Oxacillin resistance and antimicrobial susceptibility profile of Staphylococcus saprophyticus and other staphylococci isolated from patients with urinary tract infection

Isolation of lytic bacteriophages and their relationships with the adherence genes of Staphylococcus saprophyticus

OBJECTIVE

This study aimed to introduce a lytic bacteriophage against Staphylococcus saprophyticus from wastewater in Gorgan, northern Iran.

RESULTS

The vB_SsapS-46 phage was isolated from urban wastewater and formed round and clear plaques on bacterial culture. It was visualized by electron microscopy and had a large head (approximately 106 nm) and a long tail (approximately 150 nm), indicating that it belongs to the Siphoviridae family. The host range of vB_SsapS-46 was determined using a spot test on 35 S. saprophyticus clinical isolates, and it was able to lyse 12 of the 35 clinical isolates (34%). Finally, the relationship between phage sensitivity and adherence genes was assessed, revealing no significant correlation between phage sensitivity and the frequency of adherence genes. The vB_SsapS-46 phage can be used alone or in a mixture in future studies to control urinary tract infections caused by this bacterium, especially in the elimination of drug-resistant pathogens.

Staphylococcus capitis Bloodstream Isolates: Investigation of Clonal Relationship, Resistance Profile, Virulence and Biofilm Formation

Staphylococcus capitis has been recognized as a relevant opportunistic pathogen, particularly its persistence in neonatal ICUs around the world. Therefore, the aim of this study was to describe the epidemiological profile of clinical isolates of S. capitis and to characterize the factors involved in the persistence and pathogenesis of these strains isolated from blood cultures collected in a hospital in the interior of the state of São Paulo, Brazil. A total of 141 S. capitis strains were submitted to detection of the mecA gene and SCCmec typing by multiplex PCR. Genes involved in biofilm production and genes encoding enterotoxins and hemolysins were detected by conventional PCR. Biofilm formation was evaluated by the polystyrene plate adherence test and phenotypic resistance was investigated by the disk diffusion method. Finally, pulsed-field gel electrophoresis (PFGE) was used to analyze the clonal relationship between isolates. The mecA gene was detected in 99 (70.2%) isolates, with this percentage reaching 100% in the neonatal ICU. SCCmec type III was the most prevalent type, detected in 31 (31.3%) isolates and co-occurrence of SCCmec was also observed. In vitro biofilm formation was detected in 46 (32.6%) isolates but was not correlated with the presence of the ica operon genes. Furthermore, biofilm production in ICU isolates was favored by hyperosmotic conditions, which are common in ICUs because of the frequent parenteral nutrition. Analysis of the clonal relationship between the isolates investigated in the present study confirms a homogeneous profile of S. capitis and the persistence of clones that are prevalent in the neonatal ICU and disseminated across the hospital. This study highlights the adaptation of isolates to specific hospital environments and their high clonality.

Comparative genomics reveals the correlations of stress response genes and bacteriophages in developing antibiotic resistance of Staphylococcus saprophyticus

IMPORTANCE

Staphylococcus saprophyticus is the second most common bacteria associated with urinary tract infections (UTIs) in women. The antimicrobial treatment regimen for uncomplicated UTI is normally nitrofurantoin, trimethoprim-sulfamethoxazole (TMP-SMX), or a fluoroquinolone without routine susceptibility testing of S. saprophyticus recovered from urine specimens. However, TMP-SMX-resistant S. saprophyticus has been detected recently in UTI patients, as well as in our cohort. Herein, we investigated the understudied resistance patterns of this pathogenic species by linking genomic antibiotic resistance gene (ARG) content to susceptibility phenotypes. We describe ARG associations with known and novel SCCmec configurations as well as phage elements in S. saprophyticus, which may serve as intervention or diagnostic targets to limit resistance transmission. Our analyses yielded a comprehensive database of phenotypic data associated with the ARG sequence in clinical S. saprophyticus isolates, which will be crucial for resistance surveillance and prediction to enable precise diagnosis and effective treatment of S. saprophyticus UTIs.

Improved Detection of mecA-Mediated β-Lactam Resistance in Staphylococcus lugdunensis Using a New Oxacillin Salt Agar Screen

Oxacillin resistance mediated by mecA in Staphylococcus lugdunensis is emerging in some geographic areas. We evaluated cefoxitin disk diffusion (DD) and a new oxacillin agar (supplemented with 2 μg/ml oxacillin and 2% sodium chloride) screen for the detection of mecA-mediated resistance in S. lugdunensis. A total of 300 consecutive, non-duplicated clinical S. lugdunensis isolates from diverse sources in Hong Kong in 2019 were tested. The categorical agreement and errors obtained between cefoxitin DD test, oxacillin agar screen and mecA PCR were analyzed. Isolates with discordant results were further tested by MIC, penicillin binding protein 2a (PBP2a) assays, population analysis and molecular typing. PCR showed that 62 isolates were mecA-positive and 238 isolates were mecA-negative. For cefoxitin DD results interpreted using S. aureus/S. lugdunensis breakpoints, the categorical agreement (CA) for two brands of Muller-Hinton agars, MH-II (Becton Dickinson) and MH-E (bioMérieux) were both 96.0%; MEs were both 0%; and VMEs were 19.4 and 12.9%, respectively. The new oxacillin agar reliably differentiated mecA-positive and mecA-negative isolates (100% CA) without any ME or VME results. The 8 isolates with false susceptibility in the cefoxitin DD testing had cefoxitin and oxacillin MICs in the susceptible range. The isolates showed heterogeneous oxacillin resistance with resistant subpopulations at low frequencies. All had positive PBP2a results and were typed as sequence type 27/SCCmec V. The findings highlight the inability of cefoxitin DD and MIC tests for reliable detection of some mecA-positive S. lugdunensis isolates.

Refrigeration temperature enhanced synergistic interaction of curcumin and 460 nm light-emitting diode against Staphylococcus saprophyticus at neutral pH

Objectives

As considered highly resistant to antibiotics like mecillinam, the rise of Staphylococcus saprophyticus (S. saprophyticus) contamination of fresh foods and food processing environments necessitates the development of a new antimicrobial approach for food safety control. This study aimed to investigate the synergistic effect of food-grade curcumin (CUR) and blue light-emitting diode (LED) on S. saprophyticus.

Materials and Methods

S. saprophyticus was subjected to the synergistic treatment at 4 and 25 °C. The influence of parameters, including CUR concentration, light dose, and pH incubation time on the inactivation of S. saprophyticus was characterized through plate counting method.

Results: 

The combined treatment of CUR and blue light irradiation significantly (P < 0.05) reduced bacterial counts and the antimicrobial effect was in a CUR concentration and light dose-dependent manner. Moreover, refrigeration temperature (4 °C) significantly (P < 0.05) enhanced the antibacterial effect at neutral pH condition (6.2–7.2), resulting in approximately 6.0 log reductions. Under acidic condition (pH 2.2–5.2), there was no significant difference in bacterial population reduction between treatments at both temperatures.

Conclusions

These findings proposed that synergistic interaction of CUR and 460 nm LED under refrigerated temperature could enhance the inactivation of S. saprophyticus at neutral pH condition.

Study of biofilm formation, structure and antibiotic resistance in Staphylococcus saprophyticus strains causing urinary tract infection in women in Ahvaz, Iran

Staphylococcus saprophyticus is the second most frequent community-acquired causative agent of acute urinary tract infection (UTI). Some strains of S. saprophyticus can create biofilms, increasing their virulence. Once biofilms have been produced, antibiotic resistance is exacerbated. Hence, the aims of the present study were the study of biofilm formation, structure and antibiotic resistance in S. saprophyticus strains causing UTIs in women in Ahvaz, Iran. Overall, 43 S. saprophyticus isolates were recovered from UTIs. Antibiotic resistance pattern and the biofilm production and structure were determined using phenotypic methods. Most S. saprophyticus isolates were resistant to erythromycin, but all isolates were sensitive to linezolid and vancomycin. Fifty-eight per cent of S. saprophyticus were multidrug resistant. Twenty-one per cent of S. saprophyticus isolates harbored the mecA gene. Biofilm formation was observed in 65% of S. saprophyticus isolates and most had polysaccharide matrix. Our data indicate high rates of antibiotic resistance and the capability of biofilm formation among S. saprophyticus isolates. The emergence of antibiotic resistance in the management of UTIs is a serious public health issue. The findings of this study could be used to improve treatment plans to control UTIs. Consequently, increased awareness of the mechanisms underlying biofilm formation and the development of drug resistance will allow UTIs to be more efficiently controlled and treated.

Coagulase-negative staphylococci in outpatient routines: the implications of switching from CLSI to BrCAST/EUCAST guidelines

Coagulase-negative staphylococci (CoNS) are frequently isolated in clinical specimens and are important reservoirs of resistance genes. In 2019, the Brazilian government set the BrCAST/EUCAST (Brazilian Committee on Antimicrobial Susceptibility Testing) guidelines as the national standard, resulting in changes in the interpretation of CoNS susceptibility tests. From outpatients, disk-diffusion susceptibility of 65 CoNS cultures were evaluated and compared using classification criteria from both CLSI and BrCAST/EUCAST. The isolates were identified using matrix assisted laser desorption ionization-time of flight (MALDI-TOF), and the presence of the mecA gene was determined. The most prevalent species were Staphylococcus saprophyticus (32.3%), S. haemolyticus (18.5%), and S. epidermidis (9.2%). Almost perfect agreement was seen between the guidelines, except concerning oxacillin and gentamicin, and the prevalence of multidrug resistant isolates increased with the use of BrCAST/EUCAST. Of all, 15 (23.1%) isolates, mainly S. epidermidis and S. haemolyticus, were positive for the mecA gene, and only three were detected when using CLSI or BrCAST/EUCAST disk-diffusion screening. This, using either guideline, could reveal the difficulty of determining oxacillin resistance. Using warning zones or molecular methods might well be indicated for CoNS. In conclusion, adoption of the BrCAST/EUCAST guidelines will result in certain artificial changes in epidemiological susceptibility profiles, and clinicians and institutions should be aware of the possible implications.

Decreased susceptibility to chlorhexidine and distribution of qacA/B genes among coagulase-negative Staphylococcus clinical samples

Background

Healthcare-associated infection (HAI) is a major public health problem. As a form of prevention and control, preparations of chlorhexidine are used extensively; however, the reduction of susceptibility to chlorhexidine has been reported. The aim of this study was to investigate the susceptibility to chlorhexidine and the distribution of the qacA/B genes in 211 clinical isolates of coagulase-negative Staphylococci (CoNS).

Methods

CoNS were identified by conventional biochemical tests. Antimicrobial susceptibility was tested by disk-diffusion. Minimum inhibitory concentration (MIC) of chlorhexidine was determined by agar dilution test; detection of the qacA/B and mecA genes were evaluated by PCR.

Results

The most frequently isolated species were S. epidermidis, S. hominis hominis, S. auricularis, and S. haemolyticus, respectively. The strains presented a multidrug resistance profile of 87%, including methicillin resistance. Reduced susceptibility to chlorhexidine was observed in 31%. The qacA/B genes were detected in samples resistant (32/32) and susceptible (17/32) to chlorhexidine. The vast majority (94%) of the samples with reduced susceptibility to chlorhexidine were multidrug resistant.

Conclusions

Our results show that qacA/B genes are not restricted to strains expressing chlorhexidine resistance. Further studies are needed to understand how the expression of these genes occurs.

In vitro Effects of Antimicrobial Agents on Planktonic and Biofilm Forms of Staphylococcus saprophyticus Isolated From Patients With Urinary Tract Infections

Bacterial biofilms play an important role in urinary tract infections (UTIs), being responsible for persistent infections that lead to recurrences and relapses. Staphylococcus saprophyticus is one of the main etiological agents of UTIs, however, little is known about biofilm production in this species and especially about its response to the antimicrobial agents used to treat UTIs when a biofilm is present. For this reason, the aim of this work was to evaluate the response of S. saprophyticus biofilms to five antimicrobial agents. Staphylococcus saprophyticus was evaluated for antimicrobial susceptibility in its planktonic form by means of minimum inhibitory concentration (MIC) and in biofilms by means of minimum inhibitory concentration in biofilm (MICB) against the following antimicrobial agents by the microdilution technique: vancomycin, oxacillin, trimethoprim/sulfamethoxazole, ciprofloxacin, and norfloxacin. Of the 169 S. saprophyticus studied, 119 produced a biofilm as demonstrated by the polystyrene plate adherence method. Biofilm cells of S. saprophyticus exhibited a considerable increase in MICB when compared to the planktonic forms, with an increase of more than 32 times in the MICB of some drugs. Some isolates switched from the category of susceptible in the planktonic condition to resistant in the biofilm state. Statistical analysis of the results showed a significant increase in MICB (p < 0.0001) for all five drugs tested in the biofilm state compared to the planktonic form. Regarding determination of the minimum bactericidal concentration in biofilm (MBCB), there were isolates for which the minimum bactericidal concentration of all drugs was equal to or higher than the highest concentration tested.

Evaluation of reference values for phenotypic tests to detect oxacillin resistance in coagulase-negative staphylococci

AIM

To evaluate the adequacy of the disc-diffusion test and E-test^® compared with detection of mecA for coagulase-negative staphylococci isolated from blood cultures, nasal swabs and wounds.

RESULTS

Agreement between all techniques was observed in 65.7% of cases. The greatest discrepancy between mecA/susceptible E-test was observed for non-epidermidis species. A resistance breakpoint ≤19 mm using the oxacillin disc was found to best classify all coagulase-negative staphylococci isolates; Staphylococcus epidermidis, ≤19 mm (oxacillin) and ≤27 mm (cefoxitin); Staphylococcus haemolyticus and Staphylococcus capitis, ≤21 mm (oxacillin) and ≤18 mm (cefoxitin); Staphylococcus warneri, MICs ≥0.75 mg/l.

CONCLUSION

Although no longer recommended by the Clinical Laboratory Standards Institute, we observed some cases in which only the oxacillin disc-diffusion test detected resistance. The discrepancy between phenotypic tests and mecA is probably due to heterogeneity and borderline resistance.

Continued in vitro cefazolin susceptibility in methicillin-susceptible Staphylococcus aureus

OBJECTIVES

In vitro trends of cefazolin and ceftriaxone susceptibilities from pediatric clinical isolates of methicillin-susceptible Staphylococcus aureus (MSSA) between 2011 and 2016 were analyzed for surveillance.

METHODS

Our laboratory continues to use agar disk diffusion for staphylococcal susceptibilities applying Clinical Laboratory Standard Institute's 2012 breakpoints.

RESULTS

A total of 3992 MSSA clinical isolates in the last 6 years were analyzed for their in vitro cefazolin and ceftriaxone susceptibilities. While all MSSA isolates exhibited cefazolin susceptibilities within the "susceptible" zone range, there have been a proportion of isolates with ceftriaxone susceptibilities falling in "intermediate" zones, ranging from 2.6% in 2011 to 8.3% in 2016.

CONCLUSIONS

Cefazolin continues to be the recommended agent for MSSA treatment at our institution, reflected by the finding that only 2% (6/321) of patients who received ceftriaxone as definitive therapy for MSSA bacteremia during the study period. We have confirmed the cefoxitin-predicted MSSA susceptibility to cefazolin, but have found concerning drifts in ceftriaxone susceptibilities by continued in vitro monitoring over the last 6 years.

Clinical and Microbiological Aspects of β-Lactam Resistance in Staphylococcus lugdunensis

Antimicrobial susceptibility results from broth microdilution MIC testing of 993 Staphylococcus lugdunensis isolates recovered from patients at a tertiary care medical center from 2008 to 2015 were reviewed. Ninety-two oxacillin-susceptible isolates were selected to assess the accuracy of penicillin MIC testing, the penicillin disk diffusion test, and three β-lactamase tests, including the cefoxitin-induced nitrocefin test, penicillin cloverleaf assay, and penicillin disk zone edge test. The results of all phenotypic tests were compared to the results of blaZ PCR. The medical records of 62 patients from whom S. lugdunensis was isolated, including 31 penicillin-susceptible and 31 penicillin-resistant strains, were retrospectively reviewed to evaluate the clinical significance of S. lugdunensis isolation, the antimicrobial agents prescribed, if any, and the clinical outcome. MIC testing revealed that 517/993 (52.1%) isolates were susceptible to penicillin and 946/993 (95.3%) were susceptible to oxacillin. The induced nitrocefin test was 100% sensitive and specific for the detection of β-lactamase compared to the blaZ PCR results, whereas the penicillin disk zone edge and cloverleaf tests showed sensitivities of 100% but specificities of only 9.1% and 89.1%, respectively. The penicillin MIC test had 100% categorical agreement with blaZ PCR, while penicillin disk diffusion yielded one major error. Only 3/31 patients with penicillin-susceptible isolates were treated with a penicillin family antimicrobial. The majority of cases were treated with other β-lactams, trimethoprim-sulfamethoxazole, or vancomycin. These data indicate that nearly all isolates of S. lugdunensis are susceptible to narrow-spectrum antimicrobial agents. Clinical laboratories in areas with resistance levels similar to those described here can help promote the use of these agents versus vancomycin by effectively designing their antimicrobial susceptibility reports to convey this message.

Antimicrobial Resistance Profile of Planktonic and Biofilm Cells of Staphylococcus aureus and Coagulase-Negative Staphylococci

The objective of the present study was to determine the antimicrobial resistance profile of planktonic and biofilm cells of Staphylococcus aureus and coagulase-negative staphylococci (CoNS). Two hundred Staphylococcus spp. strains were studied, including 50 S. aureus and 150 CoNS strains (50 S. epidermidis, 20 S. haemolyticus, 20 S. warneri, 20 S. hominis, 20 S. lugdunensis, and 20 S. saprophyticus). Biofilm formation was investigated by adherence to polystyrene plates. Positive strains were submitted to the broth microdilution method to determine the minimum inhibitory concentration (MIC) for planktonic and biofilm cells and the minimal bactericidal concentration for biofilm cells (MBCB). Forty-nine Staphylococcus spp. strains (14 S. aureus, 13 S. epidermidis, 13 S. saprophyticus, 3 S. haemolyticus, 1 S. hominis, 3 S. warneri, and 2 S. lugdunensis) were biofilm producers. These isolates were evaluated regarding their resistance profile. Determination of planktonic cell MIC identified three (21.4%) S. aureus strains that were resistant to oxacillin and six (42.8%) that were resistant to erythromycin. Among the CoNS, 31 (88.6%) strains were resistant to oxacillin, 14 (40%) to erythromycin, 18 (51.4%) to gentamicin, and 8 (22.8%) to sulfamethoxazole/trimethoprim. None of the planktonic isolates were resistant to vancomycin or linezolid. MICs were 2-, 4-, 8-, and up to 16-fold higher for biofilm cells than for planktonic cells. This observation was more common for vancomycin and erythromycin. The MBCB ranged from 8 to >256 µg/mL for oxacillin, 128 to >128 µg/mL for vancomycin, 256 to >256 µg/mL for erythromycin and gentamicin, >64 µg/mL for linezolid, and 32/608 to >32/608 µg/mL for sulfamethoxazole/trimethoprim. The results showed considerably higher MICs for S. aureus and CoNS biofilm cells compared to planktonic cells. Analysis of MBCM confirmed that even high concentrations of vancomycin were unable to eliminate the biofilms of S. aureus and CoNS species. Linezolid was the most effective drug in inhibiting staphylococci in the biofilm, without an increase in the MIC, when compared to planktonic cells. None of the isolates were resistant to this drug.

Staphylococcus saprophyticus bacteremia after ESWL in an immunocompetent woman

Staphylococcus saprophyticus is a well-known cause of uncomplicated urinary tract infections, especially in young and sexually active women. Presence in blood cultures is rare and often attributed to contamination. When bacteremia is significant, it occurs mostly in patients with hematologic malignancies and is predominantly catheter-related. However, we describe a case of significant bacteremia with S. saprophyticus associated with urinary tract infection after extracorporeal shock wave lithotripsy of an ureterolithiasis in an otherwise healthy patient.

Factors influencing linezolid-nonsusceptible coagulase-negative staphylococci dissemination among patients in the intensive care unit: a retrospective cohort study

BACKGROUND

The aim of the present study was to identify risk factors for linezolid-nonsusceptible coagulase-negative staphylococci (CNS) dissemination in the intensive care unit.

METHODS

Among the 246 patients included, 33 revealed a linezolid-nonsusceptible CNS-positive culture specimen, 68 were positive for linezolid-susceptible CNS and 145 served as controls. Isolates were characterized by phenotypic and genotypic methods to species level, susceptibility to antistaphylococcal agents and clones.

RESULTS

Among the 33 linezolid-nonsusceptible CNS patients, 29 revealed Staphylococcus epidermidis and 4 Staphylococcus capitis. All S. epidermidis strains belonged to the ST22 clone (by multilocus sequence typing), 26 carried both C2534T and T2504A and 3 strains were C2543T mutations. S. capitis strains were stratified as a common pulsed-field gel electrophoresis type and carried the G2576T mutation. Risk factors for linezolid-nonsusceptible CNS isolation were linezolid administration and mean number of linezolid-nonsusceptible CNS-positive patients in nearby beds per day.

CONCLUSIONS

These results reinforce the aspect of rational antibiotic usage, but also highlight the need for strict infection control measures to prevent the dissemination of linezolid-nonsusceptible CNS.