Abstract
Staphylococci are normally harmless commensals occurring on the skin, mucous membrane and the general environment. However, they are increasingly implicated in different infectious states. Of particular interest is the advent of methicillin-resistant Staphylococcus aureus (MRSA) with its attendance resistance to beta lactam antibiotics. Several infectious states are now emerging with staphylococci being implicated in the infections, e.g. S. saprophyticus has been implicated in urogenital infection. It would be interesting to document the prevalence of staphylococci in different infectious state. The identification of staphylococci is supposed to be a straightforward procedure, but an alarming misidentification rate is emerging in low resource laboratories, especially in places where identification is solely by growth and fermentation on mannitol salt agar (MSA). Finally, empirical treatment of any staphylococci infection will depend on local suspectibility pattern of the strains as the susceptibilities vary from environment to environment. This chapter summarizes the current knowledge regarding the prevalence, diagnosis and local susceptibility of staphylococci in different parts of the world.
Keywords
- misdiagnosis
- prevalence
- susceptibility
- staphylococci
- antibiotics
- identification
1. Introduction
Staphylococci have long history and association with mankind. From their presence in amniotic fluid, all through to adulthood, they were once regarded as harmless commensals with beneficial effects, e.g. by competing with pathogenic bacteria, but they are now implicated in life-threatening infections. Coagulase-negative staphylococci (CoNS) cause invasive infections in some vulnerable groups of patients, e.g. immunocompromised patients, preterm neonates and people with indwelling medical devices [1].
Most
The main aim of this chapter therefore is to highlight the current knowledge on prevalence, diagnosis and local susceptibility of staphylococci in different parts of the world.
2. Prevalence of staphylococci infections
2.1. Prevalence of staphylococci in different diseased condition
There are emerging facts on the role of staphylococci in central nervous system infections. In a multinational study performed with 2583 patients in 37 referral centers in 20 countries to understand the burden of community-acquired central nervous system infections between 2012 and 2014 [10], staphylococci and
The role of staphylococci in burns and skin infections is well documented. In a retrospective study of 123 patients hospitalized in the burn center of Marrakech over a period of 3 years (2013–2016), there were 103 infections per 1000 days of treatment in different infective sites (blood (18%), skin (69%), lungs (1%) and urinary tract (12%)) with the main infectious organisms being:
Staphylococci are frequently implicated in hospital-acquired bacteremia especially those associated with intravascular catheters and staphylococcal bacteremia and they are important cause of morbidity. A study that described the epidemiology of healthcare-associated bloodstream infections for 71,039 patients in 338 Polish hospitals between 2012 and 2015 found that the most frequently isolated microorganisms were staphylococci (45.6%) and most of them were coagulase-negative (64.4%) and usually caused catheter-related infections. Of 53
Immunocompromised patients are at higher risk of staphylococcal infections. In a study over a period of 1 year of
Staphylococci are frequently implicated in neonatal infections usually within 6 week after birth with diseased conditions such as skin lesions, pneumonia, bacteremia, meningitis. In an epidemiology study of neonatal infection from 2005 to 2014 in 30 UK neonatal units,
Otitis media is an inflammation of middle ear which may lead to hearing loss.
2.2. MRSA prevalence in Africa
There is variable information on prevalence of MRSA in Africa. The prevalence was lower than 50% in most African countries and higher prevalence since 2000 has been observed in many African countries (except South Africa). In South Africa, the prevalence decreased between 2006 and 2011, while it varied between 23 and 44% for 2000–2007 in Botswana. It increased from 16 to 41% between 2002 and 2007 in Tunisia; in Libya, MRSA prevalence was 31% in 2007, while in Egypt and Algeria the prevalence was 45 and 52% between 2003 and 2005, respectively, while northern Nigerian had higher MRSA prevalence than the southern part with 55 and 39% prevalence in Ethiopia and Ivory Coast, respectively [22].
In a review of 34 reports from 15 countries in Africa, CC5 is the predominant clonal complex in healthcare setting in Africa. Hospital-associated MRSA was identified in nine African countries with limited spread of European ST80-IV clone to Algeria, Egypt and Tunisia and lack of distinct difference between MRSA responsible for hospital and community infections. However, the community clones (ST8-IV and ST88-IV) were observed in the hospital and community settings in Madagascar, Angola, Príncipe, Cameroon, Ghana, Gabon, Nigeria and São Tomé [23].
The overall prevalence of MRSA was 22.6% from 142
A significant decline in antibiotic resistance was observed in Northeastern Nigeria in contrast to the worldwide trend of increasing resistance rates as stated in a study involving changes in population structure of
3. Diagnosis of staphylococci infections
Identification of staphylococci is supposed to be a simple straightforward procedure that involves culturing of clinical specimens or pure bacterial strains on Columbia agar, mannitol salt agar (MSA) or tryptic soy blood agar. If pure biochemical identification is to be used, then Gram-positive, nonmotile, non-spore-forming, facultative anaerobic cocci occurring mainly in clusters and catalase-positive strains are selected for further tests. Coagulase test will distinguish between
3.1. Overview of different staphylococci identification methods
Rapid latex and hemagglutination assays allows presumptive identification of
There are commercial and automated systems for identification of staphylococci, e.g. Staphylococcus-specialized API Staph, Vitek 2, Rapidec Staph and ID32 Staph strips (bioMérieux) system, BBL Phoenix automated microbiology system, Crystal identification system’s Rapid Gram-Positive ID kit (BD, MD), Pos ID Panel family (Siemens, Deerfield, IL), Sherlock microbial identification system (MIDI, Newark, DE) and the Biolog systems (Biolog, Hayward, CA) [6].
There are also several molecular approaches for identification of staphylococci. Conserved regions with species-specific sequences of universally occurring genes are amplified, for differentiation at the species level, e.g. 16S and 23S rRNA,
SCV strains grow on blood agar as pinpoint colonies and they are often nonreactive in normal biochemical tests because their laboratory detection could be affected by their altered metabolism and long generation time. Therefore, molecular methods, such as amplification of species-specific DNA targets or 16S rRNA partial sequencing, become the method of choice for their identification [35].
Microarray-based diagnostics test may combine identification of staphylococci with detection of virulence factors and drug resistance in strains. In positive blood culture smears, a nucleic acid hybridization assay (
Identification of MRSA is primarily by cefoxitin disk screen test, the latex agglutination test for PBP2a or selective chromogenic agars [30]. Commercial tests are also available for identification of MRSA with combined detection of
In some institutions, there is active surveillance that uses rapid laboratory techniques to evaluate nasal swab specimens and routinely screen admitted patients, e.g. high-risk patients, patients with previous MRSA infection, vascular, orthopedic, or cardiac surgery patients for MRSA.
3.2. Wrong identification of staphylococci
Due to lack of adequate resources, wrong identification of
One hundred and eight-five isolates that had been previously isolated from the nares of college students’ volunteers in Southern Nigeria were identified by various methods. Growth on MSA and slide coagulase tests was highly inaccurate for identification of
In another study by Ayeni and Odumosu [40], it was noted that some organisms are being wrongly identified as
We also studied 171 strains of CoNS which have been previously identified as
4. Susceptibility of staphylococci to antibiotics
As a basic principle, empiric use of antimicrobials should be guided by local epidemiology and antimicrobial susceptibility pattern as well as the clinical state of the patient, with final therapy determined by culture and sensitivity data. Vancomycin is the drug of choice for the treatment of MRSA infections, while clindamycin is the commonly used antimicrobial for CA-MRSA infections. However, many strains are emerging with reduced susceptibility to vancomycin for
In an antibiotic susceptibility study, 75.9% sensitivity to rifampicin, 100% sensitivity to vancomycin and linezolid was reported in catheter-related bloodstream infections in 58 (20
In another study on molecular epidemiology of trimethoprim resistance in 598 human
Susceptibility of
Daptomycin and quinupristin/dalfopristin have been proposed as an alternative to glycopeptides in the treatment of MRSA infections, while the use of telithromycin is discouraged [44]. Also, all MRSAs were sensitive to amikacin, ciprofloxacin and chloramphenicol, while all methicillin-sensitive
Osteomyelitis occurs more frequently in children, causing pains, chills and fever. Osteomyelitis regularly involves prolonged systemic antibiotic use, and dalbavancin, linezolid and vancomycin were active against staphylococci implicated in bone and joint infections [45].
All
Ayeni et al. [30] reported susceptible to fusidic acid, rifampicin clindamycin, vancomycin and linezolid, with observed high resistance to penicillin and trimethoprim in 185 staphylococci, which had been previously isolated from the nares of college students’ volunteers in Southern Nigeria. In another study by Ayeni et al. [31] where the current resistant pattern of
Another study in our group determined antimicrobial resistance of staphylococci isolated from urogenital tracts of humans with a presumptive diagnosis of urinary tract infection in 45 urogenital samples (endocervical swab, high vaginal swab and urine) from outpatients at Igbinedion University Teaching Hospital between April and May 2010. Ten isolates (22% of the total samples) of staphylococci were obtained. All the isolates were multidrug resistant with exhibited resistance to ≥5 antimicrobials and 100% resistance to ciprofloxacin, nitrofurantoin, augmentin, ampicillin and ceftriazone. All CoNS strains were susceptible to doxycycline, while
Ceftobiprole and ceftaroline are new cephalosporins active against
4.1. Susceptibility of staphylococci to non-antibiotic substances
Other natural and beneficial bacteria have been found to be effective against staphylococci in vitro. This has been demonstrated in previous studies. The first discussion is on medicinal plants that have been proven over many generations to be effective against several infectious diseases. The plants from the genus
Lactic acid bacteria (LAB) are beneficial bacteria with good antimicrobial activities against many pathogenic bacteria. We reported good inhibition of growth of uropathogenic
In a recently published co-culture study that we did with LAB and MRSA, the cell free supernatant of
5. Conclusion
Staphylococci are implicated in various infectious states in different parts of the world with high prevalence. However, characteristics growth on mannitol salt agar is insufficient to differentiate between
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