Nasal Carriage and Associated Factors of Methicillin-Resistant Staphylococcus Aureus Among Medicine and Health Science Students of Arba Minch University, Arba Minch, Ethiopia

Individuals with Methicillin-Resistant Staphylococcus aureus (MRSA) colonized nasal cavities were at greater risk of developing the infection and can serve as potential reservoirs of transmission. Aim of this study is to determine the extent of nasal carriage and associated factors linked to MRSA in medical and health science students of Arba Minch University (AMU), Ethiopia. An institution based cross-sectional study was conducted at AMU from 01st August through 30th November, 2020. A systematic sampling technique was used to recruit the participants. Socio-demographic data were collected using a structured questionnaire. Nasal swabs were collected and S. aureus were identified following standard microbiological methods. Methicillin resistance was tested using cefoxitin disk and antimicrobial susceptibility tests were performed by Kirby-Bauer disk diffusion. Biofilm forming ability was phenotypically detected by micro-titer plate assay. Descriptive statistics and multivariable logistic regression analysis were done by Statistical Package for Social Service (SPSS) version 25. Overall prevalence of Staphylococcus aureus and MRSA were 27.1% (70/258) and 7.4% (19/258) respectively. Methicillin-Resistant S. aureus carriage was higher among medical interns, 16.9% (11/65); isolates were co-resistant to antibiotics, such as trimethoprim-sulfamethoxazole (63.2%) and tetracycline (48.4%). Multidrug resistance (MDR) was observed among 52.6% (10/19) of the isolates. Besides, 31.4% (6/19) of MRSA were biofilm producers and all of them were MDR. Multivariable analysis showed that students having >2 years of mean exposure to hospital [p= 0.048, AOR: 4.99, 95% CI: 1.01-24.66] and those who share clothing and sports equipment [p=0.017, AOR: 5.43, 95% CI: 1.35-21.83] were statistically significant. The overall prevalence of nasal MRSA among students were comparatively lower than that observed in other studies done in Ethiopia itself. An alarming factor is that, 60% of MDR-MRSA were biofilm producers.

Mupirocin Resistance of Staphylococcus aureus in Clinical Isolates of National Hospital and in the Nasal Carriage of Healthy Undergraduates in Colombo, Sri Lanka

Introduction and Objectives : Mupirocin resistance in Staphylococcus aureus is increasingly reported in many parts of the world. This study was conducted with the objective of describing high-level and low-level mupirocin resistance of S. aureus in clinical isolates and nasal carriage. Materials and Methods : A descriptive study was conducted including 45 nasal isolates of S. aureus collected from healthy university students in Colombo and 249 clinical isolates of S. aureus from the patient specimens in National Hospital of Sri Lanka. All of the confirmed S. aureus strains were tested for methicillin resistance using cefoxitin disc (30μg). S. aureus isolates were considered methicillin-resistant if the diameter of zone of inhibition was 21mm or less (CLSI, 2017). The S. aureus isolates were then tested for mupirocin resistance. Disk diffusion method was utilized with 5μg and 200μg mupirocin discs to determine low-level and high-level resistances respectively. The criterion employed for interpretation of mupirocin resistance was a combination of the widely accepted criterion described by Finlay, Miller, and Poupard (1997) for low-level mupirocin resistance and CLSI (2017) criterion for high-level mupirocin resistance. If both inhibition zone diameters for 5μg disk and 200μg were ≥14mm, the isolate was considered mupirocin sensitive. If 5μg disc displays <14mm and 200 μg disk displayed ≥14mm inhibition zone diameter, the isolate was considered to be mupirocin low level resistant. If there is no inhibition zone in 200μg disk, the isolate was considered as mupirocin high level resistant. Results : From the 45 nasal carriage isolates, 33 (73%) were Methicillin sensitive Staphylococcus aureus (MSSA) and 12 (27%) were Methicillin Resistant Staphylococcus aureus (MRSA). Among the clinical isolates, majority (n=158, 63%) were MRSA while only 91 (37%) MSSA. An overall mupirocin resistance rate of 4.4% among S. aureus was observed. Low-level mupirocin resistance was observed in 3.7% Staphylococcus aureus isolates and high-level mupirocin resistance was observed in 0.7% isolates. Mupirocin low-level and high-level resistance in MRSA isolates were 5.3% and 0.6% respectively. MSSA isolates demonstrated 1.6% (n=2) and 0.8% (n=1) mupirocin low-level and high-level resistances respectively. None of the nasal isolates were resistant to mupirocin while 6% (n=15) mupirocin low-level resistance and 0.8% (n=2) mupirocin high-level resistance was observed in clinical isolates. Conclusion : This initial survey of mupirocin resistance among S. aureus in a country with fairly high usage of mupirocin emphasizes that although the overall mupirocin resistance is relatively low in this population, regular surveillance of mupirocin resistance remains a necessity.

Investigation of extramammary sources of Group B Streptococcus reveals its unusual ecology and epidemiology in camels

Camels are vital to food production in the drylands of the Horn of Africa, with milk as their main contribution to food security. A major constraint to camel milk production is mastitis, inflammation of the mammary gland. The condition negatively impacts milk yield and quality as well as household income. A leading cause of mastitis in dairy camels is Streptococcus agalactiae, or group B Streptococcus (GBS), which is also a commensal and pathogen of humans and cattle. It has been suggested that extramammary reservoirs for this pathogen may contribute to the occurrence of mastitis in camels. We explored the molecular epidemiology of GBS in camels using a cross-sectional study design for sample collection and phenotypic, genomic and phylogenetic analysis of isolates. Among 88 adult camels and 93 calves from six herds in Laikipia County, Kenya, GBS was detected in 20% of 50 milk samples, 25% of 152 nasal swabs, 8% of 90 oral swabs and 3% of 90 rectal swabs, but not in vaginal swabs. Per camel herd, two to four sequence types (ST) were identified using Multi Locus Sequence Typing (MLST). More than half of the isolates belonged to ST617 or its single-locus variant, ST1652, with these STs found across all sample types. Capsular serotype VI was detected in 30 of 58 isolates. In three herds, identical STs were detected in milk and swab samples, suggesting that extramammary sources of GBS may contribute to the maintenance and spread of GBS within camel herds. This needs to be considered when developing prevention and control strategies for GBS mastitis. The high nasal carriage rate, low recto-vaginal carriage rate, and high prevalence of serotype VI for GBS in camels are in stark contrast to the distribution of GBS in humans and in cattle and reveal hitherto unknown ecological and molecular features of this bacterial species.

Antimicrobial resistance determinants are associated with Staphylococcus aureus bacteraemia and adaptation to the healthcare environment: a bacterial genome-wide association study

Staphylococcus aureus is a major bacterial pathogen in humans, and a dominant cause of severe bloodstream infections. Globally, antimicrobial resistance (AMR) in S. aureus remains challenging. While human risk factors for infection have been defined, contradictory evidence exists for the role of bacterial genomic variation in S. aureus disease. To investigate the contribution of bacterial lineage and genomic variation to the development of bloodstream infection, we undertook a genome-wide association study comparing bacteria from 1017 individuals with bacteraemia to 984 adults with asymptomatic S. aureus nasal carriage. Within 984 carriage isolates, we also compared healthcare-associated (HA) carriage with community-associated (CA) carriage. All major global lineages were represented in both bacteraemia and carriage, with no evidence for different infection rates. However, kmers tagging trimethoprim resistance-conferring mutation F99Y in dfrB were significantly associated with bacteraemia-vs-carriage (P=10-8.9-10-9.3). Pooling variation within genes, bacteraemia-vs-carriage was associated with the presence of mecA (HMP=10-5.3) as well as the presence of SCCmec (HMP=10-4.4). Among S. aureus carriers, no lineages were associated with HA-vs-CA carriage. However, we found a novel signal of HA-vs-CA carriage in the foldase protein prsA, where kmers representing conserved sequence allele were associated with CA carriage (P=10-7.1-10-19.4), while in gyrA, a ciprofloxacin resistance-conferring mutation, L84S, was associated with HA carriage (P=10-7.2). In an extensive study of S. aureus bacteraemia and nasal carriage in the UK, we found strong evidence that all S. aureus lineages are equally capable of causing bloodstream infection, and of being carried in the healthcare environment. Genomic variation in the foldase protein prsA is a novel genomic marker of healthcare origin in S. aureus but was not associated with bacteraemia. AMR determinants were associated with both bacteraemia and healthcare-associated carriage, suggesting that AMR increases the propensity not only to survive in healthcare environments, but also to cause invasive disease.

Molecular Epidemiology, Virulence Factors, Antibiotic Resistance and Risk Factors for Nasal Carriage of Staphylococcus aureus in A Teenage Student Population: High Prevalence of Oxacillin Susceptible MRSA Isolates

Background: Asymptomatic carriage of Staphylococcus aureus can lead to endogenous infections and cross-transmission to other individuals. Objectives: The prevalence, molecular epidemiology, antibiotic resistance, and risk factors for nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) were studied in school children in Ardabil, Iran. Methods: Totally, 510 nasal samples were collected during 2017. Isolates were identified and subjected to antimicrobial susceptibility testing, identification of oxacillin resistance, and molecular typing. Results: Totally, 13.5% of volunteers were positive for methicillin-susceptible Staphylococcus aureus (MSSA) and 17.5% colonized with mecA positive S. aureus strains, including 6.07% oxacillin-resistant MRSA (OR-MRSA) and 11.56% oxacillin-susceptible MRSA (OS-MRSA). Excluding β-lactam antibiotics, high resistance rate was observed for erythromycin (71%), tetracycline (25.8%), clindamycin (35%) in our isolates. Surprisingly, 11% of the isolates [OR-MRSA (25.8%), OS-MRSA (10.1%), and MSSA (5.7%) isolates] were resistant to mupirocin. Moreover, 18 (58%), 29 (49%), and 29 (42%) of OR-MRSA, OS-MRSA, and MSSA isolates were multidrug-resistant (MDR), respectively. Overall, 97.48% of isolates carried ≥ 3 toxin encoding genes. The pvl gene was found in 46 (29%) isolates. In comparison, 25.50% of MRSA (9.60% OR-MRSA and 34% OS-MRSA) and 33% of MSSA isolates carried pvl gene. SCCmec type IV had the highest rate among OR-MRSA (87%) and OS-MRSA (74.5%) isolates, which indicates CA-MRSA phenotype. Eleven and 21 spa types were identified in OR-MRSA, and OS-MRSA isolates, respectively. The most common spa types were t11332 (14.3%) and t012 (11.4%) in OS-MRSA isolates. ERIC-PCR revealed high genetic diversity among isolates. The number of students in classroom and incomplete antibiotic course were associated with OS-MRSA nasal carriage. Conclusions: This study showed a high proportion of MDR CA-MRSA nasal carriage among Iranian healthy school children community.