synergy testing of coagulase-negative staphylococci isolated from prosthetic joint infections using Etest and with a focus on rifampicin and linezolid.

In recent years, coagulase-negative staphylococci (CoNS) have been increasingly recognised as causative agents of various infections, especially in immunocompromised patients and related to implanted foreign body materials. CoNS, and especially Staphylococcus epidermidis, transform into a stationary growth phase and produce biofilm when involved in a foreign body infection, making them difficult to eradicate with antimicrobials. Rifampicin has the ability to penetrate biofilm, but resistance may develop rapidly. To reduce the emergence of resistance, rifampicin should be combined with additional antimicrobials, of which several different ones have been proposed, including the relatively new class of antimicrobials, oxazolidinones, represented by linezolid. Thirty-seven CoNS isolates from patients with prosthetic joint infection were investigated by synergy testing using Etest. Nine antimicrobial combinations, based on either rifampicin or linezolid, were tested. For 16 (43%) of the isolates, a synergistic (n = 5), additive (n = 14) and/or antagonistic (n = 11) effect were identified. In conclusion, Etest is an objective and easily performed in vitro method for antimicrobial synergy testing. However, each isolate requires testing for the specific combination considered for treatment.

Propionibacterium acnes as an etiological agent of arthroplastic and osteosynthetic infections--two cases with specific clinical presentation including formation of draining fistulae.

This report describes two patients with orthopaedic implant infections, with specific clinical presentations including formation of draining fistulae. Propionibacterium acnes was isolated in multiple cultures in both cases. Phenotypic and genetic characterisation of the isolates clearly emphasizes the significance of P. acnes as an etiological agent of implant infections. These infections are insidious with delayed presentation of symptoms and may have been overlooked because of the consideration of P. acnes as a contaminating commensal as well as the frequent use of suboptimal culture procedures.

Methicillin-resistant Staphylococcus saprophyticus in Sweden carries various types of staphylococcal cassette chromosome mec (SCCmec).

Staphylococcus saprophyticus is a common cause of uncomplicated urinary tract infections and is usually susceptible to the antimicrobial agents used for their treatment. However, S. saprophyticus resistant to beta-lactam antibiotics and carrying mecA has been reported. Eight Swedish isolates of mecA-positive S. saprophyticus with diverse origin carrying at least three different types of staphylococcal cassette chromosome mec (SCCmec) are described here.