PCR-based detection of genes encoding virulence determinants in Staphylococcus aureus from bovine subclinical mastitis cases

Biofilm formation, agr typing and antibiotic resistance pattern in methicillin-resistant Staphylococcus aureus isolated from hospital environments

Biofilm development significantly enhances the virulence of methicillin-resistant Staphylococcus aureus (MRSA), leading to severe infections and decreased susceptibility to antibiotics, especially in strains associated with hospital environments. This study examined the occurrence of MRSA, their ability to form biofilms, agr typing, and the antibiotic resistance profiles of biofilm-forming MRSA strains isolated from environmental surfaces at Mymensingh Medical College Hospital (MMCH). From 120 swab samples, 86 (71.67%) tested positive for S. aureus. MRSA was identified in 86 isolates using the disk diffusion technique, and by polymerase chain reaction (PCR), 56 (65.1%) isolates were confirmed to carry the mecA gene. The Crystal Violet Microtiter Plate (CVMP) test revealed that 80.35% (45 isolates) were biofilm-forming and 19.6% (11 isolates) were non-biofilm-forming. Out of 45 biofilm producer isolates 37.5% and 42.9% isolates exhibited strong and intermediate biofilm-forming characteristics, respectively. Molecular analysis revealed that 17.78% of MRSA isolates carried at least one gene related to biofilm formation, specifically icaA, icaB, and icaD genes were discovered in 13.33%, 8.89%, 6.67% of the MRSA isolates, respectively. In agr typing, the most prevalent group was agr I (71.11%), followed by group III (17.78%) and group II (11.11%). Group IV was not detected. The distribution of agr gene groups showed a significant difference among biofilm-forming isolates (p < 0.05). In agr group I, 18.75% of isolates carried the icaA gene, 12.5% carried the icaB gene, and 9.37% carried the icaD gene. Biofilm-forming genes were not detected in any of the isolates from agr groups II or III. There are no statistically significant differences between agr groups and the presence of these genes (p > 0.05). Antibiotic resistance varied significantly among agr groups, with agr group I displaying the highest resistance, agr group II, and agr group III exhibiting the least resistance (p < 0.05). Seventy-three (73.3%) of the isolates were multi-drug resistant, with agr group I displaying nineteen MDR patterns. The occurrence of MRSA in hospital environments and their capacity to form biofilm raises concerns for public health. These findings support the importance of further research focused on agr quorum sensing systems as a basis for developing novel antibacterial agents.

Zoonotic linkage and environmental contamination of Methicillin-resistant Staphylococcus aureus (MRSA) in dairy farms: A one health perspective

Methicillin-Resistant Staphylococcus aureus (MRSA) is a ubiquitous public health challenge, with its prevalence in human, animal, and environmental interfaces posing significant concerns. This study aimed to characterize and detect the zoonotic linkages of MRSA within the cow-environment-human interfaces in dairy farms to address the One Health perspective. A comprehensive investigation, involving 636 samples (an equal number of raw milk and cow nasal swab samples, along with varying numbers of human nasal swab and environmental samples), revealed an overall MRSA prevalence of 13.4% (n = 271/636). Notably, environmental samples exhibited the highest prevalence (19.3%), emphasizing the potential role of farm surroundings in MRSA transmission, while the lowest prevalence was found in raw milk at 11.8% (n = 31/263). The prevalence in cow nasal swabs and human nasal swabs was 13.3% (n = 35/263) and 15.1% (n = 8/53), respectively. Multiplex PCR analysis revealed the presence of different Staphylococcal enterotoxin (SEa, SEb, SEc, and SEd), and exfoliative toxin-producing genes (Eta, Etb) within the MRSA isolates underlining their potential to induce public health threats. All MRSA isolates exhibited complete resistance to Oxacillin (100%) and Amoxicillin (100%), while the highest sensitivity was observed for Vancomycin (85.8%). Furthermore, these MRSA strains demonstrated varying degrees of resistance to other commonly used antimicrobial drugs, including Cefoxitin (75.3%), Ceftarolin (71.2%), Sulfamethoxazole-Trimethoprim (63.5%), Ciprofloxacin (60%), and Gentamicin (49.5%). Detection of MRSA in cow, human, and environmental samples within the same farm vicinity highlights the risk of zoonotic transmission of MRSA from cows to humans through environmental interfaces. Phylogenetic analysis of the mecA gene in MRSA isolates from all sources within the same farm revealed a high similarity index (>84%) among them suggesting a shared evolutionary origin. Moreover, the MRSA isolates from milk samples showed a close evolutionary relationship with isolates from Kenya and Brazil, while the isolates from humans and the environment displayed noticeable resemblance to isolates from several Asian countries. The findings emphasize the importance of collaborative efforts under the One Health framework to address this multifaceted issue and ensure the safety of our food supply and public health.

Detection of Staphylococcus Isolates and Their Antimicrobial Resistance Profiles and Virulence Genes from Subclinical Mastitis Cattle Milk Using MALDI-TOF MS, PCR and Sequencing in Free State Province, South Africa

Staphylococcus species are amongst the bacteria that cause bovine mastitis worldwide, whereby they produce a wide range of protein toxins, virulence factors, and antimicrobial-resistant properties which are enhancing the pathogenicity of these organisms. This study aimed to detect Staphylococcus spp. from the milk of cattle with subclinical mastitis using MALDI-TOF MS and 16S rRNA PCR as well as screening for antimicrobial resistance (AMR) and virulence genes. Our results uncovered that from 166 sampled cows, only 33.13% had subclinical mastitis after initial screening, while the quarter-level prevalence was 54%. Of the 50 cultured bacterial isolates, MALDI-TOF MS and 16S rRNA PCR assay and sequencing identified S. aureus as the dominant bacteria by 76%. Furthermore, an AMR susceptibility test showed that 86% of the isolates were resistant to penicillin, followed by ciprofloxacin (80%) and cefoxitin (52%). Antimicrobial resistance and virulence genes showed that 16% of the isolates carried the mecA gene, while 52% of the isolates carried the Lg G-binding region gene, followed by coa (42%), spa (40%), hla (38%), and hlb (38%), whereas sea and bap genes were detected in 10% and 2% of the isolates, respectively. The occurrence of virulence factors and antimicrobial resistance profiles highlights the need for appropriate strategies to control the spread of these pathogens.

Identification of the Enterotoxigenic Potential of Staphylococcus spp. from Raw Milk and Raw Milk Cheeses

This study aimed to genotypic and phenotypic analyses of the enterotoxigenic potential of Staphylococcus spp. isolated from raw milk and raw milk cheeses. The presence of genes encoding staphylococcal enterotoxins (SEs), including the classical enterotoxins (sea-see), non-classical enterotoxins (seg-seu), exfoliative toxins (eta-etd) and toxic shock syndrome toxin-1 (tst-1) were investigated. Isolates positive for classical enterotoxin genes were then tested by SET-RPLA methods for toxin expression. Out of 75 Staphylococcus spp. (19 Staphylococcus aureus and 56 CoNS) isolates from raw milk (49/65.3%) and raw milk cheese samples (26/34.7%), the presence of enterotoxin genes was confirmed in 73 (97.3%) of them. Only one isolate from cheese sample (1.3%) was able to produce enterotoxin (SED). The presence of up to eight different genes encoding enterotoxins was determined simultaneously in the staphylococcal genome. The most common toxin gene combination was sek, eta present in fourteen isolates (18.7%). The tst-1 gene was present in each of the analyzed isolates from cheese samples (26/34.7%). Non-classical enterotoxins were much more frequently identified in the genome of staphylococcal isolates than classical SEs. The current research also showed that genes tagged in S. aureus were also identified in CoNS, and the total number of different genes detected in CoNS was seven times higher than in S. aureus. The obtained results indicate that, in many cases, the presence of a gene in Staphylococcus spp. is not synonymous with the ability of enterotoxins production. The differences in the number of isolates with genes encoding SEs and enterotoxin production may be mainly due to the limit of detection of the toxin production method used. This indicates the need to use high specificity and sensitivity methods for detecting enterotoxin in future studies.

Antimicrobial resistance patterns of Staphylococcus aureus isolated from apparently healthy pet cats of Bangladesh

Objective

This study sought to determine the occurrence, molecular identification, antimicrobial-resistant trends, and gene distribution of Staphylococcus aureus in pet cats and their owners' hand swabs.

Materials and Methods

From different places and clinics in Mymensingh and Dhaka, 168 pet cat samples and 42 hand swab samples from cat owners were obtained. The organisms were scrutinized by assessing the outcomes using conventional and molecular techniques. The disc diffusion technique was applied to find the resistance pattern against 12 antibiotics, and genes were discovered by targeting specific genes using PCR.

Results

The occurrence of pathogenic S. aureus in pet cats was 7.74%, while it was 9.50% in pet owners' hand swabs, and 25.0% of the pet owner's hand swabs contained these genes. Staphylococcus aureus was utterly resistant to amoxicillin, ampicillin, cefixime, erythromycin, and imipenem in both pet cat and hand swabs of pet owner samples. All S. aureus isolates had a multidrug-resistant phenotype, and 1 from pet cats (O19) and 1 from pet owner hand swabs (H9) were resistant to all 12 antibiotics in the 7 antimicrobial classes. Several antibiotic-resistance genes were detected by PCR.

Conclusion

The study confirmed multidrug-resistant pathogenic S. aureus in pet cats and their owners in Bangladesh, indicating a major health risk to both people and cats. Thus, a holistic and integrated one-health approach between veterinary and medical specialists is needed to mitigate the global distribution of these zoonotic antibiotic-resistant S. aureus strains.

Virulence genes and antibiotic resistance profiles of Staphylococcus aureus isolated from bovine mastitis milk samples

Background

The increasing importance of antibiotic resistance shows the need for determining indices of the epidemiology of infection.

Aims

This study aimed to determine the virulence genes and antibiotic resistance profiles of Staphylococcus aureus isolated from bovine mastitis cases.

Methods

A total of 200 cattle were selected based on California Mastitis Test (CMT) results, and the samples were cultured in the laboratory. Grown colonies were examined by conventional phenotypic methods and confirmed using PCR amplification of 16S rRNA gene. The prevalence of the virulence genes was also defined. The results of phenotypic and molecular tests were compared using SPSS software by McNemar test. Then, the confirmed isolates were tested for antibiotic susceptibility using the disc diffusion method.

Results

Of the 200 positive CMT cattle, 24 animals were positive for S. aureus and confirmed using 16S rRNA gene amplification. Statistical analysis showed that the phenotypic and genotypic tests of hemolysin genes were not significantly different (P>0.01). PCR analysis revealed the presence of coa and clfa genes in more than half of the cases. Overall, nine genetic profiles of virulence factors were found among S. aureus isolates. The highest and lowest resistance rates were against penicillin and gentamicin, respectively.

Conclusion

Our findings showed a high rate of antibiotic resistance. So, accurate and fast diagnosis and antimicrobial susceptibility tests should be considered before prescribing the drugs.

Phenotypic and Genotypic Detection of Biofilm-Forming Staphylococcus aureus from Different Food Sources in Bangladesh

Staphylococcus aureus is a major foodborne pathogen. The ability of S. aureus to produce biofilm is a significant virulence factor, triggering its persistence in hostile environments. In this study, we screened a total of 420 different food samples and human hand swabs to detect S. aureus and to determine their biofilm formation ability. Samples analyzed were meat, milk, eggs, fish, fast foods, and hand swabs. S. aureus were detected by culturing, staining, biochemical, and PCR. Biofilm formation ability was determined by Congo Red Agar (CRA) plate and Crystal Violet Microtiter Plate (CVMP) tests. The icaA, icaB, icaC, icaD, and bap genes involved in the synthesis of biofilm-forming intracellular adhesion compounds were detected by PCR. About 23.81% (100/420; 95% CI: 14.17−29.98%) of the samples harbored S. aureus, as revealed by detection of the nuc gene. The CRA plate test revealed 20% of S. aureus isolates as strong biofilm producers and 69% and 11% as intermediate and non-biofilm producers, respectively. By the CVMP staining method, 20%, 77%, and 3% of the isolates were found to be strong, intermediate, and non-biofilm producers. Furthermore, 21% of S. aureus isolates carried at least one biofilm-forming gene, where icaA, icaB, icaC, icaD, and bap genes were detected in 15%, 20%, 7%, 20%, and 10% of the S. aureus isolates, respectively. Bivariate analysis showed highly significant correlations (p < 0.001) between any of the two adhesion genes of S. aureus isolates. To the best of our knowledge, this is the first study in Bangladesh describing the detection of biofilm-forming S. aureus from foods and hand swabs using molecular-based evidence. Our findings suggest that food samples should be deemed a potential reservoir of biofilm-forming S. aureus, which indicates a potential public health significance.

Molecular detection of vancomycin and methicillin resistance in Staphylococcus aureus isolated from food processing environments

Staphylococcus aureus is a well-known foodborne pathogen. The aim of this study was to investigate the presence of S. aureus isolated from serving utensils in food processing environments in Mymensingh city, Bangladesh and to determine their antibiogram and resistance determinants. A total of 120 environmental samples were collected from different food settings. Isolation and identification were conducted using conventional biochemical tests. Molecular identification of isolates and detection of methicillin and vancomycin resistance were done using primer-specific polymerase chain reaction (PCR) targeting Tuf, nuc, mecA, and mecC genes. Antibiotic sensitivity tests were performed, and resistance genes were also detected by amplifying bla TEM , vanA, vanB, and vanC genes. Among the 120 samples, 81 (67.5%) were positive for Staphylococcus spp. and 41 (50.62%) were positive for the nuc-gene. Among the 41 isolates, 5 (12.20%) were positive for mecA, but none were positive for the mecC gene. A total of 12.2% of the isolates were vanC-positive, of which 4 isolates (9.76%) were also positive for the mecA gene. Antibiotic sensitivity testing revealed that all S. aureus isolates (100%) from hotel samples were sensitive to ciprofloxacin and chloramphenicol, 90.32% were sensitive to doxycycline, and 80.65% were sensitive to streptomycin. Conversely, all isolates (100%) were resistant to ampicillin, and 29.03% were resistant to vancomycin. All S. aureus isolates obtained from non-hotel samples were susceptible to chloramphenicol, ceftriaxone, ciprofloxacin, doxycycline, meropenem, and vancomycin; however, 40% of isolates were resistant to novobiocin. Among the hotel isolates, 29 (93.55%) of the ampicillin-resistant isolates harbored the blaTEM gene while 5 (55.55%) of the vancomycin-resistant isolates harbored the vanC gene. Four of the five vanC positive isolates were also positive for the mecA gene. The presence of methicillin-resistant S. aureus (MRSA) which is also vancomycin-resistant in food processing environments is a threat to public health. This is the first report on the molecular detection of methicillin and vancomycin-resistant S. aureus isolated from food processing environments in Bangladesh.

Higher seasonal temperature enhances the occurrence of methicillin resistance of Staphylococcus aureus in house flies (Musca domestica) under hospital and environmental settings

Antimicrobial resistance (AMR) emergence in commensal and pathogenic bacteria is a global health issue. House flies (Musca domestica) are considered as biological and mechanical vectors for pathogens causing nosocomial infections, including methicillin-resistant Staphylococcus aureus (MRSA). However, the prevalence of antimicrobial resistance and the role of temperature on the occurrence of Staphylococcus aureus and MRSA in house flies in a hospital environment have not been studied. A total of 400 house flies were collected in winter and summer from four hospital-associated areas in Mymensingh, Bangladesh. Detection of S. aureus and MRSA in flies was done by culturing, staining, and PCR methods targeting nuc and mec genes (mecA and mecC), respectively. Disc diffusion test was used to detect resistance phenotype against six antimicrobials. Logistic regression models were constructed to assess the effect of temperature on the frequency of antimicrobial resistance, and on the presence of the nuc and mecA genes, and location of samples in and around a hospital environment. By PCR, S. aureus was detected in 208 (52%) samples. High frequencies of resistance (≥ 80% of isolates) to amoxicillin, azithromycin, and oxacillin were observed by disk diffusion test. Increase in temperature had a positive effect on the occurrence of S. aureus and MRSA isolates as well as on their resistance to individual and multiple antimicrobials. Among the study areas, hospital premises had increased odds of having S. aureus. Increased temperature of summer significantly increased the occurrence of MRSA in house flies in and around the hospital environment, which might pose a human and animal health risk.

Prevalence and Characterization of Coagulase Positive Staphylococci from Food Products and Human Specimens in Egypt

Methicillin-resistant Staphylococcus aureus (MRSA) strains have veterinary and public health importance as they are responsible for a wide range of difficult to treat infections and food poisoning. Two hundred samples (50 samples each of minced meat, beef luncheon, Karish cheese, and human samples (pus swab from open wounds)) were cultured, and MRSA strains were identified using disk diffusion tests and mecA gene-based PCR. A total of 35% (70/200) of the examined samples were confirmed as coagulase-positive S. aureus in minced meat (46%), beef luncheon (44%), Karish cheese (44%), and human samples (22%). The MRSA strains showed resistance to amoxicillin (91.4%), penicillin (97.1%), cefoxitin (85.7%), cephradine (82.9%), tetracycline (57.2%), and erythromycin (52.8%). More than half of the tested S. aureus isolates harbored the mecA gene. The sequence analysis of the mecA gene from the minced meat, Karish cheese, and human samples revealed high genetic similarities between the S. aureus isolates from these sources. In conclusion, our findings indicate a risk for the transmission of the mecA gene of S. aureus across the food chain between humans and animal food products. Further studies should focus on finding additional epidemiological aspects of the MRSA strains in food chain.

Characterization of Staphylococcus aureus Isolates From Cases of Clinical Bovine Mastitis on Large-Scale Chinese Dairy Farms

Bovine mastitis is a prevalent disease that causes serious economic problems globally in the dairy industry. Staphylococcus aureus is an important pathogen of bovine mastitis. This study was conducted to characterize S. aureus isolates from clinical bovine mastitis cases in large-scale dairy herds in China. S. aureus was isolated from 624 clinical mastitis cases and confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). In total, 62 S. aureus isolates were obtained. Cluster analysis, genetic diversity, quantification of biofilm formation, antimicrobial resistance, and detection of virulence genes were performed on these isolates of S. aureus. Eight isolates harbored the mecA gene and were sensitive to oxacillin. MALDI-TOF MS cluster analysis revealed that the 62 isolates were divided into three major clusters (I, II, III) and eight main groups (A–H) at the distance level of 700. The agr II was the most prevalent (56.5%). The 62 S. aureus isolates were assigned to seven spa types. The most common spa type was t529(58.1%), followed by t2196 (14.5%), t518 (14.5%), t571(6.5%), t034 (3.2%), t2734 (1.6%), and t730 (1.6%). Five STs were identified from seven representative isolates as follows: ST630/CC8, ST97/CC97, ST50, ST398, and ST705. All isolates had the ability to form biofilm. Antimicrobial resistance was most frequently observed to ciprofloxacin (29%), followed by penicillin (24.2%), and streptomycin (9.6%). All isolates harbored the fnbA, clfB (100%), icaA, and icaD genes. This study provides the basis for the development of bovine mastitis prevention program on large-scale dairy farms.

Isolation and molecular-based identification of bacteria from unhatched leftover eggs of ducks in selected mini-hatcheries of Kishoreganj, Bangladesh

Objectives:

The study was designed for isolation and identification of the bacteria present in unhatched leftover eggs of duck in selected mini-hatcheries of Kishoreganj, Bangladesh.

Materials and Methods:

A total of 54 unhatched discarded eggs were collected as samples from different mini-hatcheries of Tarail and Itna Upazilas of Kishoreganj and aseptically carried to the laboratory in the icebox. Surface washings (n = 54) and inner contents (n = 54) were collected and enriched in Luria–Bertani broth followed by the isolation of pure colonies of different bacteria onto eosin methylene blue agar, mannitol salt agar, Salmonella–Shigella agar, and blood agar plates. Identification of the bacterial isolates was done by cultural properties, staining, and biochemical tests followed by molecular detection by Polymerase chain reaction.

Results:

Of 108 samples, 62 were found positive for Salmonella spp. (76%), 59 for E. coli (54%), 52 for Staphylococcus spp. (48%), and 5 for Clostridium spp. (9%). From the egg surface samples, Staphylococcus spp. were recovered in the highest (67%) followed by Salmonella spp. (59%), E. coli (56%), and Clostridium spp. (9%). From the inner contents of eggs, Salmonella spp. were recovered in the highest (56%), followed by E. coli (53%) and Staphylococcus spp. (30%).

Conclusion:

The isolated bacteria might be associated with the decreased hatchability and embryo mortality in the mini-hatcheries of duck.

Virulent methicillin resistant Staphylococcus aureus (MRSA) in street vended foods

Street foods are one of the important sources of foodborne infections and Staphylococcus aureus is an important infectious agent transmitted through various sources including street foods. The methicillin-resistant S. aureus (MRSA) are of public health significance, hence the study was taken to assess the street foods as a source of MRSA, for which 430 street vended foods of animal origin (meat, milk, eggs and their products) and associated environmental samples were processed for isolation and characterization. A total of 52 (12.1%) S. aureus were isolated and resistant was observed to oxacillin (36.5%), cefoxitin (25%) and penicillin G (82.7%) by disc diffusion test. On genotypic screening, mecA and blaZ have detected in 17.3% and 69.2% isolates, respectively. The virulence typing identified nuc, coa, clfA, spA, FnbA and enterotoxin A (sea) genes in 100%, 96.2%, 30.8%, 55.8, 50% and 7.7% isolates, respectively. Genetic diversity among the isolates was observed by enterobacterial repetitive intergenic consensus PCR with a D value of 0.77. The presence of virulent MRSA in street vended foods trigger the public health concern and emphasis to educate the consumers and street food vendors about quality and safety of such foods.

Characterization of Staphylococcus aureus isolated from chicken and quail eggshell

Objectives:

This study was conducted to assess the prevalence and characterization of Staphylococcus aureus from chicken and quail eggshells and to study the antibiogram of the isolates.

Materials and methods:

A total of 300 eggs (220 chicken eggs and 80 quail eggs) were collected from different retail shops and farms in Mymensingh district. Swabs taken from the egg surfaces were cultured on Mannitol Salt Agar for the isolation of S. aureus. Polymerase chain reaction was conducted for confirmatory identification of the bacterial species targeting nuc gene, followed by confirmation of methicillin-resistant S. aureus by targeting the mecA gene. Antibiotic sensitivity test of the isolated bacteria was done against commonly used antibiotics by the disk diffusion method.

Results:

The prevalence of Staphylococcus spp. and S. aureus in the chicken eggshell surface was 20.45% and 10.45%, respectively. Similarly, the prevalence of Staphylococcus spp. and S. aureus in quail eggshell surface was 16.25% and 5%, respectively. Overall, 27 isolates were identified as S. aureus, of which 23 were from the chicken eggshell surface and four from quail eggshell surface. Among the seven isolates tested, overall four (57.14%) were positive for the nuc gene. On the other hand, the mecA gene could be detected in three (50%) S. aureus out of six oxacillin resistant isolates. The antibiogram study indicated that most of the isolates were resistant to the antibiotics under β-lactam group.

Conclusion:

The present study concludes that chicken and quail egg surface harbor multidrug-resistant bacteria which may cause public health hazards, if these antibiotic-resistant bacteria are transferred to a human.

Comparative genome analysis of 24 bovine-associated Staphylococcus isolates with special focus on the putative virulence genes

Non-aureus staphylococci (NAS) are most commonly isolated from subclinical mastitis. Different NAS species may, however, have diverse effects on the inflammatory response in the udder. We determined the genome sequences of 20 staphylococcal isolates from clinical or subclinical bovine mastitis, belonging to the NAS species Staphylococcus agnetis, S. chromogenes, and S. simulans, and focused on the putative virulence factor genes present in the genomes. For comparison we used our previously published genome sequences of four S. aureus isolates from bovine mastitis. The pan-genome and core genomes of the non-aureus isolates were characterized. After that, putative virulence factor orthologues were searched in silico. We compared the presence of putative virulence factors in the NAS species and S. aureus and evaluated the potential association between bacterial genotype and type of mastitis (clinical vs. subclinical). The NAS isolates had much less virulence gene orthologues than the S. aureus isolates. One third of the virulence genes were detected only in S. aureus. About 100 virulence genes were present in all S. aureus isolates, compared to about 40 to 50 in each NAS isolate. S. simulans differed the most. Several of the virulence genes detected among NAS were harbored only by S. simulans, but it also lacked a number of genes present both in S. agnetis and S. chromogenes. The type of mastitis was not associated with any specific virulence gene profile. It seems that the virulence gene profiles or cumulative number of different virulence genes are not directly associated with the type of mastitis (clinical or subclinical), indicating that host derived factors such as the immune status play a pivotal role in the manifestation of mastitis.

Analysis of virulence genes and accessory gene regulator (agr) types among methicillin-resistant Staphylococcus aureus strains in Iran

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) strains are a major cause of hospital-acquired infections and are considered a serious public health concern. MRSA isolates have abundant virulence factors that are the basis for their pathogenicity. The accessory gene regulator (agr) locus co-ordinates the expression of these genes. The aim of this study was to determine the presence and frequency of various virulence genes encoding enterotoxins and adhesins as well as to identify agr specificity groups in MRSA isolates.

METHODS

This descriptive study included a total of 296 MRSA strains isolated from clinical samples collected in Tehran Heart Center (Tehran, Iran) between October 2004 and March 2013. Following DNA extraction, PCR-based assays were used to evaluate the presence of various virulence genes. IBM SPSS Statistics for Windows v.21.0 was used for statistical analysis.

RESULTS

The results indicated that the most frequent toxin genes were see (120/296; 40.5%), followed by sea (79/296; 26.7%); the other genes were encoded less frequently. The presence of seb and seh was not found in any of the isolates. Furthermore, the most frequent adhesin genes were clfA, spa, cna, map/eap and bbp, found in 281 (94.9%), 275 (92.9%), 267 (90.2%), 265 (89.5%) and 264 (89.2%) isolates, respectively. The majority of isolates belonged to agr group I (53.0%), followed by agr group III (1.4%). None of the isolates belonged to agr group II.

CONCLUSIONS

The relatively high frequency of various virulence genes suggests the emergence and pathogenic potential of MRSA isolates containing these genes in the study area.

Antimicrobial susceptibility, virulence genes, and randomly amplified polymorphic DNA analysis of Staphylococcus aureus recovered from bovine mastitis in Ningxia, China

Staphylococcus aureusis the leading pathogen involved inbovine mastitis, but knowledgeabout antimicrobial resistance, virulence factors, and genotypes of Staphylococcus aureus resulting in bovine mastitis in Ningxia, China, is limited. Therefore, antimicrobial susceptibility, virulence gene, and randomly amplified polymorphic DNA (RAPD) analyses of Staph. aureus were carried out. A total of 327 milk samples from cows with clinical and subclinical mastitis in 4 regions of Ningxia were used for the isolation and identification of pathogens according to phenotypic and molecular characteristics. Antimicrobial susceptibility against 22 antimicrobial agents was determined by disk diffusion. The presence of 8 virulence genes in Staph. aureus isolates was tested by PCR. Genotypes of isolates were investigated based on RAPD. Results showed that 35 isolates obtained from mastitis milk samples were identified as Staph. aureus. The isolates were resistant to sulfamethoxazole (100%), penicillin G (94.3%), ampicillin (94.3%), erythromycin (68.6%), azithromycin (68.6%), clindamycin (25.7%), amoxicillin (11.4%), and tetracycline (5.7%). All of the isolates contained one or more virulence genes with average (standard deviation) of 6.6±1.6. The most prevalent virulence genes were hlb (97.1%), followed by fnbpA, hla, coa (94.3% each), nuc (85.7%), fnbpB (80%), clfA (77.1%), and tsst-1 (40%). Nine different gene patterns were found and 3 of them were the dominant gene combinations (77.1%). Staphylococcus aureus isolates (n=35) were divided into 6 genotypes by RAPD tying, the genotypes III and VI were the most prevalent genotypes. There was greatvariation in genotypes of Staph. aureus isolates, not only among different farms, but also within the same herd in Ningxia province. The study showed a high incidence of Staph. aureus with genomic variation of resistance genes, which is matter of great concern in public and animal health in Ningxia province of China.

Polymorphism in spa gene of Staphylococcus aureus from bovine subclinical mastitis

Aim:

The virulence-associated protein-A of Staphylococcus aureus, encoded by spa gene shows a variation in length in different strains. In this study, the spa gene variation in S. aureus strains was studied which were isolated from subclinical cases of bovine mastitis.

Materials and Methods:

About 38 isolatesof S. aureus were recovered from Holstein–Friesian (HF) crossbred (n=16) and Rathi cattle (n=22) with subclinical mastitis as per standard procedures, and these isolates were subjected to amplification of spa gene (X-region) by polymerase chain reaction and calculation of number of tandem repeats were done.

Results:

Of the 16 isolates from H-F crossbred cattle, all with the exception of one isolate produced spa amplicon. Seven isolates produced amplicons of 200 bp, one produced 160 bp, and other seven produced spa amplicon of 150 bp with calculated number of 6, 5, and 4 repeats, respectively, whereas nine different types of amplicons were produced by 22 S. aureus isolates from Rathi cattle, viz., 280, 250, 240, 200, 190, 180, 170, 150, and 140 bp with 10, 8, 8, 6, 6, 6, 5, 4, and 4 repeats, respectively. One of the isolates from Rathi cattle produced two spa amplicons (150 and 190 bp).

Conclusion:

A greater polymorphism was observed in the S. aureus isolates from Rathi cattle than from H-F crossbreds with subclinical mastitis.

Typing of Staphylococcus aureus obtained from mastitic milk of cattle and buffalo on the basis of two virulence-associated genes (spa and clfA)

Aim:

The present study was undertaken to type Staphylococcus aureus isolates from cattle and buffalo mastitic milk on the basis of spa (X-region) and clfA genes, both responsible for producing virulence factors.

Material and Methods:

In the present investigation S. aureus isolates were isolated as per standard protocols. Typing of S. aureus was carried out by molecular detection of spa and clfA gene by polymerase chain reaction.

Results:

All the 32 isolates from cattle (16) and buffalo (16) were divisible into seven spa types with amplicon sizes ranging between 120 and 380bp. The cattle isolates produced seven different spa amplicons of 120, 150, 200, 250, 280, 300, and 330 bp with 3, 4, 6, 8, 10, 11 and 12 number of tandem repeats, respectively whereas buffalo isolates were divisible into five spa types with amplicons of 150, 200, 250, 330 and 380 bp having calculated number of repeats of 5, 7, 9, 12, and 14, respectively. Of the total isolates, 24 were considered pathogenic on the basis of more than seven number of tandem repeats. In the present investigation, clfA gene was amplified in 27 isolates from cattle and buffalo producing two different amplicons of 900 and 1000 bp sizes showing polymorphism. The most (71.80%) of the isolates produced amplicons of 900 bp while amplicon size of 1000 bp was produced by four (12.5%) of the isolates.

Conclusion:

The presence of these genes with a wide degree of polymorphism confirmed the pathogenic potential of S. aureus and their association with clinical manifestations in mastitis among cattle and buffalo.

Bacterial Quality and Prevalence of Foodborne Pathogens in Edible Offal from Slaughterhouses in Korea

Edible offal meats have recently received significant attention worldwide. However, studies evaluating the microbial quality of diverse edible offal and specifically investigating contamination by pathogens that cause foodborne illnesses are rare. Our study was conducted to investigate the microbiological quality of six kinds of edible offal produced from 11 pigs and 8 cattle slaughterhouses in the Republic of Korea and the prevalence of pathogenic microorganisms such as Salmonella, Clostridium perfringens, Staphylococcus aureus, and Escherichia coli O157:H7 in these products. The values for aerobic plate counts, coliform counts, and E. coli counts in red offal were 1.00 to 6.70, 0 (below 10 CFU) to 4.78, and 0 to 4.00 log CFU/g, respectively. For green offal, the values were 3.00 to 7.00, 1.48 to 6.30, and 0 to 6.00 log CFU/g, respectively. The most frequently detected foodborne pathogen was Salmonella (23.8% prevalence in pig offal and 7.1% prevalence in cattle offal), followed by C. perfringens (11.1 and 7.1%, respectively) and S. aureus (12.7 and 2.4%, respectively). None of the offal samples tested positive for E. coli O157:H7. Considering the microbial quality of offal from Korean slaughterhouses and the prevalence of foodborne pathogens in this material, more refined hygienic standards such as a hazard analysis critical control point system for processing, packing, and transporting edible offal are necessary for preventing further contamination.

Frequency of specific agr groups and antibiotic resistance in Staphylococcus aureus isolated from bovine mastitis in the northeast of Iran

Staphylococcus aureus is generally regarded as a leading cause of mastitis in dairy cattle. The aim of this study was to investigate the pattern of agr groups and any possible relationship between agr groups and antibiotic resistance among S. aureus strains isolated from bovine mastitis in Northeast of Iran. For this purpose, a total of 300 bovine mastitic milk samples were taken from dairy industry farms of Khorasan Razavi Province, Iran. S. aureus were isolated and identified according to the standard methods. Antibiotic susceptibility testing was conducted by disk diffusion method. In this study a total of 31 isolates of S. aureus were evaluated for agrD gene polymorphism by specific primers. Most of the isolates belonged to agr group I (54.8%), followed by agr group III (25.8%) and agr group II (19.4%). There was not any isolates belonging to group IV. Resistance to methicillin in agr group I isolates was more than other groups. Agr groups II and III were quite susceptible to methicillin. Due to high prevalent of S. aureus isolates and high antibiotic resistance rate in bovine mastitic isolates, it is important to verify the characteristics of S. aureus strains in Iran.

Comparative analysis of agr groups and virulence genes among subclinical and clinical mastitis Staphylococcus aureus isolates from sheep flocks of the Northeast of Brazil

Staphylococcus aureus is one of the most frequent mastitis causative agents in small ruminants. The expression of most virulence genes of S. aureus is controlled by an accessory gene regulator (agr) locus. This study aimed to ascertain the prevalence of the different agr groups and to evaluate the occurrence of encoding genes for cytotoxin, adhesins and toxins with superantigen activity in S. aureus isolates from milk of ewes with clinical and subclinical mastitis in sheep flocks raised for meat production The agr groups I and II were identified in both cases of clinical and subclinical mastitis. Neither the arg groups III and IV nor negative agr were found. The presence of cflA gene was identified in 100% of the isolates. The frequency of hla and lukE-D genes was high - 77.3 and 82.8%, respectively and all isolates from clinical mastitis presented these genes. The sec gene, either associated to tst gene or not, was identified only in isolates from subclinical mastitis. None of the following genes were identified: bbp, ebpS, cna, fnbB, icaA, icaD, bap, hlg, lukM-lukF-PV and se-a-b-d-e.

Misidentification of vancomycin-resistant Staphylococcus aureus as coagulase-negative Staphylococcus

Reduced vancomycin susceptibility in Staphylococcus aureus in many cases appears to be associated with changes in biological characteristics, including reduced coagulase activity, cell wall thickening, slow growth, smaller colonies, decreased pigment formation and less or no haemolysis. Whether these changes affect identification by routine methods has not been reported. In this study, 24 vancomycin-susceptibility-reduced coagulase-negative staphylococci (CoNS) strains (including 22 Staphylococcus haemolyticus strains and two Staphylococcus epidermidis strains) were retested by PCR-based detection of Staphylococcus aureus-specific genes (nuc, coa and 16S rRNA). The results showed that six isolates identified by conventional biochemical tests as S. haemolyticus contained nuc, coa and 16S rRNA genes. These six strains were serial-passaged daily on nutrient agar without vancomycin supplementation, and vancomycin-susceptible revertants were obtained after 15 continuous passages. Revertant isolates were coagulase-positive and were identified as S. aureus by automated testing methods. This suggests that biochemical changes in S. aureus strains with reduced vancomycin susceptibility should be highlighted and that the detection of these strains requires more attention and improved techniques.

Detection of virulence-associated genes in Staphylococcus aureus isolated from bovine clinical mastitis milk samples in Guangxi

Staphylococcus aureus is recognized worldwide as a pathogen causing many serious diseases in humans and animals and is one of the most common etiological agents of clinical and subclinical bovine mastitis. The purpose of this study was to determine the presence of genes encoding clfA, fnbA, fnbB, cap5, cap8, hla, hlb, nuc, sea, and tst of S. aureus strains (n = 39) isolated from bovine clinical mastitis in Guangxi by polymerase chain reaction amplification. The results of the present study indicated that all isolates were found to contain one or more virulence-associated genes. The most frequently encountered genes were fnbA (97 %) and nuc (90 %), followed by hla (85 %) and hlb (82 %), respectively. None of the investigated S. aureus strains harbored fnbB and sea genes. The data in the present study showed a relatively wide distribution of the genes fnbA and nuc among the investigated isolates, indicating that they play an important role on bovine mastitis pathogenesis. The study provides a valuable insight into the virulence-associated genes of this important pathogen.

Molecular characterization of intercellular adhesion gene in Staphylococcus aureus isolated from bovine mastitic milk

Biofilm formation in Staphylococcus aureus is considered an important virulence factor in bovine mastitis. Intercellular adhesion gene A (icaA) is a significant genetic determinant that contributes in biofilm formation. The aim of the present study was to determine the presence of the icaA gene in S. aureus isolated from bovine mastitis from seven states of India. A total of 88 out of 150 Staphylococcus aureus strains were found to be positive for biofilm marker icaA gene by PCR. The icaA gene was confirmed by dot blot hybridization in 41 of 150 S. aureus strains tested. Results obtained with dot blot hybridization were comparable to those obtained with PCR. Partial sequences of the icaA gene of the two S. aureus isolates showed deletion of some bases in different positions that might reduce/stop transcription leading to no biofilm formation. PCR was found to be a rapid test but dot blot hybridization was more accurate than PCR for detection of icaA genes. This study showed that detection of biofilm marker the icaA gene in S. aureus would allow the detection of virulence factors present in mastitis and early application of corrective measures.

Genotypic Characterization of Staphylococcus aureus Obtained from Humans and Bovine Mastitis Samples in India

AIM AND BACKGROUND

Staphylococcus aureus is a major human pathogen that also causes important infections in cattle and sheep. The present study aimed to test genetic diversity among strains of S. aureus isolated from cattle (n=34) and humans (n=22) by DNA typing.

MATERIALS AND METHODS

Fluorescent amplified fragment length polymorphism (FAFLP) is the genotyping tool used in the study. The presence of the mecA and Panton-Valentine leukocidin (PVL) genes among these strain groups was also checked.

RESULTS

A dendrogram deduced from FAFLP showed that all the strains clustered into 10 groups (A-J) with a relative genetic divergence of less than 8%. Sixty-seven percent of the isolates from bovine sources clustered together in two clades (A and H), while another major cluster with 13 isolates (59%) (Cluster G) had all strains from a human host. The remaining strains from both the hosts clustered independently into smaller clusters with the exception of two strains of human origin, which clustered along with a bovine cluster. Thirteen strains belonging to cluster G were highly clonal. About 77% of strains obtained from human infections were methicillin-resistant S. aureus (MRSA), whereas only 29% of strains from bovine origin were MRSA. Only three strains from human origin showed PVL positive, while no strain from cattle had PVL genes. The complete absence of PVL genes in all the bovine strains in the study appears to be significant.

CONCLUSIONS

FAFLP can be successfully applied to assess the genetic relationship of S. aureus isolates from different hosts. The study also provided the valuable epidemiological data on S. aureus from bovine sources in India, which is lacking.

Characterization of genes encoding virulence determinants and toxins in Staphylococcus aureus from bovine milk in Central Italy

The aim of this study was to evaluate the genotypic characteristics of Staphylococcus aureus isolates (n=170) from bovine milk collected from seven dairy farms in Italy. On the basis of cultural and biochemical properties and by amplification of the 23S rRNA specific to S. aureus, all isolates were identified as S. aureus. To genotypically characterize S. aureus isolates, genes encoding virulence determinants (nuc, clfA, spa-IgG-binding, spa-X-region, fnbA and fnbB, cap5 and cap8) and staphylococcal enterotoxins (sea, seb, sec, sed, see, seg, seh, sei, sej) were investigated using a PCR technique. The results showed that the isolates of S. aureus in each farm had the same genotypic characteristics, while the isolates genotipically differed between the different farms. The present study might help to understand the distribution of prevalent S. aureus strains in dairy farms.

Isolation from sewage influent and characterization of novel Staphylococcus aureus bacteriophages with wide host ranges and potent lytic capabilities

Staphylococcus aureus is a gram-positive pathogen that causes a variety of diseases, including bovine mastitis, which has severe economic consequences. Standard antibiotic treatment results in selection of resistant strains, leading to a need for alternative treatments, such as bacteriophage therapy. Forty-nine S. aureus isolates were obtained from the milk of mastitic cows for use in screening of staphylococcal phages. Fifteen isolates which were positive for both coagulase and hemolysin were assayed by PCR for variation in the X region and the immunoglobulin G-binding region of the protein A gene (spa) and in the carboxy terminus of the coagulase gene (coa) and for the presence of enterotoxin C, G, H, and I genes. The host ranges of 52 phages isolated from sewage influent were determined by performing spot tests with the 15 S. aureus isolates, and two phages were subsequently chosen for further analysis. PhiSA039 had the widest host range, producing clear plaques on 13 of the 15 isolates (87%), while PhiSA012 produced clear plaques on 8 isolates (53%) and was the only phage that produced a clear plaque on a nonmastitic S. aureus strain. Transmission electron microscopy revealed that the phages were similar sizes and belonged to the Myoviridae family. Measurement of optical densities during coculture with S. aureus isolates confirmed the breadth of the PhiSA039 host range and showed that PhiSA012 had potent lytic capability. PhiSA012-resistant bacteria did not appear for three of seven isolates tested (43%) after 65 h of incubation. These two phages are proposed as candidates for phage therapy of bovine mastitis.

Molecular typing of Staphylococcus aureus isolated from bovine mastitis based on polymorphism of the coagulase gene in the north west of Iran

The objective was to investigate the genotypic characteristics and distribution of Staphylococcus aureus in 9 dairy herds of Tabriz and Urmia regions which are located in east and west Azerbaijan provinces, respectively, Iran. In this study 58 S. aureus isolates were recovered from 370 milk samples of cows with clinical and subclinical mastitis. S. aureus isolates were identified on the basis of the cultural and biochemical properties as well as by amplification of the aroA gene specific to S. aureus and then were analyzed using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) of the coagulase gene (coa). Amplification of the variable region of the coa gene from these isolates produced five different PCR products ranging in size from approximately 490 bp to 850 bp. To obtain RFLP patterns of the PCR products they were subjected to digestion with restriction endonuclease HaeIII and the fragments separated by gel electrophoresis. Nine coa gene RFLP patterns, numbered I-IX, were observed, with 23 isolates (39.66%) assigned to RFLP pattern I and 14 isolates (24.14%) assigned to RFLP pattern III. Five out of nine patterns were found in both regions and four of nine patterns were only found in one region. The results demonstrated that several variants of the coa gene are present in the studied regions, but only a few of them were predominant, suggesting contagious transmission, a common source, or host adaptation of subset of the population of S. aureus strains. This study also indicated that genetic heterogeneity among S. aureus isolates recovered from bovine mastitis may be exists within and among herds in different regions.