Evaluation of protein A gene polymorphic region DNA sequencing for typing of Staphylococcus aureus strains

Effects of sub-inhibitory concentrations of nafcillin, vancomycin, ciprofloxacin, and rifampin on biofilm formation of clinical methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infections are often difficult to treat because of their biofilm-forming ability and antimicrobial resistance. We investigated the effects of sub-minimal inhibitory concentrations (MICs) of antibiotics on MRSA biofilm formation. Clinical MRSA isolates were grown with sub-MICs (1/256-1/2 × MICs) of nafcillin, vancomycin, ciprofloxacin, and rifampin. The biofilm biomass was measured using crystal violet staining. Of the 107 MRSA isolates tested, 63 (58.9%) belonged to sequence type 5 (ST5), and 44 (41.1%) belonged to ST72. The MIC50/MIC90 values of nafcillin, vancomycin, ciprofloxacin, and rifampin were 256/512, 1/2, 64/512, and 0.008/0.03 mg/L, respectively. The sub-MICs of nafcillin, vancomycin, ciprofloxacin, and rifampin promoted biofilm formation in 75 (70.1%), 49 (45.8%), 89 (83.2%), and 89 (83.2%) isolates, respectively. At sub-MICs of nafcillin, the factors associated with strong biofilm induction were the ST5 strain (P = 0.001) and agr dysfunction (P = 0.005). For the sub-MICs of ciprofloxacin, the associated factors were the ST5 strain (P = 0.002), staphylococcal protein A type t002 strain (P < 0.001), and ciprofloxacin resistance (P < 0.001). Among the sub-MICs of rifampin, only ST5 was associated with strong biofilm induction (P = 0.006). Because the sub-MICs of rifampin were much lower than clinically relevant concentrations, we further tested the capability of biofilm induction in 0.03[Formula: see text]32 mg/L of rifampin. At these concentrations, rifampin-induced biofilm formation was rare in rifampin-susceptible MRSA [1.0% (1 of 100)] but common in rifampin-resistant MRSA [71.4% (5 of 7), P < 0.001]. Induction of biofilm biomass at sub-MICs of antibiotics is common in clinical MRSA isolates and is differentially affected by the MRSA strain and antibiotic class.

IMPORTANCE

Bacteria can be exposed to sub-MICs of antibiotics at the beginning and end of a dosing regimen, between doses, or during low-dose therapies. Growing evidence suggests that sub-MICs of antimicrobials can stimulate MRSA biofilm formation and alter the composition of the biofilm matrix. Pevious studies have found that sub-MICs of oxacillin, methicillin, and amoxicillin promote biofilm formation in some community-acquired MRSA (CA-MRSA). We evaluated biofilm induction by sub-MICs of four different classes of antibiotics in 44 CA-MRSA and 63 healthcare-associated MRSA (HA-MRSA) strains. Our study indicated that sub-MICs of nafcillin, vancomycin, ciprofloxacin, and rifampin frequently promote biofilm induction in clinical MRSA isolates. Strong biofilm induction in sub-MICs of nafcillin, ciprofloxacin, and rifampin was more frequent in HA-MRSA than in CA-MRSA. Antibiotic-induced biofilm formation depends on the antibiotic class, MRSA strain, and antibiotic resistance. Our results emphasize the importance of maintaining effective bactericidal concentrations of antibiotics to treat biofilm-related infections.

Puerperal mastitis caused by limited community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) clones

Objective

To outline the epidemiology of puerperal mastitis caused by methicillin-resistant Staphylococcus aureus (MRSA) and evaluate the effect of an infection control bundle on its incidence.

Methods

A surge in MRSA puerperal mastitis was noted in a community hospital in September 2009. MRSA samples from mastitis cases and the environment underwent typing using multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec), gene encoding surface protein A (spa), accessory gene regulator (agr), and pulsed-field gel electrophoresis (PFGE). The phenotypic characteristics, including superantigen toxin profiles, gene encoding Panton-Valentine leucocidin (pvl), and minimal inhibitory concentration (MIC) against vancomycin, were ascertained. Subsequently, an infection control bundle emphasizing contact precautions was introduced, and mastitis incidence rates pre- and post-intervention were compared.

Results

The majority of cases occurred within 6 weeks post-delivery in first-time mothers. Of the 42 S. aureus isolates (27 from mastitis and 15 from colonized staff and environmental sources), 25 (92.6%) clinical and 3 (20%) colonized MRSA were identified as ST59-SCCmecVT-spa t437-agr group I with a vancomycin MIC of 1 mg/L, pvl-positive, and predominantly with a consistent toxin profile (seb-selk-selr). PFGE revealed 13 patterns; pulsotype B exhibited clonal relatedness between two clinical and three colonized MRSA samples. Post-intervention, the incidence of both mastitis and MRSA mastitis notably decreased from 13.01 to 1.78 and from 3.70 to 0.99 episodes per 100 deliveries, respectively.

Conclusion

Distinct community-associated MRSA (CA-MRSA) clones were detected among puerperal mastitis patients and colonized staff. The outbreak was effectively controlled following the implementation of a targeted infection control bundle.

Genomic epidemiology of the primary methicillin-resistant Staphylococcus aureus clones causing invasive infections in Paraguayan children

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major human pathogens. It could carry numerous resistance genes and virulence factors in its genome, some of which are related to the severity of the infection. An observational, descriptive, cross-sectional study was designed to molecularly analyze MRSA isolates that cause invasive infections in Paraguayan children from 2009 to 2013. Ten representative MRSA isolates of the main clonal complex identified were analyzed with short-read paired-end sequencing and assessed for the virulome, resistome, and phylogenetic relationships. All the genetically linked MRSA isolates were recovered from diverse clinical sources, patients, and hospitals at broad gap periods. The pan-genomic analysis of these clones revealed three major and different clonal complexes (CC30, CC5, and CC8), each composed of clones closely related to each other. The CC30 genomes prove to be a successful clone, strongly installed and disseminated throughout our country, and closely related to other CC30 public genomes from the region and the world. The CC5 shows the highest genetic variability, and the CC8 carried the complete arginine catabolic mobile element (ACME), closely related to the USA300-NAE-ACME+, identified as the major cause of CA-MRSA infections in North America. Multiple virulence and resistance genes were identified for the first time in this study, highlighting the complex virulence profiles of MRSA circulating in the country. This study opens a wide range of new possibilities for future projects and trials to improve the existing knowledge on the epidemiology of MRSA circulating in Paraguay.

IMPORTANCE

The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) is a public health problem worldwide. The most frequent MRSA clones identified in Paraguay in previous studies (including community and hospital acquired) were the Pediatric (CC5-ST5-IV), the Cordobes-Chilean (CC5-ST5-I), the SouthWest Pacific (CC30-ST30-IV), and the Brazilian (CC8-ST239-III) clones. In this study, the pan-genomic analysis of the most representative MRSA clones circulating in invasive infection in Paraguayan children over the years 2009-2013, such as the CC30-ST30-IV, CC5-ST5-IV, and CC8-ST8-IV, was carried out to evaluate their genetic diversity, their repertoire of virulence factors, and antimicrobial resistance determinants. This revealed multiple virulence and resistance genes, highlighting the complex virulence profiles of MRSA circulating in Paraguay. Our work is the first genomic study of MRSA in Paraguay and will contribute to the development of genomic surveillance in the region and our understanding of the global epidemiology of this pathogen.

Methicillin-resistant staphylococci in clinical bovine mastitis: occurrence, molecular analysis, and biofilm production

Staphylococcus aureus is an important pathogen that causes mastitis in cattle, and the emergence of methicillin-resistant S. aureus (MRSA) poses a threat to veterinary and human medicine. The aims of the study were to investigate the prevalence of MRSA and methicillin-resistant coagulase-negative staphylococci (MR-CoNS) isolated from clinical mastitis, their ability to form biofilms, and the antimicrobial susceptibility of S. aureus strains. In addition, the Staphylococcal Cassette Chromosome mec (SCCmec) type, spa type and the presence of Panton-Valentine Leucocidin in MRSA were evaluated. A total of 326 staphylococcal strains were screened by multiplex-PCR for S. aureus and Staphylococcus intermedius group (SIG) identification. The S. aureus strains (n = 163) were subjected to phenotypic testing for antimicrobial susceptibility and biofilm formation. Molecular analysis was performed on MRSA mecA-positive strains. Of 163 S. aureus isolates, 142 strains (87.1%) were resistant to at least one antibiotic, and all 19 MRSA strains were resistant to at least four out of five antibiotics tested. All S. aureus strains harboured the icaA gene and were biofilm producers. Nineteen MR-CoNS strains were also isolated. The most prevalent spa types among MRSA were t001 (57.9%) and t037 (31.6%), while one MRSA was type t008 and one was type t041. Most MRSA were SCCmec type I (63.2%) and III (31.6%) and only one strain was type IV. None of the MRSA isolates had the PVL gene. The prevalence of multidrug-resistant S. aureus in bovine mastitis is a serious concern. The finding of MRSA with spa types predominant in humans and infrequent in Italian cows and with SCCmec infrequently found in bovine milk or cheese suggest a human origin of these strains. The ability of MRSA and MR-CoNS involved in bovine mastitis to be transferred to humans and vice versa poses a public health concern.

The origin of sequence type 72 community-associated methicillin-resistant Staphylococcus aureus (MRSA) and fusidic acid (FA) resistant sequence type 5 MRSA: Analysis of FA resistance and spa type in a single center in South Korea

INTRODUCTION

We investigated the prevalence of fusidic acid (FA) resistance in MSSA and MRSA stratified by sequence (ST) and spa types, and determined the prevalence of FA resistance mechanisms.

METHODS

From August 2014 to April 2020, S. aureus blood isolates were collected in Asan Medical Center, Seoul, South Korea. Antimicrobial susceptibility tests were performed using broth microdilution and interpreted according to EUCAST's FA criteria. We performed spa typing for fusA mutation presence and acquired FA resistance determinants (fusB, fusC, and fusD) by PCR.

RESULTS

Of the 590 MRSA isolates, 372 were FA resistant, and among 425 MSSA isolates, 136 were resistant. Of the 380 ST5-MRSA isolates, 350 were FA resistant, whereas only 1 of 14 ST5-MSSA isolates was FA resistant. Conversely, of the 163 ST72-MRSA isolates, only 8 were resistant, whereas 37 of 42 ST72-MSSA were resistant. The fusA mutation (80%) was the most common determinant. The one FA resistant ST5-MSSA isolate belonged to the t2460 spa type, the most common spa type (24 of 35 isolates) of FA resistant ST5-MRSA. In addition, t324 and t148, which are minor spa types of ST72-MSSA, were susceptible to FA, in contrast to other ST72-MSSA spa types, and the major spa type of ST72-MRSA (110 of 163 isolates).

CONCLUSIONS

FA resistance was common in ST5-MRSA and ST72-MSSA, and rare in ST5-MSSA and ST72-MRSA. Our findings suggest that minor clones of ST5-MSSA isolates, with the fusA mutation and minor clones of ST72-MSSA susceptible to FA, may have evolved to harbor the mecA gene.

Hybrid Illumina-Nanopore assembly improves identification of multilocus sequence types and antimicrobial resistance genes of Staphylococcus aureus isolated from Vermont dairy farms: comparison to Illumina-only and R9.4.1 nanopore-only assemblies

Antimicrobial resistance (AMR) in Staphylococcus aureus is a pressing public health challenge with significant implications for the dairy industry, encompassing bovine mastitis concerns and potential zoonotic threats. To delve deeper into the resistance mechanisms of S. aureus, this study employed a hybrid whole genome assembly approach that synergized the precision of Illumina with the continuity of Oxford Nanopore. A total of 62 isolates, collected from multiple sources from Vermont dairy farms, were sequenced using the GridION Oxford Nanopore R9.4.1 platform and the Illumina platform, and subsequently processed through our long-read first bioinformatics pipeline. Our analyses showcased the hybrid-assembled genome's superior completeness compared to Oxford Nanopore (R9.4.1)-only or Illumina-only assembled genomes. Furthermore, the hybrid assembly accurately determined multilocus sequence typing (MLST) strain types across all isolates. The comprehensive probe for antibiotic resistance genes (ARGs) using databases like CARD, Resfinder, and MEGARES 2.0 characterized AMR in S. aureus isolates from Vermont dairy farms, and revealed the presence of notable resistance genes, including beta-lactam genes blaZ, blaI, and blaR. In conclusion, the hybrid assembly approach emerged as a tool for uncovering the genomic nuances of S. aureus isolates collected from multiple sources on dairy farms. Our findings offer a pathway for detecting AMR gene prevalence and shaping AMR management strategies crucial for safeguarding human and animal health.

Molecular Epidemiological Characterization of Methicillin-Resistant Staphylococcus aureus from Bloodstream Infections in Northern Japan: Increasing Trend of CC1 and Identification of ST8-SCCmec IVa USA300-Like Isolate Lacking Arginine Catabolic Mobile Element

Methicillin-resistant Staphylococcus aureus (MRSA) is a major infectious disease pathogen, and its molecular epidemiological profile has been changing. In this study, a total of 279 MRSA isolates were collected from patients with bloodstream infection (BSI) in Hokkaido, northern main island of Japan, for a 2-year period from August 2019 to July 2021. CC5 (ST5/ST764)-MRSA-IIa (SCCmec-IIa) (47%, n = 132) and CC1 (ST1/ST2725/ST2764)-MRSA-IVa (42%, n = 116) were found to be major lineages, with CC8-MRSA-IVa being lower prevalence (5%, n = 13). CC1-MRSA-IVa showed a relatively increased proportion compared with our previous study (22%, 2017-2019). Seven isolates with SCCmec IVa (2.5%) were positive for Panton-Valentine leukocidin genes on ΦSa2usa and belonged to ST8/spa-t008/agr-I/coa-IIIa, showing genetic features of the USA300 clone. Among these isolates, six isolates harbored arginine catabolic mobile element (ACME) type I typical to the USA300 clone, while it was not detected in an isolate (strain R3-8). Whole genomic analysis of strain R3-8 revealed that its chromosome was highly similar to the USA300 strain TCH1516, but lacked ACME, carrying a plasmid genetically close to that of USA300 strains. The present study revealed increasing trend of CC1-MRSA-IV and occurrence of a novel variant of the USA300 clone among MRSA from BSI in northern Japan.

Impact of human created environments in the pathogenic potential and antimicrobial resistance of staphylococci from wild neotropical primates in Brazil

The non-human primate (NHP) Leontopithecus rosalia is an endangered species native of Brazil and lives in forest fragments with different levels of contact with humans (natural, private and urban). Other NHPs - Callithrix spp. - were introduced by humans and co-exist and interact with the native species in these forests. To evaluate if living in or close to human-modified environments could constitute a risk for L. rosalia, we compared the prevalence, genetic background, antibiotic susceptibility and virulence gene content of staphylococci collected from the native and the introduced species from different forest fragments. We found that presence in human-dominated environments increased the colonization rate of L. rosalia with Mammaliicoccus sciuri (former Staphylococcus sciuri) from 18 % to 85 % (p = 0.0001) and of Callithrix spp with Staphylococcus aureus from 6 % to 100 % (p = 0.0001). According to molecular typing data obtained differences probably resulted from dissemination of these bacterial species from the invader NHP species and from humans. Changes in microbiota were paralleled by an increase in the prevalence of Panton-Valentine Leukocidin gene and in resistance to beta-lactams, macrolides and/or lincosamides as exposure to human environment increased. In particular, erythromycin resistance in S. aureus from Callithrix spp. increased from 0 % to 50 % and resistance rate to at least one antibiotic in coagulase-negative staphylococci species from L. rosalia increased from 13 % to 56 % (p = 0.0003). Our results showed that contact of native animal species with human-created environments increased the content of antimicrobial resistant and pathogenic bacteria on their commensal microbiota, which ultimately can impact on their health. IMPORTANCE: Endangered animal species are vulnerable to environmental alterations and human activities have been repeatedly identified as factors driving drastic changes in the natural landscape. It is extremely important to monitor changes in the environment surrounding protected species, because this could lead to early detection of any potential threats. In this study, we found that the contact of L. rosalia - a protected non-human primate from Brazil - with human environments is related to changes in their commensal microbiota. These included an increase in the number of pathogenic and antibiotic resistant bacteria, which have a higher potential to cause infections that are more difficult to treat. We provided evidence for the harmful impact human contact has on L. rosalia. Also, our results suggest that monitoring of commensal microbiota of protected animal species might be a useful way of sensing the risks of protected species to human exposure.

Molecular Characteristics and Pathogenicity of Staphylococcus aureus Exotoxins

Staphylococcus aureus stands as one of the most pervasive pathogens given its morbidity and mortality worldwide due to its roles as an infectious agent that causes a wide variety of diseases ranging from moderately severe skin infections to fatal pneumonia and sepsis. S. aureus produces a variety of exotoxins that serve as important virulence factors in S. aureus-related infectious diseases and food poisoning in both humans and animals. For example, staphylococcal enterotoxins (SEs) produced by S. aureus induce staphylococcal foodborne poisoning; toxic shock syndrome toxin-1 (TSST-1), as a typical superantigen, induces toxic shock syndrome; hemolysins induce cell damage in erythrocytes and leukocytes; and exfoliative toxin induces staphylococcal skin scalded syndrome. Recently, Panton-Valentine leucocidin, a cytotoxin produced by community-associated methicillin-resistant S. aureus (CA-MRSA), has been reported, and new types of SEs and staphylococcal enterotoxin-like toxins (SEls) were discovered and reported successively. This review addresses the progress of and novel insights into the molecular structure, biological activities, and pathogenicity of both the classic and the newly identified exotoxins produced by S. aureus.

Detection of mecA positive staphylococcal species in a wastewater treatment plant in South Africa

We investigated the prevalence of antibiotic resistant staphylococci and detection of resistant, virulence, and Spa genes in a South African wastewater treatment plant. Species identified were Staphylococcus aureus, S. lentus, S. arlettae, S. cohnii, S. haemolyticus, S. nepalensis, S. sciuri (now Mammaliicoccus sciuri), and S. xylosus. Isolates showed high resistance to methicillin (91%), ampicillin (89%), ciprofloxacin (86%), amoxycillin (80%), ceftazidime (74%), and cloxacillin (71%). Multiple antibiotic resistance (MAR) index for the isolates exceeded 0.2 (0.50-0.70). Among the isolates, 77% were mecA-positive. All S. aureus strains were positive for nuc and 7 Spa gene types. The present study highlights possibility of treated wastewaters being potential reservoir for antibiotic-resistant staphylococci. This is a cause for concern as wastewater effluents are decanted into environmental waters and these are, in many cases, used for various purposes including recreation (full contact), religious (full body submersion), and drinking water for some rural communities and water for livestock.

Macrolide-Lincosamide Resistance and Virulence Genes in Staphylococcus aureus Isolated from Clinical Specimens in Ardabil, Iran

Background & Objective

Staphylococcus aureus causes various hospital- and community-acquired infections. This study aimed to investigate the phenotypic and genotypic characteristics of erythromycin and inducible clindamycin resistance, virulence gene profiles, and spa types of S. aureus isolates collected from patients in Ardabil Province, Iran.

Methods

A total of 118 clinical S. aureus isolates, including 50 (42.4%) methicillin-resistant S. aureus (MRSA) and 68 (57.6%) methicillin-susceptible S. aureus (MSSA) strains, were investigated. Resistance patterns were determined by the disk diffusion method and minimum inhibitory concentration (MIC) test. Inducible macrolide-lincosamide-streptogramin B (iMLSB) resistance was detected using D-test method. The polymerase chain reaction (PCR) was used to identify the virulence and resistance-encoding genes. Additionally, the spa types of the isolates were determined using the PCR, followed by sequencing.

Results

In total, 49.1% (58/118) and 44% (52/118) of the isolates were resistant to erythromycin and clindamycin, respectively. Overall, 13.5% (16/118) of the isolates showed the iMLSB resistance phenotype. The ermC gene (72.4% [42]) was the most frequent erythromycin resistance-encoding gene, followed by ermA (60.3% [35]), ermB (60.3% [35]), ermTR (51.7% [30]), and msrA (15.5% [9]) genes among erythromycin-resistant isolates. The virulence genes hla, hld, sea, LukS PV, tst, seb, sed, eta, sec, and etb were detected in 93.2%, 74.5%, 70.3%, 32.2%, 29.6%, 17%, 8.5%, 8.5%, 5.9%, and 4.2% of the isolates, respectively. Ten different spa types were identified for 58 erythromycin-resistant S. aureus strains, of which t030 and t078 types were the most common types.

Conclusion

A high frequency of macrolide- and lincosamide-resistant S. aureus isolates with different genetic backgrounds of resistance and virulence may be found in patients in Ardabil Province, Iran.

Detection, Identification and Diagnostic Characterization of the Staphylococcal Small Colony-Variant (SCV) Phenotype

While modern molecular methods have decisively accelerated and improved microbiological diagnostics, phenotypic variants still pose a challenge for their detection, identification and characterization. This particularly applies if they are unstable and hard to detect, which is the case for the small-colony-variant (SCV) phenotype formed by staphylococci. On solid agar media, staphylococcal SCVs are characterized by tiny colonies with deviant colony morphology. Their reduced growth rate and fundamental metabolic changes are the result of their adaptation to an intracellular lifestyle, regularly leading to specific auxotrophies, such as for menadione, hemin or thymidine. These alterations make SCVs difficult to recognize and render physiological, biochemical and other growth-based methods such as antimicrobial susceptibility testing unreliable or unusable. Therefore, diagnostic procedures require prolonged incubation times and, if possible, confirmation by molecular methods. A special approach is needed for auxotrophy testing. However, standardized protocols for SCV diagnostics are missing. If available, SCVs and their putative parental isolates should be genotyped to determine clonality. Since their detection has significant implications for the treatment of the infection, which is usually chronic and relapsing, SCV findings should be specifically reported, commented on, and managed in close collaboration with the microbiological laboratory and the involved clinicians.

Occurrence and Patterns of Enterotoxin Genes, spa Types and Antimicrobial Resistance Patterns in Staphylococcus aureus in Food and Food Contact Surfaces in Singapore

Staphylococcus aureus contamination of food and food contact surfaces is a public health concern given its virulent and antimicrobial-resistant properties worldwide. In this study, a total of 181 MSSA isolates were analyzed for SE genes, antimicrobial resistance patterns, and spa types. Overall, 24.9% of isolates were positive for SE gene detection, with sea being the most prevalent classical SE (18.8%). The most predominant sample sources for SE gene contamination were hand swabs for sea (6/48), meat dishes for seb (3/14) and seafood dishes for sec (2/24). Antimicrobial resistance was also observed at relatively high frequencies for the clinically important antibiotics penicillin G and ampicillin (both 54.7%), followed by tetracycline (14.9%) and azithromycin (8.8%). In addition, characterization of spa types revealed spa type t5078 to be the most predominant (40.3%), with significant associations between spa types t127 and t5521 and the sea gene. This study offers insights into the enterotoxin gene and antimicrobial resistance profiles of S. aureus in cooked or ready-to-eat food to inform future surveillance and epidemiological studies.

Staphylococcus nasal colonization in three species of non-human primates

Bacterial nasal colonization is common in many mammals and Staphylococcus represents the main pathogen isolated. Staphylococcus nasal carriage in humans constitutes a risk factor for Staphylococcus infections pointing out the need for animal experimentation for nasal colonization studies, especially for vaccine development. A limitation in addressing this hypothesis has been a lack of appropriate animal model. Murine models do not mimic human nasal colonization studies. Non-human primates (NHP) remain the best classical models for nasal colonization studies. In this study, we analyzed nasal colonization between two species of Old World monkeys (cynomolgus and rhesus) and a New World monkey (squirrel monkey) from breeding colony at Fiocruz (Brazil). Sixty male and female NHP with the average age of 1-21 years old, comprising twenty animals of each species, were analyzed. Nine different Staphylococcus species (S. aureus, S. cohnii, S. saprophyticus, S. haemolyticus, S. xylosus, S. warneri, S. nepalensis, S. simiae, and S. kloosi) were identified by MALDI-TOF and 16S rRNA gene sequence analyses. Antibiotic resistance was not detected among the isolated bacterial population. S. aureus was the main isolate (19 strains), present in all species, predominant in cynomolgus monkeys (9/20) and squirrel monkeys (7/20). spa typing was used to examine the clonal structure and genetic profile of Staphylococcus aureus isolates. Eight (8) spa types were identified among the S. aureus strains. A major cluster was identified, corresponding to a new spa type t20455, and no spa types found in this study were seen before in Brazil.

MRSA in bulk tank milk of dairy herds in Germany - changes over time

OBJECTIVE

Methicillin-resistant Staphylococcus aureus (MRSA) have repeatedly been isolated from dairy herds. It was the purpose of this study to compare the results of 3 subsequent national scale cross-sectional investigations in dairy herds in Germany on the prevalence of MRSA in bulk tank milk and the characteristics of the isolates.

MATERIAL AND METHODS

The investigations were carried out in 2010, 2014 and 2019, respectively. MRSA were isolated from 25 ml of bulk tank milk using a double selective enrichment protocol. Samples were distributed across the country according to the regional dairy cattle population.

RESULTS

The prevalence of MRSA in bulk tank milk samples was lower in 2010 than in 2014 and tended to decrease until 2019. Prevalence was higher in samples from conventional than from organic herds and increased with herd size. Most isolates (75/78) were assigned to the clonal complex 398 and the spa-types t011 and t034. Resistance of the isolates to other antimicrobials than beta-lactams decreased over time.

CONCLUSIONS

MRSA remain present in the German dairy population and are found more frequently in larger vs. smaller herds and in conventional vs. organic herds.

CLINICAL RELEVANCE

MRSA should be considered in biosecurity protocols and with respect to occupational health of farm staff. Presence of MRSA in raw milk supports the recommendation not to drink unpasteurized raw milk.

Prevalence and characteristics of foodborne pathogens from slaughtered pig carcasses in Korea

The introduction of bacteria into slaughterhouses can lead to microbial contamination in carcasses during slaughter, and the initial level of bacteria in carcasses is important because it directly affects spoilage and the shelf life. This study was conducted to investigate the microbiological quality, and the prevalence of foodborne pathogens in 200 carcasses from 20 pig slaughterhouses across Korea. Distribution of microbial counts were significantly higher for aerobic bacteria at 3.01–4.00 log10 CFU/cm2 (42.0%) and 2.01–3.00 log10 CFU/cm2 (28.5%), whereas most of Escherichia coli showed the counts under 1.00 log10 CFU/cm2 (87.0%) (P &lt; 0.05). The most common pathogen isolated from 200 carcasses was Staphylococcus aureus (11.5%), followed by Yersinia enterocolitica (7.0%). In total, 17 S. aureus isolates from four slaughterhouses were divided into six pulsotypes and seven spa types, and showed the same or different types depending on the slaughterhouses. Interestingly, isolates from two slaughterhouses carried only LukED associated with the promotion of bacterial virulence, whereas, isolates from two other slaughterhouses carried one or more toxin genes associated with enterotoxins including sen. In total, 14 Y. enterocolitica isolates from six slaughterhouses were divided into nine pulsotypes, 13 isolates belonging to biotype 1A or 2 carried only ystB, whereas one isolate belonging to bio-serotype 4/O:3 carried both ail and ystA. This is the first study to investigate microbial quality and the prevalence of foodborne pathogens in carcasses from slaughterhouses nationally, and the findings support the need for ongoing slaughterhouse monitoring to improve the microbiological safety of pig carcasses.

Staphylococcus aureus nasal colonization level and intracellular reservoir: a prospective cohort study

Staphylococcus aureus is a major pathogen in humans. The nasal vestibule is considered as the main reservoir of S. aureus. However, even though the nasal cavity may also be colonized by S. aureus, the relationships between the two sites are still unclear. We conducted a prospective study in humans to assess the S. aureus colonization profiles in the vestibule and nasal cavity, and to investigate the presence of intracellular S. aureus in the two sites. Patients undergoing ear, nose, and throat surgery were swabbed during endoscopy to determine S. aureus nasal load, genotype, and presence of intracellular S. aureus. Among per-operative samples from 90 patients, the prevalence of S. aureus carriage was 32.2% and 33.3% in the vestibule and the nasal cavity, respectively. The mean S. aureus load was 4.10 and 4.25 log₁₀ CFU/swab for the nasal vestibule and nasal cavity, respectively (P > 0.05). Genotyping of S. aureus revealed that all nasal strains isolated from a given individual belong to the same clonal complex and spa-type. An intracellular carriage was observed in 5.6% of the patients, all of whom exhibited a S. aureus vestibule load higher than 3 log₁₀ CFU/swab. An intracellular niche was observed in the vestibule as well as in the nasal cavity. In conclusion, the nasal cavity was also found to be a major site of S. aureus carriage in humans and should draw attention when studying host-pathogen interactions related to the risk of infection associated with colonization.

Bacterial Genotype, Carrier Risk Factors, and an Antimicrobial Stewardship Approach Relevant to Methicillin-resistant Staphylococcus aureus Prevalence in a Population of Macaques Housed in a Research Facility

Methicillin-resistant Staphylococcus aureus (MRSA) remains a significant problem for human and animal health and can negatively affect the health status of macaques and other nonhuman primates (NHP) in research colonies. However, few publications provide guidance on the prevalence, genotype, or risk factors for macaques with MRSA and even fewer on how to effectively respond to MRSA once identified in a population. After having a clinical case of MRSA in a rhesus macaque, we sought to determine the MRSA carrier prevalence, risk factors, and genotypes of MRSA in a population of research NHPs. Over a 6-wk period in 2015, we collected nasal swabs from 298 NHPs. MRSA was isolated from 28% (n = 83). We then reviewed each macaque's medical record for a variety of variables including animal housing room, sex, age, number of antibiotic courses, number of surgical interventions, and SIV status. Analysis of these data suggests that MRSA carriage is associated with the room location, age of the animal, SIV status, and the number of antibiotic courses. We used multilocus sequence typing and spa typing on a subset of MRSA and MSSA isolates to determine whether the MRSA present in NHPs was comparable with common human strains. Two MRSA sequence types were predominant: ST188 and a novel MRSA genotype, neither of which is a common human isolate in the United States. We subsequently implemented antimicrobial stewardship practices (significantly reducing antimicrobial use) and then resampled the colony in 2018 and found that MRSA carriage had fallen to 9% (26/285). These data suggest that, as in humans, macaques may have a high carrier status of MRSA despite low clinically apparent disease. Implementing strategic antimicrobial stewardship practices resulted in a marked reduction in MRSA carriage in the NHP colony, highlighting the importance of limiting antimicrobial use when possible.

Dissemination of epidemic ST239/ST241-t037-agrI-SCCmecIII methicillin-resistant Staphylococcus aureus in a Tunisian trauma burn intensive care unit

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen causing health care-infections in the world, especially in burns. The aim of this study was to assess the extent of dissemination of MRSA isolated from burn patients in Burn Intensive Care Unit in Tunisia and to evaluate the frequency of virulence and antibiotics resistance genes. Among the 72 S. aureus isolates analyzed in the study, 54% were MRSA. The majority of MRSA (94.8%) were multidrug resistant and they had a high resistance rates to kanamycin (94.8%), tobramycin (90%), tetracycline (94.8%) and ciprofloxacin and rifampicin (87%, each). The gene aac(6')-Ie-aph(2″)-Ia conferring resistance to kanamycine and tobtamycin were detected in all isolates and the aph(3')-Ia gene conferring resistance to gentamicin were detected in 2.8% of resistant isolates. Tetracycline resistance genes tet(M), tet(K) and tet(L) were detected in 100%, 10.8% and 2.8% of the isolates, respectively. The SCCmec type III and the agr type I were the most predominant (69.2% and 90%, respectively). The 27 SCCmecIII-agrI isolates were clustered into two PFGE types A and B. The two representative isolates of PFGE clusters A and B belonged to ST239-t037 and ST241-t037 respectively. As conclusion, our results showed a high prevalence of MRSA in trauma burn intensive care unit belonging to two multidrug resistant clones ST239/ST241-agrI-t037-SCCmecIII MRSA. We also demonstrated that MRSA was disseminated between burn patients.

Changes in the Protein Profile in Staphylococcal Strains from Patients Infected with the SARS-CoV-2 Virus

Staphylococcus aureus strains are particularly often isolated from patients with SARS-CoV-2 infection. The aim of the current research was to determine whether the SARS-CoV-2 virus infection affects the protein profile of S. aureus. Bacteria were isolated from the forty swabs collected from the patients in the hospitals of the Pomeranian region. MALDI-TOF MS spectra were obtained using a Microflex LT instrument. Twenty-nine peaks were identified. The peak (2,430) is described here for the first time and was unique for the isolates from patients infected with the SARS-CoV-2 virus. These results support the hypothesis of bacterial adaptation to the conditions caused by viral infection.

High Prevalence of Clonal Complex 398 Methicillin-Susceptible and -Resistant Staphylococcus aureus in Pig Farms: Clonal Lineages, Multiple Drug Resistance, and Occurrence of the Staphylococcal Cassette Chromosome mec IX

High prevalence of livestock-associated methicillin-susceptible and -resistant Staphylococcus aureus (LA-MSSA and LA-MRSA, respectively) in livestock farms, particularly pig farms, is an increasingly serious threat to food safety and public health. In this study, 173 S. aureus (84 MRSA and 89 MSSA) isolates from healthy pigs, farm environments, and farm workers in Korea were examined to determine the (1) genetic diversity of S. aureus isolates (sequence type [ST], spa, and agr types), (2) staphylococcal cassette chromosome mec (SCCmec) types of MRSA isolates, and (3) multidrug resistance (MDR) phenotypes of MRSA and MSSA isolates. Clonal complex 398 (CC398) genotypes of MRSA and MSSA isolates, particularly CC398-spa type t571-agr I lineages, displaying MDR phenotypes were highly prevalent in pig farms. High prevalence of CC398-t571 MRSA and MSSA was more frequently associated with weaning piglets and growing pigs. Moreover, the same clonal lineages of S. aureus isolates colonized both pigs and farm workers, suggesting the transmission of antimicrobial-resistant CC398 MRSA and MSSA between pigs and humans in the pig farms. Furthermore, two dominant SCCmec types, SCCmec V and SCCmec IX, were identified in CC398 MRSA isolates colonizing healthy pigs. To the best of our knowledge, this is the first report of a CC398 LA-MRSA isolate carrying SCCmec IX in Korea. Collectively, these results suggest widespread distribution of the CC398 lineage among MRSA and MSSA isolates in pigs, farm environments, and farm workers in Korea.

Antimicrobial Resistance, SCCmec, Virulence and Genotypes of MRSA in Southern China for 7 Years: Filling the Gap of Molecular Epidemiology

As the prevalence of Staphylococcus aureus infections is of worldwide concern, phenotype and genotype in prevalent MRSA strains require longitudinal investigation. In this study, the antibiotic resistance, virulence gene acquisition, and molecular type were determined on a large scale of nosocomial S. aureus strains in Southern China during 2009-2015. Bacterial identification and antimicrobial susceptibility to 10 antibiotics were tested by Vitek-2. Virulence genes encoding staphylococcal enterotoxins (SEA, SEB, SEC, SED, and SEE), exfoliative toxins (ETA and ETB), Panton-Valentine leukocidin (PVL), and toxic shock syndrome toxin (TSST) were detected by PCR, with SCCmec typing also conducted by multiplex PCR strategy. Genotypes were discriminated by MLST and spaA typing. MLST was performed by amplification of the internal region of seven housekeeping genes. PCR amplification targeting the spa gene was performed for spa typing. No resistance to vancomycin, linezolid, or quinupristin and increase in the resistance to trimethoprim/sulfamethoxazole (55.5%) were identified. A total of nine SCCmec types and subtypes, thirteen STs clustered into thirteen spa types were identified, with ST239-SCCmec III-t037 presenting the predominant methicillin-resistant S. aureus (MRSA) clone. Typically, SCCmec type IX and ST546 were emergent types in China. Isolates positive for both pvl and tsst genes and for both eta and etb genes were also identified. Important findings in this study include: firstly, we have provided comprehensive knowledge on the molecular epidemiology of MRSA in Southern China which fills the gap since 2006 or 2010 from previous studies. Secondly, we have presented the correlation between virulence factors (four major groups) and genotypes (SCCmec, ST and spa types). Thirdly, we have shown evidence for earliest emergence of type I SCCmec from 2012, type VI from 2009 and type XI from 2012 in MRSA from Southern China.

Staphylococcus aureus Host Spectrum Correlates with Methicillin Resistance in a Multi-Species Ecosystem

Although antibiotic resistance is a major issue for both human and animal health, very few studies have investigated the role of the bacterial host spectrum in its dissemination within natural ecosystems. Here, we assessed the prevalence of methicillin resistance among Staphylococcus aureus (MRSA) isolates from humans, non-human primates (NHPs), micromammals and bats in a primatology center located in southeast Gabon, and evaluated the plausibility of four main predictions regarding the acquisition of antibiotic resistance in this ecosystem. MRSA strain prevalence was much higher in exposed species (i.e., humans and NHPs which receive antibiotic treatment) than in unexposed species (micromammals and bats), and in NHP species living in enclosures than those in captivity-supporting the assumption that antibiotic pressure is a risk factor in the acquisition of MRSA that is reinforced by the irregularity of drug treatment. In the two unexposed groups of species, resistance prevalence was high in the generalist strains that infect humans or NHPs, supporting the hypothesis that MRSA strains diffuse to wild species through interspecific transmission of a generalist strain. Strikingly, the generalist strains that were not found in humans showed a higher proportion of MRSA strains than specialist strains, suggesting that generalist strains present a greater potential for the acquisition of antibiotic resistance than specialist strains. The host spectrum is thus a major component of the issue of antibiotic resistance in ecosystems where humans apply strong antibiotic pressure.

Staphylococci isolated from cats in Italy with superficial pyoderma and allergic dermatitis: Characterisation of isolates and their resistance to antimicrobials

BACKGROUND

In cats, superficial pyoderma traditionally is considered rare and few reports are available. There is a particular lack of studies concerning Staphylococcus species associated with pyoderma in subjects affected by allergic skin diseases.

HYPOTHESIS/OBJECTIVES

(i) To evaluate the association between Staphylococcus spp. and superficial pyoderma in allergic cats and (ii) to characterise isolated staphylococci and analyse their antimicrobial resistance patterns.

ANIMALS

Forty-one cats with allergic dermatitis and superficial pyoderma in Italy.

MATERIALS AND METHODS

Skin swabs were cultured for the isolation of Staphylococcus spp. Species identification was performed by matrix-assisted laser desorption/ionisation time of flight mass spectrometry and 16S-rRNA sequencing. Staphylococcus aureus isolates were further characterised by staphylococcal protein A gene-typing. Antimicrobial susceptibility was performed by the disk diffusion method.

RESULTS

Staphylococci were isolated from 36/41 cats sampled and 39 different isolates were identified. Uneven distribution of staphylococcal species was observed among different body locations. The 39 isolates were S. aureus (n = 15), S. felis (n = 10), S. pseudintermedius (n = 8) and other staphylococci (n = 6). Eight different S. aureus spa-types associated with human clonal complexes were identified. Antimicrobial resistance was observed to penicillin (56.4%), tetracycline (46.2%), enrofloxacin (33.3%), erythromycin (28.2%), amikacin (25.6%), clindamycin (23.1%), marbofloxacin (15.4%), gentamicin (12.8%), trimethoprim-sulfamethoxazole (10.3%), chloramphenicol (7.7%) and cefoxitin/oxacillin (5.1%). Fifteen isolates (38.4%) were multidrug-resistant while meticillin resistance was associated only with S. pseudintermedius.

CONCLUSIONS AND CLINICAL RELEVANCE

These results confirm that S. aureus, S. pseudintermedius, and S. felis are frequently associated with superficial pyoderma in allergic cats. Semi-synthetic penicillins remain a suitable first-line treatment in this study, yet the high prevalence of antimicrobial resistant isolates suggests that antimicrobial susceptibility testing should be performed routinely.

High genetic diversity and zoonotic potential of Staphylococcus aureus strains recovered from bovine intramammary infections in Colombians dairy herds

Genotyping of Staphylococcus aureus isolated from mastitis has become a fundamental tool to understand its complex epidemiology and to evaluate spillover events. The aim of this study was to describe the frequency of genotypes of the S. aureus strains isolated from intramammary infections by spa typing technique, and to evaluate the association between genotypes and the ability to form biofilm under in vitro conditions. Sixty-six strains of S. aureus recovered from bovines intramammary infections on 56 dairy herds located in 14 municipalities of the department of Antioquia were characterized. The majority of strains (65/66) were isolated from milk samples collected from dairy cows with subclinical intramammary infections. Nineteen different spa types were found in this study, t521 (19.70%), t267 (15.15%), and t605 (12.12%) being the most frequent. The strains from the t605 spa type showed the highest biofilm production. The high frequency of spa types with zoonotic potential found in this study, identified cattle as an important reservoir of theses clones for people in close proximity, such as milkers and consumers of unpasteurized dairy products.

Clinical and Bacteriological Analyses of Biofilm-Forming Staphylococci Isolated from Diabetic Foot Ulcers

Background

Diabetes mellitus is a chronic disease that is associated with increased morbidity and mortality. Unfortunately, foot ulcers and amputations due to diabetes are very common in developing countries. The purpose of this study was to characterize the clinical presentation of diabetic foot ulcer (DFU) infections, isolate the causative agent, and analyze the biofilm formation and distribution of biofilm-related genes among isolated Staphylococci.

Material and Methods

The study included 100 diabetic patients suffering from DFUs attending Assiut University Hospital. Swabs were collected and antimicrobial susceptibility testing of the isolates was performed. Biofilm formation was tested phenotypically among staphylococcal isolates and the frequency of different biofilm genes was analyzed by PCR. Clinical presentations of diabetic foot ulcers were correlated with bacterial genetic characteristics. Spa types were determined using DNA Gear-a software.

Results

Microbiological analysis showed that 94/100 of the DFUs were positive for bacterial growth. The majority of infections were polymicrobial (54%, n=54/100). Staphylococci were the most commonly detected organisms, of which S. aureus represented 37.5% (n=24/64), S. haemolyticus 23.4% (n=15/64), S. epidermidis 34.3% (n=22/64) and other CNS 4.7% (n=3/64). Interestingly, co-infection with more than one species of Staphylococci was observed in 17.1% (n=11/64) of samples. A high level of antibiotic resistance was observed, where 78.1% (n=50/64) of Staphylococci spp were multidrug-resistant (MDR). Phenotypic detection showed that all isolated Staphylococci were biofilm-formers with different grades. Analysis of biofilm-forming genes among Staphylococci showed that the most predominant genes were icaD, spa, and bap. Isolates with a higher number of biofilm-related genes were associated with strong biofilm formation. Sequencing of the spa gene in S. aureus showed that our isolates represent a collection of 17 different spa types.

Conclusion

The majority of DFUs in our hospital are polymicrobial. Staphylococci other than S.aureus are major contributors to infected DFUs. MDR and biofilm formation are marked among isolates, which is paralleled by the presence of different categories of virulence-related genes. All severely infected wounds were associated with either strong or intermediate biofilm formers. The severity of DFU is directly related to the number of biofilm genes.

spa Typing of Methicillin-Resistant Staphylococcus aureus Based on Whole-Genome Sequencing: the Impact of the Assembler

Sequencing of the spa gene of methicillin-resistant Staphylococcus aureus (MRSA) is used for assigning spa types to e.g., detect transmission and control outbreaks. Traditionally, spa typing is performed by Sanger sequencing but has in recent years been replaced by whole-genome sequencing (WGS) in some laboratories. Spa typing by WGS involves de novo assembly of millions of short sequencing reads into larger contiguous sequences, from which the spa type is then determined. The choice of assembly program therefore potentially impacts the spa typing result. In this study, WGS of 1,754 MRSA isolates was followed by de novo assembly using the assembly programs SPAdes (with two different sets of parameters) and SKESA. The spa types were assigned and compared to the spa types obtained by Sanger sequencing, regarding the latter as the correct spa types. SPAdes with the two different settings resulted in assembly of the correct spa type for 84.8% and 97.6% of the isolates, respectively, while SKESA assembled the correct spa type in 98.6% of cases. The misassembled spa types were generally two spa repeats shorter than the correct spa type and mainly included spa types with repetition of the same repeats. WGS-based spa typing is thus very accurate compared to Sanger sequencing, when the best assembly program for this purpose is used. IMPORTANCE spa typing of methicillin-resistant Staphylococcus aureus (MRSA) is widely used by clinicians, infection control workers, and researchers both in local outbreak investigations and as an easy way to communicate and compare MRSA types between laboratories and countries. Traditionally, spa types are determined by Sanger sequencing, but in recent years a whole-genome sequencing (WGS)-based approach has become increasingly used. In this study, we compared spa typing by WGS using different methods for assembling the genome from short sequencing reads and compared to Sanger sequencing as the gold standard. We find substantial differences in correct assembly of spa types between the assembly methods. Our findings are therefore important for the quality of WGS based spa typing data being exchanged by clinical microbiology laboratories.

Low-level colonization of methicillin-resistant Staphylococcus aureus in pigs is maintained by slowly evolving, closely related strains in Finnish pig farms

BACKGROUND

Over the past two decades, livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has become widely prevalent in pig production in Europe. The carriage status of LA-MRSA is known to vary among individual pigs, but bacterial load in pigs has rarely been studied. We assessed the quantity of LA-MRSA in nasal and skin samples of pigs and investigated the genetic diversity of the strains together with sequenced strains from national surveillance and pathology samples from the Finnish Food Authority. On two farms with assumed MRSA-positive status, farm 1 and farm 2, 10 healthy pigs were sampled three times during 2 weeks from the nares and skin (study A). On farm 1, 54 additional pigs were sampled and from confirmed MRSA-positive animals, 10 were randomly selected and transported to a clean, controlled environment for further sampling (study B). From the samples taken on farms 1 and 2 and in the controlled environment, MRSA was isolated both by direct plating and enrichment on selective media. spa types, multilocus sequence types, staphylococcal cassette chromosome mec types, resistance and virulence genes were determined. Core genome multilocus sequence typing (cgMLST) analysis was performed, including the sequences deriving from the surveillance/pathology samples from the Finnish Food Authority.

RESULTS

All pigs on farm 1 carried LA-MRSA in the nares at all three time points and five pigs on farm 2 at one time point. Nasal quantity varied between 10 and 10³ CFU/swab and quantity on the skin between 10 and 10² CFU/swab. In the controlled environment, MRSA was detected in at least one of the nasal samples from each animal. spa type t034 was predominant. cgMLST showed one cluster with minimum allele differences between 0 and 11.

CONCLUSIONS

The study shows predominantly low-level carriage (< 10³ CFU/swab) of LA-MRSA on farms. In the controlled environment we observed a decline in nasal carriage but constant skin carriage. cgMLST showed that strains of spa type t034 are closely related at the national level.

Molecular epidemiology and phenotypes of invasive methicillin-resistant vancomycin-intermediate Staphylococcus aureus in Taiwan

BACKGROUND

Patients with invasive infections caused by methicillin-resistant Staphylococcus aureus (MRSA), especially those with an elevated minimal inhibitory concentration (MIC) of vancomycin (VA), are likely to have treatment failure and poor outcomes. The aim of this study was to delineate and correlate the genotypes and phenotypes of clinical VA-intermediate S. aureus (VISA) from invasive infections in Taiwan.

METHODS

Between 2006 and 2010, a total of 670 non-duplicate MRSA isolates were collected from patients with invasive infections, mostly from blood, as part of a nationwide antimicrobial surveillance program named Tigecycline in vitro Surveillance in Taiwan. Among them, 10 (1.5%) VISA (VA MIC = 4 mg/L) isolates were identified. Molecular typing with staphylococcal cassette chromosome mec (SCCmec), multilocus sequence typing, staphylococcal protein A (spa), mec-associated hypervariable region (dru), accessory gene regulator (agr), and pulse-field gel electrophoresis, and phenotypic analysis including antibiotic susceptibility testing, gene encoding Panton-Valentine leukocidin (pvl), and superantigenic toxin profiles, were analyzed.

RESULTS

All but one isolate was defined as molecular health-care-associated MRSA: 6 as SCCmecIII-ST239-spa t037-agrI-dru7 (1 isolate) and dru14 (5 isolates), 2 as SCCmecII-ST5-spa t586-agrII-dru4, and one as SCCmecII-ST89-spa t3520-agrIII-dru7. One isolate was defined as SCCmecIV-ST59-spa t437-agrI-dru8, which was categorized as molecular community-associated MRSA. Five pulsotypes were identified; only one had a positive D-test and 3 were insusceptible to daptomycin (MIC ≧1 mg/L). Five isolates possessed sea-selk-selq, among them 4 belonged to SCCmecIII-ST239-spa t037-agrI.

CONCLUSION

In this study, VISA was rarely isolated from invasive MRSA infections, and most cases harbored limited genotypes and corresponding phenotypes.

Genomic characterization of two community-acquired methicillin-resistant Staphylococcus aureus with novel sequence types in Kenya

Staphylococcus aureus is a clinically important bacteria with high antimicrobial resistance (AMR) challenge globally. The emergence of methicillin-resistant Staphylococcus aureus (MRSA) clones with unique sequence types have been identified in the community showing evidence that the epidemiology of MRSA globally is changing and requires continual surveillance. We utilized whole genome sequencing to characterize two community acquired-MRSA (CA-MRSA) strains isolated from wound swabs from community-onset infections in two health facilities in Kenya. The two strains belonged to multilocus sequence type (MLST) sequence type (ST) 7460, and ST 7635. The resistance genes detected showed that the novel STs are carriers of clinically relevant resistance genes. Linezolid and mupirocin resistance was observed, yet mupirocin is not commonly used in the country. Mutations within resistance genes were also detected and the pathogenicity toward the human host matched various pathogenic global S. aureus families, e.g., S. aureus subsp. aureus USA300. Multidrug efflux transporters, important in antimicrobial resistance including restriction enzymes type I and type IV were detected. Plasmids identified showed similarities with the plasmids in other clinically significant non-staphylococcal species, such as Pseudomonas aeruginosa, Escherichia coli, Morganella morganii, and Enterococcus faecium. Both STs belong to clonal complex 8 (CC8) which is the most successful MRSA clone in Kenya. Spa type t30 to which ST 7635 belongs has not been reported in the country. The results of this study further highlight the need for epidemiological studies to reveal circulating strains and antimicrobial resistance spread between hospitals and the community. The genomic research highlights resistance to anti-staphylococcal broad-spectrum antimicrobials not used frequently in the country, jeopardizing successful MRSA treatment since most health facilities do not perform genotypic resistance tests for routine patient management. Preliminary insights into unidentified STs of CA-MRSA in Kenya show the need for molecular epidemiological surveillance studies to further understand the diversity of S. aureus in Africa.

Risk factors for antimicrobial resistance among Staphylococcus isolated from pets living with a patient diagnosed with methicillin-resistant Staphylococcus aureus infection

It has been suggested that pets play a critical role in the maintenance of methicillin-resistant (MR) and multidrug-resistant (MDR) Staphylococcus spp. in the household. We examined risk factors for carriage of antimicrobial-resistant coagulase-positive staphylococci, with particular attention to Staphylococcus aureus and Staphylococcus pseudintermedius isolated from pets living in households of people diagnosed with methicillin-resistant S. aureus (MRSA) skin or soft-tissue infection. We analyzed data collected cross-sectionally from a study conducted in 2012 that evaluated the transmission of MRSA and other staphylococci from humans, their pets and the environment (Pets and Environmental Transmission of Staphylococci [PETS] study). We used unadjusted and adjusted stratified logistic regression analyses with household-clustered standard errors to evaluate the association between demographic, healthcare-related, contact-related and environmental risk factors and MDR Staphylococcus spp. isolated from dogs and cats. Staphylococcal isolates obtained from dogs (n = 63) and cats (n = 47) were included in these analyses. The use of oral or injectable antimicrobials by the pets during the prior year was the main risk factor of interest. Based on our results, 50% (12/24) of S. aureus, 3.3% (1/30) of S. pseudintermedius and 25% (14/56) of other coagulase-positive staphylococci (CPS) were determined to be MDR. S. aureus isolates were more likely to be MDR compared with S. pseudintermedius. We did not find a significant statistical association between the use of oral or injectable antimicrobials in the prior year and the presence of MDR bacteria. The results suggest that drivers of antimicrobial resistance in household staphylococci may vary by bacterial species, which could have implications for one health intervention strategies for staphylococci and inform the investigation of other reverse zoonoses, such as COVID-19.

Characteristics of Virulence Genes of Clinically Isolated Staphylococci in Jingzhou Area

Purpose

The aim of this study was to further understand the distribution characteristics of staphylococcal virulence genes in the Jingzhou area, in order to provide a basis for clinically effective treatments and prevention and control measures.

Methods

A total of 181 strains of staphylococci were collected from Jingzhou Hospital Affiliated to Yangtze University from April 2013 to April 2021, which were divided into the methicillin-resistant Staphylococcus aureus (MRSA) strains and the methicillin-sensitive Staphylococcus aureus (MSSA) strains and coagulase-negative staphylococci (CoNS) by an antimicrobial susceptibility test and PCR method. The 73 MRSA strains were classified by staphylococcal cassette chromosome mec (SCCmec) and Staphylococcus protein A (Spa). Sea, sec, seh, sek, seb, seq, sep, Tsst-1, clfA, clfB, fnbA, hla, hld, hlg, lukE, bbp, cna, eap, ebpS, sdrC, sdrD, sdrE, and Pvl genes were also detected in all strains. The χ² test was used for statistical analysis for comparison between groups.

Results

The 181 strains of staphylococci were divided into 97 strains of MRSA, 54 strains of MSSA, and 30 strains of CoNS. 73 MRSA strains were derived from clinical specimens such as lower respiratory tract, secretions, sepsis secreted by tissue infection, urine, and hydrothorax. There were 70 strains that can be identified including SCCmec types and 15 Spa types of all strains, while the most popular types were SCCmecIII-t030 and SCCmecIV-t437 from lower respiratory tract specimens. There were four virulence genes that were detected including seb, seq, clfB, and hld in CoNS strains, while the detection rates of these four virulence genes in Staphylococcus aureus were higher than that of CoNS, and the differences were statistically significant, P < 0.05(P=0.004, P=0.001, P=0.001, P=0.001). 23 virulence genes were detected in 151 strains of Staphylococcus aureus, among which the detection rate of the Tsst-1 gene was the lowest and that of the clfB gene was the highest, and the other genes were 4.6%∼98.0%. The detection rates of sea, sek, seb, seq, sep, cna, eap, ebpS, sdrC, and sdrE virulence genes in MRSA were higher than that of MSSA, and the differences were statistically significant, P < 0.05 (P=0.001, P=0.001, , P=0.001, P=0.001, P=0.009, , P=0.019, P=0.001, , P=0.001, P=0.001, , P=0.003).

Conclusion

The mainly prevalent type of MRSA strains in Jingzhou is SCCmecIII-t030 in lower respiratory tract specimens. Virulence genes of Staphylococcus aureus and antibiotic drug resistance rates are also different from other regions. In this experiment, virulence genes were also detected in CoNS, suggesting that more attention should be paid to the prevention and treatment of these strains clinically.

Risk Factors of Recurrent Infection in Patients with Staphylococcus aureus Bacteremia: a Competing Risk Analysis

Although several clinical variables have been reported as risk factors for recurrence of Staphylococcus aureus infection, most studies have not considered competing risk events that may overestimate the risk. In this study, we performed competing risk analysis to identify risk factors related to 90-day recurrence in patients with S. aureus bacteremia (SAB) using a large cohort data from a single tertiary hospital in South Korea. All adults who experienced SAB during admission were prospectively enrolled from August 2008 to December 2019. After the day of the first positive blood culture, recurrence and all-cause mortality were assessed for 90 days. Recurrence was defined as a development of symptoms or signs of infection with or without repeated bacteremia after >7 days of negative blood culture and clinically apparent improvement. Subdistribution hazard ratios (sHR) for recurrence and all-cause mortality were estimated using Fine and Gray models. Of 1,725 SAB patients, including 885 cases (51.3%) of methicillin-resistant S. aureus (MRSA) bacteremia, 85 (5.0%) experienced recurrence during the study period. In a multivariate Fine and Gray regression model, the presence of a vascular graft (subdistribution HR [sHR], 3.48; 95% confidence interval [CI], 1.90-6.40), nasal MRSA carriage (sHR, 2.10; 95% CI, 1.28-3.44), methicillin resistance (sHR, 1.69; 95% CI, 1.00-2.84), and rifampicin resistance (sHR, 2.20; 95% CI, 1.12-4.33) were significantly associated with 90-day recurrence. In a large cohort of SAB patients with a high prevalence of MRSA, indwelling vascular graft, nasal MRSA carriage, methicillin resistance, and rifampicin resistance were potential risk factors for recurrence of S. aureus infection.

Clinical impact of and microbiological risk factors for qacA/B positivity in ICU-acquired ST5-methicillin-resistant SCCmec type II Staphylococcus aureus bacteremia

Concern about resistance to chlorhexidine has increased due to the wide use of the latter. The impact of the qacA/B and smr chlorhexidine tolerance genes on the outcome of methicillin-resistant Staphylococcus aureus (MRSA) infections is unclear. We evaluated the prevalence and clinical impact of, and microbiological risk factors for, qacA/B tolerance in MRSA bacteremia. MRSA bacteremia that occurred more than two days after intensive care unit admission between January 2009 and December 2018 was identified from a prospective cohort of S. aureus bacteremia in a tertiary-care hospital from South Korea. A total of 183 MRSA blood isolates was identified, and the major genotype found was ST5-MRSA-II (87.4%). The prevalences of qacA/B and smr were 67.2% and 3.8%, respectively. qacA/B-positive isolates were predominantly ST5-MRSA-II (96.7% [119/123]), the dominant hospital clone. In a homogenous ST5-MRSA-II background, qacA/B positivity was independently associated with septic shock (aOR, 4.85), gentamicin resistance (aOR, 74.43), and non-t002 spa type (aOR, 74.12). qacA/B positivity was found to have decreased significantly in ST5-MRSA-II in association with a decline in qacA/B-positive t2460, despite the increasing use of chlorhexidine since 2010 (P < 0.001 for trend). Continuous surveillance of the qac genes, and molecular characterization of their plasmids, are needed to understand their role in MRSA epidemiology.

Antimicrobial Susceptibility Profiles and Molecular Characterisation of Staphylococcus aureus from Pigs and Workers at Farms and Abattoirs in Zambia

Pigs have been shown to be a reservoir for recently emerging livestock-associated Staphylococcus aureus (LA-SA), including methicillin resistant strains in many countries worldwide. However, there is sparse information about LA-SA strains circulating in Zambia. This study investigated the prevalence, phenotypic and genotypic characteristics of S. aureus from pigs and workers at farms and abattoirs handling pigs in Lusaka Province of Zambia. A total of 492 nasal pig swabs, 53 hand and 53 nasal human swabs were collected from farms and abattoirs in selected districts. Standard microbiological methods were used to isolate and determine antimicrobial susceptibility patterns of S. aureus. Polymerase Chain Reaction was used to confirm the species identity and detect antimicrobial resistance and virulence genes of isolates, whereas genetic diversity was evaluated using spa typing. Overall prevalence of S. aureus was 33.1%, 37.8% for pigs and 11.8% for humans. The isolates were resistant to several antibiotics with resistance ranging from 18% to 98% but were all susceptible to vancomycin. Typical LA-SA spa types were detected. The presence of plasmid mediated resistance genes such as tetM (12.8%), other resistance determinants and immune evasion cluster genes among the isolates is of great public health concern. Thus, continuous surveillance of S. aureus using a “One health” approach is warranted to monitor S.aureus infections and spread of antimicrobial resistance.

High prevalence and expression of antiseptic resistance genes among infectious t037/ST239 methicillin-resistant Staphylococcus aureus (MRSA) strains in North Khorasan Province, Iran

OBJECTIVES

Staphylococcus aureus is an important infectious agent and the majority of methicillin-resistant S. aureus (MRSA) infections are of nosocomial origin. To define the level and distribution of antiseptic resistance among infectious S. aureus strains we studied MRSA and methicillin-susceptible S. aureus (MSSA) isolates collected from different infection sites in an assortment of patients.

MATERIALS AND METHODS

S. aureus isolates were investigated for in vitro susceptibility to antiseptic agents and detection of qacA/B, smr, vanA, and mecA genes.

RESULTS

Among the S. aureus isolates we studied, 25 and 41 were MRSA and MSSA, respectively. The mean of minimum inhibitory concentrations (MICs) for benzethonium chloride (BTC) among MRSA was statistically significantly higher than for MSSA (26 µg/ml versus 11.7 µg/ml, P=0.003) while there was no significant difference between MRSA and MSSA for benzalkonium chloride (BKC) and chlorhexidine digluconate (CHG). The qacA/B genes were carried in 68% of the MRSA and 58.2% of MSSA (P=0.601), while smr was carried in 39% of MRSA and 29.3% of MSSA strains (P=1.000). In 15 out of 25 cases, MRSA ST239 with spa types t037, t030, and t7688 was isolated from the infection site with 86.6% of them carrying a resistance gene (qacA/B or qacA/B + smr).

CONCLUSION

The frequent presence of antiseptic resistance genes and a consequently elevated MIC against antiseptics among ST239 MRSA emphasizes the importance of mandatorily monitoring MRSA for effective infection control.

Prevalence and Antimicrobial Resistance of Staphylococcus aureus and Coagulase-Negative Staphylococcus/Mammaliicoccus from Retail Ground Meat: Identification of Broad Genetic Diversity in Fosfomycin Resistance Gene fosB

Staphylococcus is a major bacterial species that contaminates retail meat products. The objective of this study was to clarify the prevalence, antimicrobial resistance and genetic determinants of Staphylococcus/Mammaliicoccus species in retail ground meat in Japan. From a total of 146 retail ground meat samples (chicken, pork, mixed beef/pork) purchased during a 5-month period, 10 S. aureus and 112 isolates of coagulase-negative staphylococcus (CoNS)/Mammaliicoccus comprising 20 species were recovered. S. aureus isolates were classified into five genetic types, i.e., coa-IIa/ST5, coa-VIc/ST352 (CC97), coa-VIIb/ST398, coa-Xa/ST15, and coa-XIc/ST9, which were all related to those of livestock-associated clones. All the staphylococcal isolates were mecA-negative and mostly susceptible to all the antimicrobials tested, except for ampicillin among S. aureus (resistance proportion; 50%). Among CoNS, the fosfomycin resistance gene fosB was prevalent (30/112; 26.8%), primarily in S. capitis, S. warneri, and S. saprophyticus. Phylogenetic analysis of fosB revealed the presence of seven clusters, showing broad diversity with 65–81% identity among different clusters. In the CoNS isolates from ground meat samples, fosB was assigned into three clusters, and S. saprophyticus harbored the most divergent fosB with three genetic groups. These findings suggested the circulation of multiple fosB-carrying plasmids among some CoNS species.

Prevalence and Diversity of Staphylococcus aureus and Staphylococcal Enterotoxins in Raw Milk From Northern Portugal

Staphylococcus aureus and staphylococcal enterotoxins are a serious public health concern associated with hospital and community-acquired illnesses. Dairy animals frequently shed S. aureus into the milk supply which can lead to food poisoning in humans. This study aims to investigate the prevalence and genetic diversity of S. aureus and staphylococcal enterotoxins in raw milk from the main dairy region of mainland Portugal. S. aureus was found in 53.0% (95% CI: 40.6-65.4%) of 100 raw cow's milk samples collected from bulk cooling tanks. The highest contamination level was 3.4 log10 CFU.mL^-1, and in some samples more than one S. aureus strain was identified. Staphylococcal enterotoxins (SEA-SEE) were detected in one sample. Spa typing revealed 62 distinct S. aureus isolates, being t529 (17.7%, 95% CI: 8.2-27.3%) and t1403 (16.1%, 95% CI: 7.0-25.3%) the predominant types, commonly associated with livestock infection or carriage. The antimicrobial susceptibility test showed that 35.5% of the S. aureus isolates were resistant to at least one antimicrobial agent, with resistance to penicillin being the highest (32.3%, 95% CI: 20.6-43.9%) followed by tetracycline (24.2%, 95% CI: 13.5-34.9%), ciprofloxacin (16.1%, 95% CI: 7.0-25.3%) and chloramphenicol (16.1%, 95% CI: 7.0-25.3%). Moreover, five isolates (8.1%, 95% CI: 1.3-14.8%) were identified as methicillin-resistant S. aureus (MRSA, cefoxitin resistant). Regarding virulence/resistance genes, 46,8% (95% CI: 34.4-59.2%) isolates harbored at least one enterotoxin-encoding gene, and the seg gene was the most frequently detected (41.9%, 95% CI: 29.7-54.2%) followed by the sei (40.3%, 95% CI: 28.1-52.5%), sec (6.5%, 95% CI: 0.3-12.6%), seh (4.8%, 95% CI: 0.0-10.2%), and sea (1.6%, 95% CI: 0.0-4.7%) genes. Five (8.1%, 95% CI: 1.3-14.8%) non-enterotoxigenic isolates carried the mecA gene (corresponding to isolates phenotypically classified as MRSA), and 4.8% (95% CI: 0.0-10.2%) enterotoxigenic strains also had the tsst-1 gene. Our study confirm that raw milk can be a zoonotic source of S. aureus, including enterotoxigenic and MRSA strains. Furthermore, the majority of enterotoxigenic isolates were found to contain genes encoding SEs (SEG, SEH and SEI) not routinely screened. This shows the need for a broader SE screening in food safety control, as well as the relevance of risk mitigation measures to control S. aureus transmission along the food chain in Portugal.

Molecular Characterization of Staphylococcus aureus Strains Isolated from Mobile Phones

The widespread use of mobile phones (MP) among healthcare personnel might be considered as an important source of contamination. One of the most pathogenic bacteria to humans is Staphylococcus aureus, which can be transmitted through the constant use of MP. Nevertheless, which specific type of strains are transmitted and which are their sources have not been sufficiently studied. The aim of this study is to determine the source of contamination of MP and characterize the corresponding genotypic and phenotypic properties of the strains found. Nose, pharynx, and MP samples were taken from a group of health science students. We were able to determinate the clonality of the isolated strains by pulsed-field gel electrophoresis (PFGE) and spa gene typing (spa-type). Adhesin and toxin genes were detected, and the capacity of biofilm formation was determined. Several of the MP exhibited strains of S. aureus present in the nose and/or pharynx of their owners. methicillin-susceptible Staphylococcus aureus (MSSA), hospital-acquired methicillin-resistant S. aureus (HA-MRSA), and community-acquired methicillin-resistant S. aureus (CA-MRSA) strains were found, which indicated a variety of genotypes. This study concludes that MP can be contaminated with the strains of S. aureus present in the nose and/or pharynx of the owners; these strains can be of different types and there is no dominant genotype.

A One Health Approach Molecular Analysis of Staphylococcus aureus Reveals Distinct Lineages in Isolates from Miranda Donkeys (Equus asinus) and Their Handlers

Donkeys (Equus asinus) are in decline in Europe. Occupational exposure to farm animals has been associated with increased staphylococci carriage. We aimed to isolate S. aureus and coagulase-negative staphylococci (CoNS) from donkeys and handlers and characterize the antimicrobial resistance profiles and genetic lineages of S. aureus strains. Oral and nasal swab samples were collected from 49 Miranda donkeys and 23 handlers from 15 different farms. Staphylococci species were identified by MALDI-TOF MS. The presence of antimicrobial resistance genes and virulence factors was investigated by PCR. Molecular typing was performed in S. aureus isolates. From the 49 donkey samples, 4 S. aureus (8.2%) and 21 CoNS (42.9%) were isolated. Ten handlers (43.5%) were carriers of S. aureus and 4 (17.4%) carried CoNS. The CoNS isolates showed resistance to several classes of antimicrobials encoded by the mecA, aph (3′)-IIIa, ant (4′)-Ia, tetM, tetK, lnuA, ermB, ermC, dfrA and dfrG genes. S. aureus isolates were resistant to penicillin, aminoglicosides and tetracycline harboring the blaZ, aph (3′)-IIIa, tetL, tetM and tetK genes. All S. aureus isolates from donkeys belonged to ST49 and spa-type t208 while the strains isolated from the handlers were ascribed to 3 STs and 7 spa-types. However, human isolates were from different STs than the donkey isolates. Donkeys are mainly colonized by methicillin-resistant S. sciuri. S. aureus transmission between donkeys and their handlers appears not to have occurred since the isolates belonged to different genetic lineages.

Nocturnal Birds of Prey as Carriers of Staphylococcus aureus and Other Staphylococci: Diversity, Antimicrobial Resistance and Clonal Lineages

Owls are nocturnal predators that inhabit urbanized and farmlands. They are in direct contact with other animals, both livestock and small wild rodents that they mostly feed on. Staphylococci can be both commensal and pathogenic bacteria that are widespread across the various ecological niches. We aimed to isolate staphylococci from owls and to characterize their antimicrobial resistance, virulence factors and genetic lineages. Swab samples were collected from the throat and cloaca of 114 owls admitted to two rehabilitation centers in Portugal. The identification of staphylococci species was performed by MALDI-TOF. Staphylococci antimicrobial resistance and virulence genes were investigated by means of the disk diffusion method and PCR. Staphylococcus aureus isolates were characterized by MLST, agr and spa-typing. Of the tested animals, 66 isolates were recovered, including 10 different species of staphylococci, of which 25 were coagulase-positive (CoPS) and 41 were coagulase-negative (CoNS). Twenty-three S. aureus were isolated, of which one mecC-MRSA was identified. The isolates were mainly resistant to penicillin, aminoglycosides, clindamycin and tetracycline. mecC-MRSA belonged to ST1245 and spa-type t843 and the remaining S. aureus were ascribed to 12 STs and 15 spa types. A high diversity of clonal lineages was identified among the S. aureus isolated from wild owls. Owls feed mainly on small rodents often exposed to waste and anthropogenic sources, which may explain the moderate prevalence of S. aureus in these animals.

The Prevalence and Molecular Biology of Staphylococcus aureus Isolated from Healthy and Diseased Equine Eyes in Egypt

This work aimed to characterize S. aureus isolates from the eyes of healthy and clinically affected equines in the Kafrelsheikh Governorate, Egypt. A total of 110 animals were examined for the presence of S. aureus, which was isolated from 33 animals with ophthalmic lesions and 77 healthy animals. We also investigated the antimicrobial resistance profile, oxacillin resistance mechanism, and the major virulence factors implicated in many studies of the ocular pathology of pathogenic S. aureus. The association between S. aureus eye infections and potential risk factors was also investigated. The frequency of S. aureus isolates from clinically affected equine eyes was significantly higher than in clinically healthy equids. A significant association was found between the frequency of S. aureus isolation from clinically affected equine eyes and risk factors including age and season but not with sex or breed factors. Antimicrobial resistance to common antibiotics used to treat equine eyes was also tested. Overall, the isolates showed the highest sensitivity to sulfamethoxazole (100%) and the highest resistance to cephalosporin (90.67%) and oxacillin (90.48%). PCR was used to demonstrate that mecA was present in 100% of oxacillin- and β-lactam-resistant S. aureus strains. The virulence factor genes Spa (x region), nuc, and hlg were identified in 62.5%, 100%, and 56%, of isolates, respectively, from clinically affected equines eyes. The severity of the eye lesions increased in the presence of γ-toxin-positive S. aureus. The phylogenetic tree of the Spa (x region) gene indicated a relationship with human reference strains isolated from Egypt as well as isolates from equines in Iran and Japan. This study provides insight into the prevalence, potential risk factors, clinical pictures, zoonotic potential, antimicrobial resistance, and β-lactam resistance mechanism of S. aureus strains that cause eye infection in equines from Egypt.

Sequencing Independent Molecular Typing of Staphylococcus aureus Isolates: Approach for Infection Control and Clonal Characterization

Staphylococcus aureus is a major bacterial human pathogen that causes a wide variety of clinical manifestations. The main aim of the presented study was to determine and optimize a novel sequencing independent approach that enables molecular typing of S. aureus isolates and elucidates the transmission of emergent clones between patients. In total, 987 S. aureus isolates including both methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) isolates were used to evaluate the novel typing approach combining high-resolution melting (HRM) analysis of multilocus sequence typing (MLST) genes (mini-MLST) and spa gene (spa-HRM). The novel approach's discriminatory ability was evaluated by whole-genome sequencing (WGS). The clonal relatedness of tested isolates was set by the BURP and BURST approach using spa and MLST data, respectively. Mini-MLST classified the S. aureus isolates into 38 clusters, followed by spa-HRM classifying the isolates into 101 clusters. The WGS proved HRM-based methods to effectively differentiate between related S. aureus isolates. Visualizing evolutionary relationships among different spa-types provided by the BURP algorithm showed comparable results to MLST/mini-MLST clonal clusters. We proved that the combination of mini-MLST and spa-HRM is rapid, reproducible, and cost-efficient. In addition to high discriminatory ability, the correlation between spa evolutionary relationships and mini-MLST clustering allows the variability in population structure to be monitored. IMPORTANCE Rapid and cost-effective molecular typing tools for Staphylococcus aureus epidemiological applications such as transmission tracking, source attribution and outbreak investigations are highly desirable. High-resolution melting based methods are effective alternative to those based on sequencing. Their good reproducibility and easy performance allow prospective typing of large set of isolates while reaching great discriminatory power. In this study, we established a new epidemiological approach to S. aureus typing. This scheme has the potential to greatly improve epidemiological investigations of S. aureus.

Selection of Staphylococcus aureus in a murine nasopharyngeal colonization model

Staphylococcus aureus nasal colonization is a risk factor for infection. A large proportion of the population are identified as potential S. aureus carriers yet we only partially understand the repertoire of genetic factors that promote long-term nasal colonization. Here we present a murine model of nasopharyngeal colonization that requires a low S. aureus inoculum and is amenable to experimental evolution approaches. We used this model to experimentally evolve S. aureus using successive passages in the nasopharynx to identify those genetic loci under selection. After 3 cycles of colonization, mutations were identified in mannitol, sorbitol, arginine, nitrite and lactate metabolism genes promoting key pathways in nasal colonization. Stress responses were identified as being under selective pressure, with mutations in DNA repair genes including dnaJ and recF and key stress response genes clpL, rpoB and ahpF. Peptidoglycan synthesis pathway genes also revealed mutations indicating potential selection for alteration of the cell surface. The murine model used here is versatile to question colonization, persistence and evolution studies. We studied the human pathogen Staphylococcus aureus in our search to determine factors that contribute to its ability to live in the human nose and throat. The anterior nares and nasopharynx are considered primary habitats but we do not understand how the pathogen adapts as it moves from one person to the next. We first determined sustained survival of the pathogen over multiple days in the nasopharynx that might act as a good model for human persistence due to the low numbers of bacteria needed for it to establish. By using successive rounds of colonization of the nasopharynx across different mice we revealed that multiple genetic changes in the S. aureus occurred. These changes were found in genes associated with the cell surface and metabolism and might indicate adaptation to the niche. One gene showed an accumulation of multiple mutations supporting a key contribution in adaptation but the role of the protein it encodes is not yet known. The contribution of these genes and genetic changes are unclear but indicate an area for future research to better understand how this common human pathogen is so successful at human colonization and survival.

MRSA outbreak in a Neonatal Intensive Care Unit in a developed country: importance of rapid detection of reservoirs and implementation of intervention measures

We described a MRSA bloodstream infection outbreak that was rapidly identified and controlled in a Neonatal Intensive Care Unit after implementation of a bundle of measures, including PCR-screening and HCW decolonization. We found 35% of healthcare workers(HCW) colonized with S. aureus by PCR, one of them that presented skin lesion positive for MSSA (same clone and spa type than two patients). Our findings raise the hypothesis that the outbreak could be related to HCW colonization.

Clonal Distribution and Antibiotic Susceptibility of Staphylococcus aureus from Pediatric Patients: 8-Year Trends in a Children's Hospital in Colombia

Emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains in healthcare settings has changed the hospital epidemiology of MRSA in the last few years. Despite a global increase in MRSA frequency, infections caused by methicillin-susceptible S. aureus (MSSA) have persisted in healthcare settings and the community. Staphylococcus aureus isolates were collected between 2009 and 2017 at the Children's Hospital of a Caribbean city in South America. Methicillin-resistant isolates were subjected to SCCmec typing. Representative isolates were analyzed by multilocus sequence typing (MLST) and spa typing. Antibiotic susceptibility was assessed by agar dilution method. D-zone test was performed in erythromycin-resistant isolates to determine macrolide/lincosamide/streptogramin resistance. Spa typing revealed 10 different spa types. The main epidemic clones circulating during the study period were: ST8-MRSA-IVc, ST923-MRSA-IVa and ST8-MRSA-IVa. The study found high frequencies of PVL genes and resistance to erythromycin and clindamycin in the isolates. This study provides the first description of the population structure of MRSA and MSSA causing infections attended in the participating Children's Hospital. ST8-MRSA-IVc, ST923-MRSA-IVa and ST8-MRSA-IVa were the most prevalent in the isolate population.