Community-associated methicillin-resistant Staphylococcus aureus: It's not just in communities anymore

Novel multidrug-resistant sublineages of Staphylococcus aureus clonal complex 22 discovered in India

Staphylococcus aureus is a major pathogen in India causing community and nosocomial infections, but little is known about its molecular epidemiology and mechanisms of resistance in hospital settings. Here, we use whole-genome sequencing (WGS) to characterize 478 S. aureus clinical isolates (393 methicillin-resistant Staphylococcus aureus (MRSA) and 85 methicilin-sensitive Staphylococcus aureus (MSSA) collected from 17 sentinel sites across India between 2014 and 2019. Sequencing results confirmed that sequence type 22 (ST22) (142 isolates, 29.7%), ST239 (74 isolates, 15.48%), and ST772 (67 isolates, 14%) were the most common clones. An in-depth analysis of 175 clonal complex (CC) 22 Indian isolates identified two novel ST22 MRSA lineages, both Panton-Valentine leukocidin+, both resistant to fluoroquinolones and aminoglycosides, and one harboring the the gene for toxic shock syndrome toxin 1 (tst). A temporal analysis of 1797 CC22 global isolates from 14 different studies showed that the two Indian ST22 lineages shared a common ancestor in 1984 (95% highest posterior density [HPD]: 1982-1986), as well as evidence of transmission to other parts of the world. Moreover, the study also gives a comprehensive view of ST2371, a sublineage of CC22, as a new emerging lineage in India and describes it in relationship with the other Indian ST22 isolates. In addition, the retrospective identification of a putative outbreak of multidrug-resistant (MDR) ST239 from a single hospital in Bangalore that persisted over a period of 3 years highlights the need for the implementation of routine surveillance and simple infection prevention and control measures to reduce these outbreaks. To our knowledge, this is the first WGS study that characterized CC22 in India and showed that the Indian clones are distinct from the EMRSA-15 clone. Thus, with the improved resolution afforded by WGS, this study substantially contributed to our understanding of the global population of MRSA. IMPORTANCE The study conducted in India between 2014 and 2019 presents novel insights into the prevalence of MRSA in the region. Previous studies have characterized two dominant clones of MRSA in India, ST772 and ST239, using whole-genome sequencing. However, this study is the first to describe the third dominant clone, ST22, using the same approach. The ST22 Indian isolates were analyzed in-depth, leading to the discovery of two new sublineages of hospital-acquired Staphylococcus aureus in India, both carrying antimicrobial resistance genes and mutations, which limit treatment options for patients. One of the newly characterized sublineages, second Indian cluster, carries the tsst-1 virulence gene, increasing the risk of severe infections. The geographic spread of the two novel lineages, both within India and internationally, could pose a global public health threat. The study also sheds light on ST2371 in India, a single-locus variant of ST22. The identification of a putative outbreak of MDR ST239 in a single hospital in Bangalore emphasizes the need for routine surveillance and simple infection prevention and control measures to reduce these outbreaks. Overall, this study significantly contributes to our understanding of the global population of MRSA, thanks to the improved resolution afforded by WGS.

Methicillin-resistant Staphylococcus aureus, Samoa, 2007-2008

TOC Summary: A wide range of MRSA genotypes cause wound infections.

Little is known about the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in most Pacific Island nations. Relatively high rates of MRSA have been reported in Polynesian people living outside the Pacific Islands. To determine the prevalence and characteristics of MRSA, we assessed wound swabs from 399 persons with skin and soft tissue infection living in Samoa. MRSA was isolated from 9% of study participants; 34 of the 196 S. aureus isolates were MRSA. Five MRSA genotypes were identified; the 3 most common were USA300, the Queensland clone, and a sequence type 1 MRSA strain that shares <85% homology with the sequence type 1 MRSA strain common in the region (WA MRSA-1). The Southwest Pacific MRSA clone was identified but accounted for only 12% of MRSA isolates. The high prevalence of MRSA in Samoa provides impetus for initiatives to improve antimicrobial drug resistance surveillance, infection control, and antimicrobial drug use in Pacific Island nations.

First identification of methicillin-resistant Staphylococcus aureus MLST types ST5 and ST45 and SCCmec types IV and Vt by multiplex PCR during an outbreak in a respiratory care ward in central Taiwan

We used molecular typing methods to investigate an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infections in a respiratory care ward in Taiwan. From March to June 2006, the incidence of MRSA infection increased 3.75-fold. The overall carrier rates among the health care workers (HCWs) were 31.3% (total S. aureus), 16.4% (MRSA), and 14.9% (methicillin-sensitive SA, MSSA). Pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), antibiograms derived from susceptibility testing of MRSA isolates, and multiplex polymerase chain reaction (PCR) provided strong epidemiologic and microbiologic evidence that the outbreak of MRSA infections at our hospital was linked to the same PFGE pulsotype A SCCmec type II, pvl-negative, MLST ST5 strain of MRSA isolated from seven HCWs and five patients. The outbreak was controlled by application of topical fucidin ointment to the anterior nares in all colonized HCWs. Multiplex PCR combined with PFGE and MLST is a feasible method for outbreak investigations in routine clinical laboratories.

Methicillin-resistant Staphylococcus aureus, Samoa, 2007-2008

Little is known about the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in most Pacific Island nations. Relatively high rates of MRSA have been reported in Polynesian people living outside the Pacific Islands. To determine the prevalence and characteristics of MRSA, we assessed wound swabs from 399 persons with skin and soft tissue infection living in Samoa. MRSA was isolated from 9% of study participants; 34 of the 196 S. aureus isolates were MRSA. Five MRSA genotypes were identified; the 3 most common were USA300, the Queensland clone, and a sequence type 1 MRSA strain that shares <85% homology with the sequence type 1 MRSA strain common in the region (WA MRSA-1). The Southwest Pacific MRSA clone was identified but accounted for only 12% of MRSA isolates. The high prevalence of MRSA in Samoa provides impetus for initiatives to improve antimicrobial drug resistance surveillance, infection control, and antimicrobial drug use in Pacific Island nations.

Methicillin-resistant Staphylococcus aureus in Spain: molecular epidemiology and utility of different typing methods

In a point-prevalence study performed in 145 Spanish hospitals in 2006, we collected 463 isolates of Staphylococcus aureus in a single day. Of these, 135 (29.2%) were methicillin (meticillin)-resistant S. aureus (MRSA) isolates. Susceptibility testing was performed by a microdilution method, and mecA was detected by PCR. The isolates were analyzed by pulsed-field gel electrophoresis (PFGE) after SmaI digestion, staphylococcal chromosomal cassette mec (SCCmec) typing, agr typing, spa typing with BURP (based-upon-repeat-pattern) analysis, and multilocus sequence typing (MLST). The 135 MRSA isolates showed resistance to ciprofloxacin (93.3%), tobramycin (72.6%), gentamicin (20.0%), erythromycin (66.7%), and clindamycin (39.3%). Among the isolates resistant to erythromycin, 27.4% showed the M phenotype. All of the isolates were susceptible to glycopeptides. Twelve resistance patterns were found, of which four accounted for 65% of the isolates. PFGE revealed 36 different patterns, with 13 major clones (including 2 predominant clones with various antibiotypes that accounted for 52.5% of the MRSA isolates) and 23 sporadic profiles. Two genotypes were observed for the first time in Spain. SCCmec type IV accounted for 6.7% of the isolates (70.1% were type IVa, 23.9% were type IVc, 0.9% were type IVd, and 5.1% were type IVh), and SCCmec type I and SCCmec type II accounted for 7.4% and 5.2% of the isolates, respectively. One isolate was nontypeable. Only one of the isolates produced the Panton-Valentine leukocidin. The isolates presented agr type 2 (82.2%), type 1 (14.8%), and type 3 (3.0%). spa typing revealed 32 different types, the predominant ones being t067 (48.9%) and t002 (14.8%), as well as clonal complex 067 (78%) by BURP analysis. The MRSA clone of sequence type 125 and SCCmec type IV was the most prevalent throughout Spain. In our experience, PFGE, spa typing, SCCmec typing, and MLST presented good correlations for the majority of the MRSA strains; we suggest the use of spa typing and PFGE typing for epidemiological surveillance, since this combination is useful for both long-term and short-term studies.

Update on bacterial pathogens: virulence and resistance

The present article is an update of the literature on bacterial pathogens. Recognizing the interest and scientific and public health importance of infections produced by bacterial pathogens with new virulence mechanisms and/or new mechanisms of resistance to antimicrobial agents, a multidisciplinary group of Spanish physicians and microbiologists organized a joint session and revised the most important papers produced in the field during 2006. Each article was analyzed and discussed by one of the members of the panel. This paper focus on a variety of diseases that pose major clinical and public health challenges today; and include infections produced by community-acquired methicillin-resistant Staphylococcus aureus and S. aureus small colony variants, infections produced by multiply resistant coagulase-negative staphylococci, pneumococcal infections, human listeriosis, meningococcal disease, Haemophilus influenzae, pertussis, Escherichia coli, ESBL-producing organisms, and infections due to non-fermenters. After a review of the state of the art, papers selected in this field are discussed.

Antimicrobial therapy of multidrug-resistant Streptococcus pneumoniae, vancomycin-resistant enterococci, and methicillin-resistant Staphylococcus aureus

Antibiotic resistance among pneumococci, enterococci, and staphylococci has become increasingly important in recent decades. Clinicians should be familiar with the nuances of antibiotic susceptibility testing and interpretation in selecting antibiotics for these infections. The clinical significance of penicillin-resistant Streptococcus pneumoniae, macrolide-resistant S pneumoniae, and multidrug-resistant S pneumoniae is discussed. The clinical spectrum and therapeutic approach to Enterococcus faecalis (i.e., vancomycin-sensitive enterococci) and E faecium (i.e., vancomycin-resistant enterococci) are discussed. Differences in therapeutic approach between methicillin-sensitive Staphylococcus aureus and methicillin-resistant S aureus (MRSA) infections are reviewed. Differences between in vitro susceptibility testing and in vivo effectiveness of antibiotics for hospital-acquired MRSA (HA-MRSA) are described. Finally, the clinical features of infection and therapy of HA-MRSA and community-acquired MRSA (CA-MRSA) infections are compared.