Successful Treatment of Carbapenem-Resistant Acinetobacter baumannii Meningitis with Sulbactam-Durlobactam.

BACKGROUND: The treatment of carbapenem-resistant Acinetobacter baumannii/calcoaceticus complex (CRAB) presents significant treatment challenges. METHODS: We report the case of a 42-year-old woman with CRAB meningitis who experienced persistently positive cerebrospinal fluid (CSF) cultures for 13 days despite treatment with high-dose ampicillin-sulbactam and cefiderocol. On day 13, she was transitioned to sulbactam-durlobactam and meropenem; four subsequent CSF cultures remained negative. After 14 days of sulbactam-durlobactam, she was cured of infection. Whole genome sequencing investigations identified putative mechanisms that contributed to reduced cefiderocol susceptibility observed during cefiderocol therapy. Blood and CSF samples were collected pre-dose and 3-hours post initiation of a sulbactam-durlobactam infusion. RESULTS: The CRAB isolate belonged to sequence type 2. An acquired blaOXA-23 and an intrinsic blaOXA-51-like (i.e., blaOXA-66) carbapenemase gene were identified. The paradoxical effect (i.e., no growth at lower cefiderocol dilutions but growth at higher dilutions) was observed by broth microdilution after 8 days of cefiderocol exposure but not by disk diffusion. Potential markers of resistance to cefiderocol included mutations in the start codon of piuA and piuC iron transport genes and a A515V substitution in PBP3, the primary target of cefiderocol. Sulbactam and durlobactam were detected in CSF at both timepoints, indicating CSF penetration. CONCLUSIONS: This case describes successful treatment of refractory CRAB meningitis with the administration of sulbactam-durlobactam and meropenem and highlights the need to be cognizant of the paradoxical effect that can be observed with broth microdilution testing of CRAB isolates with cefiderocol.

Clinical significance of Nosocomiicoccus ampullae isolated from blood cultures.

IMPORTANCE: Nosocomiicoccus species are recently described as members of the Staphylococcaceae family. With their inclusion in commercial matrix-assisted laser desorption/ionization-time of flight mass spectrometry databases, Nosocomiicoccus species can now be identified when Gram-positive cocci in clusters are detected in positive blood cultures. However, their clinical significance is not known, making it difficult for the clinical microbiology laboratory to decide the extent of work-up. Based on our study, Nosocomiicoccus species demonstrate low pathogenicity and opportunistic potential. If isolated from a single blood culture set, limited work-up should be performed to an extent similar to other possible blood culture contaminants.

An NDM-Producing Escherichia coli Clinical Isolate Exhibiting Resistance to Cefiderocol and the Combination of Ceftazidime-Avibactam and Aztreonam: Another Step Toward Pan-ß-Lactam Resistance.

Background: Cefiderocol and ceftazidime-avibactam plus aztreonam (CZA-ATM) are preferred treatment regimens for New Delhi metallo-ß-lactamase (NDM)-producing infections. Methods: We report the case of a US patient who traveled to India to receive a renal transplant. He subsequently experienced pyelonephritis by an NDM-producing Escherichia coli. Broth microdilution and the broth disk elution method indicated resistance to all ß-lactams, including cefiderocol and CZA-ATM. Whole-genome sequencing investigations were undertaken to identify resistance mechanisms. Results: An E. coli isolate belonging to sequence type (ST) 167 containing a blaNDM-5 gene was identified on a plasmid of the IncFIA/IncFIB/IncFIC replicon groups. When compared with the genome of another ST167 E. coli clinical isolate containing blaNDM-5 and exhibiting susceptibility to cefiderocol and CZA-ATM, a 12-base pair insertion in ftsI, translating to a 4-amino acid duplication in PBP3, was identified. Moreover, a blaCMY-59 gene was harbored on an IncI-γ replicon type, and frameshift mutations were identified in the cirA iron transport gene. Conclusions: This is the first clinical case of a US patient harboring an NDM-producing isolate exhibiting resistance to all available ß-lactam agents. The isolate's unexpected resistance to cefiderocol and CZA-ATM was likely due to a combination of (1) a modified PBP3 (increased MICs to both regimens), (2) truncated iron-binding protein (increased cefiderocol MIC), and (3) a blaCMY gene (reduced CZA-ATM activity). E. coli ST167 clinical isolates harboring blaNDM-5 genes are a recognized international high-risk clone. When coupled with the additional mechanisms identified in our patient's isolate, which is not uncommon for this high-risk clone, pan-ß-lactam resistance may occur.

Evaluation of Piperacillin-Tazobactam Testing against Enterobacterales by the Phoenix, MicroScan, and Vitek2 Tests Using Updated Clinical and Laboratory Standards Institute Breakpoints.

In 2022, the Clinical and Laboratory Standards Institute (CLSI) updated piperacillin-tazobactam (TZP) breakpoints for Enterobacterales, based on substantial data suggesting that historical breakpoints did not predict treatment outcomes for TZP. The U.S. Food and Drug Administration (FDA) has not yet adopted these breakpoints, meaning commercial manufacturers of antimicrobial susceptibility testing devices cannot obtain FDA clearance for the revised breakpoints. We evaluated the Phoenix (BD, Sparks, MD), MicroScan (Beckman Coulter, Sacramento, CA), and Vitek2 (bioMérieux, Durham, NC) TZP MICs compared to reference broth microdilution for a collection of 284 Enterobacterales isolates. Phoenix (n = 167 isolates) demonstrated 84.4% categorical agreement (CA), with 4.2% very major errors (VMEs) and 1.8% major errors (MEs) by CLSI breakpoints. In contrast, CA was 85.0% with 4.3% VMEs and 0.8% MEs for the Phoenix with FDA breakpoints. MicroScan (n = 55 isolates) demonstrated 80.0% CA, 36.4% VMEs, and 4.8% MEs by CLSI breakpoints and 81.8% CA, 44.4% VMEs, and 0.0% MEs by FDA breakpoints. Vitek2 (n = 62 isolates) demonstrated 95.2% CA, 6.3% VMEs, and 0.0% MEs by CLSI and 96.8% CA, 0.0% VMEs, and 2.2% MEs by FDA breakpoints. Overall, the performance of the test systems was not substantially different using CLSI breakpoints off-label than using on-label FDA breakpoints. However, limitations were noted with higher-than-desired VME rates (all three systems) and lower-than-desired CA (MicroScan and Phoenix). Laboratories should consider adoption of the revised CLSI breakpoints with automated test systems but be aware that some performance challenges exist for testing TZP on automated systems, regardless of breakpoints applied.

Progressive Development of Cefiderocol Resistance in Escherichia coli During Therapy is Associated With an Increase in blaNDM-5 Copy Number and Gene Expression.

BACKGROUND: As cefiderocol is increasingly being prescribed in clinical practice, it is critical that we understand key mechanisms contributing to acquired resistance to this agent. METHODS: We describe a patient with acute lymphoblastic leukemia and a New Delhi metallo-ß-lactamase (NDM)-5-producing Escherichia coli intra-abdominal infection in whom resistance to cefiderocol evolved approximately 2 weeks after the start of treatment. Through whole-genome sequencing (WGS), messenger RNA expression studies, and ethylenediaminetetraacetic acid inhibition analysis, we investigated the role of increased NDM-5 production and genetic mutations contributing to the development of cefiderocol resistance, using 5 sequential clinical E. coli isolates obtained from the patient. RESULTS: In all 5 isolates, blaNDM-5 genes were identified. The minimum inhibitory concentrations for cefiderocol were 2, 4, and >32 µg/mL for isolates 1-2, 3, and 4-5, respectively. WGS showed that isolates 1-3 contained a single copy of the blaNDM-5 gene, whereas isolates 4 and 5 had 5 and 10 copies of the blaNDM-5 gene, respectively, on an IncFIA/FIB/IncFII plasmid. These findings were correlated with those of blaNDM-5 messenger RNA expression analysis, in which isolates 4 and 5 expressed blaNDM-5 1.7- and 2.8-fold, respectively, compared to, isolate 1. Synergy testing with the combination of ceftazidime-avibactam and aztreonam demonstrated expansion of the zone of inhibition between the disks for all isolates. The patient was successfully treated with this combination and remained infection free 1 year later. CONCLUSIONS: The findings in our patient suggest that increased copy numbers of blaNDM genes through translocation events are used by Enterobacterales to evade cefiderocol-mediated cell death. The frequency of increased blaNDM-5 expression in contributing to cefiderocol resistance needs investigation.

Pan-drug resistant Providencia rettgeri contributing to a fatal case of COVID-19.

Following prolonged hospitalization that included broad-spectrum antibiotic exposure, a strain of Providencia rettgeri was cultured from the blood of a patient undergoing extracorporeal membrane oxygenation treatment for hypoxic respiratory failure due to COVID-19. The strain was resistant to all antimicrobials tested including the novel siderophore cephalosporin, cefiderocol. Whole genome sequencing detected ten antimicrobial resistance genes, including the metallo-ß-lactamase bla NDM-1, the extended-spectrum ß-lactamase bla PER-1, and the rare 16S methyltransferase rmtB2.

Molecular Epidemiology of Ceftriaxone Non-Susceptible Enterobacterales Isolates in an Academic Medical Center in the United States.

BACKGROUND: Knowledge of whether Enterobacterales are not susceptible to ceftriaxone without understanding the underlying resistance mechanisms may not be sufficient to direct appropriate treatment decisions. As an example, extended-spectrum ß-lactamase (ESBL)-producing organisms almost uniformly display non-susceptibility to ceftriaxone. Regardless of susceptibility to piperacillin-tazobactam or cefepime, carbapenem antibiotics are the treatment of choice for invasive infections. No such guidance exists for ceftriaxone non-susceptible organisms with mechanisms other than ESBL production. We sought to investigate the molecular epidemiology of ceftriaxone non-susceptible Enterobacterales. METHODS: All consecutive Escherichia coli, Klebsiellapneumoniae, Klebsiella oxytoca, or Proteus mirabilis clinical isolates with ceftriaxone MICs of ≥2 mcg/mL from unique patients at a United States hospital over an 8-month period were evaluated for ß-lactamase genes using a DNA microarray-based assay. RESULTS: Of 1929 isolates, 482 (25%) had ceftriaxone MICs of ≥2 mcg/mL and were not resistant to any carbapenem antibiotics. Of the 482 isolates, ESBL (blaCTX-M, blaSHV, blaTEM) and/or plasmid-mediated ampC (p-ampC) genes were identified in 376 (78%). ESBL genes were identified in 310 (82.4%), p-ampC genes in 2 (0.5%), and both ESBL and p-ampC genes in 64 (17.0%) of the 376 organisms. There were 211 (56%), 120 (32%), 41 (11%), and 4 (1%) isolates with 1, 2, 3, or 4 or more ESBL or p-ampC genes. The most common ESBL genes were of the blaCTX-M-1 group (includes blaCTX-M-15) and the most common p-ampC gene was the blaCMY-2. CONCLUSIONS: There is considerable diversity in the molecular epidemiology of ceftriaxone non-susceptible Enterobacterales. An understanding of this diversity can improve antibiotic decision-making.

Performance of Five Commercial Identification Platforms for Identification of Staphylococcus delphini.

The Staphylococcus intermedius group (SIG) is a collection of coagulase-positive staphylococci consisting of four distinct species, namely, Staphylococcus cornubiensis, Staphylococcus delphini, Staphylococcus intermedius, and Staphylococcus pseudintermedius SIG members are animal pathogens and rare causes of human infection. Accurate identification of S. pseudintermedius has important implications for interpretation of antimicrobial susceptibility testing data and may be important for other members of the group. Therefore, we sought to evaluate the performance of five commercially available identification platforms with 21 S. delphini isolates obtained from a variety of animal and geographic sources. Here, we show that automated biochemical platforms were unable to identify S. delphini to the species level, a function of its omission from their databases, but could identify isolates to the SIG level with various degrees of success. However, all automated systems misidentified at least one isolate as Staphylococcus aureus One matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) system was able to identify S. delphini to the species level, suggesting that MALDI-TOF MS is the best option for distinguishing members of the SIG. With the exception of S. pseudintermedius, it is unclear if other SIG members should be routinely identified to the species level; however, as our understanding of their role in animal and human diseases increases, it may be necessary and important to do so.

Differentiating Streptococcus pseudoporcinus from GBS: could this have implications in pregnancy?

BACKGROUND: Streptococcus agalactiae (GBS) is a common pathogen known to cause neonatal and maternal infectious morbidity. Streptococcus pseudoporcinus (S pseudoporcinus) is a separate, recently identified ß-hemolytic gram-positive coccus that can cause false-positive results on standard GBS agglutination testing assays. OBJECTIVE: To determine the prevalence and clinical implications of Streptococcus pseudoporcinus colonization in pregnancy. MATERIALS AND METHODS: This is a 2-year retrospective cohort study comparing pregnant women colonized with GBS to those colonized with S. pseudoporcinus. A proteomics method of identification, namely, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, was used to distinguish between S. pseudoporcinus and GBS colonization. Antibiotic susceptibility testing was carried out on all specimens. Maternal and neonatal chart reviews were conducted to identify predictors of S. pseudoporcinus colonization and to compare maternal and neonatal outcomes. RESULTS: S. pseudoporcinus colonization occurred in 1.6% of all pregnancies. A total of 2.5% of all GBS-positive results by agglutination assay were false positive, instead reflecting S. pseudoporcinus colonization. Clindamycin resistance among S. pseudoporcinus isolates is uncommon. S. pseudoporcinus colonization in pregnancy is independently associated with African American race, tobacco use, and body mass index ≥35. Preterm premature rupture of membranes or spontaneous preterm birth was more common in patients colonized with S. pseudoporcinus. CONCLUSION: Although the prevalence of S. pseudoporcinus colonization is low, it primarily occurs in African American women and is associated with preterm premature rupture of membranes or spontaneous preterm birth when compared to individuals colonized with GBS.

Two-Site Evaluation of the Colistin Broth Disk Elution Test To Determine Colistin In Vitro Activity against Gram-Negative Bacilli.

Limited methods for colistin MIC determination are available to clinical microbiology laboratories. The purpose of this study was to evaluate the accuracy of the colistin broth disk elution (CBDE) test compared to that of broth microdilution (BMD) for identifying colistin MICs. CBDE was compared to colistin BMD using a collection of Gram-negative bacilli tested at two U.S. microbiology laboratories. The isolates tested included 121 retrospective clinical isolates, 45 prospective clinical isolates, and 6 mcr-1-positive Escherichia coli isolates. CBDE was performed with four 10-ml cation-adjusted Mueller-Hinton broth tubes per isolate, to which 0, 1, 2, and 4 colistin 10-µg disks were added, generating final concentrations in the tubes of 0 (growth control), 1, 2, and 4 µg/ml, respectively. MICs were evaluated visually and interpreted using Clinical and Laboratory Standards Institute breakpoints. Site 2 also compared CBDE to the reference broth macrodilution (BMAD) method (n = 110 isolates). Overall, CBDE yielded a categorical agreement (CA) and essential agreement (EA) of 98% and 99%, respectively, compared to the results of colistin BMD. Very major errors occurred for mcr-1-producing strains, with MICs fluctuating from 2 to 4 µg/ml on repeat testing. The results for all other isolates were in CA with those of BMD. CBDE versus BMAD had an EA of 100% and a CA of 100%. Compared to currently used techniques, CBDE is an easy and practical method to perform colistin MIC testing. Some mcr-1-producing isolates yielded MICs of 2 µg/ml by CBDE and 4 µg/ml by BMD. As such, the results for isolates with colistin MICs of 2 µg/ml by CBDE should be confirmed by the reference BMD method, and isolates with MICs of ≥2 µg/ml should be evaluated for the presence of mcr genes.

Antibiotic pressure on the acquisition and loss of antibiotic resistance genes in Klebsiella pneumoniae.

Objectives: In this study, we characterize a concurrent disseminated infection with a virulent hypermucoviscous (HMV) Klebsiella pneumoniae and an OXA-181-producing XDR K. pneumoniae from a patient with recent hospitalization in India. During exposure to meropenem therapy, the highly susceptible HMV K. pneumoniae became resistant to carbapenems, consistent with the acquisition of blaOXA-181. Methods: Twelve K. pneumoniae isolates were recovered from the patient and the hospital room environment over a 3 month hospitalization. Phenotypic and molecular studies were completed to characterize the isolates. Oxford Nanopore and Illumina MiSeq WGS were performed to study phylogeny (MLST and SNPs), plasmids and virulence genes and demonstrate changes in the organism's resistome that occurred over time. Results: WGS revealed that the HMV K. pneumoniae belonged to ST23 and harboured an IncH1B virulence plasmid, while the XDR K. pneumoniae belonged to ST147 and possessed two MDR plasmids (IncR and IncFII), the blaOXA-181-bearing ColKP3 plasmid and chromosomal mutations conferring the XDR phenotype. Sequential isolates demonstrated plasmid diversification (fusion of the IncR and IncFII plasmids), mobilization of resistance elements (ompK35 inactivation by ISEcp1-blaCTX-M-15 mobilization, varying numbers of resistance genes on plasmid scaffolds) and chromosomal mutations (mutations in mgrB) leading to further antibiotic resistance that coincided with antibiotic pressure. Importantly, the HMV strain in this study was unable to preserve the carbapenem-resistant phenotype without the selective pressure of meropenem. Conclusions: To the best of our knowledge, we are the first to report a carbapenem-resistant HMV K. pneumoniae strain in the USA. Ultimately, this case demonstrates the role of antibiotic pressure in the acquisition and loss of important genetic elements.

Frequency of small-colony variants and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus in cystic fibrosis patients.

BACKGROUND: Small-colony variants (SCVs) are a distinct phenotype of Staphylococcus aureus, known for their role in chronic, difficult to treat infections, including cystic fibrosis (CF) lung disease. The goal of this study was to characterize SCV MRSA infection in an adult and pediatric CF population and to identify antibiotic susceptibility patterns unique to SCV MRSA. METHODS: We recovered methicillin-resistant S. aureus (MRSA) from respiratory culture samples from CF patients at the Johns Hopkins Hospital during a 6month study period. RESULTS: Of 1161 samples, 200 isolates (17%) were identified as MRSA, and 37 isolates from 28 patients were identified as SCV MRSA. A higher proportion of MRSA was found among SCV isolates (37/66, 56%) compared to normal colony variant (NCV) isolates (163/417, 39%), p=0.02. All SCV MRSA isolates from individual patients were susceptible to vancomycin and ceftaroline, but they demonstrated higher rates of antibiotic resistance to trimethoprim/sulfamethoxazole, moxifloxacin, and erythromycin, compared to NCV MRSA isolates. Additionally, individuals with SCV MRSA had lower lung function, higher rates of persistent MRSA infection, and higher rates of previous antibiotic use, compared to individuals with NCV MRSA. CONCLUSIONS: A significant proportion of MRSA isolates recovered from patients with CF have the SCV morphology. Compared to individuals with NCV MRSA, those with SCV MRSA have higher rates of persistent MRSA infection and lower lung function. SCV MRSA isolates were more resistant than NCV, but they are highly susceptible to vancomycin, linezolid and ceftaroline.

Face Mask Use and Persistence of Livestock-associated Staphylococcus aureus Nasal Carriage among Industrial Hog Operation Workers and Household Contacts, USA.

BACKGROUND: Industrial hog operation (IHO) workers may persistently carry antibiotic-resistant, livestock-associated Staphylococcus aureus in their nasal cavities. It is unclear whether IHO work activities can alter IHO workers' and their household members' exposure to these bacteria. OBJECTIVE: Our objective was to investigate the relationship of IHO work activities with persistence of antibiotic-resistant, livestock-associated S. aureus nasal carriage among IHO workers and their household members. METHODS: At biweekly intervals over 4 months, IHO workers and their household members completed questionnaires and provided nasal swabs that were assessed for S. aureus, multidrug-resistant S. aureus (MDRSA), and livestock-associated markers (tetracycline resistance, scn absence, spa type). We examined the association between transient and habitual IHO work activities and S. aureus nasal carriage outcomes. RESULTS: One hundred one IHO workers and 79 household members completed 1,456 study visits. Face mask use (each 25% increase) was associated with reduced odds of nasal carriage of MDRSA (odds ratio [OR]: 0.65 [95% confidence interval (CI): 0.46, 0.92], tetracycline-resistant S. aureus [OR = 0.74 (95% CI: 0.56, 0.97)], and S. aureus clonal complex (CC) 398/CC9 [OR = 0.77 (95% CI: 0.60, 0.99)]. IHO workers who ever (vs. never) gave pigs injections had higher odds of these outcomes. Among household members, living with an IHO worker who consistently ([Formula: see text] of the time) versus sometimes or never used a face mask was associated with reduced odds of carrying scn-negative S. aureus, tetracycline-resistant S. aureus, and S. aureus CC398/CC9 (OR range: 0.12-0.20, all [Formula: see text]), and consistent IHO worker coveralls use was associated with reduced odds of household member MDRSA carriage only. Living with an IHO worker who habitually had contact with [Formula: see text] hogs (vs. [Formula: see text]) was associated with higher odds of household member livestock-associated S. aureus carriage. CONCLUSIONS: Consistent face mask use was associated with reduced exposure to antibiotic-resistant, livestock-associated S. aureus among IHO workers and their household members. https://doi.org/10.1289/EHP3453.

Comparing the Outcomes of Patients With Carbapenemase-Producing and Non-Carbapenemase-Producing Carbapenem-Resistant Enterobacteriaceae Bacteremia.

BACKGROUND: Carbapenem-resistant Enterobacteriaceae (CRE) are associated with considerable mortality. As mechanisms of carbapenem resistance are heterogeneous, it is unclear if mortality differs based on resistance mechanisms. We sought to determine whether CRE resistance mechanism determination is prognostically informative. METHODS: We conducted an observational study comparing 14-day mortality between patients with carbapenemase-producing (CP)-CRE compared with non-CP-CRE bacteremia. Clinical data were collected on all patients. A comprehensive DNA microarray-based assay was performed on all isolates to identify ß-lactamase-encoding genes. RESULTS: There were 83 unique episodes of monomicrobial CRE bacteremia during the study period: 37 (45%) CP-CRE and 46 (55%) non-CP-CRE. The majority of CP-CRE isolates were bla KPC (92%), followed by bla NDM (5%) and bla OXA-48-type (3%). CP-CRE isolates were more likely to have meropenem minimum inhibitory concentrations (MICs) ≥16 µg/mL, while non-CP-CRE isolates were more likely to have meropenem MICs ≤1 µg/mL (P value < .001). A total of 18 (22%) patients died within 14 days, including 12 (32%) in the CP-CRE group and 6 (13%) in the non-CP-CRE group. Adjusting for severity of illness on day 1 of bacteremia, underlying medical conditions, and differences in antibiotic treatment administered, the odds of dying within 14 days were more than 4 times greater for CP-CRE compared with non-CP-CRE bacteremic patients (adjusted odds ratio, 4.92; 95% confidence interval, 1.01-24.81). CONCLUSION: Our findings suggest that CP-CRE may be more virulent than non-CP-CRE and are associated with poorer outcomes. This underscores the added importance of delineating underlying resistance mechanisms of CRE to direct antibiotic treatment decisions.

Livestock-Associated, Antibiotic-Resistant Staphylococcus aureus Nasal Carriage and Recent Skin and Soft Tissue Infection among Industrial Hog Operation Workers.

Swine production work is a risk factor for nasal carriage of livestock-associated (LA-) Staphylococcus aureus and also for skin and soft tissue infection (SSTI). However, whether LA-S. aureus nasal carriage is associated with increased risk of SSTI remains unclear. We aimed to examine S. aureus nasal carriage and recent (≤3 months prior to enrollment) SSTI symptoms among industrial hog operation (IHO) workers and their household contacts. IHO workers and their household contacts provided a nasal swab and responded to a questionnaire assessing self-reported personal and occupational exposures and recent SSTI symptoms. Nasal swabs were analyzed for S. aureus, including methicillin-resistant S. aureus (MRSA), multidrug-resistant-S. aureus (MDRSA), absence of scn (livestock association), and spa type. S. aureus with at least one indicator of LA was observed among 19% of 103 IHO workers and 6% of 80 household members. Prevalence of recent SSTI was 6% among IHO workers and 11% among 54 minor household members (0/26 adult household members reported SSTI). Among IHO workers, nasal carriers of MDRSA and scn-negative S. aureus were 8.8 (95% CI: 1.8, 43.9) and 5.1 (95% CI: 1.2, 22.2) times as likely to report recent SSTI as non-carriers, respectively. In one household, both an IHO worker and child reported recent SSTI and carried the same S. aureus spa type (t4976) intranasally. Prevalence of scn-negative S. aureus (PR: 5.0, 95% CI: 1.2, 21.4) was elevated among IHO workers who reported never versus always wearing a face mask at work. Although few SSTI were reported, this study of IHO workers and their household contacts is the first to characterize a relation between nasal carriage of antibiotic-resistant LA-S. aureus and SSTI. The direction and temporality of this relation and IHO workers' use of face masks to prevent nasal carriage of these bacteria warrant further investigation.

The Prevalence and Molecular Epidemiology of Multidrug-Resistant Enterobacteriaceae Colonization in a Pediatric Intensive Care Unit.

OBJECTIVE: To determine the prevalence and acquisition of extended-spectrum ß-lactamases (ESBLs), plasmid-mediated AmpCs (pAmpCs), and carbapenemases ("MDR Enterobacteriaceae") colonizing children admitted to a pediatric intensive care unit (PICU). DESIGN: Prospective study. SETTING: 40-bed PICU. METHODS: Admission and weekly thereafter rectal surveillance swabs were collected on all pediatric patients during a 6-month study period. Routine phenotypic identification and antibiotic susceptibility testing were performed. Enterobacteriaceae displaying characteristic resistance profiles underwent further molecular characterization to identify genetic determinants of resistance likely to be transmitted on mobile genetic elements and to evaluate relatedness of strains including DNA microarray, multilocus sequence typing, repetitive sequence-based PCR, and hsp60 sequencing typing. RESULTS: Evaluating 854 swabs from unique children, the overall prevalence of colonization with an MDR Enterobacteriaceae upon admission to the PICU based on ß-lactamase gene identification was 4.3% (n=37), including 2.8% ESBLs (n=24), 1.3% pAmpCs (n=11), and 0.2% carbapenemases (n=2). Among 157 pediatric patients contributing 603 subsequent weekly swabs, 6 children (3.8%) acquired an incident MDR Enterobacteriaceae during their PICU stay. One child acquired a pAmpC (E. coli containing bla DHA) related to an isolate from another patient. CONCLUSIONS: Approximately 4% of children admitted to a PICU were colonized with MDR Enterobacteriaceae (based on ß-lactamase gene identification) and an additional 4% of children who remained in the PICU for at least 1 week acquired 1 of these organisms during their PICU stay. The acquired MDR Enterobacteriaceae were relatively heterogeneous, suggesting that a single source was not responsible for the introduction of these resistance mechanisms into the PICU setting.

Recognition of Streptococcus pseudoporcinus Colonization in Women as a Consequence of Using Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Group B Streptococcus Identification.

During a 14-month period of using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for group B streptococcus (GBS) identification, we recovered 32 (1%) Streptococcus pseudoporcinus isolates from 3,276 GBS screening cultures from female genital sources (25 isolates from pregnant women and 7 from nonpregnant women). An additional two S. pseudoporcinus isolates were identified from a urine culture and a posthysterectomy wound culture. These isolates were found to cross-react with three different GBS antigen agglutination kits, PathoDx (Remel) (93%), Prolex (Pro-Lab Diagnostics) (38%), and Streptex (Remel) (53%). New approaches to bacterial identification in routine clinical microbiology laboratories may affect the prevalence of S. pseudoporcinus.

High prevalence of reduced chlorhexidine susceptibility in organisms causing central line-associated bloodstream infections.

In units that bathe patients daily with chlorhexidine gluconate (CHG), organisms causing central line-associated bloodstream infections (CLABSIs) were more likely to have reduced CHG susceptibility than organisms causing CLABSIs in units that do not bathe patients daily with CHG (86% vs 64%; P = .028). Surveillance is needed to detect reduced CHG susceptibility with widespread CHG use.

Comparison of commercial antimicrobial susceptibility test methods for testing of Staphylococcus aureus and Enterococci against vancomycin, daptomycin, and linezolid.

Three commercial antimicrobial susceptibility testing (AST) methods were compared to broth microdilution for testing of Staphylococcus aureus and enterococci against vancomycin, daptomycin, and linezolid. Despite high levels of categorical agreement and essential agreement, vancomycin MICs determined by MicroScan were often 1 log2 concentration higher and MICs determined by Phoenix 1 log2 concentration lower. Daptomycin MICs were 1 to 2 log2 concentrations higher by all AST methods, except Etest, potentially impacting definitive antimicrobial therapy for bloodstream infections due to these organisms.